A Contribution To Enlarge The Application Limits Of Residual Stress Analyses By The Hole Drilling And The Ring Core Method

The primary focus of this work is the processing – microstructure – property correlation of EBM manufactured high-alloyed austenitic CrMnNi stainless steel. Independent of the applied process parameters, to this point this alloy exhibits a fine-grained and weak textured microstructure in the as-built state upon EBM processing. As detailed in the literature review, this is opposite to numerous alloys like the benchmark AISI 316L stainless steel, which are commonly characterized by epitaxial growth of columnar grains elongated parallel to building direction. A theory for this unusual observation is presented based on a grain refinement due the process-inherent cyclic heat-treatment, i.e. repetitive reheating and partial melting of the consolidated material due to the energy input during melting of subsequent layers and resulting solid-liquid as well as solid-solid (ferritic bcc to austenitic fcc phase and vice versa) phase transformations. A calculation of the phase diagram, differential thermal II Abstract analysis and the investigation of the uppermost layers of bulky and thin-walled EBM processed structures are conducted to support this assumption. Moreover, the CrMnNi stainless steel specimens are characterized by an outstanding damage tolerance, which is demonstrated by tensile testing and examination of the fracture surfaces revealing large lack-of-fusion defects due to unsuitable process parameters. Combined EBSD and X-ray diffraction analysis attribute the high damage tolerance to a pronounced strain hardening and mitigation of the effect of defects due to the transformation-induced plasticity (TRIP) effect. The deformation-induced martensitic transformation and associated strain hardening has also been correlated to a considerable low-cycle fatigue performance even under the presence of large inhomogeneities. The chemical composition of the alloy upon EBM processing is strongly dependent on the process parameters, i.e. it is demonstrated that the evaporation rate of Mn varies with the scan strategy and volumetric energy density. This phenomenon is utilized for the fabrication of homogeneous specimens with different Mn concentrations and resulting mechanical properties.These findings are subsequently employed for a prove-of-concept of the possibility to produce functionally graded material by a spatial adjustment of the scan strategy throughout the layer-wise built-up of objects. This is a novel approach for the synthetization of functionally graded materials based on the processing of one homogenous precursor powder feedstock. In summary, the particular CrMnNi stainless steel is introduced as a novel alloy design for AM because it addresses current material-related issues inherent in layer-wise technologies and potentially further contributes to the exploitation of the full potential of AM.

This book describes the theory and practice of the Hole-Drilling Method for measuring residual stresses in engineering components. Such measurements are important because residual stresses have a "hidden" character because they exist locked-in within a material, independent of any external load. These stresses are typically created during component manufacture, for example, during welding, casting, or forming. Because of their hidden nature, residual stresses are difficult to measure and consequently are often ignored. However, they directly add to loading stresses and can cause catastrophic failure if not properly included during engineering design. Thus, there is an urgent need to be able to identify and measure residual stresses conveniently and reliably. The Hole-Drilling Method provides an adaptable and well-proven method for measuring residual stresses in a wide range of materials and component types. It is convenient to use and gives reliable results. Because of the hidden nature of residual stresses, the measurement method must necessarily be indirect, thus, additional care and conceptual understanding are necessary to achieve successful results. This book provides a practical introduction to the Hole-Drilling Method, starting from its historical roots and going on to focus on its modern practice. The various chapters describe the nature of residual stresses, the principle of hole-drilling measurements, procedures and guidance on how to make successful measurements, and effective mathematical procedures for stress computation and analysis. The book is intended for practitioners who need to make residual stress measurements either occasionally or routinely, for practicing engineers, for researchers, and for graduate engineering and science 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.

Residual Stresses presents a collection of articles that provides information regarding the use of surface treatment systems. It discusses the developments in the technology and application of surface treatment. It addresses the influence of minor stresses on the performance of materials. Some of the topics covered in the book are the introduction to self-equilibrating stresses existing in materials, the stresses that form as a consequence of welding, the stresses made by machining, and the mechanical generation of self-stresses. The analysis of the stresses caused by thermal and thermochemical surface treatments is covered. The minor stresses in composite materials are discussed. The text describes the stresses in uranium and uranium alloys. The Trepan or ring core method, centre-hole method, and Sach's method are presented. A chapter of the volume is devoted to the measurement of residual stresses. Another section of the book focuses on the application of shot peened plates to residual stress distribution. The book will provide useful information to mechanics, engineers, students, and researchers.