Determination of creep-induced residual stress in fiber-reinforced glass–ceramic matrix composites by X-ray diffraction

Residual strains were measured in the matrix of laminated SiC fiber-reinforced BMAS glass–ceramic matrix composites using X-ray diffraction. Strains were determined from the (8 2 4) plane reflections of barium osumilite phase using Cu Kα radiation and applying the sin2 ψ measurement method. The stresses in the longitudinal and transverse directions of the 0° outer ply of the as-received and creep-conditioned specimens were compared. The longitudinal residual stress in the matrix of the as-received specimen was −71 MPa. The residual stresses in the longitudinal direction of the creep-conditioned specimens were −124 and −191 MPa for the specimens that were tensile crept at 1100°C for 12 h under 75 MPa and for 30 h under 90 MPa, respectively. The increase in the compressive residual stress in the matrix of the crept specimens was attributed to the effectiveness of high-temperature creep conditioning. The measured increase in the residual stress in the matrix of the composite specimens was in agreement with the increase in the proportional limit stress obtained from the stress–strain curves.