No abstract

Elastic-plastic finite element analysis has been carried out to evaluate collapse moments of six elbows with elbow factors varying from 0.24 to 0.6. The loading conditions of combined in-plane closing/opening bending moment and varying degree of internal pressure are considered in the analysis. For each case, collapse moment is obtained by twice elastic slope method from the moment versus end-rotation curve. Based on these results, two closed-form equations are proposed to evaluate the collapse moments of elbows under combined internal pressure and in-plane closing and opening bending moment. [S0094-9930(00)00103-7]

No abstract

A large throughwall circumferential crack in an elbow subjected to in-plane bending moment can significantly reduce its collapse load. Therefore, it is very important to know the collapse moment of an elbow in the presence of a throughwall circumferential crack. The existing closed-form collapse moment equations of throughwall circumferentially cracked elbows are either too conservative or inadequate to correctly quantify the weakening effect due to the presence of the crack, especially for opening mode of bending moment. Therefore, the present study has been carried out to investigate through elastic-plastic finite element analysis the effect of a throughwall circumferential crack on the collapse moment of an elbow under in-plane bending moment. A total of 72 cases of elbows with various sizes of circumferential cracks (2θ=0–150 deg), different wall thickness (R/t=5–20), different elbow bend radii Rb/R=2,3 and two different bending modes, namely closing and opening have been considered in the analysis. Elastic-perfectly plastic stress-strain response of material has been assumed. Collapse moments have been evaluated from moment-end rotation curves by twice-elastic slope method. From these results, closed-form expressions have been proposed to evaluate collapse moments of elbows under closing and opening mode of bending moment. The predictions of these proposed equations have been compared with 8 published elbow test data and are found to be within ±11% variation except for one case.

No abstract

Piezoceramic materials exhibit different types of nonlinearities under different combinations of electric and mechanical fields. When excited near resonance in the presence of weak electric fields, they exhibit typical nonlinearities similar to a Duffing oscillator such as jump phenomena and presence of superharmonics in the response spectra. In order to model such nonlinearities, a nonlinear electric enthalpy density function (using quadratic and cubic terms) valid for a general 3-D piezoelectric continuum has been proposed in this work. Linear (i.e. proportional) and nonlinear damping models have also been proposed. The coupled nonlinear finite element equations have been derived using variational formulation. The classical linearization technique has been used to derive the linearized stiffness and damping matrices which helps in assembling the nonlinear matrices and solution of resulting nonlinear equation. The general 3-D finite element formulation is discussed in this paper. In a companion paper by Samal et al., numerical results on various typical examples are shown to match very well with the experimental observations.

This paper gives a comparative study of methods used for evaluation of mechanical properties of materials using miniature and sub-size tensile test specimens. Aim of this paper is to establish the potential of miniature tensile tests which can be useful for life estimation of any in-service-equipment and for development of new materials. Both these applications intend to use very small amount of material for evaluation of the mechanical properties. Apart from various types of novel techniques developed worldwide, the evaluation of mechanical properties from a miniature tensile test has a greater advantage as it is a direct method of measurement of mechanical properties. The paper also discusses various challenges in fabrication of miniature tensile test specimens, testing methodologies and acceptance of the test results. A comparison with the test results from conventional size specimen has been done for establishing the suitability of the miniature test specimen. For establishing the geometrical design of the miniature test specimen and its behaviour over application of tensile load, the tests have been corroborated with a finite element based analysis.

The bimetallic welds (BMWs) play a critical and indispensable role in the primary heat transport piping system of nuclear reactors. The primary heat transport system in itself is the critical part of a nuclear reactor. Any failure of this system can lead to grave consequences, not only speaking of huge monetary losses resulting from non-utilization of the reactor setup, but also immensely valuable and irreparable loss of human life. The present paper is an effort towards identifying and understanding the problems affecting the BMWs and is as well an attempt to highlight the current issues in the structural integrity assessment of structures having these welds. The basic aim of this work is to provide a clear understanding of the current structural safety issues and their importance in underpinning the use of BMWs in modern nuclear reactors.