Experimental investigation of relaxatoin kernel's approximation factors for polymer binding agent

Modern fiber-reinforced polymer composite materials subjected to high thermal and mechanical loadings often have strong nonlinear behavior and viscoelastic memory that need to be considered correctly to predict temper stresses. Using some practical results it was shown that temper thermal stresses can be lower than the predicted theoretically because of relaxation during material forming. Relaxation kernels of polymer binding agents can be derived from experimental creep curves.

For linear model of viscoelasticity with memory effect useful for many thermosetting polymers stress-strain dependence is linear and the relaxation can be considered by changing of elastic modulus due to internal restructuration of polymer. Time-dependent modulus can be approximated by exponent with constants defined from experimental creep curves.

A polymer specimen subjected to both compression force 1,8 N and 100 N and high-temperature heating up to 100оС и 150оС during 3 hours have been used to plot experimental creep curve. Instantaneous and long-termed modulus and time factor have been computed by the least-square method. These constants can be used to model viscoelastic behavior with memory of composite materials subjected to high temperatures and mechanical loadings.