基于应变损伤模型的复合材料层合板低速冲击数值模拟

提出了一种基于应变的复合材料损伤模型,考虑了复合材料冲击过程中出现的面内纤维断裂与压缩,基体开裂与挤裂。在使用Abaqus软件进行数值模拟计算时,自编的用户子程序VUMAT和Cohe-sive模型分别实现了复合材料面板的损伤和层间分层。通过对层合板在不同能量下的低速冲击的有限元模拟发现,模拟得到的分层损伤形状和面积、冲头最大挠度、接触力和凹坑深度都与试验结果吻合较好。     

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.     

不同铺层转角T700/E44 复合材料拉伸强度有限元分析

碳纤维复合材料的失效行为与复合材料内部的应力状态有关,不同铺层转角的单向碳纤维复合材料层合板的性能具有明显差异。文中利用HyperWorks 商用有限元软件建立了T700/E44 复合材料层合板拉伸模型,基于Chang-Chang 复合材料失效模型对不同铺层转角复合材料层合板的 X 向及 Y 向拉伸性能进行了数值模拟分析。研究结果表明,复合材料层合板以45° 铺层转角对称结构层合时,复合材料有着最佳的综合拉伸性能。这对高性能雷达中复合材料部件的铺层结构设计具有重要的指导意义。     

复合材料含损伤结构剩余强度分析

考虑层压结构受冲击后的“花生壳形”分层及分层损伤引起的局部不对称性和耦合效应,并考虑压缩加载过程中可能出现的多层分级屈曲,发展一种计算低能冲击层压板受压剩余强度计算方法。数值分析表明本文的预测结果与试验结果吻合良好。     

利用超声成像分析不同复合材料层压结构冲击损伤行为

复合材料各向异性和吸能的特点,在受到外来冲击作用时容易产生损伤,呈现表里迥然不同的损伤行为和分布规律。为研究不同复合材料层压结构的冲击损伤行为,设计制备树脂传递模型工艺(Resin transfer molding, RTM)缝合和预浸料复合材料层压结构两种不同成型工艺的试样,通过冲击试验模拟复合材料在外力作用下产生的冲击损伤,采用超声反射法,通过点聚焦换能器对试样进行超声B扫描成像,揭示两种复合材料层压结构试样内部断面损伤行为及其扩展规律。试验结果表明,冲击引起的试样内部损伤比表面损伤要大得多;随着冲击能量在试样内部传递,会在不同深度铺层产生新的损伤,而且损伤分布并不仅沿层间界面扩展;冲击点附近和远离冲击点附近的内部损伤具有明显不同的分布规律;RTM缝编与预浸料复合材料结构呈现明显不同的损伤行为,其中RTM缝合复合材料结构中的纵向缝线,对冲击损伤在试样内部沿层间的扩展有显然的阻止作用。研究结果对更好地理解复合材料的损伤行为、寻找新的改进复合材料层压结构损伤行为的机制有非常重要的指导意义和帮助。     

Impact behaviour of GFRP and Kevlar/epoxy sandwich composite plate: Experimental and FE analyses

In this paper, dynamic response of GFRP composite plate under ballistic impact has been studied by experimental tests and also by an efficient FE model. Material characterization of GFRP composite is performed as required for progressive damage analysis of laminate due to impact. Shock effect of impact is considered in the material modeling of composite plate. The influence of the target thickness on the ballistic performance of the composite plate is also studied by considering 3.12, 6.24 and 9.36 mm thick targets. Moreover, sandwich composite plate consisting of GFRP and Kevlar/epoxy in three different combinations of laminate layers is considered to obtain suitable combination for structural application that offer better penetration resistance. Damage pattern, contact force histories and stresses in composite plate are studied in addition to residual velocity and acceleration of projectile. Numerical results from present FE model in terms of residual velocities and damage patterns in composite plate show good agreement with the experimental results.

     

纤维金属层板铆接剩余强度影响因素研究

为研究单搭铆接接头中纤维金属层板耦合损伤行为,运用金属硬化Johnson-Cook失效准则、纤维增强复合材料三维Hashin损伤准则、脱层B-K失效理论以及刚度退化失效准则建立了纤维金属层板铆接渐进失效模型,并结合实验验证了模型的合理性。考察了单搭铆接二次弯曲效应、层板铝合金体积分数、预紧力、层板孔边距对纤维金属层板铆接强度和失效模式的影响,为提高纤维金属层板铆接剩余强度提供可靠建议。分析结果表明：二次弯曲效应加速损伤发生,从而降低层板铆接强度,其中偏心加载可以削弱二次弯曲效应,更好地提高铆接强度;层板铝合金体积分数的增大能够提高层板铆接强度,但当体积分数大于50%时层板铆接比刚度和比强度反而下降;预紧力的增加能够提高层板铆接强度和增强层板损伤抗力;随着孔边距的递增,铆接剩余强度有所提高,破坏模式由灾难性拉断失效模式逐渐转化为理想的挤压失效模式,但当孔边距达到一定数值时,铆接强度不再明显提高,而失效模式也维持为挤压破坏。     

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.     

层间增韧复合材料在静压痕力下的损伤阻抗和渐进损伤分析

在复合材料层合板层间植入韧性层是提高复合材料韧性和抗冲击能力的有效方法。为了研究层间增韧对层合板损伤阻抗的改善作用，文中通过准静态压痕试验研究层间增韧复合材料在准静态压痕力下的损伤和破坏行为，利用超声C扫描测量分层损伤面积。试验结果表明，层间增韧复合材料具有较高的分层起始载荷和分层起始能量，损伤阻抗显著提高。在相同的载荷水平下，具有较小的分层损伤面积。文中还采用有限元方法对层间增韧复合材料在静压痕力下的分层和铺层失效进行数值分析，有限元计算结果与试验结果吻合较好。     

Effect of Cycling Low Velocity Impact on Mechanical and Wear Properties of CFRP Laminate Composites

The mechanical and wear properties of CFRP laminate were investigated using a method of cycling low velocity impact, to study the trend and mechanism of impact resistance of the CFRP laminate under repeated impact during its service process. The interface responses of CFRP laminate under di erent impact kinetic energy during the cycling impact process were studied were studied experimentally, such as impact contact duration, deformation and energy absorption. The worn surface morphologies were observed through optical microscopy and a 3?D surface profiler and the cross?sectional morphologies were observed through SEM to investigate the mechanism of impact material dam?age. Based on a single?degree?of?freedom damping vibration model, the normal contact sti ness and contact damp?ing of the material in di erent wear stages were calculated. It shows the failure process of CFRP laminate damaged by accumulated absorption energy under the cycling impact of di erent initial kinetic energy. The results indicate that the sti ness and damping coe cients will change at di erent impact velocities or cycle numbers. The damage mechanism of CFRP laminates under cycling low kinetic energy is delamination. After repeated experiments, it was found that there was a threshold value for the accumulated absorption energy before the failure of the CFRP laminate.     

复合材料层合板力学性能试验研究

使用DDL300微机控制电子万能试验机,研究了复合材料层合板力学性能试验方法,得到了某无人直升机旋翼桨叶层合板试件的拉伸、压缩和纵横剪切参数。这种复合材料层合板力学性能试验、数据处理方法和试验步骤可以为其它复合材料层合板的力学性能试验提供借鉴。     

Evaluation of material properties and internal damage within CFRP and CFRP/Al sandwich panels due to impact loading

In the present paper, damage development within Carbon fiber reinforced plastic (CFRP) laminates and CFRP/Aluminum (Al) honeycomb core sandwich panels by impact loading was evaluated, and change in material properties due to the damage development was investigated. Falling weight impact tests, 3-point bending tests and cross-sectional observation were carried out. As results, it is found that falling rate of bending elastic modulus due to internal damage in the laminate only is lower than that in the upper face-sheet of the sandwich panel, and that difference in the falling rate between them becomes maximum at the impact energy of 5.1 J. As a result of investigating the relationship between reduction in bending elastic modulus and internal damage development, the reduction is caused by delamination within CFRP laminates mainly. Since total length of cracks in CFRP/Al honeycomb core sandwich panels is smaller than that in the laminates only, the sandwich panels have high impact tolerance because of absorption of impact energy by damaging Al honeycomb core.     

A study on residual fatigue bending strength and damage behavior of CFRP composites subjected to impact loadings

This paper evaluates the static and fatigue bending strengths of CFRP (carbon-fiber reinforced plastic) laminates having impact damages, e.g., foreign object damages (FOD). Composite laminates used in this experiment are CF/EPOXY and CF/PEEK orthotropy laminated plates with two-interfaces [0°₄/90°₄]_s A steel ball launched by an air gun collides against the CFRP laminates to generate impact damages. The damage growth during a bending fatigue test is observed by a scanning acoustic microscope (SAM). When the impacted side is compressed, the residual fatigue bending strength of CF/PEEK specimen P is greater than that of CF/EPOXY specimen B. On the other hand, when the impacted side is in tension, the residual fatigue bending strength of CF/PEEK specimen P is smaller than that of CF/EPOXY specimen B. In the case of impacted-side compression, the fracture is propagated from the transverse crack generated near the impact point. In the case of impacted-side tension, however, the fracture develops toward the impact point from the edge of interface-B delamination.     

Sensitivity analysis of plating conditions on mechanical properties of thin film for MEMS applications

In this paper, we report the detailed investigation into the effects of plating temperature and applied current density upon the mechanical properties of plated nickel film such as Young’s modulus and residual stresses. This method uses the resonance method of atomic force microscope, which does not require specially microfabricated cantilevers and additional experimental set-up. Thin layers of nickel are electroplated onto the tip surface of AFM cantilevers and plating thicknesses were measured at the end of each plating step. The self-deformation of the released AFM cantilever is also measured as a function of the plated nickel thickness, which is converted into the quantitative residual stress by appropriate mechanics. The measured Young’s modulus is as high as that of bulk nickel at low plating temperature and at low applied current density, but drastically drops at high temperature or current density. The dependence of Young’s modulus on the plating thickness is negligible in thin film less than few microns. The residual stress is also a strong function of the process conditions, and decreased with the elevation of the current density and plating temperature. And the intrinsic and extrinsic stresses of plated nickel are separated from the measured residual stress, and correlated with plating conditions. Dependence of the plated thickness on Young’s modulus and residual stress is also considered.     

含孔复合材料层板的力学性能研究

对复合材料开口缝合补强结构进行了实验研究,测试了不同缝合参数(针距、行距、边距、单重和双重缝合)补强对含孔复合材料层板的破坏强度,研究了孔边应力集中和缝合补强对强度、模量等力学性能参数的影响,分析讨论了孔边及邻近区域应变集中及应变分布的规律,通过实验结果和分析讨论,对复合材料开口缝合补强结构提出合理的设计方法。     

纤维环向缠绕复合材料气瓶冲击损伤容限研究

为研究纤维缠绕复合材料层CNG气瓶冲击后损伤容限问题,采用疲劳应变比率作为损伤变量,建立疲劳累积损伤模型;对气瓶缠绕层的冲击损伤剩余强度采用开孔等效计算方法,应用Nuismer—Whitney平均应力准则,关联疲劳累积损伤函数中的最大应力与拉伸载荷下的含孔层合板剩余强度的关系,建立适用于在疲劳载荷下的含孔层合板结构剩余强度的估算方法,用于复合材料CNG气瓶冲击剩余强度的预测。结果表明,文中提出的分析模型预测结果与专家提出的复合材料气瓶冲击损伤评定标准基本吻合。     

Effects of cutting edge radius and fiber cutting angle on the cutting-induced surface damage in machining of unidirectional CFRP composite laminates

Carbon fiber reinforced polymer composite laminates are anisotropic, inhomogeneous, and mostly prepared in laminate form before undergoing the finishing operations. The edge trimming process is considered as one of the most common finishing operations in the industrial applications. However, the laminate surface is especially prone to damage in the chip formation process, and the most common damage mode is burrs. Burrs may increase cost and production time because of additional machining; they can also damage the surface integrity. Many studies have been done to address this problem, and techniques for reducing burr size in material removal process has been the focus of the research. Nonetheless, the combined effects of the cutting edge radius and the fiber cutting angle on the burr formation have seldom been conducted, which in turn restricts to find out the mechanism of burr formation. The purpose of the present paper is to study the particular mechanism that leads to burr formation in edge trimming of CFRP laminates and investigate the effects of fiber cutting angle and cutting edge radius on burr formation. The results indicate that the burrs are prone to form in the fiber cutting angle range of 0° < χ < 90° when a large cutting edge radius of the tool is used for both milling and drilling of CFRP composites.     

LY12硬铝合金高速切削加工残余应力的研究

对LY12硬铝合金在高速切削加工过程中出现的高度非线性问题,采用有限元软件ABAQUS对切削过程进行仿真,得到了高速切削加工过程中的残余应力分布。讨论了高速切削加工过程中影响残余应力分布的几个关键因素:切削速度、背吃刀量、刀尖圆角半径,从而为以后获得基于残余应力的刀具参数优化方案提供了依据。     

层合复合材料板的低速冲击损伤及剩余压缩强度研究

针对复合材料层合板的冲击及冲击后的压缩破坏过程提出了一种全程分析方法。该方法应用三维逐渐累积损伤理论和分析技术,对层合板的冲击以及冲击后含损伤的层合板在压缩载荷下损伤扩展的全过程进行分析,分析中没有对冲击后层合板的损伤状态做人为假设,而是把冲击后层合板的预测损伤直接用于剩余压缩强度研究,从而不仅提高了最终失效载荷的预测精度,而且避免了为获得冲击后损伤状态参数所进行的大量试验,同时开发了模拟程序,该程序可以预测任意铺层角度、铺层厚度的层合板受外物冲击以及冲击后的损伤状态及在压缩载荷下的逐渐损伤破坏过程和最终失效载荷。通过与已有文献结果进行比较,验证了方法及程序的正确性。