| Separation joint systems are zero fault tolerant systems that have been used in complex aerospace applications such as vehicle stage separation and payload fairing removal. The structural members of separation joint systems must be able to withstand flight loads, but then completely fracture for instantaneous separation when an explosive is activated. The complex geometry and loading conditions of the structural member create a complicated stress state consisting of mixed tension and shear. A need exists to measure the fracture toughness of the material to ensure it will not support loads intended to fracture and measure its sensitivity to other variables, such as material properties, geometry variables and combinations thereof. An application based lab-scale joint toughness test was developed to measure the energy required to fracture a specimen having the geometry of a separation joint but applying a quasi-static load. The joint toughness test provides a joint toughness value, i.e. the energy needed to fracture the specimen, which exhibited sensitivity to material properties and geometry of the specimen. Fractographic and metallographic evidence confirmed the joint toughness sensitivities and revealed the independence of the fracture mechanism to the strain loading rate. |
