Papers by Author: Shien Chin Lan

Abstract: Optical fiber sensors have a number of advantages over conventional electronic sensors such as light weight, small diameter and immunity to electromagnetic interference. Despite all the advantages of optical sensors, one must recognize that optical fibers are foreign entities to the host structure, therefore will induce stress concentration in the vicinity of the embedded sensor. As an optical sensor is embedded between plies, a lenticular resin pocket exists in the composite plies. The resin pocket acts as a crack-like region, and can form the site of the initiation of the delamination under mechanical loads. In this investigation, the geometry of the lenticular resin pocket around the optical sensor is derived basing on the principal of minimum potential energy. It shows that the geometry of the resin pocket is dependent on the stiffness of the plies, the stacking sequence, the diameter of the optical fiber and the curing pressure. The stress distributions in the resin pocket and in the laminated composites are obtained by using the finite element method. The numerical results demonstrate that the stress increases rapidly in the vicinity of the optical fiber sensor, causing a high stress concentration factor. The high stress field may produce delamination and fracture in the composite.

Abstract: Piezoelectric materials have the advantage of being lightweight, temperature insensitivity low-cost, easy of implementation that can be utilized for passive and active control of structural vibration. They can be surface bonded or embedded in the structures with slight modifications and without significantly changing the structural stiffness of the system. In this investigation, two piezoelectric actuators are symmetrically embedded in a simply supported plate. Electric voltages with the same amplitude and opposite sign are applied to the two symmetric piezoelectric actuators, resulting in the bending effect on the plate. The bending moment is derived and applied to the simply supported plate. The harmonic response of the simply supported plate excited by the piezoelectric actuators is derived and compared with the finite element solution to show the validation of present approach. The effects of the location and exciting frequency of the piezoelectric actuators on the response of the plate are presented through a numerical study.

Abstract: Drop test is one of the common methods for determining the reliability of electronic products under actual transportation conditions. The aim of this study is to develop a reliable drop impact simulation technique. The test specimen of a printed circuit board is clamped at two edges on a test fixture and mounted on the drop test machine platform. The drop table is raised at the height of 50mm and dropped with free fall to impinge four half-spheres of Teflon. One accelerometer is mounted on the center of the specimen to measure the impact pulse. The commercial finite element software ANSYS/LS-DYNA is applied to compute the impact acceleration and dynamic strain on the test specimen during the drop impact. The finite element results are compared to the experimental measurement of acceleration with good correlation between simulation and drop testing. With the accurate simulation technique, one is capable of predicting the impact response and characterizing the failure mode prior to real reliability test.