Table of Content

28 May 2022, Volume 0 Issue 5

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BASIC STUDY

Effects of gradient characteristics on structural crashworthiness of negative Poisson's ratio honeycomb

ZHANG Cheng, TIE Ying, SONG Zheng-shuo

2022, 0(5):  5-11.  DOI: 10.19936/j.cnki.2096-8000.20220528.001

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Based on the concept of gradient, two kinds of negative Poisson's ratio honeycomb structures with composite gradient and thickness gradient were proposed, and the effects of different gradient characteristics on their crashworthiness were studied. Compared with the traditional non-gradient honeycomb, the platform stress and energy absorption characteristics of the two kinds of gradient structures were studied, and the strengthening mechanism was revealed by analyzing the deformation mode of the honeycomb cell during the compression process and the negative Poisson's ratio effect. The results show that the predicted compression deformation is similar to the reference results. Compared to traditional honeycomb structure, a strain of 0.6 in honeycomb composite gradient increased platform stress by 27.6% and the energy absorption by 70.5%, thickness of honeycomb alternating gradient increased platform stress by 243% and the energy absorption by 166%, and the increase rate of the platform stress of the gradient honeycomb shows a gradual mode, and the compression deformation mode shows an alternating plastic deformation. Compared with the composite gradient honeycomb structure, the alternating thickness gradient honeycomb structure has higher platform stress and specific energy absorption during the compression process. When the normal strain is 0.6, the platform stress of the alternating thickness gradient honeycomb structure is 169% higher than that of the composite material gradient honeycomb structure, and the specific energy absorption of the thickness alternately gradient honeycomb structure is 55.7% higher than that of the composite material gradient honeycomb structure, which has stronger energy absorption ability. The gradient structure has obvious effect on the negative Poisson's ratio of each honeycomb layer.

Propagation characteristics and simulation implementation of ultrasonic guided waves in CFRP laminates

LI Jun, SONG Chun-sheng, LI Min-hui, LIU Yu, WEI Zi-hang

2022, 0(5):  12-20.  DOI: 10.19936/j.cnki.2096-8000.20220528.002

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In this paper, the method of combining numerical and finite element simulation is used to study the propagation characteristics of ultrasonic guided waves in composite laminates. Firstly, the establishment process of wave dispersion equation is theoretically analyzed, and the difference of bulk wave propagation in composite materials is introduced. Then the guided wave propagation is numerically analyzed, and finally the finite element simulation model is established, and the numerical results are used to verify the correctness and effectiveness of the simulation model. The research shows that slowness and deflection angle can well characterize the propagation characteristics of bulk waves, compared with other layer dispersion curves, the symmetrical modal wave of unidirectional laminates has a dispersion-free region above the longitudinal wave velocity, the phase velocity curve and group velocity curve of guided wave propagation in composite laminates are in consistent, and the homogeneous stiffness transformation (HST) matrix component of the laminate has a greater impact on the wave propagation, the combination of numerical value and finite element provides important help for the development of guided waves in the field of composite structure health monitoring and nondestructive testing.

Buckling analysis of composite stiffened plates based on IGA method

QIN Xiao-chen, LI Chen, CHEN Cheng, GAO Li-min

2022, 0(5):  21-27.  DOI: 10.19936/j.cnki.2096-8000.20220528.003

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The Polynomial splines over Hierarchical T-meshes (PHT-splines) based Isogeometric Analysis (IGA) method is used to analyze the buckling characteristics of composite stiffened plates. The method realizes the accurate geometric modeling of the stiffened plates and the local refinement of the connection area between stiffeners and plates, as well as avoiding geometric errors, simplifying the refinement process, saving calculation time and promoting calculation efficiency. The correctness and convergence of the method are verified by numerical calculations. The effects of the ply number and ply angle of the stiffeners on the buckling characteristics of laminated stiffened plates are obtained. The results show that the buckling load of the laminated stiffened plates raises linearly along with the ply number. When the 0°-direction ply is fixed, the buckling load remains basically unchanged. When the ply number increases in 0°-direction and decreases in ±45°-direction or 90°-direction, the buckling load raises gradually.

APPLICATION RESEARCH

Off-axis central tearing behaviors and damage mechanisms of warp-knitted fabric membranes

ZHANG Ruo-nan, CHEN Jian-wen

2022, 0(5):  28-36.  DOI: 10.19936/j.cnki.2096-8000.20220528.004

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In order to explore the central tearing behaviors and damage mechanisms of biaxial warp-knitted fabric membranes, series of uniaxial central tearing tests for seven off-axis angles, including 0°, 15°, 30°, 45°, 60°, 75°, and 90°, and the development of microscopic numerical models were performed on a typical PVDF warp-knitted fabric. The variations of failure morphologies and tearing strengths of warp-knitted fabric membranes with the increase of off-axis angles were systematically analyzed. And combined with experimental and numerical results, the effects of off-axis angles on tearing strength and the micro-level load-carrying capacity and deformation mechanisms of yarns were further discussed. The results show that the yarn orientation of warp-knitted fabric has a significant effect on the direction of slit propagation and opening shape. As off-axis angles increase, a “W” shaped relationship between critical tearing strength, ultimate tearing strength and off-axis angle is presented, and an inverted “V” shaped relationship between ruptured displacement, failure displacement and off-axis angle is revealed. The yarn orientation of warp-knitted fabric also has a significant influence on the range of stress concentration and stress distribution. For 45° off-axis specimen, numerical simulation exhibits that the stress distribution is more uniform and the deformation is more sufficient than those of other off-axis angles. Therefore, 45° off-axis angle shows the largest tearing strength and is considered as the optimal load-carrying scheme. The conclusion could offer useful reference for the analysis of local crack arrest and safety assessment of architectural membrane structures.

Experimental investigation on bond behavior between BFRP-FRCM composite layer and aerated brick

ZHANG Zhen, LIAO Wei-zhang, MA Chao

2022, 0(5):  37-45.  DOI: 10.19936/j.cnki.2096-8000.20220528.005

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In order to study the bond behavior between basalt fabric reinforced polymer-fiber reinforced cementitious matrix (BFRP-FRCM) composite layer and aerated brick, the single-shear tests on BFRP-FRCM composite layer strengthening aerated bricks were conducted by considering the fibers mixed in cement-based materials, the bonding length of composite layer and the layer quantities of BFRP fiber meshes. Based on the tests results, fibers, bonding length and layer quantities influencing the bonding behavior between composite layer and block were explored. It presented that the BFRP-FRCM composite layer can significantly improve the tensile capacity of aerated brick. The bonding capacity of the composite layer becomes larger with the increase of bonding length. When it reaches the maximum value, it gradually gets smaller, i.e., the bonding length of the composite layer has an optimal value. Increasing the quantity of basalt mesh layers can increase the tensile strength of the specimen, but the bonding behavior and the utilization ratio of tensile strength will decrease. Comparing with the specimens strength with polyethylene layer, the specimens strengthened with polyvinyl alcohol layers exhibited better ductility.

Preparation and properties of T800-class carbon fiber reinforced polyimide composite for aero engine

NI Hong-jiang, LI Jun, XING Yu, DAI Xiao-xiang, ZHANG Dai-jun, CHEN Xiang-bao

2022, 0(5):  46-51.  DOI: 10.19936/j.cnki.2096-8000.20220228.031

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Aiming at the need of aero engines for high-temperature resistance polymer-matrix composites with high performance, research works were carried out on preparation and properties T800-class carbon fiber reinforced polyimide composite. Phenylacetylene(PEPA)-endcapped polyimide resin, EC-380A, was developed. Continuous fabrication technology for the T800-class fiber prepreg was established. Properties of the composite were obtained. The resin exhibits an application temperature of 370 ℃~400 ℃, and is suitable for autoclave processing. The T800-class fiber/EC-380A composite exhibits features of high-temperature resistance, high strength, high modulus and high toughness, with a room temperature tensile strength and modulus of 2 120 MPa and 169 GPa, respectively, a compressive strength after impact (CAI) of 256 MPa, and 370 ℃ retention rates of open-hole strength and modulus above 97% and 84%, respectively. Typical components have been fabricated, and exhibit sufficient safety margins.

Study on mechanical properties of CFRP-concrete interface reinforced by short chopped Kevlar fiber based on resin pre-coating technique

LIU Chang, YANG Shu-tong, YANG Song, FENG Yao-dong, XU Ming-qi

2022, 0(5):  52-60.  DOI: 10.19936/j.cnki.2096-8000.20220528.007

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In order to improve the bonding performance between CFRP (Carbon fiber reinforced polymer) and concrete, resin pre-coating technique (RPC) was used to pretreat the concrete surface, and short chopped Kevlar fibers were used to reinforce the resin layer. The interfacial bond behavior between CFRP and concrete was then analyzed by the single-lap shear test. Firstly, the effect of RPC technique was evaluated for the specimens with the same bond length. The optimal fiber content was determined upon the comparisons between the maximum bond loads with different fiber contents. Secondly, based on the optimal fiber content, the effects of different bond lengths on the bond properties with different interfacial treatments were analyzed. The results show that the optimal fiber content is 9 g/m². For the specimens with different bond lengths, the maximum bond load with RPC technique is increased by 12.7%~142.9% compared to the specimens without any interfacial treatment. Moreover, the failure mode of the reinforced interface is mainly the shear failure of the adhesive layer accompanied by few peeled concrete layers. RPC technique can fill the micro cracks in the concrete surface, and then the failure mode of peeled concrete layer with deep depth can be avoided. The bridging effect provided by the random distributed fibers strengthens the resin layer, and inhibits the development of cracks. Thus, the bond strength is improved significantly.

Patch optimization method of composite laminates considering implicit constraints

YAN Jin-shun, SUN Peng-wen, ZHAO Xiong-xiang, MA Zhi-kun, YU Ze-lin

2022, 0(5):  61-65.  DOI: 10.19936/j.cnki.2096-8000.20220528.008

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In order to solve the problem that the implicit constraints are less considered in the traditional optimization design of composite laminates, or the constraint processing is carried out by agent models and penalty functions, a patch optimization method considering implicit constraints is proposed. The direct processing of implicit constraints is realized by constructing the MATLAB-Python-ABAQUS joint simulation optimization framework. The mathematical model of patch optimization is established, which takes the discrete fiber orientation as the design variable, the minimum compliance as the objective function, the symmetry manufacturing and the strength as constraints. The joint simulation optimization and genetic algorithm are combined to solve the optimization problem. Numerical examples show that this method can effectively solve the implicit constraint, obtain the optimized ply scheme, and improve the structural performance.

Study on lightweight of carbon fiber composite battery box

KANG Yuan-chun, LIU Jun-feng, MENG Zi-wei

2022, 0(5):  66-70.  DOI: 10.19936/j.cnki.2096-8000.20220528.009

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In order to reduce the weight of the lower box of the battery box, the light material aluminum alloy and carbon fiber composite were used to replace the original Q235 steel material. After material replacement, in order to get the best thickness of new materials, a method of optimizing the thickness of aluminum alloy and carbon fiber parts is proposed by using neural network as the proxy model. The response of dimension variable was obtained by Latin hypercube test, and the optimum thickness of aluminum alloy support and reinforced beam and the thickness of carbon fiber angle were obtained based on neural network optimization. Finally, the optimal laying sequence of the box under carbon fiber is carried out in Optistruct. The optimization results show that the strength stiffness and the first mode frequency are improved while the weight of the battery box is reduced.

Effects of cellulose nanofibers on CFRP interface and damage evolution behavior

YANG Sa, ZHOU Wei, JI Xiao-long, LIU Jia, MA Lian-hua

2022, 0(5):  71-77.  DOI: 10.19936/j.cnki.2096-8000.20220528.010

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As a low-cost renewable resource, cellulose nanofibers (CNF) have shown unique advantages in the reinforcement and modification of composite materials. In this paper, cellulose nanofibers were used to reinforce carbon fiber composites. Bending test was carried out, and acoustic emission technology was used for damage assessment. Based on k-means method, the characteristic frequency range and cumulative acoustic emission energy of different damage modes were determined, and the interface strength of reinforced composites was characterized by scanning electron microscope. Results show that the damage initiation of cellulose nanofibers reinforced composites was delayed, and less acoustic emission signals appear in damage evolution. The energy of acoustic emission signals decrease during damage, and the cumulative acoustic emission energy of matrix cracking and fiber/matrix debonding decrease by 78.1% and 87.6%, respectively. Scanning electron microscope results show that cellulose nanofibers improve the interfacial properties of fiber/matrix, consequently improving the bending strength.

Study on the compressive failure mechanism of composite stiffened plate with ply drop-off structure

XUE Han, YU Yin

2022, 0(5):  78-84.  DOI: 10.19936/j.cnki.2096-8000.20220528.011

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In order to investigate the influence on composite stiffened plate load-bearing capacity, failure mode and failure location of the ply drop-off composite structure under axial compression, experimental studies were carried out for hat-shaped stringers with ordinary and ply drop-off layups. Finite Element (FE) models of composite stiffened plates with the ply drop-off structure were established by using Abaqus. The FE models adopt two-dimensional Hashin failure criterion and analyze the failure process and compressive performance of two types of composite stiffened plates. The FE models accurately predict the ultimate load, failure mode and failure location, which are in good agreement with the experimental results. The present study shows that the ultimate load obtained by the finite element (FE) method is in good agreement with the experiment. The failure load error of ply drop-off composite structure and the conventional structure is 1.1% and 4.7%, respectively, indicating that the modeling method adopted in this paper is reasonable and effective, and can provide guidance for practical engineering applications. Inaddition, it shows that appropriate ply drop-off does not influence the load-bearing capacity and failure mode of composite stiffened plate, but it may change the failure location.

Effects of crosslinker on physicochemical and mechanical properties of polyurethane

YU Kai, WANG Jun, QI Fu-min, HE Chuan

2022, 0(5):  85-91.  DOI: 10.19936/j.cnki.2096-8000.20220528.012

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Five kinds of polyurethanes resins (PU) were prepared with polymethylene polyphenyl isocyanate(PMDI) and polyether polyol and using small molecule ternary alcohols with different structures as crosslinker. The effects of crosslinker structure on heat release, rheological properties, thermal properties and mechanical properties of polyurethane were studied. The results showed that the secondary hydroxyl group and benzene ring in the molecular structure of the crosslinker prolonged the gelation time of the polyurethane resin, and slightly increased the heat resistance and T_g. The activity of polyurethane synthesized by crosslinking agent containing long unsaturated carbon chain is decreased,and the applicable period is greatly increased,but the hard segment regularity is poor,and the T_g and mechanical properties are decreased. When DIPA-PGE was used as crosslinker, the maximum T_g was 73.8 ℃. MIPA-PGE had the best comprehensive mechanical properties, and the tensile strength reached 51.6 MPa.

Study on effect of POSS on ablation properties of carbon/phenolic composite

YAO Ya-lin, LIU Jing, WANG Pang-pang, TIAN Mou-feng

2022, 0(5):  92-97.  DOI: 10.19936/j.cnki.2096-8000.20220528.013

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Using OPS, PPSQ and OAPS as modifiers, three kinds of POSS modified phenol-formaldehyde resins (PF) were synthesized. The carbon residue rate of the modified resin was compared and analyzed by TG. The result showed that the OAPS modified PF had the highest carbon residue rate, which was 11% higher than PF. The effect of OAPS on the curing process of PF resin was studied by means of IR-Rheologic synchronous analysis, and it was found that OAPS promoted the substitution reaction between hydroxymethyl and active hydrogen on benzene ring. The ablation property of the OAPS/PF/carbon composite was studied by oxygen/ethyne ablation test. The mass ablation rate is 0.030 3 g/s, 34% lower than PF resin composites.

Lightning strike design test and verification of composite laminates

HUANG Xin, WEN Yong-hong, LI Yan, TANG Hua-jing, XIA Yan-peng

2022, 0(5):  98-102.  DOI: 10.19936/j.cnki.2096-8000.20220528.014

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In order to verify the effectiveness of lightning strike protection design for aircraft carbon fiber composite material structure, a series of lightning strike tests were designed, which were based on multiple sizes of copper wire mesh with different densities and multiple sorts of aircraft lightning zones. The test results were evaluated through different methods, including the visual damage observation, thermal imaging observation and ultrasonic nondestructive testing. The lightning damage degrees and characteristics of carbon fiber composite laminates were compared and analyzed. Based on the tests, the damage situation of six different zones on the aircraft were studied, and the specimens were classified and analyzed according to the damage severity, and the composite lightning protection design measures were effective, which could ensure the flight safety of a certain type of aircraft composite structure after lightning strikes. It is recommended that the current CU195 copper mesh should be used in Zone one,but there are still optimization space. Now it is advisable to use copper mesh specification of CU142. In addition, the reasonable suggestions about the copper mesh sizes for other lightning zones have been given. It has important reference value for other similar composite material structure.

Structural design and mechanical study of composite rod joints

LIANG Xu-hao, WU Xin-rui, ZHANG Yan-da, SHEN Feng, WANG Xiao-lei, BAI Rui-xiang

2022, 0(5):  103-109.  DOI: 10.19936/j.cnki.2096-8000.20220528.015

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Composite rod joints are generally joined by glued joints. In order to further improve the connection strength between the rod and the joint, the structure design of the composite rod joint was carried out and three structural design schemes were proposed. In order to compare the advantages and disadvantages of the three design schemes, finite element analysis was carried out, tensile specimens were made and tensile tests were carried out according to current requirements. The test results show that, compared with the first and second design schemes, the third structural design scheme has higher process stability, the highest tensile load capacity and stable tensile performances, making it the optimal design scheme. The finite element analysis results of the three structural design schemes are basically consistent with the test results, and the finite element analysis method is reasonable and effective, which improves the efficiency of the study. The results of the finite element analysis and the test results provide the basis for the subsequent research work.

REVIEW

Present situation and development trend of processing technology of carbon fiber composite parts

ZHONG Ming-jian, HU Wei-jie, LIAO Xiao-tian, WEI Jun-ting, LIU Bing, HU Zhi-rong

2022, 0(5):  110-119.  DOI: 10.19936/j.cnki.2096-8000.20220528.016

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As one of the difficult-to-process materials, carbon fiber reinforced polymer (CFRP) have excellent properties such as high strength, light weight, high temperature resistance, and corrosion resistance. They are widely used in aviation, automotive, wind power and other industries, and the product market is expanding. Finishing technologies such as the dimensional accuracy and surface quality of its components have gradually become the research hotspots of many manufacturers, experts and scholars. This article reviews the characteristics of common CFRP parts processing technology, processing technology mechanism, the influence of single process parameters on processing quality and application status, discusses the improvement trend of common processing technology of CFRP parts, and prospects the development trend of high-precision processing technology of CFRP parts.

A review of sandwich panel on core structural design subjected to low-velocity impact

YANG Wen-dong, XU Shi-wei, QI Ye-xiong

2022, 0(5):  120-128.  DOI: 10.19936/j.cnki.2096-8000.20220528.017

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Sandwich structure is mainly used as lightweight structures for various engineering and structural applications, which consists of thin and hard skin and diversified core structures. It is highlighted that composite sandwich panel can provide excellent bearing capacity and crashworthiness characteristics under quasi-static and dynamic loadings. However, the composite sandwich panel is easy to be impacted by foreign materials in engineering application. Especially after being impacted under low-velocity impact, the internal structure may be damaged seriously although there is no obvious damage sign on the surface. The structure of composite sandwich panel and the core structure designs of sandwich panel in recent years are briefly reviewed, and the mechanical properties of different composite sandwich structures under low velocity impact are summarized. In addition, the damage behavior of sandwich panels with corresponding core design is discussed. Based on the research status at home and abroad, the suggestions for the research possible direction of the composite sandwich structure in future are forecasted.