Modeling The Residual Stress Distribution And Experimental Characterization Of Shot Peening On Az31b Rolled Sheet

The drive to reduce fossil fuel consumption due to its environmental impacts has generated renewed interest in employing magnesium (Mg), the lightest industrial metal, and its alloys in vehicle manufacturing. One of the qualifying metrics for structural application of Mg in transportation vehicles is its high durability. The low fatigue strength of these alloys has been an obstacle to using them in load-bearing components. Thus, methods for improving the fatigue properties of Mg alloys are of interest. Shot peening is a cold-working process employed to improve the fatigue properties of materials. The shot peening process induces compressive residual stress at the material's surface and at a layer in the order of a few hundred micrometers deep, which improves the fatigue life by retarding the crack initiation as well as growth; however, the increased surface roughness has a detrimental effect on fatigue life. These competing effects of peening have created interest in finding the optimum peening intensity that will maximize fatigue life. Modeling reduces the cost of experimentally evaluating optimum peening conditions. However, modeling the shot peening of Mg alloys remains complicated due to the anisotropic and asymmetric properties of wrought Mg alloys, and the complex unloading behavior and rate-sensitivity behavior of these materials. To address these challenges, a comprehensive experimental and numerical-analytical study of shot peening on AZ31B-H24 rolled sheet was conducted and is reported in this thesis. First residual stress distributions through the depth of the material were measured. Among the methods for residual stress measurement, X-ray diffraction (XRD) has attracted researchers' attention because: 1) it is a non-destructive method; 2) it can measure residual stress at the surface, and 3) the spatial resolution can be less than 0.3 mm. However, due to the low x-ray mass attenuation coefficient of Mg alloys, x-ray penetration in the material is significant which needs to be accounted for. The residual stresses in as-received and shot peened AZ31B-H24 rolled sheet samples were measured using the 2D-XRD method. The electro-polishing layer removal method was used to find the residual stress pattern through depth. Due to the high depth of penetration, a correction had to be made to account for the penetration depth. The results showed that the corrected residual stresses in a few tens of micrometers layer from the surface were different from the raw stresses. To better estimate the residual stress distribution in a few micrometers from the surface, the grazing-incidence x-ray diffraction (GIXD) method was applied to evaluate the stresses in the surface layer. This study also showed how small uncertainty in measuring the observed residual stress and in evaluating the depth of the polished area in layer removal leads to high uncertainty in the corrected residual stresses. The XRD results showed the creation of compressive residual stress through the depth as well as a good agreement between the XRD and hole-drilling and GIXD results. Modeling the shot peening process first requires an understanding of how Mg alloys behave at large strain values during loading-unloading. The tension-compression (TC) and compression-tension (CT) in the in-plane directions were obtained using an anti-buckling fixture. By comparing the compression part of the CT curves along the rolling direction (RD) with the ones using a cuboid sample, the negligible effect of using the anti-buckling fixture was shown. A novel fixture was designed to obtain the CT and TC curves in the through-thickness (normal direction: ND) of the rolled sheet, which is only 6.3 mm thick. FEM was employed to evaluate the consistent area for strain measurement using DIC in the designed setup. The CT and TC curves along ND were obtained using the new fixture. The results of the new fixture were verified by comparing the curves obtained by the new fixture in RD with those obtained by using the anti-buckling fixture. Different effects of shot peening on the AZ31B-H24 rolled sheet were characterized in this study by measuring the residual stress and micro-hardness distribution through the depth, followed by measuring surface roughness and texture evolution at the surface of samples shot peened under Almen intensities ranging from 0.05 mmN to 0.6 mmN. To obtain the optimum peening intensity, rotating bending fatigue tests were performed on peened samples at different intensities. It was found that increasing the peening intensity, increases the surface roughness and hardness at the surface layer. In addition, the depth of the maximum compressive stress and the depth of the induced compressive residual stress layer have a direct relation with the peening intensity. The material showed a high sensitivity to shot peening under different intensities, due to the over-peening effects in the peening on Mg alloys. Peening at the optimum intensity increases the fatigue strength moderately, from 130 MPa to 150 MPa. During investigations to find an accurate and a computationally efficient method for capturing the complex behavior of Mg alloys, it was found that stringent assumptions are needed to allow for a closed-form analytical solution when calculating residual stresses induced by shot peening. This limits the application of these models to idealized conditions. On the other hand, and because of the complex behaviors of Mg alloys, such as complex unloading behavior and rate-sensitivity, it is difficult to provide numerical solutions such as finite element that are capable of mimicking actual material's behavior once it is released from an over-strain loading state. Moreover, modeling full coverage shot peening condition is time-consuming and computationally expensive. A single-shot finite element model was combined with an analytical model using actual loading-unloading material behavior to propose a hybrid FEM-analytical model for prediction of the residual stress distribution in shot peening. First, the shot peening process was divided into a loading phase, modeling the impact of a shot and substrate, and an unloading phase, modeling the rebounding of the shot. Finite element was employed to model a single shot impingement on a substrate using the actual loading properties of the substrate. Using the results of the loading phase, an analytical model was proposed to predict stresses due to the unloading phase, using the actual unloading behavior of the material. The proposed hybrid model accounts for the actual behavior of a material, actual elastic-plastic contact analysis, strain rate effect, and friction. The model was then verified by predicting residual stresses induced in a SAE1070 and an Al2024-T351 sheet. Results were compared with the available experimental results and showed close agreements. The application of the proposed hybrid numerical-analytical model was extended to use with an asymmetric and anisotropic material that also has complex unloading behavior, i.e., Mg alloys. First, the loading state of material under peening and the effects of the material's asymmetry and anisotropy were discussed, then the numerical modeling of the loading step was provided. Finally, the actual unloading curves, measured using the designed fixture, of the material were used to estimate the residual stress profiles. The strain rate effect was also considered in the modeling. The results were matched closely with the XRD and hole-drilling experimental measurements.

Shot peening has been proved to be a powerful instrument in enhancing the resistance of materials to various kinds of stress-induced damage, particularly against damage due to cyclic loading (fatigue) in air or in aggressive environments. As shot peening can be used for a wide variety of structural components irrespective of shape and dimensions, the number of shot peening applications in many industrial branches is increasing. The use of peen forming as a technique to form large metal parts into complicated shapes is also increasing, particularly in the aerospace industry. The Conference covers all aspects of the Science, Technology and Application of Shot Peening, and was intended to attract users, manufacturers as well as scientists working in the field of "Materials Treatment by Shot Peening". Emphasis was put on the current state of knowledge and research. This book offers scientists and engineers an unique opportunity to update their knowledge on shot peening.

This book presents the proceedings of the International Conference on Residual Stresses 10 and is devoted to the prediction/modelling, evaluation, control, and application of residual stresses in engineering materials. New developments, on stress-measurement techniques, on modelling and prediction of residual stresses and on progress made in the fundamental understanding of the relation between the state of residual stress and the material properties, are highlighted. The proceedings offer an overview of the current understanding of the role of residual stresses in materials used in wide ranging application areas.

This volume presents a selection of papers from the 2nd International Conference on Computational Methods in Manufacturing (ICCMM 2019). The papers cover the recent advances in computational methods for simulating various manufacturing processes like machining, laser welding, laser bending, strip rolling, surface characterization and measurement. Articles in this volume discuss both the development of new methods and the application and efficacy of existing computational methods in manufacturing sector. This volume will be of interest to researchers in both industry and academia working on computational methods in manufacturing.

Residual stresses are a common phenomenon in composite materials. They can either add to or significantly reduce material strength. Because of the increasing demand for high-strength, light-weight materials such as composites and their wide range of applications in the aerospace and automotive industries, in civil infrastructure and in sporting applications, it is critical that the residual stresses of composite materials are understood and measured correctly. The first part of this important book reviews destructive and non-destructive testing (NDT) techniques for measuring residual stresses. Various mathematical (analytical and numerical) methods for calculation of residual stresses in composite materials are also presented. Chapters in the first section of the book discuss the simulated hole drilling method, the slitting/crack compliance method, measuring residual stresses in homogeneous and composite glass materials using photoelastic techniques, and modeling residual stresses in composite materials. The second part of the book discusses residual stresses in polymer matrix, metal-matrix and a range of other types of composites. Moreover, the addition of nanoparticles to the matrix of polymeric composites as a new technique for reduction of residual stresses is discussed. Residual stresses in composite materials provides a comprehensive overview of this important topic, and is an invaluable reference text for both academics and professionals working in the mechanical engineering, civil engineering, aerospace, automotive, marine and sporting industries. Reviews destructive and non-destructive testing (NDT) techniques for measuring residual stresses Discusses residual stresses in polymer matrix, metal-matrix and other types of composite Considers the addition of nanoparticles to the matrix of polymeric composites as a new technique for reduction of residual stresses

Fundamentals of Machine Component Design presents a thorough introduction to the concepts and methods essential to mechanical engineering design, analysis, and application. In-depth coverage of major topics, including free body diagrams, force flow concepts, failure theories, and fatigue design, are coupled with specific applications to bearings, springs, brakes, clutches, fasteners, and more for a real-world functional body of knowledge. Critical thinking and problem-solving skills are strengthened through a graphical procedural framework, enabling the effective identification of problems and clear presentation of solutions. Solidly focused on practical applications of fundamental theory, this text helps students develop the ability to conceptualize designs, interpret test results, and facilitate improvement. Clear presentation reinforces central ideas with multiple case studies, in-class exercises, homework problems, computer software data sets, and access to supplemental internet resources, while appendices provide extensive reference material on processing methods, joinability, failure modes, and material properties to aid student comprehension and encourage self-study.

The objective of this book is to assist scientists and engineers select the ideal material or manufacturing process for particular applications; these could cover a wide range of fields, from light-weight structures to electronic hardware. The book will help in problem solving as it also presents more than 100 case studies and failure investigations from the space sector that can, by analogy, be applied to other industries. Difficult-to-find material data is included for reference. The sciences of metallic (primarily) and organic materials presented throughout the book demonstrate how they can be applied as an integral part of spacecraft product assurance schemes, which involve quality, material and processes evaluations, and the selection of mechanical and component parts. In this successor edition, which has been revised and updated, engineering problems associated with critical spacecraft hardware and the space environment are highlighted by over 500 illustrations including micrographs and fractographs. Space hardware captured by astronauts and returned to Earth from long durations in space are examined. Information detailed in the Handbook is applicable to general terrestrial applications including consumer electronics as well as high reliability systems associated with aeronautics, medical equipment and ground transportation. This Handbook is also directed to those involved in maximizing the relia bility of new materials and processes for space technology and space engineering. It will be invaluable to engineers concerned with the construction of advanced structures or mechanical and electronic sub-systems.

Friction stir welding has seen significant growth in both technology implementation and scientific exploration. This book covers all aspects of friction stir welding and processing, from fundamentals to design and applications. It also includes an update on the current research issues in the field of friction stir welding and a guide for further research.

Friction Stir Welding (FSW) is known to result in a complex microstructural development, with features that remain unexplained, such as: the formation of the onion rings structure. Moreover, various microstructural factors have been suggested to control the strength in Al-Mg AA5xxx welds, without identifying their relative contribution. Furthermore, the influence of the basemetal microstructural parameters (e.g. grains, intermetallic particles, stored energy) on the microstructure-property development has not been previously investigated. These issues are addressed in the present study.

The Magnesium Technology Symposium, the event on which this collection is based, is one of the largest yearly gatherings of magnesium specialists in the world. Papers in this collection represent all aspects of the field, ranging from primary production to applications to recycling. Moreover, papers explore everything from basic research findings to industrialization. This volume covers a broad spectrum of current topics, including alloys and their properties; cast products and processing; wrought products and processing; forming, joining, and machining; corrosion and surface finishing; ecology; and structural applications. In addition, there is coverage of new and emerging applications in such areas as hydrogen storage.