Papers by Keyword: Residual Stress Analysis

Abstract: This study investigates the influence of cutting parameters on tool temperatures and residual stresses during the machining of aerospace alloys Inconel-718, Hastelloy-X, and Ti6Al4V. Experimental turning operations were conducted under predetermined cutting speeds, feed rates, and cutting depths, followed by residual stress measurements using X-ray diffraction (XRD). Maximum tool temperatures were recorded using a thermal camera. Additionally, numerical simulations were performed using DEFORM 3D under identical cutting conditions to validate the experimental findings. The results reveal that Hastelloy-X exhibited the highest residual stresses and cutting tool temperatures, while Ti6Al4V showed the lowest. A close agreement was observed between the experimental and simulation data, highlighting the accuracy of the DEFORM 3D model. This study provides a comprehensive analysis of Hastelloy-X, a material with limited prior research, contributing novel insights into its machining characteristics. The findings will aid in optimizing cutting parameters for improved performance and tool life in aerospace applications.

Abstract: Nowadays, one of the most crucial focus in the aluminium-foundry sector is the production of high-quality castings. Mainly, High-Pressure Die Casting (HPDC) is broadly adopted, since by this process is possible to realize aluminium castings with thin walls and high specific mechanical properties. On the other hand, this casting process may cause tensile states into the castings, namely residual stresses. Residual stresses may strongly affect the life of the product causing premature failure of the casting. Various methods can assess these tensile states, but the non-destructive X-Ray method is the most commonly adopted. Namely, in this work, the residual stress analysis has been performed through Sinto-Pulstec μ-X360s. Detailed measurements have been done on powertrain components realized in aluminium alloy EN AC 46000 through HPDC processes to understand and prevent dangerous residual stress state into the aluminium castings. Furthermore, a comparison with stresses induced by Rheocasting processes is underway. In fact, it is well known that Semi-Solid metal forming combines the advantages of casting and forging, solving safety and environmental problems and possibly even the residual stress state can be positively affected.

Abstract: Ultrasonic needle peening (UNP) is a post-weld high frequency mechanical impact (HFMI) treatment process. This study describes a practical method for measuring residual stress (RS) distribution after UNP and its application to a simple case. Laboratory sin²ψ XRD RS analysis is performed on an UNP single-track on a flat structural steel specimen. This situation is studied as a reference case to characterize RS creation during UNP. It is demonstrated that successive mechanical and electrochemical polishing stages combined with relatively high resolution sin²ψ XRD measurement permits to get an effective surface and in-depth characterization of longitudinal and transverse RS around the UNP groove. High magnitude longitudinal compressive RS are found in the middle of the groove whereas transverse RS compression peaks are located on both sides of the groove. Discussion is conducted about sources of error associated with the experimental method and outlook for UNP process fundamental characterization.

Abstract: In scope of the investigation of residual stresses the hole drilling method is an accepted method. The method is though not applicable for materials with high anisotropic behavior. Therefore a new algorithm is derived which allows the calculation of residual stresses in laminates made of unidirectional layers. Also the strain gauges deliver only strains on the areas where the strain gauges are applied. With the use of a high resolution imaging system and digital image correlation this area and the informational output can be widely improved. First, the derivation of the residual stress analysis algorithm is presented. For this an adequate finite element model, which is modeling the cooldown process as well as the drilling process, is set up and the surface strains are extracted. Based on this information an algorithm is derived and presented. Within the derivation a change of the layup, a possible change of the cooldown process and a variation of the drilling steps can be investigated. In consequence the input parameters of the algorithm can vary dependent on these factors. Second, the new optical testing setup with refinements to be able to measure the small deformations within micro-strains on the specimen’s surface is prepared and the concept presented. To solve the problem of casting shadows of the drill a special camera setup is being used.

Abstract: Article presents results of measurements of vital parameters of PVD coatings of potential application in medicine (joint replacements or medical tools). The phase identification, level of residual stresses and texture were determined for various coatings by X-ray diffraction method. Chemical composition of coatings was verified by means of XRF. A set of measurements reveled the existence of advantageous compressive stresses in coatings, the texture determination showed undesirable fiber texture in TiN coating and advantageous uniformity of TiCN ones. XRF analysis pointed out the necessity of careful preparation of samples during PVD process during which phenomena of inhomogeneity in chemical can be present as it is presented in the paper.

Abstract: A novel functionally gradient composite was reported in this article. The composite material are composed of plain low carbon steel Fe360 as a substrate and glass-ceramics containing ZrO₂ reinforcing particles as a coating. Based on a mathematical model of the residual stress, the geometric model and finite element analysis models of the Fe360/glass-ceramic gradient coatings were established. The residual stress of the gradient layers was calculated with the commercial software ANSYS 10.0. The results showed that the differences of thermal expansion coefficient and shrinkage rate in each layer resulting from the difference of the volume fraction of ZrO₂ in each gradient layer could make the surface layer generate suitable compressive stress. The maximum residual stress presents itself at the interface between the substrate and the gradient coatings. The layer numbers and the thickness of graded coatings have a significant effect on the residual stress.

Abstract: The deformation behavior of the magnesium base alloy AZ31 was studied by means of energy dispersive diffraction using high energy synchrotron radiation. The investigations were performed at the EDDI-beamline operated by the Hahn-Meitner-Institute at Bessy II, Berlin. In-situ stress analyses were carried out for samples subjected to purely elastic as well as elasto-plastic 4- point-bending. In addition reversely loaded states were investigated. The results impressively illustrate the potential of the energy dispersive diffraction analysis processed in transmission mode for residual stress analysis of challenging material states. Inhomogeneous loading and residual stress distributions with respect to the bending height of the prestressed bars were determined for the highly textured material state indicating different predominant deformation mechanisms during tensile loading and compressive loading, respectively. After load inversion also the predominant deformation mechanisms reverse.

Abstract: In residual stress analysis (RSA) using energy dispersive (ED) diffraction care has to be taken of the detector energy stability. For a given detector system it is demonstrated that the energy position decreases significantly with dead time. Correction of the RSA data both in reflection and scanning experiments allows a significant improvement in the reliability of RSA under different conditions. Owing the small diffraction angles in ED experiments, the effect of adjustment errors in reflection geometry is investigated revealing the need of a wide incoming beam combined with high collimation of the secondary beam. The differences in the used absorber materials are shown in respect of sample heating and beam widening due to diffuse scattering.

Abstract: Internal stresses are very important for the performance of protective hard coatings. Tensile stresses favour the formation and propagation of cracks, inducing fracture and corrosion. Medium compressive stresses hinder fatigue. But high compressive stresses, typically for hard coatings produced by PVD (physical vapour deposition) processes, support delamination in order to relax the stored elastic energy. However notwithstanding its relevance, the internal stresses are only seldom used for the optimisation and quality control of hard coatings in industry. This unsatisfying situation is caused by the deficit in efficient measuring methods. The results of thin sheets, where the stresses can be simply measured by their curvature, are not necessarily representative for the coating of thicker parts. The conventional XRD (X-ray Diffraction), based on angle-dispersive evaluation needs expensive devices and is rather time consuming. The energy-dispersive technique opens new possibilities. It is based on polychromatic radiation. The interference of the lattice plane reflections corresponding to the Bragg-equation is investigated by the diffraction intensity of the different wavelength (or photon energies), not by varying the Bragg-angle as in conventional XRD. Hence, the whole diffraction pattern can be obtained in one shoot without the use of any goniometer. This allows the construction of small and compact measuring devices and the reduction of measuring time to a few minutes. The capability of the ED-XRD (Energy Dispersive X-ray Diffraction) is demonstrated for titanium nitride and chromium nitride films deposited by cathodic vacuum arc with varying parameters. Comparisons were made with the much more time-consuming AD-XRD (Angle Dispersive X-ray Diffraction) for residual stress analysis. The results of both methods are in good agreement.

Abstract: For industrial applications concerning the nondestructive characterization of the nearsurface material condition in terms of residual stresses, work hardening, phase transformation and formation of reaction compounds there is a strong demand for X-ray diffraction measurements on large components with complex geometry. Because many regions of interest on these components are not accessible with conventional laboratory or even mobile X-ray diffractometers, a novel center- free diffractometer with two cooperating robots named "Charon XRD" has been developed at MTU Aero Engines. Using a special optical measuring system to synchronize the two six-axis robots it was possible to achieve positioning accuracies that are comparable to those of conventional stationary diffractometers. This paper describes the design and functionality of Charon XRD and presents calibration and reference measurements, along with first measurements on aero-engine components.