Effects of Thermal Loading on Fiber-Reinforced Composites With Constituents of Differing Thermal Expansivities

Abstract

Estimates of the magnitudes of elastic stresses and elastic-plastic stresses and strains were made for tungsten fiber-reinforced 80Ni + 20Cr matrix composites; heating or cooling between 80 and 2000 deg F (26.5–1093.5 deg C) was assumed. The calculated elastic stresses exceeded representative or estimated strengths of constituents. For composites with less than 0.65 volume fraction of fiber, plastic flow was considered possible, and elastic-plastic solutions indicated that stresses would be reduced but with the concomitant occurrence of sufficiently large strain ranges, particularly in the matrix, to pose a possible thermal fatigue problem. Limited experimental studies on tungsten fiber-copper matrix composites heated and cooled a number of times between 80 deg F (26.5 deg C) and 1600 deg F (877 deg C) in a conventional furnace and then heated from 80 deg F (26.5 deg C) to 1652 deg F (900 deg C) in a hot stage microscope resulted in matrix microfracture for a 70 volume fraction fiber composite and substantial matrix strain for a 40 volume fraction fiber composite.