Papers by Keyword: Residual Stress

Abstract: Welding distortion remains a significant challenge in vehicle structures incorporating aluminum components. This study investigates the application of pre-tension to mitigate welding distortion in an aluminum T-joint structure. Through finite element (FE) simulation, the mechanism by which pre-tension alters the residual stress state and reduces distortion is analyzed and comprehensively explained. Based on the findings, an optimized pre-tension condition is proposed to minimize welding distortion in the T-joint configuration.

Abstract: Conventionally, the sin²ψ method has been used as X-ray stress measurement. However, in recent years, the XRD² method and the cos α method have been put into practical use and spreading. In addition, the Fourier analysis method that shares the same measurement principle of the cos α method has been developed and is attracting attention. Therefore, in this paper, the Fourier analysis method is examined from the measurement theory and the measurement accuracy is investigated. It is reviewed that the basic equation is a finite Fourier series, and that stress can be determined from the Fourier coefficients by using coordinate transformations. Then, while comparing it with the multiple regression analysis, the accuracy of the Fourier analysis method is discussed by using numerical calculations.

Abstract: This work investigates the influence of initial residual stresses after additive manufacturing, specifically directed energy deposition, in 5xxx aluminum alloys on the fatigue crack propagation behavior. For this purpose, initial plane stress states (compressive as well as tensile) are introduced along the crack path on a C(T)50 specimen via eigenstrains, mimicking possible residual stress states after both directed energy deposition and possible post-processing. The evolution of the stress intensity factor difference is determined and used to calculate the crack propagation rate via Walker’s equation. The stress state of the vicinity of the crack tip dictates the crack behavior: Compressive stresses perpendicular to the crack path exhibit crack closure, resulting in slower propagation rates. Finally, the influence of a more local distribution of the residual stresses on the fatigue crack propagation is investigated, highlighting the importance of the position of compressive stresses relative to the crack tip for effective crack growth retardation.

Abstract: To produce functional cups by press forming, clad cups with a corrugated structure with voids like the cross section of corrugated cardboard were formed. Deep drawing, which is one type of press forming, is a plastic processing technology that forms thin sheets into three-dimensional containers. In the experiment, pure titanium TP270 and ultra-low carbon steel SPCC were used as test materials. The blank sheet thickness was 0.3 mm and the diameter was 80 mm to 90 mm. To form the corrugated cup, the roller ball die with steel balls installed on the shoulder of the die was prototyped. The steel balls were made of bearing steel JIS-SUJ2 and had diameters of 6.4 mm and 7.5 mm. The corrugated clad cup was formed by the composite die combined with a conventional die. Three conventional dies and two roller ball dies were used to obtain two corrugated layers with voids. The lubricant was a tool oil containing molybdenum disulfide powder. The sheet thickness strain distribution and residual stress distribution of the cup were evaluated. No destruction of the cup occurred during deep drawing. A regular wavy structure was observed in the cross section of the cup. The maximum reduction in the cup thickness was approximately 10 %. The residual stress on the outside of the cup was tensile stress from the bottom to the opening of the cup. The composite die made it possible to form a functional cup.

Abstract: Penstock pipelines in hydroelectric power plants are critical components whose structural integrity is paramount for reliable operation. However, they are subjected to severe operational conditions generating complex stresses, favoring low-cycle fatigue crack initiation, particularly at critical weld zones. This is exacerbated by anomalous operational cycles like repetitive emptying and filling. This study presents a comprehensive methodology combining X-ray Diffraction (XRD) with other Non-Destructive Testing (NDT) techniques to assess residual stresses and their impact on pipeline integrity. XRD quantifies net stress under empty pipeline conditions, determining superposition between intrinsic residual stresses (manufacturing, welding, service-induced) and non-hydrostatic loads (self-weight, geomechanical forces). Diffraction pattern analysis yields crucial stress distribution data [1-5], identifying critical concentration zones prone to fatigue [6-10]. Complementary NDT techniques reveal morphological discontinuities influencing material mechanical behavior. Correlating XRD and morphological findings establishes cause-effect relationships between structural state and measured residual stresses. This integrated methodology offers significant predictive maintenance advantages, providing quantitative assessment of current pipeline state and projecting future performance.

Abstract: The structural integrity of Pelton runners, crucial in hydroelectric power generation, is severely compromised by suboptimal repair practices, leading to premature failures and significant operational losses. This study presents a comprehensive analysis of five Latin American case studies (Colombia, Perú and Guatemala), revealing a direct correlation between uncontrolled residual stress and accelerated component degradation. This study demonstrates the effectiveness of integrating XRD with other Non-Destructive Testing (NDT) techniques, enabling the development of predictive models for crack propagation and the optimization of repair protocols. In addition, the results provide evidence that Pelton wheels repair transcends conventional welding, necessitating a profound understanding of residual stress distribution. Precise XRD-driven residual stress determination, pre-and post-intervention, is pivotal for implementing corrective thermal treatments and extending component lifespan. This study demonstrates that integrating XRD into maintenance protocols for Pelton runners constitutes a paradigm shift in structural integrity management. This innovative approach, by enabling precise residual stress analysis, minimizes catastrophic failures and maximizes operational efficiency within hydroelectric power generation. The findings validate the hypothesis that XRD-driven maintenance strategies significantly enhance component longevity and reliability, thereby revolutionizing industry standards.

Abstract: The 8-inch silicon carbide crystals prepared by physical vapor transport (PVT) offer a low-cost pathway for chip production, significantly enhancing the economies of scale. However, point defects， such as vacancies, interstitial atoms, and dislocated atoms produced by the temperature gradient mismatch and the fluctuation of the C/Si ratio during the growth process, seriously affect the residual stresses and the crystalline quality of the crystals. Using stress birefringence optical path difference and X-ray diffraction rocking curve detection methods, we characterized crystals annealed at different temperature. It is well-known that the residual stress of the wafer exhibits an uneven distribution, with the residual stress at the edge of the wafer significantly higher than that at the center. When the post-growth annealing temperature is below 2000°C, the residual stress of the crystal decreases rapidly due to the annihilation and transformation of point defects. However, when the temperature is increased further to 2200°C, a large number of irreparable and large-sized point defect clusters form, which severely degrade the crystalline quality of the crystal, induces lattice distortion, and lead to the generation of residual stress. Overall, the best residual stress relief is achieved at a post-growth annealing temperature of 2000°C.

Abstract: This study aimed to achieve superior sealing surface quality through a cutting process utilizing a non-rotational cutting tool. Previous research has explored the suppression of chatter vibration using indexable non-rotational cutting tools fabricated from damping alloys. The experiments employed a custom indexable tool composed of a damping material (M2052), with cemented carbide as the insert material. Prior research has indicated that non-rotating cutting tools incorporating damping alloys exhibit enhanced suppression of chatter vibrations, compared with traditional non-rotating tools. This study extends the enquiry to assess the effects of the cutting edge shape on the stability of cutting operations using non-rotational cutting tools with damping alloys. To investigate the effect of the cutting-edge shape on the machined surface, the cutting forces were measured using a dynamometer, the machined surface was measured using a white light interferometer, and the residual stresses were measured using an X-ray residual stress analyzer. Consequently, the insert with a large cutting width had a large variation in the cutting force and caused the generation of compressive residual stress, depending on the conditions. However, it is clear that the insert with a small cutting width exhibited a small variation in the cutting force and generated tensile residual stress, resulting in stable cutting.

Abstract: The purpose of this study is to investigate the effectiveness of laser peening (LP) and shot peening (SP) on the fatigue strength and harmless crack size ( of 3D additively manufactured maraging steel. LP and SP was performed under random condition and pre-optimal condition, respectively. Compressive residual stresses of 510MPa and 1650MPa could be introduced on the surface by LP and SP, respectively. Bending fatigue tests were conducted using base metal (BM) specimen, LP specimen and SP specimen. The fatigue strength of the LP and SP specimens were about 57 and 47% higher than that of BM specimen, respectively. Fatigue fracture was initiated from internal by LP and SP. The semicircular cracks less than 0.3mm and 0.1mm in the depth could be rendered harmless by LP and SP, respectively. The estimated based on fracture mechanics were similar to experimental result. The fatigue strength and was affected by the distribution of the compressive residual stress induced by LP and SP. Thus, the LP and SP process can contribute to improving the reliability of 3D additively manufactured maraging steel. Compressive residual stress is the dominant factor in improving fatigue strength and rendering surface defects harmless.

Abstract: Increasing usage of the high-strength steels in structural design requires deeper understanding of the residual manufacturing stresses effect on the product service fatigue life. The bending forming process is being examined in this work. High cycle fatigue testing of the specimens before and after the bend shaping is performed by means of the vibrational fatigue method. The manufacturing residual and the fatigue tests stress fields are estimated by means of finite element analysis. The similarity principle is used to compare the fatigue curves constructed for the specimens with different geometries based on their local stress field concentration. A comparison with reference work is provided to support the similarity premise. The implementation of the mean stress correction for the residual stress is evaluated. The goal of this work is to demonstrate a methodological integration of the finite element analysis throughout manufacturing and fatigue testing for accurizing design life estimations. It may also serve as an end-to-end review and provide an outline for similar projects.