Permittivity variations on marble beams subjected to various loading levels

Marble beams were subjected to gradually increasing three-point bending from low loading levels up to levels that significant damage was observed. After each loading step the permittivity was measured at three characteristic locations: the tensional, middle and compressional zone of each sample. The permittivity measurements were conducted in the frequency range from 1kHz to 1MHz. The permittivity values were compared for the three locations at the frequency of 10kHz. The experimental results indicate that the permittivity values decrease after each loading at the three selected locations. More specifically, the permittivity variation is more intense at the tensional zone (due to intense cracking processes) than the compressional zone, while the middle zone exhibits the lowest variation in permittivity. Thus, the damage magnitude of each sample can be estimated by permittivity measurements before the fracture of the sample.