Elevated temperature X-ray measurement of residual stresses in a fibre reinforced Al alloy

Thermal residual stresses were measured using XRD in an Al-2 percent Mg matrix with 10, 20, or 26 vol pct Al2O3 short fibers. Stress measurements were made at room temperature as well as in situ at elevated temperatures up to 250 C. The thermal stresses arise due to the difference in coefficient of thermal expansion (CTE) between the matrix and the reinforcement. The largest CTE is found in the matrix, resulting in tensile residual stresses after a temperature drop, e.g. after processing or annealing. A high fraction of reinforcement implies higher matrix stresses than a low fiber content. The stresses decrease with increasing temperature for all fiber volume fractions. Measurements are compared with calculations using a modified Eshelby model for equivalent inclusions, and a good correlation between calculations and experimental results was found. The plastic behavior of the composites was described using a model based on a rigid spherical cavity in an elastic plastic matrix. (Author)