Effects of prestrain on the tensile properties of graphite

Abstract Data are presented demonstrating the effects on the transverse tensile strength of H4LM graphite of tensile prestraining in static helium at 2500°C and 0.005/min strain rate. Strength measurements after prestraining were at 2500°, 2250°, 2000°, 1750°, 1500°, and room temperature, at strain rates of 0.005 and 2.0/min. Results are correlated with strength measurements made under similar conditions on the same graphite as-received, subjected to similar thermal cycles without prestrain, annealed at the testing temperature after prestraining, and cooled and reheated between prestraining and tensile testing. These observations and certain others previously made on the same and similar graphites are used to develop a microstructural explanation of the tensile behavior of graphite, based on localized cracking both by external loads and by stresses induced by anisotropic thermal contraction, on crack closure and healing by anisotropic thermal expansion, and on crack healing by stress-directed mass transport of carbon.