Coupon specimen–based approach for the simulation of crossbore stress and strain state

Abstract

Direct investigation of the stress and strain state of structures with crossbore geometries is typically complex to achieve. Crossbores are often located at the center of reciprocating machinery with few options for access. Thus, the number of studies that have directly characterized these structures is limited and continues to be an experimental challenge. In order to provide an alternative approach for the investigation of material performance in these structures, a coupon specimen is presented as an alternative to direct measurement. A notched tensile specimen geometry is adopted in this study and is designed to match the stress gradient in a representative crossbore intersection. An approach for specimen design is presented and the design is validated using digital image correlation to measure the full-field stress gradient. The proposed design is shown to match the stress gradient to within 10% for the first 50% of the specimen. In addition to the validation of the gradient, an initial set of fatigue experiments is also conducted in order to compare to the modified Smith–Watson–Topper fatigue life approach. Finally, a simulated autofrettage cycle is completed and the resulting residual stress is analyzed by digital image correlation.