Damage analysis of fabric-reinforced polymer composites under superimposed in-plane/out-of-plane stress conditions

该项目的目标是开发适当的测试方法，用于在叠加面内/面外应力状态下对纤维增强聚合物（FRP）进行强度分析，作为高应力轻质结构可靠设计的基础。应力的叠加状态是FRP构件（如风扇叶片或异形驱动轴）的载荷施加区域的特征，并且它们主要由面内拉伸应力或剪切应力和贯穿厚度的压应力组成。目前，对于载荷施加区域的尺寸，没有可靠的材料参数，也没有考虑应力相互作用和特定织物结构对材料失效的影响的合适的失效标准。因此，调查的重点材料是具有不同配置的平纹织物增强的碳纤维增强热固性材料。主要目标是实验和数值研究的影响，对材料强度的特征织物结构与纤维起伏伴随着联锁的相邻fabric layers.Appropriate标本设计诱导面内拉伸/全厚度压缩或剪切/全厚度压缩应力状态，将分别细化和开发，通过使用有限元法（FEM）。主要的重点将是一方面选择合适的几何参数，以减少不必要的应力峰值，另一方面减少摩擦的影响，有关的压缩负荷转移面积在压缩模具。实验测试所需的样品具有足够大的厚度和可再现的质量。此类样本的制造将采用树脂传递模塑工艺进行，该工艺适用于温度控制和固化。之后，将通过计算机断层扫描（CT）分析和记录压实和固结层压板内的真实的织物结构。实验材料测试与不同的负载路径进行使用伺服液压平面双轴试验机与四个驱动器。为了描述实验确定的断裂现象和断裂过程，将通过显微镜分析和表征试样的断裂表面。除了实验测试外，还将对具有织物增强的代表性体积单元进行有限元虚拟测试。为此，从CT分析收集的数据有关的压实织物架构内实施的有限元model.Based上的失败时序和在组合应力状态下的断裂模式的实验和数值结果，合适的方法来描述材料故障，特别是考虑到特定的织物架构将开发。

The objective of the project is the development of appropriate test methods for strength analysis of fabric-reinforced polymers (FRP) under superimposed in-plane/out-of-plane-stress states as basis for the reliable design of highly stressed lightweight structures. Superimposed states of stress are characteristic for load application areas of FRP components such as fan blades or profiled drive shafts, and they mainly consist of in-plane tension or shear stresses and through-thickness compressive stresses. Currently, for dimensioning of load application areas, there are no reliable material parameters and no suitable failure criteria which take account of stress interactions and of the influence of the specific fabric architecture to material failure. Hence, the focused materials of the investigations are carbon-fibre-reinforced thermosets with different configurations of the plain-weave fabric reinforcement. Main objectives are experimental and numerical studies on the impact on material strengths of the characteristic fabric architecture with the fibre undulation accompanied by the interlocking of adjacent fabric layers.Appropriate specimen designs for inducing in-plane tension/through-thickness compression or shear/through-thickness compression stress states will be refined and developed, respectively, by using finite element method (FEM). Main focus will be on the one hand on the selection of suitable geometric parameters to reduce unwanted stress peakes and on the other hand on diminishing frictional influences concerning the compression load transfer area at the compression dies. Necessary for the experimental tests are specimens with a sufficiently large thickness and reproducible quality. Manufacturing of such specimens will be performed with a resin transfer molding process, which is adapted regarding temperature control and curing. After that, the real fabric architecture within the compacted and consolidated laminates will be analysed and documented by means of computed tomography (CT). Experimental material tests with different load paths are performed using a servohydraulic planar biaxial testing machine with four actuators. To describe the experimentally determined fracture phenomena and the fracture processes, the fracture surfaces of the specimens will be analysed and characterised by microscopy. In addition to the experimental tests, virtual tests with FEM will be carried out on representative volume elements with fabric reinforcements. For that, the collected data from CT analyses concerning the compacted fabric architecture are implemented within the finite element model.Based on the experimental and numerical outcomes on the failure chronology and the fracture modes in the combined stress states, suitable approaches for the description of material failure especially considering the specific fabric architecture will be developed.