纤维增强复合材料压缩破坏研究进展

综述了纤维增强复合材料压缩破坏机理及影响因素,同时对目前公开发表的几种预测复合材料压缩破坏强度方法进行了介绍与分析。最后,对今后研究动向进行了展望。     

Optimization of Sandwich Composites Fuselages Under Flight Loads

The sandwich composites fuselages appear to be a promising choice for the future aircrafts because of their structural efficiency and functional integration advantages. However, the design of sandwich composites is more complex than other structures because of many involved variables. In this paper, the fuselage is designed as a sandwich composites cylinder, and its structural optimization using the finite element method (FEM) is outlined to obtain the minimum weight. The constraints include structural stability and the composites failure criteria. In order to get a verification baseline for the FEM analysis, the stability of sandwich structures is studied and the optimal design is performed based on the analytical formulae. Then, the predicted buckling loads and the optimization results obtained from a FEM model are compared with that from the analytical formulas, and a good agreement is achieved. A detailed parametric optimal design for the sandwich composites cylinder is conducted. The optimization method used here includes two steps: the minimization of the layer thickness followed by tailoring of the fiber orientation. The factors comprise layer number, fiber orientation, core thickness, frame dimension and spacing. Results show that the two-step optimization is an effective method for the sandwich composites and the foam sandwich cylinder with core thickness of 5 mm and frame pitch of 0.5 m exhibits the minimum weight.     

Buckling Failure of Interface Cracks Loaded in Shear

The paper investigates the buckling mode of failure of long interfacial cracks subjected to shear loading. A criterion which describes the transition from fracture to buckling instability failure modes is derived.     

Modeling the Response of 3D Textile Composites under Compressive Loads to Predict Compressive Strength

The compression response of 3D woven textile composites (3DWC) that consist of glass fiber tows and a polymer matrix material is studied using a combination of experiments and finite element based analyses. A previous study reported by the authors consisted of an experimental investigation of 3DWC under high strain rate loading, Pankow, Salvi, Waas, Yen, and Ghiorse (2011). Those experimental results were explained by using the finite element method to analyze the high rate deformation response of representative volume elements (RVEs) of the 3DWC, Pankow, Waas, Yen, and Ghiorse (2012). In this paper, the same modeling strategy is used to examine the quasi-static, compressive deformation response of 3DWC. The effect of using different numbers of the textile repeat unit architecture in the RVE, on the predicted compression strength, is examined. The transitions in failure modes that are seen in experiments are seen to be captured by the model that is presented here.     

GFRP约束微珠泡沫柱准静态受压性能

本研究对2根微珠泡沫柱及5根玻璃纤维复合材料(GFRP)约束微珠泡沫组合柱开展准静态轴压试验,探讨了GFRP层数、横向纤维与纵向纤维比例、泡沫密度等参数对组合柱极限承载力和吸能效应的影响,并与静态试验结果进行对比,研究不同加载速率对构件受压性能的影响规律.结果表明:准静态压缩作用下GFRP层数和泡沫密度的增加均提高了构...     

热残余应力对C/SiC复合材料界面剪切强度影响的有限元分析

根据C/SiC复合材料的属性,建立单纤维顶出的二维轴对称模型,采用有限元法对C/SiC复合材料的界面剪切强度进行数值研究,分析中考虑材料制备过程中的残余应力对界面剪切强度的影响,在细观力学层面上系统分析纤维顶出过程的界面剪应力及其相关影响因素。分析得出,残余应力会对界面造成损伤,降低界面脱粘载荷。材料的界面承受能力与热膨胀系数呈正相关,与固化温度呈负相关。     

ECAPT过程中载荷变化规律的数值模拟

为了掌握纯铝在ECAPT过程中的力学变化规律,利用刚塑性有限元技术对纯铝1100的ECAPT变形行为进行数值模拟,重点分析了载荷在挤压过程中的变化规律及产生变化的原因。结果表明:ECAPT过程大致分为载荷骤升、2次小幅度升高和载荷下降4个阶段;载荷峰值随着摩擦因数的增大迅速增大,应采取有效的润滑措施减小摩擦从而降低载荷峰值,提高模具寿命;随着摩擦因数的增大,载荷在达到各阶段峰值后下降趋势越来越明显。     

粘接界面泡沫铝夹芯板的三点弯曲失效数值模拟

对粘接界面泡沫铝夹芯板三点弯曲载荷下的变形特性进行了实验和数值模拟方面的研究。基于有限元软件ABAQUS建立了泡沫铝夹芯板的三维有限元模型,应用内聚力模型对三点弯曲过程中典型的破坏模式——面板与芯层的界面脱粘给予了合理的模拟,模拟所得的结果与实验结果比较吻合。并在此基础上分析了面板和芯层厚度对夹芯板承载能力和吸收能量能力的影响。结果表明,增加芯层的厚度能够更大程度上提高泡沫铝夹芯板的承载能力和吸收能量的能力。     

Numerical Simulation of Detonation and Multi-Material Interface Tracking

In this paper, we report high resolution simulations using a fifth-order weighted essentially non-oscillatory (WENO) scheme with a third-order TVD Runge-Kutta time stepping method to examine the features of the detonation for gas and condensed explosives. A two-stage chemical reaction model and an ignition and growth model are employed to describe the chemical reaction process for gas and condensed explosives. Based on the Steger-Warming vector flux splitting method, a splitting method is employed when the vector flux does not satisfy the homogeneity property for simulating detonation wave propagation for condensed explosives. The sensibility of flame propagation process and explosion overpressure on obstacles is also numerically performed. Meanwhile, an interface tracking algorithm is developed and coupled with a two-dimensional multi-material code indigenously for simulating the response of materials to impact, shocks and detonations. Numerical experiments are performed to investigate the influences of liner cone angle, wall thickness and initiation mode on shaped charge jet formation process. The results of calculations show good agreement with experimental results, and indicate that the interface treatment algorithm is especially suitable for simulating explosive loading on thin-wall structure such as shape charges.     

Estimate Interface Shear Stress of Woven Ceramic Matrix Composites from Hysteresis Loops

An approach to estimate the fiber/matrix interface shear stress of woven ceramic matrix composites during fatigue loading has been developed in this paper. Based on the analysis of the microstructure, the woven ceramic matrix composites were divided into four elements of 0^o warp yarns, 90^o weft yarns, matrix outside of the yarns and the open porosity. When matrix cracking and fiber/matrix interface debonding occur upon first loading to the peak stress, it is assumed that fiber slipping relative to matrix in the interface debonded region of the 0^o warp yarns is the mainly reason for the occurrence of the hysteresis loops of woven ceramic matrix composiets during unloading and subsequent reloading. The unloading interface reverse slip length and reloading interface new slip length are determined by the interface slip mechanisms. The hysteresis loops of three different cases have been derived. The hysteresis loss energy for the strain energy lost per volume during corresponding cycle is formulated in terms of the fiber/matrix interface shear stress. By comparing the experimental hysteresis loss energy with the computational values, the fiber/matrix interface shear stress of woven ceramic matrix composites corresponding to different cycles can then be derived. The theoretical results have been compared with experimental data of two different woven ceramic composites.     

A Numerical Modeling of Failure Mechanism for SiC Particle Reinforced Metal-Metrix Composites

The present work is to investigate the failure mechanisms in the deformation of silicon carbide (SiC) particle reinforced aluminum Metal Matrix Composites (MMCs). To better deal with crack growth, a new numerical approach: the MLPG-Eshelby Method is used. This approach is based on the meshless local weak-forms of the Noether/Eshelby Energy Conservation Laws and it achieves a faster convergent rate and is of good accuracy. In addition, it is much easier for this method to allow material to separate in the material fracture processes, comparing to the conventional popular FEM based method. Based on a statistical method and physical observations, the hard SiC particles are distributed randomly over the cubic space of the matrix. Four failure mechanisms are found to be critical to the accurate prediction of the mechanical properties of MMCs: a) the failure inside the matrix; b) the failure between the interface of aluminum matrix and the SiC particles; c) the fracture of the SiC particles; and d) the separation of two neighboring SiC particles. Plastic work is used as a failure criterion. It is found that the current approach can accurately predict the mechanical behavior of MMCs, including Young's moduls, stress strain curve, tensile strength, and limit strain. When the SiC volume fraction is low, the interface failure is more important; while for the case of high SiC volume fraction, all the four failure mechanisms work together to affect the mechanical property for the composite structure.     

帽型试样的绝热剪切数值模拟与温度场研究

通过选择恰当的模型和科学的空间离散化,对SHPB加载过程进行了2D数值模拟,数值重现了帽型试样高应变条件下的绝热剪切变形历程.基于应力塌陷绝热剪切形成判据分析了材料绝热剪切变形规律;利用模拟结果的应力一时间、应变一时间曲线进行了温度场的计算,确定了剪切带的类型,计算结果与实验结果吻合.     

The Influence of Interface Structure and Composition on the Response of Single-Fiber SiC/Ti-6Al-4V Composites to Transverse Tension

The cruciform specimen geometry has recently been established to investigate the transverse tensile behavior of single-fiber or multiple-fiber titanium matrix composites; however, the results on only relatively few commercially-available fibers have been reported to date. The present study reports the transverse behavior of a range of SiC fibers prepared by different manufacturers and with different surface coatings. The mechanical response of the composite and the damage present at the interfacial region have been documented. In general, the stress–strain behavior was found to be sensitive to the chemical and structural nature of the fiber–matrix interfacial region. Fibers with carbon-rich coatings were found to have a range of interfacial strengths depending on the structure of the interface layers, while uncoated fiber interfaces have a high strength. This study demonstrates the value of the single-fiber transverse cruciform test for quantitatively comparing the behavior of various fibers and coatings, and shows that it can be useful for coating development studies.     

反向挤压7075/SiCp复合材料中SiC颗粒 断裂失效的数值模拟研究

应用Deform-2D有限元软件,在挤压温度为300~450 ℃,挤压比为4~64,挤压速度为2~30 mm/s时,对喷射沉积7075/SiCp复合材料反向挤压过程中,SiC颗粒的转动与断裂失效进行了数值模拟。研究结果表明：在反向挤压过程中,SiC颗粒的转动是由基体合金的不均匀流动造成的;离中心轴线越远,流动不均匀性及SiC颗粒的转动倾向越大;基体的流动不均匀程度随挤压速度的增大和挤压比的升高而增大。在反向挤压过程中,SiC颗粒随基体运动不协调时,在较大应力作用下易发生断裂失效,且坯料外侧断裂失效分数大;当挤压比为4~25,挤压温度为400~450 ℃时,SiC颗粒断裂失效分数较小。当挤压比为16时,不同挤压温度下合理的挤压速度范围应控制在t=400 ℃、v<30 mm/s,t=425 ℃、v<20 mm/s,t=450 ℃、v<5 mm/s。     

Fracture Surface Morphology of Delamination Failure of Polymer Fiber Composites Under Different Failure Modes

The delamination of fiber reinforced polymer composites is one of the most common failures encountered in industrial applications. The most unique macroscopic and microscopic fracture surface features of the delaminations under different failure modes are of interests not only for practical failure analysis investigations but also it helps to reveal the physics behind the delamination phenomenon. In this work, fracture surface morphology of the delaminated carbon fiber polymer composites under mode I, mode II, and mixed-mode I/II loading conditions is investigated mainly with scanning electron microscopy. The unique fractographic features are identified and discussed. The results on ductile and brittle matrix composites have shown their own features, and most important of all the alignment angle of fibrils in the resin-rich ductile matrix could be correlated with the delamination mode.     

重型夹芯纸板侧压强度数值仿真分析

目的对典型重型夹芯纸板结构的侧向抗压强度进行精确的对比分析,为合理应用夹芯纸板提供依据。方法利用有限元软件Ansys分别建立蜂窝纸板及AAB型重型瓦楞纸板大尺寸规格试样的数值模型,并基于屈曲分析准则对重型瓦楞纸板纵向及蜂窝纸板2个侧向抗压强度进行研究。结果在选材、用纸量及试样尺寸规格大小相同的情况下,蜂窝纸板2个方向的侧压强度均高于AAB型重型瓦楞纸板的边压强度。结论仿真分析对蜂窝纸板和AAB型重型瓦楞纸板的选材、材料用量及尺寸规格进行了严格控制,消除了重型瓦楞纸板和蜂窝纸板的材质、耗纸量、试样尺寸规格、试样加工工艺及环境条件等因素的变化对分析结果产生的影响。     

压缩载荷下碳/环氧复合材料的动力学响应行为

以铺层顺序为[45/0/-45/00-45/90/0]s的新型碳纤维增强改性环氧树脂复合材料为研究对象,采用分离式Hopkinson(SHPB)压杆装置为加载手段,在高速冲击载荷条件下,对复合材料层合板在厚度方向和平面内纵向的动态压缩性能进行实验研究,分别得到在四种不同应变率下的应力一应变关系;并借助SEM对复合材料断口损伤形貌进行表征.结果表明:在高应变率条件下,层合板厚度方向的动态压缩强度及失效应变明显大于平面内加载方向;基体开裂、分层及剪切断裂是复合材料在动态压缩条件下的主要损伤及断裂模式.     

An Approach to Estimate Interface Shear Stress of Ceramic Matrix Composites from Hysteresis Loops

An approach to estimate interface shear stress of ceramic matrix composites during fatigue loading has been developed in this paper. By adopting a shear-lag model which includes the matrix shear deformation in the bonded region and friction in the debonded region, the matrix crack space and interface debonding length are obtained by matrix statistical cracking model and fracture mechanics interface debonding criterion. Based on the damage mechanisms of fiber sliding relative to matrix in the interface debonded region upon unloading and subsequent reloading, the unloading counter slip length and reloading new slip length are determined by the fracture mechanics method. The hysteresis loops of four different cases have been derived. The hysteresis loss energy for the strain energy lost per volume during corresponding cycle is formulated in terms of interface shear stress. By comparing the experimental hysteresis loss energy with computational values, the interface shear stress corresponding to different cycles can then be derived. The theoretical results have been compared with experimental data of three different ceramic composites.