Table of Content

28 July 2022, Volume 0 Issue 7

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BASIC STUDY

Analysis of mechanical properties and failure mechanism of variable stiffness composite laminates

LI Hui, ZHAO Chun-jiang, LIANG Jian-guo, ZENG Guang, WANG Rui, BIAN Qiang

2022, 0(7):  5-10.  DOI: 10.19936/j.cnki.2096-8000.20220728.001

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In the process of using the wing skin, the issues of insufficient bearing capacity, rigidity and stability are likely to occur. To solve these problems, the variable rigidity laminate is introduced and its mechanical properties and failure mechanism are studied. Firstly, it is proposed to use the periodic triangular wave as the fiber angle change function to optimize the fiber direction and reference path. Secondly, the mechanical model of the variable stiffness laminate is established and the representative volume element is used to predict and analyze the mechanical properties of the model. Then, based on the idea of piecewise linearization, the three-dimensional variable stiffness laminate finite element model is constructed through the MATLAB/ABAQUS. Finally, based on the Tsai-Wu tensor theory, the damage evolution, mechanical properties and failure mechanism of traditional laminates and optimized variable stiffness laminates under tension and compression conditions are analyzed. It indicates that when the reasonable fiber placement path is used for laminates, the failure of laminates caused by large local deformations can be effectively suppressed, the stress distribution of the variable stiffness laminate is more uniform, and the bearing capacity, rigidity and stability of the wing skin are improved.

Finite element analysis study on the flexural behaviour of steel-concrete composite beams strengthened with prestressed CFRP plates

GONG Wei-kang, LIU Xiao-yang, JING Yu-cai, XIANG Jun-ning, LI Xiang-guo, YANG Guo-tao

2022, 0(7):  11-19.  DOI: 10.19936/j.cnki.2096-8000.20220728.002

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In order to study the effect of different design parameters on the bending performance of the steel-concrete composite beams strengthened with prestressed CFRP plate and the strength contribution rate of the CFRP plate, finite element analysis is performed based on the experimental work of Wan^[1]. The reliability of the model is verified by the comparisons between the simulation results, experimental results and theoretical results. Based on the finite element model, a parametric study on the flexural behaviour of steel-concrete composite beams strengthened with CFRP plates is conducted. The results show that increasing the length, width, thickness and the prestress level of the CFRP plate, significantly improves the bending performance of strengthened composite beams. Besides, increasing the mono-symmetric ratio of the H-beam and the width-thickness ratio of the web can also improve the bending performance of composite beams. Moreover, the strength contribution rate of the CFRP plate increases with the increase of the length and prestress level of the CFRP plate and the width-thickness ratio of the web, but decreases with the increase of the cross-sectional area of the CFRP plate and the mono-symmetric ratio of H-beam.

Optimization design of ply structure of wind turbine blade based on strain energy

ZHAO Xiong-xiang, SUN Peng-wen, LI Jian-dong

2022, 0(7):  20-24.  DOI: 10.19936/j.cnki.2096-8000.20220728.003

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The blade performance is directly related to the service life of wind turbine, and the ply parameters are one of the key factors to determine the blade performance. The stiffness of the structure can be reflected by the magnitude of strain energy. The expression of strain energy of composite shell structure is deduced in this paper. From the view of engineering point, taking a 1.5 MW blade as the object and the minimum structural strain energy as the objective function, adopting the hierarchical optimization strategy, considering the strength and quality characteristics of the blade, the optimization mathematical model of ply parameters is established. The optimized ply angle, ply thickness distribution and ply stacking sequence are obtained by solving. The results show that the quality of the optimized blade is reduced, while the static stiffness and strength are improved. The effectiveness of the method is verified.

APPLICATION RESEARCH

Modeling of composite blade and analysis of the effect of ply parameters on strength

FENG Yu-ru, WANG Jun-li, ZHANG Bao-jun, LIU Zhi-yuan, LI Jin-yang, ZHANG Bao-sheng

2022, 0(7):  25-31.  DOI: 10.19936/j.cnki.2096-8000.20220728.004

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In this paper, the finite element analysis method is used to study the modeling of the compressor composite blade and the influence of the ply parameters on the composite blade. In the ANSYS platform, the ACP module is used to model the composite blade, and the accuracy of the composite blade modeling method is verified by comparing the modeling method of the traditional TC4 blade. The influence law of ply angle and ply thickness on the strength of composite blade was studied. The research result shows that with the increase of the ply angle, the maximum deformation of the composite blade first decreases and then increases, but the maximum equivalent stress of the blade gradually increases. Changes in ply thickness result in blade deformation and stress changes of no more than 5%. Therefore, the design emphasis should be placed on the ply angle when designing a composite blade.

Study on co-curing quality of hat-stiffened structure of resin matrix composites with different forming methods

CHANG Teng-fei, ZHAN Li-hua, LI Shu-jian, PAN Yang

2022, 0(7):  32-38.  DOI: 10.19936/j.cnki.2096-8000.20220728.005

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Traditional manual laying has the problems of unstable forming quality and low production efficiency, which is difficult to meet the production demand of the main bearing structure of complex composite materials. And the paving of the bearing structure with complex characteristics is impossible by automatic tape laying. Based on this, this paper proposes a preforming co-curing process on the basis of manual paving. Meanwhile, the effects of hand-made co-curing and preforming co-curing on the forming quality of composite hat-shaped structure are compared by using FBG sensor to monitor strain, combined with phased array ultrasonic detection, optical microscopic observation and mechanical properties test. The results show that the internal strain of the hat-shaped structure prepared by preforming is larger, which is mainly affected by the pressure in the autoclave and the silicone rubber auxiliary mold, and it is beneficial for the smooth distribution of fibers in the structure and better compaction effect. There are many kinds of internal defects in hat-shaped structure, which mainly exist in the triangle area and the joint of hat-shaped truss and skin panel. Compared with the hand-made co-curing process, the key areas of the hat-shaped structure in the preforming process (1 ℃/min heating to 60 ℃, holding for 1 h) are basically free of defects such as pores and fiber wrinkling, and the shape accuracy is evenly distributed, in which the pull-out strength is effectively increased by 21.5%.

Effect of self-assembled montmorillonite-carbon nanotubes on mechanical and interfacial properties of glass fiber-reinforced composites

HUANG Dong-hui, ZENG Shao-hua

2022, 0(7):  39-44.  DOI: 10.19936/j.cnki.2096-8000.20220728.006

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To improve interfacial properties of glass fiber composites, a self-assembly of one-dimensional (1D) tubular multi-walled carbon nanotubes (MWCNTs) and two-dimensional (2D) layered montmorillonite (Mt) was performed to prepare 1D/2D Mt-MWCNTs nanohybrid, followed by the deposition of such nanohybrid onto the surface of glass fiber fabrics. Finally, the epoxy composite containing Mt-MWCNTs was prepared based on the vacuum bag molding process. The results show that the MWCNTs in hybrids could prevent the stacking of Mt, and layered Mt also could increase the dispersion of MWCNTs; layered Mt and tubular MWCNTs could synergistically strengthen and toughen epoxy composites. Compared with blank sample without Mt-MWCNTs, the interlaminar shear strength of epoxy composites containing Mt-MWCNTs was enhanced by about 28%, tensile strength and modulus of such composite were raised by 24% and 25%, respectively, and its flexural strength and modulus were promoted by 19% and 23%, respectively; the glass transition temperature of such composite increased by nearly 5 ℃.

Experimental study on compacting performance of continuous carbon fiber reinforced thermosetting prepreg

MAN Jia-cheng, HOU Jin-sen, LI Zhe-fu, YUE Guang-quan, XU Peng, JIANG Bi-yu, LIU Wei-ping

2022, 0(7):  45-51.  DOI: 10.19936/j.cnki.2096-8000.20220728.007

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The compaction performance of the prepreg is an important indicator that affects the formation of composite materials. In order to understand the compaction performance of pre-immersion in the formation process, this paper establishes effective and stable test programs. The stress and strain of continuous carbon fiber/epoxy prepreg is carried out, using universal testing machine and self-designing device, test and characterize the prepreg in the compaction process. Four structures and process parameters such as size, thickness, temperature and rate of descent are controlled to explore the impact of these factors against compaction. The results show that size, thickness, temperature have a significant effect on stress strain results, and the rate of descent has little effect. At the same time, the test results are fitted with the stress hardening model, and the results show that there is an index relationship between stress and strain at the time of prepreg resin.

Moisture absorption/desorption characteristics of carbon fiber composite under hygrothermal/dry alternation environment

LIN Mei, ZHANG Tie-jun, FENG Yu, WANG Qi, WU Meng-ke

2022, 0(7):  52-59.  DOI: 10.19936/j.cnki.2096-8000.20220728.008

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The moisture absorption/desorption characteristics of carbon fiber composite under hygrothermal/dry alternation environment were studied. Six times high temperature and high humidity/dry environment alternation test of composite laminates were finished. By observing the microstructure of matrix and interface, the characteristics and evolution of environmental damage were analyzed. The results show that moisture absorption diffusion coefficient increased gradually, the balanced moisture content increased, and desorption time increased significantly under hygrothermal/dry alternation environment. It shows that there are some changes in material properties and microstructure. The accuracy of fitting moisture absorption/desorption test data by polynomial was good, and the equations of multiple moisture absorption/desorption were derived according to Fick's law. The micro morphology of composite interface after the fourth and sixth moisture absorption was slightly different, which indicated that interface failure of composite basically reached "saturation". Finally, "total damage" and "residual damage" were proposed to describe the environmental damage caused by hygrothermal/dry alternation environment, which provided a new idea for damage characterization and performance prediction.

Fabrication and microwave absorption properties of SiC_f/Al₂O₃/Mullite composite

GAO Hui, LUO Fa, QU Yong-ping, WANG Chun-hai

2022, 0(7):  60-65.  DOI: 10.19936/j.cnki.2096-8000.20220728.009

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Silicon carbide fiber reinforced ceramic matrix composites play a very important role in military and civil fields. The SiC_f/Al₂O₃/Mullite composite was prepared by a sol-gel method, the matrix precursor was mullite sol and the interphase was Al₂O₃. Influence of sintering temperature on the phase and morphology of powder was studied. The surface morphology of Al₂O₃ interphase and microstructure, mechanical, dielectric and absorbing properties of SiC_f/Al₂O₃/Mullite composite were analyzed. The results showed that a continuous and dense interphase was prepared by the sol-gel method, and the thickness was about 46 nm. The flexural strength and fracture displacement of the SiC_f/Al₂O₃/Mullite composite reached 234 MPa and 0.36 mm, respectively. When the thickness of composite was in the range of 3.3 mm~3.5 mm, the value of reflection loss was below -5 dB in the whole X-band. The SiC_f/Al₂O₃/Mullite composite has potential application value in the field of microwave absorbing materials.

Adsorption of copper ions in electroplating wastewater by magnetic polypyrrole composite

WANG Dong-ping

2022, 0(7):  66-70.  DOI: 10.19936/j.cnki.2096-8000.20220728.010

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In this paper, Fe₃O₄ nano microspheres were prepared by precipitation method, and then polypyrrole and Fe₃O₄ were combined under the action of ultrasonic to form polypyrrole based magnetic nanocomposites. The composites were characterized by XRD, FTIR, SEM, TEM and magnetic properties. The experimental results show that polypyrrole and Fe₃O₄ nano microspheres have been successfully compounded, and the particle size is about 200 nm, producing composites with saturation magnetization of 48 emu/g. The further experiment was carried out to study the cyclic adsorption of copper ion with composite materials as adsorbent. The adsorption efficiency of the first cycle was 94.50%, and after five cycles of adsorption, the adsorption efficiency was 88.25%. At the same time, the composite has strong magnetic properties, so that the whole cyclic adsorption process can be carried out through magnetic adsorption, which is simple, time-saving and labor-saving. Therefore, the composite has a good application prospect as a circulating adsorbent.

Application and research of ANSYS beam model in full-scale blade static test

LU Xiao-feng, ZHANG Yan-ming, MENG Dan, SU Cheng-gong

2022, 0(7):  71-74.  DOI: 10.19936/j.cnki.2096-8000.20220728.011

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In order to design full-scale blade static test specification quickly, a beam model with geometry nonlinear analysis method which was used for static test design is presented based on ANSYS. First, compared with shell model, the accuracy of beam model was verified. Then, the method was used in the full-scale blade static test. The test result reveals that the test data is coincided with the calculated data and derivation meets requirements of guideline. So the feasibility of this method was verified.

Synthesis and application of hyperbranched unsaturated resins

HUAN Sheng-min, HUANG Xiao-bo, YANG Run-miao, XIANG Meng

2022, 0(7):  75-80.  DOI: 10.19936/j.cnki.2096-8000.20220728.012

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A core-shell hyperbranched unsaturated polyester was designed and synthesized. The hyperbranched polyester formed by trimethylolpropane and 2,2-bis(hydroxymethyl)propionic acid as the core. The adduct of 2-hydroxyethyl methacrylate and isophorone diisocyanate was used as the outer shell. The product was characterized and analyzed by fourier infrared (FT-IR), nuclear magnetic resonance (¹H NMR), and thermogravimetric analysis (TG). Finally, the obtained hyperbranched unsaturated resin is modified to linear unsaturated polyester. The results show that when the addition amount of hyperbranched unsaturated resin is 3% and it can enhance the toughness of unsaturated polyester and maintain other mechanical properties. At the same time, the effect of the shell-core hyperbranched unsaturated polyester on the viscosity system of the unsaturated polyester was also studied.

Comparative analysis of data reduction method of ENF test of mode Ⅱ delamination

WANG Ya-na, ZHAO Wei

2022, 0(7):  81-92.  DOI: 10.19936/j.cnki.2096-8000.20220728.013

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Mode Ⅱ delamination is a common failure mode in composite laminate structures, so the mode Ⅱ interlaminar fracture toughness is the important mechanical property parameter needed for characterizing the interlaminar properties of composites, and required by composite structure design. There are several test methods for mode Ⅱ interlaminar fracture toughness, among which the end notched flexure (ENF) test is widely adopted in engineer practice. As for the complex driving mechanism and lots of influence factors of mode Ⅱ delamination in ENF test, researchers have proposed many data reduction methods for mode Ⅱ fracture toughness, and the obtained data would be diverse when different data reduction methods were adopted. In order to help engineers to learn deeply the differences of various data reduction methods for mode Ⅱ fracture toughness, this paper firstly systematically reviewed the mechanics, simplification conditions, derivation process and precision of different data reduction methods of mode Ⅱ interlaminar fracture toughness in ENF test, for the purpose of offering useful guidance for engineers in the field of composite materials development, testing and design.

Design and analysis of glass fiber group knotting device in winding process of water treatment tank

TIAN Hui-fang, ZHANG Guo-wu, WU Ying-feng, REN Zheng

2022, 0(7):  93-98.  DOI: 10.19936/j.cnki.2096-8000.20220728.014

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Currently, the winding of glass fiber bundle continuation is using manual knotting. This paper studied the working principle of existing knotting equipment, and designed a knotting device for glass fiber group continuation. In Creo software, the knotting device was designed in detail, and the fiber bundle continuation function of the knotting device was verified by simulation.

Preparation of conductive basalt fibers through polymer assisted deposition method

FENG Qian-qian, ZHU Fang-long

2022, 0(7):  99-102.  DOI: 10.19936/j.cnki.2096-8000.20220728.015

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The insulating properties of basalt fiber (BF)restrict its application in many fields. In order to further solve the problem, a nickel coating was successfully deposited on the basalt fiber surface by using electroless plating through polymer assisted metal deposition method. In this study, acidified basalt fibers were treated with L-cysteine hydrochloride (L-H-Cys) solution, and nickel layer was deposited on the surface of basalt fibers by electroless plating to prepare conductive functional basalt fibers. The microstructure, phase structure, adhesion and electrical conductivity of the Ni plated BF were evaluated by SEM, FTIR, XRD and electrical resistance measurements. Experimental results indicate that the nickel film consisting of dense of spherical particle and the resistance value is 14.2 Ω/cm (resistivity of 1.9 × 10^-3 Ω·cm). Even after three times of thermal cycling treatment, the nickel plated fiber still has satisfactory conductivity and its resistance value is 15.8 Ω/cm, which corresponds to resistivity of 2.1×10^-3 Ω·cm. The prepared composite fibers possess high plated layer adhesion and good electrical conductivity and present promising application prospects in the field of fiber-reinforced electromagnetic shielding composites.

The study of structural design and mechanical propeties of polyurethane composite walking board

LIU Zhi, ZHANG Bin, ZHAO Wei-wei, ZHANG Yong

2022, 0(7):  103-106.  DOI: 10.19936/j.cnki.2096-8000.20220728.016

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Based on the engineering experience and simulation method, the composite walking board with equal stiffness was designed, and the structural configuration and cross-section geometric dimensions of the composite walking board were determined. Test pieces of three kinds of felt paving methods are prepared and tested by pultrusion process. The results show that the mechanical properties of the walking board of three kinds of felt paving methods meet the standard requirements. The minimum deflection span ratio is 1/342, the bearing capacity can reach 35.4 kN, and the micro strain of the walking board changes linearly with the load before failure. Comparing the simulation results with the actual test results, it is found that the deflection value of each rib is close to the actual test results, and the change trend is consistent, which can provide theoretical data for the structural design of walking board. The pedestrian board designed and prepared in this paper can meet the requirements of railway bridge and culvert design code.

Comparative study on shear buckling load analysis methods of honeycomb sandwich panels

XIONG Hua-feng, LI Lei

2022, 0(7):  107-110.  DOI: 10.19936/j.cnki.2096-8000.20220728.017

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In this paper, three analytical methods for shear buckling load of honeycomb sandwich panels are studied. The analysis methods include engineering method, linear finite element method and nonlinear finite element method. In the engineering method, the relevant parameters were calculated, and the buckling load coefficient was obtained from the chart directly, and then the buckling load was calculated. The linear finite element method used subspace eigenvalue method to get the eigenvalues of each order. Then the buckling load was obtained as the product of the minimum eigenvalue and the loading load. In the nonlinear finite element method, the buckling load was taken as the load when the minimum principal strain of the upper and lower panels at the point of maximum displacement was separated. The shear test of honeycomb sandwich panel was carried out. The test results showed that the prediction results of engineering method were too conservative. The prediction results of linear finite element method and nonlinear finite element method were very close, and they were in good agreement with the test results.

Experimental study on chip morphology and hole wall damage in low volume fraction SiCp/Al composites drilling

ZOU Cai-yong, YAN Cheng-lei, LI Jie, LIU Chang

2022, 0(7):  111-114.  DOI: 10.19936/j.cnki.2096-8000.20220728.018

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SiCp/Al composites are widely used in the fields of electronics and aerospace due to their excellent physical properties. It is very important to study the drilling mechanism of SiCp/Al composites for obtaining high machining quality. In this paper, the drilling experiments of SiCp/Al composites were carried out under different spindle speeds (1 000 rmp~2 000 rpm) and feed rates (0.1 mm/rev~0.2 mm/rev), and the chip morphology, surface roughness and hole wall damage were studied. The results show that fan-shaped chip, C-shaped chip and cone-shaped spiral chip can be observed in macro view. Serrated damage was also observed at the end of the chip. In the micro level, there are tearing, voids, fracture, cracks and grooves on the front and back of the chip. The surface roughness of hole wall increases with the increase of feed rates and decreases with the increase of spindle speed. In addition, matrix cracks, matrix tears and voids were found at the hole wall.

REVIEW

Research progress on the tolerance of composite containment fan case

ZHANG Hao, SUN Hong-jie, SUN Jian-bo, ZHANG Jian-bao, LIU Yong-jiao, SUN Jian, LI Zhong

2022, 0(7):  115-120.  DOI: 10.19936/j.cnki.2096-8000.20220728.019

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With the continuous optimization of the material and structural design of the fan containment cases, a variety of composite containment fan cases with different structural forms have been developed. Considering the service conditions of the composite fan case, the composite fan cases need to have sufficient containment effect on the high-energy debris generated by the blade fly-off process. Therefore, tolerance has become one of the important basis for judging the quality of their work performance. In this paper, the types of composite material containment fan cases currently in service are briefly described. The characteristics and functions of tolerance evaluation methods suitable for composite material fan containment casings are summarized. The research progress of the containment damage mechanism of the composite containment fan case is summarized. The containment promotion method of composite containment fan cases is discussed. On this basis, further research on the containment of composite fan cases is prospected.

A review on mechanism and control methods of residual stress and cured deformation of composite materials

HE Liang, ZHU Pan-xing, XU Xiao-wei, WANG Jin-yun

2022, 0(7):  121-128.  DOI: 10.19936/j.cnki.2096-8000.20220728.020

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Composite materials have been widely used in aerospace, marine, and automotive areas due to their excellent mechanical and light weight properties. However, cured deformation of composites is one of the obstacles to its rapid development and application. In the present review, the mechanism that causes residual stresses and deformations is elaborated, including the mismatch of thermal expansion properties, polymerization/crystallization shrinkage, tool-part interaction, resin flow and compaction, fiber wrinkling, and gradient distribution of temperature and curing degree. Several strategies to control the formation of residual stresses and deformations are proposed, including optimization of curing parameters, tool compensation, tool-part contact optimization, and the development of new resins and curing process. The problems exist in the corresponding strategies are summarized, and perspectives of the future developments in the field of process-induced distortions are recommended.