John Gary and Abbie O'Gallagher, ACMD
Marvin Hamstad, Materials Science and Engineering Laboratory and Denver University
This is part of collaboration between NIST and the Federal Highway Department designed to improve the detection of flaws in highway structures. Over the past few years three finite element models have been developed to study elastic wave propagation in plates. The ultimate objective is to characterize the acoustic emissions generated when minute fractures occur due to stress. This is needed in order to improve the use of acoustic emission as a detection method.
The Materials Reliability Division has a contract with the Highway Department and a laboratory which can be used for experiments in this area. NIST also has extensive experience, going back over many years, in the development of sensors and standards for the measurement of displacements associated with elastic waves.
In the previous year numerical experiments were run to compare the model with waves generated in the laboratory by breaking pencil lead on a thin plate. Results from a two dimensional model which assumes cylindrical symmetry and a three dimensional finite element model were obtained. This year the results were analyzed and written up and the results have been accepted for publication in the Journal of Acoustic Emission. The 3D code has been extended to run under MPL and PVM and timing comparisons of serial and parallel operation have been made on the IBM cluster. Parallel operation is about 70% efficient compared to serial; the loss is caused by the need for an expanding mesh which is more easily generated in a serial code. This year, with the help of a summer student, the code was modified to allow mesh refinement around the source which generates the plate wave. A simple interpolation scheme was used which turned out to be sometimes unstable.
The next objective is to rewrite the mesh refinement, based on a different algorithm, in order to eliminate the instability. Then numerical experiments will be run to compare the wave generated by different source configurations.