Thermo-mechanical Coupling Analysis Of Ultrashort-pulse Laser Irradiated Thin Film Structures

With the widely application of the short or ultra short pulse laser heating,micro-electromechanical techniques and thin film structures,the comprehension of heat transfer and associated thermo-mechanical coupled behavior involving short duration and micro-scale effect is very important to improve the control accuracy of laser micro-machining process,reveal the thermal properties of thin film structures and optimize the working performance of micro-electronic device to extend its service life.Based on the Dual-phase-lag model(DPL)involving two delay time to describe the macro-and micro-heat transfer phenomena in the same framework and the generalized thermoelastic theory,the heat transfer and associated thermo-mechanical response of thin film structures(metal films and metal-ceramic functional gradient materials)with the boundary subjected to a short pulse laser is investigated in this paper.The main contents are as follows:1.The analysis of transient thermal response of thin film structure imposed on a ultra-short pulse laser irradiation.Firstly,the governing equation describing the heat conduction within the thin film is established in the context of the DPL model.An asymptotic method is then proposed by means of the Laplace transform technique and its limit theorem to derive the asymptotic solutions of the temperature field.The accuracy of this asymptotic method is validated by comparing with the numerical results of exist literature in the same calculation conditions.Finally,the effects of two phase lag time,the film thickness and material properties on temperature distribution are investigated.2.The analysis of transient thermal response of thin film with variable material properties.Similarly the governing equation of heat transfer with variable material properties is firstly proposed to reveal the heat transfer within the thin film.Then a linearized technique is introduced before the asymptotic solution of complicated equations involving variable material properties in space.The exact solutions with layered forms are obtained to reveal the effects of two phase lag time and the power law exponent on the temperature distribution.3.The analysis of transient thermo-elastic behavior of the thin film exposed on the ultra-short pulse laser irradiation.Firstly,the generalized thermo-elastic model involving the coupling effect between temperature distribution and strain rate is proposed in the context of DPL model.The asymptotic solutions of each physical field are obtained and their distributions are illustrated.The effects of characteristic parameters on thermo-elastic response are further analyzed.4.The analysis of transient thermo-elastic behavior with variable material properties.The generalized thermo-elastic model with variable material properties is proposed,in which material properties have a power-law distribution along the longitudinal direction.Similar with the Section 2,a layer method is firstly used to linearize the complicated governing equation involving variable material properties.The exact solutions with layered forms of each physical field,induced by a transient heat shock,are derived.The distributions of the displacement,temperature and stresses are illustrated and the effects of delay time and variable material properties on thermo-elastic response are also analyzed.