  Solids when rapidly and elastically stressed change temperature, the effect
proposed by Lord Kelvin is adiabatic thermo-elastic cooling or heating
depending on the sign of the stress. A fast sensitive IR camera has measured
temperature both decreasing and increasing. Temperature measurements made from
the reversible, elastic part of the stress-strain curve during fast uniaxial
tensile loading have been investigated. The isentropic temperature cooling from
the loading curve is recovered by heating after the specimen fractures when the
load is released. These measurements establish for the first time isentropic
thermal recovery in two engineering alloys. The materials tested are an AISI
4340 steel and an aluminum 2024 alloy. Measurements of the isentropic
thermo-elastic stress cooling are -0.61 K/GPa for steel and -1.7 K/GPa for
aluminum alloy. The isentropic thermo-elastic stress heating is -1.16 K/GPa for
steel and -1.6 K/GPa for aluminum alloy. The isentropic, elastic part of the
temperature is fully recoverable even after extensive plastic deformation upon
fracture.
