Smoothed Particle Hydrodynamics (SPH) modelling of transient heat transfer in pulsed laser ablation of Al and associated free-surface problems

Abstract

A smoothed particle hydrodynamics (SPH) numerical model is developed to simulate pulsed-laser ablation processes for micro-machining. Heat diffusion behaviour of a specimen under the action of nanosecond pulsed lasers can be described analytically by using complementary error function solutions of second-order differential equations. However, their application is limited to cases without loss of material at the surface. Compared to conventional mesh-based techniques, as a novel meshless simulation method, SPH is ideally suited to applications with highly nonlinear and explosive behaviour in laser ablation. However, little is known about the suitability of using SPH for the modelling of laser-material interactions with multiple phases at the micro scale. The present work investigates SPH modelling of pulsed-laser ablation of aluminium where the laser is applied directly to the free-surface boundary of the specimen. Having first assessed the performance of standard SPH surface treatments for functions commonly used to describe laser heating, the heat conduction behaviour of a new SPH methodology is then evaluated through a number of test cases for single-and multiple-pulse laser heating of aluminium showing excellent agreement when compared with an analytical solution. Simulation of real ablation processes, however, requires the model to capture the removal of material from the surface and its subsequent effects on the laser heating process. Hence, the SPH model for describing the transient behaviour of nanosecond laser ablation is validated with a number of experimental and reference results reported in the literature. The SPH model successfully predicts the material ablation depth profiles over a wide range of laser fluences 4-23 J/cm 2 and pulse durations 6-10 ns, and also predicts the transient behaviour of the ejected material during the laser ablation process. Unlike conventional mesh-based methods, the SPH model was not only able to provide the thermo-physical properties of the ejected particles, but also the effect of the interaction between them as well as the direction and the pattern of the ejection.2

An Incompressible Smoothed Particle Hydrodynamics (ISPH) Model of Direct Laser Interference Patterning

“…Cao and Shin predicted the particle motion due to phase explosion during high fluence laser ablation of metals by SPH [36]. Further, Alshaer et al used SPH to simulate the thermal ablation of aluminium at elevated fluences, particularly the ejection of particles by the recoil pressure [37]. However, the melt pool flow during nanosecond laser irradiation at moderate fluences was not studied to date using SPH.…”

Modification of the LSMPS method for the conservation of the thermal energy in laser irradiation processes

“…When i = * i , the heat flux along the direction from particle i to particle j is equal to the MPS-like flux as is clear from Equation (48). The coefficient ij should be a value such that 0 ≤ ij ≤ 1 because the coefficient ij is a coefficient to interpolate the heat flux between particles i and j as Equation (46). However, Equation (48) sometimes leads to inappropriate values, ie, * i < 0 or * i > 1.…”

“…Schwaiger proposed an improved Laplacian model for the SPH method to calculate heat conduction problems. Alshaer et al applied this formulation for the laser ablation simulation. However, there is no description for the conservation of the total thermal energy in these works, although the first‐order particle methods do not guarantee the conservation of the thermal energy as well as the least‐square–based methods.…”

Meshfree modeling of a fluid‐particle two‐phase flow with an improved SPH method

“…The SPH method was originally invented to solve astrophysical problems in the open space such as stellar collisions and motion near black holes. 22,23 Later, it was extensively studied and extended to different fields of engineering and sciences, such as multiphase flows, [24][25][26][27] free-surface flows, [28][29][30][31] dynamic response with material strength, [32][33][34][35] heat transfer and mass flow, 36,37 and many others. 21,38 Particles/points in the SPH method can freely move according to internal particle interactions and external forces.…”