Novel Designs for Interfacial Mechanical Property Enhancement and Characterization of Dissimilar Materials and Structures

摘要现代工程系统越来越多地由结合两种或两种以上材料以提高性能的材料组成。由于材料性能不匹配，破坏通常发生在材料界面或接缝处。因此，从纳米尺度到宏观尺度，准确测量不同材料界面处的界面强度对于材料开发和此类新材料的工程应用至关重要。然而，目前的界面力学测量方法由于双材料界面处特殊的“应力奇异性问题”导致数据无效。为了准确测量不同材料的内在界面力学性能，本项目通过综合分析、数值和实验研究提出了新的试样设计。初步设计的灵感来自树木的形状和力学，旨在为大多数工程材料组合在双材料角处获得最小的应力奇点。新设计不仅提高了异种材料节点的荷载传递能力，而且给出了更合理的界面强度评价。与具有严重自由边缘应力奇点的传统对接试件相比，凸型聚碳酸酯-铝和pmma -铝对接试件的静态极限拉伸载荷提高了81%，而总材料体积至少减小了15%。因此，首席研究员和他的研究小组成员计划为界面力学性能的增强和评估制定一个更广泛的研究计划。具体而言，目标是：1)测量新型界面节点在动荷载作用下的荷载传递能力的改善程度；2)进行轴对称试件设计，进行静态界面拉伸测量。所提出的活动的智力价值在于为材料力学中的一个长期问题提出了一个新的解决方案。基于树形的力学原理被用于设计新的关节试件。该项目将提供一个受生物学启发的设计的成功例子，以增进科学和技术的了解，即大自然可以为某些困难的技术问题提供有效的解决办法。由于异种材料界面/接头和失效被广泛应用于航空航天、汽车、生物医学、民用、国防、电子、材料和机械工程等领域，本研究的影响将是非常广泛的。因此，本项目的研究成果将对信息技术、纳米技术、材料与制造、民用基础设施等领域非常有益。其他更广泛的影响包括为女博士生提供支持，并与国家实验室建立研究伙伴关系。

Novel Designs for Interfacial Mechanical Property Enhancementand Characterization of Dissimilar Materials and StructuresAbstract Modern engineering systems are increasingly made of materials that combine two or more materials for improved performance. Generally, failure occurs at the material interfaces or joints due to material property mismatch. Therefore, accurate measurement of interfacial strength at the interface between dissimilar materials is critical for material development and engineering applications of such new materials, ranging from nano-scale to macro-scale. However, current methods for interfacial mechanical measurement lead to invalid data because of a special "stress singularity problem" at the bi-material interface. In order to accurately measure the intrinsic interfacial mechanical properties of dissimilar materials, this project presents novel specimen designs through an integrated analytical, numerical and experimental investigation. A preliminary design, inspired by the shape and mechanics of trees, was developed to obtain the least stress singularities at bi-material corners for most engineering material combinations. The new design not only improves the load transfer capacity of dissimilar material joints, but also yields more reasonable interfacial strength evaluation. For convex polycarbonate-aluminum and PMMA-aluminum joints, the static ultimate tensile load increased up to 81% while the total material volume reduced by at least 15% over that of traditional butt-joint specimens with severe free-edge stress singularities. Hence, the principal investigator and his research group members plan to develop a broader research program for interfacial mechanical property enhancement and evaluation. In particular, the objectives are to: 1) measure the improvement of load transfer capability of the novel interfacial joint subjected to dynamic loading 2) conduct axisymmetric specimen designs for static interfacial tensile measurements. The intellectual merit of the proposed activity consists in presenting a new solution to a long-term problem in mechanics of materials. The mechanics principles underlying tree shapes are used to design novel joint specimens. The project will provide a successful example of biologically inspired design to enhance scientific and technological understanding, i.e., nature may provide efficient solutions for certain difficult technological problems. The impact of the proposed research will be very broad since dissimilar material interfaces/joints and failure are widely employed in aerospace, automobile, biomedical, civil, defense, electronic, material and mechanical engineering fields. Therefore, the research results from this project will be very beneficial to information technology, nano technology, materials and manufacturing and civil infrastructure. Other broader impacts include providing support for a female doctoral student and developing research partnership with national laboratories.