Toward the development of high-speed microscopic ESPI system for monitoring laser heating/drilling of alumina (Al(2)O(3)) substrates.

摘要

The problem of cracking/failure of ceramic substrates during the laser shaping process (i.e. heat treatment, drilling, scribing, and cutting) due to large localized thermal stresses within the narrow heat-affected zone on the ceramics has been acknowledged by designers and electronic parts manufacturing industries. In addition to the large localized thermal stresses in the heat-affected zone, the brittle nature of ceramics catalyze the possibility of cracking/failure of the ceramic substrates during the laser shaping process. The knowledge of the stress distribution in the ceramic substrate is important in understanding the cracking/failure problem and solving it. Since it is impossible to measure stress directly, the physical parameters of the actual system subjected to the operating conditions, such as temperatures or displacements that can be related directly to stresses, can be measured experimentally.; This research examined ceramic behavior under laser shaping. Specifically, it was conducted to develop an optimum optical measurement system in order to identify and measure the thermal deformation of alumina (Al2O 3) substrates during the laser heating/drilling process. Necessary research and development was performed to build a special electronic speckle pattern interferometry setup called high-speed microscopic ESPI (HSM-ESPI) system to measure transient out-of-plane deformation. By using commercial software the images of speckle patterns were image-processed to quantify whole-field transient out-of-plane displacement measurements. A CO2 laser beam radiation was used as the thermal loading and it was applied at the center of the substrates during the experiments. Local laser heating and drilling experiments were conducted depending on laser beam intensity. Another optical system, laser displacement meter (LDM), that measures single point absolute out-of-plane deformation, was setup to verify HSM-ESPI results.; A finite element model (FEM) was developed in ABAQUS to perform non-linear thermal and mechanical finite element analysis of deformation behavior of the alumina substrate under a focused CO2 laser beam irradiation.; Some out-of-plane deformation images taken by the HSM-ESPI indicate fringe pattern discontinuities that represent cracks. These cracks directly affect deformation behavior of the alumina. Therefore, cracking behavior of the alumina substrate was studied by using Acoustic Emission (AE) and Scanning Acoustic Microscope (SAM).; The experimental works and the analysis show that the designed HSM-ESPI system provide excellent experimental basis for whole-field, transient deformation measurements of ceramic substrates during the laser shaping process. A deformation history of the ceramic surface during the laser shaping process with millisecond temporal resolution is obtained, restricted only by the camera frame rate, the camera resolution and laser power available.