【作者】 王放；

【导师】 张俊乾；

【作者基本信息】 重庆大学 ， 固体力学， 2004， 硕士

【摘要】 复合材料是指由两种或者两种以上的材料所组成的一种有用的多相材料。作为一种新型材料,它具有传统单一材料所不可能具备的优越性能,以其优良的层间力学性能和较低的制造成本,尤其是在航天和航空领域上具有很好的应用前景。但是,随着复合材料应用的不断增加,复合材料结构的损伤与失效将不可避免。然而与金属材料相比,复合材料具有更为复杂的失效模式,即金属在静态和循环载荷下,断裂大多是单个裂纹或者是几个裂纹的行核和扩展,其失效模式较为单一;而复合材料的断裂则是多种失效形式(比如基体开裂、界面脱粘、纤维断裂和分层等)的起始及其相互之间的作用,并且还依赖于诸多参数,如纤维、树脂的性能、铺层顺序、固化过程、环境温度以及使用条件等。各种损伤都会或多或少地对复合材料面内的力学性能产生不同程度的影响,尤其对强度而言更为明显。为了从理论上研究损伤对复合材料层合板面内力学性能的影响,Zhang建立了等效约束模型(Equivalent Constraint Model,ECM),它能够预测层合板中各个铺层在损伤状态下的应力-应变关系以及刚度与损伤关系。基于ECM模型,建立了复合材料对称层合板的强度分析模型:认为层合板中的主受力层才控制着层合板的最后断裂和寿命的终结,即如果层合板中主受力层的纤维被拉断,则层合板发生失效破坏,层合板将不再承受外加载荷,此时所对应的应力值就为层合板的强度。所以,问题的关键就是通过ECM模型和经典层合板理论得到主受力层的应力场分布。采用这种强度预测模型,分析了不同的材料体系、铺层结构以及加载方式对复合材料对称层合板强度的影响,描绘了层合板在外加载荷条件下的应力-应变曲线和层合板的失效包络面以及不同层合板强度预测值同实验数据的比较。研究结果表明:在各种不同的材料体系、铺层结构和加载方式下,层合板的强度是迥然不同的。通过与实验数据的比较,认为基于ECM模型对包含有多层基体裂纹的复合材料层合板进行相关的强度预测是合理、可行并且有效的,它较好地模拟了铺层开裂和刚度退化的机理。同其它强度计算模型相比,文中所提出的计算复合材料对称层合板强度的方法简洁准确,物理概念清晰,大大简化了计算难度和运算过程。更多还原

【Abstract】 As a new type of materials, composite has an encouraging prospect of practical applications, especially in aeronautic and aerospace industries because of fairly excellent through-thickness properties and lower cost of manufacture, which is a useful multiphase material made of not less than two materials, and at the same time it has unique predominant performance, which other traditional unitary materials don’t possess. With increasing developments of composite materials, however, it is no avoidance that there are some local damages and fractures. Compared with metal materials, the composite materials own more complex fracture models, i.e. the fracture model of the former appears that there are only some isolate cracks, when they are under static or periodic loading, whereas the latter’s rupture is combined with many fracture and their interaction, such as matrix cracking, interface non-glue, fiber failure and fatigue delaminations and so on. Meanwhile, it also depends on other parameters: properties of fiber or resin, lay-up configurations, solidifying temperature, environmental temperature, working conditions. It is no doubt that all damages will more or less affect in-plane mechanical performances of composite materials, in particular ultimate strength. In order to research damages’ effects on in-plane mechanical performances of composite laminates, the equivalent constraint model is established by Zhang to analyze it, which can constitute the relations between stress and strain of the considered lamina under damages and the ones between its stiffness and damages. Based upon the ECM model, a new analytic model for predicting the ultimate strength of general symmetric laminates is studied: it is reckoned that the primary load-bearing lamina controls the final failure of the laminates. Thus composite laminates will be thoroughly destroyed if the fiber of the primary load-bearing lamina is fractured. As a result, the laminates will not bear additional loads any more. Then the current stress corresponds to the ultimate strength of the composite laminates. In that case, the key is to attain the stress field of the primary load-bearing lamina through the ECM and the classical laminate theory.Applying this new model for predicting strength, we investigate different lamina properties, lay-up configurations and combined loading conditions’ effects on the strength and draw stress-strain behaviors and failure envelopes of composite laminates and comparative figures between the predicted values and experimental ones for some <WP=6>arrangements of the laminates. It is obviously clear that different conditions may reach entirely different results. If we compare the predicted values with experimental datum, we can draw a useful conclusion that it is reasonable and effective to predict the strength of the general symmetric laminates containing multi-layer cracks through the ECM model. The model can well stimulate matrix cracking and stiffness degradation of every lamina in laminates. Compared to other computational models for predicting the strength, the method proposed by the author in this paper is more compact and accurate. In addition, its physical concept is legible and it can greatly simplify the difficulty and the process for computing it.更多还原