Viscoelastic fracture characterization of polymeric solids

Vita.Almost all engineering materials exhibit creep and relaxation behavior. The observed magnitude depends on temperature, stress level and loading duration. Some polymers are further influenced by moisture contents as well. Attempts to predict the crack initiation and propagation in fracture of polymeric solid materials are complicated by all such variables. In this study, hard viscoelastic polymeric solid materials were used to develop the viscoelastic fracture characterizing parameter. Fracture mechanism at the crack tip or in the neighborhood of crack tip is affected by those time-dependent material behaviors. A continuum aspect of time-dependent fracture mechanics approach was utilized. In the time-independent material, a fracture mechanics theory has been well established. However, viscoelastic polymeric solids are the time-dependent materials, and analysis methods are more complicated due to the time-dependency and therefore analysis methods are rare. In this study, single specimen test method called "calibration curve" method was used. A hyperbolic tangent function was introduced as a new calibration function to develop the whole crack growth resistance curve. The basic idea for the development of this calibration curve method came from the key curve method. Unlike the key curve method, the calibration curve method curve-- fits for an assumed deformation path during the crack growth process using the normalization scheme of dimensional analysis. This calibration curve contains all the information needed to generate both the fracture toughness value at crack initiation and the crack growth resistance curve for a growing crack. Using those calibration curves at different displacement rate loadings, the time function was developed to relate the viscoelastic quantities in the physical viscoelastic domain to the reference quantities in the reference elastic domain. The reference hyperbolic tangent calibration function was determined in the reference elastic domain using the same time function..