Jarno Jokinen

Apparent Fracture Toughness Versus Micro-Scale Fracture Toughness of Interfaces—The Challenge of Critical Values

This study aims to shed light on the conflict between macroscopic fracture toughness and small-scale measures of interface strength when the interface is simulated with an increasing resolution. In the design of practical structures, crack initiation is the critical, limiting phase of material behavior and needs to be defined by lucid means. In this study, we model an example structure, namely a fracture test specimen, including a bi-material interface having micro-roughness and thermal residual stresses. The initiation of secondary cracks, which is one of the microscopic mechanisms leading to crack coalescence, is studied. The work focuses on the effects of the bi-materials Youngs modulus, residual stresses, and flaws. The simulation of crack propagation shows that the overall crack tip loading mode mixity distribution is not essentially affected when the Youngs modulus of the bi-materials coating is doubled. The analysis of the secondary crack initiation due to interfacial flaws in turn showed that increasing the Youngs modulus of either the bi-materials substrate or coating resulted in immediate interface collapse via an elongated ‘damage region’ along the interface.

Lateral Indentation and Impact Analyses on Curved Composite Shells

In the framework of materials used for structural applications, reliability and adoption of specific materials for certain use is heavily influenced by its behavior upon impact, together with the capability of sustaining damage. Methods for measuring these features include, for example, indentation and low-velocity impact testing, which are generally performed on flat panels. However, geometry of the structure plays an important role in the impact properties of the final object [5, 13]; it should then be taken into account when simulating impact and damage.