The quantitative evaluation of the filler volume fraction was made by incorporating the Rosencwaig-Gersho theory with the Maxwell-Garnet effective medium theory in homogeneous and graded two phase composites.
The variation of the photoacoustic signal was measured along the sedimentation direction of aluminum-epoxy composites prepared by the sedimentation method. The photoacoustic signal decreased exponentially along the sedimentation direction due to the increse in the effective thermal conductivity as the aluminum concentration increases, which could be understood from the relationship of the photoacoustic signal to the thermal conductivity of the Rosencwaig-Gersho theory. Quantitative estimation of the aluminum volume fraction was made from the variation of the photoacoustic signal incorporating the Rosencwaig-Gersho theory and the Maxwell-Garnet effective medium theory. The aluminum volume fraction in the epoxy-matrix increased exponentially from 0 to 50% along the sedimentation direction in agreement with the result of quantitative image analysis within 5%, which justifies the use of the photoacoustic method in determining the filler volume fraction in two-phase composites.
The cavity volume fraction was higher at the nearly center part of gauge length than that at the shoulder parts in each superplastically deformed sample. The local fluctuation of cavity volume fraction arised from local inhomogeneous superplastic deformation and the fluctuation was greater for the specimen of higher percentage elongation due to the increased inhomogeneous deformation and the coalescence of cavities. The averaged cavity volume fraction increased linearly with percentage elongation which indicated the linear dependence of cavity volume fraction with percentage elongation. The averaged cavity volume fraction increased with depth.
The variation of the photoacoustic signal in graded aluminum-epoxy was measured with varying chopping frequency to evaluate the quantitative aluminum volume fraction with depth. The decrease of the normalized photoacoustic signal with decreasing chopping frequency was attributed to the increase of the averaged thermal effusivity due to the increase of the aluminum concentration with depth. Estimation of the quantitative aluminum volume fraction was made from the variation of the photoacoustic signal by incorporating Rosenwaig-Gersho theory combined with the Maxwell-Garnet effective medium theory. The aluminum volume fraction evaluated from the variation of the photoacoustic signal was in agreement with quantitative image analysis to within 3% which justified the use of the photoacoustic method in determining the filler volume fraction and its depth profile in graded two phase composites.
