Experimental Analysis of Low-Velocity Impact Behaviors of Carbon Fiber Composite Laminates

Manufacture processing of composite laminates often leads to unequal thickness of lamina and different impact responses. However, almost all existing works neglected this problem because they considered equal thickness for each lamina. This paper aims to study the influence of unequal thickness of each lamina on the impact behaviors of composite laminates by experiments. Effects of the layup patterns and impact energy are mainly studied. Results in terms of the impact experiments of carbon fiber composite laminates show that subtle difference for the thickness of the total laminate leads to relatively large errors for the impact responses, especially for the impact force-deflection curves. Also, the ratio of absorbed energy to the impact energy increases with the specimen thickness. Therefore, the practical design of composite laminates should be taken into account this difference fully due to manufacturing.     

Oblique Low-Velocity Impact on Fiber-Metal Laminates

In the present study, oblique low-velocity impact (OLVI) on GLARE fiber-metal laminates (FMLs) has been modeled using finite element analysis (FEA) for the first time. Two types of boundary conditions (BCs) can be considered for impactor in the low-velocity impact: constrained (if the impact angle between the impactor and target remains constant during and after the contact) and free (if rotation of the impactor and change in angle with respect to the target is likely) BCs. The more details of these BCs are described in the paper. The OLVI is numerically modeled for four different impact angles. Effect of BC types and impact angle on energy absorption, as well as maximum contact force, is investigated. Due to lack of experimental results for the OLVI on FMLs in the open literature, the authors had to validate the present modelling via the experimental data of the perpendicular low-velocity impact. An excellent agreement was obtained between the numerical results and the experimental data. The results of present study reveal that at the same impact angle, the maximum contact force and energy absorption are greater for the constraint oblique impact (Constrained OLVI). In addition, in the Constrained OLVI, the maximum energy absorption occurs at larger impact angles, while this occurs at smaller impact angles for free oblique impact (Free OLVI). The conclusion to be drawn from all of the cases studied in this paper is that the maximum contact force occurs in the Constrained OLVI with smaller impact angles. Moreover, the maximum energy absorption takes place in the Constrained OLVI at higher impact angles.     

碳纤维编织复合材料层合板抗侵彻性能研究

通过弹道冲击实验开展了碳纤维编织复合材料层合板的抗侵彻性能研究,进行了动态响应分析和损伤模式分析。建立了基于Hashin失效和Yeh分层失效准则的渐进损伤模型,运用ABAQUS有限元软件模拟了碳纤维编织复合材料层合板的侵彻失效过程,采用Lambert-Jonas公式拟合了柱状弹侵彻层合板弹道极限曲线,对比分析了碳纤维编织复合材料层合板侵彻实验与数值模拟的弹道极限速度及损伤形貌。结果表明,层合板侵彻损伤模式主要为分层、纤维断裂和基体开裂失效,弹道极限速度数值模拟结果与实验结果吻合较好。     

The Effects of Debonding on the Low-Velocity Impact Response of Steel-CFRP Fibre Metal Laminates

The effect of metal-composite debonding on low-velocity impact response, i.e. on contact force–central deflection response, deformation profiles and strains on the free surfaces was studied. We focused on type 2/1 fibre metal laminate specimens made of stainless steel and carbon fibre epoxy layers, and tested them with drop-weight impact and quasi-static indentation loadings. Local strains were measured with strain gauges and full-field strains with a 3-D digital image correlation method. In addition, finite element simulations were performed and the effects of debonding were studied by exploiting cohesive elements. Our results showed that debonding, either the initial debonding or that formed during the loading, lowers the slope of the contact force–central deflection curve during the force increase. The debonding formation during the rebound phase was shown to amplify the rebound of the impact side, i.e. to lower the ultimate post-impact deflection. The free surface strains were studied on the laminate’s lower surface at the area outside the debond damage. In terms of in-plane strains, debonding formation during impact and indentation, as well as the initial debonding, lowered the peripheral strain and resulted in a positive change in the radial strain.     

碳纤维增强树脂基复合材料层合板的损伤阻抗表征

通过落锤冲击试验与准静态压痕试验研究了碳纤维增强树脂基复合材料层合板的损伤阻抗,发现两种试验中,复合材料层合板都具有三个损伤阶段。两种试验都具有两个表征损伤阶段变化的拐点:第一个拐点为分层拐点,表征分层起始;第二个拐点为损伤拐点,表征分层扩展趋于饱和。本文建议利用一个三维坐标点(x,y,z,其中x为第二拐点对应的冲击能量,y为相应的凹坑深度,z为分层投影面积)表示的损伤拐点来衡量材料抵抗冲击的能力,此损伤拐点不仅仅代表了材料抵抗冲击的关键点,也揭示了此时的内部损伤状态。     

平面编织复合材料层压板的冲击失效行为

对复合材料层压板进行不同能量的落锤冲击试验,根据凹坑深度将冲击损伤分为无损伤、目视不可检、目视可检与穿透损伤4个等级。通过C-扫描检测、热揭层、损伤截面观察等方法,研究了不同等级损伤的失效特征、失效模式与失效过程。结果表明,不同等级损伤的失效模式不同,目视不可检损伤主要为分层失效,目视可检损伤主要为分层与基体开裂,穿透损伤主要为纤维断裂。损伤达到穿透前后的失效过程也存在差异。     

Mechanical Response of CFRP Laminates Subjected to Low-Velocity Oblique Impact

Applied Composite Materials - The mechanical response of CFRP laminates under low-velocity oblique impact was investigated using finite element simulation and experimental test in this paper. Based...     

碳纤维复合材料层合板低速冲击损伤应力分析

目的 为掌握碳纤维复合材料板在低速冲击载荷作用下的损伤规律,延缓失效破坏,对其冲击损伤的应力状态进行研究。方法 基于ABAQUS平台,建立碳纤维复合材料层合板低速冲击有限元模型,采用Hashin失效准则和VUMAT用户子程序,对碳纤维复合材料层合板的冲击过程进行数值模拟,同时考虑层合板层内与层间失效,以此来研究低速冲击条件下复合材料的损伤机理,分析冲击损伤过程中的应力变化趋势,讨论应力的分布状态。重点研究铺层角度及铺层距离冲头远近对应力的影响。结果 不同角度铺层的应力传播轨迹均沿着纤维方向和垂直于纤维方向同时扩展,应力均先增加至极限值而后迅速下降;铺层角度越大,板料的承载能力越弱,0°铺层的极限应力为1 432 MPa,而90°铺层的极限应力降至1 206 MPa;离冲头越远的铺层应力越小,达到峰值的时间更早且率先下降,说明远离冲头的铺层更早发生失效。结论 揭示了碳纤维层合板在低速冲击载荷作用下的应力状态及其对损伤的影响规律,能够为复合材料层合板零件设计提供参考。     

T700/6421复合材料层板低速冲击后损伤特性

对未增韧及增韧后的T700/6421复合材料层板进行了低速冲击实验,讨论了表面凹坑深度(D)、表面凹坑直径(R)、冲击后压缩强度(CAI)及冲击能量(E)的关系,并通过记录冲击过程中的接触力与时间的变化分析了冲击时的损伤过程。实验结果表明,增韧后的复合材料其更容易出现深凹坑及更大的表面凹坑直径,更容易实现目视明显可见损伤(VID)的效果,并通过分析冲击历程响应发现:低速冲击过程中复合材料层板起始产生分层损伤时的时间与冲击能量并没有必然的联系。     

The Effect of Hydrothermal Aging on the Low-Velocity Impact Behavior of Multi-Walled Carbon Nanotubes Reinforced Carbon Fiber/Epoxy Composite Pipes

Chemical transmission lines, petroleum and natural gas lines, pressure vessels, and pipes used in thermal facilities are expected to maintain their mechanical properties for many years without being damaged and not to be corroded in working conditions. The composite materials are the right candidate for these harsh conditions due to their superior properties. Reinforcement of nanoadditives to composite materials improves both the mechanical properties and the resistance to environmental conditions, thereby increasing the lifetime. In this study, multi-walled carbon nanotube (MWCNT) reinforced [±?55°] carbon fiber/epoxy composite pipes produced with filament wound method were used. It was hydrothermally aged in 80 °C distilled water for 1, 2, 3 weeks in order to examine the effect of environmental conditions. In order to investigate its resistance against loads that may occur in working conditions, ring tensile tests (ASTM D 2290–16 procedure A), and low-velocity impact tests at 5, 10, 15 J, energy levels were carried out. The effect of hydrothermal aging on neat and MWCNT added epoxy composite had been examined by considering the aging period. Consequently, the impact resistance of neat and MWCNT added samples decreased with the aging process. Besides, tangential tensile strength loss was 17% in MWCNT reinforced sample and 13% in the neat sample.

     

国产炭纤维复合材料层合板高温单钉连接性能试验

对国产CCF300/GW300复合材料层合板与铝合金板单钉连接结构在常温以及200℃和300℃高温环境下的拉伸性能进行试验研究,分析了连接试件的高温拉伸破坏行为,以及温度、铺层形式、连接螺栓直径对于条件挤压强度的影响。研究发现,高温越高其条件挤压强度保持率越低,300℃时条件挤压强度仅为常温的30%;90°铺层比例越高...     

Impact Damage to Composite Laminates: Effect of Impact Location

Accidental impact loading of Composite laminates during manufacture and in-service can occur in different locations including near the edge or on the edge of a composite structure. This paper describes investigation of the effect of impact to composite laminates and compares the damage arising from central, near edge and on edge impact events. The damage tolerance of impact damaged laminates using both compression and tension tests has been measured. These results reveal the different damage mechanisms arising from different locations of impact. These different damage mechanisms have been investigated using X-Ray computed tomography. Impact on the edge of composite laminates is found to lead to smaller damage area, but more fibre failure; the severity of this damage is not revealed in standard compression after impact tests.     

复合材料层板低速冲击后疲劳性能实验研究

通过对T300/5405复合材料层板进行低速冲击后的压-压疲劳实验,研究含不同冲击损伤层板的压缩性能与其在多级应力水平下的疲劳寿命与损伤扩展,并讨论冲击能量、应力水平、损伤扩展对层板疲劳寿命的影响。结果表明:冲击损伤明显降低层板的剩余强度;在低应水平下,冲击能量越大,含冲击损伤层板的疲劳寿命越小;疲劳实验中损伤经历平稳扩展和快速扩展两个阶段,其中平稳扩展阶段约占总体寿命的80%,快速扩展阶段约占总体寿命的20%,损伤扩展速率随着应力水平降低而减小。     

温度对碳纤维平纹布正交层合板拉伸疲劳性能的影响

温度环境可降低复合材料的疲劳性能,在确定复合材料结构寿命时须考虑温度的影响.本试验测量了碳纤维平纹布正交层合板在低温干态(CTD)、常温干态(RTD)和高温干态(ETD)环境下的拉伸疲劳性能,获得了三种环境下复合材料的S-N曲线,分析了温度对复合材料疲劳性能的影响.基于试验结果,建立了温度条件下复合材料疲劳性能有限元分析模型,对复合材料的疲劳寿命进行了估算并分析了其损伤机理.线性拟合结果显示:在106 疲劳寿命下,与RTD环境疲劳最大应力相比,CTD环境疲劳最大应力略有降低,而ETD环境疲劳最大应力下降明显. CTD环境下,试验件的疲劳破坏断口比较齐整,纤维基本在同一纵向位置断裂,断口附近基体基本完好,无分层现象;RTD环境下,试验件断口处也没有明显分层现象;ETD环境下,试验件出现了明显的分层,同时还有纤维拔出,且断口处基体开裂程度严重.有限元分析表明,CTD环境下试验件的疲劳断裂呈现脆断的特征,断裂截面平整,断裂区域窄;RTD与ETD环境下试验件的纤维疲劳断裂损伤的断裂截面不平整,断口不一,断裂区域相对较宽.     

Micromechanical Analysis of Interphase Damage for Fiber Reinforced Composite Laminates

In the present study, the initiation and evolution of the interphase damage and their influences on the global stress-strain relation of composite laminates are predicted by finite element analysis on a micromechanical unit cell model. A thin layer of interphase elements is introduced and its stress-strain relation is derived based on a cohesive law which describes both normal and tangential separations at the interface between the fiber and matrix. In addition, a viscous term is added to the cohesive law to overcome the convergence difficulty induced by the so-called snap-back instability in the numerical analysis. The matrix behavior is described by a recently developed nonlinear viscoelastic constitutive model. As application examples, glass fiber/epoxy unidirectional laminates under off-axis loadings are analyzed. One-quarter of the unit cell is used in the analysis accounting for the geometrical symmetry of the model, and the corresponding periodic boundary conditions for combined global shear and normal loading are derived. Results show that the initiation and evolution of the interphase damage can be well simulated and the predicted global stress-strain responses are in good agreement with the experimental results.     

Damage Investigation in Drilling of Glass Fiber Reinforced Plastic Composite Laminates

Machining of fiber reinforced plastic is a process that is substantially different from metals. The inherent anisotropy in the material system makes the material removal mechanism quite complex. Drilling composite materials is necessary to ascertain the structural integrity of intricate composite products. Drilling of laminated structures results in extensive damage around the drilled hole. This study is an attempt to quantify and propose mathematical models for drilling-induced damage in terms of the cutting speed and the feed speed. Mathematical models have also been proposed for the resulting thrust force and the torque. Four different drill point geometries, namely 4-faceted, 8-faceted, parabolic, and Jodrill, are investigated in this study.     

内埋光纤光栅的复合材料层压板拉伸应变研究

利用内埋在复合材料层间的光纤光栅(Fiber Bragg Grating,FBG)传感器监测复合材料层压板在拉伸过程中的应变变化,并与复合材料层压板试样表面粘贴的应变片测得数据进行对比,同时研究了光纤光栅的埋植位置对复合材料力学性能的影响。探索了FBG传感器在复合材料应变监测中的有效性和可靠性。结果表明:内埋于复合材料层间的FBG传感器可以有效反映复合材料层压板在受到拉伸载荷过程中的应变变化,对比FBG传感器与应变片测得的实验结果,二者所测得的应变变化趋势吻合良好,而且埋植光纤光栅对复合材料层压板的拉伸强度影响较小。     

缝合复合材料可用性--环境条件下层合板的冲击后压缩性能

为了解决缝合复合材料在航空航天结构中的应用问题,对国内生产的缝合/树脂膜渗透成型工艺复合材料层合板在三种不同环境条件下的低速冲击后压缩性能进行试验研究.结果表明,缝合改变了含冲击损伤层合板的压缩破坏机理,可以大幅度提高层合板在干态常温下的冲击后剩余压缩强度,但是对湿态高温下层合板的冲击后剩余压缩强度影响不大;缝合方向对冲击损伤面积和剩余压缩强度的影响较小,其中以0°缝合较为有利.     

Micromechanical Modeling of Impact Damage Mechanisms in Unidirectional Composite Laminates

Composite laminates are susceptible to the transverse impact loads resulting in significant damage such as matrix cracking, fiber breakage and delamination. In this paper, a micromechanical model is developed to predict the impact damage of composite laminates based on microstructure and various failure models of laminates. The fiber and matrix are represented by the isotropic and elastic-plastic solid, and their impact failure behaviors are modeled based on shear damage model. The delaminaton failure is modeling by the interface element controlled by cohesive damage model. Impact damage mechanisms of laminate are analyzed by using the micromechanical model proposed. In addition, the effects of impact energy and laminated type on impact damage behavior of laminates are investigated. Due to the damage of the surrounding matrix near the impact point caused by the fiber deformation, the surface damage area of laminate is larger than the area of ??impact projectile. The shape of the damage area is roughly rectangle or elliptical with the major axis extending parallel to the fiber direction in the surface layer of laminate. The alternating laminated type with two fiber directions is more propitious to improve the impact resistance of laminates.     

Residual Stiffness of Cracked Cross-Ply Composite Laminates Under Multi-Axial In-plane Loading

In this paper, the Equivalent Constraint Model (ECM) together with a 2-D shear lag stress analysis approach is applied to predict residual stiffness properties of polymer and ceramic matrix [0/90 _n /0] cross-ply laminates subjected to in-plane biaxial loading and damaged by transverse and longitudinal matrix cracks. It is found that the longitudinal Young’s modulus, shear modulus and major Poisson’s ratio undergo large degradation as the matrix crack density increases, with Poisson’s ratio appearing to be the most affected by transverse cracking. In cross-ply laminates with thick 90° layer strip-shaped delaminations begin to initiate and grow from the tips of matrix cracks at the 0°/90° interface. These delaminations contribute to further stiffness degradation of such laminates, and hence have to be taken into account in failure analysis models. The thickness of the 90° layer plays an important role; the thicker the 90° layer, the bigger stiffness reduction suggesting a size (volume) effect at ply level. In SiC/CAS cross-ply laminates reduction in the longitudinal modulus occurs mainly due to transverse cracks, while the shear modulus appears to be the most affected by the presence of longitudinal cracks. The shear modulus reduction ratio predicted previously by a semi-empirical formula is, in the most of cases, within 10% of the current ECM/2-D shear lag approach value. In some cases, though, the error of the semi-empirical finite element expression can be as big as 20% since it fails to capture damage mode interaction.