Design of a New Testing Fixture for Tangential Stress Measurements in Pipes

Experimental estimation of acurate material properties are key elements to the design of machine components and structures. In general, the elastic properties were determined using uniaxial tensile tests regardless of the final shape of the product including pipes, which exhibit different elastic properties in the longitudinal and tangential directions due to their manufacturing process. Several attempts have been made to estimate the mechanical properties of pipes along their longitudinal directions including ASTM D2290 and exhibited inconsistent results; thereby, calling for further design and analysis. This paper, therefore, presents various design alternatives to the ring hoop tensile test adopted in the ASTM D2290 standard through finite element modeling. The design optimization consisted of varying the ring width, dogbone width, dogbone gauge length, and the spacing between the two D-blocks to obtain the optimum values of the varying parameters that provide uniform normal stress across the cross-sectional area of the dogbone and more representative mechanical response. Finite element results revealed that the proposed dogbone sample design has an optimum length to width ratio of 4 with an orientation angle between 75° to 105° with respect to the horizontal axis. The proposed model was compared to adopted test methods such as ASTM D2290 and resulted in comparable stress contours uniformity across the dogbone gauge length but different contact pressure values. it was also found that the contact pressure for the ASTM ring hoop tensile test is higher than that for the proposed model by 22%.