COMPOSITES SCIENCE AND ENGINEERING

EXPERIMENTAL INVESTIGATION ON IMPACT RESISTANCE OF COMPOSITE CORNERS

ZU Lei, HU Hai-xiao, WANG Ji-hui, LI Shu-xin

2014, 0(10): 5-10.

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The polymeric composite laminates show relatively high impact sensitivity. Even the low-energy impact on the laminates in service is easy to cause invisible damages and the degradation of the strength and stiffness and thus severely threaten the safety of the laminates. The bending stiffness degradations of glass fiber reinforced vinylester composite corners made of five lay-ups are respectively observed with the aid of four-point bending tests. The influence of various lay-ups and impact energy levels on the impact resistance of the composite corners is evaluated. The results conclude that the increase in the impact energy leads to more impact damage and lower residual bending stiffness; the impact damage areas of the five specimens exhibit basically identical tendency with their stiffness degradation. The closer fiber angles of two adjacent layers result in the higher bending stiffness and the lower after-impact stiffness degradation of the composite corners. It is further indicated that the [45°/0°/-45°/90°] lay-up produces the lowest after-impact stiffness degradation of the composite corners and the cross-ply specimens have the lowest impact resistance.

STUDY ON THE PYROLYSIS PERFORMANCE OF PHENYL-PHENOL MODIFIED PHENOLIC RESIN

QIN Xiao-ting, LIU Yu-jian, ZHANG Yan, FANG Jun

2014, 0(10): 11-15.

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The pyrolysis mechanism of the phenyl-phenol modified phenolic resin (PPR)is investigated by using thermogravimetic analysis (TGA), pyrolysis-gas chromatogram-mass spectrum (Py-GC-MS) and fourier transform infrared spectrum (FT-IR). The results indicate that methylene has higher activity than other groups in the resins, which tends to break and further react with phenolic hydroxyl, accompanying with the release of phenols, benzodiazepines and methyl derivatives at 450℃. At higher temperature,the structural rearrange reactions take place, and the structure transforms into anthracene, phenanthrene or amorphous carbon through further dehydrogenation coking reaction. According to the results of Py-GC-MS, the amount of volatile released from the phenyl-phenol modified PF is less than that from the ordinary PF under the same condition,which demonstrate better thermal stability of PPR.

THE RESEARCH ON THE INTERFACIAL DEBONDING OF FIBER-REINFORCED SEALING COMPOSITE SUBJECTED TO ALTERNATING LOAD

WU Deng-ke, GU Bo-qin

2014, 0(10): 16-20.

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The interfacial debonding is the major form of interface failure of fiber-reinforced sealing composites, which can be regarded as a special crack growth of interfacial debonding. Based on the shear-lag model, the interfacial crack growth regularity of fiber-reinforced sealing composites subjected to alternating loads was investigated. In consideration of the damage of debonding interface and the inhomogeneity of the damage distribution because of fatigue load as well as Poisson’s ratio of fibers, a equivalent Paris equation was proposed, and the relationships between some fatigue variables and number of cycles were studied, including fatigue crack growth length, crack growth rate and interfacial friction coefficient.

STUDY OF THE SECTIONAL SIZE EFFECTS OF AXIAL COMPRESSION PERFORMANCE OF CONFINED CONCRETE SHORT COLUMNS WITH BFRP SHEETS

LIU Hua-xin, SUN Ying-ming, WANG Xue-zhi, XING Xian-cai

2014, 0(10): 21-26.

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In order to study the axial compression performance, five different section height to width ratio of confined concrete rectangular short columns with BFRP sheets were characterized by axial compressive test. According to section height to width ratio and the layers of BFRP sheets, all specimens were divided into 15 groups, and every group has 3 specimens. The axial compressive strength, peak strain and stress-strain relationship of all specimens were also investigated by the theoretical analysis and numerical simulation. The results indicate that crack development and damage morphology are basically the same in each group. For the axial compressive strength of the specimens in each group, there is an obvious cross-sectional size effect. With the changes of specimen cross-sectional aspect ratio, peak strain is relatively discrete. The strength model agrees well with the experimental results. And the axial compressive strength of confined concrete short column can be well simulated by using ANSYS finite element analysis software.

STRESS ANALYSIS IN BONDLINE OF CENTER-CRACKED METAL PLATE BONDED WITH COMPOSITE PATCHES BASED ON TOM THEORY

HAO Jian-bin, MU Zhi-tao, LI Xu-dong

2014, 0(10): 27-31.

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For the damaged structure repaired with bonded composite patches, based on the TOM theory, an improved Rose L R F theoretical solution is proposed, in which the shear effect among the skin thickness is considered. The assumption of linear shear stress distributions through the thickness of the skin is adopted in the analysis. The analytical results showed good agreements with the FEM result, which verifies the validity of the proposed analytical model. The effects of the skin thickness on the adhesive shear distributions are presented. It is shown that the improved solutions are more close to numerical results than Rose L R F solution when the thickness of the skin is relatively thin (i.e., the ratio of the thickness to the length is less than 0.1).

FEM SIMULATION AND EXPERIMENTAL STUDY OF COMPOSITE CASE DOME WITH HOLES

YANG Le, ZHANG Hao-zhe, YANG Xi-jun, LIU Hong-cheng

2014, 0(10): 32-36.

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Numerical and Hydrostatic test method were used to analyze the foe dome with holes of filament winding composite case. A layered solid element was used to simulate the filament winding composite dome with varying thickness.The results reveal that the numerical analysis results of the deformation of the dome agreed with hydrostatic test results. The maximum displacement was located in the fore mental part of the fore dome with holes, and the displacement gradient was decreased towards the euuato. Higher strain distribution along the fiber was located in the pitch circle of the hole edge side anbout 2/3 zone, and the strain significantly was decreaing out the range. And, strain graduslly increases to both sides through the generatrix direction of center hole,the maximum is less than 2100ε.

STRESS ANALYSIS OF COMPOSITE/METAL DOUBLE-SIDED BONDED JOINTS UNDER THERMO-MECHANICAL LOADS

SU Wei-guo, MU Zhi-tao, LI Xu-dong

2014, 0(10): 37-41.

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A stress analysis model involving adhesive material nonlinearity under thermo-mechanical loading condition is developed to characterize adhesive stress distribution of composite/metal double-sided adhesively bonded joints. The maximum strain criterion is used to predict the initial failure of the adhesive based on the failure mode. The finite element analysis is conducted to validate the present closed-form solutions. The numerical results indicate that the analytical solutions and their simplifications correlate well with the nonlinear finite element computations. The present mathematical techniques and analysis approaches are critical to the successful design, analysis and implementation of bonded repairs.

RELIABILITY EVALUATION AND MACRO-PARAMETERS PREDICTION ANALYSIS OF THE FIBRE-REINFORCED COMPOSITE

LIU Wan-lei, CHANG Xin-long, ZHANG Xiao-jun, HU Kuan

2014, 0(10): 42-47.

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This study gives a detailed analysis of the composite macro-parameters distributions which derived from the micro-parameters uncertainties using Monte-Carlo method based on the Bridge-model. Random variable based micro and macro-scale reliability analyses are critically compared based on the analytical stress tensor components of a rectangular simply supported orthotropic. The results show that the elastic and shear modulus of the composite follow Normal distribution, while the tensile strength of the composite follows Weibull distribution. This study also demonstrates that the results of the composite plate reliability derived from macro and micro parameters are similar, which implies the micro-parameter can be used directly to evaluate the reliability of the composite.

PROPERTIES AND MANUFACTURE OF BAMBOO REINFORCED EPOXY VINYL RESIN

LI Hong-bin, LI Wei, LUO Yong-kang

2014, 0(10): 48-52.

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Compared with the traditional steel guardrail, bamboo reinforced composite guardrail has many advantages, such as light weight, low cost, corrosion resistance, environment friendly and renewable. But surface of bamboo fiber had complex composition which influence the interfacial properties of the composites. In this paper, bamboo was used as a reinforcing material to reinforce epoxy vinyl resin to make the bamboo composite by using vacuum assisted molding method. The effects of chemical modification by alkali treatment with silane coupling agent and the number of bamboo layer on bending strength and impact toughness in composite were studied. And, the failure mode of impact section of unidirectional composites was analyzed. The results show that the bending strength of modified bamboo reinforced composite increased by 31.95%, 46.72%, 29.58% under different layer structure conditions, and the impact toughness increased respectively by 25.62%, 29.74%, 28.61%, but the flexural and impact properties of unidirectional composites is the best. When the number of bamboo layer is: 15 layers in the unidirectional composites, impact absorbing energy is 13.55J, tensile strength is 270MPa, bending strength is 340MPa, which can meet the highway guardrail requirements on the raw Q-235 on the main performance. The failure mode of impact section is bamboo fiber pull-out fracture, matrix crack, fiber/matrix interfacial debonding and shear layer, as found by SEM in unidirectional composite. The results have some significance for guiding the preparation of highway anti-collision guardrail made of composites.

PROPERTIES OF LONG CARBON FIBER REINFORCED POLYPHENYLENE SULFIDE (LCF/PPS) COMPOSITES BY WET PROCESS

XU Chun-fei, ZHOU Xiao-dong

2014, 0(10): 53-57.

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Long carbon fibers and PPS fibers were mixed in the stirring kettle and prepared to hybrid fibers by wet process. The LCF/PPS composites were prepared with the dry hybrid fibers by compression molding process. The influence of CF content and length and the CF content in the dispersion kettle on notched impacted strength and flexural performances was studied. And the effects of the mechanical property and CF dispersion in the composites were studied by the SEM fracture morphology of the composites. The result shows that the best properties were obtained, where the notched izod impact strength was 49.1kJ/m², the flexural strength was 178.51MPa and the flexural modulus was 18.56GPa, when the CF content was 45wt%, CF length was 9mm and CF content in the dispersion kettle was 0.5g/L. The good fiber dispersion and cohesiveness between CF and resins were observed by SEM in the cross section of the composite.

STUDY ON THE RESISTANCE CHARACTERISTICS OF CARBON FABRIC

DING Hai-bin, ZENG Jing-cheng, PENG Chao-yi, YANG Fu-biao

2014, 0(10): 58-61.

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Resistance characteristics of carbon fabric play a significant role in studying the anti-icing composites materials. The effects of length, width and layers number on resistance features of T300 carbon fabric were studied. Besides, the resistance of carbon fabric is compared with its composite materials. The results show that resistance increases with length of carbon fabric linearly, but it decreases with width and layers number nonlinearly, which is different to common conductors inverse ratio. Resin infusion can reduce the resistance of carbon fabric by 0.1Ω, which is negligible.

THE IMPACT COMPRESSIVE BEHAVIORS OF BIAXIAL WARP-KNITTED COMPOSITE

FANG Fang, PAN Zhong-xiang

2014, 0(10): 62-65.

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In this paper, compressive behaviors of bi-axial warp-knitted (BWK) composite under impact loading at various strain rates were investigated. The stress vs. strain curves and the relevant failure modes with different compressive loading strain rates in three orthogonal directions were obtained from the test system of Split Hopkinson Pressure Bar (SHPB) and MTS test machine. The results indicated that the biaxial warp-knitted (BWK) composite was strain rate sensitive. The failure stress and the compressive modulus were increased with the increasing of strain rate while the failure strain was decreased. With the increase of the strain rate, the damage is more serious and failure mode is clearer. In addition, the compressive properties along the out-plane direction was much better than those of the in-plane direction. Differences of compressive properties were also observed between the warp direction and the weft direction. Thus, the composite was verified to be anisotropic. The photographs of the damaged composites at various strain rates showed that at out-plane direction the main failure mode was the interlaminar shear failure, while at in-plane direction the delamination was the main failure mode except the shear failure at quasi-static compression. This paper provides a better understanding of the failure mechanism of bi-axial warp-knitted (BWK) composite.

STUDY ON PROPERTIES OF ZIRCONIUM ACETATE MODIFIED PHENOLIC RESIN COMPOSITES

LI Zhe, ZHOU Quan, CHEN Qi, NI Li-zhong

2014, 0(10): 66-69.

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Phenolic resin (PF) was widely used as matrix resin for ablative materials due to its excellent mechanical properties and ablation resistance. However, the char yield of traditional phenolic resin was too low to meet the higher requirement on ablative materials. Based on this background, a kind of zirconium acetate modified phenolic resin (ZPF) was prepared in this work, which had higher char yield than pure phenolic resin (PF). Then glass fiber reinforced zirconium acetate modified phenolic resin (GF/ZPF) composites were prepared. The effects of zirconium content on flexural strength and linear ablation rate of the composites were studied. And the changes of linear ablation rate and ablation morphologies of the composites with ablation time were observed and analyzed. The results showed that the char yield of ZPF was 68.7% at 1000℃, which increased by 21.7% than that of PF. The flexural strength of GF/ZPF composites reached up to 642MPa when the zirconium content of the resin was 14%. With the increase of the zirconium content from 10% to 15%, the linear ablation rate was reduced from 0.0305 mm/s to 0.0208mm/s. In addition, the linear ablation rate was rarely changed with increased ablation time, which indicated that the GF/ZPF composites had excellent ablation properties.

FATIGUE TIME ANALYSIS ON DIFFERENT AUTOFRETTAGE PRESSURE OF GLASS FIBER HOOP-WRAPPED COMPOSITE CYLINDERS

CHENG Zhi-gang

2014, 0(10): 70-74.

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This paper analyzed the fatigue times of glass fiber hoop-wrapped composite cylinder under different autofrettage pressure. By adopting the new stress range-cycle times curve instead of the JB 4732 standard, the fatigue life under different autofrettage pressure was calculated. The results indicate that the cylinder can not meet the fatigue life if no autofrettage.

THERMAL EQUILIBRIUM AND MANUFACTURE TECHNIC OF FRP TANKS WITH JACKET

CHENG Ai-lin, DU Hui-bo, ZHANG Guo-jun

2014, 0(10): 75-77.

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This article analyzed the corrosion resistance, strength and temperature control of the FRP jacketed tank materials suitable for food production industry, and puts forward the FRP jacketed tank of special manufacture technology and thermal equilibrium analysis method.

STATE OF THE ART REPORT ON REINFORCED CONCRETE BEAMS WITH NSM PRESTRESSED FRP TENDONS

ZHANG Chun-sheng, ZHAO Xu, DING Ya-hong

2014, 0(10): 78-83.

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According to the research status of FRP materials, the development of FRP reinforcement technology was introduced based on literatures at home and abroad. And, the characteristics of NSM prestressed FRP and some engineering application problems were analyzed. The results show that NSM prestressed FRP reinforcement is an effective strengthening method. However, some factors such as practical tension and anchor system and different parameters should be further explored.

RESEARCH PROGRESS OF COMPOSITE LEAF SPRING

YANG De-xu, ZHU Hai-feng, ZHANG Lin-wen

2014, 0(10): 84-89.

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This paper summarizes the research and application situation of the composite leaf spring. The raw material selection, molding process, equipment, structure design and performance test problems were analyzed. And, some corresponding suggestions for the future development of composite leaf spring were put forward.

DEVELOPMENT OF BRAIDING MACHINE AND BRAIDING TECHNOLOGY

ZHAO Zhan, Md. Hasab Ikbal, LI Wei

2014, 0(10): 90-95.

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Braiding technique is one of the most important preform manufacturing techniques. Braiding technology has been improved to fabricate near-net-shaped fiber preforms of complex shaped composite materials with variable cross-section,impact tolerance, delamination resistance and creep deformation resistance. Braiding structure materials are widely used in the areas of engineering, aeronautics and astronautics, automotive, etc. In this article, braiding machines, their working principle, braided structures and representative models are illustrated and introducd. The applications of braiding structure materials and the current research direction of braiding machines are also discussed.

THE UNDERSTANDING OF THE DESIGNABLE IDEA OF COMPOSITE MATERIALS

ZHANG Lin-wen

2014, 0(10): 96-97.

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