Targeted Use Of Forming Induced Residual Stresses In Metal Components

Residual stresses are considered critical to quality in conventional manufacturing strategies. This is where the DFG’s Priority Programme 2013 comes in, looking instead at the opportunities and possibilities for improving the properties of components by targeted use of residual stresses. In the years 2017 to 2023, research teams from all over Germany were able to prove the stability, controllability and usefulness of residual stresses in flat and solid forming manufacturing processes of metallic components. In addition, the cross-project working groups achieved many insights into the fundamental understanding, simulation and, in particular, industry-oriented measurement of residual stresses. The extensive results of these six years of research activities are presented in this final report.

The focus of the Congress will be leading-edge manufacturing processes. Topics include manufacturing at extreme speed, size, accuracy, methodology, use of resources, interdisciplinarity and more. Contributions from production and industrial engineering are welcome. Challenges from the areas of manufacturing, machines and production systems will be addressed. Production research constantly pushes the boundaries of what is feasible. The Congress "Production at the leading edge of technology" will highlight production processes that are advancing into areas that until recently were considered unfeasible, also in terms of methodology, use of resources and interdisciplinarity. But where does the search for new limits lead? Which limitations do we still have to overcome, which ones do we not want to overcome? The aim of the German-speaking colloquium is to establish connections between the research locations and to intensify the overall transfer of results and experience with industrial users.

In this collection, scientists and engineers from across industry, academia, and government present their latest improvements and innovations in all aspects of metal forming science and technology, with the intent of facilitating linkages and collaborations among these groups. Chapters cover the breadth of metal forming topics, from fundamental science to industrial application.

Annotation Examines the factors that contribute to overall steel deformation problems. The 27 articles address the effect of materials and processing, the measurement and prediction of residual stress and distortion, and residual stress formation in the shaping of materials, during hardening processes, and during manufacturing processes. Some of the topics are the stability and relaxation behavior of macro and micro residual stresses, stress determination in coatings, the effects of process equipment design, the application of metallo- thermo-mechanic to quenching, inducing compressive stresses through controlled shot peening, and the origin and assessment of residual stresses during welding and brazing. Annotation c. Book News, Inc., Portland, OR (booknews.com)

This conference book contains papers presented at the 8th GACM Colloquium on Computational Mechanics for Young Scientists from Academia and Industry. The conference was held from August 28th – 30th, 2019 in Kassel, hosted by the Institute of Mechanics and Dynamics of the department for civil and environmental engineering and by the chair of Engineering Mechanics / Continuum Mechanics of the department for mechanical engineering of the University of Kassel. The aim of the conference is, to bring together young scientits who are engaged in academic and industrial research on Computational Mechanics and Computer Methods in Applied Sciences. It provides a plattform to present and discuss recent results from research efforts and industrial applications. In more than 150 presentations, given by young scientists, current scientific developments and advances in engineering practice in this field are presented and discussed. The contributions of the young researchers are supplemented by a poster session and plenary talks from four senior scientists from academia and industry as well as from the GACM Best PhD Award winners 2017 and 2018.

A physically-based dislocation theory of plasticity is derived within an extended continuum mechanical context. Thermodynamically consistent flow rules at the grain boundaries are derived. With an analytical solution of a three-phase periodic laminate, dislocation pile-up at grain boundaries and dislocation transmission through the grain boundaries are investigated. For the finite element implementations, numerically efficient approaches are introduced based on accumulated field variables.

The dimensional instability of metallic materials, following machining (or any method of material removal), is a common problem in the aerospace industry. This is because large parts have to be manufactured to very close tolerances and as much as 95% of the initial material may need to be removed. For machined, relatively complex, aerospace parts it would not be uncommon to see around 50% difference in the simulated results from the actual results, with even simple geometries showing around 19%-40% error. It is believed that a significant portion of these errors are due to a lack of: understanding of how the residual stresses redistribute following material removal; residual stress measuring capabilities; finite element (FE) modelling capabilities; knowledge of the additional residual stresses induced from the machining process (from varying cutting speeds, feed rates, tools, temperatures etc) and finally how the multiaxial residual stresses alter the shape of the part. This project improves the knowledge base of many of these topics. This work involved the development of an automated layer removal method for residual stress measurements in cold rolled sheet metal. This was needed due to the number of residual stress measurements that were required for modelling purposes. The method can determine the residual stresses in the rolling direction for cold rolled sheet material using a single strain gauge. Moreover, it is simple to set up and the total cost of the test rig and subsequent measurements is relatively low. Furthermore, in this project, a number of sheet metal aluminium parts were formed to different radii. The parts were then subsequently chemically milled in stages; the dimensional changes following each material removal being measured. This process was simulated using a commercially available FE package called PAM-STAMP. The FE results for distortion did not show good agreement when compared to the measured results; however, the residual stress measurements provided an unexpected understanding into the cause of the error. The results of the project improve the understanding of how residual stress change the shape of components and give an insight into the modelling parameters needed.

ADVANCED MATERIALS and MANUFACTURING TECHNIQUES for BIOMEDICAL APPLICATIONS The book provides essential knowledge for the synthesis of biomedical products, development, nanomaterial properties, fabrication processes, and design techniques for different applications, as well as process design and optimization. In origin, biomaterials can come from nature or be synthesized in the laboratory with a variety of approaches that use metals, polymers, ceramic, or composite materials. They are often used or adapted for various biomedical applications. Biomaterials are commonly used in scaffolds, orthopedic, wound healing, fracture fixation, surgical sutures, artificial organ developments, pins and screws to stabilize fractures, surgical mesh, breast implants, artificial ligaments and tendons, and drug delivery systems. The sixteen chapters in Advanced Materials and Manufacturing Techniques in Biomedical Applications cover the synthesis, processing, design, manufacturing, and characterization of advanced materials; self-healing, bioinspired, nature-resourced, nanobiomaterials for biomedical applications; and manufacturing techniques such as rapid prototyping, additive manufacturing, etc. Audience The book is for engineers, technologists, and researchers working in the area of biomedical engineering and manufacturing techniques. It is also appropriate for upper-level undergraduate and graduate students.

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.

Additive manufacturing (AM) of parts using a layer by layer approach has seen a rapid increase in application for production of net shape or near-net shape complex parts, especially in the field of aerospace, automotive, etc. Due to the superiority of manufacturing complex shapes with ease in comparison to the conventional methods, interest in these kinds of processes has increased. Among various methods in AM, laser powder bed fusion (LPBF) is one of the most widely used techniques to produce metallic components. As in all manufacturing processes, residual stress (RS) generation during manufacturing is a relevant issue for the AM process. RS in AM are generated due to a high thermal gradient between subsequent layers. The impact of residual stresses can be significant for the mechanical integrity of the built parts and understanding the generation of RS and the effect of AM process parameters is therefore important for a broader implementation of AM techniques. The work presented in this licentiate thesis aims to investigate the influence of build orientation on the RS distribution in AM parts. For this purpose, L-shaped Inconel 718 parts were printed by LPBF in three different orientations, 0°, 45°, and 90°, respectively. Inconel 718 was selected because it is a superalloy widely used for making gas turbine components. In addition, IN718 has in general good weldability which renders it a good material for additive manufacturing. Residual stress distributions in the parts removed from the build plate were measured using neutron diffraction technique. A simple finite element model was developed to predict the residual stresses and the effect of RS relaxation due to the separation of the parts and build plate. The trend of residual stress distribution predicted was in good agreement with experimental results. In general, compressive RS at the part center and tensile RS near the surface were found. However, while the part printed in 0° orientation had the least amount of RS in all three principal directions of part, the part built in 90° orientation possessed the highest amount of RS in both compression and tension. The study has shown that residual stress distributions in the parts are strongly dependent on the building process. Further, it has shown that the relaxation of RS associated with the removal of the parts from the build plate after printing has a great impact on the final distribution of residual stress in the parts. These results can be used as guidelines for choosing the orientations of the part during printing.