US-Turkey Cooperative Research: Three-Dimensional Effects in the Fracture of Functionally Graded Materials

项目描述：该项目支持伊利诺伊州厄巴纳市伊利诺伊大学航空航天系John M. Lambros博士和土耳其伊斯坦布尔Bogazici大学机械工程系Gunay Anlas博士之间的合作研究。功能梯度材料（fgm）是一种具有连续空间变化特性的材料，通常由金属/陶瓷组合组成，其相对体积分数连续变化。fgm是同时提供结构支撑和热、冲击或磨损保护的候选材料。到目前为止，它们的广泛应用尚未实现，部分原因是缺乏对这种连续非均匀材料的力学理解，特别是它们的断裂响应。虽然文献中存在一些解析和数值结果，但这些结果主要是二维的，并且通常涉及对称（即I型）条件。存在的实验研究要少得多，但理论和实验之间的关系充其量是脆弱的，因为理论结果的有效性在实验情况下通常是渐进的，是不清楚的。重点将放在FGM断裂的三个研究较少的方面：(i) FGM中裂纹尖端的三维应力的发展取决于属性梯度，（ii）实际情况下裂纹FGM渐近场的有效性程度，以及（iii）近尖端混合模式条件（无论是来自负载还是材料梯度不对称）对上述两者的影响。二（2D）和三（3D）维有限元模拟将对裂纹梯度板的物理相关几何形状（三点和四点弯曲，边缘裂纹，紧致张力）进行。结果将揭示尖端前的穿透厚度应力的发展，并将为渐近理论的有效区域提供一个内边界。结果将通过与Lambros博士开发的基于聚合物的女性生殖器切割模型的实验进行比较来验证。该研究将有助于扩展对女性生殖器官断裂过程的基本理解，特别是关于三维应力发展，渐近场的优势和近尖端条件的混合模式。Alnas博士的专长是复合材料，界面和梯度材料断裂的理论和数值分析领域。大多数2D和3D模拟将在土耳其使用ABAQUS作为主要平台进行。其他的实验，以及一些与之直接相关的模拟，将在UIUC进行。一个短期的计划之旅和每年至少两次会议将轮流在美国和土耳其举行。Drs。兰布罗斯和安拉斯将由各自的研究生陪同。Bogazici大学的研究生将有机会在UIUC的实验装置中工作。将在土耳其和UIUC开设涉及女性生殖器切割的高级课程。UIUC的美国研究人员和研究生将有机会与他们的土耳其伙伴合作。

0322271 LambrosDescription: This project supports a cooperative research between Dr. John M. Lambros, Department of Aeronautics and Astronautics, University of Illinois, Urbana, Illinois and Dr. Gunay Anlas, Department of Mechanical Engineering, Bogazici University, Istanbul, Turkey. Functionally Graded Materials (FGMs) are materials possessing a continuous spatial variation of properties and typically are composed of a metal/ceramic combination in which their relative volume fractions are continuously varied. FGMs are candidate materials for simultaneously providing both structural support and thermal, impact or wear protection. Their widespread use has not materialized thus far, partially because of a lack of understanding of the mechanics of such continuously inhomogeneous materials, and in particular their fracture response. Although several analytical and numerical results exist in the literature, these are primarily two-dimensional and most often involve symmetric (i.e. mode I) conditions. Far fewer experimental studies exist, but the relation between theory and experiment is tenuous at best since the validity of theoretical results, usually asymptotic in nature, in experimental situations is not clear. Emphasis will be placed on three less studied aspects of the fracture of FGMs: (i) the development of three dimensional stresses at a crack tip in an FGM as dependent on the property gradient, (ii) the extent of validity of asymptotic fields in actual situations of cracked FGMs, and (iii) the influence of near tip mixed mode conditions (whether from loading or material gradient asymmetry) on both of the above. Two (2D) and three (3D) dimensional finite element simulations will be performed on physically relevant geometries (three and four point bend, edge crack, compact tension) of cracked graded plates. The results will shed light on the development of through thickness stresses ahead of the tip and will provide an inner boundary for the region of validity of the asymptotic theory. The results will be verified by comparison with experiments on the polymer-based model FGM that Dr. Lambros has developed. The research will help extend fundamental understanding of the processes involved in the fracture of FGMs, especially in regard to three dimensional stress development, dominance of asymptotic fields and mixed mode near tip conditions. Scope: Dr. Alnas' expertise is in the areas of theoretical and numerical analysis of fracture of composites, interfaces and graded materials. Most of the 2D and 3D simulations will be performed in Turkey using ABAQUS as the main platform. Additional experiments, as well as some simulations directly linked to them, will be performed at UIUC. A short planning trip and at least two meetings a year will be held alternately in the United States and Turkey. Drs. Lambros and Anlas will be accompanied by their respective graduate students. Bogazici University graduate students will have the opportunity to work with the experimental set-ups at UIUC. Advanced courses involving FGMs will be developed in Turkey and UIUC. American researchers and graduate students at UIUC will have a chance to cooperate with their Turkish partners.