Nonlinear Bimodulus Model and Strength Criterion of 3D Carbon-Carbon Material

Abstract

Biaxial loading setup and large shear strain gage are designed to achieve the tension-tension, tension-compression, compression-compression and tension-shear test ings on planar specimens. Based on the experimental results, the constitutive equations and strength criterion are established. To determine whether the tensile or compressive modulus should be used in case of combined stress state with tensile stress in one direction and compressive stress in the other, this paper suggests that it depends on the senses of the fiber stresses instead of on those of principal stresses. Symmetry of the elastic stiffness matrix is attained by assuming the existence of strain potential. Experimental results show that the nonlinearity of the stress-strain relationship stems only from the shear behavior. Strength data are fitted with quadratic function separately in each quadrant in a stress plane. Both the constitutive equations and the strength criterion thus established agree with the experimental results fairly well.