Local Stress Calculation Research Articles

A cumulative model of fatigue crack growth

A model of fatigue crack growth based on an analysis of elastic/plastic stress and strain at the crack tip is presented. It is shown that the fatigue crack growth rate can be calculated by means of the local stress/strain at the crack tip. The local stress and strain calculations are based on the general solutions given by Hutchinson, Rice and Rosengren. It is assumed that a small highly strained area existing at the crack tip is responsible for the fatigue crack growth. It is also assumed that the fatigue crack growth rate depends mainly on the width, x∗, of the highly strained zone and on the strain range, Δϵ∗, within the zone. A relationship between stress intensity factor K and the local strain and stress has been developed. It is possible to calculate the local strain for a variety of crack problems. Then, the number of cycles N∗ required for material failure inside the highly strained zone is calculated. The fatigue crack growth rate is calculated as the ratio x∗N∗.The calculated fatigue crack growth rates were compared to the experimental ones. Two alloys steels and two aluminium alloys were analyzed. Good agreement between experimental and theoretical results is obtained.

A method of elastic-plastic stress and strain calculation at a notch root

An energy-based method of local elastic-plastic stress and strain calculation is presented. It was shown that the theoretical stress concentration factor k t can be related to the unit elastic strain energy at a notch root. The relation also holds when localized plastic yielding occurs at the notch root. It was shown that the method predicts the local strain more accurately than the use of Neuber's rule. Several different materials and notches were analysed. The calculated strains were compared with the measured strains. It was shown that the energy-based method can easily be used for a simulation of the local strain-stress history near a notch root.

The KWU PCI modelling approach

Since PCI fuel rod failures are generally attributed to stress corrosion cracking of the clad, mechanical as well as chemical aspects must be considered in PCI modelling. Transient fission gas release, amplified by a thermal feedback effect, is expected to be very important with regard to both aspects. In view of the limited possibilities to describe analytically the complex mechanisms contributing to PCI failures, KWU uses a semiempirical PCI approach to evaluate the experimental results from ramp tests and power reactor experience and to develop preliminary PCI failure criteria. In parallel to the empirical approach, systematic PCI investigations are performed. To calculate stresses and strains during ramps, including fuel and clad plasticity and creep, the code SENATOR has been developed. The ANSYS code is used for the calculation of local stress and strain effects.

Finite-element analysis of rectangular plates with rectangular inserts

The present investigation deals with the stress distribution in the vicinity of rectangular inserts in finite rectangular plates. This problem is more complex due to the singularities at the corners of the inserts. In this paper, the finite-element technique is used to determine the deformations and, subsequently, the stresses. The paper treats the problem in a generalized form in the sense that the size and orientation of the insert are taken as variables. The finite rectangular plate is subjected to a uniform axial tensile load. The material of the plate and that of the insert are considered to be different. Element selections are made which are optimal with regard to accuracy and computational effort. The local element stresses which generate considerable discontinuity at the element nodes are plotted. Averaging process for the local stress calculations is discussed and these are compared with the results available1 which are obtained by experimental techniques.