Effects of Gage Section Geometry on Tensile Material Properties by Digital Image Correlation

Accurate material property data in both the elastic and plastic ranges of deformation is essential for accurate material representation in finite element simulations of vehicle systems. Variation of post formed material properties across a part are often of interest in different types of analyses, such as metal forming or fatigue life, for example. Depending on a part's shape it is not always possible to cut standard size tensile test specimens from all areas of interest across the part. Smaller size specimens with curved or tapered gage section may have to be used to promote strain localization and fracture at or near the gage center. This paper presents comparison of quasi-static tensile properties determined using two specimen gage section geometries, straight and tapered. Specifically, the following questions are addressed. How do the engineering strains computed from two-dimensional strain fields obtained by DIC compare to strains measured during standard tensile tests? What is the effect of a small taper in the specimen gage section on measured tensile properties and does it depend on the material? How does the difference in measured properties due to gage section geometry, if any, compare to the overall variation in material properties and what are its practical implications for use in finite element analysis? Tensile properties were determined using digital image correlation (DIC) method which enables computation of two-dimensional strain fields from a series of digital images acquired during each test. Contour plots of strain localization and evolution were examined on DP600 steel, TPN-W 780 steel and magnesium ZEK100 alloy.