An analytical model to evaluate influence of negative Poisson's ratio architecture on fatigue life and energy conversion performance of wearable thermoelectric generator

High performance, high stretchability and high strength are the urgent demands for the wearable thermoelectric generators. This paper proposes a novel idea of the stretchable thermoelectric generator with the negative Poisson's ratio architecture (NPR-TEG). Based on the thermoelastic fracture mechanics and the heat conduction law, the fatigue life and electric power output of the NPR-TEG under the thermo-electro-mechanical coupling loads are systematically analyzed. The theoretical analyses demonstrate that the negative Poisson's ratio architecture can greatly improve the flexibility and strength of the thermoelectric devices. An analytical model to evaluate effect of cracking at the interface between the thermoelectric leg and the electrode on the power output is proposed. It is found that the existence of crack slightly degenerates the power output unless the entire interface is delaminated. The crack location has little effect on the power output. The critical crack length for the electrode delaminating from the thermoelectric leg increases to a peak value and then decreases with the angle between the electrode and the thermoelectric leg. Under the cyclical tensile strain of 20%, fatigue life of the NPR-TEG with an angle of 60° is around 1000 times longer than that of the traditional bulk thermoelectric devices. The angle is optimized to enhance the fatigue life of the NPR-TEG. Results show that the optimal angle is mainly determined by the length of the thermoelectric leg and the thickness of the electrode. The relevant research results can provide a guideline for designing, manufacturing and assessing performance of the NPR-TEG.