Materials Science Forum Vols. 524-525

Abstract: This paper reports experimental characterisation of stress heterogeneities in a French RPV bainitic steel (16MND5) determined by X-Ray diffraction during in-situ tensile testing at low temperature (until –150°C). Results are compared successfully to simulation results, obtained by post-processing of Finite Elements computations of realistic 3D aggregates.

Abstract: Hole drilling along with X-Ray diffraction, is one of the most widely used techniques for measuring residual stress, but the conventional approach is limited in the near surface detail that can be resolved. Because of concerns regarding the levels of induced residual stress that might develop during machining and surface treatment processes, there is significant interest in developing a technique that can obtain near surface residual stress information by the application of fine increment hole drilling. Through a cross comparison with X-ray diffraction and neutron diffraction the procedure of fine incremental drilling has been validated, and the advantages of this technique demonstrated.

Abstract: The aim of this paper is to determine the incremental residual stress profile in depth of a complex shape. The authors have adapted the hole drilling method in a crankshaft and more precisely in the filet area. A new set of calibration coefficients have been determined using the finite elements method in order to analyse residual stresses in the structure.

Abstract: This paper describes a method for extending the capability of the contour method to allow for the measurement of spatially varying multi-axial residual stresses in prismatic, continuously-processed bodies. Currently, the contour method is used to determine a 2D map of the residual stress normal to a plane. This work uses an approach similar to the contour method to quantify multiple components of eigenstrain in continuously-processed bodies, which are used to calculate residual stress. The result of the measurement is an estimate of the full residual stress tensor at every point in the body. The methodology is presented and the accuracy is assessed for a representative test case using a numerical experiment. Finally, a measurement is performed on a thick laser peened plate of 316L stainless steel to show that the approach is valid under real experimental conditions.

Abstract: This paper presents the results of an experimental validation of the deep hole drill residual stress measurement method. A validation test specimen was fabricated and plastically loaded to impose a permanent residual stress field within the specimen. The validation test specimen was designed to provide a variety of stress profiles as a function of location within the specimen. A finite element analysis of the validation test specimen was performed in order to provide a reference solution for comparison to the deep hole drill experimental results. Results from experimental testing of the validation test specimen agree well with the finite element analysis reference solution, thereby providing further validation of the deep hole drill method to measure residual stresses.

Abstract: Residual stresses can arise in engineering components as part of their manufacturing or can also be introduced deliberately as part of surface treatment procedures. A precise knowledge of the level of residual stresses that exist in engineering components is necessary in analysis and quality control as well as for accurate prediction of components lifetime. Therefore, reliable methods of determining the magnitude and distribution of residual stresses are required in order to quantify their effect and to avoid detrimental failures. On the other hand on-site portable and nonor near non-destructive methods are required for practical use. The hole-drilling method shows a great potential in measuring and evaluating residual stresses in practical applications. This paper presents results and problems on residual stress measurements performed by the holedrilling method on real components, including forming applications of rolling, punching and cutting, and machine component applications of gears and shafts. Presented results clearly indicate the importance of residual stress information for proper design and use of engineering components.

Abstract: The use of Laser Assisted Machining (LAM) can improve different aspects of the machinability of high strength materials. A study was undertaken to determine the optimum cutting parameters and to quantify their influence on fatigue strength according to the type of microstructure created. Two different materials were studied: a bearing steel (100Cr6 / AISI 52100) and an aeronautical titanium alloy (Ti6Al4V). In the bearing steel a significant increase of the fatigue resistance was observed due to the transformation of the surface layer into martensite. For the titanium alloy, a slight reduction in the fatigue strength was found as in this case the microstructure and residual stress state of the surface layer was less beneficial. The surface roughness has also been measured and no significant variation has been observed for different laser powers in each material.

Abstract: Machining residual stresses are considered as part of surface integrity and a consequence of the machining process. Theses stresses are closely correlated with the corresponding process parameters, including the work material properties. As it is well known, not only the mechanical but also the physical properties of the work materials have great influence on machining residual stress. This was demonstrated in the present work through studying the residual stress and work hardening induced by the turning of AISI 316L and AISI 1045 steels. The residual stresses were determined at the workpiece surface and in-depth using the X-ray diffraction technique. To understand the influence of the work material properties on the residual stress and work hardening distributions, the mechanical and thermal phenomena occurring during the cutting process were studied, using a t developed experimental procedure. The experimental setup included a piezoelectric dynamometer to determine the cutting forces, and thermal imaging equipment developed to assess the temperature distribution in the deformation zone in turning. The results showed that the cutting forces and temperatures in the machining of 316L steel are much higher than those in the machining of 1045 steel. Thus, machining 316L steel, when compared to 1045 steel, results in higher superficial residual stresses and stronger in-depth residual stress gradients, higher superficial work-hardening and greater thickness of the work hardened layer.

Abstract: In this paper, the effect of a high pressure water jet, directed into the tool chip interface, on surface residual stresses and chip shape, in face turning of AISI 316L stainless steel has been investigated. Tests have been carried out with a standard cutting tool. This tool is not specifically meant for the machining of this type of material. The cutting speeds used were 80 m/min and 150 m/min, with a constant feed rate of 0.1 mm/rev and a constant cutting depth of 0.1 mm. Three jet pressures were used: 20, 50 and 80 MPa. Residual stress profiles have been analysed using the X-ray diffraction method in both longitudinal and transversal directions. The results show that by using a high pressure jet directed into the tool-chip interface, it is possible to create a well fragmented chip in contrast to the continuous chip formed using dry turning. It is also possible to control the chip shape and increase tool life. When the jet pressure is increased the residual stress at the surface decreases however it is increased by an increase in cutting speed. It can be concluded that surface residual stresses can be reduced by the introduction of a high pressure water jet. A reduction in the residual stress value by about 20 to 40 % can be observed when using high pressure water jet assisted turning compared to dry turning. Also, it has been observed that the jet pressure does not have a great influence on the depth affected by residual stress and by hardening.