When composite materials undergo dynamic loadings of either cyclic or impact nature, a correlated temperature change arises. In fact, the linear elastic straining determines a volume change that is associated to a temperature change induced by the Thermoelastic Effect. The Thermoelastic Effect is then a peculiar thermos-mechanical coupling heat source by means of which the severity of material straining can be revealed through a measurement of temperature changes. When loading is dynamic, then the temperature change is also modulated by the loading waveform. An interesting case is that of a sudden load drop consequent to a brittle fracture or crack pop-in propagation. In this case, the load dropping event is accompanied by a temperature change that is also of a spike nature. This rapid and generally localised temperature change is then followed by gradual attenuation and recovery of uniformity due to heat conduction with the surroundings. In this work, the above phenomena have been exploited on CFRP and GFRP modified Transverse Cut Tensile (mTCT) samples. These are peculiar coupons where transverse notches and pre-crack delaminations are introduced during preparation so that a pure mode II loading is obtained at the delaminations tips when the sample is subject to tensile loading. An infrared camera has been used to measure temperature from both the front and side faces of the mTCT sample. Temperature is then sampled during both quasi-static and fatigue sinusoidal tensile loadings. In the first case, it is seen that instable fracture onset determines a load drop, and the sudden elastic strain release produces a spike of thermoelastic signal that can be readily detected by the IR camera. This allows to detect the exact instant of fracture onset and the corresponding actual load level, thus allowing to evaluate fracture toughness values. In the case of fatigue loading, the work shows how the delamination growth can be monitored by sampling temperature and performing a signal processing in the frequency domain to extract the thermoelastic signal over the stared sample surface. The full-field map of the thermoelastic signal can then be used to evaluate the delamination front straightness, growth and growth rate during sustained fatigue loading. Conclusions are drawn highlighting how the temperature signal can be a highly informative metric in the case of dynamic loading and dynamic events in polymer composites structures.