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Numerical simulation of dynamic crack propagation in functionally graded glass-filled epoxy (FG) beams using a regularized variational formulation is presented. The Griffith’s theory based hybrid phase field approach for diffusive fracture is taken, which is able to accurately simulate complex behaviors of dynamic crack growth in FGMs. The FG beams under impact loads experimented by Kirugulige and Tippur (Exper. Mech. 2006; 46:269–281) are considered, taking the same configurations, material property, crack location, and other relevant assumptions. The crack paths, crack length, crack velocity, energies, etc., computed through the hybrid phase field model are numerically analyzed, and some of those results are directly compared with the experimental data. Due to lack of necessary information regarding impact loading profiles and boundary conditions in setting the tests, the simulations become difficult as an inappropriate definition of loading and boundary conditions can significantly alter the outputs of numerical solutions. This issue is important and thus is discussed. Two specific loading profiles, the constant and the linear displacement velocities, are taken into account, while free-free FG beams are considered. We show that good agreements of crack paths between the experiment and phase field approaches can be obtained. Numerical results also confirm a significant effect of elastic gradients on final crack paths. Similar to the experimental results, we also found that the crack path kinks significantly when situated on the stiffer side compared to the compliant side of the FG specimen.

Laser drilling of silicon carbide (SiC) wafer in air (dry ablation) and underwater by using ns pulsed infrared (1064 nm) Nd:YAG laser is investigated. In order to suggest optimal parameters of via processing in SiC wafer, the effects of pulse number, laser fluence, water film thickness, and focus position are evaluated. As compared with dry ablation vias, decreasing etching rate, increasing via diameter, and generation of cracks in high-energy regime are observed in liquid-assisted processing. However, it is found that it can create vias without debris, HAZ, cracks. Also, optimal parameter set for infrared pulse laser processing under water is found to be the laser fluence of less than 10 J/cm2 and water thickness of 1 mm.

This work presents a fundamental study about ablation threshold, absorption coefficient and absorption mechanism of silicon carbide (SiC) in the laser drilling process. Experimental study has been performed on single infrared (1064 nm) ns pulse laser ablation of SiC at various fluence values. Hole diameters were measured to predict the absorption threshold. Based on the ablation threshold, an average absorption coefficient of SiC at infrared wavelength during the laser ablation process is calculated. The result is discussed based on absorption coefficient dependence on doping concentration and temperature in semiconductor. A preliminary model is proposed that accounts for the heat conduction and surface evaporation to predict the cross-sectional shape of drilling hole. Analytical modeling results are in good agreement with observed features produced from the laser. The paper will conclude with suggestions for further research and potential applications for the work.

Laser beam shaping techniques are important to optimize a large number of laser-material processing applications and laser-material interaction studies. The authors have developed a novel fluidic laser beam shaper (FLBS) with merits such as flexiblility, versatility and low cost. This work presents a fundamentally new approach for laser beam shaping by using FLBS. A Gaussian beam profile is transformed to a flat top beam and annular beam profile in the focal plane. The shaped laser beam is used for laser drilling to investigate the influence of the laser intensity profile in laser processing. The paper concludes with suggestions for future research and potential applications for further the work.Copyright © 2013 by ASME

This research presents a novel fluidic lens based on thermal lens effect. Effects of the pump power and the pump beam intensity distribution to the probe beam profile in the dual thermal lens system are investigated experimentally and theoretically. A model, which accounts for heat conduction, natural heat convection and ray tracing in inhomogeneous medium is developed to predict the characteristics of the thermal lens system. Numerical results show the advantage of the uniform pump beam in reducing the spherical aberration compared with the Gaussian pump beam. An experiment with the uniform pump beam is carried out to confirm the numerical prediction. Experimental results show a good agreement with the calculated results. Finally, the pump power is varied to adjust the focal length of the system.

A three-dimensional transient two-phase isothermal model has been developed for the cathode side of a proton exchange membrane fuel cell (PEMFC). This has been done in order to fully investigate the effects and the time variation of liquid water formation as well as the gas phase transport under the start up condition. It is considered that the generated water in the cathode catalyst layer (CL) is liquid water and that the gas diffusion layer (GDL) is hydrophobic. A non-equilibrium water condensation-evaporation is also assumed. The time variations of liquid water distribution in along-channel and through-plane directions are investigated. This is to determine the liquid water accumulation at the start up time (above the channel under the CL), then the movement of the liquid water in the domain and the final accumulation at the steady state condition (above the rib and near the CL). It has also been found that it takes less time for a high average current density to attain the steady state condition which is due to the capillary pressure gradient inside the porous media. Validation of the numerical results has been implemented via a polarization curve comparison with the experimental data. Both sets show good agreement.

A numerical model of the thermoreflectance of doped SiC substrate and typical numerical results are presented. The model considers the temporal response of the electron temperature and the number density of the electronic carriers. Calculated results show steep increase of electron temperature and the resulting increase of reflectivity. As a result, the reflected laser pulse by the substrate is compressed in time domain by means of the temporal response of the thermoreflectance characteristics of SiC substrate. Thermal analysis of the electrons reveals the interesting feature of the thermoreflectance response as a function of pulse intensity, pulse width, or doping concentration. The technique can be used for the compression of ultrashort pulse laser light.Copyright © 2013 by ASME

Laser drilling of silicon carbide (SiC) wafer in air (dry ablation) and underwater by using ns pulsed infrared (1064 nm) Nd: YAG laser is investigated. In order to suggest optimal parameters of via processing in SiC wafer, the effects of pulse number, laser fluence, water film thickness, and focus position are evaluated. As compared with dry ablation vias, decreasing etching rate, increasing via diameter, and generation of cracks in high-energy regime are observed in liquid-assisted processing. However, it is found that it can create vias without debris, HAZ, cracks. Also, optimal parameter set for infrared pulse laser processing under water is found to be the laser fluence of less than 10 J/cm2 and water thickness of 1mm.

Laser measurement and laser processing techniques have been gaining strong attention from various applications [1,2]. This research aims at the development of a fluidic laser beam shaper, and in order to fulfill the objective, characteristics of the thermal lens effect are studied. This phenomenon has the optical property of a concave lens since the refractive index distribution on the optical axis is formed when the liquid is irradiated. One reason for the refractive index distribution in the liquid is the temperature distribution in the liquid when it is irradiated. In this research, effects of the pump power and propagation distance of the probe beam to probe beam profile are investigated experimentally and theoretically, in order to develop fluidic laser beam shaper. It is indicated that, by controlling some parameters in thermal lens system as pump power (in the regime of linear optics) and absorption coefficient, input Gaussian beam can be converted into flat-top beam profile. The relationship among the distance to obtain a flat-top beam, pump power and absorption coefficient is investigated to show the flexibility of fluidic laser beam shaper in many fields of laser application.

Recent advances in measurement techniques using the photothermal effect have drawn more and more attention to the application in various fields. Especially, laser measurements are becoming increasingly important for the thermal design of electronic devices because these measurements can be applied to non-invasive and non-destructive measurement [1, 2]. We focus on the transient lens effect, which is a well-known photo-thermal phenomenon. As this effect is caused by the change of thermal properties or other physical properties, the measurements using this effect have the possibility to measure various materials information. This phenomenon has the optical property of a concave lens since the refractive index distribution on the optical axis is formed when the liquid is irradiated. One reason for the refractive index distribution in the liquid is the temperature distribution in the liquid when it is irradiated. In this research we investigate the interaction between refractive index and temperature distribution on the Transient lens effect, in order to develop fluidic optical devices

A three-dimensional steady-state two-phase non-isothermal model which couples the water and thermal management has been developed in order to numerically investigate the spatial distribution of the interfacial mass transfer phase-change rate in the cathode side of a proton exchange membrane fuel cell (PEMFC). A non-equilibrium evaporation-condensation phase change rate is incorporated in the model which allows a supersaturation and undersaturation take place. The differences of non-equilibrium phase and equilibrium assumption inside the gas diffusion layer (GDL) has been addressed by comparing the corresponding liquid saturation and temperature distributions. Regarding water management, the assumption of isothermal model versus the non-isothermal model has been investigated. A parametric study has been also carried out to investigate the effects of operation conditions namely as the channel inlet humidity, cell operating temperature and inlet mass flow rate on the phase-change rate. Since the exact values of the phase change constants for the hydrophobic GDL has not been specified yet, the effects of the phase-change constant on the liquid saturation distribution are demonstrated.