短繊維強化樹脂複合材料の残留応力の新X線測定法

抄録

The X-ray diffraction method is used to measure the residual stress in injection-molded plates of short-fiber reinforced plastics (SFRP) made of crystalline thermoplastics, polyphenylene sulphide (PPS), reinforced by carbon fibers with 30 mass%. Based on the orientation of carbon fibers, injection molded plates can be modeled as three-layered lamella where the core layer is sandwiched by two skin layers. The stress in the matrix in the skin layer was measured by Cr-Kα radiation by the sin²ψ method. Since the X-ray penetration depth is shallow, the state of stresses measured by X-rays in FRP can be assumed to be plane stress. The X-ray measurement of stress in carbon fibers was not possible because of high texture. A new method was proposed to evaluate the macrostress in SFRP from the measurement of the matrix stress. According to micromechanics analysis of SFRP, the matrix stresses in the fiber direction, σ₁^m and perpendicular to the fiber direction, σ₂^m, and shear stress τ₁₂^m can be expressed as the functions of the applied (macro) stresses, σ₁^A, σ₂^A, τ₁₂^A as follows: σ₁^m = α₁₁σ₁^A + α₁₂σ₂^A, σ₂^m = α₂₁σ₁^A + α₂₂σ₂^A, τ₁₂^m = α₆₆τ₁₂^A, where α₁₁, α₁₂, α₂₁, α₂₂, α₆₆ are stress-partitioning coefficients. Using skin-layer strips cut parallel, perpendicular and 45° to the molding direction, the stress in the matrix was measured under the uniaxial applied stress and the stress-partitioning coefficients of the above equations were determined. Once these relations are established, the macrostress in SFRP can be determined from the measurements of the matrix stresses by X-rays. Microscopic phase stresses due to the mismatch of the thermal expansion coefficient between matrix and fiber was negligible in X-ray stress measurement of the skin layer.