纤维分布不均匀的层压板表征与弯曲性能研究

基于MATLAB图像处理技术,本文开发了用于测定复合材料纤维分布状态的计算机图像处理程序。以T300/BMP316复合材料为对象,采用三点弯曲法研究了纤维分布均匀性对复合材料弯曲性能的影响,用有限元方法分析了纤维分布不均匀的复合材料弯曲变形时的应力分布,提出了运用抗弯系数R评价其性能。结果表明,基于MATLAB图象处理技术可快速准确地测定纤维增强复合材料的纤维密实指数,确定纤维的分布状态。纤维分布不均的T300/BMP316复合材料弯曲性能受纤维分布方式和载荷方向的影响极大,抗弯系数R反映了纤维分布与性能的关系。     

Effects of fly ash in composites fabricated by injection molding

In this study, the effects of fly ash in composites fabricated by injection molding are examined. Taguchi design of experiment was first utilized to estimate the effects different injection molding conditions and content ratios of fly ash have on a linear low‐density polyethylene (LLDPE)‐fly ash composite. The results reveal that the content of fly ash is highly significant and contributive to the shrinkage ratio and bending strength. For these reasons, LLDPE and polypropylene (PP) composites with different size particles of fly ash were fabricated and the mechanical properties were investigated. The particle size was changed by grinding fly ash with a planetarium ball mill. The shrinkage ratio, bending strength and flexural modulus of LLDPE composites containing raw fly ash were found to improve. The shrinkage ratio and flexural modulus of PP composites containing ground fly ash were also found to improve. Homogenization analysis using the finite element method was then used to calculate the Von Mises stress distributions and homogenized elastic matrix of PP composites containing ground fly ash. The homogenized elastic matrix was used to validate the experimental flexural modulus. The results show that the homogenized elastic matrix is in good agreement with the experimental flexural modulus. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

A comparative analysis of woven jute/glass hybrid polymer composite with and without reinforcing of fly ash particles

The objective of this research article is to compare the mechanical and tribological properties of jute‐glass‐fiber‐reinforced epoxy (J‐G‐E) hybrid composites with and without fly ash particulate filler. A dry hand lay‐up technique is used to fabricate all the laminates. The properties including flexural strength, tensile strength, flexural modulus, and erosion behavior of all the composites are evaluated as per American Society for Testing and Materials (ASTM) standards. The fly ash particulate‐filled hybrid composite shows a better mechanical and tribological property. The maximum flexural strength and flexural modulus are obtained for GJGJ+ 5 wt% fly ash filler epoxy composites. Whereas the maximum tensile strength is obtained for GJJG+ 10 wt% fly ash filler epoxy composites. Scanning Electron Microscopy (SEM) analysis also has been carried out to categorize mechanical and tribological behavior of composites. POLYM. COMPOS. 37:658–665, 2016. © 2014 Society of Plastics Engineers     

Flexural properties of S‐2 glass and TR30S carbon fiber‐reinforced epoxy hybrid composites

A study on the flexural properties of hybrid composites reinforced by S‐2 glass and TR30S carbon fibers is presented in this article. Test specimens were made by the hand lay‐up process in an intraply configuration with varying numbers of glass/epoxy laminas substituted for carbon/epoxy laminas. These specimens were then tested in the three point bend configuration in accordance with ASTM D790‐07 at a span to depth ratio of 32. The failed specimens were examined under an optical microscope, and the results show that the dominant failure mode is at the compressive side. The flexural behavior was also simulated by finite element analysis (FEA). Based on the FEA results, the flexural modulus and flexural strength were calculated. Good agreement is found between the experiments and FEA. It is shown that flexural modulus decreases with increasing percentage of S‐2 glass fibers, positive hybrid effects exist by substituting carbon fibers for glass fibers, and applying a thin layer of S‐2 glass fiber‐reinforced polymer on the compressive surface yields the highest flexural strength. The modeling approach presented will pave a way to the effective design of hybrid composites. POLYM. COMPOS., © 2012 Society of Plastics Engineers     

Predictive modeling of microcracking in carbon‐fiber/epoxy composites at cryogenic temperatures

The temperature at which microcracking occurred in symmetrical cross‐ply carbon‐fiber/epoxy composite materials was predicted with a yield‐stress‐based failure model. A fracture mechanics analysis of the in situ strength of the ply groups in a composite material was combined with a compound beam determination of thermal stress development to create the predictive model. This approach, unlike many other models, incorporated the change in the material properties with temperature with the room‐temperature properties of the laminate to predict the low‐temperature behavior of the ply groups. Dynamic mechanical analysis was used to assess microcracking at cryogenic temperatures through the observation of discontinuities in the material properties during failure. Four different material systems were studied, and the model accurately predicted the onset temperature for microcracking in three of the four cases. It was shown that the room‐temperature properties of a fiber‐reinforced polymeric composite laminate, appropriately modified to account for property variations at low temperatures, could be used to predict transverse microcracking as a response to thermal stresses at cryogenic temperatures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1104–1110, 2004     

玄武岩纤维增强塑料筋混凝土梁受弯破坏形态有限元分析

设计并制作了3根新型的玄武岩纤维增强塑料筋（BFRP筋）增强混凝土梁,并对其进行三分点加载试验和有限元分析。结果表明,BFRP筋混凝土梁的受弯破坏形态有别于传统的钢筋混凝土梁,其破坏截面均位于加载点附近。梁内的销栓作用对BFRP筋的受力非常不利;较大的裂缝宽度不仅会影响到BFRP筋混凝土梁的正常使用,还会影响到梁的受弯破坏形态;BFRP筋突出的表面变形特征、较低的横向抗剪强度和弹性模量等对上述破坏形态的发生有着重要影响;加载点处BFRP筋混凝土较为严重的局部黏结破坏、较大的销栓作用、应力集中效应和较大的裂缝宽度等使BFRP筋处于复杂的不利受力状态,这是造成上述破坏形态的主要原因。     

Failure behavior of resorcinol–formaldehyde latex coated aramid short‐fiber‐reinforced rubber sealing under transverse tension

Composites composed of rubber, sepiolite fiber, and resorcinol–formaldehyde latex‐coated aramid short fibers were prepared. Mechanical and morphological characterizations were carried out. To investigate the effect of interfacial debonding on the failure behavior of short‐fiber‐reinforced rubber composites, a micromechanical representative volume element model for the composites was developed. The cohesive zone model was used to analyze the interfacial failure. We found that computational results were in good agreement with the experimental results when the interfacial fracture energy was 1 J/m² and the interfacial strength was 10 MPa. A parametrical study on the interface and interphase of the composite was conducted. The results indicate that a good interfacial strength and a choice of interphase modulus between 40 and 50 MPa enhanced the ductile behavior and strength of the composite. The ductile properties of the composite also increased with increasing interfacial fracture energy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41672.     

Experimental investigation and numerical simulation of granite powder filled polymer composites for wind turbine blade: A comparative analysis

This paper describes the mechanical, thermo‐mechanical, and thermal behavior of unfilled E‐glass fiber (10–50 wt%) reinforced polymer (GFRP) composites and granite powder filled (8–24 wt%) GFRP composite in different weight percentages, respectively. The void fraction of unfilled glass epoxy composite is decreased from 7.71% to 3.17% with the increase in fiber loading from 10 to 50 wt%. However, void fraction for granite powder filled GFRP composites show reverse in trend. The granite powder addition in glass‐epoxy composites show significant improvement in hardness (37–47 Hv), impact strength (31.56–37.2 kJ/m²), and stress intensity factor (by 14.29% for crack length of 5 mm) of the composites. The thermo‐mechanical analyses also show strong correlation with the mechanical performance of the composites. The minimum difference of 0.17 GPa in storage and flexural moduli are observed for unfilled 20 wt% glass epoxy composite; whereas, maximum difference of 0.71 GPa is recorded for unfilled 50 wt% glass epoxy composite. Moreover, the numerical and experimentally measured thermal conductivity of unfilled and granite powder filled epoxy composites are within the lower and upper bound values. Hence, a successful attempt is presented for mechanical analysis of full scale model by finite element analysis. The results show that finite element analysis predicted reasonably actual stress value and tip deflection of wind turbine blade. POLYM. COMPOS., 38:1335–1352, 2017. © 2015 Society of Plastics Engineers     

Mapping of stress distribution in woven‐fabric composites

Mapping of the stress distribution in composite materials, both at the fiber/matrix interface and in the composite constituents, is important to understand the material mechanical response. Stress mapping can help predict composite behavior under certain stresses especially failure or delamination. In this work, two analytical models were proposed to map the stress distribution at fiber, matrix and fiber/matrix interface utilizing the concept of stress superposition. The first model dealt with the fiber in the longitudinal direction considering axisymmetric conditions. The second model addressed the fiber stress distribution in the transverse direction. Experimental data from four‐point flexural tests of woven fabric composites was processed using the Graphical Integrated Numerical Analysis (pcGINA) to obtain the maximum stress in the target laminate and this value was used as the input for the two analytical models. The value for the maximum interfacial shear stress was calculated using the models and results were compared to pull‐out fiber test values obtained from literature. Good agreement was observed between the model calculations and the literature data. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Stress profiles around broken fibers in unidirectional composites using influence superimposition technique

The stress transfer from broken to its unbroken adjacent neighboring fibers in unidirectional fibrous composites under a tensile loading applied in the fiber axis is analyzed using a two‐dimensional (2D) shear lag model. The numerical solutions to the governing equations is greatly simplified by the assumptions that the displacements perpendicular to the fiber direction can be ignored, and the axial displacements are uniform over the cross section of any fiber. Using an influence function superimposition technique, closed‐form analytical expressions are used to predict stress profiles in both the fiber and matrix because of any number and arbitrary array of fiber breaks in the presence of matrix shear failure. These are compared to stress concentrations predicted using the finite element analysis (FEA). It is shown that the 2D modeling presented here does generalize the governing equations to include interactions with multiple damage events. The micromechanical model is vital to develop the basic mechanics that are necessary to understand failure behavior of the composite produced by the failure of one or more of its components. POLYM. COMPOS., 2013 © 2013 Society of Plastics Engineers     

Prediction of failure and fracture mechanisms of polymeric composites using finite element analysis. Part 2: Fiber reinforced composites

A robust finite element scheme for the micro‐mechanical modeling of the behavior of fiber reinforced polymeric composites under external loads is developed. The developed model is used to simulate stress distribution throughout the composite domain and to identify the locations where maximum stress concentrations occur. This information is used as a guide to predict dominant failure and crack growth mechanisms in fiber reinforced composites. The differences between continuous fibers, which are susceptible to unidirectional transverse fracture, and short fibers have been demonstrated. To assess the validity and range of applicability of the developed scheme, numerical results obtained by the model are compared with the available experimental data and also with the values found using other methods reported in the literature. These comparisons show that the present finite element scheme can generate meaningful results in the analysis of fiber reinforced composites.     

Evaluating the mechanical performance of supercritical CO2 fabricated polymide 6,6/PMMA,fiber reinforced composites

Recent advancements in SC CO₂ mediated synthesis and material processing have led to polymer‐polymer blends and composite materials with complex morphologies, exhibiting long‐range order and orientation on multiple length‐scales from the nanometer to the centimeter scale. The material under consideration in this work is a polyamide 6,6 (nylon)/poly (methyl methacrylate) (PMMA) fiber‐reinforced composite that was fabricated in a unique SC CO₂ assisted process. The tensile and flexural properties of these unique composites are studied and the evolution of damage and energy dissipation are monitored through cyclic loading and microscopic analysis of post‐stressed composite cross sections. It is shown that this morphology leads to improved flexural modulus and increased ultimate strength with only a small decrease in tensile modulus. These composites also exhibited significant improvements in stress distribution and load transfer without the use of fiber sizing agents for fiber/matrix compatibilization.     

Mechanical properties of pineapple leaf fiber-reinforced polyester composites

Pineapple leaf fiber (PALF) which is rich in cellulose, relatively inexpensive, and abundantly available has the potential for polymer reinforcement. The present study investigated the tensile, flexural, and impact behavior of PALF-reinforced polyester composites as a function of fiber loading, fiber length, and fiber surface modification. The tensile strength and Young's modulus of the composites were found to increase with fiber content in accordance with the rule of mixtures. The elongation at break of the composites exhibits an increase by the introduction of fiber. The mechanical properties are optimum at a fiber length of 30 mm. The flexural stiffness and flexural strength of the composites with a 30% fiber weight fraction are 2.76 GPa and 80.2 MPa, respectively. The specific flexural stiffness of the composite is about 2.3 times greater than that of neat polyester resin. The work of fracture (impact strength) of the composite with 30% fiber content was found to be 24 kJ m⁻². Significant improvement in the tensile strength was observed for composites with silane A172-treated fibers. Scanning electron microscopic studies were carried out to understand the fiber-matrix adhesion, fiber breakage, and failure topography. The PALF polyester composites possess superior mechanical properties compared to other cellulose-based natural fiber composites. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1739–1748, 1997     

Concentration effect of γ‐glycidoxypropyltrimethoxysilane on the mechanical properties of glass fiber–epoxy composites

In this study, glass fibers were modified using γ‐glycidoxypropyltrimethoxysilane of different concentrations to improve the interfacial adhesion at interfaces between fibers and matrix. Effects of γ‐glycidoxypropyltrimethoxysilane on mechanical properties and fracture behavior of glass fiber/epoxy composites were investigated experimentally. Mechanical properties of the composites have been investigated by tensile tests, short beam tests, and flexural tests. The short‐beam method was used to measure the interlaminar shear strength (ILSS) of laminates. The tensile and flexural properties of composites were characterized by tensile and three‐point bending tests, respectively. The fracture surfaces of the composites were observed with a scanning electron microscope. On comparing the results obtained for the different concentrations of silane solution, it was found that the 0.5% GPS silane treatment provided the best mechanical properties. The ILSS value of heat‐cleaned glass fiber reinforced composite is enhanced by ∼59% as a result of the glass fiber treatment with 0.5% γ‐GPS. Also, an improvement of about 37% in tensile strength, about 78% in flexural strength of the composite with the 0.5% γ‐GPS treatment of glass fibers was observed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Numerical modeling of the impact response of fiber–metal laminates

This article models the impact response of fiber–metal laminates (FMLs) based on a polypropylene (PP) fiber/PP matrix composite and two types of aluminum alloy. Here, a finite element analysis is used to model the impact behavior of FMLs at velocities up to 150 m/s. The PP‐based composite was modeled as an isotropic material with a specified tensile cut‐off stress to allow for the automatic removal of failed elements. The aluminum was modeled as an elasto‐plastic material with a specified shear failure strain and a tensile failure cut‐off stress. The deformed response of the structures and the resulting failure modes were compared with the experimental data. The variation of the maximum permanent displacement versus normalized impact energy was also predicted and compared with the impact test data and good agreement was observed. Finally, the decay of the kinetic energy of the projectile with time was determined for each of the targets and used to characterize their impact resistance. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Influence of fly ash cenospheres on performance of coir fiber‐reinforced recycled high‐density polyethylene biocomposites

Recycled high‐density polyethylene (RHDPE)/coir fiber (CF)‐reinforced biocomposites were fabricated using melt blending technique in a twin‐screw extruder and the test specimens were prepared in an automatic injection molding machine. Variation in mechanical properties, crystallization behavior, water absorption, and thermal stability with the addition of fly ash cenospheres (FACS) in RHDPE/CF composites were investigated. It was observed that the tensile modulus, flexural strength, flexural modulus, and hardness properties of RHDPE increase with an increase in fiber loading from 10 to 30 wt %. Composites prepared using 30 wt % CF and 1 wt % MA‐g‐HDPE exhibited optimum mechanical performance with an increase in tensile modulus to 217%, flexural strength to 30%, flexural modulus to 97%, and hardness to 27% when compared with the RHDPE matrix. Addition of FACS results in a significant increase in the flexural modulus and hardness of the RHDPE/CF composites. Dynamic mechanical analysis tests of the RHDPE/CF/FACS biocomposites in presence of MA‐g‐HDPE revealed an increase in storage (E′) and loss (E″) modulus with reduction in damping factor (tan δ), confirming a strong influence between the fiber/FACS and MA‐g‐HDPE in the RHDPE matrix. Differential scanning calorimetry, thermogravimetric analysis thermograms also showed improved thermal properties in the composites when compared with RHDPE matrix. The main motivation of this study was to prepare a value added and low‐cost composite material with optimum properties from consumer and industrial wastes as matrix and filler. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42237.     

Research on the mechanical properties prediction of carbon/epoxy composite laminates with different void contents

The influence of the porosity on the static mechanical strength of the carbon fiber fabric reinforced epoxy composites laminates was investigated. The tensile, compressive, bending, and interlaminar strength test on the CFRP laminates with porosity of 0.33% and 1.50% were conducted and simulated by a finite element analysis model. The article proposes the failure criterion of the static mechanical strength of the fabric fiber reinforced composites based on the improved Hashin failure criterion that is suitable for the undirectional composite laminates. The basic composite strength parameters are used to evaluate the mechanical properties of CFRP laminates with different porosities. A finite element analysis model is established by using software ABAQUS™ combined with the sudden stiffness degradation model. The experiment results show that the tensile, compressive, bending, and interlaminar strength decrease with the increasing porosities. The tensile, compressive, bending, and interlaminar strength of the fabric carbon fiber reinforced epoxy composites laminates are simulated accurately by the finite element model. POLYM. COMPOS., 14–20, 2016. © 2014 Society of Plastics Engineers     

Bleached extruder chemi‐mechanical pulp fiber‐PLA composites: Comparison of mechanical,thermal, and rheological properties with those of wood flour‐PLA bio‐composites

An environmentally friendly bleached extruder chemi‐mechanical pulp fiber or wood flour was melt compounded with poly(lactic acid) (PLA) into a biocomposite and hot compression molded. The mechanical, thermal, and rheological properties were determined. The chemical composition, scanning electron microscopy, and Fourier transform infrared spectroscopy results showed that the hemicellulose in the pulp fiber raw material was almost completely removed after the pulp treatment. The mechanical tests indicated that the pulp fiber increased the tensile and flexural moduli and decreased the tensile, flexural, and impact strengths of the biocomposites. However, pulp fiber strongly reinforced the PLA matrix because the mechanical properties of pulp fiber‐PLA composites (especially the tensile and flexural strengths) were better than those of wood flour‐PLA composites. Differential scanning calorimetry analysis confirmed that both pulp fiber and wood flour accelerated the cold crystallization rate and increased the degree of crystallinity of PLA, and that this effect was greater with 40% pulp fiber. The addition of pulp fiber and wood flour modified the rheological behavior because the composite viscosity increased in the presence of fibers and decreased as the test frequency increased. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44241.     

纤维缠绕复合材料压力容器CAD/CAE/CAM一体化研究

本文用APDL参数设计语言编制的程序可同时进行压力容器缠绕过程的动态仿真模拟及应力分析,可将实际缠绕参数直接用于应力分析,分析后得到的仿真数据可直接用于数控缠绕机进行生产,实现了纤维缠绕复合材料压力容器CAD/CAE/CAM一体化.本文用微分几何理论推导出纤维缠绕复合材料压力容器的非测地线缠绕轨迹、包角方程及绕丝头运动方程.在应力分析过程中考虑了几何非线性和物理非线性.采用叠层的增量本构关系,以分段线性表示单层非线性应力-应变曲线,对损伤后引起的刚度降低进行了实验研究,实验特别研究了面内剪切破坏和层间剪切破坏对纵向弯曲刚度的影响.结果表明纤维缠绕复合材料压力容器损伤后,弯曲刚度的降低是影响轴向变形的重要因素.     

碳化硅纤维热处理对单向碳化硅纤维增强磷酸铝基复合材料性能的影响

用不同条件热处理的碳化硅纤维制备了单向连续碳化硅纤维增强磷酸铝基复合材料.研究了碳化硅纤维热处理的温度、时间及热处理方法对制成的复合材料性能的影响.测试了复合材料的断裂强度,相对介电常数和介电损耗.通过扫描电镜分析复合材料的微观形貌,并使用电子探针对碳化硅纤维/磷酸铝基体界面进行了微区元素分析.结果表明:碳化硅纤维热处理降低了复合材料的介电常数和介电损耗;纤维/基体界面之间未发生任何化学反应.由于热处理使纤维/基体形成了强结合界面,大大降低了复合材料的力学性能.快速热处理方式直接降低纤维的自身强度.