Micro Drilling Simulation of Ultra-Short Pulsed Laser Ablation of Glass

The purpose of this study is to estimate ablated crater depth with sufficient numerical accuracy when multishot channels of ultra-short pulsed laser are executed formicro drilling processes on thin glass plates. In this analytical model, the plasma model, in which the free electron density and the complex dielectric function of the Lorentz model are evaluated, is applied to estimate the ablated regions and the regions damaged by laser ablation when glass is considered to be a dielectric material. The absorption coefficient and the threshold fluence are important parameters in the evaluation of the ablated crater depth and ablation rate. The parameters obtained in this numerical analysis are in agreement with the experimental results and are computed quantitatively to several laser irradiation conditions. The experimental results and analysis results are examined for multi-shot channels. In an experiment involving laser ablation using multi-shot laser beams, ablation rates for the initial shot are lower than subsequent ablation rates. The effectiveness of the modified absorption coefficient and modified threshold fluence for initial shots is confirmed for the reduction of ablation rate

Finite Element Analysis for Optimal Heating Condition in Thermal Stress Cleaving of Brittle Materials Using Laser Irradiation

An optimal condition of thermal stress cleaving was investigated by assuming the element-by-element temperature rise situation using finite element method. The obtained thermal stress cleaving condition is found to be optimal for the symmetrical cleaving of a rectangular plate.9th International Conference on Fracture and Damage Mechanics, FDM 2010; Nagasaki; 20 September 2009 through 22 September 200

Heat transfer enhancement of aluminum boiling surface with micro-grooves fabricated by laser

Owing to recent advances in the manufacture of electronic devices, efficient cooling and heat-dissipation systems are required to achieve efficient technological performance. In this regard, looped thermosyphons have been studied with the intent of improving their heat-dissipation performance. The key technique is to improve the boiling heat transfer with a modified surface. This study presents the boiling characteristics of the selected working fluid, R1234ze(E), on a microtextured boiling surface fabricated using Laser Interference Surface Structuring (LISS). Compared with the unfabricated surface, the grid-grooved LISS-fabricated surfaces exhibit significant enhancements in the boiling heat transfer coefficients. An enhancement of 240—275% in the maximum heat transfer coefficient based on the untreated surface was observed. However, a significant heat transfer degradation was observed at higher heat fluxes. Additionally, to examine the effect of wicking induced by microgrooves on the critical heat flux, the capillary force was quantified using a dimensionless wicking number with ethanol utilized for the test boiling surfaces. The test surfaces with numerous irregular small cavities exhibited the highest values. These surfaces also exhibited the highest critical heat flux. The measured critical heat flux in the thermosyphon increased monotonically with an increasing wicking number

Accurate Solutions of Stress Intensity Factors of Standard Fracture Test Specimens

Practically exact solutions of stress intensity factor for several two-dimensional standard specimens were calculated and shown in numeric tables. The solutions were confirmed to converge until 6 significant figures through a systematical computation of discretization analysis. The convergence analyses were carried out by using a general purpose program based on a body force method.9th International Conference on Fracture and Damage Mechanics, FDM 2010; Nagasaki; 20 September 2009 through 22 September 200

Simulation of Crack Growth in Thermal Stress Cleaving Using Line Heat Source

The crack growing behavior in a brittle rectangular plate under transient thermal stress is studied. The transient thermal stress imposed to the rectangle here is that of due to a line heater such as an electric resistance wire which supposed to be perfectly contact to the surface of material. When the heater is placed on the symmetrical axis of the rectangle, the crack propagates just along the heating line, therefore, this situation can be used for dividing a thin rectangular plate into equal two pieces. Contrast to the symmetrical case, on the other hand, the warping of crack propagation path is observed when the heater is placed other than the symmetrical position. The main objective of the present study is to clarify the mechanism of crack path warping in the case of unsymmetrical cleaving through the crack propagation simulation. The simulated and the observed crack path show good agreement with each other and factors which make the crack path warp are understood