Adhesive wear and frictional performance of bamboo fibres reinforced epoxy composite

The aim of the present work is to investigate the adhesive wear and frictional performance of BMBFRE composite. Adhesive wear performance of BMBFRE composite was found to be superior for AP-O. The frictional performance of BMBFRE composite was found to be greater at low sliding velocity for AP-O by 44% relative to the high sliding velocity. The temperature differential of BMBFRE composite for AP-O to the sliding direction gave lower interface temperatures of about 31.4% and 13.2% as compared to R-O and P-O. The predominant wear mechanisms for AP-O was back film transfer associated with the formation of fine grooves on the worn surfaces.     

Investigations on the influence of graphite filler on dry sliding wear and abrasive wear behaviour of carbon fabric reinforced epoxy composites

In this experimental study, the dry sliding wear and two-body abrasive wear behaviour of graphite filled carbon fabric reinforced epoxy composites were investigated. Carbon fabric reinforced epoxy composite was used as a reference material. Sliding wear experiments were conducted using a pin-on-disc wear tester under dry contact condition. Mass loss was determined as a function of sliding velocity for loads of 25, 50, 75, and 100 N at a constant sliding distance of 6000 m. Two-body abrasive wear experiments were performed under multi-pass condition using silicon carbide (SiC) of 150 and 320 grit abrasive papers. The effects of abrading distance and different loads have been studied. Abrasive wear volume and specific wear rate as a function of applied normal load and abrading distance were also determined.The results show that in dry sliding wear situations, for increased load and sliding velocity, higher wear loss was recorded. The excellent wear characteristics were obtained with carbon-epoxy containing graphite as filler. Especially, 10 wt.% of graphite in carbon-epoxy gave a low wear rate. A graphite surface film formed on the counterface was confirmed to be effective in improving the wear characteristics of graphite filled carbon-epoxy composites. In case of two-body abrasive wear, the wear volume increases with increasing load/abrading distance. Experimental results showed the type of counterface (hardened steel disc and SiC paper) material greatly influences the wear behaviour of the composites. Wear mechanisms of the composites were investigated using scanning electron microscopy. Wear of carbon-epoxy composite was found to be mainly due to a microcracking and fiber fracture mechanisms. It was found that the microcracking mechanism had been caused by progressive surface damage. Further, it was also noticed that carbon-epoxy composite wear is reduced to a greater extent by addition of the graphite filler, in which wear was dominated by microplowing/microcutting mechanisms instead of microcracking.     

Kevlar-129纤维复合材料的弹道侵彻数值仿真

基于 AUTODYN有限元软件,研究了Kevlar-129纤维增强复合材料的抗侵彻性能。通过质量为10 g的 FSP破片对厚度为8、10、12、14、16以及18 mm 的六组 Kevlar 纤维靶板进行撞击模拟,获得了 FSP破片贯穿6组靶板的弹道极限,并分析了靶板的弹道极限、比吸收能随板厚的变化关系。结果表明,在板厚8-18 mm范围内,Kevlar纤维靶板的弹道极限随板厚的增加呈线性增长;在此范围内,靶板的比吸收能也呈近似线性增长,但在板厚为10-16 mm时,增长稍缓。对比还发现,比吸收能随板厚的变化规律与靶板面密度的变化规律几乎相同,二者都可用于描述Kevlar-129纤维复合材料靶板在 FSP 破片碰撞下比吸收能的变化。     

Estimation of residual strength of components of composite constructions after low-speed impact

A methodology of computing the damageability of composite materials at low-speed impact is suggested. The methodology is based on applying a fracture criterion of the monolayer and following computation of material damageability taking the interaction of different damage evolution mechanisms into account. This approach allows us to obtain the distribution of damageability parameters in the surface of the monolayer and the width of material at an arbitrary moment of time until complete destruction of the construction component, computing the degradation of elastic properties, and the position and sizes of delamination regions after the impact. Applying this methodology for estimating residual strength permits the avoidance of excessive conservatism of the projected strength of construction components from composite materials which have incurred impact damage.     

Experimental investigations of surface roughness in orthogonal turning of unidirectional glass-fiber reinforced plastic composites

Cutting parameters and the resulting cutting forces have a great effect on the machinability of materials during the turning process. The effects of cutting parameters on machinability have been examined by many researchers and studies on determination of suitable cutting conditions for various materials are still under investigation. In this study, surface roughness of unidirectional glass-fiber reinforced plastic composite was examined on the basis of cutting parameters such as depth of cut, feed rate, tool geometry, and cutting speed. The surface quality was found to relate closely to the feed rate, cutting speed, and cutting tool.     

碳纤维复合材料数控加工研究

碳纤维复合材料是一种大量应用于航天航空领域的具有优良综合性能的难加工材料.在概要介绍其基本特性、切削机理的基础上,对用于碳纤维复合材料的切削刀具特征及切削参数作了初步研究,并给出了切削试验数据和应用实例.     

The filler content of the dental composite resins and their influence on different properties

The purpose of this study was to compare the inorganic content and morphology of one nanofilled and one nanohybrid composite with one universal microhybrid composite. The Vickers hardness, degree of conversion and scanning electron microscope of the materials light‐cured using LED unit were also investigated. One nanofilled (Filtek? Supreme XT), one nanohybrid (TPH®₃) and one universal microhybrid (Filtek? Z‐250) composite resins at color A₂ were used in this study. The samples were made in a metallic mould (4 mm in diameter and 2 mm in thickness). Their filler weight content was measured by thermogravimetric analysis (TG). The morphology of the filler particles was determined using scanning electron microscope equipped with a field emission gun (SEM‐FEG). Vickers hardness and degree of conversion using FT‐IR spectroscopy were measured. Filtek? Z‐250 (microhybrid) composite resin shows higher degree of conversion and hardness than those of Filtek? Supreme XT (nanofilled) and TPH®₃ (nanohybrid) composites, respectively. The TPH₃® (nanohybrid) composite exhibits by far the lowest mechanical property. Nanofilled composite resins show mechanical properties at least as good as those of universal hybrids and could thus be used for the same clinical indications as well as for anterior restorations due to their high aesthetic properties. Microsc. Res. Tech. 75:758–765, 2012. © 2011 Wiley Periodicals, Inc     

Manufacture of reinforced antifrictional epoxy fluoroplastics by winding

A method of manufacturing frictional components from antifrictional polymer composites is investigated. The conditions of structure formation corresponding to good physicomechanical and tribological properties are determined.     

Impact damages and residual bending strength of CFRP composite laminates subjected to impact loading

The purpose of this study is to confirm the decreasing in residual bending strength, and the failure mechanisms experimentally when CFRP composite laminates are subjected to foreign object damage (FOD). Composite laminates used in this test are CFRP orthotropic laminated plates, which are stacked with two-interfaces [0^o ₆/90^o ₆] _sym and four-interfaces [0^o ₃/90^o ₆/0^o ₃] _sym . When the specimen was subjected to transverse impact by a steel ball, the delamination area generated by the impact damage was observed by using the SAM (scanning acoustic microscope). Also, the fracture surfaces obtained by three-point bending test were observed by using the SEM (scanning electron microscope). Further, failure mechanisms were investigated based on the observed delamination areas and fracture surfaces.     

Estimating the effect of misorientation of fibers on stiffness and strength of profiled composite elements

The paper aims to justify the methods for calculating the composite details with curvilinear trajectories of fiber stacking. The novelty of the approach is defined by the fact that following the traditional techniques of stacking the fabrics or prepregs, the mechanics of composites considers quasihomogeneous materials formed by rectilinear families of fibers. The field of application of the developed approaches is related to the prospect of creating profiled composite structural elements using the principles of biomechanical strength [1].     

Wear behaviour of carbon nanotube reinforced epoxy resin composites

This paper deals with the effect of a multi-walled carbon nanotube (MWCNT) reinforcement on the wear behaviour of Epoxy (EP) composites. Firstly, various dispersion methods were compared. Secondly, the optimum CNT amount was evaluated. In a third step, dry lubricants were added to the optimised EP/CNT composite. Finally, the influence of the steel counterpart (martensitic bearing steel 100Cr6 and austenitic stainless steel X5CrNi18-10) was studied. The preparation method was found to have a decisive effect on the wear behaviour of the composite. A pre-treatment of the CNTs in concentrated nitric acid proved beneficial. Even more important was the mixing method. A dual asymmetric centrifuge delivered so good wear results that the pre-treatment could be skipped. The optimum CNT content was at about 1 wt%, regardless of the preparation method. The lowest wear rates were found after addition of 10 wt% graphite. MoS₂ proved to be less effective and Polytetrafluorethylene (PTFE) even increased the wear. The wear rates against the unalloyed martensitic steel were far higher than against austenitic stainless steel.     

典型复合材料加筋壁板优化设计

针对复合材料加筋壁板的稳定性优化问题提出了一种用混合罚函数法、Powell法、黄金分割法、改进的坐标轮换法和遗传算法相结合的混合优化算法.并通过优化程序实现了以加筋板的屈曲载荷最大为目标的优化设计,最后通过算例验证了优化方法的有效性,同时对优化结果进行了深入地分析.得到的结论对加筋板的设计有一定的指导意义.     

Post-buckling behavior of carbon fiber epoxy composite plates

In this study, the pre-buckling and post-buckling behaviors of layered composite plates which were made of woven carbon fiber fabric with a circular hole in the middle were investigated experimentally and numerically. Firstly, load-displacement graphs of composite plates with different hole diameters were experimentally obtained under compressive load. Then the numerical load-displacement graphs of the plates were found with the ANSYS package program which used the finite element method. As a result, after linear buckling experimental and numerical results were found to be compatible with each other. In addition, damage behavior of plates after buckling with the aid of Tsai-Wu damage criterion was obtained similar to experimental results. The increase in hole diameter did not change the load-displacement behavior characteristics of the plates after buckling. However, it has reduced maximum damage load and maximum failure displacement. The stress at the perimeter of the hole increased significantly with the increase of the vertical displacement with immediately after the buckling but later was not significantly affected by this increase.

     

Tribological behaviour of glass fibre bundles reinforced epoxy gradient composites

Abstract

The short fibre bundles separated from the machining waste of a printed circuit board manufacturing plant were used in preparing functionally graded composites using polysulphide modified epoxy resin. Glass fibre bundles were thouroughly mixed with epoxy, which is getting polymerised with time and centrifugal force was applied to achieve graded dispersion of glass fibre bundles. The centrifugation time was varied to obtain different gradient profiles. Optical microstructures confirmed the graded dispersion of glass fibres bundles in the epoxy matrix. Increase in distance towards the centrifugation force direction increases the glass fibre concentration. Gradient characteristics in the composite have been observed in wear and friction measurements, which were conducted using a pin-on-disc machine. Worn surfaces of samples were analysed with the help of SEM. Both sliding (adhesive) and abrasive wear rates of glass fibre reinforced epoxy gradient composites reduced with increasing centrifugation time. Reduction in wear rate in glass fibre epoxy gradient composites has been attributed to the better interface bonding between epoxy coated fibre bundles and the epoxy matrix and hardening property of glass fibre. It has been found that capability to sustain pressure limit increased from 0·59 to 0·79 MPa on centrifuging the sample upto 2 min and reached to 1·19 MPa with increasing the centrifugation time to 30 min.     

The erosion of carbon fibre reinforced plastic by repeated liquid impact

The erosion of unidirectional carbon fibre reinforced plastic by repeated impact with a liquid jet, has been studied at velocities of up to 90 m/s. The long fibre axis was in the plane of impact. The resistance to erosion is better for type 2 fibre composites than for type 1, but in absolute terms not particularly high; it is virtually independent of fibre volume loading and decreases very rapidly with increasing impact velocity. A certain number of impacts is needed before damage is observed. Then individual fibres are cracked and removed from the surface, and pits develop. It is suggested that failure is started by transverse compression fatigue of the fibres. The performance of composites in which the fibres are end-on to the water jet is better.     

Some observations on the interlaminar strength of composite laminates

Definition of the influence of interlaminar stresses on the failure characteristics of composite laminates may require the development of novel experimental characterization procedures. The so-called free edge problem in laminate elasticity offers a cnovenient mechanism to accomplish this purpose because of the high interlaminar stresses in the neighbourhood of a free boundary. The detailed design of a laminate specimen which can exhibit catastrophic delamination induced by interlaminar tension is presented, along with a preliminary failure hypothesis to characterize this mode of rupture and the associated experimental demonstration of the phenomena.     

A study on low-velocity impact damage of Z-pin reinforced laminates

Based on a low-velocity impact test, four main modes of low-velocity impact damage, including matrix cracking, delaminating, fiber failure and matrix crushing, are taken into account. By using the proper failure criterion, the lowvelocity impact damage of z-pin reinforced laminates can be realized. The results of FEM simulation, which indicate that a z-pin makes the area of delamination reduced by approximately 50%, are in good agreement with the experimental C-scan results.     

Tribological behaviors of graphite/epoxy two-phase composite coatings

To obtain a composite coating possessing both good conductivity and high wear resistance, a series of coatings with conductive graphite and epoxy resin were designed. The seepage critical value (SCV) of conductive coatings was used to identify the transformation between continuous phase and dispersed phase for graphite/epoxy composite coatings. Before SCV, the coatings were insulated with epoxy resin as continuous phase and the wear behavior was primarily characterized of adhesive wear with local adhesive spalling of epoxy resin. After SCV, the coatings appeared conductivity and the surface resistance decreased monotonically with the increase of graphite content. Both the curves of friction coefficient vs. graphite content and wear rate vs. graphite content showed the same model with two valleys at graphite content of 30% and 50%, respectively. At graphite content of 50%, an optimal solid lubricant film was obtained which leaded to the lowest friction coefficient and wear rate, due to a possible dynamic equilibrium between the transfer and spalling of debris. The tribological behaviors of these coatings were evaluated using a ring-on-block tribo-tester under dry sliding friction.     

复合材料飞机结构的低速冲击损伤特性影响因素研究

阐述了复合材料结构低速冲击试验方案及步骤并进行了试验;介绍了低速冲击损伤特征,对损伤特性的影响因素包括冲头直径、冲击位置、铺层厚度等进行了分析,给出了相关曲线;总结了各参数对损伤特性的影响规律,为进一步研究复合材料结构冲击阻抗提供了参考.研究结果表明:相同冲击能量下,钝头冲击产生较小的凹坑,但分层面积较大;凹坑深度、损伤面积均随着冲击能量的增加而增加;与凹坑深度相比,损伤面积分散性较大;筋条间冲击损伤面积最小,缘条边缘冲击损伤面积最大;层压板越厚,损伤阻抗越大.