Presented master thesis deals with computational modelling (simulation) of welding process. Its main goal is to determine the residual stresses and deformations arising after welding. SYSWELD and ANSYS are used for simulation, both based on the finite element method. Specifically, the processes of welding fillet and butt welds are solved. Results from both software are compared with each other and verified by experimental results.

Since grinding is often the last process of a manufactured part, caution has to be taken in order to ensure the integrity of the surface. The role of grinding induced residual stresses can be important in fatigue or wear resistance. In most cases we cannot evaluate accurately and easily their distribution. On this purpose, many scientists are working on the modeling of grinding and its effects on a many points. The main aim of this work is to analyse of residual stresses influenced by grinding parameters.

In many instances the predominant factor contributing to structural failure in welded parts is the residual stress which exists before the part is put into service. In this investigation an attempt is made to study the changes in residual stresses caused by vibrational stress relief (VSR). VSR is a fairly new idea in stress relief and there is no substantial evidence of its success in reducing residual stresses. This thesis documents the residual stress distributions found in 5/16 inch thick, 22 inch diameter welded fabricated tubes after VSR.

Indiana University-Purdue University Indianapolis (IUPUI) / Process induced dimensional changes in composite parts has been the topic of interest for many researchers. The residual stresses that are induced in composite laminates during curing process while the laminate is in contact with the process tool often lead to dimensional variations such as spring-in of angles and warpage of flat panels. The traditional trial-and-error approach can work for simple geometries, but composite parts with complex shapes require more sophisticated models. When composite laminates are subjected to thermal stresses, such as the heating and cooling processes during curing, they can become distorted as the in-plane and the throughthickness coeffcients of thermal expansion are di erent, as well as chemical shrinkage of the resin, usually cause spring-in. Deformed components can cause problems during assembly, which significantly increases production costs and affects performance. This thesis focuses on predicting these shape deformations using software simulation of composite manufacturing and curing. Various factors such as resin shrinkage, degrees of cure, difference between through thickness coeffcient of thermal expansion of the composite laminate are taken into the consideration. A cure kinetic model is presented which illustrates the matrix behavior during cure. The results obtained using the software then were compared with the experimental values of spring-in from the available literature. The accuracy of ACCS package was validated in this study. Analyzing the effects of various parameters of it was estimated that 3D part simulation is an effective and cost and time saving method to predict nal shape of the composite part.

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<p> Manufacturing processes such as cold-bending flat sheet to a small radius produces a rather complex residual stress state through the thickness of light gauge structural steel sections. When the load-application device is released the sheet exhibits a phenomenon called "spring-back".</p> <p> The purpose of this research was to develop an exact method of computing the residual stresses in a wide sheet of ideal plastic metal after spring back and subsequently to study their effect on the behaviour of cold-formed sections. An approximate analysis based on the assumption of elastic spring back is presented for comparison purposes. It is demonstrated that plastic flow occurs within a thin core of sheet below the neutral axis and that the spring back is not completely elastic beyond a certain curvature. Such behaviour is particularly significant in cases where the radius of bend is of the same order as the thickness. An exact analysis based on a more realistic approach is then performed considering the adjustments in the stress components due to the plastic core. Computer programs have been developed to calculate the residual stresses associated with any given radius of bend. It is found that the choice of one yield criterion rather than the other does not have any effect on the present analysis and the stress components for Von Mises' material are (2/√3) times the components for Tresca's material. Furthermore, the effect of lateral stretching on the behaviour of cold-formed sections is briefly viewed.</p> <p> The purpose of the experimental work in this thesis was to verify the validity of some of the assumptions made in the analysis.</p> <p> Conclusions are drawn and suggestions made for further research.</p> / Thesis / Master of Engineering (MEngr)

Compressive residual stresses induced by tensile overloads, compressive under loads, or by a cold-expansion process in specimens containing a circular hole and their influence on subsequent fatigue crack growth in aluminum alloys are studied. The finite element method is used to calculate residual stresses. The superposition method, which uses crack-tip stress intensity factors for cases involving remote loading and residual stresses, is used to calculate crack growth life for three kinds of tests from the literature: (1) fatigue of a circular hole specimen after an overload or under load, (2) single crack growing from a circular hole after a severe tensile overload, and (3) single crack growing from a circular hole after cold-working, reaming and notching. All specimens were subjected to subsequent constant amplitude loading. The superposition method worked fairly well for most cases, but tended to over predict fatigue life for small cracks and for cracks growing under residual stresses, which produce compressive (maximum and minimum) stress intensity factors.

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