Ph.D. Thesis Defense by Tieyu Zheng
Wednesday, October 6, 1999

(Dr. Steven Danyluk, advisor)

"A Study of Residual Stresses in Thin Anisotropic Plates"

Abstract

This thesis concerns the development of non-contact, nondestructive measurement techniques and the analytical tools to extract the in-plane residual stresses in thin anisotropic plates. Silicon is used as a model material to validate these studies.

Previous research has shown that the in-plane residual stresses in a thin silicon plate interacts with its out-of-plane displacement when the plate is subjected to bending. Energy analysis shows that this interaction exists when the plate is subjected to large deflections. The theory of thin anisotropic plates with large deflection was employed to study the interaction. The in-plane residual stresses were also simulated by the imposition of the thermal stresses in an FEM model. Two experimental techniques were used to obtain the residual stresses: shadow moiré and near infrared transmission photoelasticity. A phase stepping technique was incorporated with the shadow moiré to get an improved sensitivity of deflection, and a FEM optimization scheme was developed to extract the in-plane residual stresses by comparing the measured deflection with that of the FEM simulation. A new near infrared phase stepping polariscope with fringe multiplier was also used to obtain the residual stresses in thin single crystal silicon plates. The stress sensitivity was found to be three orders of magnitude better than the currently used polariscopes.