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

0322271 LambrosDescription：该项目支持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)是一种性能具有连续空间变化的材料，通常由相对体积分数连续变化的金属/陶瓷组合组成。功能梯度材料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，它们的广泛使用还没有实现，部分原因是对这种持续不均匀的材料的力学缺乏了解，特别是对它们的断裂响应缺乏了解。尽管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(即模式I)条件。现有的实验研究要少得多，但理论和实验之间的关系充其量也是微不足道的，因为理论结果在实验情况下的有效性并不清楚，理论结果通常是渐近的。重点讨论功能梯度材料断裂的三个较少研究的方面：(I)功能梯度材料中裂纹尖端三维应力的发展，(Ii)裂纹功能梯度材料实际情况下渐近场的有效范围，以及(Iii)近尖端混合模式条件(无论是来自加载还是材料梯度不对称)对上述两方面的影响。对含裂纹梯度板的物理相关几何形状(三点弯曲、四点弯曲、边裂纹、紧凑拉伸)进行二维和三维有限元模拟。这一结果将有助于揭示尖端前方贯穿厚度应力的发展，并将为渐近理论的有效区域提供一个内部边界。结果将通过与Lambros博士开发的基于聚合物的FGM模型的实验进行比较来验证。这一研究将有助于扩展对功能梯度材料断裂过程的基本理解，特别是关于三维应力发展、渐近场的优势和尖端附近的混合模式条件。工作范围：阿尔纳斯博士的专长是复合材料、界面和分级材料断裂的理论和数值分析。大部分2D和3D模拟将在土耳其进行，使用ABAQUS作为主要平台。UIUC将进行更多的实验，以及一些与之直接相关的模拟实验。一次短暂的计划之旅和每年至少两次会议将在美国和土耳其轮流举行。兰布罗斯博士和安拉斯博士将由他们各自的研究生陪同。Bogazici大学的研究生将有机会与UIUC的实验装置一起工作。将在土耳其和UIUC开发涉及女性生殖器的高级课程。UIUC的美国研究人员和研究生将有机会与他们的土耳其合作伙伴合作。

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.