| Abstract: | As a 6061-T6 aluminum coupon specimen is stretched, energy is being converted from mechanical work to heat. This irreversible process of material damage is detected experimentally by measuring the change in surface temperature. Contrary to the ordinary notion that the material would heat up when loaded, it actually cools before returning to the ambient condition. The recovery time was approximately 26 sec for a displacement rate of 8.467·10−5 m/sec and 200 sec when the displacement rate is reduced by one of magnitude. Cooling and heating is a rate dependent process. Three sets of temperature data were obtained for each of the displacement rates and they coincide with those prediced from the energy density theory that accounts for the nonhomogeneous dissipation of energy at every location in the specimen.Unlike any classical theories in mechanics, the energy density theory determines the stress and strain response of each element in the specimen only from a knowledge of the initial material stiffness and the displacement time rate. This is necessary because the local strain rates for elements near the center and edge of the specimen can differ by a wide margin. The so-called uniaxial stress and strain curve is then obtained by taking the average of all the elements. The results agreed extremely well with those measured experimentally for the 6061-T6 aluminum. Obtained analytically are also the thermal conductivity coefficients that are loading rate dependent and anisotropic in character due to stretching in the longitudinal direction. Their values tend to stabilize beyond the cooling/heating period. |
