The effects of ply orientation angle of composite flexures on stability of hingeless rotor blade system are studied.The composite hingeless rotor blade system is simplified as a hub,a flap flexure and a lag flexure.pi...The effects of ply orientation angle of composite flexures on stability of hingeless rotor blade system are studied.The composite hingeless rotor blade system is simplified as a hub,a flap flexure and a lag flexure.pitch bearing and main blade.The kinematics formulations are inferred by employing the moderate deflection beam theory.The shear deformation and warping related to torsion are considered.The quasi-steady strip theory with dynamic inflow effects is applied to obtain the aerodynamic loads acting on the blade.Based on these.the set of finite element formulations of a hingeless rotor blade system is worked out.The numerical results show that the ply angle of the composite flexures has great effects on the aeroelastic stability of rotor blade.展开更多
There is a lack of consensus on the optimal surgical approach for splenic flexure malignancies.Surgeons face the challenge of balancing successful oncological outcomes with the morbidity and functional effects of exte...There is a lack of consensus on the optimal surgical approach for splenic flexure malignancies.Surgeons face the challenge of balancing successful oncological outcomes with the morbidity and functional effects of extended colonic resection,considering the variable‘watershed’vasculature and lymphatic anatomy of the splenic flexure.While there is an increasing body of evidence supporting the oncological safety of a more conservative segmental resection,most of the data stems from retrospective single center studies.This article reviews the management strategies and examines the evidence supporting various surgical approaches to splenic flexure malignancies.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
To improve the rigidity and flexibility of conventional grouting materials,one visionary approach is to replace Portland cement with a composite cementitious system containing circulating fluidized bed fly ash(CFBFA)a...To improve the rigidity and flexibility of conventional grouting materials,one visionary approach is to replace Portland cement with a composite cementitious system containing circulating fluidized bed fly ash(CFBFA)and calcium carbide slag(CS),while adding ethylene-vinyl acetate(EVA)copolymer and CO_(2)as modifiers to enhance its properties.In this research,CFBFA and CS assumed the role of cementitious constituents,with EVA and CO_(2)serving as the modifying agent.A comprehensive exploration of the mechanism underlying the CO_(2)+EVA modified composite cementitious system was undertaken,delving into the differences of its compressive,bending,and flexural strengths.The addition of CO_(2)further improved the flexibility and rigidity of the materials and effectively improve the material's microstructure.It was worth noting that when CO_(2)+EVA co-modified CFBFA-CS composite cementitious materials,the flexibility and rigidity of the cementitious materials were significantly enhanced,and the bending strength,flexural strength and compressive strength were significantly increased by 48.76%,166.7%and 40.56%,respectively,and the 28 d density was reduced by 6.91%.These results provided a theoretical basis for the realization of avant-garde cementitious materials with functional properties.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
Self-healing(SH)polymer composites are a transformative achievement in polymer material technology that offers significant potential to extend the lifespan and reliability of materials.This work presents a novel appro...Self-healing(SH)polymer composites are a transformative achievement in polymer material technology that offers significant potential to extend the lifespan and reliability of materials.This work presents a novel approach to developing a hybrid natural-synthetic reinforced polymer composite with SH behavior using urea-free,non-toxic,environment-friendly material encapsulating resin,and hardener within a multicavity microcapsule(MC).This MC offers multiple healing because of its multicavity structure.These Xerogel MCs are integrated into hybrid bamboo/recycled glass fiber reinforced epoxy composite(25 wt% and 40 wt%)and were evaluated for their flexural strength,healing efficiency,moisture absorption,and thermal behavior.The results demonstrated that the composite containing 40 wt% exhibited the highest initial flexural strength and modulus retention after multiple healing cycles,approaching 80.67% and 61.34% respectively at 1st and 2nd cycles of healing efficiency.The behavior of self-healing hybrid composites(SHHC)in different environmental conditions was also investigated.Thermal Analysis TGA and DTA done on hybrid and other SH composites.Scanning electron microscopy shows the surface morphology of Xerogel MCs before and after damage,composite fractured surface,and how Healing Agent(HA)gets released and acquires surface after fracture.To ensure functional groups and chemical reactions between each component of the composite,FTIR analysis confirmed the successful encapsulation of HA inside MC.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
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
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
The damage processes of ordinary concrete and high strength concrete, attacked by solutions of 2. 5%, 5. 0% and 10% Na2SO4（mass fraction）are studied. And the effects of flexural loads with stress ratios of 25% and 5...The damage processes of ordinary concrete and high strength concrete, attacked by solutions of 2. 5%, 5. 0% and 10% Na2SO4（mass fraction）are studied. And the effects of flexural loads with stress ratios of 25% and 50% of the initial flexural strength on the damage process of concrete are also investigated. The results show that the damage process of concrete attacked by sulfate salt exhibits an initial damaged stage, a performance improving stage and a performance worsening stage. When the concentration of Na2SO4 in a solution increases from 2. 5% to 5.0%, the service time of the concrete decreases approximately 25%. Furthermore, it decreases to even 40% with an increase in a Na2SO4 concentration up to 10%. And the flexural load accelerates the deterioration rate of the concrete in the latter period. The stress ratio increases from 0 to 25%, the failure time of the concrete decreases 15% ; and the failure time decreases between 25% and 35% when the stress ratio increases from 25% to 50%. In addition, sulfate corrosion products of concrete are studied by SEM （scanning electron microscopy）, EDS （energy disperse spectroscopy） and XRD（X-ray diffraction）.展开更多
Al？50%SiC （volume fraction） composites containing different sizesofSiC particles （average sizesof 23, 38 and 75 μm） were prepared by powder metallurgy. The influences of SiC particle sizes and annealing on the p...Al？50%SiC （volume fraction） composites containing different sizesofSiC particles （average sizesof 23, 38 and 75 μm） were prepared by powder metallurgy. The influences of SiC particle sizes and annealing on the propertiesof the compositeswere investigated. The results show that SiC particles are distributed uniformly in the Al matrix. The coarse SiC particles result in higher coefficient of thermal expansion （CTE） and higher thermal conductivity （TC）, while fine SiC particles decrease CTE and improve flexural strength of the composites. The morphology and size of SiC particles in the composite are not influenced by the annealing treatment at 400℃for 6h. However, the CTE and the flexural strength of annealed composites are decreased slightly, and the TCis improved. The TC, CTE and flexural strength of the Al/SiC composite with averageSiC particlesize of75 μm are 156 W/（m·K）, 11.6×10^-6K^-1 and 229 MPa, respectively.展开更多
Four kinds of iron oxide pigments were added into wood-fiber/high-density-polyethylene composites （WF/HDPE） at three different concentrations, to determine the effects of pigments on the changes in the color and mec...Four kinds of iron oxide pigments were added into wood-fiber/high-density-polyethylene composites （WF/HDPE） at three different concentrations, to determine the effects of pigments on the changes in the color and mechanical properties of the composites before and after UV accelerated weathering. HDPE, wood fibers, pigments and other processing additives were dry-mixed in a high-speed mixer. The mixtures were extruded by two-step extrusion process with a self-designed twin-screw/single-screw extruder system. Color of the samples was determined according to CIE 1976 L^＊a^＊b^＊ system by a spec- trophotometer and the bending properties were tested to evaluate the mechanical properties before and after accelerated UV weathering. The result shows that the modulus of elasticity of WF/HDPE did not obvi- ously changed after incorporating with the pigments, but the bending strength increased. After accelerated aging for 2000 h, both color and mechanical properties significantly changed. Iron oxide red and black performed better than the other two pigments, and the pigments dosage of 2.28% in the composites is favourable.展开更多
The Al/Si/SiC composites with medium volume fraction for electronic packaging were fabricated by gas pressure infiltration.On the premise of keeping the machinability of the composites,the silicon carbide particles,wh...The Al/Si/SiC composites with medium volume fraction for electronic packaging were fabricated by gas pressure infiltration.On the premise of keeping the machinability of the composites,the silicon carbide particles,which have the similar size with silicon particles（average 13 μm）,were added to replace silicon particles of same volume fraction,and microstructure and properties of the composites were investigated.The results show that reinforcing particles are distributed uniformly and no apparent pores are observed in the composites.It is also observed that higher thermal conductivity（TC） and flexural strength will be obtained with the addition of SiC particles.Meanwhile,coefficient of thermal expansion（CTE） changes smaller than TC.Models for predicting thermal properties were also discussed.Equivalent effective conductivity（EEC） was proposed to make H-J model suitable for hybrid particles and multimodal particle size distribution.展开更多
Piezoelectric actuator has high stiffness, high frequency and infinite control precision, but a short output displacement which is often 1/1 000 of its length. In order to meet the requirements that tools feeding shou...Piezoelectric actuator has high stiffness, high frequency and infinite control precision, but a short output displacement which is often 1/1 000 of its length. In order to meet the requirements that tools feeding should be long-travel, high-frequency and high-precision in non-circular precision turning, a new one-freedom flexure hinge structure is put forward to amplify the output displacement of piezoelectric actuator. Theoretical analysis is done on the static and dynamic characteristics of the structure, differential equations are presented, and it is also verified by the finite element method. It's proved by experiments that the output displacement of the structure is 293 μm and its resonant frequency is 312 Hz.展开更多
文摘The effects of ply orientation angle of composite flexures on stability of hingeless rotor blade system are studied.The composite hingeless rotor blade system is simplified as a hub,a flap flexure and a lag flexure.pitch bearing and main blade.The kinematics formulations are inferred by employing the moderate deflection beam theory.The shear deformation and warping related to torsion are considered.The quasi-steady strip theory with dynamic inflow effects is applied to obtain the aerodynamic loads acting on the blade.Based on these.the set of finite element formulations of a hingeless rotor blade system is worked out.The numerical results show that the ply angle of the composite flexures has great effects on the aeroelastic stability of rotor blade.
文摘There is a lack of consensus on the optimal surgical approach for splenic flexure malignancies.Surgeons face the challenge of balancing successful oncological outcomes with the morbidity and functional effects of extended colonic resection,considering the variable‘watershed’vasculature and lymphatic anatomy of the splenic flexure.While there is an increasing body of evidence supporting the oncological safety of a more conservative segmental resection,most of the data stems from retrospective single center studies.This article reviews the management strategies and examines the evidence supporting various surgical approaches to splenic flexure malignancies.
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funded by National Natural Science Foundation of China(22378241)。
文摘To improve the rigidity and flexibility of conventional grouting materials,one visionary approach is to replace Portland cement with a composite cementitious system containing circulating fluidized bed fly ash(CFBFA)and calcium carbide slag(CS),while adding ethylene-vinyl acetate(EVA)copolymer and CO_(2)as modifiers to enhance its properties.In this research,CFBFA and CS assumed the role of cementitious constituents,with EVA and CO_(2)serving as the modifying agent.A comprehensive exploration of the mechanism underlying the CO_(2)+EVA modified composite cementitious system was undertaken,delving into the differences of its compressive,bending,and flexural strengths.The addition of CO_(2)further improved the flexibility and rigidity of the materials and effectively improve the material's microstructure.It was worth noting that when CO_(2)+EVA co-modified CFBFA-CS composite cementitious materials,the flexibility and rigidity of the cementitious materials were significantly enhanced,and the bending strength,flexural strength and compressive strength were significantly increased by 48.76%,166.7%and 40.56%,respectively,and the 28 d density was reduced by 6.91%.These results provided a theoretical basis for the realization of avant-garde cementitious materials with functional properties.
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%.
文摘Self-healing(SH)polymer composites are a transformative achievement in polymer material technology that offers significant potential to extend the lifespan and reliability of materials.This work presents a novel approach to developing a hybrid natural-synthetic reinforced polymer composite with SH behavior using urea-free,non-toxic,environment-friendly material encapsulating resin,and hardener within a multicavity microcapsule(MC).This MC offers multiple healing because of its multicavity structure.These Xerogel MCs are integrated into hybrid bamboo/recycled glass fiber reinforced epoxy composite(25 wt% and 40 wt%)and were evaluated for their flexural strength,healing efficiency,moisture absorption,and thermal behavior.The results demonstrated that the composite containing 40 wt% exhibited the highest initial flexural strength and modulus retention after multiple healing cycles,approaching 80.67% and 61.34% respectively at 1st and 2nd cycles of healing efficiency.The behavior of self-healing hybrid composites(SHHC)in different environmental conditions was also investigated.Thermal Analysis TGA and DTA done on hybrid and other SH composites.Scanning electron microscopy shows the surface morphology of Xerogel MCs before and after damage,composite fractured surface,and how Healing Agent(HA)gets released and acquires surface after fracture.To ensure functional groups and chemical reactions between each component of the composite,FTIR analysis confirmed the successful encapsulation of HA inside MC.
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 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 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The National High Technology Research and Develop-ment Program of China(863 Program)(No.2003AA33X100)the NationalNatural Science Foundation of China(No.50708046,50739001).
文摘The damage processes of ordinary concrete and high strength concrete, attacked by solutions of 2. 5%, 5. 0% and 10% Na2SO4（mass fraction）are studied. And the effects of flexural loads with stress ratios of 25% and 50% of the initial flexural strength on the damage process of concrete are also investigated. The results show that the damage process of concrete attacked by sulfate salt exhibits an initial damaged stage, a performance improving stage and a performance worsening stage. When the concentration of Na2SO4 in a solution increases from 2. 5% to 5.0%, the service time of the concrete decreases approximately 25%. Furthermore, it decreases to even 40% with an increase in a Na2SO4 concentration up to 10%. And the flexural load accelerates the deterioration rate of the concrete in the latter period. The stress ratio increases from 0 to 25%, the failure time of the concrete decreases 15% ; and the failure time decreases between 25% and 35% when the stress ratio increases from 25% to 50%. In addition, sulfate corrosion products of concrete are studied by SEM （scanning electron microscopy）, EDS （energy disperse spectroscopy） and XRD（X-ray diffraction）.
基金Project support by the 2015 Shandong Province Project for Outstanding Subject Talent Group,China
文摘Al？50%SiC （volume fraction） composites containing different sizesofSiC particles （average sizesof 23, 38 and 75 μm） were prepared by powder metallurgy. The influences of SiC particle sizes and annealing on the propertiesof the compositeswere investigated. The results show that SiC particles are distributed uniformly in the Al matrix. The coarse SiC particles result in higher coefficient of thermal expansion （CTE） and higher thermal conductivity （TC）, while fine SiC particles decrease CTE and improve flexural strength of the composites. The morphology and size of SiC particles in the composite are not influenced by the annealing treatment at 400℃for 6h. However, the CTE and the flexural strength of annealed composites are decreased slightly, and the TCis improved. The TC, CTE and flexural strength of the Al/SiC composite with averageSiC particlesize of75 μm are 156 W/（m·K）, 11.6×10^-6K^-1 and 229 MPa, respectively.
基金supported by the National Natural Science Foundation of China (30671644, 30771680)
文摘Four kinds of iron oxide pigments were added into wood-fiber/high-density-polyethylene composites （WF/HDPE） at three different concentrations, to determine the effects of pigments on the changes in the color and mechanical properties of the composites before and after UV accelerated weathering. HDPE, wood fibers, pigments and other processing additives were dry-mixed in a high-speed mixer. The mixtures were extruded by two-step extrusion process with a self-designed twin-screw/single-screw extruder system. Color of the samples was determined according to CIE 1976 L^＊a^＊b^＊ system by a spec- trophotometer and the bending properties were tested to evaluate the mechanical properties before and after accelerated UV weathering. The result shows that the modulus of elasticity of WF/HDPE did not obvi- ously changed after incorporating with the pigments, but the bending strength increased. After accelerated aging for 2000 h, both color and mechanical properties significantly changed. Iron oxide red and black performed better than the other two pigments, and the pigments dosage of 2.28% in the composites is favourable.
基金Project (60776019) supported by the National Natural Science Foundation of ChinaProject (61-TP-2010) supported by the Research Fund of the State Key Laboratory of Solidification Processing (NWPU),China
文摘The Al/Si/SiC composites with medium volume fraction for electronic packaging were fabricated by gas pressure infiltration.On the premise of keeping the machinability of the composites,the silicon carbide particles,which have the similar size with silicon particles（average 13 μm）,were added to replace silicon particles of same volume fraction,and microstructure and properties of the composites were investigated.The results show that reinforcing particles are distributed uniformly and no apparent pores are observed in the composites.It is also observed that higher thermal conductivity（TC） and flexural strength will be obtained with the addition of SiC particles.Meanwhile,coefficient of thermal expansion（CTE） changes smaller than TC.Models for predicting thermal properties were also discussed.Equivalent effective conductivity（EEC） was proposed to make H-J model suitable for hybrid particles and multimodal particle size distribution.
文摘Piezoelectric actuator has high stiffness, high frequency and infinite control precision, but a short output displacement which is often 1/1 000 of its length. In order to meet the requirements that tools feeding should be long-travel, high-frequency and high-precision in non-circular precision turning, a new one-freedom flexure hinge structure is put forward to amplify the output displacement of piezoelectric actuator. Theoretical analysis is done on the static and dynamic characteristics of the structure, differential equations are presented, and it is also verified by the finite element method. It's proved by experiments that the output displacement of the structure is 293 μm and its resonant frequency is 312 Hz.
