Auteliano Antunes dos Santos Junior

Progression of plastic strain on heavy-haul railway rail under random pure rolling and its influence on crack initiation

Abstract The present work evaluates the plastic strain accumulation on railway rails for heavy-haul transportation and the effect of them on the life cycle and the stress-strain responses considering random loading passes of normal loads on the top of rail for wheel-rail pure rolling conditions. The normal pressure distribution on the contact region was estimated by the Hertz theory and applied on the surface of the rail in a tridimensional elastoplastic finite element model. Multiaxial Dang Van criterion was applied to estimate the life to crack nucleation. The results show that the level of plastic accumulation presents distinct magnitudes depending on the position analyzed, reaching similar plastic accumulation in analogous positions on the subsurface after several passes, for two different starting positions. That result is fundamental for life analyses, since indicates that, no matter the starting point, the computed life cycles always stabilizes after a few number of cycles. From that, the fatigue life to shelling can be estimated using high cycle models.

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 performed considering these efforts, always aiming to ensure smooth operation and no failures. To learn more about these efforts, numerical 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 measurement places 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. In this work we will focus on obtaining the stresses in a flat surface of the rod. The region corresponds to the inner portion of the rod body, excluding only the edges of it that are slightly higher. In this region it’s easier to obtain the stress and strain fields than in the whole rod, which has many non-planar regions with a relatively complex geometry, especially near the ends. To plan the experiments, an experimental design was developed, based mainly on the concepts of Design of Experiments — DOE, to eliminate or at least reduce the influence of the noise over the results. The tests were performed with a forged connecting rod from a local manufacturing, which was submitted to compressive efforts. Finally we present the results of the measurements of the stress and strain fields obtained by the ESPI technique.Copyright