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

界面力学性能增强的新设计和不同材料和结构的表征摘要现代工程系统越来越多地由两种或两种以上材料组合而成，以提高性能。通常，由于材料特性不匹配，会在材料界面或接头处发生失效。因此，准确测量不同材料界面处的界面强度对于纳米尺度到宏观尺度的这种新材料的材料开发和工程应用至关重要。然而，由于双材料界面存在特殊的“应力奇异性问题”，现有的界面力学测量方法导致测量数据无效。为了准确测量不同材料的固有界面力学性能，本项目通过综合分析、数值和实验研究，提出了新颖的试件设计。受树木形状和力学的启发，开发了一种初步设计，以获得大多数工程材料组合的双材料拐角处最小的应力奇异性。新的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估。与传统对接试件相比，凸形聚碳酸酯-铝和聚甲基丙烯酸甲酯-铝材对接试件的静态极限拉伸载荷提高了81%，而总材料体积减少了至少15%，自由边应力奇异性严重。因此，首席研究员和他的研究小组成员计划开发一个更广泛的研究计划，以提高和评估界面力学性能。特别是，其目的是：1)测量在动态载荷作用下新型界面接头的载荷传递能力的改善；2)进行静态界面拉伸测量的轴对称试件设计。拟议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种新的解决方案。树形状背后的力学原理被用来设计新颖的接头试件。该项目将提供一个生物启发设计的成功范例，以增进对科学和技术的理解，即大自然可以为某些技术难题提供有效的解决方案。由于不同材料的界面/接头和失效在航空航天、汽车、生物医学、民用、国防、电子、材料和机械工程领域广泛使用，因此拟议研究的影响将是非常广泛的。因此，该项目的研究成果将对信息技术、纳米技术、材料以及制造业和民用基础设施非常有利。其他更广泛的影响包括为一名女博士生提供支持，以及与国家实验室发展研究伙伴关系。

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.