Size Effect Stemming from Specimen Geometry on Mechanical Properties of an Aluminum Alloy

In this effort, variation of mechanical properties with the geometry of Al6061 specimens was studied, while the grain size was unchanged. Young's modulus, yield strength, ultimate tensile strength, and fracture strain of dog-bone specimens with cross sections varying from 0.4 mm x 0.4 mm to 12.7 mm x 7 mm were measured from uniaxial tension tests. Four sets of specimens were used, corresponding to varying: cross-sectional area; thickness; aspect ratio; and gauge length. Digital image correlation of natural speckles on the small specimens was used to measure full-field strains, in order to avoid the effect of additional devices or paint on the measured mechanical properties. Changes in microstructures were observed through metallography. A decrease in Young's modulus, yield strength, ultimate tensile strength, and fracture strain was observed when the cross-sectional area, thickness, and aspect ratio were reduced while the opposite trend was seen in the reduction of the gauge length.