Mechanical Testing of Micro-specimens of Al6061-T6 Using DIC for Strain Measurement

Abstract

Tensile properties of metals are typically measured using dog-bone shaped specimens having dimensions as per specifications imposed by international standards organizations. However, these properties may be influenced by the size of the specimen, especially when the cross-sectional dimensions are lower. At lower length scales, microstructure could have an effect on the mechanical behavior. In this study, tensile experiments were conducted to investigate the effect of cross-sectional dimensions on Young’s modulus of Al6061-T6 materials. Due to the small size of the specimens, digital image correlation, a non-contact measurement technique was used to obtain strain filed in the gage section of the specimen. Spray paint or toner powder were used to produce speckle pattern on the specimen surface for better correlation of the images. For specimens having the thickness of the order of a fraction of a mm, the natural gray pattern observed on the surface of the specimen was found to provide a good speckle pattern. This natural speckle pattern was used to correlate the images instead of synthetic speckles, to avoid the effect of paint on the Young’s modulus being measured on specimens with cross-sectional dimensions below 1 mm. Young’s modulus was found to be constant at about 67 GPa for specimens whose area of cross-section was more than 3 mm2. When the area of cross-section was lesser, Young’s modulus was found to decrease with a decrease in area of cross-section. Larger spread in Young’s modulus was also observed in the specimens with area of cross-section < 1 mm2.