RESEARCH IN DISTURBED STATE CONSTITUTIVE MODELLING AND COMPUTATIONAL FINITE ELEMENT METHODS


Disturbed State Concept for Constitutive Modelling
    The disturbed state concept (DSC) is a unified approach for constitutive modelling of engineering materials (solids) and interfaces/joints.  It allows for elastic, plastic and creep strains, microcracking, damage and softening, cyclic fatigue failure, instability (liquefaction), and stiffening under thermomechanical and environmental loadings.  It has been used and validated with respect to laboratory test behavior of materials and interfaces/joints such as clays, sands, rocks, concrete, ceramic composites, metal alloys (Pb-Sn) and silicon crystals; and interfaces between soil and structural materials, rock joints and joints in electronic chip-substrate systems.

    The DSC and its specialized versions (e.g. HISS model) have been implemented in nonlinear finite element procedures for static, dynamic and time dependent (creep) analysis of a wide range of problems:

      1) Static, dynamic, and earthquake analysis:
        • Solids
        • Structures and foundations
        • Piles/footings
        • Dams
        • Retaining structures, etc.
        • Tunnels
        • Liquefaction
      2) Seepage, consolidation, and settlement analysis

      3) Thermoviscoplastic analysis in electronic packaging:  chip-substrate, BGA, PEM, etc. including cyclic fatigue failure and reliability

    Advantages

    The DSC is a fundamental approach based on the consideration of interacting mechanisms of components (relative intact and fully adjusted parts) in a deforming material element due to internal self-adjustment of its microstructure.  It provides a hierarchical framework which includes most of the previously available models such as elastic, plastic, thermoviscoplastic, damage and softening, as special cases.  It provides robust and consistent computations for localization, instability in the microstructure, and avoids spurious or pathological mesh dependence.  It provides implicity for microcrack interaction, characteristic dimension, and nonlocal aspects, without such external enrichment as microcrack kinematics, Cosserat and gradient theories.