Stress and deformation in tubular metallic parts of auto seats

The structural and material behaviour of parts of automobile seats must be known as extensively as possible. In order to assess deformation and failure in lightweight metallic tubular structural parts of auto seats a pseudo-dynamic procedure, to be briefly described herein, was devised. The deformation of circular section tubes subjected to centred transversal force can be assessed by measuring strain or the bending of the tubes. Most frequently contact gauges are used in this process. The authors employed optical noncontact microtopographic inspection using the MICROTOP.06.MFC microtopographer developed at the Microtopography' laboratory of the Physics Department of the University of the Minho. The system will be briefly described as well as the inspection methodology used. Bending radius can me directly measured. For stronger deformations however bending radius measures becomes unreliable and full topographic inspection must be performed. Roughness statistical parameters can also be calculated. If the surface of the tubes in the area where maximum deformation is expected to occur (located by finite elements simulation models) is textured to a certain level of roughness, changes in the roughness values after deformation were expected to be measurable. A direct correlation between the deformation state/tension, strain and stress, and surface' roughness, in particular the average roughness, was found. Results will be presented and discussed.