Characterization and constitutive modeling of composite materials under static and dynamic loading

Composite materials were characterized under quasi-static and dynamic loading, and a constitutive model was proposed to describe the nonlinear multi-axial behavior of the materials at varying strain rates. The material investigated was a unidirectional carbon-fiber/epoxy composite. Multi-axial experiments were conducted at three strain rates, quasi-static (10 ₄s₁), intermediate (1 s₁), and high (180-400 s₁), using offaxis specimens to produce stress states combining transverse normal and in-plane shear stresses to verify the model. A Hopkinson-bar apparatus and offaxis specimens loaded in this system were used for multi-axial characterization of the material at high strain rates. Stress-strain curves under tension and compression were obtained for various loading orientations with respect to the fiber direction. A nonlinear constitutive model is proposed following an elastic-plastic approach. It is based on a potential function in the form of a linear combination of deviatoric and dilatational deformation components. The model is able to describe the rate-dependent behavior under multi-axial states of stress including tensile and compressive loading. Experimental results were in good agreement with predictions of the proposed constitutive model.