Measured through-the-thickness thermal diffusivity of carbon fiber reinforced composite materials

The thermal diffusivity of carbon fiber reinforced composite materials is d ependent on fiber. matrix, and porosity volume fractions. Since the carbon fiber thermal conductivity is much greater than the epoxy resin matrix ther mal conductivity, thermal diffusivity is a good indicator of the fiber volu me fraction. In this study. through-the-thickness thermal diffusivity image s were obtained nondestructively on carbon fiber reinforced composite plate s, and the values varied from 0.0035 to 0.0062 cm(2)/s. The fiber and poros ity volume fractions were measured destructively. and their values varied f rom 56.0 to 70.5% and from 0.9 to 7.2%. respectively. The destructive test data were used as a standard for comparison of three commonly used transver se equivalent thermal conductivity models: the Stacked Plate. the mixed flo w Cylindrical Fiber model, and the Composite Circular Assemblage model. In these models, a porosity correction is also studied. There was very good ag reement between the Composite Circular Assemblage and Cylindrical Fiber mod el when porosity levels were less than 2%. The porosity correction helped t o reduce the chi-squared value by 24% in the Cylindrical Filament model. Fi nally, the potential is discussed to image fiber volume fraction nondestruc tively using the described thermal measurement system.