The Thermoelastic Theory Of Porous Media With Strain Rate And Its Application Research

With the emergence of new technology,the research of unsteady heat transfer process is increasingly significant.However,the classical thermoelastic theory cannot accurately describe the second sound effect of unsteady heat transfer.Therefore,many scholars have proposed the generalized thermoelastic theory to describe the thermoelastic coupling effect in unsteady heat transfer.Generally speaking,the strain rate is assumed that relatively small and ignored in the constitutive equation of the classical thermoelasticity.However,in the unsteady heat transfer process under some extreme conditions,such as ultra-high temperature gradient,ultra-short laser pulse heating,etc.,the strain rate has a vital influence on the dynamic response of the structure.Therefore,considering the strain rate in the generalized thermoelastic theory,which reflects the mechanical response of the structure more realistically.Porous materials are substances that contain pores or spaces between solid material through which liquid or gas can pass,which have been extensively used in electronic communications,aerospace,bio-medicine and petrochemical,etc.due to their attractive attributes such as low relative density,thermal and acoustical insulation and good permeability.With the extensive application of porous materials in production and life,the precise description of the coupling effect between temperature field,volume fraction field and strain field are of great significance for exploring the heat transfer and elastic deformation of porous media.Based on the existing research results,scholars have done a lot of valuable research work on the generalized thermoelastic coupling problem of porous media.However,scholars have only considered the thermal relaxation effect for porous thermoelastic materials,and have not extended the relevant theoretical studies to consider the strain relaxation effect into the study of porous thermoelastic materials.In the present work,a linear thermoelastic theory for porous materials is established by extending the existing theory,in which strain relaxation and thermal relaxation are included.Based on the thermodynamic laws,the constitutive relations are derived,and then the corresponding constitutive equations are obtained by specifying the generalized free energy.Further,by combining the existing theory,the non-Fourier's heat conduction law and the obtained constitutive equations,the linear thermoelastic theory for porous materials is formulated.To apply the newly established theory,the generalized thermoelastic coupling problem of the viscoelastic porous half body is investigated.The related research contents include:(1)A linear theory including both the strain relaxation and the thermal relaxation for thermoelastic materials with voids is established by extending the existing theory.To apply the newly established theory,the dynamic response of a half-space with voids is considered.The half-space with voids is subjected to a thermal shock and a mechanical shock simultaneously on its bounding surface.The distribution of the non-dimensional temperature,displacement,stress as well as the volume fraction field at different values of time,thermal relaxation factor,strain relaxation factor and the magnitude of the mechanical shock are obtained and illustrated graphically.(2)The present work devotes to investigating the dynamic response of a porous half-space heated by a non-Gaussian laser beam on its boundary surface based on the newly established linear thermoelastic theory with strain and thermal relaxations.The distribution of the non-dimensional temperature,displacement,stress as well as the volume fraction field at different values of time,thermal relaxation factor and strain relaxation factor are obtained and illustrated graphically.Moreover,comparisons are taken with the results in the absence and presence of the void parameter.(3)Based on the thermoelastic theory of viscoelastic porous media considering both the strain rate and the temperature change rate,the dynamic response of a half-space with voids is considered.The half-space with voids is subjected to a thermal shock on its bounding surface.The distribution of the non-dimensional temperature,displacement,stress as well as the volume fraction field at different values of time,thermal relaxation factor and strain relaxation factor are obtained and illustrated graphically.