Yuh Chao - US grants

Measurement of the normal displacement of a three-dimensional body subjected to arbitrary loading or boundary displacements has been a major problem for experimentalists for the past century. Elaborate optical methods including holography and speckle interferometry are only applicable to the two dimensional problem where the specimen surface is plane. Recently, improvements in video cameras and computers (storage capacity) have led to significant advances in image analysis which can be effectively employed to record displacements. The approach is to record and store in pixel form the surface features of the specimen in its deformed and undeformed state. Intensity interpolation methods are then employed to identify small subsets on the specimen and to determine the displacement of these subsets. The method has been established for two-dimensional bodies undergoing plane deformation. The proposed program will extend these methods to three- dimensional specimens by utilizing two video cameras and stereo imaging procedures to obtain the images required for displacement determinations. Advanced methods of image correlation methods will be employed to achieve sub-pixel accuracy in the displacement measurements.

This project will study three dimensional deformation fields in the vicinity of stationary and growing cracks. A project with both analytical and experimental components will be conducted. Finite element methods will also be used to asses the role of thickness on near tip deformation fields.

A loading frame will be purchased for projects involving the use of two dimensional and three dimensional computer vision to study the surface deformation near a growing crack and a static crack, and optical measurements of strain at high temperatures near 1000oC. The research will extend strain measurement techniques to lower size scales to study deformation and fracture phenomena at the grain scale.

9512456 Sutton This Academic Research Infrastructure (Instrumentation) Award is to partially fund the development of a materials characterization facility with emphasis on testing in an aggressive environment. The long range goal of the research involved is life-prediction methodologies using mathematical models which incorporate accurate material parameters. Much existing data shows that safety throughout the lifetime of a structure is extremely sensitive to the environment, however except in very special cases there is inadequate ability to predict how safety changes as structures age. This facility will contribute to providing better experimental data in this area. ***

Weld Mechanics - Residual Stress, Material Inhomogeneity and Fracture

Investigator: Yuh J. Chao, chao@sc.edu
Sponsor: University of South Carolina
Office of Sponsored Programs and Research
Columbia, SC 29208


ABSTRACT

A major concern with weldments is to establish and quantify the role played by residual stress and material inhomogeneity in the fracture process. The researcher will investigate the mechanics of weldments in both the fabrication process and the potential fracture events in service. The theoretical work will include (a) the development of fundamental fracture mechanics parameters or advanced procedures that can characterize the fracture of solids containing residual stress and material inhomogeneity and (b) the numerical modeling of the entire process of welding, fabrication of fracture testing samples, and fracture mechanics testing. The modeling work will be integrated, refined and validated with experimental and metallurgical studies at DOE laboratories.

Funding is requested to partially support ten US researchers/educators to attend the International Conference on Experimental Mechanics, November 8-11, 2008 in Nanjing, China. The conference has been an important event in experimental mechanics held every two years attracting many scientists, engineers and researchers from academia, government laboratories, and industry internationally. The objectives of the conference are to bring together researchers and engineers to discuss recent advances in experimental mechanics and to serve as a catalyst for international collaboration and partnership in the broad area of experimental mechanics.

The US delegates will be selected from a pool of active researchers in US. It is anticipated that a number of delegates from USA will be the keynote/plenary speakers of the conference. The conference will serve as a vehicle/forum to build partnership toward international collaboration benefiting US higher education in general.