| Scope and method of study. Experiments were conducted on polyurethane foam to determine its compressive strength/modulus, relaxation behavior, fracture toughness, as well as residual tensile strength after repetitive compression at room temperatures and -170°C.; Findings and conclusions. Results indicate that, in general, both the Young's modulus and collapse strength increase with the increase of the strain rate at both room temperature and -170°C. The relationship between Young's modulus and strain rate, between collapse strength and strain rate were fitted into equations. A Prony series was constructed for the average modulus at different strain rates. Young's relaxation master curve was constructed based on time-temperature superposition principle to show property change as a function of time. The critical stress intensity factor and critical energy release rates are determined to be 110.25 KPa.m1/2 and 22.25 J/m2, respectively, from testing of three-point bending specimens with a crack parallel to the fiber plane. Residual tensile strength has been determined to reduce by 40% after 100 cycles of compression at the amplitude about 55% of the collapse compressive strength. |
