含分层损伤复合材料（CFRP）层合板结构屈曲和后屈曲力学行为研究

发布时间：2018-07-14 11:01

【摘要】：碳纤维增强复合材料(Carbon Fiber Reinforced Plastic,CFRP)具有轻质高强、耐疲劳性好、有效吸收冲击载荷等优点,广泛应用于航空航天领域。由于CFRP层合板结构在装配、修理过程中的工器具跌落碰撞,在使用过程中的外物冲击,使得层合板表面产生不易观察但在其内部大量存在的分层损伤。这种分层损伤出现概率较高,使结构在低载荷下发生屈曲失稳和分层损伤扩展,同时还可能引起其他形式的破坏,致使结构提前发生整体失稳和破坏。由于分层损伤是导致复合材料层合板结构提前失稳破坏的一种常见破坏形式,本文着重研究了含分层损伤CFRP复合材料层合板结构屈曲及后屈曲力学行为,以及伴随屈曲行为产生的CFRP结构表面损伤的损伤机理及其损伤扩展规律。作者分别采用解析方法、数值模拟法和数字图像相关实验方法对在四点弯曲作用下含分层损伤CFRP层合板结构的分层屈曲力学行为以及由分层屈曲进一步驱动的层间分层损伤扩展问题进行了详细的研究,主要包括以下内容:首先,根据分层屈曲的屈曲形貌,构建了反映含分层层合板结构在弯曲载荷作用下屈曲力学行为的理论简化模型,并推导出含分层损伤CFRP层合板结构屈曲临界载荷的计算公式,该公式充分考虑了复合材料的各向异性和层合属性。其次,本文研究了含冲击损伤和人造缺陷的CFRP层合板的屈曲和后屈曲力学行为。根据分层损伤分布位置以及屈曲形貌的特征,提出了用理想人工缺陷代替冲击分层损伤的创新思路,避免了冲击实验的不确定性对含冲击损伤CFRP层合板结构屈曲行为变化规律的影响。采用图像分解法,研究了二者在四点弯曲作用下的屈曲及后屈曲力学行为,证明了含人造缺陷CFRP层合板结构可替代含冲击分层损伤CFRP层合板结构用于含分层层合板的屈曲和后屈曲力学行为的研究。并研究了分层损伤几何因子对CFRP层合板结构屈曲后屈曲力学行为影响的敏感度,发现分层面积大于某一阀值时,层合板结构发生以分层屈曲为主导的破坏形式,且随着分层面积的增加分层屈曲临界载荷值降低;发现分层形状对分层屈曲形貌和分层扩展路径有着重要的影响;发现分层方向对屈曲形貌和分层扩展路径无明显影响,且对临界屈曲载荷值的影响不大。最后,本文采用数值法研究含分层损伤CFRP层合板结构的屈曲和后屈曲行为,构建了反映含分层损伤CFRP层合板结构由初始加载到整个结构最终破坏过程中分层扩展和复合材料本身损伤等现象的有限元模型。基于Dávila and Camanho准则,建立了单层板损伤判定准则和复合材料损伤退化的本构方程。并通过图像分解法,证明了所构建的有限元数值模型可以准确的反映分层屈曲形貌、分层损伤扩展路径以及复合材料本身损伤的破坏模式和位置。
[Abstract]:Carbon Fiber reinforced Plastics (CFRP) has been widely used in aerospace industry due to its advantages of light and high strength, good fatigue resistance, effective absorption of impact load, and so on. Due to the falling impact of the workmanship during the assembly and repair of CFRP laminates and the impact of external objects during the use of CFRP laminates, the laminated plates have a lot of delamination damage which is not easy to observe but exists in the inner part of the laminates. This kind of delamination damage has a high probability of appearing, which causes buckling instability and delamination damage expansion of the structure under low load, and may also cause other forms of damage, resulting in the overall instability and failure of the structure ahead of time. As delamination damage is a common failure form of composite laminated plate structures, the buckling and post-buckling behaviors of CFRP composite laminates with delamination damage are studied in this paper. And the damage mechanism and damage propagation law of CFRP structure caused by buckling behavior. The authors adopted analytical methods, The delamination buckling behavior of CFRP laminated structures with delamination damage and the delamination damage propagation problem driven by delamination buckling are studied in detail by numerical simulation and digital image correlation experiments. The main contents are as follows: firstly, according to the buckling morphology of layered buckling, a theoretical simplified model is constructed to reflect the buckling behavior of laminated structures under bending loads. A formula for calculating the critical buckling load of CFRP laminated plates with delamination damage is derived, which takes fully into account the anisotropy and lamination properties of composite materials. Secondly, the buckling and post-buckling behaviors of CFRP laminated plates with impact damage and artificial defects are studied. According to the location of delamination damage distribution and the characteristics of buckling morphology, an innovative idea of replacing impact delamination damage with ideal artificial defects is put forward. The influence of the uncertainty of impact test on the buckling behavior of CFRP laminates with impact damage is avoided. The buckling and postbuckling mechanical behaviors of the two were studied by image decomposition method under the action of four points bending. It is proved that CFRP laminates with artificial defects can be used to study the buckling and post-buckling behavior of laminated CFRP laminates with impact delamination instead of those with impact delamination. The sensitivity of geometric factors of delamination damage to the post-buckling mechanical behavior of CFRP laminates is studied. It is found that when the delamination area is larger than a certain threshold, the delamination buckling is the dominant failure mode. With the increase of delamination area, the critical load value of delamination buckling decreases, the delamination shape has an important influence on the delamination buckling morphology and delamination extension path, and the delamination direction has no obvious effect on the delamination morphology and delamination extension path. And the critical buckling load has little effect. Finally, the buckling and post-buckling behaviors of CFRP laminated structures with delamination damage are studied by numerical method. The finite element model of laminated CFRP structures with delamination damage from initial loading to the ultimate failure process of the whole structure and the damage of the composite material is established. Based on the D 谩 vila and Camanho criterion, the damage criterion of single layer plate and the constitutive equation of damage degradation of composite materials are established. Through the image decomposition method, it is proved that the finite element numerical model can accurately reflect the delamination buckling morphology, delamination damage propagation path and damage mode and location of composite material itself.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB33

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