低速冲击后三维中空夹层复合材料的压缩损伤容限

为了研究低速冲击后三维中空夹层复合材料的压缩损伤容限(剩余压缩强度),制作了满足要求的实验件并进行了剩余压缩强度对比实验.采用数码照片和外观检测等方法对压缩破坏损伤发展的过程进行了研究,分析了压缩破坏机理.结果表明,冲击损伤严重影响了三维中空夹层复合材料板的抗压能力,剩余压缩强度随冲击能量的增加而减少;三维中空夹层复合材料的压缩破坏主要由前面板控制,前面板发生局部屈曲的载荷与板的压缩破坏载荷几乎相等;表面蒙皮不仅能减少冲击损伤,而且能使板内的损伤显露在表面,容易让人发现.     

三维正交机织复合材料弹道侵彻有限元模拟

测试复合材料弹道侵彻性质,得到复合材料弹道侵彻过程中子弹的入射速度和剩余速度及冲击破坏形态。基于复合材料的真实细观结构,建立细观结构模型,运用商用有限元软件ABAQUS/Explicit计算复合材料弹道侵彻破坏过程。研究发现三维正交复合材料不同破坏机制:三维正交机织复合材料不产生冲击分层,纤维断裂和基体开裂是主要吸能模式,复合材料冲击破坏是最主要的破坏模式。     

玄武岩纤维增强不饱和聚酯层压复合材料低速冲击损伤性能

研究0°单向、0°/90°交错和平纹织物三种不同铺层方式玄武岩纤维增强复合材料低速冲击加载力学性能。在实验中,通过手糊成型法并在硫化机上加热加压制备层压复合材料,且在Instron9250落锤冲击测试仪上完成层压复合材料低速冲击试验,得到载荷-挠度曲线和载荷-时间曲线,用于分析三种不同铺层方式玄武岩纤维增强不饱和聚酯树脂层压复合材料低速冲击加载力学性能。通过观察层压复合材料破坏形态来分析其破坏方式。实验结果表明:0°/90°交错层压复合材料和平纹织物增强层压复合材料抗低速冲击性能优于0°单向层压复合材料;0°单向层压复合材料破坏方式为裂纹沿着纤维方向伸展,而0°/90°交错层压复合材料和平纹织物层压复合材料破坏只发生在冲击点附近局部区域。     

含z向纤维增强的连续纤维增强树脂基复合材料冲击性能研究进展

层合复合材料受到冲击载荷时会产生严重分层破坏,z向增强纤维的引入可明显改善层间韧性,提高复合材料的抗冲击性能.本文首先对纤维增强复合材料的冲击过程进行了阐述,并综述了近年来z向纤维增强复合材料冲击研究成果,包括缝合结构、z-pin结构和三维纺织结构.从实验方法和数值模拟两方面进行总结,介绍了低速、高速冲击的破坏模式、损...     

不同结构纺织复合材料准静态侵彻实验分析及有限元模拟

本文研究了两种不同结构三维结构纺织复合材料——三维正交机织玻璃纤维,不饱和树脂复合材料和双轴向纬编针织玻璃纤维／不饱和树脂复合材料在MTS材料试验机上的准静态侵彻测试。以纯铝MTS实验数据为标定,分析了准静态侵彻载荷一位移曲线及其破坏机理,比较了不同结构纺织复合材料以及纯铝的位移一载荷曲线,由此计算得到位移与吸能关系曲线。同时根据复合材料各自织物中纤维束排列及织物成型特点,分别建立了复合材料的细观结构模型和单胞模型。编写用户子程序（VUMAT）,用ABAQUS软件进行了有限元模拟。结果表明：三维纺织复合材料各自损伤结果和载荷-位移曲线与实验结果吻合较好,证明有限元的有效性。三维正交结构复合材料抗侵彻能力优于双轴向纬编针织复合材料,但是破坏过程中其抗侵彻能力幅值变化差异大,没有针织复合材料抗侵彻能力稳定。     

低速冲击下含金属内衬的纤维缠绕容器损伤特征

本文基于低速冲击动力学理论和复合材料层合结构损伤破坏准则,采用以不协调模式的八节点块三维有限单元法,研究了在空载和满载下含金属内衬的纤维缠绕容器在冲击下的力学行为,并预测了其冲击损伤分布。在分析中应用修正的Hertzian接触法则来计算在冲击载荷下冲击体和缠绕结构之间的接触力;在时域中采用Newm ark方法求解。通过典型数例研究结果表明,在相同能量的冲击载荷作用下,满载(内压)下的纤维缠绕容器较空载容器更易发生基体开裂和分层破坏。     

三维角联锁机织复合材料三点弯曲疲劳的细观结构效应

依据层层接结三维角联锁机织复合材料的结构特点,建立能真实反映细观结构特征的大型精细实体几何结构模型;基于非弹性滞后能疲劳破坏准则,用有限元法计算三维角联锁机织复合材料在三点弯曲低周交变循环载荷下的变形和刚度降解,揭示疲劳过程中三维角联锁机织复合材料内部应力分布特征和变形特征,分析纱线与树脂的破坏机理,阐述该复合材料在循环载荷下发生疲劳破坏的结构效应。结果表明,经纱在疲劳过程中承担大部分的载荷,且不同的组分呈现不同的破坏扩展过程。本文研究结果和研究方法将可进一步扩展至三维机织复合材料工程结构设计。     

格栅结构受力分析与载荷重构研究

本文基于有限元软件自动生成系统(FEPG),编制了先进复合材料格栅结构(AGS)在低速冲击作用下的有限元分析程序,实现了AGS在低速冲击载荷作用下的响应分析,通过实验验证了FEPG生成程序的正确性.将有限元与遗传算法相结合进行了载荷重构的初步研究,采用遗传算法对载荷进行了时程重构,为复杂结构的载荷重构提供了依据.     

三维正交机织复合材料准静态侵彻实验和有限元模拟

用钢制侵彻体对三维正交机织复合材料在MTS材料试验机上作准静态侵彻测试，得到的准静态侵彻位移一载荷曲线用来研究材料的能量吸收和破坏模式。根据三维机织复合材料的细观结构建立单胞模型，结合应力更新原理编写用户子程序（VUMAT）。利用ABAQUS有限元软件及用户子程序模拟实验过程，得到的位移一载荷曲线与实验对比，可以看出有限元计算得到的结果与真实实验比较吻合，表明单胞的建立和用户子程序的编写是正确的。     

玻璃纤维复合材料层合板冲击后的压缩强度

对不同厚度的二维编织环氧玻璃纤维层合板进行落锤冲击试验及冲击后压缩破坏试验,以研究低速冲击对复合材料层合板剩余压缩强度(CAI)的影响。用透光描影及热揭层方法对冲击损伤形式进行描述。讨论了损伤宽度、损伤面积与冲击能量及剩余压缩强度、模量间的关系,并建立有限元模型,采用开口等效及软化夹杂等分析方法对材料的冲击后压缩强度值进行估算。     

The tension failure mechanisms of composite stepped bonding repairs and joints for the aircraft primary load-bearing structures

Stepped and scarf topology are still the preferred choices for repairs and joints of composite primary load-bearing structures. The stepped bonding scheme is easy to be implemented in real engineering process. The precise stress distribution, load capacity, damage mode and failure mechanism are not adequately clear. This paper adopts static stress analysis of FEM (Finite Element Method), experimental studies and CDM (Continuum Damage Mechanics) to reveal the tension failure mechanism for composite stepped bonding structures. In the static stress analysis, the mesoscale FEM model considered the adhesive thickness was created. It investigated the detail stress distribution and concentration of the step topology adhesive. Then seven specimens with tensile load were studied experimentally through relation of load-deformation and the appearance of damage. For more details, the adhesive damage was simulated by using CZM (Cohesive Zone Model) which includes the mix-mode fracture of normal force and sliding shear force. The process of damage propagation evolution can be clearly observed in the simulation results. The damage initiates at the vertical location of steps adhesive and propagates to the horizontal overlaps adhesive. Simulation for predicting the ultimate load capacity coincides with experiments. This paper’s work will be useful for designing and analyzing the full composite materials airframe and wing repaired by stepped bonding technique.     

四步法三维编织复合材料弯曲疲劳行为实验研究

采用MTS 810.23仪器对一种四步法三维编织复合材料结构在应力比为R(σmin/σmax)=0.1、频率为3Hz正弦波条件下进行三点弯曲疲劳测试,研究三维编织复合材料弯曲疲劳性能。通过实验仪器测试准静态三点弯曲和不同应力下三点弯曲疲劳性质得到Data数据,通过对数据分析获得σ-N曲线和最大最小挠度曲线,对比不同应力水平下材料破坏形态从而揭示材料弯曲疲劳机理。实验结果:50%应力水平下,试样经过106次以上的循环仍然没有破坏,80%、70%和60%应力下材料失效的圈数分别是12 833、50 370、101 652。材料疲劳加载下刚度降解和挠度变化趋势相似,材料弯曲疲劳极限为50%,材料σ-N曲线呈三段式,材料低应力水平下疲劳寿命离散性高于高应力水平。     

Anisotropic continuum damage model for prediction of failure in flax/polypropylene fabric composites

An anisotropic continuum damage modeling approach was applied to model failure of a composite of unidirectional flax in a polypropylene matrix under quasi‐static tensile loading. Tensile, compressive and shear stiffness, and strength values of the composite were characterized according to ASTM standards, and the damage was quantified by optical microscopy. Based on the experimental strength and damage values, an anisotropic strain‐dependent material damage model was developed and implemented in the finite element program ABAQUS. This was combined with geometric models of the fabric composites incorporating the yarn geometry. Good agreement was observed between the experimental and numerical stress–strain curves, and the failure strength prediction by the model was within 3.1% of the experimental value. This study shows that combining a geometric model closely incorporating the actual geometry of a fabric composite with an experimentally determined material degradation model can yield good predictions of the mechanical behaviour of the composite. POLYM. COMPOS., 37:2588–2597, 2016. © 2015 Society of Plastics Engineers     

四点弯曲载荷作用下复合材料分层演化行为探索

为探索玻璃纤维增强复合材料在四点弯曲载荷作用下分层演变行为及分层缺陷对复合材料承受负荷能力和服役期限的影响,经过设置相异位置的人为分层缺陷,在万能试验机上对试样实施四点弯曲试验,由声发射记录全过程,并通过试样的撞击累积-时间-幅度历程图、载荷-时间-相对能量历程图、声发射撞击信号定位图等判断复合材料分层损伤的破坏程度。结果表明,接近试件表面的分层缺陷加快了材料破坏扩展进程,分层缺陷所在的位置很大程度地改变了复合材料的弯曲性能,分层缺陷越靠近试件表面,对试件损害力度越大,试件服役能力越差。     

柔性复合材料梯形撕裂实验性研究及破坏机理分析

采用梯形撕裂法对柔性复合材料的撕裂破坏进行分析,得出随织物中纱线的逐根断裂,受力三角区会逐渐增大,因此撕裂强力会出现一个最大值。通过在MTS-810材料实验机上进行撕裂破坏性实验,得到柔性复合材料在撕裂过程中的载荷-位移曲线,通过观察撕裂曲线,分析讨论了柔性复合材料梯形撕裂破坏机理以及影响破坏形态的因素。     

Numerical analysis of adhesively bonded T-joints with structural sandwiches and study of design parameters

Adhesively bonded T-joints are extensively used in assembling sandwich structures. The advantage of adhesive bonded joints over bolted or riveted joints is that the use of fastener holes in mechanical joints inherently results in micro and local damages to the composite laminate during their fabrication. One type of adhesive joint in such structures is the T-joint between sandwich panels. The aim of this research paper is to study, by numerical analysis, the effect of fillet geometry and core material of sandwich panels on the performance of T-joints. The base angle of the core triangle (fillet) is the most important geometry parameter of the triangular T-joint. Nine geometrical models with different base angles of the core triangle are made to investigate the effect of the base angle on the performance of the T-joints. It should be mentioned that the base angle in the triangular foam is changed, so that the final volume of the filler is kept constant in all the cases. Different foams with different stiffness are used to model the core of the panels to study the effect of the core material of sandwich panels. To model the adhesive between joint components, contact elements and cohesive zone material models are used. Therefore, failure of adhesive and separation of joint elements can be modeled. Damage and core shear failure of the base panel are modeled by using a written macro-code in the ANSYS finite element method (FEM) program. The ultimate strength of the joint in each case is calculated by modeling adhesive failure and core shear failure of the sandwich panels. Finally, the results of FEM are validated by experimental results available in the literature. In general, the failure load predicted by the FEM is within 5% of the experimental results. The best angle of the core triangle was found to be 45°. Also, the results showed that by changing the core material of the sandwich panel, the joint failure load is also changed.     

三维正交机织复合材料弹道冲击实验及破坏模式

本文用钢芯弹对三维机织复合材料作弹道冲击测试。得到了弹体的入射速度和剩余速度,比较了常见几种材料的弹道性能评价参数的差异,并考察侵彻破坏模式和靶体最后的损伤破坏形态。在300-800m/s冲击速度范围下观测了材料的冲击破坏形态,发现机织复合材料受弹面和子弹出射面破坏形态不一样,受弹面主要是以纤维的压缩、剪切破坏以及基体开裂为主,出射面以纤维的拉伸、厚度方向的纱线断裂为主要破坏模式。通过对破坏模式和形态的分析,可以帮助建立更加准确的破坏准则,从而在设计抗弹材料时起到一定的作用。     

含初始脱粘缺陷复合材料加筋壁板渐进压溃过程的数值模拟

建立了预测含初始脱粘缺陷复合材料加筋壁板渐进压溃响应的数值分析模型。该模型综合考虑了复合材料层合板的纤维失效、基体失效和纤维-基体剪切失效三种典型的面内损伤模式,并通过编写用户自定义材料子程序VUMAT实现面内失效类型的判断和相应材料性能的折减;在壁板和筋条连接界面应用虚裂纹闭合技术(VCCT)计算层间裂纹前缘的应变能释放率,并结合B-K混合模式准则控制缺陷的起裂以模拟脱粘的扩展演化过程;采用显式动力学方法准静态分析结构在压缩载荷下的屈曲、后屈曲直至最终压溃的响应过程。数值分析结果与文献试验、数值结果吻合良好,验证了模型的合理性和有效性,并详细研究了复合材料脱粘加筋壁板的损伤演化过程和渐进压溃行为。     

The hygrothermal effect on the fatigue behavior of carbon fiber/ peek laminate composites (I)

The hygrothermal effects on the fatigue behavior of the Carbon/PEEK laminated composites before and after impact damage were examined in this study. The [0/45/90/-45]_2s AS-4/PEEK laminated composites were immersed in 80°C hot water for 45, 90 and 200 days,and subjected to falling weight impact with an energy of 8.58 J and then immersed in 80°C hot water for 45 days. It was found that the tensile strength of AS-4/PEEK laminated composites decreased with the increase of exposure period. The injured AS-4/PEEK composites were subjected to a static load and a tensiontension fatigue load at various levels of stress amplitudes. The effect of stress amplitude on the fatigue life was studied. The experimental fatigue life under different stress amplitude tests were estimated by the median rank order statistic cumulative distribution function. Then,the fitting curves for estimated data were analyzed by the Weibull distribution function. The S-N curves for a series of cyclic loads at various survival probabilities were presented. The damage behaviors of composites after fatigue load test were also investigated by scanning electron microscope(SEM). Results indicated the fatigue lives of immersed specimens were shorter than those without hygrothermal effect, the impact damage affects the fatigue life of composite significantly.