Craze development in high-impact polystyrene (HIPS)

Craze damage development in high-impact polystyrene (HIPS) has been studied experimentally, theoretically and numerically. In the experimental program, six different grades of compression-molded HIPS were investigated. The results were analyzed and compared to understand the significance of morphological features of the blends, such as the particle volume fraction, size and its distribution in achieving the desired effects.; Toughening glassy polystyrene (PS) into the HIPS depends on characteristics of crazing. The statistical nature of craze formation has been studied in terms of craze density, craze orientation and craze size. Craze density in the HIPS was determined first and corresponding density and cumulative functions of craze orientation and craze size were obtained at different strain levels. The results reveal that cumulative and density distributions of craze length follow the form of a three-parameter Weihull's function. Cumulative and density distributions of craze orientation can be described with a normal distribution function.; Additional experiments were conducted to examine the characteristics of craze damage and its evolution. Craze damage development, thermodynamic driving force, and damage evolution under uniaxial loading were addressed. Results show that craze damage increases initially with strain but eventually approaches to a saturation state. Further loading does not cause an appreciable amount of damage increase. An orthotropic craze damage theory has been developed, based on a continuum damage mechanics approach. A damage tensor is introduced, and constitutive equations for the damaged polymer are derived. Theoretical predictions of damage mechanics variables are compared with experimental results.; Micromechanics modeling based on a finite element method has been conducted to obtain occluded particle volume fraction and size effects on craze formation in a HIPS polymer. Numerical results show that stress concentrations at the equator of a particle is amplified with increasing occluded particle volume fraction. Crazes are most probably initiated from the large particle's equator in a HIPS with a bimodal particle distribution. Craze interactions are also modeled with an observed HIPS microstructure to address their potential growth under stress.