N. Siva Prasad

Estimation of residual stresses in weldments using adaptive grids

Abstract Residual stress is a critical determining factor for the strength and service life of welded structures. Owing to its importance, a number of researchers have worked to estimate the residual stresses in the weldments. In the present work the residual stresses in butt welds were estimated using an elasto-plastic nonlinear finite element model. The temperature distribution was calculated by a finite element model using adaptive grid techniques. The temperature dependent mechanical properties were considered. The results were compared with the experimental results available in the literature.

Stress distribution in interference joints

The use of the finite element method in predicting the stress distribution in an interference joint is illustrated and the results of a study of the influence of various parameters on these stresses is reported.

An adaptive mesh generation scheme for finite element analysis

Abstract Adaptive grid generation is a relatively new scheme for finite element analysis. A number of algorithms have been suggested by several authors. The methods have many limitations in their implementation. In this paper a simplified method for adaptive mesh generation by dividing complex domain into convex polygons based on Joe and Simpson and Delaunay triangulation is presented. The algorithm is applied to a number of two-dimensional problems to demonstrate the suitability of the method.

A finite element approach to the design and dynamic analysis of platform type robot manipulators

Abstract The design of a closed-loop platform-type robot manipulator using the finite element method is presented. The present approach aims at the optimization of the manipulator geometry and prediction ot the actuator parameters. Beam elements and triangular plate elements are used for the finite element model. Manipulators having six spherical-prismatic-spherical (6 SPS) pairs and of tetrahedron construction have been compared for their dynamic performance.

Effect of manufacturing errors on load distribution in large diameter slewing bearings of fast breeder reactor rotatable plugs

Fuel and other subassemblies in fast breeder reactor are handled through a combination of small rotatable plug, large rotatable plug and transfer arm. Rotation of the plugs is facilitated through large slewing bearings. These bearings are subjected to heavy loads and moments. Manufacturing errors on the rolling elements and races influence the load sharing among the elements. As a result, higher load acting on a rolling element causes excessive local deformation and unacceptable indentation. The higher load can also cause excessive sub-surface shear stress and fatigue failure of rolling races. Too stringent tolerances demand sophisticated machines, whereas liberal tolerances mean compromise on the performance and life of the bearing. There are no established methods for design of slewing bearings that include the influence of manufacturing errors. Hence, an attempt has been made to find the influence of manufacturing errors on load distribution among the rolling elements using finite element method. It is observed that size error on the ball and waviness error (waviness spacing and height) on the raceway are the two influencing factors on load distribution. To study the influence of waviness error on the raceway, three sectors of bearing simulating waviness spacing of 10.8°, 18° and 36° with different waviness (peak-to-valley) height of 30 µm, 50 µm and 75 µm are analysed. It is observed that waviness height has larger influence on the load distribution among bearing balls when compared to waviness spacing.

A finite element analysis for the design of a conveyor pulley shell

Abstract A finite element analysis of the cylindrical shell of a conveyor pulley is carried out. Deformations and stresses in the shell are calculated. The load is expanded into a Fourier series. The results obtained by the analysis are found to be in good agreement with the analytical and experimental results obtained by Lange. A parametric study is made, varying the wrap angle and belt tension. This approach is useful in the design of a conveyor pulley shell with improved accuracy.

Effect of thermal loading on sealing behavior of single and twin-gasketed flange joints

Gasketed flange joints are usually subjected to internal pressure at high temperature. The most important requirement of flange joint is to provide leak-free joint under operating condition. In the present study, temperature-dependent nonlinear gasket properties of spiral-wound gasket at elevated temperatures are obtained experimentally and included in the analysis. The relaxation of gasket contact stress in both single and twin-gasketed joints at elevated temperatures is compared. It is observed that the ability to withstand internal pressure decreases with increase in temperature in both single and twin-gasketed flange joints. But, the twin-gasketed flange joint is found to withstand higher internal pressure than single-gasketed joint at a given bolt preload and temperature. The influence of gasket seating surface rotation on the distribution of gasket radial contact stress at elevated temperature is studied. The effect of elevated temperature on flange stresses of twin-gasketed joint is also examined.

Finite element study of residual stresses and distortions in arc welding with a trailing liquid nitrogen heat sink

Purpose – The purpose of this paper is to study the effect of trailing liquid nitrogen (LN2) heat sink on arc welding of mild steel plates. The effect on temperature field, stress and distortions are studied using experimental and numerical methods.Design/methodology/approach – The methodology consists of experimental and numerical methods. The temperature measured at a point near the arc is used to estimate the cooling capacity of the heat sink using inverse heat transfer (IHT) method. The estimated cooling flux is applied to the finite element model to study the stress and distortions using LN2 heat sink. The stresses are measured using X‐ray diffraction technique and the distortions using dial gauges.Findings – IHT method has been employed in estimating the cooling capacity of the LN2 jet. This has been applied to welding to study the effect on weld induced stresses and distortions. The method can be extended to calculate the heat removal rate in various manufacturing processes where cooling is employe...

Strength Prediction in Multi-pin Joints from Equivalent Material Properties in Composite Laminates.

The present work aims to predict failure in composite laminate joints from equivalent material properties. Three- and four-pin joints made of glass fiber/epoxy with [45°/− 45/°]s and [0°/90°/°l]s lay up are considered. A 3D finite element analysis is performed to study the propagation of damage and to predict failure load. Progressive damage analysis is carried out using von-Mises stress as the failure when the stress exceeds the laminate strength. Failure in three- and four-pin joints by equivalent material properties predicted the strength of the joint close to the experimental values with a degradation factor of 0.12.

Estimation of residual stresses in weldments using a nine-noded degenerated shell element

Abstract Residual stresses due to welding have been estimated using a nine-noded degenerated shell element with assumed strains. It is well known that shell elements are capable of handling three-dimensional (3-D) configurations with less computational effort when compared to the full 3-D analysis. The temperature field in the entire weld domain has been calculated using a 3-D brick element. The temperature variation so obtained is utilised to find the distribution of the stress field using the concept of through-thickness integration. Thermal strains at individual Gauss points are calculated and the same are integrated to obtain the nodal loads. Thermo-elasto–plastic formulations using a von-Mises yield criterion with linear isotropic hardening has been employed. The formulations are validated with 2-D and 3-D experimental results available in the literature. It was established that this method can be used for estimating residual stresses in shell-like structures.