COMPOSITES SCIENCE AND ENGINEERING

Study on mechanical properties of composite pre-tightening tooth connection under bending-compression coupling

LI Fei, GAO Xunpeng, ZHAO Qilin, WANG Zhengxing, SHI Lin

2023, 0(8): 5-13. DOI: 10.19936/j.cnki.2096-8000.20230828.001

Asbtract ( 73 )

PDF (13815KB) ( 93 )

References | Related Articles | Metrics

Studies have shown that the pre-tightening force tooth connection joint in the structure will not only be affected by the axial force, but also be affected by the bending moment at the same time. However, at this stage, the mechanical properties of composite pre-tightening force tooth connection under the coupling effect of bending moment and axial force have not been studied. In this paper, the test method of composite pre-tightening force tooth connection under bending-compression coupling is studied, and the loading of the joint under bending-compression load is realized by hydraulic jack and universal testing machine. Secondly, axial compression, pure bending and bending-compression coupling tests were carried out on the joint, and the force transmission mechanism of the joint under different loads was obtained. The results show that the effect of the joint under bending-compression coupling can be approximately regarded as the linear superposition of pure bending and axial compression under corresponding loads. The existence of bending moment will greatly affect the mechanical properties of joints, so the influence of bending moment on the bearing capacity of joints should be fully considered in the design of joints.

Strengthening-toughening design method of carbon fiber/epoxy resin interface

WANG Qinyu, ZHUO Jiagui, LI Xinding, DU Pengcheng, WANG Wen, ZHU Dalei, TAN Jianping

2023, 0(8): 14-18. DOI: 10.19936/j.cnki.2096-8000.20230828.002

Asbtract ( 118 )

PDF (5274KB) ( 117 )

References | Related Articles | Metrics

To improve the interfacial strength and toughness of carbon fiber/epoxy resin composites simultaneously, a novel “rigid-soft” interface layer was constructed via dispersing rigid multi-walled carbon nanotubes (MWCNT) and soft thermoplastic polyurethane (TPU) in N, N-Dimethylformamide solution by ultrasonic and depositing them on carbon fiber surface by dip-coating technique. Scanning electron microscopy, atomic force microscopic, fourier transform infrared spectroscopy and Raman spectroscopy were used to characterize the surface of CF. The interfacial shear strength (IFSS) and pull-out displacement of CF/epoxy resin composites were tested by fiber pull-out testing. The results show that: MWCNT and TPU can uniformly distributed on the surface of CF by above method. Compared with pristine CF, the IFSS and pull-out displacement of modified CF were respectively improved by 163.3% and 52.8% due to the hydrogen bonding and mechanical interlocking between MWCNT and TPU, which indicates the “rigid-soft” interface layer have a positive effect on the enhancement for the interfacial strength and toughness of carbon fiber/epoxy resin composites.

Numerical simulation of fatigue delamination in composite laminates based on cohesive zone model

XIANG Genyang, FENG Dianshi

2023, 0(8): 19-25. DOI: 10.19936/j.cnki.2096-8000.20230828.003

Asbtract ( 173 )

PDF (5500KB) ( 215 )

References | Related Articles | Metrics

In order to study the delamination behaviour of composite laminates subjected to fatigue loading, an improved fatigue damage rate strategy was proposed based on cohesive zone model (CZM). This strategy only requires the fatigue crack growth rate Paris law as the input parameters while no crack tip tracking or additional parameter fitting is needed. The proposed fatigue damage rate strategy was implemented into the commercial software ABAQUS/Explicit via a user written subroutine VUMAT, and the fatigue damage processes of composite unidirectional laminates under mode Ⅰ, mode Ⅱ and Ⅰ/Ⅱ mixed-mode loading scenarios were simulated, and the results show that the improved model can effectively simulate the fatigue delamination of composite laminates. Finally, error analysis and mesh sensitivity analysis of the model were carried out, and it is shown that longer fatigue cohesive zone lengths can clearly improve the computational accuracy of the proposed model.

Study on terminal amino polyether toughened modified bisphenol A type epoxy resin

ZHANG Weijun, WANG Dan, YANG Kaikai, CHEN Feng

2023, 0(8): 26-33. DOI: 10.19936/j.cnki.2096-8000.20230828.004

Asbtract ( 89 )

PDF (4904KB) ( 129 )

References | Related Articles | Metrics

Aiming at the process problem of poor toughness and easy cracking of bisphenol A epoxy resin after crosslinking and curing, the terminal amino polyether is used to toughen and modify the epoxy resin. The curing process of resin glue before and after toughening was studied by viscometer and differential scanning calorimeter and the curing system was determined. The curing kinetic equation of the toughened epoxy resin was derived by curing kinetic analysis. The effects of flexibilizer on T_g value and thermal decomposition performance of resin casting body were studied by DSC method, DMA method and TG method. The mechanical properties of resin casts and composites before and after toughening were tested, and the cross-sectional morphology of castings and composites was analyzed by SEM and the fracture mechanism was speculated. The results showed that when 15 parts of toughening agent were added, the tensile strength of the cast reached a maximum of 69.8 MPa, which was 54.1% higher than before toughening. The impact toughness of the cast has increased by 42.4% compared with before toughening. At this time, the mechanical properties of the composite materials have increased significantly compared with before toughening, and the purpose of toughening and strengthening has been achieved.

Effect of multifunctional hydroxyl phenyl epoxy modified epoxy resin on thermal and bonding properties of composites

YAN Hongchen, SHI Fenghui, ZHANG Baoyan, MA Zhaodan, WANG Tingting

2023, 0(8): 34-38. DOI: 10.19936/j.cnki.2096-8000.20230828.005

Asbtract ( 119 )

PDF (2352KB) ( 137 )

References | Related Articles | Metrics

With self-made epoxy resin as the matrix, a multifunctional hydroxyl phenyl epoxy as modifier, a new self-adhesive epoxy resin was prepared by melt-mixing method. The glass fiber reinforced epoxy resin composite was prepared using this resin. The effect of different contents of modifier on thermal and bonding properties of epoxy composites was investigated. The results indicate that the addition of multifunctional hydroxyl phenyl epoxy is beneficial to the increase of glass-transition temperature and decrease of the drum peel strength in the meantime. When the weight ratio of multifunctional hydroxyl phenyl epoxy is 20%, the glass-transition temperature increases from 151.9 ℃ to 172.6 ℃ and the drum peel strength decreases from 56.88 (N·mm)/mm to 39.5 (N·mm)/mm, which can meet the design index requirements of honeycomb sandwich structures and has good engineering application prospects.

Quasi-static compressive mechanical behavior of Ti-based amorphous alloy/SiC ceramic matrix composites

WU Guanghui, LUO Zhengbin

2023, 0(8): 39-43. DOI: 10.19936/j.cnki.2096-8000.20230828.006

Asbtract ( 116 )

PDF (10660KB) ( 57 )

References | Related Articles | Metrics

The deformation and fracture mechanism of Ti-based amorphous alloy/SiC ceramic matrix composites were studied through quasi-static compression test, which provides the basis for the composition design and engineering application of this kind of materials. The specimens were composed of Ti-based amorphous alloy and SiC ceramic skeleton with different porosities. Under different strain rates, the mechanical properties of the specimens were tested under axial quasi-static compression at room temperature, and the microstructure and cross-section characteristics of the specimens were observed. The results show that the quasi-static compressive strength of the composites with 85% volume fraction of SiC reaches 2 343 MPa, and the compressive strength increases with the increase of SiC content. In the range of the strain rate under quasi-static loading, the strength of the composites and each phase is insensitive to the strain rate, and the fracture characteristics are typical brittle fracture. The crack propagation is mainly at the interface of SiC phase and two phases, and the relative crack propagation of Ti-based amorphous is hindered. The constraint of SiC relative to Ti-based amorphous phase induces the formation of multiple shear bands in Ti-based amorphous phase and improves the deformation capacity of composites. However, the constraint of Ti-based amorphous relative to SiC phase leads to serious fragmentation of SiC phase and enhances the bearing capacity of composites.

Study on property of the mode Ⅰ delamination for stitched composite laminates

ZHANG Dongzhe, LI Zuojun

2023, 0(8): 44-50. DOI: 10.19936/j.cnki.2096-8000.20230828.007

Asbtract ( 59 )

PDF (5734KB) ( 92 )

References | Related Articles | Metrics

Due to the low interlaminar strength of traditional composite laminates, stitching technology has been widely used to improve their interlaminar properties. In order to study the mode Ⅰ delamination performance of the stitched composite laminates, the double cantilever beam (DCB) model was used to calculate the mode Ⅰ delamination failure load. Then the effects of different stitch density and diameter for the interlaminar failure load of the composite laminates were discussed. The result show that the stitching technology can hinder the delamination propagation for the composite laminates model. The delamination front in the stitched composite laminates model is a wavy line, while the delamination front of the unstitched composite laminates model is a straight line. The increase of stitch density will improve the interlaminar failure load of the composite laminates model. Compared with the unstitched composite laminates model, the interlaminar failure load of the model with stitch density of 10 mm×10 mm, 7.5 mm×7.5 mm, 5 mm×5 mm and 2.5 mm×2.5 mm increases by about 7 times, 9 times, 10 times and 15 times, respectively. The increase of the stitch diameter will also improve the interlaminar failure load of the composite laminates model. The maximum interlaminar failure load of the model with the stitch diameter of 1 000 Dan and 2 000 Dan is about 1.5 times and 2 times that of the model with the stitch diameter of 500 Dan, respectively.

Preparation and performance research of anisotropic fluorinated polyimide/carbon nanotubes composite films

LI Chunman, LI Shuangwen

2023, 0(8): 51-56. DOI: 10.19936/j.cnki.2096-8000.20230828.008

Asbtract ( 67 )

PDF (6381KB) ( 67 )

References | Related Articles | Metrics

In the future, lightweight, flexible and directionally conductive composites will have very important research and application value in the fields of microelectronic devices, aerospace and so on. Composites with highly anisotropic properties can be prepared by microstructural design and interface compatibility control. The fluorinated polyimide (f-PI)/carbon nanotubes (CNTs) was prepared by compounding the surface modified aligned CNTs with f-PI. Due to the improved interfacial compatibility between surface modified CNTs and polymer matrix, f-PI/CNTs composite films exhibit excellent thermal stability, mechanical properties and high light transmission. In spite of the extremely small amounts of the CNTs in a polymer matrix, the obtained uniform f-PI/CNTs composite films are characterized by a variety of excellent anisotropic properties. As a result, the tensile strength along the longitudinal direction of the highly aligned CNTs is 33.1% higher than that in perpendicular direction.

Optimization of carbon fiber wound reinforced cylinder composites and self-tightening process

ZHAO Guanxi, LI Ming, GUO Yongzhi, HE Taibi, HAN Rui

2023, 0(8): 57-65. DOI: 10.19936/j.cnki.2096-8000.20230828.009

Asbtract ( 109 )

PDF (11466KB) ( 97 )

References | Related Articles | Metrics

In order to improve the bearing capacity and safety of carbon fiber composite gas cylinders, the mechanical properties of carbon fiber/epoxy resin wound layer materials were studied in this paper. Firstly, two different resin formulations were proposed and resin castings were prepared. The analysis showed that CYD-128 resin system had higher elongation at break, but lower modulus and poorer strength than O-lin resin. The tensile strength of NOL ring of carbon fiber composite was prepared and compared under different resin formulations, and O-lin resin was selected as the matrix of carbon fiber composite. T700-12K carbon fibers from three different manufacturers in China were subjected to multiwire tensile test and SEM test on fracture surface. According to the experimental results, Hengshen carbon fibers were selected as composite reinforcement. Furthermore, the influence of the self-tightening process on the stress level and fatigue life of the carbon fiber wound cylinder was analyzed by finite element numerical simulation. The self-tightening process was optimized according to the DOT-CFFC standard, and the stress intensity of the composite cylinder liner was reduced to different degrees under the best self-tightening pressure. According to the above composite materials and self-tightening process, the carbon fiber wound cylinder was prepared, and the hydraulic bursting test and normal temperature pressure cycle test were carried out. The results show that the bursting pressure and fatigue life of the cylinder are improved compared with the relevant standards, which provides a reference for optimizing the industrial production and safe use of compressed natural gas and hydrogen storage and transportation equipment.

WTB-Net: A lightweight wind turbine blade surface defect recognition algorithm based on ShuffleNet V2

ZHANG Rui, WEN Chuanbo

2023, 0(8): 66-71. DOI: 10.19936/j.cnki.2096-8000.20230828.010

Asbtract ( 119 )

PDF (7064KB) ( 76 )

References | Related Articles | Metrics

As the defect detection technology of wind turbine blades has not been widely used and the robustness of traditional detection methods is poor, this paper proposes a lightweight wind turbine blade surface defect identification algorithm WTB-Net. 2 569 images of wind turbine blades from a coastal wind farm in East China are captured by an unmanned aircraft, and the WTB surface defect dataset is established through screening and classification and data expansion. Based on ShuffleNet V2 core backbone feature extraction network, SKNet, a selective convolutional kernel attention mechanism, is introduced to adaptively adjust the perceptual field size, enhance useful features and suppress useless features. Finally, the activation function Leaky-ReLU is used to reduce the appearance of silent neurons and avoid the deactivation of neurons caused by using ReLU when the input is negative. The experimental results show that the algorithm achieves an accuracy of 98.12% on the WTB dataset, which is 6.53% better than ShuffleNet V2, and the number of model parameters is only 1.4 M.

Experimental study on mechanical properties of high strength solid buoyancy materials under cyclic loading

ZHANG Hailong, ZHANG Shaowei

2023, 0(8): 72-77. DOI: 10.19936/j.cnki.2096-8000.20230828.011

Asbtract ( 119 )

PDF (12706KB) ( 77 )

References | Related Articles | Metrics

In view of the domestic solid buoyancy materials of hollow glass beads for “Fendouzhe” human-occupied vehides (HOV), using a controlled temperature isostatic pressure test device, 1 018 cyclic load tests at 110 MPa hydrostatic pressure were carried out. For the materials before and after hydrostatic pressure cyclic load test, quasi-static tensile, compression, impact, stress relaxation and dynamic mechanical thermal analysis tests were carried out respectively. The mechanical properties of materials before and after cyclic loading were analyzed. Finally, X-ray micro-CT was used to analyze the microstructure of the material. The results show that: After 1 018 cycles of 110 MPa hydrostatic pressure loading, the tensile strength, elongation at break, compressive strength, tensile elastic modulus and compressive elastic modulus of the material are greatly reduced,and the macroscopic mechanical properties of the material are decreased. X-ray micro-CT showed that: After cyclic loading, the internal hollow glass microspheres had a good shape and no significant change in microsphere breakage rate. The internal hollow glass microspheres of solid buoyancy had a good compressive performance. The change of the properties of solid buoyancy materials is mainly due to the change of the properties of resin substrate, which leads to material aging and property attenuation.

Study on fractal dimension and mechanical properties of basalt polypropylene fiber concrete pore structure

ZHAO Jing, LI Xiaofeng, GUO Li

2023, 0(8): 78-84. DOI: 10.19936/j.cnki.2096-8000.20230828.012

Asbtract ( 112 )

PDF (5335KB) ( 66 )

References | Related Articles | Metrics

Based on the experiments, the influence of basalt-polypropylene fiber on the compressive strength and splitting tensile strength of concrete is discussed. The fractal dimension of concrete pore structure is calculated by using the fractal model of optical method. The experimental results show that hybrid fibers can improve the compressive strength and splitting tensile strength of concrete. When the content of basalt fiber (BF) and polypropylene fiber (PF) was 0.05%, the synergistic effect of hybrid fiber was the strongest. The maximum increment of compressive strength and splitting tensile strength is 5.97% and 8.46% respectively. However, when the fiber content is too high, the hybrid fiber will adversely affect the mechanical properties of specimens. The pore structure of basalt-polypropylene fiber reinforced concrete (BPFRC) shows obvious fractal characteristics, and its fractal dimension ranges between 2.297 and 2.482. Fractal dimension has a strong correlation with porosity and spacing coefficient. The fractal dimension decreases significantly with the increase of porosity and increases with the increase of spacing coefficient. Fractal dimension is positively correlated with compressive strength and splitting tensile strength. Therefore, the fractal dimension of pore structure can be used to evaluate the micro pore structure of concrete and reflect the influence of the complexity of pore structure on the macroscopic mechanical properties of concrete.

Analysis of influence of fiber placement path on quality of composite fuselage “L” shape shear tie

WANG Lin, TIAN Cha, SU Jiazhi, YU Jingjing, CHANG Liang

2023, 0(8): 85-91. DOI: 10.19936/j.cnki.2096-8000.20230828.013

Asbtract ( 108 )

PDF (8507KB) ( 77 )

References | Related Articles | Metrics

Automated fiber placement (AFP) is one of the significant processes to realize manufacturing composite fuselage shear tie automatically. Path planning is the key factor of the AFP process, fiber placement path will affect the fiber angular deviation, covering and efficiency, etc. In the present study, two fiber placement paths for polymer matrix composite fuselage shear tie were designed and analyzed, also the two cured parts were inspected to explore the quality effect related on fiber placement path. The results show that for the AFP process of this part, angular deviation of the overlap & gap mixed fiber placement path is better than that of gap only fiber placement path, but its covering and efficiency are worse than that of gap only fiber placement path. For the shear tie by AFP and single-side mould, these two different fiber placement paths have a different degree of effect on appearance and thickness of the part.

Tension-tension fatigue properties of surface-functionalized multi-walled carbon nanotubes modified glass fiber reinforced resin matrix composites

LIU Shuaiwen, SHEN Jinrong, JI Xinzhu, ZHANG Qiangxian, FANG Yuan

2023, 0(8): 92-100. DOI: 10.19936/j.cnki.2096-8000.20230828.014

Asbtract ( 105 )

PDF (7112KB) ( 106 )

References | Related Articles | Metrics

The effects of surface-functionalized multi-walled carbon nanotubes (MWCNTs) on the fatigue properties of glass fiber reinforced resin matrix composites were investigated by tension-tension fatigue tests. Based on the test data, the linearizable exponential function and the power function S-N curve models were selected to quantitatively analyze the fatigue life of composites. The results showed that the fatigue properties of the aminated MWCNTs (MWCNTs-NH₂) modified epoxy resin specimens were better than those of the carboxylated MWCNTs (MWCNTs-COOH) modified epoxy resin specimens; while the fatigue properties of the MWCNTs-COOH modified unsaturated polyester resin specimens were better than those of the MWCNTs-NH₂ modified unsaturated polyester resin specimens. When the contents of MWCNTs-NH₂ and MWCNTs-COOH were both 0.2wt%, the fatigue properties of the modified composites reached the best. The correlation coefficient of the power function linear fitting results was higher than that of the exponential function linear fitting results, and the fitting accuracy was more accurate, and the fatigue life prediction results of composites of this model were also in good agreement with the test results.

Analysis of needle changing mechanism of prefabrication stitching device of hard sandwich structure

SUI Kang, DONG Jiuzhi, CHEN Yunjun, JIANG Xiuming

2023, 0(8): 101-107. DOI: 10.19936/j.cnki.2096-8000.20230828.015

Asbtract ( 54 )

PDF (3953KB) ( 67 )

References | Related Articles | Metrics

The carbon fiber is used as the suture line in the suture device of sandwich structure with pre-punch function, and the optimized Tufting suture process is selected for suture. During the suture process, the needle change mechanism swings with the cylinder as the power source to realize the switch between the suture needle and the pre-punch needle. In order to make the swing process of the needle change stable, the needle change mechanism is simplified as a swing guide rod mechanism, and chose the method of Lagrange dynamics modeling. MTALAB was used to solve the dynamic equation, and the motion curves of each part of the needle exchange mechanism with time variation were obtained. Use of mechanical system dynamics simulation analysis software (ADAMS) built the virtual prototype model of suture device simulation. The theoretical analysis results were compared with the simulation results, then the accuracy of dynamic analysis of needle changing mechanism was proved. The experiment of solid prototype verified the effectiveness of the optimized Tufting suture process, and the needle changing mechanism met the working requirements, it establishes a theoretical basis for the improvement of the suture device and control system design of the prefabricated body suture device of sandwich structure with hard interlayer.

Study on repairing of crack of helicopter tailboom inner skin

MEN Kunfa, HAN Liu, WANG Naiwen

2023, 0(8): 108-111. DOI: 10.19936/j.cnki.2096-8000.20230828.016

Asbtract ( 67 )

PDF (5084KB) ( 72 )

References | Related Articles | Metrics

Tailboom is the principal structure of the helicopter, and the helicopter rear structure global/local finite element mode is built. Based on the finite element analysis result, it is confirmed that there is a high stress level in the tailboom inner skin antenna opening hole area, the crack is produced and propagated under fatigue load. The crack is repaired by using two methods of thin aluminum sheet and glass fabric. From the result of finite element analysis results of different repair schemes, the stress leve decreased 72% and 81% respectively compared with the original structure. Combined with the repair process and parameters, the glass fiber fabric is chosen to repair the crack, it is confirmed by several helicopters over half a year and 500 flight hours, the tailboom inner skin has no more failure. The reliability of repairing tailboom skin crack was verified.

Research and application of needle roller hole method on peeling properties of rigid polyurethane foam sandwich structure

YAO Zhongqiang, TANG Pengfei, GU Yuhui, LI Junxiang

2023, 0(8): 112-114. DOI: 10.19936/j.cnki.2096-8000.20230828.017

Asbtract ( 81 )

PDF (3699KB) ( 58 )

References | Related Articles | Metrics

In order to verify the method of improving the peel strength when the large-sized, shaped-surface rigid polyurethane (PU) foam is used as the core foam, the rigid polyurethane (PU) foam with different surface processing methods is used as the research object, and the roller peel strength is used to characterize the bonding performance of the foam and the panel, the possibility of batch implementation on the surface of large-sized and special-shaped foam is evaluated by the convenience of processing, and the comprehensive material cost is evaluated by the increase of resin consumption in the processing method. Tests show that multi-axis machine tools can improve the peel strength of polyurethane (PU) foam sandwich composites by processing shallow grooves, blade deep slits, needle roll holes, etc. The method of using needle roll holes can improve the peel strength and processing. It has obvious advantages over other processing methods in terms of ease of operation and material cost. This research content has a good guiding significance for the improvement of the peel strength of polyurethane (PU) foams with larger sizes and special-shaped surfaces.

Deformation control technology for honeycomb during the manufacture of large curvature honeycomb sandwich structures

LIU Qi, CHENG Yanna, XU Xiaowei, WANG Xiaokai, HAN Qiangru, ZHAO Zhiyong

2023, 0(8): 115-120. DOI: 10.19936/j.cnki.2096-8000.20221128.032

Asbtract ( 81 )

PDF (8705KB) ( 92 )

References | Related Articles | Metrics

To prevent severe tensile and extrusion deformation between the honeycomb cores due to bending during the manufacture of large curvature honeycomb sandwich structures and to ensure the excellent mechanical properties of honeycomb sandwich structures, the honeycomb deformation is governed by means of grooving. Bending tests were designed for honeycombs of different thicknesses and widths at different bending radii, and a method was proposed to evaluate the deformation of honeycomb cores by extracting the upper surface contours of the honeycombs after bending. The effects of bending radius and thickness on the deformation of honeycombs were investigated. Based on the proposed honeycomb grooving deformation control method, the grooving parameters of a honeycomb sandwich fairing part are designed and verified. The results show that the deformation of honeycomb increases with the increase of bending radius and decreases with the increase of thickness; the grooving spacing can be linearly fitted with the bending radius and honeycomb thickness; after the grooved honeycomb sandwich fairing part is bent, the maximum spacing of the grooves is less than 1 mm after bending, which meets the manufacturing accuracy requirements of the part.

Research progress on toughening modification technology of epoxy resin and its application in aerospace advanced composites

LU Haijun, LI Yafeng, ZHANG Dujuan, HUANG Hao

2023, 0(8): 121-128. DOI: 10.19936/j.cnki.2096-8000.20230828.019

Asbtract ( 173 )

PDF (902KB) ( 233 )

References | Related Articles | Metrics

Epoxy is a widely used matrix material in aerospace field because of its good bonding ability, dielectric properties and good processing performance. However, the poor fracture toughness of curing epoxy resin caused by the high cross-linking density greatly limits its application in aerospace advanced composites. In this paper, the recent development of epoxy resin toughened by hyperbranched polymers, thermotropic liquid crystal polymer, interpenetrating polymer networks and nanoparticles is reviewed, and the application in aerospace field was introduced and prospected.

Table of Content