Local and non-local damage model with extended stress decomposition for concrete

In this work, a new damage model for concrete is proposed with an extension of the stress decomposition (limited to biaxial cases), to capture shear damage due to the opposite signed principal stresses. To extract the pure shear stress, the assumption is made that one component of the shear stress is a minimum absolute of the two principal stresses. The opposite signed principal stresses are decomposed into shear stress and uniaxial tensile/compressive stress. A local model is implemented in Abaqus UMAT and it is further extended to a non-local model by utilization of the gradient theory. The concept of three length scales (tension, compression, and shear) is kept the same as the recently proposed nonlocal damage model by the authors. The nonlocal model is implemented in the Abaqus UEL-UMAT subroutine with an eight-node quadrilateral user-defined element, having five degrees of freedom at corner nodes (displacement in X/Y direction and tensile/compressive and shear nonlocal equivalent strain) and two degrees of freedom at internal nodes. Some examples of a local model including uniaxial and biaxial loading are addressed. Also, five examples of mixed crack mode and mode-I cracking are presented to comprehensively show the performance of this model.

Assessment of the Cyclic Behavior of Structural Components Using Novel Approaches

To extend the life of a structure, or a component, which is subjected to cyclic thermomechanical loading history, one has to provide safety margins against excessive inelastic deformations that may lead either to low-cycle fatigue or to ratcheting. Direct methods constitute a convenient tool toward this direction. Two direct methods that have been named residual stress decomposition method (RSDM) and residual stress decomposition method for shakedown (RSDM-S) have recently appeared in the literature. The first method may predict any cyclic elastoplastic state for a given cyclic loading history. The second method RSDM-S that is based upon RSDM is suggested for the shakedown analysis of structures. Both methods may be directly implemented in any finite-element (FE) code. An elastic perfectly plastic material with a von Mises yield surface has been assumed. In this work, through their application to structures that are used as benchmarks in the literature, both methods, applied together, prove their efficiency and capacity to determine shakedown boundaries and reveal unsafe conditions.