Abstract：Theories of elasticity，plasticity，thermoplasticity，thermoviscoplasticity，continuum damage are often used to develop constitutive models for engineering materials. A new and unified approach which possess a number of advantages compared to the foregoing and available models is introduced，namely the disturbed state concept (DSC). The DSC is based on the idea that a deformed material element can be treated as a mixture of two constituent parts in the relative intact (RI) and fully adjusted (FA) states，referred to as reference states. During external loading，the material experiences internal changes in its microstructure due to a process of self-adjustment. And as a consequence，the initial RI state transforms continuously to the FA state. The self-adjustment process may involve relative motions of material particles and lead to microcracking and damage or strengthening. The disturbances are caused in the observed response with respect to the responses under the two states. Then，the observed response is expressed in terms of the responses for the RI and FA states that are determined from laboratory tests on material specimens. The research results show that the DSC can develop unified constitutive models for engineering materials，which include，hierarchically，other previous continuum and damage models as special cases.
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