Influence of Surface Roughness on Mechanical Properties Of Joints

Mechanical properties of joints are dependent on the geometry of surface defects caused during manufacture of the adherends. This paper presents experimental results on the influence of the roughness, due to grinding and sand blasting, on tensile properties of joints. We studied specimens made of low carbon steel rods, bonded by an epoxy resin containing mineral fillers. The surfaces were prepared with various roughness conditions: 2 grindings (coarse and fine), 8 grindings with sand blasting (combination of 2 grindings and 4 diameters of sand particles), and one shot blasting. The roughness parameters were measured, particularly the total depth and the average spacing of roughness. These measurements showed that the prepared surfaces had well defined and reproducible roughness. Electric strain gauges at specific points on the metallic parts were used; these provided measurements of local strains (at ±1 μm/m) during the loading. The variation of these strains represents indirectly the joint behavior: the elastic limit, the appearance of micro-cracks and their propagation up to failure.