Geometry and length scale selection in patterned interfaces with application to materials design.

摘要

Material improvements in mechanical design have been long related to the chemical modification of its main constituents. In recent years, with the advance in new manufacturing process and material manipulation techniques at the macro-, micro-, and nano-scales, new promising strategies to enhance material performance without a variation on its intrinsic chemical configuration have become possible. In this research we focus on a novel concept by which morphological modifications at the material interface (e.g., geometrical patterns) can be used to significantly improve the interface resistance to crack propagation, towards the development of advanced fracture resistant materials.;A detailed combined computational/experimental approach is developed to unveil the crack propagation mechanisms and fracture toughness in interfaces with geometrical patterns (e.g. patterned interfaces). Computational analyses using the finite element numerical method are performed to study the role of the patterned geometry in the crack propagation where no analytic governing equations have been developed yet.;A series of double cantilever beam tests were also designed, developed and executed to evaluate the range of validity of the numerical simulation results. Key relationships between the interface resistance to crack propagation and the pattern geometry in the mm-scale were also obtained from the experimental tests analysis. Using linear elastic fracture mechanics, the J-integral method and the cohesive zone model we were able to develop a series of interface design guidelines for fracture resistant material design. The interface fracture toughness was studied with respect to the pattern size and shape, considering failure mechanisms at different material length scales, and between identical and bimaterial interfaces. The role of material elastic-plastic deformation in the toughening with patterned interfaces was also studied. Many results were obtained from the analyses preformed. For example, it was found that on bimaterial interfaces, the pattern geometry can be designed to improve fracture toughness by enhancing plastic deformation. We also found that depending on the bimaterial elastic mismatch, mechanisms such as discontinuous crack growth can reduce the resistance to crack propagation in the interface. We were able to relate the length scale of the fracture process zone to the geometry of the pattern and the interface fracture toughness, and we also developed several simple analytic equations that can be used to explain many mechanisms associated to interface toughening. As such, this research represents a step towards the understanding of crack propagation resistance in patterned interfaces, where the fracture resistance optimization by the modification of their interface morphology at multiple scales is the ultimate goal.