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As the electronics field is increasingly developing in the direction of high-speed transmission and high connection density, the copper clad laminates widely used in 5G equipment have technical requirements such as low dielectric constant, low dielectric loss, high thermal conductivity, high reliability, et al. Polytetrafluoroethylene (PTFE) copper clad laminates are widely used in high-frequency microwave circuits because of their excellent dielectric properties and chemical stability. However, the preparation of existing PTFE copper clad laminates has related problems in the whole chain of monomer purification, resin polymerization, filler modification, composite materials to product processing, which limits their practical applications. This paper summarizes the development process of copper clad laminates in recent years, and proposes methods to solve the performance of PTFE from the aspects of molecular design and sequence distribution control of high cohesive PTFE, controllable impurity content of the whole process of high purity PTFE and green industrialization technology, new filler preparation and surface treatment technology, composition and interface design of multi-phase and multi-component PTFE composite materials, processing rheology and structural uniformity control of copper clad laminates, etc., so as to develop a system basic theory from the aspects of resin structure, filler modification, composite to molding processing, and the preparation of high-performance PTFE copper clad laminate. [ABSTRACT FROM AUTHOR]

Interfaces between nacreous tablets are crucial to the outstanding mechanical properties of nacre in natural shells and inspired by the “brick-and-mortar ” structure and remarkable mechanical performance of nacre. Excellent research has been conducted to probe the effect of interfaces on strength and toughness of nacre, providing critical guidelines for the design of human-made laminated composites. Herein, a class of graphene oxide (GO) based artificial nacre composite material with self-healing capacity due to non-covalent bonding interactions was fabricated by functionalization of GO with ellagic acid through π-π stacking followed by evaporation-induced self assembling process between ellagic acid modified graphene oxide(EGO) and polyurethane(PU). The artificial nacre displays a strict “brick-and-mortar ” structure, with EGO nanosheets as the brick and PU as the mortar. The structure of EGO was characterized by infrared spectroscopy, potential analyzer and X-ray diffraction, and the mechanical properties of PU-EGO were tested by universal testing machine. The results show that ellagic acid (ELA) is successfully adsorbed on GO surface, and when the mass ratio of PU to EGO is 3∶1, the tensile strength and toughness of the material reach 111.2 MPa and 81.5 MJ/m3, respectively (9.6 times and 1.8 times higher than that of PU), attributing to the interlayer slip of GO by breaking and recombing the π-π bond dynamically through which the energy can dissipate when PU-EGO is subjected to tensile stress. In addition, owning to the existence of noncovalent bonds, the resulting polymer composites display good recyclability. This work provides a pathway for the development of artificial nacre with self-healing capacity and recyclability. [ABSTRACT FROM AUTHOR]

The emission characteristics of VOCs (volatile organic compounds) from laminate flooring were investigated and their impacts on indoor environment evaluated in order to provide basic data for the study of harmful gas release from laminate flooring, and to provide reference for producers and consumers to evaluate their effects on indoor air quality. In this study, Shuang Xiang laminate flooring was selected and sampled with 1 m 3 climate chamber method. The sampled VOCs were analyzed by GC-MS (gas chromatography-mass spectrometry) and according to the forestry industry standards LY/ T 3230-2020 “Classification of volatile organic compound emissions contents from wood-made panels and their finishing products” and LY/ T 3229 - 2020 “ Specification for indoor carrying capacity of wood-based panels and finishing products based on volatile organic compounds emission”, the laminate flooring on indoor air quality was evaluated. Results showed that the TVOC release of this laminate flooring gradually decreased with time and reached the release equilibrium at day 28. The VOCs released were mainly olefins, aromatic hydrocarbons and alkanes, with small amounts of aldehydes, ketones, lipids and alcohols. In one cycle, the release level of naphthalene on the 3rd day of the laminate flooring did not meet the Class I standard, and the release levels of several major pollutants were Class I at the rest of the time. VOCs composite index of laminate flooring decreased with the increase of time after the 3rd day, and according to the composite index grading standard, the VOCs release class of laminate flooring on the 3rd day was Class Ⅱ, and the indoor air quality was qualified, and the VOCs release class of the rest of the time was Class I, and the indoor air quality was excellent. The TVOC release rate of this laminate flooring gradually decreased with time, in line with the mass transfer principle. After the VOCs were released in equilibrium, the release class is in line with Class I. The calculated composite index was in line with Class I. The indoor air quality was excellent and consumers can use it with confidence [ABSTRACT FROM AUTHOR]

To investigate the ability of energy absorption of composite beams with corrugated web in the crash process, the drop tests of composite beams with corrugated web are carried out, and the morphology of fracture, load and energy history curves are obtained. Based on the ABAQUS/Explicit platform, a simulation analysis model is developed to simulate the impact collapse process of composite beams with corrugated web by secondary development. The improved Hashin criterion and Choi‑Chang criterion are used with Cohesive interface element. The anisotropy and progressive damage of composite laminates are implemented. Specific energy absorption (SEA) and average loads are obtained by numerical simulation, which is verified by experimental results. Based on this model, further studies on the energy absorption of composite beams with corrugated web are analyzed with different wavenumbers. The progressive damage of corrugated web beams under impact loads are simulated by the developed FE model. The relative errors of average crushing load are small, which verifies the validity of the FE model. When the wave length of web is defined, the length of corrugated web beams has influence on energy absorption under impact. The shorter beam with corrugated web is instability and ineffective in energy absorption. [ABSTRACT FROM AUTHOR]

Wheat bran is the outer layer of the wheat kernel, particularly as a source of fiber in the food industry. The mechanical properties of the structural layers generally dominate the quality and efficiency of the superfine grinding of wheat bran. The sample preparation of the wheat bran structural layer can be the prerequisite for the tensile test of mechanical properties. Manual stripping can be widely used to completely separate the intermediate and aleurone layer, in order to prepare the wheat bran structural layer samples. The “two-layer theory” and “three-layer theory” have been formed at present. The sample length can reach 8mm using manual stripping without any microscopic device. However, it is still lacking consistence in the actual manual stripping of wheat bran structural layers. In this study, the feasible evaluation was performed on the manual stripping of the intermediate and aleurone layer, according to the preparation requirements of wheat bran structural layers. Five aspects were considered, such as the microstructure, geometric characteristics, mechanical properties, actual stripping situation, and the mixing law of Young’s modulus of wheat bran. The results showed that it was very difficult to obtain the complete, pure, large-size samples of intermediate and aleurone layers described in the recent research literature by manual stripping without any microscopic device. And the constitutive relations of intermediate layer and aleurone layer given by previous researchers did not satisfy the mixing law of laminate composite. The main reasons were as follows: 1) There was basically no gap between the intermediate and the aleurone layer, resulting in a large contact interface between the two layers. At the same time, since the contact interface between the intermediate and the aleurone layer was a rough surface with concave and convex pits, it was difficult to strip them manually. 2) There were a larger length-thickness ratio and the width-thickness ratio of the intermediate and the aleurone layer, reaching 200:1 and 80:1 respectively. There was a greater interlaminar adhesion between the two layers. 3) similar mechanical characteristic curves were found in the intermediate and the aleurone layer. As such, two kinds of structural layer samples were assumed as the same material, leading to hardly stripping them manually. 4) There were relatively complete intermediate layers after manual stripping, whereas, the aleurone layers were basically debris, failing to meet the length requirement of the wheat bran structural layer samples. At the same time, the stripping of the intermediate and the aleurone layer was considered a scraping process rather than a tearing, according to the “three-layer theory”. It infers that there was no pure in the prepared samples of the intermediate and the aleurone layer at present, indicating the residues of cell tissue in each other. Only in this way, an explanation was proposed for the relatively close thickness and mechanical properties of the two kinds of samples. The tensile mechanical test of wheat bran structural layers using the “two-layer theory” was also conducted to verify the universal applicability of the mixing law of Young’s modulus of laminated composite materials. The inaccuracy of experimental data was further revealed on the mechanical properties of the intermediate and aleurone layer samples using the “three-layer theory” and the defects of the empirical compound formula of Young’s modulus. The above research solved the doubts about the difficulties in manually separating the intermediate and aleurone layer. On the premise that the mechanical properties of wheat bran structural layers are known, the functional relationship between the mechanical properties of wheat bran structural layers and the dynamic parameters of the superfine grinding equipment can be constructed by using finite element and discrete element numerical simulation technology, which can provide basic theoretical guidance for the optimization and improvement of the superfine grinding performance of wheat bran. [ABSTRACT FROM AUTHOR]

Due to the high specific strength and stiffness, the use of continuous fiber reinforced composites instead of traditional metal materials to achieve structural lightweight has been widely considered by designers. However, the structural complexity brings great challenges to the design and optimization of composite lamination. Aimed at the problem of multiple constraints in the design of aviation composite laminates, the ply information of the structure was accurately expressed with gradually constructed design variables. Based on the classical genetic algorithm framework and the characteristics of all design variables, the genetic operators in the lamination optimization algorithm were defined, and the repair strategy was introduced to ensure that each generation of solutions could satisfy the design constraints and be distributed in the feasible region. Finally, the elite reservation strategy was used to improve the local optimization ability of the algorithm, which can reduce the computation cost of the lamination design of complex composite structures. Through the resolution of the classical benchmark problem and the comparison with the existing optimization results, the global and local optimization ability of the proposed lamination optimization algorithm was verified. The work provides theoretical supports for the optimization of composite lamination design in engineering practice. [ABSTRACT FROM AUTHOR]

To avoid transverse shear locking and improve the accuracy, the RES-DSG3 method was proposed through the incorporation of the non-isoparametric DSG method with a novel edge-based smoothing technique based on global coordinates, and all the integration of smoothed matrices can be calculated along the boundary segments of smoothed cells without coordinate mapping. Based on the 1st-order shear theory, the RES-DSG3 method was used to analyze free vibration natural frequencies of laminated composite plates with different material parameters, edge-thickness ratios and boundary conditions. The free vibrations of the composite plates were analyzed numerically. The calculation of the example verifies the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A new detection method using the power function of modal curvature differences as damage index was proposed to accurately identify the location and extent of composite material damage. Based on the APDL language of ANSYS, the Shell181 element was used to establish the simply supported laminate model, and the intra-laminar fiber failure model was constructed according to the Camanho damage criterion. The natural frequency of the laminate and the modal displacement of mesh nodes were obtained by modal analysis. The Gaussian curvature of the surface was obtained by the difference method, and the change of the Gaussian curvature difference before and after damage with the damage location and extent was studied. The square of the Gaussian curvature difference was used to increase the gap between the peak value and that of the other regions, which was defined as the modal displacement unevenness coefficient to detect the intra-laminar damage location and extent. The results show that the modal displacement unevenness coefficient improves the accuracy of the damage location detection, and it increases with the rise of the damage extent. The research conclusions provide guidance for improving the non-destructive testing methods for the intra-laminar damage of composite laminates. [ABSTRACT FROM AUTHOR]

Based on the classical laminated plate theory and the cohesive zone model, a theoretical model for general delamination cracked laminates was established for crack propagation of pure mode Ⅱ ENF specimens. Compared with the conventional beam theory, the proposed model fully considered the softening process of the cohesive zone and introduced the nonlinear behavior of ENF specimens before failure. The predicted failure load is smaller than that under the beam theory and closer to the experimental data in literatures. Compared with the beam theory with only fracture toughness considered, the proposed model can simultaneously analyze the influences of the interface strength, the fracture toughness and the initial interface stiffness on the load-displacement curves in ENF tests. The results show that, the interface strength mainly affects the mechanical behavior of specimens before failure, but has no influence on crack propagation. The fracture toughness is the main parameter affecting crack propagation, and the initial interface stiffness only affects the linear elastic loading stage. The cohesive zone length increases with the fracture toughness and decreases with the interface strength. The effect of the interface strength on the cohesive zone length is more obvious than that of the fracture toughness. When the adhesive zone tip reaches the half length of the specimen, the adhesive zone length will decrease to a certain extent. [ABSTRACT FROM AUTHOR]

After rolling, a large amount of residual stress will be generated in Mg-Al laminates, which will greatly affect the subsequent processing and service performance of the laminates. In this paper, the surface residual stress of Mg-Al laminates after annealing treatment of different processes was measured by iXRD-X ray residual stress detector,and the surface microstructure of the laminates was analyzed by SEM-EBSD technology. The results show that the surface residual stress of laminates is anisotropic along the plane before annealing, and the surface residual stress of laminates in different passes is different . The elimination mechanism of residual stress is different under different annealing processes. Recovery annealing is at low temperature, recovery and recrystallization coexist at medium temperature,and recrystallization annealing is at high temperature. The local orientation difference ( KAM) can reflect the distribution of dislocation density and thus characterize the residual stress. The smaller the KAM, the better the elimination effect of residual stress. The results are helpful to improve the subsequent processing performance and expand the application range of Mg-Al laminates. [ABSTRACT FROM AUTHOR]

The failure process of the open-pored T300/1034-C carbon fiber composite laminate with a ply angle of [ 00 I ( ± 45°) /3 ( 90° ) 3]s under tensile load was studied by using 2-D shell elements and 3-D solid elements in the ABAQUS finite element software. First, the shell element and continuous shell element carbon fiber composite material models were established with the ABAQUS finite element software, and the internal failure of the layer was simulated using the built-in 2-D Hashin criterion and degradation model. However, the 2-D model did not consider the interaction between the failures of each layer, and by writing the material subroutine VUMAT, the 3-D Hashin criterion and the equivalent stress-strain bilinear degradation method based on the fracture energy were introduced, and the solid element was used to simulate the carbon fiber composite material failure behavior. Through the simulation of three element models, the results showed that the stress concentration caused by the opening will make the fiber and matrix of the laminate more likely to fail during the stretching process and become the source of cracks; during the failure process of laminates, they all show a failure development trend from " X-shape" to "hourglass-shape", and eventually break in the width direction; compared with the traditional shell element and continuous shell element, the simulation accuracy of the solid model is closer to the experimental value. The simulation limit failure loads of the three elements differ from the literature data by 26. 1%, 31. 1%, and 8. 64%, respectively. [ABSTRACT FROM AUTHOR]

To investigate the time-varying vertical mechanical properties of laminated scrap tire rubber pads ( STRPs) within the design reference period of building structure ( 50 years), the tests of aging coupled with loading were carried out on the 61 groups of 7-layer STRP bearings that were subjected to aging for 31, 62, 93, 124, and 154 h and loading of 5 MPa, separately, and the traditional aging tests without loading were also carried out under the same conditions. And then, the results of two groups were compared. The STRP failure feature, vertical bearing capacity, and vertical stiffness/ deflection in different aging time were studied through vertical mechanical experiment and scanning electron microscopic. It is concluded that, as the aging time increases, the cracks of STRP surface propagate, the carbon black particles inside the tire move toward the surface of STRP, the vertical stiffness of STRP increases but vertical deformation performance of STRP declines, while the ultimate bearing capacity of STRP changes little. [ABSTRACT FROM AUTHOR]

In order to explore and establish the mathematical model of the greater interlaminar stress at the internal interface of the part caused by the mismatch of the thermal expansion coefficient between the metal and the composite during the forming process of the fiber-reinforced metal laminate. First of all, in order to simplify the mechanical model of fiber-reinforced metal laminates reasonably, through analyzing the influence of the change of three-dimensional anisotropic scale of simple asymmetric fiber-reinforced metal laminates on the warpage degree after forming and demoulding, it is found that the magnitude of interlaminar stress is mainly related to the proportion of metal and composite materials in the laminates. Then the mechanical model of the laminated plate is simplified into two-dimensional model by using the obtained law. Based on the analysis of elastic mechanics and theoretical mechanics, the mathematical model of interlaminar stress of unidirectional asymmetric fiber-reinforced metal laminates is obtained. By dividing symmetrical laminates into several asymmetrical laminates, the interlaminar stress expression of fiber metal laminates in asymmetric laminates is successfully extended to standard symmetrical laminates. Because it is impossible to measure the interlaminar stress directly, the theoretical value of interlaminar normal stress will be obtained indirectly based on the relationship between interlaminar shear stress and interlaminar normal stress. The stress value measured by the fiber grating sensor is compared with the stress value obtained by the theoretical model, and the maximum error does not exceed 3.504%, which verifies the accuracy of the theoretical model of the interlayer stress of the fiber metal laminate. [ABSTRACT FROM AUTHOR]

The progressive failure model of the composite laminate with a hole in the axial tension process was set up based on ABAQUS. The matrix tension failure, the matrix compression failure, the fiber tension failure and the fiber compression failure were considered by selecting two-dimensional Hashin as the damage criterion. The load condition and the failure mode were discussed, and the effects of the ply angle and the size of the center hole on the ultimate load were analyzed. The results showed that the dominant failure modes are matrix tension failure and the fiber tension failure, and the fibers are the strength source of the composite laminate. When the load direction does not agree with the fiber direction, the mechanical performance of the composite laminate degenerates. The mechanical performance of the composite laminate becomes worse as the center hole becomes larger, and is linear with the size of the center hole. [ABSTRACT FROM AUTHOR]

The buckling of composite laminate plates was analyzed with the nth-order shear deformation theory. The virtual work principle was used to derive the governing equations for the critical buckling of laminate pates under in-plane loads. The comparison between the present results and the results of previous literatures shows good agreement and high calculation accuracy. [ABSTRACT FROM AUTHOR]

Taking advantages of the BP neural network in nonlinear mapping and generalization capabilities for multi‐parameter problems，the BP neural networks with three hidden layers were constructed to predict the compressive strength of laminates containing embedded fiber wrinkles. The compressive failure was numerically simulated based on a three‐dimensional damage model with the LaRC criterion. The numerical results were used as data samples for the networks training. An algorithm based on the golden section method was proposed to quickly determine the range of the neurons number in the hidden layer of the BP neural networks. Then the best number of the neurons was finally determined by comparing the prediction results and the assessment indicators of different cases. The results show that，the error of the strengths of the laminates with the maximum wrinkle angles of 5.6° ，9.9° and 11.4° predicted by the developed BP neural networks are 3.4%，4.6%，and -0.01%，respectively. The approach developed in the present work to predict the strength of composite materials based on the BP neural networks provides an effective way for the strength evaluation of composite materials in application. [ABSTRACT FROM AUTHOR]

The out-of-plane stress of composite laminated plates and shells is of great significance to the initia¬tion and expansion of interlaminar delamination. Firstly, the formulation of classical non-compatible displace¬ment finite element is given out briefly. And then, based on the modified Hellinger-Reissner (H-R) principle, the relationship between out-of-plane stress variables and displacement variables is derived. The finite element linear system of out-of-plane stress provides convenience for the introduction of out-of-plane stress boundary conditions. At the same time, the uniqueness and continuity of the out-of-plane stress at the node can be ob¬tained directly by the finite element linear system. Compared with the results of non-compatible displacement finite element method, the proposed method can improve the accuracy of numerical results obviously, and the computational efficiency and resource requirements are superior to the non-compatible symplectic element method and the non-compatible generalized mixed element method. [ABSTRACT FROM AUTHOR]

A series of numerical simulations were performed to investigate the effects of geometric parameters on cooling performance of a laminate porous plate with a sparse hole array，under a given coolant massflow rate per unit wall-surface area and the combustor linear representative conditions. The relationship between impinging-hole number，pin-fin and film-holes number is 1∶10∶1. Among the current ranges of geometric parameters，it is found that the film-hole diameter and impinging-hole diameter have relatively stronger influence on overall cooling effectiveness and pressure drop across the laminate porous plate. Increasing film-hole diameter is helpful for improving overall cooling effectiveness and reducing pressure drop. Increasing film-hole diameter results a reduction of pressure drop and overall cooling effectiveness. The variation of pin-fin diameter or impinging distance has nearly no influence on the pressure drop. The increase of pin-fin diameter results in a little increase of overall cooling effectiveness. Small dimensionless impinging distances seems to be a little advantageous. [ABSTRACT FROM AUTHOR]

Due to the special surface treatment technology, the bond behavior of CFRP-to-stainless steel interface is different from that of normal CFRP-to-steel and CFRP-to-aluminum alloy interfaces. In order to study the bond behavior of CFRP-to-stainless steel interface, a total of 22 stainless steel plates bonded with CFRP laminates were fabricated. The main test parameters were the width of CFRP laminates (30, 40, 50mm), the number of CFRP layers (1, 2, 3 layer) and the bonding length of CFRP laminates to stainless steel (50, 75, 100, 130, 180mm). In addition, some of the specimens were provided with transversely bonded CFRP at their end for additional anchorage, to consider the influence of transversely bonded CFRP on bond behavior of CFRP-to-stainless steel interface. The test results show that when the actual length of the CFRP laminate is longer than the effective bond length, the ultimate load maintains in a relatively stable state. The ultimate load rises with the increase of CFRP width. Meanwhile, the ultimate load rises sharply with the increase of the number of layers of CFRP laminates, but the utilization efficiency of CFRP laminates decreases when the number of CFRP layer is more than 2.The transversely bonded CFRP can effectively improve the ultimate load of the specimens, and longer transversely bonded CFRP leads to a larger increase in the ultimate load. The length, width and bonded layers of CFRP laminates have little effect on the debonding load. But the transversely bonded CFRP can obviously improve the debonding load. The safety coefficient of CFRP-to-stainless steel interface increases with the increase of the width and number of CFRP layers. Finally, compared with the CFRP-to-steel interface, the effective bond length of CFRP-to-stainless steel interface is slightly larger. [ABSTRACT FROM AUTHOR]

To study the protection design of fiber reinforced composite laminates subjected to fragment cluster penetration, the failure mechanism of fiber reinforced laminates subjected to fragment cluster penetration is studied by using the transient nonlinear finite element, and the failure process and failure mode of fiber reinforced composite laminates under fragment cluster penetration are analyzed, the enhancement effect of fragment penetration ability is clarified, and the influence factors of fragment number, initial velocity and spacing are studied. Based on the above research, an equivalent method of armour piercing ability is proposed. The results show that the penetration ability of fragment cluster is stronger than that of single fragment, and can be equivalent with that of single fragment with increased length, which provides the reference for the armor protection design method of structure when penetrated by fragment cluster. [ABSTRACT FROM AUTHOR]

The surface mechanical attrition treatment (SMAT), as a technology that the metal sample surface is hit in random directions by a large amount of tiny hard balls in high frequency vibration within a short period of time, was applied to aluminium laminates. Then, the metal's grain sizes, especially those near the surface, got smaller; and therefor the metal's yield strength got enhanced. After the SMAT process, the aluminium laminates' ultimate stress and ultimate strain decreased a little, while the yield stress increased obviously. The glass fibre reinforced aluminium laminates were fabricated through heat pressing process with SMATed aluminium and glass fibre epoxy prepreg. From the tensile tests and theoretical calculation, the results show that the SMATed aluminium effectively improves the yield strength of the aluminium-based composite. [ABSTRACT FROM AUTHOR]

The milling experiments of C/SiC composite with PCD tools are conducted, and surface formation mechanism is analyzed by observing surface/subsurface damages. The effect of milling parameters on surface topography and surface roughness is discussed with the analysis of cutting force. The results show that C/SiC composite is removed in the mechanism of brittle fracture. Laminated fracture, pull-out and fracture in bundle of carbon fiber can be observed on the machined surface. The effect of milling parameters on surface roughness is basically the same with that on surface topography. The higher cutting speed can improve the surface quality, the bigger axial depth of cut will worsen the surface quality and the feed per tooth has no significant influence on surface quality. [ABSTRACT FROM AUTHOR]

In order to promote the application of UV-curing technology, the mechanical properties and the microstructure of the UV-curing epoxy composite are studied. On this basis, the UV-curing epoxy composite is used to repair the pre-damaged laminated beams for studying its repairing performance. The results reveal that, the mechanical properties of the UV-curing epoxy composite are favorable, compaired with the thermal curing composite, and the bonding between resin matrix and fiber is good. The UV-curing epoxy composite patches significantly increase the tensile strength of the damaged laminated beams, and the strength of the repaired samples can reach 84. 1% of the standard samples and is 1.21 times the strength of the unrepaired samples. Fiber reinforced UV-curing resin is a fast and effective method for repairing damaged composite laminates. [ABSTRACT FROM AUTHOR]

A method is developed to predict numerically the damage of composite laminates with more plies under low velocity impact loading. The Puck criterion for 3D stress states is adopted to model the intralaminar damage including matrix cracking and fiber breakage, and to obtain the orientation of the fracture plane due to matrix failure. According to interlaminar delamination mechanism, a new delamination criterion is proposed. The influence of transverse and through-thickness normal stress, interlaminar shear stress and damage conditions of adjacent plies on delamination is considered. In order to quickly and efficiently predict the impact-induced damage of composite laminates with more plies, an approach, which can predict the specific damage of several plies in a single solid element, is proposed by interpolation on the strains of element integration points. Moreover, the proposed model can predict specific failure modes. A good agreement between the predicted delamination shapes and sizes and the experimental results shows correctness of the developed numerical method for predicting low velocity impact damage on composite laminates. [ABSTRACT FROM AUTHOR]

The numerical simulation researches about the process of vibrating screen had been done using the EDM (discrete element method). The relationship of loose and structural parameters based on the concept of density was analyzed. The influence of feeding rate on the laminate based on the concept of the fine particle ratio was analyzed. The result showed, the best parameters are: wire diameter is 0.75 mm, aperture is 0.7 mm, the inclination is 25°; the best feeding rate on best stratification is 4e +04 p/s. [ABSTRACT FROM AUTHOR]

As a three-dimensional layer enhancement technology, Z-pin technology is suitable for manufacturing composite prepreg laminates and also can effectively improve inter laminar properties of composite laminates. In order to manufacture Z-pin cylindrical and conical shape composite parts efficiently, an ultrasonic assistant insertion system is proposed, and the general plan is worked out to meet all the technical requirements of ultrasonic transfer insertion automation. The prototype machine is designed, a series of function debugging are made and verification experiments are carried out on the machine. The results show that the system meets all technical requirements of ultrasonic assistant insertion process. It is capable to carry out ultrasonic assistant insertion automatically, as a result, the system is much more efficient than the existing equipment as much as 6 times. [ABSTRACT FROM AUTHOR]

Based upon the data and observation from the low velocity impact experiment on interlayer-toughened composite laminates, a finite element model(FEM) is developed to quantificationally study the mechanical behavior of interlayer-toughened laminates subject to low velocity impact using ABAQUS. In this model, a VUMAT subroutine is used to define the constitutive relationships and to predict the stress-based failure criteria of a composite lamina. Typical failure modes, including fiber tensile failure, fiber compress failure, matrix crushing and matrix cracking, are considered in the subroutine. The stiffness reduction of failed elements is also included. Cohesive elements are introduced into the model in the region between two neighboring layers in the laminate. A quadratic nominal stress criterion and a power law fracture criterion are adopted to predict the initiation and evolution of delamination. The FEM prediction results show a good agreement with experimental data, which validates FEM developed in this study. [ABSTRACT FROM AUTHOR]

A stiffness degradation model with two parameters is presented to describe the composite laminate's characteristic stiffness degradation rule under cyclic loading. The normalized stiffness degradation curves processed by this model agrees well with each other for different specimens under the same fatigue loading. Therefore a new fatigue life prediction method is presented considering the specimen's individual historical fatigue information and the stiffness degradation rule. Four kinds of E-glass/Epoxy laminates and five kinds of laminates with central holes are tested to verify the presented method. Results show that the fatigue life of composite specimen can be accurately predicted when considering its individual historical information. The prediction results agree fairly well with the experimental results by adopting the residual stiffness data about the characteristic damage state(CDS) only. [ABSTRACT FROM AUTHOR]