| With rapid development of the ultrashort pulse laser technology(10-18s-10-12 s,attosecond-picosecond)and wide application of the microelectronic devices,thermo-mechanical coupling problem involving ultrashort time has attracted more and more attention.The existing studies have pointed out that the infinite speed of heat waves predicted by the classical theory of thermoelasticity based on classical Fourier heat conduction law is not well consistent with the experimental observations when the time of heating is on the order of the thermal relaxation time or the characteristic dimension of medium is less than or same as mean free path of heat carrier.In order to meet the need of development of ultrashort pulse laser technology and microelectronics devices and to overcome the disadvantages of classical thermoelastic theory,to accurately describe the thermo-mechanical coupling phenomenon involving very short time situation,the people establish the various generalized thermoelastic theories describing the wave effect of heat propagation(the speed of heat propagation is finite),that are labeled as L-S(Lord-Shulman),G-L(Green-Lindsay)and G-N(Green-Naghdi)generalized thermoelastic theories.The three theories can characterize the finite speed of heat propagation in the medium to show second sound effects in solids.The accomplishment of heat transfer in metal material is mainly through electron-phonon coupling,the heating process can be divided into two steps: firstly,the electrons are heated by absorbing energy directly;then,the lattices are heated by the collision betwween electrons and phonons(lattices),and so that the temperature in metal go up and the energy is spreaded to more distant.Because of its special heat transfer mechanism in metals,the ultrafast thermoelastic theory is established.In this paper,firstly,based on the theories of generalized thermoelasticity,the transient thermoelastic coupling behavior of interface of laminated composite plate and magneto-thermo-elastic multifield coupling problems of functional gradient medium and porous materials with considering micropolar effect and microstretch effect,and generalized thermoelasticity of electromagnetic elastic medium subjected to thermal shock are investigated by using finite element method.Secondly,based on the theory of ultrafast thermoelasticity,the ultrafast thermoelastic problem for single-layered and double-layered metal film under laser pulse heating are studied with considering the temperature-dependent thermodynamic properties of material.And considering the thermal wave effect of electrons,proposing the hyperbolic two-step heat transfer-molecular dynamics method(HTTM-MD)model,and using the proposed model to investigate ultrafast thermoelastic coupling response in gold films under femtosecond laser heating.Finally,from the point of view of wave in physics,based on generalized thermoelasticity theory,the expression of thermal elastic wave velocity with high frequency induced by thermal shock are derived,and the influence of multi-field coupling effect on thermal wave and elastic wave are discussed.The innovative works are:1)The finite element governing equations of G-L generalized thermoelastic theory are established.The transient thermoelastic behavior of interface of composite plate under thermal shock are studied.The evolution characteristics of temperature,deformation,stress near interface of composite plate are investigated in two different coefficients of thermal conductivity,heat capacity,thermal relaxation time,and density of two layers.Not only the influence of material parameters on the thermal behavior of the composite plate interface,but also the influence degree of the material parameters on the thermal behavior is obtained.2)Based on G-N thermoelastic theory II,III model,Appling finite element method to discuss the two-dimensional thermoelastic coupling problem of a function gradient body with cylindrical cavity.Material parameters are assumed to vary as power of the radius of cylindrical cavity and the surface of cavity is subjected to thermal shock.The thermoelastic response of infinite functionally graded body is obtained.The effect of functional gradient parameter on the thermoelastic response of material is also discussed,and the effect of damping coefficient in type III of G–N theory is also studied.3)Two-dimensional thermoelastic problems of a thermoelastic plate whose surface subjected to a zonal time-dependent thermal shock and placed in a magnetic field is studied with considering micropolar effect and microstretch effect of materials.It is found that the microstructure effects have a great influence on thermoelastic behavior of plate,wherein the microstretch effect has a great influence on thermomechanical response;the micropolar effect has only a slight influence on the mechanical response.4)Considering the material properties varying as the change of temperature,studying the generalized electromagnetic thermoelastic behavior of porous half space placed in a magnetic field whose surface subjected to thermal shock.The comparison among the results predicted by different theories is made and the application scope and features of generalized theory and classical theories are obtained.Through the comparison of results obtained under considering temperature-dependent properties with absolute temperature and temperature-dependent properties with the reference temperature,there are great diffence between two kinds of forms,impling that when studying the thermoelastic problemof media subjected to thermal shock,especially the material whose properties are sensitive to temperature,considering temperature-dependent properties is very necessary.5)Based on ultrafast thermoelastic theory,ultrafast thermoelastic coupling problem of metal film under laser heating is studied.Ultrafast thermomechanical responses of single-layered and double-layered gold films under ultrashort laser pulse irradiation are discussed.Due to the thermal properties of electrons in metal is sensitive to temperature,the characteristics of electrons temperature-dependent are considered in the study.The effects of hot blast force of electrons is also discussed,and finding that the absolute value of displacement will become larger when the hot blast force of electrons is considered,especially in the early stage of the laser heating,where will have a ultrafast deformation and the damage for the material is fatal;similarly,considering hot blast force of electrons,the absolute value of stress will also change.So in the early stage of the laser heating,considering the effects of hot blast force of electrons is very necessary for accurate prediction of response.6)Accounting for thermal relaxation effect of electrons,proposing the hyperbolic two-step heat transfer-molecular dynamics method(HTTM-MD)model,and appling the HTTM-MD model to simulate the ultrafast thermomechanical behavior in gold films under laser pulses with different duration irradiation.The nonthermal ablation phenomenon in gold film under femtosecond laser irradiation and the effects of temperature-dependent material properties are also discussed,and finding that when the pulse duration is shorter than or the same order of magnitude of the electronic thermal relaxation time,the thermal relaxation effect has a great influence in the thermoelastic behavior of materials,and this moment the traditional parabolic two-step heat transfer-molecular dynamics method(TTM-MD)model is failed in the prediction.7)On the basis of the characteristics of propagation of elastic wave in solids,each deformation wave will be accompanyed a temperature wave.According to this principle,the expressions of velocity of thermoelastic coupling wave are derived based on the generalized thermoelastic theories,and by simplifing the expressions for various special cases to prove the correctness of the expression derived and to deepen the understanding of concept of thermoelastic coupling.The effects of thermal relaxation time and material parameters on the velocity of thermoelastic coupled wave are also discussed. |
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