Considering the non-linear elastic behaviour of concrete, the normal stress at fibre ends and thermal effect on shear stress and normal stress in fibre, the traditional shear-lag theory of stress transfer in short fibre reinforced concrete-matrix composites is improved.

Development of dilatancy theory and constitutive model of sand;

The characteristics of the rock strength and failure under triaxial compressions are theoretically analyzed in detail with the twin shear theory and the results are compared with experimental data.

Twin shear theory is abroad applied to engineering practice presently; according to twin shear theory and related flow rule,the isotropy enhanced rule is adopted; and the equivalent plastic deformation is regarded as enhanced parameter; and then the explicit expression of twin shear two parameters theory unification elastoplastic constitutive model is deduced in terms of consistency condition.

Taking the cohesive force on the fictitious crack as the corresponding boundary condition,the variant layers in the shear lag model were introduced using the modified shear lag theory.

At first,according to the basic principles in the composite material mechanics and the linear elastic fracture mechanics and based on the modified shear lag theory and by introducing the variable layer in different zones,the layered shear lag model is built.