Thermal Shock Fracture Mechanics Analysis Based On Non-fourier Heat Conduction Theory

There are unprecedented challenges in many heat conduction problems appear in modern high technologies such as the stability control of superconducting coil,short-pulse laser heating and thermal barrier coatings of the combustor in the engine.The development of these technologies need deep knowledge of thermoelasticity and fracture mechanics of engineering materials and structures in severe environments such as ultralow temperature and ultrahigh heat flux and in small scale.The result predicted by classical Fourier heat conduction law is away from the actual data observed in the experiment.The thermoelasticity and fracture models based on non-Fourier heat conduction theory are essential and urgent.This thesis studies the thermal shock fracture problems of the cylinders,plates,coatings and sandwich composite plates based on dual-phase-lag non-Fourier heat conduction theory.The solution models for the thermal shock fracture problems are established by applying integral transformations and singular integral equations method.The thermoelasticity response and fracture mechanics response of the structures are systematically analyzed in a dimensionless system.The main contents and results of the thesis are:(1)The theoretical models for the thermal shock fracture problems of cylinders,plates and laminated structures are established.The effects of the phase lags and geometry feature size of materials on the thermoelasticity response of structure and crack-tip field is analyzed.A deep knowledge of thermoelasticity and fracture mechanics of the structures in severe environments such as ultralow temperature,ultrahigh heat flux and micro scale is provided.Non-Fourier effect can be ignored when the duration of thermal shock has a lager magnitude than phase lag or if the geometry feature size of materials two orders greater in magnitude than the characteristic length of heat conduction.(2)The ratios of the properties between materials in laminated structures are introduced as structure parameters to describe the property difference of structural components.The effects of the property difference of structural components on the thermoelasticity response and fracture mechanics response are analyzed.Two specify factors which can accurately predict the coupling effects of four thermal property differences between the structural components on the thermoelasticity fields are proposed.The results are useful for the optimization designs of laminated structures.(3)The solution models for the thermal shock fracture problems of a penny-shaped crack with considering mass inertia effect are established.The ratio of the heat wave speed to the stress wave speed is introduced as an inertia argument.The coupling effects of mass inertia and non-Fourier heat conduction on the fracture mechanics response is analyzed.The general validity condition of the quasi-static hypothesis is presented.The effect of mass inertia can be ignored if the thermal wave speed has a lager magnitude than the shear wave speed.It helps the engineer balance the accuracy and efficiency in computing.(4)The solution models for the thermal shock fracture problems of piezoelectric plates are established with considering mass inertia effect.The piezoelectric effect on the thermal fracture mechanics response is analyzed.The mass inertia significantly increases the electric displacement intensity at the crack tip in the case of symmetric thermal shock.The piezoelectric effect on the thermal fracture mechanics response can be ignored if the plate subjects to thermal load only.The results in this thesis are useful for the designs and safe service of the thermal protection system and piezoelectric components in microscope or work severe environments such as ultralow temperature and ultrahigh heat flux.