低速冲击下CFRP层合板的损伤分析与数值模拟

为研究碳纤维层合板在低速冲击载荷下的损伤过程，按照国家标准测定了平纹编织碳纤维层合板的冲击强度，并设定不同冲击能量进行冲击试验，分析层合板的损伤形式及演化过程。根据冲击试验条件，利用Abaqus软件建立了层合板的复合材料有限元模型，基于Hashin失效准则和渐进损伤演化理论，模拟层合板在不同冲击能量下的层内损伤和层间损伤。结果表明，随着冲击能量增大，基体拉伸损伤与纤维压缩损伤最容易发生，但基体压缩损伤最先完全失效，宏观表现为局部凹陷；分层损伤最先出现在冲击表面，以松树型损伤模式逐步向背面扩展。     

单向石墨纤维增强铝合金复合材料轴向压缩损伤演化与断裂力学行为研究

针对单向石墨纤维增强铝合金复合材料(CF/Al复合材料),采用细观力学数值模拟与准静态压缩试验相结合的方法研究了其轴向压缩渐进损伤与断裂力学行为,并分析了纤维体积分数对CF/Al复合材料压缩力学性能的影响。结果表明,基于纤维正六边形排布RVE建立的细观力学有限元模型对CF/Al复合材料轴向准静态压缩变形力学行为的计算结果与实验结果吻合良好。复合材料轴向压缩时首先在界面处发生损伤,界面损伤的累积随后引起局部界面失效并诱发基体合金的损伤,变形后期纤维发生失效并导致复合材料产生轴向45°压缩破坏,压缩断口呈现出界面脱粘和局部纤维断裂共存的微观形貌,表明界面脱粘及其导致的纤维断裂是诱发复合材料轴向压缩失效的主要机理。轴向压缩载荷作用下基体合金塑性变形损伤后不易发生失效,纤维性能是决定复合材料轴向压缩力学性能的主要因素,增加纤维体积分数有利于提高复合材料的轴向压缩弹性模量和极限强度。     

基于细观力学有限元法的碳纤维增强铝合金复合材料横向拉伸行为研究

针对真空压力浸渗制备的碳纤维增强铝合金复合材料（CF/Al复合材料）,分别采用延性损伤本构和内聚力界面本构定义基体合金和界面的损伤演化与失效行为。建立其细观力学单胞有限元模型,数值模拟获得了复合材料横向拉伸变形中基体合金和界面的细观损伤演化和失效过程,通过复合材料横向拉伸应力-应变试验曲线与数值模拟曲线对比,验证所建立细观力学有限元模型的可靠性。结合力学试验和拉伸断口分析,探索CF/Al复合材料横向拉伸变形时断裂力学行为规律及其失效机理。     

碳纤维复合材料板冲击损伤计算及超声检测

文章采用显式有限元法、三维Tsai—Wu失效准则和刚度折算准则来模拟T300／QY8911矩形层压板低速冲击下逐渐损伤的过程,预测了复合材料冲击损伤的程度。根据HB72242—1995《复合材料构件通用技术条件》、GJB289521997《碳纤维复合材料层合板和层合件通用规范》要求制作冲击试样,进行低能量冲击试验。采用超声C扫描检测不同能量冲击作用造成的损伤,将有限元计算结果和超声C扫描检测结果进行对比。结果表明,在损伤面积尺寸确定方面,有限元分析的结果和超声C扫描检测结果吻合较好,三维Tsai—wu失效准则和刚度折算准则适合模拟分析碳纤维复合材料板冲击损伤,超声C扫描检测可以较好地检测出冲击能量高于4．5J的分层损伤。     

钛合金点阵夹芯结构弯曲性能

通过理论、试验、数值模拟3种方法研究3D打印钛合金金字塔型点阵夹芯结构在两端简支三点弯曲载荷下的响应,试验中通过裂纹观测仪监测加载过程。结果表明:在弯曲载荷下,夹芯结构损伤区域主要在弯矩最大中线处附近;试件首先在上面板出现塑性变形,随着第一层杆件的屈曲,载荷迅速下降。通过扫描电子显微镜(SEM)观测断口形貌,验证面板及杆件均为弯曲变形失效。基于ABAQUS软件,建立结点刚硬点阵夹芯结构有限元模型,对结构的渐进损伤过程进行预测,获得损伤起始位置、损伤扩展、破坏载荷及最终破坏模式等结果,模拟结果与试验结果吻合较好。通过有限元模型分析宽度方向不同单胞列数的影响,结果表明列数越多,边界影响越小,结构承载能力越强。     

T300碳纤维复合材料损伤声发射信号的有监督模式识别

对T300碳纤维复合材料板拉伸断裂过程进行了声发射监测。在试验和渐进损伤分析的基础上,应用K-means聚类判定了[0°/90°]_(14)T300碳纤维复合材料板拉伸断裂信号的失效形式,并对该聚类模型进行了有监督的训练和测试,将其应用到相似未知损伤信号中,很好地完成了模式识别。试验结果为今后实时监测碳纤维复合材料损伤提供了科学依据。     

复合材料层合板的微观损伤机理

通过对玻璃/环氧和碳纤维/环氧复合材料层合板进行施加循环拉伸载荷实验，利用扫描电子显微镜观察分析，得知不同循环加载次数下复合材料层合板的微观损伤机理可分为3类：基体损伤、界面损伤和纤维损伤。     

SiC单纤维增强TC17复合材料横向拉伸性能研究

采用单纤维十字架结构试样测试分析了SiC纤维增强TC17复合材料横向力学性能,利用SEM对拉伸断口及横切面进行了显微观察,分析了界面失效位置,并结合有限元数值模拟计算,研究了界面损伤失效机制及裂纹扩展规律。结果表明,在横向载荷的作用下,单纤维试样应力-应变曲线的非线性拐点应力为(271±12) MPa,该点是界面完全失效的起始点。基于双线性内聚力模型的有限元分析结果与实验结果一致,表明复合材料界面失效模式为剪切失效,裂纹萌生于反应层和碳涂层的界面。有限元分析预测的裂纹萌生位置在与加载方向成40°～50°的圆周之间,实验中不同最大载荷下裂纹出现在与拉伸方向成24°～68°之间不同位置,预测宽度略小于实验结果,这种差异的主要原因是有限元模拟中界面设定为理想刚性界面且沿周向一致,而实际碳涂层和反应层的界面是非光滑的,沿圆周存在微缺陷。裂纹萌生后,在剪切应力作用下沿轴向和周向同时扩展,在沿周向扩展过程中,0°附近界面在径向拉伸应力作用下先于90°附近界面失效,随后90°附近界面在周向剪切应力作用下失效。界面完全失效后,应力重新分配,随载荷增加,界面张开程度加大,基体局部出现屈服,直至材料完全断裂。     

碳纤维增强复合材料双面埋头压铆模拟分析

铆接技术作为一种不可拆卸的连接方式,在飞机装配过程中被广泛使用，同时碳纤维增强复合材料由于自身优异的力学性能也成为了航空工业中热门。在碳纤维增强复合材料铆接的过程中,铆钉的变形会对铆接的碳纤维增强复合材料造成损伤,从而影响铆接的质量以及其使用寿命。针对这一问题，使用有限元仿真软件ABAQUS创建复合材料双面埋头压铆三维模型，通过ABAQUS子程序接口编写VUMAT用户材料自定义程序，分别取Hashin准则和Puck准则的优势作为三维失效准则，选用合理的刚度退化方式对压铆后的复合材料的渐进损伤进行分析。通过ABAQUS对复合材料压铆过程模拟，得到铆钉在压铆过程中的成形规律和复合材料层合板的主要损伤失效形式为基体的压缩和拉伸、纤维压缩以及其损伤失效的扩展方向。     

C_f/Al复合材料横向拉伸微观损伤与力学性能的有限元分析

根据石墨纤维增强铝基复合材料(C_f/Al基复合材料)显微组织特征构建了其代表性体积单元(RVE),通过基体合金的延性损伤模型和纤维的最大应力失效模型,建立了基于内聚力界面模型的细观力学有限元模型并结合试验结果验证了其可靠性,在此基础上分析了纤维含量对复合材料横向拉伸损伤演化与力学行为的影响。结果表明,基于正六边形纤维排布RVE建立的细观力学模型能够准确预测复合材料横向拉伸力学性能。横向拉伸过程中首先发生界面损伤,随应变增加界面损伤累积,引起局部界面失效并诱发附近基体合金的损伤与失效,最终导致复合材料横向开裂,拉伸断口呈现界面脱粘和基体合金撕裂共存的微观形貌。提高纤维含量增加了界面数量和面积,从而降低了复合材料横向拉伸弹性模量和极限强度。     

Multiscale modeling of failure in metal matrix composites

A multiscale approach to composite failure, in which detailed information on small-scale micromechanics is incorporated approximately yet accurately into larger-scale models capable of simulating extensive damage evolution and ultimate failure, is applied to the deformation and failure of a Ti–matrix composite. The composite is reinforced with SiC fibers under conditions of matrix yielding and interfacial sliding via Coulomb friction. Specifically, a fully three-dimensional finite element model is employed to investigate the load transfer from broken to unbroken fibers as a function of applied stress and interface friction coefficient. With a von Mises matrix yield criterion, constraint effects permit the matrix to carry some of the transferred load near the fiber break, a feature not captured in previous composite models. The single-break results for stress concentrations are then used as the discrete Green's functions for load transfer in the full composite, and the predicted load transfer around a seven-fiber-break cluster is shown in good agreement with finite element results. The Green's function model is then used to predict overall damage evolution and composite failure for an IMI-834 Ti/SCS-6 SiC system for various interface friction coefficients. The composite tensile strength is rather insensitive to the friction coefficient and, for values of μ comparable to those measured experimentally, the predicted tensile strength is in excellent agreement with the measured value. Analytic models for scaling of the tensile strength to very large sizes are then shown to agree well with strengths obtained from simulations. These results suggest that the hierarchical coupling approach used here may be useful for approaching a wide variety of damage and failure problems in fiber composites.     

大厚径碳纤维复合材料三维钻削有限元仿真及试验研究

针对CR929远程宽体客机承力构件制孔出口分层缺陷预测难、制孔载荷预测试验成本高等问题,开展大孔径碳纤维增强树脂基复合材料(CFRP)三维钻削仿真及试验研究。首先基于ABAQUS用户自定义子程序接口,利用Fortran语言编写CFRP宏观力学本构模型;随后建立大孔径CFRP三维钻削仿真过程有限元模型,并验证其正确性;最后利用有限元模型预测不同加工参数下的制孔轴向力、扭矩及出口分层损伤。研究结果表明:基于三维实体单元建模的复合材料,三维钻削有限元仿真模型可以可靠地预测制孔过程中的轴向力、扭矩。在CFRP出口处嵌入黏结单元可以预测制孔出口分层的形状。在相同工艺参数条件下, 制孔的轴向力、扭矩、出口分层的仿真预测与试验结果最大相对误差分别为15.0%、19.0%、12.4%。      

Monitoring Damage Evolution in a Titanium Matrix Composite Shaft Under Torsion Loading Using Acoustic Emission

The damage behaviors of a titanium matrix composite shaft under torsion loading were monitored using the acoustic emission technique. The composite shaft with SiC fibers at ± 45° orientations was prepared by the solid-state fabrication process. Both the torsional rigidity and torsional strength of the TMC shaft were improved by SiC fibers. The acoustic emission responses during the loading–unloading–reloading, under quasi-static and cyclic torsion tests were investigated. Multiple acoustic emission signals were grouped as mechanical noise, matrix deformation, interface debonding and fiber fracture using amplitude, waveform shape and frequency centroid parameters. A substantial reduction of signals generated by matrix deformation was found in the reloading test. During the quasi-static torsion test, interface debonding and progressive breaks of SiC fibers occurred. According to different acoustic emission behaviors, the failure process in the torsion fatigue test can be divided into three stages: the initial stage, the fiber fracture stage and the fast fracture stage.     

Multi-scale modeling to predict sub-surface damage applied to laser-assisted machining of a particulate reinforced metal matrix composite

A multi-scale finite element model (FEM) is developed to predict the post machined sub-surface damage in a particle reinforced metal matrix composite (MMC) subjected to laser-assisted machining (LAM). The MMC studied is an A359 aluminum matrix composite reinforced with 20% by volume fraction silicon carbide particles. In this model, molecular dynamics (MD) simulations are carried out to parameterize traction–separation laws for the aluminum–silicon carbide interface. The parameterized traction–separation laws are then input into a finite element model, in the form of a cohesive zone model to subsequently simulate the sub-surface damage. In this manner, the multi-scale hierarchical model successfully bridges the atomic, micro and macro scales. Average values of the predicted quantities are compared with experimental results, and the favorable agreement confirms the validity of the multi-scale FEM.     

复合材料齿轮弯曲强度仿真与试验研究

三维编织复合材料的性能与编织参数密切相关,为了研究碳纤维编织复合材料齿轮的弯曲性能及其与编织参数的关系,提出复合材料及齿轮弯曲性能预测模型。基于代表性体积单胞法和均质化思想建立复合材料的细观、宏观双尺度模型,采用体积平均法、借助有限元手段预测复合材料及齿轮的弯曲性能。并且,采用四步法编织及模压成型方法制备两对碳纤维编织复合材料齿轮,通过试验获得特定编织参数下复合材料及齿轮的弯曲性能。预测结果与试验结果吻合良好,验证了预测模型的准确性。最后,进行了多组编织参数下复合材料及齿轮弯曲性能的预测,得到了编织角和纤维体积分数对复合材料及齿轮弯曲性能的影响规律,并给出了使复合材料齿轮弯曲性能最佳的编织参数。     

缝合复合材料层合板疲劳寿命预测

复合材料层合板疲劳损伤机理和寿命预测是关系到现代航空结构损伤容限设计的关键问题。通过对复合材料层合板疲劳损伤特征研究,从应变等效性出发,结合经典刚度降法,建立层合板疲劳寿命预测两阶段宏观唯象模型,弥补了经典刚度降法和S-N曲线模型的不足。应用此模型对新型的缝合复合材料层合板进行了相关分析与研究,并将预测结果与试验结果进行了对比。结果表明,所建立的疲劳寿命预测模型结果与试验结果吻合良好,可为缝合复合材料的失效分析与工程应用奠定一定的理论基础。     

Numerical Study and Experimental Validation of Effect of Varying Fiber Crack Density on Stiffness Reduction in CFRP Composites

Representative volume element (RVE) has commonly been used to predict the stiffness of undamaged composite materials using finite element analysis (FEA). However, never has been an independently measured true microstructural damage quantity used in FEA to predict composite stiffness. Hence, in this work, measured fiber crack density in unidirectional fiber composite (generated using controlled fatigue loading) was used to predict reduction in stiffness using a RVE. It was found that the stiffness changes with change in depth of the volume element along the fiber direction and asymptotically reaches a constant value beyond a critical length called representative depth. It was argued that this representative depth should be more than the minimum of two characteristic length scales, twice of ineffective length and average length of broken fibers. Effective stiffness obtained from FEA of the optimum-sized RVE was in excellent agreement with the experimental results for given microstructural damage state.