Debonding failure and size effects in micro-reinforced composites

• Published in: International journal of plasticity 2010, Vol.26 (1), p.149-165
• Main Authors: Legarth, Brian Nyvang, Niordson, Christian F.
• Format: Article
• Language: English
• Subjects: A. Debonding; A. Microstructures; B. Elastic–viscoplastic strain-gradient plasticity; B. Micro-reinforced composite material; C. Finite elements; Condensed matter: structure, mechanical and thermal properties; Cross sections; Debonding; Defects and impurities in crystals; microstructure; Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.); Exact sciences and technology; Failure; Fracture mechanics (crack, fatigue, damage...); Fundamental areas of phenomenology (including applications); Inelasticity (thermoplasticity, viscoplasticity...); Mathematical models; Physics; Plasticity; Reinforcement; Solid mechanics; Stress-strain relationships; Structural and continuum mechanics; Structure of solids and liquids; crystallography; Voids
• ISSN: 0749-6419; 1879-2154
• DOI: 10.1016/j.ijplas.2009.07.001

Failure in micro-reinforced composites is investigated numerically using the strain-gradient plasticity theory of Gudmundson [Gudmundson, P., 2004. A unified treatment of strain gradient plasticity. Journal of the Mechanics and Physics of Solids 52 (6) 1379–1406] in a plane strain visco-plastic formulation. Bi-axially loaded unit cells are used and failure is modeled using a cohesive zone at the reinforcement interface. During debonding a sudden stress drop in the overall average stress–strain response is observed. Adaptive higher-order boundary conditions are imposed at the reinforcement interface for realistically modeling the restrictions on moving dislocations as debonding occurs. It is found that the influence of the imposed higher-order boundary conditions at the interface is minor. If strain-gradient effects are accounted for a void with a smooth shape develops at the reinforcement interface while a smaller void having a sharp tip nucleates if strain-gradient effects are excluded. Using orthogonalization of the plastic strain gradient with three corresponding material length scales it is found that, the first length scale dominates the evaluated overall average stress–strain response, the second one only has a small effect and the third one has an intermediate effect. Finally, studies of reinforcement having elliptical cross-sections show rather significant gradients of stress which is not seen for the corresponding circular cross-sections. Also, an increased drop in the overall load carrying capacity is observed for cross-sections elongated perpendicular to the principal tensile direction compared to the corresponding circular cross-sections.