Thermal-electrical-mechanical Coupling Behavior Of Layered Thermoelectric Materials And Structures

Thermoelectric materials can achieve energy conversion between heat and electricity through Seebeck effect,Peltier effect and Thomson effect.They are widely used for power generation and refrigeration,due to their features of large operating temperature range,easy to control,reliable operation,no mechanical moving parts and other characteristics.In order to improve performance and adapt to different working environments,layered thermoelectric materials and structures are more and more applied in engineering applications.Thermoelectric materials generally work in the environment of large temperature difference.Thermal stresses in them are often unavoidable.This will greatly affect the safety of layered thermoelectric materials and their devices.Therefore,investigation of thermal-electrical-mechanical coupling behavior of these advanced materials and structures is critical for their reliable applications.This provides theoretical reference and practical guidance for structural strength,reliability and lifetime of these thermoelectric systems.This thesis establishes a series of solution models for coupled thermal-electrical-mechanical behavior of layered thermoelectric structures by applying singular integral equations method,energy minimization principle,variable separation method and complex-variable method.The main contents and results of the thesis are:(1)Based on elastic membrane model and elastic plate model,the problem of stress concentration is analyzed.The singular integral equations are obtained and solved based on Chebyshev polynomial.Effects of electric current density,material properties and geometry size of thermoelectric thin film/substrate systems on stress concentration are analyzed.It is observed that even though lowing thermal conductivity is an effective method to enhance thermoelectric figure of merit,it is more likely to strengthen local stress concentration.Thus,for designing thermoelectric devices,a balance between the thermoelectric performance and structural reliability issue should be made.(2)Under consideration of thermal-electrical coupling,the solution models for wrinkling and edge debonding in thermoelectric thin film/substrate systems are established.Effects of electric current density on the critical temperature of wrinkling occurrence and local stress concentration at debonding edge are identified.It is observed that the critical temperature decreases and the degree of stress concentration is weakened when the applied electric current density is reduced.On the other hand,effects of material properties and geometry size of thermoelectric thin film/substrate structures on wrinkling and edge debonding are analyzed.(3)Fracture mechanics response of layered thermoelectric structures with Thomson effect,thermal and electrical contact resistances is obtained.The results show that temperature difference on layered thermoelectric structure surfaces increases as thermal contact resistances on hot side and cold side are reduced,which is favorable to increase the performance of thermoelectric system.Reducing the thermal contact resistance on cold side and increasing the thermal contact resistance on hot side can reduce local thermal stress concentration.The electric potential difference at the interface increases with reducing thermal contact resistance on hot and cold sides.When Thomson effect is considered,effect of thermal contact resistances on electric potential difference at interface is more obvious.In addition,electrical flux near the crack tip is very large and thermoelectric materials have good electrical ductility.Therefore,an electric saturation model with electric field reaching a saturation limit in front of the crack is developed under consideration of electrical nonlinearity at the crack tip.The expressions of electrical flux and energy flux are obtained based on electric field saturation model.(4)Thermal-electrical-mechanical coupling behavior of layered thermoelectric cylindrical shells and spherical shells under thermal shock are researched.Effects of the value and direction of applied electric current density,material properties difference and geometry size of layered shells on thermoelasticity response are analyzed.The expressions of stresses at surfaces and interfaces under different work environment are obtained.The dynamic models established in this thesis can be used to obtain the value and location of the maximum stress in layered thermoelectric shells.The results in this thesis are useful for designing and ensuring safe service of layered thermoelectric materials and structures in complex work environments such as large temperature difference and high heat flux.