Finite Element Simulation Of Measurement Of Interface Tensile Strength By Laser Spallation Technique

The laser pulse induced spallation technique has been used in recent years to successfully measure the tensile strength of interfaces between coatings of micron thickness and substrates in nondispersive and nondissipative bimaterial systems of interest in composites with strong but brittle components. Finite element simulation of in situ measurement of the film-matrix interface strength was the most concern of this paper.Instead of in previously reported measurements the experimentally measured free surface velocity, enegry and pessure of laser pulse in the present article allowed definition of the loading conditions in the numerical model. On the basis of theory for laser hypervelocity impact dynamics, experiment was predigested into two relative but non-coupling processes, i.e. transient thermal analysis and transient dynamics analysis. In the former, the procedure employed for the solution of thermal equation was the generalized trapezoidal rule. In the latter, the Crank-Nicholson difference time integration method was employed for the solution of wave equation.Based on the experiments, we firstly have analyzed the process of laser shocking single substrate to verify the computer programs by confrontation the laser-induced epicentral displacements at the opposite side with experimental displacement. A two-layer model for the laser generation of ultrasound in films-matrix laminates has been secondly proposed to study the propagation of stress wave and to evaluate the spall resistance of sputtered films. The analyzed result showed the dynamic adhesive strength of the TiN coating and the 304 stainless steel substrates is 183.64Mpa. It is theoretically proved that the interface stress triggering the film pry-offs was not single superimposition of pressure pulse and reflected tensile pulse, but multi-superimposition of pressure and tensile pulses.