Cruciform specimen design for testing advanced aeropropulsion materials under cyclic in-plane biaxial loading

Investigating material behavior under complex stress states is often done using in-plane biaxial loading approach. Utilizing such techniques requires using cruciform type specimens fabricated from plate material tested by gripping the specimen at four locations and loaded along two orthogonal axes. Servohydraulic systems are generally used in this application which is similar to those used for uniaxial testing. These kind of testing capabilities are currently being conducted at NASA Glenn Research Center via a new in-house testing facility. This is in support of the development of major components for the Stirling Radioisotope Generator (SRG). It is also used to assist in the generation of an analytical life prediction methodology [1] and to experimentally verify the flight-design component's life. Further, this work is intended to carry the immediate goal of developing a specimen design that is fully compatible with the in-plane biaxial testing systems installed at NASA Glenn Research Center [2]. Thus, details of the specimen design and its applicability to the ongoing experimental activities are being reported and discussed. Finite element analyses were carried out to optimize the geometry of specimen and to evaluate the stress response under biaxial loading conditions [3, 4]. The material of interest used in this research is nickel based superalloy. The data presented concluded that the specimen can be used to investigate the deformation behavior under general forms of biaxial loading. The provided measurement and observation are limited to 1-in [2.54 cm] diameter circular region at the specimen center.