【作者】 王波；

【导师】 矫桂琼；

【作者基本信息】 西北工业大学 ， 固体力学， 2003， 博士

【摘要】 三维编织复合材料是纺织复合材料的一种，三维编织技术可以制造任意复杂形状的构件并且三维编织复合材料具有更高的抗冲击性能和损伤容限，使三维编织复合材料的研究受到高度的关注。三维编织陶瓷基复合材料还具有轻质、耐高温、抗冲刷性能好的特点，是航天、航空发动机以及航天飞机热结构用的理想材料。 对于三维编织复合材料尤其是三维编织陶瓷基复合材料力学行为的认识还只是处于初级阶段，还需要一个逐步认识逐步了解的过程。只有对三维编织复合材料的力学性能进行更深入的研究，才能更好地指导材料的设计和应用。基于这一前提，本文对三维编织复合材料的力学行为进行了研究。本文的研究工作主要包括： 1．通过对三维编织T300／QY9512树脂基复合材料和三维编织C／SiC陶瓷基复合材料的基本力学性能进行试验，系统地研究了这两种材料的基本力学性能、应力—应变曲线特性、损伤演化、破坏特征以及其声发射特性，发现两种复合材料具有相同的拉伸破坏模式和压缩破坏模式，拉伸破坏主要是由纤维束断裂控制，而压缩破坏则主要表现为界面的滑移和纤维束的剪切和压缩的破坏；两种复合材料的四点弯曲模量和强度均高于拉伸值，与单向复合材料明显不同，这是因为编织结构的表面和内部不同，表面的模量和强度均比内部高的缘故。 2．同时我们还发现三维编织C／SiC复合材料具有以下特性：拉伸、压缩的应力—应变曲线具有明显的非线性特性，这种伪塑性特性是因为材料内部有大量的初始孔穴和微裂纹，加载的过程中材料的损伤缓慢发展导致的；声发射数据表明在达到破坏载荷的70％～80％之前，损伤发展较慢，但之后损伤迅速发展，直到破坏；通过加—卸载方法发现在拉伸过程中试件的卸载模量和残余应变和材料的损伤变化有关，提出了用卸载模量和残余应变来表征拉伸试验中损伤演化的非线性方程。另外，通过进一步的分析发现三维编织C／SiC复合材料中纤维束的就位性能远远低于其摘要原位性能，这正是C/siC复合材料的拉伸性能远低于T300/QY9512复合材料的主要原因。3.提出了一种预测三维编织复合材料弹性性能的单胞模型，考虑了各类单 胞中纤维体积含量不同以及表面单胞、角单胞中纤维的弯曲因素，预测 了三维编织T300/QY9512复合材料和三维编织c/siC复合材料的弹性性 能，预测结果与试验结果吻合较好;分析了纤维体积含量和编织角对材 料性能的影响以及试件的形式和尺寸对所测得性能数据的影响;同时还 初步预测了三维编织SIC/siC复合材料的弹性性能;通过进一步的分析， 发现纤维束的各向异性程度和基体、纤维的模量差别对复合材料的主泊 松比vl:影响很大，从理论上解释了三维编织复合材料主泊松比v，:较大 的原因。4.通过试验和有限元分析发现，造成对三点弯曲试验测得的三维编织复合 材料的弯曲模量远低于四点弯曲试验结果的原因:材料的各向异性和泊 松比对于三点弯曲试验的压头和支座处的局部接触变形影响很大.从而 论证了对于三维编织复合材料，测试弯曲模量和强度使用四点弯曲试验 更合适。5.通过对三维编织T300/QY9512复合材料和三维编织C/SIC复合材料的破 坏机理分析，建立了以内部单胞为基础的纤维失效模型和单向复合材料 杆失效模型和相应的应变失效判据:对三维编织T300/Q Y9512复合材料 和三维编织C/SIC复合材料的纵向拉伸和纵向压缩强度进行预测，预测 值与试验值吻合较好:通过分析，还得到了两种三维编织复合材料纵向 拉伸、压缩强度与纤维体积含量和编织角以及试件的形式和尺寸的关 系。更多还原

【Abstract】 Three dimensional braided composite is one kind of textile composite. Structures with complex shape can be manufactured easily by three dimensional braiding technologies. Three dimensional braided composite has higher impact resistance and higher damage tolerance than other textile composite have. That attracts much more attentions. Three dimensional braided ceramic matrix composites (CMC) also have characters such as low density, high temperature resistance and wash out resistance. It is a potential high temperature structure material used in airplane engine and space shuttles.It is a long way to understand mechanical properties of three dimensional braided composite. In order to instruct material design and material application, mechanical properties of three dimensional braided composite should be investigated thoroughly. Based on previous reason, study on mechanical behaviors of three dimensional braided composite was carried out.The following works are included in this thesis.1. Experiments of three dimensional braided T300/QY9512 composite and three dimensional braided C/SiC composite was conducted. And characters of stress-strain curves, damage development, and failure were analyzed. The following properties were found. Tensile and compress failure mode of two composites are the same. Tensile failure was caused by fiber fracture and compress failure was caused by interface failure and fiber bundle’s shear, compress failure. For two materials shear modulus of four point bending are greater than those of tensile test. It is because of the different properties between interior and surface of specimens.2. For three dimensional braided C/SiC composite, stress-strain curve shows a nonlinear character. It induced by initial voids and microcracks in materials. Acoustic Emission data reveal that damage develops slowly before the load reaches its failure value. Damage develops fast after that period. And a nonlinear formula with parameter of unloading modulus and residual strain was brought out to describe damage development in tensile test. It is also found that mechanical properties of C fiber are much less than those of T300 fiber bundles.3. An unit cell model taking account of the difference among unit cells was established to predict elastic properties of three dimensional braided T300/QY9512 composites and three dimensional braided C/SiC composite. Predicted results agreed well with test results. Influence of fiber volume content and braiding angle on specimens’ elastic properties was analyzed. Furthermore the influence of shape and dimension were analyzed. Elastic properties of three dimensional braided SiC/SiC composite were predicted. The conclusion that anisotropy of fiber bundles and modulus difference between matrix and fiber bundles influence specimens’ Poission’s ratio was also concluded.4. Experimental and Finite Element Analysis of three point bending (TPB) test were conducted. It is found material’s anisotropy of anisotropic materials and poission’s ratio of isotropic materials all had influence on contact deformation between specimen and fixture. So it is wise to get flexural properties using four point bending test.5. A failure criterion for three dimensional braided composite was introduced to predict composite’s strength. Prediction values of two braided composites agree well with their experimental values. Influence of fiber volume content and braiding angle on specimens’ strength was analyzed. The influence of shape and dimension were also analyzed更多还原