Mechanical characterization of orthotropic materials by means of speckle interferometry and simulated annealing

Mechanical characterization of orthotropic materials is a complicated reverse engineering problem. Researchers developed many different methods based on theoretical/numerical formulations or on experimental techniques. In the last few years, integrated techniques that determine elastic constants by comparing experimental results with numerical data have been developed. For this reason, the present work is concerned with a novel hybrid procedure that includes an optical technique (Electronic Speckle Pattern Interferometry, ESPI) and a numerical optimization technique (Simulated Annealing, SA). The rationale behind SISAMAC - the acronym stands for Speckle Interferometry Simulated Annealing MAterial Characterization - is that the difference between the displacement field found experimentally and the displacement field obtained with FEM analyses can be minimized by means of an optimization algorithm which finally finds the values of the elastic constants. In order to prove feasibility of the SISAMAC procedure, in-plane elastic properties of an orthotropic laminate (8-ply woven fiberglass-epoxy) used as substrate for printed circuit boards have been determined. Three-point-bending experimental tests have been carried out. Results show the ability of SISAMAC to accurately determine the elastic constants of the material to be characterized. In fact, the residual error between the displacements measured by ESPI and those computed at the end of the optimization-based identification process is less than 3%.