Influence of notch geometry and interface on stress concentration and distribution in micro-tensile bond strength specimens

Objectives Describe stress distribution and compare stress concentration factor (Kt) for homogeneous micro-specimens with different notch geometries and stick-shaped homogeneous and bimaterial specimens by means of finite element (FE) analysis. Methods Axisymmetric models were created for homogeneous specimens with different notches and for stick-shaped homogeneous and bimaterial specimens. FE mesh was refined at areas of expected stress concentration and boundary conditions included an applied tensile stress in the axial direction. Linear elastic analysis was used. Results For hourglass homogeneous specimens, Kt equaled 1.32 and 1.12 for a notch radius of 0.6 mm and 3.3 mm, respectively. A non-uniform axial (σzz) stress distribution was found in the notch cross-section, with values at the outer edge being 78% and 25% larger than at the center. In addition, a triaxial stress state was generated. Stick-shaped and dumbbell homogeneous specimens presented Kt = 1 and a uniform, uniaxial stress distribution along the entire cross-section. Shear stresses were zero for all homogeneous specimens. When an adhesive interface was added to the stick-shaped specimen, an area of localized axial stress concentration (Kt = 1.55) was detected at the bimaterial joint near the outer edge. Normal stresses σrr and σθθ and shear stress τzr were also non-zero at the free-edge. Conclusions Dumbbell or stick-shaped specimens are favored for μTBS testing, as they do not present stress concentrations due to geometry. However, dissimilar mechanical properties of joint components will lead to stress concentrations and non-uniform multi-axial stresses, although to a lesser extent.