Showing papers by "Exponent published in 1979"

Surface residual stresses, surface topography and the fatigue behavior of Ti-6AI-4V

Abstract: Fatigue tests have been conducted on Ti-6Al-4V from 293 to 589 K to determine the influence of surface residual stresses and surface topography on low and high cycle fatigue properties. Four types of machined surfaces as well as shot peened surfaces were included in the investigation. It was found that surface residual stresses play a key role in controlling the development of microcracks and, therefore, overall fatigue lives at both room and elevated temperature. X-ray measurement of the stability of surface residual stresses under thermal activation and/or cyclic loading demonstrated that, for the conditions studied, cyclic loading was primarily responsible for residual stress decay. In addition, the magnitude of the decay was dependent on the relationship between the sign of the residual stress and the sign of the imposed mean strain. Finally, it was demonstrated that the sharpness of machining grooves is more important than their depth in controlling fatigue resistance.

A stress corrosion cracking model for pellet-cladding interaction failures in light-water reactor fuel rods

Abstract: A model for pellet-cladding interaction (PCI) fracture of light-water reactor (LWR) fuel rods is presented, the basis of which is that Zircaloy cladding fails by iodine stress corrosion cracking (SCC). Laboratory data on iodine SCC of irradiated Zircaloy provide the primary input to the model, but unirradiated Zircaloy SCC data and theoretical analyses are utilized to broaden the regime of validity to encompass the various power reactor observations. The PCI model postulates a threshold stress below which cladding cracks are unable to form. The cladding hoop stress must exceed this threshold for a finite time at any particular fission product iodine availability for the crack(s) to form. Crack formation is the controlling event in cladding failure due to SCC, and therefore, "remedies" must address the situation at the cladding inner surface.

Computer analysis of shells of revolution using asymptotic results

Abstract: It is suggested that asymptotic results for the behavior of thin shells can be incorporated in a general computer code for the analysis of a complex shell structure. The advantage when compared to existing finite difference or finite element codes is a substantial reduction in computational labor with the capability of working to a specified level of accuracy. A reduction in user preparation time and dependance on user judgment is also gained, since mesh spacing can be internally generated. The general theory is described in this paper, as well as the implementation in the computer code FAST 1 (Functional Algorithm for Shell Theory) for the analysis of the general axisymmetric shell structure with axisymmetric loading.