Methodology for Measuring Stress and Strain Fields in Connecting Rods Using Laser Interferometry (ESPI)

The understanding of how mechanical stresses influence in the behavior of automotive components is of great interest to the automotive industry. The design of products must be made considering these efforts, always aiming to ensure smooth operation and no failures. To learn more about these efforts, a finite element simulation can be done. However, the results obtained from these simulations must be confirmed by carrying out physical experiments. Many methods are available to obtain the stress/strain fields of the object been tested, among which the best known and widespread is the use of strain-gauges. This technique requires a relatively long time of preparation as well as several measurements to obtain the full stress/strain field. The laser interferometry technique, on the other hand, reduces considerably the testing time to obtain the full stress/strain field, and no intervention on the object is required. This work aims to present a methodology for measuring stress/strain fields in connecting rods, using an Electronic Speckle Pattern Interferometry (ESPI) device. We begin with a review of basic concepts of optics, necessary to understand the interferometer technique, followed by a brief presentation of the Electronic Speckle Pattern Interferometry (ESPI) as the method used in the measurements. Then an experimental design is done, based mainly on the concepts of Design of Experiments - DOE, to eliminate or reduce the influence of the noise over the results. During the tests it will be used a forged connecting rods manufactured by ThyssenKrupp Metalurgica de Campo Limpo which will be submitted to compressive efforts. Finally we present the results of the measurements of stress and strain fields obtained by the ESPI technique as well as comparisons of these measures with simulations and classical results.