Fracture Problems in Nonhomogeneous Material Systems: Tailored Materials, Graded Interfacial Zones and Bonded Layers

研究功能梯度材料、材料界面和层状正交各向异性材料的断裂力学。该计划的重点将放在新材料系统中的断裂相关问题上，其中强度，韧性，疲劳和腐蚀性能以及残余应力可以通过控制加工过程中的成分剖面来控制。功能梯度材料本质上是精细复合材料或纳米复合材料，它们是通过对组成材料的体积分数通过厚度进行分级来实现材料所需的热机械性能变化而合成的。这种通过厚度逐渐改变材料成分来分级界面区域和涂层性能的新工艺具有一些非常重要的优点。首先，该工艺平滑了应力分布，并大大降低了应力集中因素，从而降低了由于残余应力和热应力而导致失效的可能性。其次，在大多数情况下，它提高了粘合强度。新工艺的第三个优点是提高了材料的断裂韧性和疲劳、腐蚀裂纹扩展参数。第二部分研究了材料的正交异性，特别是粘结层界面区的结构和厚度对分层和断裂穿透问题中裂纹驱动力的影响。

Fracture mechanics of functionally gradient materials and material interfaces and layered orthotropic materials will be studies. The emphases in the program will be on the fracture related issues in new material systems in which strength, toughness, fatigue and corrosion properties along with the residual stresses may be controlled by controlling the composition profile during processing. Functionally gradient materials are essentially fine composites or nano composites which are synthesized to achieve a desired thermomechanical property variation in the material by grading the volume fractions of the constituent materials through the thickness. This new process of grading the properties of the interfacial regions and coatings by gradually varying the material composition through the thickness appears to have some very important advantages. First, the process smooths the stress distribution and drastically reduces the stress concentration factors thereby reducing the likelihood of failure due to residual and thermal stresses. Secondly, it improves the bonding strength, in most cases quite considerably. The third advantage of the new technique is the improvement one obtains in fracture toughness and fatigue and corrosion crack growth parameters of the material. The second part of the program deals with the investigation of the influence of material orthotropy, particularly the structure and thickness of interfacial zones in bonded layers on the crack driving force in delamination and fracture penetration problems.