The fundamental shear horizontal（SH0） wave has several unique features that are attractive for long-range nondestructive testing（NDT）. By a careful design of the geometric configuration, electromagnetic acoustic t...The fundamental shear horizontal（SH0） wave has several unique features that are attractive for long-range nondestructive testing（NDT）. By a careful design of the geometric configuration, electromagnetic acoustic transducers（EMATs） have the capability to generate a wide range of guided wave modes, such as Lamb waves and shear-horizontal（SH） waves in plates. However, the performance of EMATs is influenced by their parameters. To evaluate the performance of periodic permanent magnet（PPM） EMATs, a distributed-line-source model is developed to calculate the angular acoustic field cross-section in the far-field. Numerical analysis is conducted to investigate the performance of such EMATs with different geometric parameters, such as period and number of magnet arrays, and inner and outer coil widths. Such parameters have a great influence on the directivity of the generated SH0 waves that arises mainly in the amplitude and width of both main and side lobes. According to the numerical analysis, these parameters are optimized to obtain better directivity. Optimized PPM EMATs are designed and used for NDT of strip plates. Experimental results show that the lateral boundary of the strip plate has no perceivable influence on SHO-wave propagation, thus validating their used in NDT. The proposed model predicts the radiation pattern ofPPM EMATs, and can be used for their parameter optimization.展开更多
Cohesive element is developed from the Dugdal-Barenblatt model in the field of fracture mechanics. The mechanical constitutive relation of cohesive element can be artificially assumed depending on the specific applica...Cohesive element is developed from the Dugdal-Barenblatt model in the field of fracture mechanics. The mechanical constitutive relation of cohesive element can be artificially assumed depending on the specific applications. It has been successfully applied in the study of crystal plasticity/brittle fracture process and decohesion between delaminations. In this paper, tensile experiments of large steel plate with different length of pre-existing cracks are conducted. Based on commercial software ABAQUS, cohesive element is adopted to simulate the tensile tests, and appropriate parameter values are obtained by fitting displacement-force curves. Using these parameters, a numerical method is presented by applying cohesive element to thermo-elastic-plastic finite element method （TEP-FEM） to simulate plate rigid restraint cracking （PRRC） tests. By changing constitutive relation of cohesive element, dimensions of the model and welding conditions, the influence of welding restraint intensity and welding conditions on the crack propagation are discussed, respectively. Three types of welding cold cracking are simulated. Significant influence of welding cold cracking on resistant stress in welding line is captured by this numerical method.展开更多
Brucellosis is a zoonotic disease of economic importance. The clinical manifestations vary in humans;therefore a good diagnostic test is required to confirm the disease. The serum tube agglutination (SA) test, though ...Brucellosis is a zoonotic disease of economic importance. The clinical manifestations vary in humans;therefore a good diagnostic test is required to confirm the disease. The serum tube agglutination (SA) test, though still the most widely test used, can be problematic for the diagnosis of chronic infections. The other supplementary tests, such as the complement fixation (CF) test and ELISA, require special equipment, reagents and trained personnel. The Rose Bengal plate (RBP) test has shown potential as a good rapid diagnostic test. This is a report of serum samples from suspected cases of brucellosis that were tested using the RBP, SA and CF tests. The RBP test was shown to have a better relative sensitivity and as good specificity as the SA when compared with the CF test, and may be a useful initial diagnostic test for hospitals in remote rural areas if properly conducted with well stored antigen.展开更多
A full-scale composite floor plate was tested to investigate the flexural behavior and in-plane effects of the floor slab in a grillage of composite beams that reduces the tendency for longitudinal splitting of the co...A full-scale composite floor plate was tested to investigate the flexural behavior and in-plane effects of the floor slab in a grillage of composite beams that reduces the tendency for longitudinal splitting of the concrete slab along the line of the primary beams. This is important in cases where the steel decking is discontinuous when it is orientated parallel to the beams. In this case, it is important to demonstrate that the amount of transverse reinforcement required to transfer local forces from the shear connectors can be reduced relative to the requirements of Eurocode 4. The mechanism under study involved in-plane compression forces being developed in the slab due to the restraining action of the floor plate, which was held in position by the peripheral composite beams;while the secondary beams acted as transverse ties to resist the forces in the floor plate that would otherwise lead to splitting of the slab along the line of the primary beams. The tendency for cracking along the center line of the primary beam and at the peripheral beams was closely monitored. This is the first large floor plate test that has been carried out under laboratory conditions since the Cardington tests in the early 1990s, although those tests were not carried out to failure. This floor plate test was designed so that the longitudinal force transferred by the primary beams was relatively high (i.e., it was designed for full shear connection), but the transverse reinforcement was taken as the minimum of 0.2% of the concrete area. The test confirmed that the primary beams reached their plastic bending resistance despite the discontinuous decking and transverse reinforcement at the minimum percentage given in Eurocode 4. Based on this test, a reduction factor due to shear connectors at edge beams without U-bars is proposed.展开更多
Good interlayer interface performance is the key to maintaining the stability of CRTSⅡslab ballastless track structure.In a project,the tangential cohesion parameters of CRTSⅡslab ballastless track structure are gen...Good interlayer interface performance is the key to maintaining the stability of CRTSⅡslab ballastless track structure.In a project,the tangential cohesion parameters of CRTSⅡslab ballastless track structure are generally measured by horizontal push plate test,so as to measure the interlayer interface performance.Horizontal push plate contraction scale and full scale tests of CRTSⅡslab ballastless track structure are carried out to obtain the tangential force-displacement relation curve of the interlayer interface,thus obtaining the parameters of cohesion model.A threedimensional progressive damage analysis model for CRTSⅡslab ballastless track structure is established,the whole process inversion of the horizontal push plate test is carried out,and the reliability of the contraction scale test results is verified by means of simulation and comparative analysis of test results.The results show that the greater the tangential stiffness of the interlayer interface of the track structure,the weaker the interlayer deformation coordination capability;the more significant the non-uniformity of the interface damage,the more likely the stress concentration;the greater the fracture toughness,the less likely the disjoint in the interlayer interface of the track structure.展开更多
In this paper, a compression-to-tension conversion technique is developed by applying predominant mode I loading test, using a servo-controlled compression system. The technique is applied to thin mortar plate specime...In this paper, a compression-to-tension conversion technique is developed by applying predominant mode I loading test, using a servo-controlled compression system. The technique is applied to thin mortar plate specimens of different widths that include a prefabricated crack on either a single side to facilitate unilateral crack propagation, or prefabricated cracks positioned on both sides asymmetrically with respect to the specimen midpoint to facilitate bilateral crack propagation under direct tensile stress with a loading rate of 0.001 mm/s. The results show that the main pathways of unilateral crack propagation governing specimen failure are fluctuated locally, but present an approximately straight line overall in the absence of pre-existing internal defects. However, the pathways of bilateral crack propagation are relatively complex, although they present similar characteristics. Analysis results suggest that bilateral crack propagation can be basically divided into three stages, i.e. a stage of linear propagation, a stage representing deviation from the other crack, and a stage where one crack approaches either the other crack or approaches the opposite edge of the specimen, and thereby forming a continuous crack through the specimen. In addition, the stressestrain curves of bilateral crack specimens do not vary significantly around the point of peak stress prior to specimen failure, which means that the specimens do not fail instantaneously.展开更多
The statistical testing models of the plate tectonic units and the hypothesis of their rigidity is presented by using the dense geodetic data, and to a certain extent the established statistic value c...The statistical testing models of the plate tectonic units and the hypothesis of their rigidity is presented by using the dense geodetic data, and to a certain extent the established statistic value can be regarded as a quantitative index to compare the rigidity degrees of different blocks. The several conclusions about the global megaplates and the regional tectonics of China are tested and verified by actual calculations, which testifies the effectiveness of this method in testing the rigidity degree and delineating their boundaries.展开更多
The stress on a test specimen during tensile testing is generally measured by a strain gauge. This method has some problems in that it would influence the measurement conditions of the tensile test and can evaluate on...The stress on a test specimen during tensile testing is generally measured by a strain gauge. This method has some problems in that it would influence the measurement conditions of the tensile test and can evaluate only the position at which the strain gauge is attached. The acoustoelastic method is proposed as a method replacing the strain gauge method. However, an ultrasonic sensor with a piezoelectric oscillator requires a coupling medium to inject an ultrasonic wave into a solid material. This condition, due to the error factor of the stress measurement, makes it difficult for the ultrasonic sensor to move on the specimen. We then tried to develop a non-contact stress measurement system during tensile testing using an electromagnetic acoustic transducer (EMAT) with an SH0-plate wave and S0-Lamb wave. The EMAT can measure the propagation time in which the ultrasonic wave travels between a receiver and a transmitter without a coupling medium during the tensile testing and can move easily. The interval between the transmitter and the receiver is 10mm and can be moved along the parallel direction or the vertical direction of the tensile load. The transit time was measured by a cross-correlation method and converted into the stress on the test specimen using the acoustoelastic method. We confirmed that the stress measurement using an SH0-plate wave was superior to that with an S0-Lamb wave.展开更多
The non-destructive testing(NDT)of debonding in stainless steel composites plate(SSCP)is performed by infrared thermography,finite element analysis(FEA)software ANSYS is taken as the simulative tool,and 2D simulative ...The non-destructive testing(NDT)of debonding in stainless steel composites plate(SSCP)is performed by infrared thermography,finite element analysis(FEA)software ANSYS is taken as the simulative tool,and 2D simulative model has been set up to investigate effect of the thickness of coating and/or substrate on the detectibility of debonging in SSCPs.Two parameters,namely the maximum defect temperature difference and defect appearing index,are defined to evaluate the detectivity of defects,and their computational methods and formulas are given respectively.The preliminary changing tendency of the maximum defect temperature difference and defect appearing index with the thickness of coating and/or substrate is found by numerical simulation.展开更多
A composite shear wall concept based on concrete filled steel tube （CFST） columns and steel plate （SP） deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipat...A composite shear wall concept based on concrete filled steel tube （CFST） columns and steel plate （SP） deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements： CFST columns; SP deep beams; and reinforced concrete （RC） strips. The RC strips are intended to allow the core structural elements - the CFST columns and SP deep beams - to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.展开更多
The correlations between thermal and physical properties were studied through thermal conductivity measurements, hardness tests, salt spray tests (AASS) among the surface treatment samples named K20, K40 with thicknes...The correlations between thermal and physical properties were studied through thermal conductivity measurements, hardness tests, salt spray tests (AASS) among the surface treatment samples named K20, K40 with thickness of 20, 40 μm respectively and raw sample named K00. In thermal conductivity measurements, there are little differences among the samples as K00, K20 and K40, they exhibit 153.39, 150.69 and 149.76 W/(m·K), respectively. According to hardness tests, K00, K20 and K40 exhibit 87.9, 259.7 and 344.8 in Vickers values. In the result of salt spray tests to examine the effects on corrosion resistance, K00, K20 and K40 exhibit the grade of 3?5, 2.0?9.8 and 10, respectively. The mutual relation of the above results was analyzed. It is found that the surface treatments do not affect the thermal conductivity of aluminum and result in the improvement of physical properties. As a result of the technology, the surface improvement of aluminum alloy specimen is achieved without thermal degradation. It validates the ability of the aluminum plate heat exchangers with surface treatment to enhance the corrosion resistance. Present work is performed as the first fundamental threshold in the process of aluminum plate heat exchangers development to check out its possibility, therefore the next step-experimental and numerical study of practical aluminum plate heat exchangers will be made.展开更多
Bending fatigue tests were carried out on cruciform welded joints of China-made platform steel E36-Z35 with plate thickness of 16mm, 32mm and 40mm. The tests consisted of testing in air and in sea water with and witho...Bending fatigue tests were carried out on cruciform welded joints of China-made platform steel E36-Z35 with plate thickness of 16mm, 32mm and 40mm. The tests consisted of testing in air and in sea water with and without cathodic protection (-850mV. SCE). The sea water corrosion fatigue tests were conducted at loading frequency of 0.2 Hz and sea water temperature of 20°C. The test results show an obvious reduction in fatigue strength of welded joints with increasing plate thickness in all the three test conditions. The present paper proposes different thickness corrections for fatigue strength and fatigue life of welded joints in air and in sea water with and without cathodic protection respectively. In addition, an explanation for thickness effect on fatigue life of welded joints is given by using the theory of fracture mechanics.展开更多
In eddy current testing, the law of attenuation of eddy current(EC) is of great concern. In conductive half space under the excitation of uniform magnetic field, the EC density decreases exponentially in the depth dir...In eddy current testing, the law of attenuation of eddy current(EC) is of great concern. In conductive half space under the excitation of uniform magnetic field, the EC density decreases exponentially in the depth direction. However, in conductor with finite thickness tested by coil, the distribution of EC in the depth direction is more complicated. This paper studies the characteristics of EC attenuation in metallic plate of finite thickness. Simulation results show that there is an EC reflection at the bottom of plate, which changes the law of EC attenuation. A new concept, namely the equivalent attenuation coefficient, is proposed to quantify the speed of EC attenuation. The characteristics of EC attenuation are utilized to explain the nonmonotonic relation between coil voltage and plate thickness. Procedure of selecting frequency is discussed. Thereafter, measurement of plate thickness is carried out and accurate result is obtained.展开更多
The purpose of this study was to compare the biomechanical stability obtained by using our technique featured an anatomical plate and compression bolts versus that of the conventional anatomic plate and cancellous scr...The purpose of this study was to compare the biomechanical stability obtained by using our technique featured an anatomical plate and compression bolts versus that of the conventional anatomic plate and cancellous screws in the fixation of intraarticular calcaneal fractures.Eighteen fresh frozen lower limbs of cadavers were used to create a reproductive Sanders type-Ⅲ calcaneal fracture model by using osteotomy.The calcaneus fractures were randomly selected to be fixed either using our anatomical plate and compression bolts or conventional anatomic plate and cancellous screws.Reduction of fracture was evaluated through X radiographs.Each calcaneus was successively loaded at a frequency of 1 Hz for 1000 cycles through the talus using an increasing axial force 20 N to 200 N and 20 N to 700 N,representing the partial weight bearing and full weight bearing,respectively,and then the specimens were loaded to failure.Data extracted from the mechanical testing machine were recorded and used to test for difference in the results with the Wilcoxon signed rank test.No significant difference was found between our fixation technique and conventional technique in displacement during 20-200 N cyclic loading(P=0.06),while the anatomical plate and compression bolts showed a great lower irreversible deformation during 20-700 N cyclic loading(P=0.008).The load achieved at loss of fixation of the constructs for the two groups had significant difference:anatomic plate and compression bolts at 3839.6±152.4 N and anatomic plate and cancellous screws at 3087.3±58.9 N(P=0.008).There was no significant difference between the ultimate displacements.Our technique featured anatomical plate and compression bolts for calcaneus fracture fixation was demonstrated to provide biomechanical stability as good as or better than the conventional anatomic plate and cancellous screws under the axial loading.The study supports the mechanical viability of using our plate and compression bolts for the fixation of calcaneal fracture.展开更多
Background: There is a large assortment of modalities for the surgical treatment/management of distal radius fractures (DRFs), where the most widely used is the fixed-angle volar plating (VLP) system, which, sometimes...Background: There is a large assortment of modalities for the surgical treatment/management of distal radius fractures (DRFs), where the most widely used is the fixed-angle volar plating (VLP) system, which, sometimes, is referred to as the “surgical modality of choice”. While outcomes with each modality are usually good to excellent, each has its share of shortcomings and complications. Thus, there is scope for improvements to existing modalities and/or introduction of new ones. Study Purpose: We introduce a novel modality, namely, the prototype of an intramedullary injectable bioresorbable polymer-bioresorbable balloon osteosynthesis (IPBO) system, and investigated its plausibility. Experimental Procedures: The biomechanical performance of a construct comprising a synthetic distal radius (fourth-generation Sawbones?) on which a simulated fracture was created (4-mm wide osteotomy positioned 25 mm from the most distal end of the radius) and fixated with a placement of the IPBO system (SIPBO Construct) was compared to that when the fixation was with an approved Ti-6Al-4V alloy VLP system (SVLP Construct), under a clinically-relevant compressive loading protocol. Performance involved determination of quantitative parameters of the construct (initial longitudinal stiffness (ICLS), final longitudinal stiffness (FCLS), and load-to-failure (Pf)) and observation and recording of features of the construct at the fracture point. We also determined the quantitative parameters for the intact synthetic distal radius (control). Results: For each of the quantitative parameters, the range of values for SIPBO Construct was within that for SVLP Construct, suggesting that the IPBO System is a plausible modality. Also, for SIPBO Construct, failure occurred within the polymer zone, whereas, for SVLP Construct, some failure features were fracture of the cortical wall and of the dorsal proximal fragments. Conclusion: The findings suggest that the IPBO system is plausible. As such, it merits further study;for example, determination of the influence of fracture gap fill ratio (defined as the proportion of the fracture gap that is filled by the expanding balloon as the polymer is injected into the balloon) on a large collection of quantitative biomechanical parameters.展开更多
In this study, the interaction between cylindrical specimen made ofhomogeneous, isotropic, and linearlyelastic material and loading jaws of any curvature is considered in the Brazilian test. It is assumed thatthe spec...In this study, the interaction between cylindrical specimen made ofhomogeneous, isotropic, and linearlyelastic material and loading jaws of any curvature is considered in the Brazilian test. It is assumed thatthe specimen is diametrically compressed by elliptic normal contact stresses. The frictional contactstresses between the specimen and platens are neglected. The analytical solution starts from the contactproblem of the loading jaws of any curvature and cylindrical specimen. The contact width, correspondingloading angle （2 ^0）, and elliptical stresses obtained through solution of the contact problems are used asboundary conditions for a cylindrical specimen. The problem of the theory of elasticity for a cylinder issolved using Muskhelishvili＇s method. In this method, the displacements and stresses are represented interms of two analytical functions of a complex variable. In the main approaches, the nonlinear interactionbetween the loading bearing blocks and the specimen as well as the curvature of their surfacesand the elastic parameters of their materials are taken into account. Numerical examples are solved usingMATLAB to demonstrate the influence of deformability, curvature of the specimen and platens on thedistribution of the normal contact stresses as well as on the tensile and compressive stresses actingacross the loaded diameter. Derived equations also allow calculating the modulus of elasticity, totaldeformation modulus and creep parameters of the specimen material based on the experimental data ofradial contraction of the specimen.展开更多
基金supported by National Natural Science Foundation of China(Grant Nos.51075012,10772008)Beijing Municipal Natural Science Foundation of China(Grant No.1122005)
文摘The fundamental shear horizontal（SH0） wave has several unique features that are attractive for long-range nondestructive testing（NDT）. By a careful design of the geometric configuration, electromagnetic acoustic transducers（EMATs） have the capability to generate a wide range of guided wave modes, such as Lamb waves and shear-horizontal（SH） waves in plates. However, the performance of EMATs is influenced by their parameters. To evaluate the performance of periodic permanent magnet（PPM） EMATs, a distributed-line-source model is developed to calculate the angular acoustic field cross-section in the far-field. Numerical analysis is conducted to investigate the performance of such EMATs with different geometric parameters, such as period and number of magnet arrays, and inner and outer coil widths. Such parameters have a great influence on the directivity of the generated SH0 waves that arises mainly in the amplitude and width of both main and side lobes. According to the numerical analysis, these parameters are optimized to obtain better directivity. Optimized PPM EMATs are designed and used for NDT of strip plates. Experimental results show that the lateral boundary of the strip plate has no perceivable influence on SHO-wave propagation, thus validating their used in NDT. The proposed model predicts the radiation pattern ofPPM EMATs, and can be used for their parameter optimization.
文摘Cohesive element is developed from the Dugdal-Barenblatt model in the field of fracture mechanics. The mechanical constitutive relation of cohesive element can be artificially assumed depending on the specific applications. It has been successfully applied in the study of crystal plasticity/brittle fracture process and decohesion between delaminations. In this paper, tensile experiments of large steel plate with different length of pre-existing cracks are conducted. Based on commercial software ABAQUS, cohesive element is adopted to simulate the tensile tests, and appropriate parameter values are obtained by fitting displacement-force curves. Using these parameters, a numerical method is presented by applying cohesive element to thermo-elastic-plastic finite element method （TEP-FEM） to simulate plate rigid restraint cracking （PRRC） tests. By changing constitutive relation of cohesive element, dimensions of the model and welding conditions, the influence of welding restraint intensity and welding conditions on the crack propagation are discussed, respectively. Three types of welding cold cracking are simulated. Significant influence of welding cold cracking on resistant stress in welding line is captured by this numerical method.
文摘Brucellosis is a zoonotic disease of economic importance. The clinical manifestations vary in humans;therefore a good diagnostic test is required to confirm the disease. The serum tube agglutination (SA) test, though still the most widely test used, can be problematic for the diagnosis of chronic infections. The other supplementary tests, such as the complement fixation (CF) test and ELISA, require special equipment, reagents and trained personnel. The Rose Bengal plate (RBP) test has shown potential as a good rapid diagnostic test. This is a report of serum samples from suspected cases of brucellosis that were tested using the RBP, SA and CF tests. The RBP test was shown to have a better relative sensitivity and as good specificity as the SA when compared with the CF test, and may be a useful initial diagnostic test for hospitals in remote rural areas if properly conducted with well stored antigen.
基金part of a collaborative project between the Steel Construction Institute, the University of Stuttgart, the University of Luxembourg, Arcelor Mittal S.A., and the University of Bradford funded by the European Community’s Research Fund for Coal and Steel (RFSR-CT-2012-00030)
文摘A full-scale composite floor plate was tested to investigate the flexural behavior and in-plane effects of the floor slab in a grillage of composite beams that reduces the tendency for longitudinal splitting of the concrete slab along the line of the primary beams. This is important in cases where the steel decking is discontinuous when it is orientated parallel to the beams. In this case, it is important to demonstrate that the amount of transverse reinforcement required to transfer local forces from the shear connectors can be reduced relative to the requirements of Eurocode 4. The mechanism under study involved in-plane compression forces being developed in the slab due to the restraining action of the floor plate, which was held in position by the peripheral composite beams;while the secondary beams acted as transverse ties to resist the forces in the floor plate that would otherwise lead to splitting of the slab along the line of the primary beams. The tendency for cracking along the center line of the primary beam and at the peripheral beams was closely monitored. This is the first large floor plate test that has been carried out under laboratory conditions since the Cardington tests in the early 1990s, although those tests were not carried out to failure. This floor plate test was designed so that the longitudinal force transferred by the primary beams was relatively high (i.e., it was designed for full shear connection), but the transverse reinforcement was taken as the minimum of 0.2% of the concrete area. The test confirmed that the primary beams reached their plastic bending resistance despite the discontinuous decking and transverse reinforcement at the minimum percentage given in Eurocode 4. Based on this test, a reduction factor due to shear connectors at edge beams without U-bars is proposed.
文摘Good interlayer interface performance is the key to maintaining the stability of CRTSⅡslab ballastless track structure.In a project,the tangential cohesion parameters of CRTSⅡslab ballastless track structure are generally measured by horizontal push plate test,so as to measure the interlayer interface performance.Horizontal push plate contraction scale and full scale tests of CRTSⅡslab ballastless track structure are carried out to obtain the tangential force-displacement relation curve of the interlayer interface,thus obtaining the parameters of cohesion model.A threedimensional progressive damage analysis model for CRTSⅡslab ballastless track structure is established,the whole process inversion of the horizontal push plate test is carried out,and the reliability of the contraction scale test results is verified by means of simulation and comparative analysis of test results.The results show that the greater the tangential stiffness of the interlayer interface of the track structure,the weaker the interlayer deformation coordination capability;the more significant the non-uniformity of the interface damage,the more likely the stress concentration;the greater the fracture toughness,the less likely the disjoint in the interlayer interface of the track structure.
基金support provided by the Strategic Program of Chinese Academy of Sciences (Grant No. XDB10030400)the Hundred Talent Program of Chinese Academy of Sciences (Grant No. Y323081C01)
文摘In this paper, a compression-to-tension conversion technique is developed by applying predominant mode I loading test, using a servo-controlled compression system. The technique is applied to thin mortar plate specimens of different widths that include a prefabricated crack on either a single side to facilitate unilateral crack propagation, or prefabricated cracks positioned on both sides asymmetrically with respect to the specimen midpoint to facilitate bilateral crack propagation under direct tensile stress with a loading rate of 0.001 mm/s. The results show that the main pathways of unilateral crack propagation governing specimen failure are fluctuated locally, but present an approximately straight line overall in the absence of pre-existing internal defects. However, the pathways of bilateral crack propagation are relatively complex, although they present similar characteristics. Analysis results suggest that bilateral crack propagation can be basically divided into three stages, i.e. a stage of linear propagation, a stage representing deviation from the other crack, and a stage where one crack approaches either the other crack or approaches the opposite edge of the specimen, and thereby forming a continuous crack through the specimen. In addition, the stressestrain curves of bilateral crack specimens do not vary significantly around the point of peak stress prior to specimen failure, which means that the specimens do not fail instantaneously.
文摘The statistical testing models of the plate tectonic units and the hypothesis of their rigidity is presented by using the dense geodetic data, and to a certain extent the established statistic value can be regarded as a quantitative index to compare the rigidity degrees of different blocks. The several conclusions about the global megaplates and the regional tectonics of China are tested and verified by actual calculations, which testifies the effectiveness of this method in testing the rigidity degree and delineating their boundaries.
文摘The stress on a test specimen during tensile testing is generally measured by a strain gauge. This method has some problems in that it would influence the measurement conditions of the tensile test and can evaluate only the position at which the strain gauge is attached. The acoustoelastic method is proposed as a method replacing the strain gauge method. However, an ultrasonic sensor with a piezoelectric oscillator requires a coupling medium to inject an ultrasonic wave into a solid material. This condition, due to the error factor of the stress measurement, makes it difficult for the ultrasonic sensor to move on the specimen. We then tried to develop a non-contact stress measurement system during tensile testing using an electromagnetic acoustic transducer (EMAT) with an SH0-plate wave and S0-Lamb wave. The EMAT can measure the propagation time in which the ultrasonic wave travels between a receiver and a transmitter without a coupling medium during the tensile testing and can move easily. The interval between the transmitter and the receiver is 10mm and can be moved along the parallel direction or the vertical direction of the tensile load. The transit time was measured by a cross-correlation method and converted into the stress on the test specimen using the acoustoelastic method. We confirmed that the stress measurement using an SH0-plate wave was superior to that with an S0-Lamb wave.
基金the National Natural Science Foundation of China(No.51075388)the Fundamental Research Funds for the Central Universities (No.2009KJ05)
文摘The non-destructive testing(NDT)of debonding in stainless steel composites plate(SSCP)is performed by infrared thermography,finite element analysis(FEA)software ANSYS is taken as the simulative tool,and 2D simulative model has been set up to investigate effect of the thickness of coating and/or substrate on the detectibility of debonging in SSCPs.Two parameters,namely the maximum defect temperature difference and defect appearing index,are defined to evaluate the detectivity of defects,and their computational methods and formulas are given respectively.The preliminary changing tendency of the maximum defect temperature difference and defect appearing index with the thickness of coating and/or substrate is found by numerical simulation.
基金National Natural Science Foundation of China under Grant No.51148009National Natural Science Foundation of China under Grant No.50978005Project High-level Personnel in Beijing under Grant No.PHR20100502
文摘A composite shear wall concept based on concrete filled steel tube （CFST） columns and steel plate （SP） deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements： CFST columns; SP deep beams; and reinforced concrete （RC） strips. The RC strips are intended to allow the core structural elements - the CFST columns and SP deep beams - to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.
文摘The correlations between thermal and physical properties were studied through thermal conductivity measurements, hardness tests, salt spray tests (AASS) among the surface treatment samples named K20, K40 with thickness of 20, 40 μm respectively and raw sample named K00. In thermal conductivity measurements, there are little differences among the samples as K00, K20 and K40, they exhibit 153.39, 150.69 and 149.76 W/(m·K), respectively. According to hardness tests, K00, K20 and K40 exhibit 87.9, 259.7 and 344.8 in Vickers values. In the result of salt spray tests to examine the effects on corrosion resistance, K00, K20 and K40 exhibit the grade of 3?5, 2.0?9.8 and 10, respectively. The mutual relation of the above results was analyzed. It is found that the surface treatments do not affect the thermal conductivity of aluminum and result in the improvement of physical properties. As a result of the technology, the surface improvement of aluminum alloy specimen is achieved without thermal degradation. It validates the ability of the aluminum plate heat exchangers with surface treatment to enhance the corrosion resistance. Present work is performed as the first fundamental threshold in the process of aluminum plate heat exchangers development to check out its possibility, therefore the next step-experimental and numerical study of practical aluminum plate heat exchangers will be made.
文摘Bending fatigue tests were carried out on cruciform welded joints of China-made platform steel E36-Z35 with plate thickness of 16mm, 32mm and 40mm. The tests consisted of testing in air and in sea water with and without cathodic protection (-850mV. SCE). The sea water corrosion fatigue tests were conducted at loading frequency of 0.2 Hz and sea water temperature of 20°C. The test results show an obvious reduction in fatigue strength of welded joints with increasing plate thickness in all the three test conditions. The present paper proposes different thickness corrections for fatigue strength and fatigue life of welded joints in air and in sea water with and without cathodic protection respectively. In addition, an explanation for thickness effect on fatigue life of welded joints is given by using the theory of fracture mechanics.
基金Supported by National Natural Science Foundation of China(Grant No.51277154)Xiamen Key Laboratory of Optoelectronic Transducer Technology+1 种基金Fujian Key Laboratory of Universities and Colleges for Transducer TechnologyInnovative Talents Program of Far East NDT New Technology&Application Forum
文摘In eddy current testing, the law of attenuation of eddy current(EC) is of great concern. In conductive half space under the excitation of uniform magnetic field, the EC density decreases exponentially in the depth direction. However, in conductor with finite thickness tested by coil, the distribution of EC in the depth direction is more complicated. This paper studies the characteristics of EC attenuation in metallic plate of finite thickness. Simulation results show that there is an EC reflection at the bottom of plate, which changes the law of EC attenuation. A new concept, namely the equivalent attenuation coefficient, is proposed to quantify the speed of EC attenuation. The characteristics of EC attenuation are utilized to explain the nonmonotonic relation between coil voltage and plate thickness. Procedure of selecting frequency is discussed. Thereafter, measurement of plate thickness is carried out and accurate result is obtained.
文摘The purpose of this study was to compare the biomechanical stability obtained by using our technique featured an anatomical plate and compression bolts versus that of the conventional anatomic plate and cancellous screws in the fixation of intraarticular calcaneal fractures.Eighteen fresh frozen lower limbs of cadavers were used to create a reproductive Sanders type-Ⅲ calcaneal fracture model by using osteotomy.The calcaneus fractures were randomly selected to be fixed either using our anatomical plate and compression bolts or conventional anatomic plate and cancellous screws.Reduction of fracture was evaluated through X radiographs.Each calcaneus was successively loaded at a frequency of 1 Hz for 1000 cycles through the talus using an increasing axial force 20 N to 200 N and 20 N to 700 N,representing the partial weight bearing and full weight bearing,respectively,and then the specimens were loaded to failure.Data extracted from the mechanical testing machine were recorded and used to test for difference in the results with the Wilcoxon signed rank test.No significant difference was found between our fixation technique and conventional technique in displacement during 20-200 N cyclic loading(P=0.06),while the anatomical plate and compression bolts showed a great lower irreversible deformation during 20-700 N cyclic loading(P=0.008).The load achieved at loss of fixation of the constructs for the two groups had significant difference:anatomic plate and compression bolts at 3839.6±152.4 N and anatomic plate and cancellous screws at 3087.3±58.9 N(P=0.008).There was no significant difference between the ultimate displacements.Our technique featured anatomical plate and compression bolts for calcaneus fracture fixation was demonstrated to provide biomechanical stability as good as or better than the conventional anatomic plate and cancellous screws under the axial loading.The study supports the mechanical viability of using our plate and compression bolts for the fixation of calcaneal fracture.
文摘Background: There is a large assortment of modalities for the surgical treatment/management of distal radius fractures (DRFs), where the most widely used is the fixed-angle volar plating (VLP) system, which, sometimes, is referred to as the “surgical modality of choice”. While outcomes with each modality are usually good to excellent, each has its share of shortcomings and complications. Thus, there is scope for improvements to existing modalities and/or introduction of new ones. Study Purpose: We introduce a novel modality, namely, the prototype of an intramedullary injectable bioresorbable polymer-bioresorbable balloon osteosynthesis (IPBO) system, and investigated its plausibility. Experimental Procedures: The biomechanical performance of a construct comprising a synthetic distal radius (fourth-generation Sawbones?) on which a simulated fracture was created (4-mm wide osteotomy positioned 25 mm from the most distal end of the radius) and fixated with a placement of the IPBO system (SIPBO Construct) was compared to that when the fixation was with an approved Ti-6Al-4V alloy VLP system (SVLP Construct), under a clinically-relevant compressive loading protocol. Performance involved determination of quantitative parameters of the construct (initial longitudinal stiffness (ICLS), final longitudinal stiffness (FCLS), and load-to-failure (Pf)) and observation and recording of features of the construct at the fracture point. We also determined the quantitative parameters for the intact synthetic distal radius (control). Results: For each of the quantitative parameters, the range of values for SIPBO Construct was within that for SVLP Construct, suggesting that the IPBO System is a plausible modality. Also, for SIPBO Construct, failure occurred within the polymer zone, whereas, for SVLP Construct, some failure features were fracture of the cortical wall and of the dorsal proximal fragments. Conclusion: The findings suggest that the IPBO system is plausible. As such, it merits further study;for example, determination of the influence of fracture gap fill ratio (defined as the proportion of the fracture gap that is filled by the expanding balloon as the polymer is injected into the balloon) on a large collection of quantitative biomechanical parameters.
文摘In this study, the interaction between cylindrical specimen made ofhomogeneous, isotropic, and linearlyelastic material and loading jaws of any curvature is considered in the Brazilian test. It is assumed thatthe specimen is diametrically compressed by elliptic normal contact stresses. The frictional contactstresses between the specimen and platens are neglected. The analytical solution starts from the contactproblem of the loading jaws of any curvature and cylindrical specimen. The contact width, correspondingloading angle （2 ^0）, and elliptical stresses obtained through solution of the contact problems are used asboundary conditions for a cylindrical specimen. The problem of the theory of elasticity for a cylinder issolved using Muskhelishvili＇s method. In this method, the displacements and stresses are represented interms of two analytical functions of a complex variable. In the main approaches, the nonlinear interactionbetween the loading bearing blocks and the specimen as well as the curvature of their surfacesand the elastic parameters of their materials are taken into account. Numerical examples are solved usingMATLAB to demonstrate the influence of deformability, curvature of the specimen and platens on thedistribution of the normal contact stresses as well as on the tensile and compressive stresses actingacross the loaded diameter. Derived equations also allow calculating the modulus of elasticity, totaldeformation modulus and creep parameters of the specimen material based on the experimental data ofradial contraction of the specimen.
