【作者】 刘刚；

【导师】 果立成；

【作者基本信息】 哈尔滨工业大学 ， 力学， 2019， 博士

【摘要】 作为一种典型的新型复合材料,三维机织复合材料由于其良好的整体性、沿厚度方向出色的力学性能以及较强的抗冲击性能而被广泛应用于航空航天器、民用建筑、体育装备、医学设备等领域。然而,三维机织复合材料的非均匀性、各向异性以及内部存在的裂纹、空隙等,使得这种材料的损伤演化规律十分复杂,对其力学性能及渐进损伤机理的研究成为一个巨大挑战。为了对三维机织复合材料的力学性能及渐进损伤机理有充分了解和认识,本文采用实验和数值模拟方法,对三维机织复合材料的拉伸和剪切刚度、强度以及渐进损伤过程与失效机理进行了研究,并提出了研究三维机织复合材料拉伸和剪切失效行为的方法。首先,详细介绍并分析了三维机织复合材料的国内外研究进展,就三维机织复合材料的细观几何结构、准静态实验和渐进损伤失效模型等方面展开综述。重点回顾了三维机织复合材料准静态单轴拉伸、沿±45°纤维方向拉伸和剪切载荷下刚度、强度性能的实验和数值仿真研究进展。明确了本论文的研究目的与意义。其次,开展了三维机织复合材料的准静态单轴拉伸和沿±45°纤维方向拉伸实验研究。采用三维数字图像(3D DIC)技术测试了三维机织复合材料的刚度、强度性能,记录了材料的力学响应及破坏过程。通过高速相机和光学显微镜观测了试件断裂过程与失效后的宏细观断口形貌,详细分析并确定了三维机织复合材料在单轴拉伸和沿±45°纤维方向拉伸载荷下的失效模式和破坏机理。同时,提出了一种针对三维机织复合材料剪切性能的试验方法,开展了三维机织复合材料的静态剪切实验研究。分别采用V型缺口梁剪切实验方法和短梁剪切实验方法,研究了三维机织复合材料在面内和层间剪切载荷下刚度、强度性能,获取了三维机织复合材料的非线性力学响应及破坏过程。通过观测试件失效后的宏细观断口形貌,重点分析并确定了三维机织复合材料在剪切载荷下的失效模式和破坏机理。并根据实验需要设计出了针对三维机织复合材料不同厚度的V型缺口梁试件的剪切实验卡具。根据三维机织复合材料细观结构确定了接近真实结构的细观单胞模型。在实验分析基础上,结合多相有限元法,建立了一种适用于三维机织复合材料的单轴拉伸渐进失效模型。该模型采用改进的Puck准则和抛物面准则,在纤维束和基体的细观尺度上考虑了纤维束的断裂、纤维束内的纤维间开裂以及基体断裂。应用ABAQUS软件平台结合多相有限元法编写了VUMAT材料用户子程序,预报了三维机织复合材料在准静态单轴拉伸载荷下的刚度、强度性能,以及该材料的单轴拉伸渐进损伤和失效过程,并将数值模拟结果与实验测试结果进行了对比。最后,针对三维机织复合材料在剪切载荷下出现的大变形问题,提出了一种适用于三维机织复合材料的剪切非线性渐进失效模型。该模型充分考虑了引起材料剪切非线性的原因,认为设在剪切载荷作用下,纤维束在产生应变的同时也发生了刚体转动,纤维束的局部坐标系会随着纤维束的偏转而实时变化。因此,在纤维束损伤模型中考虑Green-Naghdi客观率并引入随体坐标系来“扣除”刚体转动的影响。该模型在单轴拉伸渐进损伤模型的基础上,引入最大剪应力准则作为纤维束和基体的剪切失效判据。基于多相有限元法,建立了沿±45°纤维方向拉伸、V型缺口梁剪切和短梁剪切有限元模型。预测出了三维机织复合材料宏观尺度下沿±45°纤维方向拉伸和剪切载荷下的刚度、强度性能,以及该材料的剪切非线性行为及渐进失效过程。将数值模拟结果与实验测试结果进行了对比分析,发现结果吻合良好。本文提出的剪切非线性渐进失效模型能够有效预报三维机织复合材料的剪切非线性渐进损伤规律。更多还原

【Abstract】 As a new type of composite material,three-dimensional(3D)woven composites are widely used in aerospace vehicles,civil arcthecture,sports equipments and medical devices,owing to their mulifarious advantages such as excellent mechanical properties in the thickness direction,perfect impact damage resistance and good integrity.However,the inhomogeneity,anisotropy and unadvoidable cracks or voids within the 3D woven composites result in the complexity of the damage evolvement process of this type of composite.Thus to investigate the mechanical behaviors and damage evolvement mechanisms of 3D woven composites becomes a big chal enge.Aimming to fully understand the mechanical behaviors and progressive damdage mechanisms of this kind of material.This thesis focuses on the tensile and shear stiffness,strength and progressive damage progress as well as failure mechanism of 3D woven composites by using experimental and numerical simulation methods.Methods for studying the tensile and shear failure behavior of three-dimensional woven composites have been proposed.Firstly,the recent research progress of 3D woven compsites including the mesoscale geometric structure,quasi-static experiments and the damage evolvement models are summarized and analyzed.Focuses are on the research development of mechanical properties(stiffness and strength)of 3D woven composites experimenally and numerically under quasi-static uniaxial tensile,tension along ±45° degree fiber direction and shear loads.The purpose and significance of this thesis are clearified.Secondly,experimental investigation on quasi-static uniaxial tensile and along ±45° degree fiber directional tensile behaviors of 3D woven composites are conducted.The stiffness,strengths properties and mechanical response as well as the damage process of this kind of material are measured and tested by 3D Digital Image Correlation(3D DIC)technique.Macro and meso fractographic appearances of failured specimens are observed by a Optical Microscope.The damage modes and failure mechanism of 3D woven composites under quasi-static uniaxial and along ±45° degree fiber directional tensile loads are analyzed and determined in detail.Meanwhile,a test method for shear properties of 3D woven composites is proposed.A modified V-notched beam test fixture suitable for specimens with different thicknesses of 3D woven composites are proposed and designed based on standard apparatus as needed.V-notched beam shear test method and short-beam shear test method are applied respectively to inspect the in-plane and interlaminar shear properties of this material.Nonlinear shear responses and progressive damage process of 3D woven composites are obtained.Macroscopic and mesoscopic fractographic appearances of failured specimens are observed and analyzed at length to obtain the damage modes and failure mechanism of the 3D woven composites.Based on the structure of 3D woven composites,a mesoscale representative volume cell(RVC)model approximates to the real structure is determined.Combined with the multiphase finite element method,a tensile progressive failure model for 3D woven composites is established.The improved Puck criteria and parabolic criterion are adopted in this model with considering the fiber breakage,inter-fiber fracture and matrix crack in the level of the fiber yarn and the matrix.The progressive damage model is implemented into a user-defined material subroutine VUMAT in ABAQUS software to predict the stiffness,strength properties as well as the damage progression and failure process of 3D woven composites under uniaxial tension.Results of numerical simulation and experimental observations are compared and discussed.Finally,a shear nonlinear model for 3D woven composites is proposed to solve the large deformation problem under shear loads.This model fully considers the cause of material shear nonlinearity,and holds the view that the deformation of the fiber bundle generates together with the rigid body rotation under shear load,and the local coordinate system of the fiber bundle will change in real time with the deflection of the fiber bundle.Therefore,the Green-Naghdi objectivity is considered in the bundle damage model and the body-following coordinate system is introduced to "deduct" the effect of rigid body rotation.On the basis of the uniaxial tensile damage model,the Maximum Shear Stress criteria is introduced as the shear failure criteria of the faber yarns and the matrix.Combining with the multiphase finite element method,macroscopic finite element models of along ±45° degree fiber directional tension,Vnotched beam shear and short-beam shear are established with considering the damage progression of the fiber yarn and the matrix in mesoscale level.The stiffness,strengths properties as well as shear damage evolvement and failure progress of 3D woven composites are predicted and analyzed.Numerical and experimental are compared and discussed.Results are in good agreement and the assumption is correct.The shear nonlinear progressive failure model proposed in this thesis can effectively predict the shear nonlinear progressive damage law of 3D woven composites.更多还原