Significance of cyclic loading parameters on the flexural response of the GFRP composites

Automotive design calls for weight reduction, considering fuel consumption and vehicle dynamics as well. Application of composite materials for suspensions and other structural members is in that direction. Owing to their high specific strength and inherent structural damping qualities, composites can be an alternative to metallic materials, especially with the suspension-springs. Further, epoxy composites can resist environmental influences, facilitating easier maintenance. In this study, we assessed the flexure response of GFRP composite exposed to pre flexure cyclic loading. This was to simulate the loading environment of an automobile leaf spring. Experiments were conducted with Taguchi’s DOE using L9 orthogonal array with two factors and three levels. The test specimens were prepared by hand lay-up technique with four layers of (0/0/0/0, 0/30/60/0, 0/90/90/0 and 0/45/0/-45) orientation. Constant peak amplitude cyclic loading was imposed on the specimen by an eccentric disc in a radial drilling machine. The flexural modulus of the cyclic loaded specimen was obtained by three point bend test as per ASTM D790. Assessment of the test results by ANOVA, S/N ratio and regression analysis indicated that the flexural modulus of the pre flexural cyclic loaded composite is significantly influenced by the loading parameters (loading cycle and frequency), and the flexural modulus can be enhanced with reduced fiber orientation interactions within the lay-up at critical operating conditions. The damage pattern influenced by fibre orientation in the lay-up sequence is ascertained by SEM images.

     

Effect of E-Glass fibre and ply orientation on the mechanical behaviour of FRP composites used for pressure pipe

The main goals of this experimental investigation were to compare the mechanical behaviour of resins reinforced with different woven fabrics (bidirectional and quadriaxial rovings), manufactured with the classical hand lay-up process, and to find the more appropriate industrial pressure pipe. In order to realize such applications, several mechanical properties need to be evaluated. So, a focus was essentially done on the evaluation of the effect of resin and E-Glass fibre ply orientation on the mechanical properties such as tensile strength and flexural strength of the studied composite laminates. An experimental failure analysis was carried out to observe the crack paths and failure mechanisms in the investigated laminate composites. From the main results, it was found that the composites based on R500 fabrics show the best behaviour in tensile while the laminates based on RM fabrics present the best flexural properties. The quadriaxial composite laminates (QA/VE and QA/UP) with stacking sequences of [0°, +45°, 90°, ?45°] present a very ductile tensile behaviour and the highest interlaminar fracture resistance. Consequently, they can be more appropriate for the industrial pressure pipe.     

Experimental investigations of damage analysis in drilling of woven glass fiber-reinforced plastic composites

This paper presented a new comprehensive approach to select cutting parameters for damage factor in drilling of glass fiber-reinforced polymer (GFRP) composite material. The influence of drilling on surface quality of woven GFRP plastic composite material was investigated experimentally. Drilling tests were carried out using carbide drills of 8 mm in diameter at 50, 70, and 90 m/min cutting speeds and at 0.06, 0.12, and 0.18 mm/rev feed rates. Damage factor was investigated based on hole entrance and exit. Analysis of variance (ANOVA) test was applied to the experimental results. The compared values were employed by Duncan test to identify which groups were significantly different from other groups.     

应力波载荷作用下CFRP、GFRP层板动态拉伸性能的实验研究

介绍了Hopkinson杆冲击拉伸实验设备以及实验技术,推导了应力、应变的计算公式。利用Hopkinson杆加载装置对CFRP、GFRP层合板进行了冲击拉伸实验研究,得到不同应变率下CFRP、GFRP层板的应力、应变(бε)曲线,以及断裂强度、拉伸模量、断裂应变等力学参数,以期对复合材料层板在冲击拉伸情况下动态力学行为和变形、破坏机理有一个初步的认识。     

Fatigue damage of quasi-isotropic composite laminates under tensile loading in different directions

The purpose of this work is to investigate fatigue damage of quasi-isotropic laminates under tensile loading in different directions. Low cycle fatigue tests of [0/−60/60]_s laminates and [30/−30/90]_s laminates were carried out. Material systems used are AS4/Epoxy and AS4/PEEK. The fatigue damage of [30/−30/90]_s is very different from that of [0/−60/60]_s. The experimental results are compared with the result obtained from the method for determining strain energy release rate components proposed by the authors. The analytical results were in good agreement with the experimental results. It is proved that the failure criterion based on the strain energy release rate is an appropriate approach to predict the initiation and growth of delaminations under cyclic loading.     

Drilling-induced damage in uni-directional glass fiber reinforced plastic (UD-GFRP) composite laminates

Uni-directional glass fiber reinforced plastic (UD-FRP) composite materials are a feasible alternative to structural members that bear loads in only one direction. FRP composite materials have excellent properties in the direction of the fibers. Drilling- induced damage acts as an inhibitor to their application, as the holes act as stress concentration sites for failure under loading. The present study is an attempt to study the influence of drilling-induced damage on the residual tensile strength of uni-directional composite laminates and to propose a mathematical model correlating the residual strength with the drilling parameters. A finite element model (FEM) is also developed to study the drilling-induced damage in composite laminates.     

Effect of ply lay-up and curing pressure on void content in GFRP laminates of unsaturated polyester resin-reinforced woven E-glass fibers

This paper describes a laminate curing process by hand lay-up of plain-weave woven Glass fiber-reinforced polymer (GFRP) composite composed of unsaturated polyester resin reinforced with E-glass fiber fabric, EWR-600B. Symmetrical and non-symmetrical ply orientation arrangements were introduced with respect to different curing pressures to produce consistent composite panels according to the British standard code: BS 1268 (2001) for evaluations of void content and physical properties. Quantitative analysis of volume and weight fractions and void volume content were investigated according to the ASTM code: D 2734. Woven GFRP composites fabricated under different curing pressures of 351.2 (35.8 kg/m²), 687.7 (70.1 kg/m²), 1020.2 (104 kg/m²) and 1355.7 Pa (138.2 kg/m²) showed minimal significant effect on volume and weight fractions of symmetrical and non-symmetrical ply lay-up arrangement, whereas 4 % void content still fulfilled the limit of medium quality composite.     

基于HyperWorks 的不同铺层方式复合材料剪切强度有限元分析

剪切强度和剪切韧性是反映复合材料构件在复合受力状态下承载能力及耗能能力的重要指标,不同铺层方式的单向玻璃纤维与短切玻璃纤维混杂增强复合材料层合板的层间剪切性能有明显差异。文中基于HyperWorks 商用有限元软件建立了精确的复合材料层合板模型,通过数值模拟分析不同铺层方式复合材料层合板的层间剪切性能。研究结果表明,铺层材料对复合材料层合板的层间剪切性能影响较大,而铺层顺序对复合材料层合板的层间剪切性能影响较小。     

Effect of prestress level on the strength of CFRP composite laminate

The effect of fiber prestressing has been investigated on the tensile strength, modulus strength, flexural properties and residual stresses of Carbon fiber reinforced polymer (CFRP) composites. Unidirectional carbon fiber in an epoxy resin has been examined under different prestressing levels (0, 5, 10, 15, 20, 30, 45, 60, 80 MPa) at ambient temperature and 50 % fiber volume fraction. A new method was implemented to produce the prestressed laminates for several standard tests. The results showed that prestressing on 3-ply unidirectional carbon fibers improved the fiber tensile strength to 99 % and the tensile modulus to 31 %. Similarly on 8-ply unidirectional carbon fibers has improved the fiber flexural strength to 63 % and flexural modulus to 81 %. A new technique was used to measure the residual stresses and tensile modulus of the composite laminate by recording the final extension and the remaining load directly after the curing process and releasing the applied load.

     

Mechanical properties of bio-absorbable PLA/PGA fiber-reinforced composites

This study investigated important mechanical properties, the flexural strength and flexural modulus, of polyglycolic acid (PGA) fiber-reinforced polylactic acid (PLA) composites fabricated by melt-mixing. The flexural strength and flexural modulus were estimated using three-point bending tests conducted at 37°C. Both the flexural strength and flexural modulus were increased by PGA fiber reinforcement. Viscoelastic properties were also investigated using dynamic mechanical analysis (DMA) under tensile loading. Results show that PGA fiber, which acts as the nucleate agent of PLA, restrains the molecular chains of PLA. That restraint reduces deformation at the same stress condition, thereby improving the PLA flexural properties.     

Evaluation of a novel approach to a delamination factor after drilling composite laminates using a core–saw drill

Drilling is the most commonly applied method for hole making of fiber-reinforced materials owing to the need for structure joining. Delamination is the most common defect during drilling because of the heterogeneity of both the fibers and the matrix. The delamination, in general, is an irregular shape and size, containing long and fine breaks and cracks at the exit of the drilled hole, especially in the drilling of carbon-fiber-reinforced plastic (CFRP). On the other hand, a core–saw drill is designed to reduce the threat of chip removal in drilling composite materials. Since the thrust force of core–saw drill is distributed toward the periphery, the core–saw drill allows a larger critical thrust force than the twist drill at the onset of delamination when drilling composite materials. The aim of this paper is to present a novel approach of the equivalent delamination factor (F _ed) to characterize drilling-induced delamination using a core–saw drill and compare it with the adjusted delamination factor (F _da) and the conventional delamination factor (F _a). The experimental results indicated that the F _ed obtained is considered suitable for characterizing delamination at the exit of a hole after drilling CFRP.     

MODELING AND OPTIMIZATION OF PROCESS PARAMETERS FOR DELAMINATION IN DRILLING GLASS FIBER REINFORCED PLASTIC (GFRP) COMPOSITES

Glass fiber-reinforced composite materials are used in varieties of applications due to their excellent properties. Drilling is an indispensable process for this kind of materials. Delamination due to drilling is an important concern and is to be reduced. In the present work, drilling tests were carried out on computer numeric control (CNC) drilling machine. The parameters considered for the drilling investigations were spindle speed, feed rate and diameter of the drill bits. Multiple regression analysis is used for the modeling of process parameters in drilling of GFRP composites. Taguchi's S/N ratio analysis and desirability-based approach are used for the optimization of process parameters for studying the delamination in drilling of GFRP composites. The results revealed that the factor feed rate and drill diameter are the most influential parameters which affects the delamination in drilling of GFRP composites. The interaction between the parameters also affects the delamination in drilling of GFRP composites.     

Effect of surface treatment on mechanical properties of glass fiber/stainless steel wire mesh reinforced epoxy hybrid composites

This paper investigates the effect of surface treatment for glass fiber, stainless steel wire mesh on tensile, flexural, inter-laminar shear and impact properties of glass fiber/stainless steel wire mesh reinforced epoxy hybrid composites. The glass fiber fabric is surface treated either by 1 N solution of sulfuric acid or 1 N solution of sodium hydroxide. The stainless steel wire mesh is also surface treated by either electro dissolution or sand blasting. The hybrid composites are fabricated using epoxy resin reinforced with glass fiber and fine stainless steel wire mesh by hand lay-up technique at room temperature. The hybrid composite consisting of acid treated glass fiber and sand blasted stainless steel wire mesh exhibits a good combination of tensile, flexural, inter-laminar shear and impact behavior in comparison with the composites made without any surface treatment. The fine morphological modifications made on the surface of the glass fiber and stainless steel wire mesh enhances the bonding between the resin and reinforcement which inturn improved the tensile, flexural, inter- laminar shear and impact properties.     

Ultimate strength of composite laminates with free-edge delamination

The present paper deals with the free edge effect of composite laminates by using a generalized quasi-three dimensional analysis and experimental verification of an analysis performed for laminates with Teflon inserted on interfaces to simulate initial free-edge delamination. We performed tensile tests for laminates [30₂/?30₂/90]_s carbon-epoxy laminates with free-edge delamination under uniaxial tension. The experiment reveals that extensional stiffness of the laminate decreases by the initiation of the delamination, and that strength of the laminate without delamination is smaller than that of the laminates with delamination. Generalized quasi-three dimensional finite element technique, which employs energy release rate and maximum stress criteria, is developed to estimate behavior of the laminate after initial delamination. The numerical result by use of this technique predicts the ultimate strength of the laminates with sufficient accuracy according as the comparison with an experimental stress-strain curve. In the experiment conducted both for the laminate with initial delamination and the laminate without initial delamination, an unexpected results were obtained that is the ultimate load of the laminate without initial delamination was lower than that of the laminate with initial delamination. We presented clear explanation on the phenomenon occurred and developed the method to predict the nonlinear behavior of the laminate with or without initial delamination.     

损伤复合材料层板胶接修理的优化设计

针对复合材料单面胶接修理结构建立力学分析模型,并通过试验验证模型的可靠性.利用该模型分析补片参数对胶接修理效果的影响,得到优化设计的补片参数.计算分析和验证试验均表明,补片直径为孔径的2～3倍、厚度为孔深的45%～60%、铺排和母板一致时,修理结构的强度恢复能达到最大值.     

基于三维CDM的复合材料开口层合板失效分析

建立了复合材料层合板三维连续介质损伤力学模型,并将该模型应用于复合材料开口层合板的损伤破坏分析中。与相关试验中开口层合板强度和损伤破坏情况对比分析表明:本文模型能够有效地模拟开口层合板从初始损伤到完全破坏的全过程,具有较高的计算精度和良好的数值模拟收敛性。基于该模型,详细分析了在单向拉伸载荷作用下开口层合板不同铺层的损伤破坏情况。     

Investigation of the effect of temperature and layup on the press forming of polyvinyl chloride-based composite laminates and fiber metal laminates

Semi-crystalline thermoplastic-based composite laminates and fiber metal laminates have a narrow forming temperature window, which limits formability of these products. The intention of this study was investigation of non-melting amorphous polyvinyl chloride as a proper matrix to increase the formability and forming temperature window of these products. For this, [45/?45] and [0/90] layups of polyvinyl chloride-based composite laminates and fiber metal laminates were produced using the film-stacking procedure and later press formed into channel sections at six temperatures in the range of 80 to 200 °C. The effects of the layups and forming temperatures on the forming loads and spring back of the formed profiles were measured, and their effects on the fiber buckling, wrinkling, and delamination of the profiles were evaluated using optical microscope images. The effects of layups and forming temperatures on the deformation mechanisms were also analyzed using the grid strain analysis method. Of the fiber metal laminates, 160 °C was found as the minimum forming temperature, and for the composite laminates, 120 and 160 °C were found as the minimum proper forming temperatures of [45/?45] and [0/90] layups, respectively. Finally, the forming temperature windows and formability of polyvinyl chloride matrix composite laminates and fiber metal laminates were found higher than semi-crystalline matrices.     

Mechanical characterization of jute-basalt hybrid composites with graphene as nanofiller

Natural fibre composites, due to their biodegradable and eco friendly nature, are being explored for potential application in wide areas. But their strengths need to be enhanced. Hybridization of the natural fibres with incorporation of nanofillers helps to tailor the properties of nanofillers, and individual fibers and enhance the properties of resultant composite. The present work aims to explore the mechanical propertis of jute-basalt hybrid composites by incorporating graphene nanofillers of varying concentrations. Basalt, jute and jute-basalt hybrid composites with varying concentrations of graphene (0 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 1 wt%) are prepared. Effect of hybridization of different fibers and influence of graphene on mechanical properties are analyzed. The effect of nature of top and bottom laminates on mechanical properties is also observed. Maximum improvement in tensile strength, flexural strength and hardness is found to be 13 %, 29 % and 55 %, respectively, with hybrid composite containing 1 wt.% graphene compared to hybrid composite without graphene. Impact strength is found to be highest for hybrid composite containing 0.4 wt.% graphene with 17 % increase compared to hybrid composite without graphene.

     

玻璃纤维筋断裂强度的理论和实验研究

玻璃纤维筋(glass fiber reinforced polymer rebar,GFRP筋)是一种具有较好的抗拉、耐腐蚀和抗电、磁等性能的纤维复合材料,在特殊环境下可以用来代替普通钢筋.文中通过自行设计的实验装置,测试GFRP筋的破坏强度和弹性模量,并利用载荷距离加权局部分配法则和破坏柱元的概念,用统计破坏理论分析计算纤维筋棒的断裂强度,与试验结果对比基本一致.     

Machinability of Kevlar® 49 Composite Laminates While Using Standard TiN Coated HSS Drills

This article addresses the machinability of plain weave Kevlar® 49 prepeg composite laminates of different thickness while using 135° split-point TiN coated 6 mm diameter HSS drills. The effect of composite preparation parameters and the drilling conditions on the machinability of the laminates is assessed using the drilling thrust force, cutting torque, and specific cutting energy. The thickness and processing time of the laminates as well as the drilling process parameters were found to influence the maximum value of thrust force and torque as well as the quality of drilled holes. The wear features of the drills used in machining Kevlar composites have been found to be different from the conventional wear patterns that occur during drilling metals and alloys.