This paper aims to experimentally and numerically probe fatigue behaviours and lifetimes of 3D4D(three-dimensional four-directional)braided composite I-beam under four-point flexure spectrum loading.New fatigue damage...This paper aims to experimentally and numerically probe fatigue behaviours and lifetimes of 3D4D(three-dimensional four-directional)braided composite I-beam under four-point flexure spectrum loading.New fatigue damage models of fibre yarn,matrix and fibre–matrix interface are proposed,and fatigue failure criteria and PFDA(Progressive Fatigue Damage Algorithm)are thus presented for meso-scale fatigue damage modelling of 3D4D braided composite I-beam.To validate the aforementioned model and algorithm,fatigue tests are conducted on the 3D4D braided composite I-beam under four-point flexure spectrum loading,and fatigue failure mechanisms are analyzed and discussed.Novel global–local FE(Finite Element)model based on the PFDA is generated for modelling progressive fatigue failure process and predicting fatigue life of 3D4D braided composite I-beam under four-point flexure spectrum loading.Good agreement has been achieved between experimental results and predictions,demonstrating the effective usage of new model.It is shown that matrix cracking and interfacial debonding initially initiates on top surface of top flange of I-beam,and then gradually propagates from the side surface of top flange to the intermediate web along the braiding angle,and considerable fiber breakage finally causes final fatigue failure of I-beam.展开更多
Piezoelectric actuators are widely utilized in positioning systems to realize nano-scale resolution. However, the backward motion always generates for some piezoelectric actuators, which reduces the working efficiency...Piezoelectric actuators are widely utilized in positioning systems to realize nano-scale resolution. However, the backward motion always generates for some piezoelectric actuators, which reduces the working efficiency. Bionic motions have already been employed in the field of piezoelectric actuators to realize better performance. By imitating the movement form of seals, seal type piezoelectric actuator is capable to realize large operating strokes easily. Nevertheless, the conventional seal type piezoelectric actuator has a complicated structure and control system, which limits further applications. Hence, an improved bionic piezoelectric actuator is proposed to realize a long motion stroke and eliminate backward movement with a simplified structure and control method in this study. The composition and motion principle of the designed actuator are discussed, and the performance is investigated with simulations and experiments. Results confirm that the presented actuator effectively realizes the linear movement that has a large working stroke stably without backward motion. The smallest stepping displacement ΔL is 0.2 μm under 1 Hz and 50 V. The largest motion speed is 900 μm/s with 900 Hz and 120 V. The largest vertical and horizontal load are 250 g and 12 g, respectively. This work shows that the improved bionic piezoelectric actuator is feasible for eliminating backward motion and has a great working ability.展开更多
BACKGROUND Left colon cancer surgery relies on laparoscopic hemicolectomy,with digestive tract reconstruction critical.End-to-side anastomosis(ESA)and side-to-side anastomosis(SSA)anastomoses are common,but their comp...BACKGROUND Left colon cancer surgery relies on laparoscopic hemicolectomy,with digestive tract reconstruction critical.End-to-side anastomosis(ESA)and side-to-side anastomosis(SSA)anastomoses are common,but their comparative outcomes,especially in splenic flexure handling and efficacy,need clarification.This study compares ESA and SSA to guide surgical practice.AIM To compare the clinical outcomes of laparoscopically assisted left hemicolectomy with ESA and SSA.METHODS A total of 334 patients were included,with 105 patients from the First Affiliated Hospital of Xiamen University and 229 patients from the First Affiliated Hospital of Fujian Medical University,between January 1,2012,and May 31,2020.The patients were divided into two groups:146 cases in the ESA group and 188 cases in the SSA group.Clinical data from both groups were compared,and the survival prognosis was followed up.RESULTS The operation time for the ESA group was significantly shorter than that of the SSA group(197.1±57.7 minutes vs 218.6±67.5 minutes,χ2=4.298,P=0.039).There were no significant differences between the two groups in intraoperative blood loss,postoperative pain score at 48 hours,time to first bowel movement,number of lymph nodes dissected,or postoperative complications such as anastomotic leakage,bleeding,stenosis.and adhesive intestinal obstruction at 6 months,12 months,and 24 months(P>0.05).Specifically,the incidence of complications like anastomotic leakage was 2.1%in the ESA group vs 4.3%in the SSA group(P=0.264).The 5-year disease-free survival(DFS)rate was 66.4%for the ESA group and 63.9%for the SSA group(P=0.693).There were no significant differences in the overall survival rate between the two groups.The incidence of splenic laceration was significantly higher in the SSA group(3.7%vs 0.7%,P=0.018).Overall,the 5-year DFS was 66.4%for ESA and 63.9%for SSA,with no significant difference in survival between the groups(P=0.693).CONCLUSION Both laparoscopically assisted left hemicolectomy with ESA and SSA are feasible and offer comparable long-term outcomes.ESA may reduce the need for splenic flexure dissociation,particularly when the tumor is located at the descending colon or its junction with the sigmoid colon,and especially in obese patients,elderly individuals with multiple complications,or those with severe adhesions in the splenic flexure of the surgical field.展开更多
A novel elastic metamaterial is proposed with the aim of achieving lowfrequency broad bandgaps and bandgap regulation.The band structure of the proposed metamaterial is calculated based on the Floquet-Bloch theorem,an...A novel elastic metamaterial is proposed with the aim of achieving lowfrequency broad bandgaps and bandgap regulation.The band structure of the proposed metamaterial is calculated based on the Floquet-Bloch theorem,and the boundary modes of each bandgap are analyzed to understand the effects of each component of the unit cell on the bandgap formation.It is found that the metamaterials with a low elastic modulus of ligaments can generate flexural wave bandgaps below 300 Hz.Multi-frequency vibrations can be suppressed through the selective manipulation of bandgaps.The dual-graded design of metamaterials that can significantly improve the bandgap width is proposed based on parametric studies.A new way that can regulate the bandgap is revealed by studying the graded elastic modulus in the substrate.The results demonstrate that the nonlinear gradient of the elastic modulus in the substrate offers better bandgap performance.Based on these analyses,the proposed elastic metamaterials can pave the way for multi-frequency vibration control,low-frequency bandgap broadening,and bandgap tuning.展开更多
This paper proposes a method to generate Bessel-like collimated beams with suppressed side lobes using the flexural vibration modes of a fixed boundary circular plate,which is excited by a longitudinally vibrating tra...This paper proposes a method to generate Bessel-like collimated beams with suppressed side lobes using the flexural vibration modes of a fixed boundary circular plate,which is excited by a longitudinally vibrating transducer in a ring excitation manner.The factors affecting the generation of Bessel-like collimated beams are investigated by theoretical analysis,numerical simulation and experimental methods.The results indicate that Bessel-like wave can be generated by a thin circular plate with fixed boundaries.The third-order mode of the circular plate can be modified to generate a collimated beam with suppressing side lobes when it is excited in a ring excitation manner and the excitation position lies between the first two nodal circles of the plate.As the excitation radius increases,the main lobe width of the resulting Bessel-like collimated beam decreases,the extent of the focusing region increases,and the amplitude of the side lobes initially increases and then decreases.Based on the simulation results,a prototype Bessel-like collimated beam generation system is made and measured experimentally.The experimental results are in good agreement with the numerical results.The Bessel-like collimated beam can be generated by the proposed system,which has potential application in the fields of long-range detection,imaging of highly attenuated materials,and airflow acceleration.展开更多
With an increased utilization of carbon fiber reinforced polymers(CFRPs)in high temperature environments,investigating their effects on materials becomes exceedingly important.This study presents a comparative investi...With an increased utilization of carbon fiber reinforced polymers(CFRPs)in high temperature environments,investigating their effects on materials becomes exceedingly important.This study presents a comparative investigation of thermo-oxidative aging effects on the flexural performance of two carbon fiber reinforced composite laminates(CFRCLs):a quasi-isotropic plain-woven CFRCL and a quasi-isotropic unidirectional layup CFRCL(designated as PW-CFRCL and UD-CFRCL,respectively).The CFRCLs were subjected to thermo-oxidative aging for specific durations,and their flexural strength was evaluated through three-point bending tests.The flexural strength of the laminates decreased with the prolonged aging duration.Despite having lower fiber content,PW-CFRCLs showed higher flexural strength than UD-CFRCLs.After eight days of aging,the flexural strength of PW-CFRCLs decreased by merely 4%-5%,while that of UD-CFRCLs decreased by 11%-14%.After 32 days of aging,the thinner PW-CFRCL with the lowest fiber content exhibited the highest flexural strength(595.52 MPa),followed by the thinner UD-CFRCL(549.83 MPa),then the thicker PW-CFRCL(445.29 MPa)and finally,the thicker UD-CFRCL(393.90 MPa).The decline in flexural properties of the laminates was primarily attributed to matrix cracking and interface debonding resulting from matrix oxidation.To validate the universality of this result,the finite element method was employed,showing a good correlation with the experimental findings.展开更多
Ultrahigh-performance concrete(UHPC)is a groundbreaking kind of concrete that distinguishes itself from conventional concrete through its unique material properties.Understanding and managing the time-dependent charac...Ultrahigh-performance concrete(UHPC)is a groundbreaking kind of concrete that distinguishes itself from conventional concrete through its unique material properties.Understanding and managing the time-dependent characteristics of these materials is essential for their effective use in various construction applications.This study presents an experimental evaluation of the compressive and bending properties of the UHPC incorporating polypropylene,steel,and glass fibers.Based on ACI-211 guidelines,the UHPC mix was designed by using three types of aggregates:limestone,andesite,and quartzite,along with 5%fiber content(at varying percentages of 0,5%,10%,15%,and 20%)relative to the cementitious materials,and three different water-to-cement(w/c)ratios(0.24,0.3,and 0.4)were used.In this research,the compressive and flexural strength tests were conducted.The results show that increasing the values of the fibers significantly enhances the compressive strength of the studied samples.Furthermore,the utilization of fibers markedly improves the bending strength of the samples,demonstrating a strong correlation with the yield resistance of the material.Also,findings show that using steel fibers increases the compressive and bending strength of the tested samples more than polypropylene and glass fibers.For instance,in UHPC samples with 0.4 w/c,the average compressive strength values are 82.2 MPa,70.3 MPa,and 67.1 MPa for steel,polypropylene,and glass fibers,respectively.Also,in the flexural strength test,the modulus of rupture is obtained as an average of 6.24 MPa,5.24 MPa and 4.83 MPa for UHPC samples with steel,polypropylene and glass fibers,respectively.展开更多
Corn starch was used as a templating agent,and an oxide mixture containing alumina,magnesia,zirconia and yttria was added in the sol-gel state.After slip casting,curing at 85℃,drying and sintering,high-performance po...Corn starch was used as a templating agent,and an oxide mixture containing alumina,magnesia,zirconia and yttria was added in the sol-gel state.After slip casting,curing at 85℃,drying and sintering,high-performance porous alumina ceramics were obtained.The properties of the porous alumina ceramics were analyzed by means of SEM,XRD,flexural strength and porosity.The research findings showed that,when the starch content was 1 wt%,the prepared ceramic mainly consisted of four phases:α-Al_(2)O_(3),MgAl_(2)O_(4),ZrO,and YSZ.The flexural strength reached 157.27 MPa,the flexural strength of the green body was about 3 MPa,and the porosity was around 30%.展开更多
This study investigates the low-velocity impact and post-impact flexural properties of 3D integrated woven spacer composites,focusing on their orthotropic behavior when tested along two principal directions,i.e.,warp(...This study investigates the low-velocity impact and post-impact flexural properties of 3D integrated woven spacer composites,focusing on their orthotropic behavior when tested along two principal directions,i.e.,warp(X-type)and weft(Y-type)directions.The same composite material was tested in these orientations to evaluate the differences in impact resistance and residual bending strength.Specimens were fabricated via vacuum-assisted molding and tested at 2,3,5,and 7 J impact energies using an Instron Ceast 9350 drop-weight impact testing machine,in accordance with ASTM D7136.Post-impact flexural tests were performed using a four-point bending method in accordance with ASTM D7264.The absorbed energy increased from 1.97 to 6.98 J,and the panel damage area ranged from 121 to 361 mm^(2) as impact energy roses.Specimens tested in the weft direction(Y-type)showed greater residual strength(up to 15.83 N)and displacement(up to 0.538 mm)than those tested in the warp direction(X-type).Ultrasonic C-scan imaging revealed localized matrix cracking and fiber failure damage patterns.Results emphasize the directional differences in impact resistance and residual bending properties,highlighting the importance of material orientation in structural applications.This study provides a foundation for utilizing 3D woven spacer composites in lightweight,damage-tolerant structural components.展开更多
In this work,a small amount of Al_(2)O_(3)powders(≤0.3 wt%)were incorporated into the Sm_(2)Co_(17)-type sin-tered magnets,obtaining both high mechanical and magnetic properties.It is found that 0.1%weight percentage...In this work,a small amount of Al_(2)O_(3)powders(≤0.3 wt%)were incorporated into the Sm_(2)Co_(17)-type sin-tered magnets,obtaining both high mechanical and magnetic properties.It is found that 0.1%weight percentage of Al_(2)O_(3)doping is enough to enhance the flexural strength by about 20%(∼180 MPa for the case of the c-axis parallel to height).Meanwhile,the(BH)max remains around 219 kJ/m^(3),and Hcj is 2052 kA/m,which is over 95%of that of the original magnets without doping.The promising improvement in flexural strength is mainly attributed to the grain size effective refinement caused by Sm_(2)O_(3)particles including newly-formed ones from the reaction of the Al_(2)O_(3)powder and Sm in the matrix.Furthermore,the grain size of the magnets decreases significantly with increasing of Al_(2)O_(3)doping up to 0.3 wt%.Espe-cially,the grain size of 0.3 wt%Al_(2)O_(3)doped magnets is refined by 37%.However,the flexural strengths(for the c-axis parallel to height and the c-axis parallel to width cases)of the magnets decrease sequen-tially and are even lower than that of the original magnet.The microstructure investigations indicate that the decrease in flexural strength may closely be correlated to the larger cell size and the incomplete cell boundaries phase.The obtained results infer that the flexural strength is susceptible to not only grain size but also the cellular structure of the magnets.展开更多
A flexure hinge is a major component in designing compliant mechanisms that o ers unique possibilities in a wide range of application fields in which high positioning accuracy is required. Although various flexure hin...A flexure hinge is a major component in designing compliant mechanisms that o ers unique possibilities in a wide range of application fields in which high positioning accuracy is required. Although various flexure hinges with di erent configurations have been successively proposed, they are often designed based on designers' experiences and inspirations. This study presents a systematic method for topological optimization of flexure hinges by using the level set method. Optimization formulations are developed by considering the functional requirements and geometrical constraints of flexure hinges. The functional requirements are first constructed by maximizing the compliance in the desired direction while minimizing the compliances in the other directions. The weighting sum method is used to construct an objective function in which a self-adjust method is used to set the weighting factors. A constraint on the symmetry of the obtained configuration is developed. Several numerical examples are presented to demonstrate the validity of the proposed method. The obtained results reveal that the design of a flexure hinge starting from the topology level can yield more choices for compliant mechanism design and obtain better designs that achieve higher performance.展开更多
The thin-walled tube flexure（TWTF） hinges have important potential application value in the deployment mechanisms of satellite and solar array, but the optimal design of the TWTF hinges haven＇t been completely solv...The thin-walled tube flexure（TWTF） hinges have important potential application value in the deployment mechanisms of satellite and solar array, but the optimal design of the TWTF hinges haven＇t been completely solved, which restricts their applications. An optimal design method for the qusai-static folding and deploying of TWTF hinges with double slots is presented based on the response surface theory. Firstly, the full factorial method is employed to design of the experiments. Then, the finite element models of the TWTF hinges with double slots are constructed to simulate the qusai-static folding and deploying non-linear analysis. What＇s more, the mathematical model of the TWTF flexure hinge quasi-static folding and deploying properties are derived by the response surface method. Considering of small mass and high stability, the peak moment of quasi-static folding and deploying as well as the lightless are set as the objectives to get the optimal performances. The relative errors of the objectives between the optimal design results and the FE analysis results are less than 7%, which demonstrates the precision of the surrogate models. Lastly, the parameter study shows that both the slots length and the slots width both have significant effects to the peak moment of quasi-static folding and deploying of TWTF hinges with double slots. However, the maximum Mises stress of quasi-static folding is more sensitive to the slots length than the slots width. The proposed research can be applied to optimize other thin-walled flexure hinges under quasi-static folding and deploying, which is of great importance to design of flexure hinges with high stability and low stress.展开更多
Large-deflection flexure pivot is widely used in high precision rotation application, but there are less flexure configurations and simple and convenient design methods, This paper presents a novel large-deflection cu...Large-deflection flexure pivot is widely used in high precision rotation application, but there are less flexure configurations and simple and convenient design methods, This paper presents a novel large-deflection curved-compliant annulus-shaped flexure pivot composed of six curved beam flexure elements. It can offer more than lO^angular stroke theoretically. Firstly, main-motion pseudo-rigid-body method is introduced to establish the flexure pivot model. Although pseudo-rigid-body method can be used to analyze the large-deformation flexure pivot performance, the method is definitely a laborious and difficult task for designing this novel flexure pivot. In order to simply the designing process, dimension-design graphs based on the parametric models and finite element analysis is presented. Using the dimension-design method as a tool, the designers can determine the optimal geometry rapidly, based on the stiffness and rotation demands of an annulus-shaped flexure pivot. Finally, dimension-design graph examples are given whose primary design aims to achieve a rotation stroke of annulus-shaped flexure pivot. The finite element analysis results show that the relative designing error between anticipative rotation stroke and graph design result is less than 4%. The dimensionless method used in designing annulus-shaped flexure pivot can reduce design process in both time and complexity. The novel annulus-shaped flexure pivot and dimension-design method are helpful supplement to configuration and design method of large-deflection flexure pivot.展开更多
Conventional flexible joints generally have limited range of motion and high stress concentration. To overcome these shortcomings, corrugated flexure beam（CF beam） is designed because of its large flexibility obtain...Conventional flexible joints generally have limited range of motion and high stress concentration. To overcome these shortcomings, corrugated flexure beam（CF beam） is designed because of its large flexibility obtained from longer overall length on the same span. The successful design of compliant mechanisms using CF beam requires manipulation of the stiffnesses as the design variables. Empirical equations of the CF beam stiffness components, except of the torsional stiffness, are obtained by curve-fitting method. The application ranges of all the parameters in each empirical equation are also discussed. The ratio of off-axis to axial stiffness is considered as a key characteristic of an effective compliant joint. And parameter study shows that the radius of semi-circular segment and the length of straight segment contribute most to the ratio. At last, CF beam is used to design translational and rotational flexible joints, which also verifies the validity of the empirical equations. CF beam with large flexibility is presented, and empirical equations of its stiffness are proposed to facilitate the design of flexible joint with large range of motion.展开更多
Flexure mechanisms with decoupled characteristics have been widely utilized in precision positioning applications.However,these mechanisms suffer from either slow response or low load capability.Furthermore,asymmetric...Flexure mechanisms with decoupled characteristics have been widely utilized in precision positioning applications.However,these mechanisms suffer from either slow response or low load capability.Furthermore,asymmetric design always leads to thermal error.In order to solve these issues,a novel 2-DOF decoupled mechanism is developed by monolithically manufacturing sets of statically indeterminate symmetric（SIS） flexure structures in parallel.Symmetric design helps to eliminate the thermal error and Finite Element Analysis（FEA） results show that the maximum coupling ratio between X and Y axes is below 0.25% when a maximum pretension force of 200 N is applied.By ignoring the mass effect,all the SIS flexure structures are simplified to ＂spring-damper＂ components,from which the static and dynamics model are derived.The relation between the first resonant frequency of the mechanism and the load is investigated by incorporating the load mass into the proposed dynamics model.Analytical results show that even with a load of 0.5 kg,the first resonant frequency is still higher than 300 Hz,indicating a high load capability.The mechanism＇s static and dynamic performances are experimentally examined.The linear stiffnesses of the mechanism at the working platform and at the driving point are measured to be 3.563 0 N·μm-1 and 3.362 1 N·μm-1,respectively.The corresponding estimation values from analytical models are 3.405 7 N·μm-1 and 3.381 7 N·μm-1,which correspond to estimation errors of-4.41% and 0.6%,respectively.With an additional load of 0.16 kg,the measured and estimated first resonant frequencies are 362 Hz and 365 Hz,respectively.The estimation error is only 0.55%.The analytical and experimental results show that the developed mechanism has good performances in both decoupling ability and load capability;its static and dynamic performance can be precisely estimated from corresponding analytical models.The proposed mechanism has wide potentials in precision positioning applications.展开更多
The current research of kinetostatic characteristics in flexure mechanisms mainly focus on the improvement of accuracy. To reduce or eliminate the parasitic motion is considered as an approach by using the common know...The current research of kinetostatic characteristics in flexure mechanisms mainly focus on the improvement of accuracy. To reduce or eliminate the parasitic motion is considered as an approach by using the common knowledge of symmetry. However, there is no study on designing the flexure mechanisms with symmetrical features as many as possible for better kinetostatic performance, when considering the resulting cost by the symmetry. In this paper, the concept of degree of symmetry(DoS) is proposed for the first time, which is committed to symmetry design in the phase of conceptual design. A class of flexure mechanisms with 0?DoS, 1?DoS, 2?DoS and 3?DoS are synthesized respectively based on the Freedom and Constraint Topology method. Their overall compliance matrices in an analytical form formulated within the framework of the screw theory are used to analyze and compare the effect of different number of DoS on the kinetostatic characteristics for flexure mechanisms. The finite element analysis(FEA) simulations are implemented to verify the analytical results. These results show that the higher the DoS is, the smaller the parasitic motion error will be. The flexure model with 3?DoS is optimized according to the overall compliance matrix and then tested by using the FEA simulation. The testing result shows that with the best combination parameters, the parasitic motion error for 3?DoS mechanism is almost eliminated. This research introduces a design principle which can alleviate the unwanted parasitic motion for better accuracy.展开更多
A novel 6-PSS flexible parallel mechanism was presented,which employed wide-range flexure hinges as passive joints.The proposed mechanism features micron level positioning accuracy over cubic centimeter scale workspac...A novel 6-PSS flexible parallel mechanism was presented,which employed wide-range flexure hinges as passive joints.The proposed mechanism features micron level positioning accuracy over cubic centimeter scale workspace.A three-layer back-propagation(BP) neural network was utilized to the kinematics analysis,in which learning samples containing 1 280 groups of data based on stiffness-matrix method were used to train the BP model.The kinematics performance was accurately calculated by using the constructed BP model with 19 hidden nodes.Compared with the stiffness model,the simulation and numerical results validate that BP model can achieve millisecond level computation time and micron level calculation accuracy.The concept and approach outlined can be extended to a variety of applications.展开更多
This paper presents a precise solution to predict the behavior of steel fiber reinforced concrete(SFRC) under the four point bending test(FPBT).All the force components at the beam section(before and after cracking) a...This paper presents a precise solution to predict the behavior of steel fiber reinforced concrete(SFRC) under the four point bending test(FPBT).All the force components at the beam section(before and after cracking) are formulated by applying these assumptions:a realistic stress-strain model is used for concrete behavior in compression,a linear response is considered for the uncracked tension region in a concrete constitutive model,and an exponential relationship is proposed as a stress-crack opening in the crack region which requires two parameters.Then the moment capacity of the critical cracked section is calculated by using these forces and satisfying equilibrium law at the section.Parametric studies are done on the behavior of SFRC to assess the sensitivity of the solution.Finally,this solution is validated with some existing experimental data.The result shows the proposed solution is able to estimate the behavior of SFRC under FPBT.展开更多
This paper presents the design, development, and control of a large range beam flexure-based nano servo system for the micro-stereolithography （MSL） process. As a key enabler of high accuracy in this process, a comp...This paper presents the design, development, and control of a large range beam flexure-based nano servo system for the micro-stereolithography （MSL） process. As a key enabler of high accuracy in this process, a compact desktop-size beam flexure-based nanopositioner was designed with millimeter range and nanometric motion quality. This beam flexure-based motion system is highly suitable for harsh operation conditions, as no assembly or maintenance is required during the operation. From a mechanism design viewpoint, a mirror-symmetric arrangement and appropriate redundant constraints are crucial to reduce undesired parasitic motion. Detailed finite element analysis （FEA） was conducted and showed satisfactory mechanical features. With the identified dynamic models of the nanopositioner, real-time control strategies were designed and implemented into the monolithically fabricated prototype system, demonstrating the enhanced tracking capability of the MSL process. The servo system has both a millimeter operating range and a root mean square （RMS） tracking error of about 80 nm for a circular traiectorv.展开更多
基金supported by the National Natural Science Foundation of China(No.12472340).
文摘This paper aims to experimentally and numerically probe fatigue behaviours and lifetimes of 3D4D(three-dimensional four-directional)braided composite I-beam under four-point flexure spectrum loading.New fatigue damage models of fibre yarn,matrix and fibre–matrix interface are proposed,and fatigue failure criteria and PFDA(Progressive Fatigue Damage Algorithm)are thus presented for meso-scale fatigue damage modelling of 3D4D braided composite I-beam.To validate the aforementioned model and algorithm,fatigue tests are conducted on the 3D4D braided composite I-beam under four-point flexure spectrum loading,and fatigue failure mechanisms are analyzed and discussed.Novel global–local FE(Finite Element)model based on the PFDA is generated for modelling progressive fatigue failure process and predicting fatigue life of 3D4D braided composite I-beam under four-point flexure spectrum loading.Good agreement has been achieved between experimental results and predictions,demonstrating the effective usage of new model.It is shown that matrix cracking and interfacial debonding initially initiates on top surface of top flange of I-beam,and then gradually propagates from the side surface of top flange to the intermediate web along the braiding angle,and considerable fiber breakage finally causes final fatigue failure of I-beam.
基金supported by The Key Science and Technology Plan Project of Jinhua City,China:2023-3-084,2023-2-011Zhejiang Provincial"Revealing the list and taking command"Project of China KYH06Y22349Open Fund Project of Key Laboratory of CNC Equipment reliability,Ministry of Education JLU-cncr-202407.
文摘Piezoelectric actuators are widely utilized in positioning systems to realize nano-scale resolution. However, the backward motion always generates for some piezoelectric actuators, which reduces the working efficiency. Bionic motions have already been employed in the field of piezoelectric actuators to realize better performance. By imitating the movement form of seals, seal type piezoelectric actuator is capable to realize large operating strokes easily. Nevertheless, the conventional seal type piezoelectric actuator has a complicated structure and control system, which limits further applications. Hence, an improved bionic piezoelectric actuator is proposed to realize a long motion stroke and eliminate backward movement with a simplified structure and control method in this study. The composition and motion principle of the designed actuator are discussed, and the performance is investigated with simulations and experiments. Results confirm that the presented actuator effectively realizes the linear movement that has a large working stroke stably without backward motion. The smallest stepping displacement ΔL is 0.2 μm under 1 Hz and 50 V. The largest motion speed is 900 μm/s with 900 Hz and 120 V. The largest vertical and horizontal load are 250 g and 12 g, respectively. This work shows that the improved bionic piezoelectric actuator is feasible for eliminating backward motion and has a great working ability.
文摘BACKGROUND Left colon cancer surgery relies on laparoscopic hemicolectomy,with digestive tract reconstruction critical.End-to-side anastomosis(ESA)and side-to-side anastomosis(SSA)anastomoses are common,but their comparative outcomes,especially in splenic flexure handling and efficacy,need clarification.This study compares ESA and SSA to guide surgical practice.AIM To compare the clinical outcomes of laparoscopically assisted left hemicolectomy with ESA and SSA.METHODS A total of 334 patients were included,with 105 patients from the First Affiliated Hospital of Xiamen University and 229 patients from the First Affiliated Hospital of Fujian Medical University,between January 1,2012,and May 31,2020.The patients were divided into two groups:146 cases in the ESA group and 188 cases in the SSA group.Clinical data from both groups were compared,and the survival prognosis was followed up.RESULTS The operation time for the ESA group was significantly shorter than that of the SSA group(197.1±57.7 minutes vs 218.6±67.5 minutes,χ2=4.298,P=0.039).There were no significant differences between the two groups in intraoperative blood loss,postoperative pain score at 48 hours,time to first bowel movement,number of lymph nodes dissected,or postoperative complications such as anastomotic leakage,bleeding,stenosis.and adhesive intestinal obstruction at 6 months,12 months,and 24 months(P>0.05).Specifically,the incidence of complications like anastomotic leakage was 2.1%in the ESA group vs 4.3%in the SSA group(P=0.264).The 5-year disease-free survival(DFS)rate was 66.4%for the ESA group and 63.9%for the SSA group(P=0.693).There were no significant differences in the overall survival rate between the two groups.The incidence of splenic laceration was significantly higher in the SSA group(3.7%vs 0.7%,P=0.018).Overall,the 5-year DFS was 66.4%for ESA and 63.9%for SSA,with no significant difference in survival between the groups(P=0.693).CONCLUSION Both laparoscopically assisted left hemicolectomy with ESA and SSA are feasible and offer comparable long-term outcomes.ESA may reduce the need for splenic flexure dissociation,particularly when the tumor is located at the descending colon or its junction with the sigmoid colon,and especially in obese patients,elderly individuals with multiple complications,or those with severe adhesions in the splenic flexure of the surgical field.
基金Project supported by the National Natural Science Foundation of China(Nos.11872233,U2341231,and 12102245)。
文摘A novel elastic metamaterial is proposed with the aim of achieving lowfrequency broad bandgaps and bandgap regulation.The band structure of the proposed metamaterial is calculated based on the Floquet-Bloch theorem,and the boundary modes of each bandgap are analyzed to understand the effects of each component of the unit cell on the bandgap formation.It is found that the metamaterials with a low elastic modulus of ligaments can generate flexural wave bandgaps below 300 Hz.Multi-frequency vibrations can be suppressed through the selective manipulation of bandgaps.The dual-graded design of metamaterials that can significantly improve the bandgap width is proposed based on parametric studies.A new way that can regulate the bandgap is revealed by studying the graded elastic modulus in the substrate.The results demonstrate that the nonlinear gradient of the elastic modulus in the substrate offers better bandgap performance.Based on these analyses,the proposed elastic metamaterials can pave the way for multi-frequency vibration control,low-frequency bandgap broadening,and bandgap tuning.
基金Project supported by the National Natural Science Foundation of China(Grant No.12474440).
文摘This paper proposes a method to generate Bessel-like collimated beams with suppressed side lobes using the flexural vibration modes of a fixed boundary circular plate,which is excited by a longitudinally vibrating transducer in a ring excitation manner.The factors affecting the generation of Bessel-like collimated beams are investigated by theoretical analysis,numerical simulation and experimental methods.The results indicate that Bessel-like wave can be generated by a thin circular plate with fixed boundaries.The third-order mode of the circular plate can be modified to generate a collimated beam with suppressing side lobes when it is excited in a ring excitation manner and the excitation position lies between the first two nodal circles of the plate.As the excitation radius increases,the main lobe width of the resulting Bessel-like collimated beam decreases,the extent of the focusing region increases,and the amplitude of the side lobes initially increases and then decreases.Based on the simulation results,a prototype Bessel-like collimated beam generation system is made and measured experimentally.The experimental results are in good agreement with the numerical results.The Bessel-like collimated beam can be generated by the proposed system,which has potential application in the fields of long-range detection,imaging of highly attenuated materials,and airflow acceleration.
基金National Natural Science Foundation of China(No.12372130)。
文摘With an increased utilization of carbon fiber reinforced polymers(CFRPs)in high temperature environments,investigating their effects on materials becomes exceedingly important.This study presents a comparative investigation of thermo-oxidative aging effects on the flexural performance of two carbon fiber reinforced composite laminates(CFRCLs):a quasi-isotropic plain-woven CFRCL and a quasi-isotropic unidirectional layup CFRCL(designated as PW-CFRCL and UD-CFRCL,respectively).The CFRCLs were subjected to thermo-oxidative aging for specific durations,and their flexural strength was evaluated through three-point bending tests.The flexural strength of the laminates decreased with the prolonged aging duration.Despite having lower fiber content,PW-CFRCLs showed higher flexural strength than UD-CFRCLs.After eight days of aging,the flexural strength of PW-CFRCLs decreased by merely 4%-5%,while that of UD-CFRCLs decreased by 11%-14%.After 32 days of aging,the thinner PW-CFRCL with the lowest fiber content exhibited the highest flexural strength(595.52 MPa),followed by the thinner UD-CFRCL(549.83 MPa),then the thicker PW-CFRCL(445.29 MPa)and finally,the thicker UD-CFRCL(393.90 MPa).The decline in flexural properties of the laminates was primarily attributed to matrix cracking and interface debonding resulting from matrix oxidation.To validate the universality of this result,the finite element method was employed,showing a good correlation with the experimental findings.
文摘Ultrahigh-performance concrete(UHPC)is a groundbreaking kind of concrete that distinguishes itself from conventional concrete through its unique material properties.Understanding and managing the time-dependent characteristics of these materials is essential for their effective use in various construction applications.This study presents an experimental evaluation of the compressive and bending properties of the UHPC incorporating polypropylene,steel,and glass fibers.Based on ACI-211 guidelines,the UHPC mix was designed by using three types of aggregates:limestone,andesite,and quartzite,along with 5%fiber content(at varying percentages of 0,5%,10%,15%,and 20%)relative to the cementitious materials,and three different water-to-cement(w/c)ratios(0.24,0.3,and 0.4)were used.In this research,the compressive and flexural strength tests were conducted.The results show that increasing the values of the fibers significantly enhances the compressive strength of the studied samples.Furthermore,the utilization of fibers markedly improves the bending strength of the samples,demonstrating a strong correlation with the yield resistance of the material.Also,findings show that using steel fibers increases the compressive and bending strength of the tested samples more than polypropylene and glass fibers.For instance,in UHPC samples with 0.4 w/c,the average compressive strength values are 82.2 MPa,70.3 MPa,and 67.1 MPa for steel,polypropylene,and glass fibers,respectively.Also,in the flexural strength test,the modulus of rupture is obtained as an average of 6.24 MPa,5.24 MPa and 4.83 MPa for UHPC samples with steel,polypropylene and glass fibers,respectively.
文摘Corn starch was used as a templating agent,and an oxide mixture containing alumina,magnesia,zirconia and yttria was added in the sol-gel state.After slip casting,curing at 85℃,drying and sintering,high-performance porous alumina ceramics were obtained.The properties of the porous alumina ceramics were analyzed by means of SEM,XRD,flexural strength and porosity.The research findings showed that,when the starch content was 1 wt%,the prepared ceramic mainly consisted of four phases:α-Al_(2)O_(3),MgAl_(2)O_(4),ZrO,and YSZ.The flexural strength reached 157.27 MPa,the flexural strength of the green body was about 3 MPa,and the porosity was around 30%.
基金funded by Open Foundation of the State Key Laboratory of Advanced Inorganic Fibers and Composites(Grant No.KF2024SYS02)the Jiangsu Province Special Fund for Carbon Peaking and Carbon Neutrality Technology Innovation(Grant No.BE2022008)the Prioritized Academic Program Development for Higher Education Institutions in Jiangsu.
文摘This study investigates the low-velocity impact and post-impact flexural properties of 3D integrated woven spacer composites,focusing on their orthotropic behavior when tested along two principal directions,i.e.,warp(X-type)and weft(Y-type)directions.The same composite material was tested in these orientations to evaluate the differences in impact resistance and residual bending strength.Specimens were fabricated via vacuum-assisted molding and tested at 2,3,5,and 7 J impact energies using an Instron Ceast 9350 drop-weight impact testing machine,in accordance with ASTM D7136.Post-impact flexural tests were performed using a four-point bending method in accordance with ASTM D7264.The absorbed energy increased from 1.97 to 6.98 J,and the panel damage area ranged from 121 to 361 mm^(2) as impact energy roses.Specimens tested in the weft direction(Y-type)showed greater residual strength(up to 15.83 N)and displacement(up to 0.538 mm)than those tested in the warp direction(X-type).Ultrasonic C-scan imaging revealed localized matrix cracking and fiber failure damage patterns.Results emphasize the directional differences in impact resistance and residual bending properties,highlighting the importance of material orientation in structural applications.This study provides a foundation for utilizing 3D woven spacer composites in lightweight,damage-tolerant structural components.
基金supported by the National Key Research and Development Program of China(Nos.2021YFB3503100,2022YFB3505303,2021YFB3501500)the Major Projects in the Inner Mongolia Autonomous Region of China.
文摘In this work,a small amount of Al_(2)O_(3)powders(≤0.3 wt%)were incorporated into the Sm_(2)Co_(17)-type sin-tered magnets,obtaining both high mechanical and magnetic properties.It is found that 0.1%weight percentage of Al_(2)O_(3)doping is enough to enhance the flexural strength by about 20%(∼180 MPa for the case of the c-axis parallel to height).Meanwhile,the(BH)max remains around 219 kJ/m^(3),and Hcj is 2052 kA/m,which is over 95%of that of the original magnets without doping.The promising improvement in flexural strength is mainly attributed to the grain size effective refinement caused by Sm_(2)O_(3)particles including newly-formed ones from the reaction of the Al_(2)O_(3)powder and Sm in the matrix.Furthermore,the grain size of the magnets decreases significantly with increasing of Al_(2)O_(3)doping up to 0.3 wt%.Espe-cially,the grain size of 0.3 wt%Al_(2)O_(3)doped magnets is refined by 37%.However,the flexural strengths(for the c-axis parallel to height and the c-axis parallel to width cases)of the magnets decrease sequen-tially and are even lower than that of the original magnet.The microstructure investigations indicate that the decrease in flexural strength may closely be correlated to the larger cell size and the incomplete cell boundaries phase.The obtained results infer that the flexural strength is susceptible to not only grain size but also the cellular structure of the magnets.
基金Supported by National Natural Science Foundation of China(Grant Nos.51605166,51820105007)Fundamental Research Funds for the Central Universities of China
文摘A flexure hinge is a major component in designing compliant mechanisms that o ers unique possibilities in a wide range of application fields in which high positioning accuracy is required. Although various flexure hinges with di erent configurations have been successively proposed, they are often designed based on designers' experiences and inspirations. This study presents a systematic method for topological optimization of flexure hinges by using the level set method. Optimization formulations are developed by considering the functional requirements and geometrical constraints of flexure hinges. The functional requirements are first constructed by maximizing the compliance in the desired direction while minimizing the compliances in the other directions. The weighting sum method is used to construct an objective function in which a self-adjust method is used to set the weighting factors. A constraint on the symmetry of the obtained configuration is developed. Several numerical examples are presented to demonstrate the validity of the proposed method. The obtained results reveal that the design of a flexure hinge starting from the topology level can yield more choices for compliant mechanism design and obtain better designs that achieve higher performance.
基金supported by National Natural Science Foundation ofChina(Grant No.50935002)
文摘The thin-walled tube flexure（TWTF） hinges have important potential application value in the deployment mechanisms of satellite and solar array, but the optimal design of the TWTF hinges haven＇t been completely solved, which restricts their applications. An optimal design method for the qusai-static folding and deploying of TWTF hinges with double slots is presented based on the response surface theory. Firstly, the full factorial method is employed to design of the experiments. Then, the finite element models of the TWTF hinges with double slots are constructed to simulate the qusai-static folding and deploying non-linear analysis. What＇s more, the mathematical model of the TWTF flexure hinge quasi-static folding and deploying properties are derived by the response surface method. Considering of small mass and high stability, the peak moment of quasi-static folding and deploying as well as the lightless are set as the objectives to get the optimal performances. The relative errors of the objectives between the optimal design results and the FE analysis results are less than 7%, which demonstrates the precision of the surrogate models. Lastly, the parameter study shows that both the slots length and the slots width both have significant effects to the peak moment of quasi-static folding and deploying of TWTF hinges with double slots. However, the maximum Mises stress of quasi-static folding is more sensitive to the slots length than the slots width. The proposed research can be applied to optimize other thin-walled flexure hinges under quasi-static folding and deploying, which is of great importance to design of flexure hinges with high stability and low stress.
基金supported by National Natural Science Foundation of China(Grant No. 50675007)Program for New Century Excellent Talents in University of China (Grant No. NCET-06-0165)
文摘Large-deflection flexure pivot is widely used in high precision rotation application, but there are less flexure configurations and simple and convenient design methods, This paper presents a novel large-deflection curved-compliant annulus-shaped flexure pivot composed of six curved beam flexure elements. It can offer more than lO^angular stroke theoretically. Firstly, main-motion pseudo-rigid-body method is introduced to establish the flexure pivot model. Although pseudo-rigid-body method can be used to analyze the large-deformation flexure pivot performance, the method is definitely a laborious and difficult task for designing this novel flexure pivot. In order to simply the designing process, dimension-design graphs based on the parametric models and finite element analysis is presented. Using the dimension-design method as a tool, the designers can determine the optimal geometry rapidly, based on the stiffness and rotation demands of an annulus-shaped flexure pivot. Finally, dimension-design graph examples are given whose primary design aims to achieve a rotation stroke of annulus-shaped flexure pivot. The finite element analysis results show that the relative designing error between anticipative rotation stroke and graph design result is less than 4%. The dimensionless method used in designing annulus-shaped flexure pivot can reduce design process in both time and complexity. The novel annulus-shaped flexure pivot and dimension-design method are helpful supplement to configuration and design method of large-deflection flexure pivot.
基金Supported by National Natural Science Foundation of China(Grant Nos.51205134,91223201)Doctoral Fund of Ministry of Education of China(Grant No.20120172120001)Research Project of State Key Laboratory of Mechanical System and Vibration,China(Grant No.MSV201405)
文摘Conventional flexible joints generally have limited range of motion and high stress concentration. To overcome these shortcomings, corrugated flexure beam（CF beam） is designed because of its large flexibility obtained from longer overall length on the same span. The successful design of compliant mechanisms using CF beam requires manipulation of the stiffnesses as the design variables. Empirical equations of the CF beam stiffness components, except of the torsional stiffness, are obtained by curve-fitting method. The application ranges of all the parameters in each empirical equation are also discussed. The ratio of off-axis to axial stiffness is considered as a key characteristic of an effective compliant joint. And parameter study shows that the radius of semi-circular segment and the length of straight segment contribute most to the ratio. At last, CF beam is used to design translational and rotational flexible joints, which also verifies the validity of the empirical equations. CF beam with large flexibility is presented, and empirical equations of its stiffness are proposed to facilitate the design of flexible joint with large range of motion.
基金supported by National Natural Science Foundation of China (Grant No. 51175372)National Key Special Project of Science and Technology of China (Grant No. 2011ZX04016-011)
文摘Flexure mechanisms with decoupled characteristics have been widely utilized in precision positioning applications.However,these mechanisms suffer from either slow response or low load capability.Furthermore,asymmetric design always leads to thermal error.In order to solve these issues,a novel 2-DOF decoupled mechanism is developed by monolithically manufacturing sets of statically indeterminate symmetric（SIS） flexure structures in parallel.Symmetric design helps to eliminate the thermal error and Finite Element Analysis（FEA） results show that the maximum coupling ratio between X and Y axes is below 0.25% when a maximum pretension force of 200 N is applied.By ignoring the mass effect,all the SIS flexure structures are simplified to ＂spring-damper＂ components,from which the static and dynamics model are derived.The relation between the first resonant frequency of the mechanism and the load is investigated by incorporating the load mass into the proposed dynamics model.Analytical results show that even with a load of 0.5 kg,the first resonant frequency is still higher than 300 Hz,indicating a high load capability.The mechanism＇s static and dynamic performances are experimentally examined.The linear stiffnesses of the mechanism at the working platform and at the driving point are measured to be 3.563 0 N·μm-1 and 3.362 1 N·μm-1,respectively.The corresponding estimation values from analytical models are 3.405 7 N·μm-1 and 3.381 7 N·μm-1,which correspond to estimation errors of-4.41% and 0.6%,respectively.With an additional load of 0.16 kg,the measured and estimated first resonant frequencies are 362 Hz and 365 Hz,respectively.The estimation error is only 0.55%.The analytical and experimental results show that the developed mechanism has good performances in both decoupling ability and load capability;its static and dynamic performance can be precisely estimated from corresponding analytical models.The proposed mechanism has wide potentials in precision positioning applications.
基金Supported by National Natural Science Foundation of China(Grant No.51575017)
文摘The current research of kinetostatic characteristics in flexure mechanisms mainly focus on the improvement of accuracy. To reduce or eliminate the parasitic motion is considered as an approach by using the common knowledge of symmetry. However, there is no study on designing the flexure mechanisms with symmetrical features as many as possible for better kinetostatic performance, when considering the resulting cost by the symmetry. In this paper, the concept of degree of symmetry(DoS) is proposed for the first time, which is committed to symmetry design in the phase of conceptual design. A class of flexure mechanisms with 0?DoS, 1?DoS, 2?DoS and 3?DoS are synthesized respectively based on the Freedom and Constraint Topology method. Their overall compliance matrices in an analytical form formulated within the framework of the screw theory are used to analyze and compare the effect of different number of DoS on the kinetostatic characteristics for flexure mechanisms. The finite element analysis(FEA) simulations are implemented to verify the analytical results. These results show that the higher the DoS is, the smaller the parasitic motion error will be. The flexure model with 3?DoS is optimized according to the overall compliance matrix and then tested by using the FEA simulation. The testing result shows that with the best combination parameters, the parasitic motion error for 3?DoS mechanism is almost eliminated. This research introduces a design principle which can alleviate the unwanted parasitic motion for better accuracy.
基金Project(2002AA422260) supported by the National High Technology Research and Development Program of ChinaProject(2011-6) supported by CAST-HIT Joint Program,ChinaProject supported by Harbin Institute of Technology (HIT) Overseas Talents Introduction Program,China
文摘A novel 6-PSS flexible parallel mechanism was presented,which employed wide-range flexure hinges as passive joints.The proposed mechanism features micron level positioning accuracy over cubic centimeter scale workspace.A three-layer back-propagation(BP) neural network was utilized to the kinematics analysis,in which learning samples containing 1 280 groups of data based on stiffness-matrix method were used to train the BP model.The kinematics performance was accurately calculated by using the constructed BP model with 19 hidden nodes.Compared with the stiffness model,the simulation and numerical results validate that BP model can achieve millisecond level computation time and micron level calculation accuracy.The concept and approach outlined can be extended to a variety of applications.
文摘This paper presents a precise solution to predict the behavior of steel fiber reinforced concrete(SFRC) under the four point bending test(FPBT).All the force components at the beam section(before and after cracking) are formulated by applying these assumptions:a realistic stress-strain model is used for concrete behavior in compression,a linear response is considered for the uncracked tension region in a concrete constitutive model,and an exponential relationship is proposed as a stress-crack opening in the crack region which requires two parameters.Then the moment capacity of the critical cracked section is calculated by using these forces and satisfying equilibrium law at the section.Parametric studies are done on the behavior of SFRC to assess the sensitivity of the solution.Finally,this solution is validated with some existing experimental data.The result shows the proposed solution is able to estimate the behavior of SFRC under FPBT.
基金The authors would like to acknowledge support from the Open Foundation of the State Key Laboratory of Tribology ＆ Institute of Manufacturing Engineering （SKL2016B05）, and the National Natural Science Foundation of China （NSFC） （61327003）.
文摘This paper presents the design, development, and control of a large range beam flexure-based nano servo system for the micro-stereolithography （MSL） process. As a key enabler of high accuracy in this process, a compact desktop-size beam flexure-based nanopositioner was designed with millimeter range and nanometric motion quality. This beam flexure-based motion system is highly suitable for harsh operation conditions, as no assembly or maintenance is required during the operation. From a mechanism design viewpoint, a mirror-symmetric arrangement and appropriate redundant constraints are crucial to reduce undesired parasitic motion. Detailed finite element analysis （FEA） was conducted and showed satisfactory mechanical features. With the identified dynamic models of the nanopositioner, real-time control strategies were designed and implemented into the monolithically fabricated prototype system, demonstrating the enhanced tracking capability of the MSL process. The servo system has both a millimeter operating range and a root mean square （RMS） tracking error of about 80 nm for a circular traiectorv.
