Stress Simulation Of Skutterudite-based Thermoelectric Devices

Thermoelectric(TE)devices usually work at high temperature and large temperature difference for a long time.Thermal stress is inevitable in the device,which will lead to cracking of TE legs or desoldering of electrode,and then causes device failure.Therefore,how to suppress the thermal stress is the most essential to improve the mechanical reliability of TE devices.In past decades,the research on device design and integration have mainly focused on the improvement of conversion efficiency and output power,while mechanical reliability of thermoelectric devices has not been well studied.In this thesis,the thermal stress of thermoelectric device have been discussed by using the finite element simulation,focusing on three typical devices: skutterudite single-stage,skutterudite / bismuth telluride cascade and skutterudite / bismuth telluride segmented devices,under a service temperature drop of 800 K at hot side and room temperature at cold side.The effects of device structure factors on the thermal stress distribution in these three kinds of devices are discussed.The structure factors mainly include device installation mode,ceramic substrate configuration,electrode / ceramic substrate / barrier layer thickness and thermoelectric leg section shape / height / gap.The main achievements are summarized as below:1.The multi-parameter mechanical optimization design of single-stage skutterudite thermoelectric device is carried out to obtain the minimum thermal stress,and the weight of each structural factor on the stress is obtained through comparative analysis.The results show that,among all structure factors considered in the simulation,the device installation mode,the configuration of ceramic substrate and the ratio of the thickness of ceramic substrate and electrode give significant influence on the thermal stress.For example,loading 2 MPa normal pressure on the split ceramic substrate at the hot side of device instead of fixing installation can reduce the thermal stress on the thermoelectric leg by 90%,and increasing the thickness of the copper electrode at the hot side can relieve 50% of the thermal stress on the thermoelectric leg.2.The multi-parameter mechanical optimization design of the skutterudite /bismuth telluride cascade thermoelectric device is carried out.Besides the influence factors involved in simulation of the single-stage thermoelectric device,the ratio of height of skutterudite / bismuth telluride is also taken into account.Similar to the singlestage device,the installation mode of the device is still the most sensitive factor.Changing the installation mode of the hot side from fixing to normal pressure of 2 MPa can relieve more than 85% of the stress.The stress on the n-type skutterudite thermoelectric leg is greatly affected by the ratio of the thickness of electrode and the ceramic plate,and the smaller ratio of the thickness of ceramic substrate / electrode leads smaller thermal stress.Furthermore,reducing the ratio of the height of skutterudite / bismuth telluride benefit to reduce the stress on the n-type skutterudite.3.The multi-parameter mechanical optimization design is carried out on the segmented skutterudite / bismuth telluride thermoelectric device.In addition to the factors involved in the cascade thermoelectric device,the barrier layer thickness is also taken into account.The results show that the main factors affecting the segmented thermoelectric device are the device installation mode,ceramic substrate configuration,thermoelectric leg height and barrier layer thickness.Similar to the single-stage and cascade devices,the installation mode of the device has the greatest impact on the stress.Changing the installation mode from fully fixing at the both sides to applying normal pressure at the hot side,the stress is reduced from 500 MPa to 100 MPa.Furthermore,the ratio of the height of thermoelectric leg has unignorable influence on the stress,and the position of maximum stress on the thermoelectric leg changes with its height;the thinner barrier layer is beneficial to alleviate the stress of the thermoelectric leg.