Showing papers on "Residual stress published in 2013"

Electron Beam Additive Manufacturing of Titanium Components: Properties and Performance

Abstract: This research evaluates the fatigue properties of Ti-6Al-4V specimens and componentsproduced by Electron Beam additive manufacturing. It was found that the fatigue per-formance of specimens produced by additive manufacturing is significantly lower thanthat of wrought material due to defects such as porosity and surface roughness. However,evaluation of an actual component subjected to design fatigue loads did not result in pre-mature failure as anticipated by specimen testing. Metallography, residual stress, staticstrength and elongation, fracture toughness, crack growth, and the effect of post process-ing operations such as machining and peening on fatigue performance were alsoevaluated. [DOI: 10.1115/1.4025773]Keywords: additive manufacturing, electron beam, titanium, fatigue, fracture

Practical residual stress measurement methods

Abstract: Residual stresses play major roles in engineering structures, with highly beneficial effects when designed well, and catastrophic effects when ignored. With ever-increasing concern for product performance and reliability, there is an urgent need for a renewed assessment of traditional and modern measurement techniques. Success critically depends on being able to make the most practical and effective choice of measurement method for a given application.

Comparison of mechanisms of advanced mechanical surface treatments in nickel-based superalloy

Abstract: Mechanical surface enhancement techniques are used to introduce compressive residual stresses to enhance the fatigue life and corrosion resistance of metallic components. In this study, we compare the effects of three advanced mechanical surface enhancements treatments: laser shock peening, cavitation shotless peening and ultrasonic nano structure modification on residual stress, hardness, plastic deformation and changes in near surface microstructure introduced in a Ni-Base superalloy, IN718 SPF(Super plastic forming). Coupons of the alloy were peened using two different conditions of each treatment and results compared to achieve a better understanding of underlying mechanisms of these techniques. Results indicate that there are significant differences in mechanisms of these surface treatments leading to differences in material response.

The Contour Method

Abstract: The contour method is a mechanical measurement technique for mapping residual stresses in engineering structures. First introduced in 2000 [1, 2], it relies on the surface deformation that results from stress relaxation over a newly cut plane to calculate the residual stresses that existed in the component before the cut. The main advantage of the contour method is its ability to produce a 2-D map of residual stress acting normal to the cut surface. Other mechanical techniques, such as hole drilling, deep hole drilling, layer removal and slitting, produce single residual stress line profiles. The typical uncertainty for the Contour Method is around 30 MPa for steel and 10 MPa for aluminium [3].

Process induced residual stresses and distortions in pultrusion

Abstract: In the present study, a coupled 3D transient Eulerian thermo-chemical analysis together with a 2D plane strain Lagrangian mechanical analysis of the pultrusion process, which has not been considered until now, is carried out. The development of the process induced residual stresses and strains together with the distortions are predicted during the pultrusion in which the cure hardening instantaneous linear elastic (CHILE) approach is implemented. At the end of the process, tension stresses prevail for the inner region of the composite since the curing rate is higher here as compared to the outer regions where compression stresses are obtained. The separation between the heating die and the part due to shrinkage is also investigated using a mechanical contact formulation at the die-part interface. The proposed approach is found to be efficient and fast for the calculation of the residual stresses and distortions together with the temperature and the cure distributions.

Investigation of Residual Stresses Induced during the Selective Laser Melting Process

Abstract: The selective laser melting process (SLM), belonging to the family of additive manufacturing processes, can create complex geometry parts from a CAD file. Previously, only prototypes were created by SLM, but now this process is used to manufacture quickly and directly functional parts. For example, in the PEP (Pole Europeen de la Plasturgie), this process is used to fabricate tooling parts or injection molds with cooling channels that can’t be obtained by conventional routes. During the process, the laser beam generates violent heating and cooling cycles in the material inducing important thermal gradients in the consolidated part. The cyclic thermal expansions and contractions exceeding the maximum elastic strain of the material induce heterogeneous plastic strains and generate internal stresses the level of which can reaches the yield stress of the material and cracks may appear during the process. This paper deals with the measurement and analysis of residual stresses during the selective laser melting of a simple part in maraging steel. The objective of this study is the analysis of experimental results to validate the numerical model previously presented in [1]. Some authors have investigated the residual stresses produced in SLM parts using different experimental measurement methods such as the incremental hole drilling method in [2], the layer removal method see in [3] and [4] or the non-destructive method, by neutron diffraction in [5]. A new method is proposed to evaluate the residual stresses induced during the SLM process, a rosette is fixed on the bottom face of the support. The residual stresses in the created part are calculated from strain and temperature variations when the fused layer is consolidating during the cooling between two layers. Process parameters like the powder thickness or the time cooling between successive layers are studied in this paper. [1] L. Van Belle, G. Vansteenkiste, J.C. Boyer, Comparisons of numerical modeling of the selective laser melting, Key Engineering Materials Vols. 504-506 (2012) pp 1067-1072 [2] C. Casavola, S.L. Campanelli, C. Pappalettere, Experimental analysis of residual stresses in the selective laser melting process, Proceedings of the XIth International Congress and Exposition, June 2-5, 2008 Orlando, Florida USA [3] M. Shiomi, K. Osakada, K. Nakamura, T. Yamashita, F. Abe, Residual stress within metallic model made by selective laser melting process, CIRP Annals - Manufacturing Technology, Vol. 53, No. 1. (2004), pp. 195-198 [4] T. Furumoto, T. Ueda, M.S. Abdul Aziz, A. Hosokawa and R. Tanaka, Study on reduction of residual stress induced during rapid tooling process, influence of heating conditions on residual stress, Key Engineering Materials Vols. 447-448 (2010) pp 785-789 [5] M. Zaeh, G. Branner, Investigation on residual stresses and deformation in selective laser melting, Production Engineering, Volume 4, Number 1 (2010)

Microstructure, residual stress, and fracture of sputtered TiN films

Abstract: Morphology, structure, residual stress, hardness, and fracture toughness of magnetron sputtered titanium nitride (TiN) thin films, deposited at 300 °C with a thickness in the 0.3- to 2-μm range, were characterized. Film microstructure, the origin of residual stress, and its effect on the fracture toughness and hardness were analyzed. The grain size increased with the film thickness, with 1- to 2-μm-thick films having high pore density. For the 2-μm film, subgrains appeared at grain boundaries. X-ray diffraction showed (200) to (111) preferred orientation transition. The stress in the TiN films changed from highly compressive (− 1.1 GPa) to tensile with the film thickness, reaching 0.68 GPa. Larger grain size, initial porosity, and subgrain generation are reasons for significant changes in the residual stress. Average hardness measured by nanoindentation is 23.2 ± 0.6 GPa. The hardness of the films in compression is higher than in tension. Hardness variation with the film thickness is mainly due to the grain size and microstructure effects. The fracture toughness decreases with the film thickness, depending on the stress state and value. Compressive stress can significantly improve TiN film fracture toughness, while tensile stress seriously degrades it.

Residual stress of 460 MPa high strength steel welded box section: Experimental investigation and modeling

Abstract: An experimental study is presented to investigate and model the residual stress in 460 MPa high strength steel welded box sections using the sectioning method. A total of six square box sections with various width-thickness ratios and thicknesses of steel plates were tested and over 2000 original readings were obtained to quantify the magnitude and distribution of both compressive and tensile residual stresses. The effects of width-thickness ratio and plate thickness on residual stresses, the human error and interaction of the four component plates were clarified. The compressive residual stress magnitude was found to be significantly correlated with the sectional dimensions; while for the tensile stresses near the weld region no clear correlation was found. The human error obtained through the comparison of experimental results measured by two persons for the same section was quite small. No residual stress interaction among four component plates was identified due to the residual stress equilibrium within each plate. Finally, a distribution model and its simplified form were established in this study, and a good agreement was found in the comparison with experimental results.

Cyclic loading of a SiC-fiber reinforced ceramic matrix composite reveals damage mechanisms and thermal residual stress state

Abstract: This study reports on the effects of axial thermal residual stresses, cyclic loading and presence of notches on the tensile performance of a SiC-fiber-reinforced barium–magnesium–alumina–silicate (BMAS) ceramic matrix composite. The residual stress state of the composite was experimentally measured by interrogation of the tensile curves at a uniquely well-defined common intersection point of unloading–reloading cycles in the tensile domain. Notch presence was critical on the material’s mechanical response and promoted catastrophic failure shortly after the achievement of a saturated matrix crack state. The result of cyclic loading was an increase by 20% in sustainable stress throughout loading, as compared to pure tension. Scatter in elastic properties within specimens of different notch-to-width ratios was reconciled with theoretical expectations by application of a translation vector approach in the stress–strain plane, based on the material’s residual stress state. Acoustic emission and infrared thermography provided valuable insight into damage identification, location and sequence.

Investigations of Bearing Failures Associated with White Etching Areas (WEAs) in Wind Turbine Gearboxes

Abstract: A critical problem for wind turbine gearboxes is failure of rolling element bearings where axial cracks form on the inner rings. Metallurgical analyses show that the failure mode is associated with microstructural alterations manifested by white etching areas (WEAs) and white etching cracks (WECs). This article presents field experience from operating wind turbines that compares performance of through-hardened and carburized materials. It shows that through-hardened bearings develop WEA/WECs and fail with axial cracks, whereas carburized bearings do not. In another comparison of two rotor bearings with different carburized metallurgies, one bearing developed WEA/WECs and failed by macropitting, whereas the other bearing did not develop WEAs or WECs and did not fail. The field experience shows that a carburized bearing that has a core with low carbon content, high nickel content, greater compressive residual stresses, and a higher amount of retained austenite provides higher fracture resistance and makes c...

Effect of overlap rate on recrystallization behaviors of Laser Solid Formed Inconel 718 superalloy

Abstract: The effect of overlap rate on the residual stress, recrystallization nucleation location and the distribution of recrystallized grains of LSFed Inconel 718 superalloy were investigated. It is found that the as-deposited microstructures with different overlap rates have the similar characteristics including that columnar grains grow along the deposition direction. The overlap area possesses higher residual stress compared with the inner-pass area, and the position of peak residual stress is closer to previous pass. The increase in the overlap rate will broaden the variation range of the residual stress. During heat treatment, the recrystallization nucleation first occurs in the overlap area with the lower overlap rate, and then expands to both overlap area and inner-pass area paralleling with the increasing of the overlap rate. Although the overlap rate is only one of basic factors in the Laser Solid Forming process, it plays an important role in controlling residual stress distribution, material microstructure and mechanical properties. The higher overlap rate adopted, the finer and the more evenly distributed grains could be obtained through recrystallization for LSFed Inconel 718 superalloy.

Residual stress of 460 MPa high strength steel welded i section: Experimental investigation and modeling

Abstract: A reliable estimation of residual stress within steel sections is important in steel structural design and construction, especially for high strength steel which has been increasingly used in recent years. An experimental investigation was conducted in this paper to quantify the residual stresses in 460 MPa steel welded I sections using sectioning method. The magnitude and distribution of both compressive and tensile residual stresses were obtained based on 1972 sets of original data measured from eight different sections. The effects of width-thickness ratios of the flange and web, steel plate thickness, weld type and interaction of the flange and web were investigated. It was found that the compressive residual stress magnitude was largely related to the sectional dimension, while no direct correlation was found with the weld type and size for tensile ones. No residual stress interaction between the flange and web was identified because of the stress equilibrium within each individual part. In addition, a distribution model was proposed in this paper and well described the experimental results, which can be used to investigate and design the buckling behavior of 460 MPa high strength steel members.