Papers by Keyword: Residual Stress

Abstract: Boring process, also referred to internal turning, is commonly used to machine critical features of landing gear components like struts, brackets, and main cylinders. Over the past years, extensive research efforts have addressed the stability of the process by developing instrumented boring bars and advanced monitoring techniques. However, although the surface integrity characteristics, particularly the residual stresses, are crucial for structural components, it hasn’t been considered and its evolution over the boring conditions still not well understood. Hence, the present paper proposes a comprehensive investigation on the effects of boring conditions on the surface integrity of the aluminum alloy 7175-T74 commonly used in landing gear components. A parametric analysis has shown that lower cutting forces and surface roughness can be achieved using a larger insert nose radius. It was also found that feed rate, cutting speed and depth of cut experienced strong interaction effects with the machining mode (dry/wet) regarding the resultant cutting force and surface roughness. Results have also shown that wet boring conditions generated compressive residual stresses. An optimal boring condition was obtained using Grey relational analysis (GRA) – Taguchi method. Further investigation is required to refine the obtained optimal machining condition by considering the GRA results and the parametric analysis outcomes.

Abstract: Shot peening mechanical treatment surface, commonly used to improve material surface mechanical properties, as fatigue and wear resistance increase, induces deformations in the material crystal lattice, characterized by the presence of stress. Additionally, plasma nitriding, another surface treatment used to minimize failures in austenitic stainless steels, can produce resistant surface layers, composed of the interstitial nitrogen atoms accommodated in austenitic structure, increasing the layer hardness. Thus, the present work aims to study the residual stress and layer formation on austenitic stainless steel F138 surface, after different treatment conditions. Plasma nitriding treatment after shot peening differences were analyzed. Residual stress was investigated by X-ray diffraction, using sin²ψ method. Samples of surface morphology and formed layer were analyzed by scanning electron microscopy (SEM) and X-ray diffraction. Previous shot peening treatment to plasma nitriding promotes the formation of a less homogeneous layer, with microcracks and induced residual stress increase. It was observed the formation of iron nitrides and expanded austenite after plasma nitriding treatment. Surface residual stress induction after shot peening and plasma nitriding treatments can be efficient methods to improve material mechanical properties.

Abstract: Next generation rolls such as super-cermet rolls and all-ceramic rolls can be manufactured using only sleeve assembly type rolls, which have the advantage of being able to reuse the shaft by replacing the damaged sleeves. However, in some cases, failures with unknown causes may occur such as circumferential slippage, shaft pull-out or residual bending deformation at the shrink-fit interface. Such slipping failures cannot be prevented by conventional design concept. This is because even if the resistant torque is greater than the motor torque, the circumferential slippage will occur. Through numerical simulation and miniature roll experiment, the following results are obtained. 1) Even under free rolling condition without motor torque, the circumferential slippage occurs. 2) The slippage is caused by the accumulation of irreversible slip during the roll rotation. 3) The motor torque accelerates the sip amount significantly. 4) The geometry of slippage defect can be identified experimentally. 5) The fatigue strength of sleeve assembly rolling rolls can be evaluated by using √area parameter characterizing the identified slip defects. 6) By preventing the slip damage, the fatigue strength of sleeve rolls can be nearly equal to that of conventional solid rolls without shrink-fit.

Abstract: The circular saw blade is an important tool for wood processing. The controllable residual stress formed by tensioning process has a clear influence on the critical rotational speed of the circular saw blade. Due to the diversification of the circular saw blade structure and tensioning method, the influence of the residual stress field on the critical rotational speed of the circular saw blade should be further studied. In this paper, four types of circular saw blades are built using the finite element method. Circular elastic thermal expansion and annular elastic thermal expansion zones are used to produce a certain distribution of residual stress field for the circular saw blade. The critical rotational speed of circular saw blade with residual stress field is determined using the finite element method and vibration theory. The results of the theoretical analysis show that, when the tangential tensile stress with sufficient value is formed on the outer edge of the four types of circular saw blades, their critical rotational speed is increased compared with those without residual stress, and it is also increased with the increase of the tangential tensile stress.

Abstract: This paper studies the effect of the direct energy deposition (DED) process parameters varying within 20% on the geometric accuracy and formation of residual stresses in the products. In the course of the study, an experiment was carried out according to Taguchi's L9 plan to fabricate samples by varying the laser travel speed, effective focusing distance, feed rate of metal powder composition, and process pause, which were then compared with the rates of geometry change and crystal lattice distortion. The obtained results were subjected to statistical analysis using correlation, regression and factor analysis to determine the influence and significance of factors. As a result, correlations between the process parameters and sample characteristics were identified. As correlation and factor analysis showed, a change in process factors within 20% does not significantly affect most of the quality parameters, except for the level of residual stresses. Geometric and strain parameters are weakly correlated with each other, but no statistically significant correlations were found between them. The analysis of variance showed that the fusion rate and powder flow rate have the greatest influence on the geometric accuracy parameters. These factors have the most significant statistical influence on the response, indicating the importance of controlling these parameters to achieve high geometry accuracy. Regression analysis allowed to obtain adequate models of residual stress level. It was found that the model for residual stress level by planes (200) is more reliable than the model for residual stress level by crystallographic plane (111). The obtained data allow to optimize the DED process in order to achieve a given geometric accuracy and reduce residual stresses in the manufactured products.

Abstract: Post weld heat treatment is heating objects in the furnace to certain temperatures and times after the object has been welded. PWHT is expected to reduce residual stress on objects due to the welding process. In this case, we warm up annealing (holding in a furnace) at a temperature of 750 °C with a heating time of 40 minutes. We use MIG welding (metal inert gas) and a metal filler FS 705-6 with a diameter of 0.8 mm, with a total of 3 layers. First, the object will be formed according to the standard and welded in three layers with MIG welding. Then, the object will be cut and formed according to the tensile test standards, after which the tensile test and hardness test will test it to determine the mechanical characteristics of the object. From the testing that has been carried out, it is known that objects without PWHT have a higher stress and hardness value than objects with PWHT, with a stress value of 346.57 MPa and the highest hardness value of 93.5 HRB at the 3rd welding point. However, objects with PWHT have higher elasticity and strain values, with an elasticity value of 3.32 MPa, and the strain value of objects with PWHT is 13.1.

Abstract: Titanium alloy fasteners are extensively used in advanced fields such as aerospace due to their corrosion resistance, high-temperature endurance, low density, and high strength-to-weight ratio. In practical applications, fatigue failure is the primary failure mode for these fasteners. Besides the operational environment, the manufacturing process, especially surface treatment techniques, plays a crucial role in affecting the fatigue life of titanium alloy fasteners. This paper examines the impact of three surface treatment processes-rolled fillet, pulsed anodization, and molybdenum disulfide coating－on the fatigue life of titanium alloy fasteners through orthogonal experiments. The study finds that both rolled fillet and molybdenum disulfide coating significantly influence the fatigue life. This effect is associated with residual stresses, where compressive residual stress initially increases with rolling pressure but subsequently decreases, and reduces as the thickness of the molybdenum disulfide lubricating film rises.

Abstract: Ti-6Al-4V, renowned for its high strength and corrosion resistance, is a preferred material in aerospace and marine applications for lightweight structures due to its durability in challenging environments. Typically, GTAW welding is used for it’s fabrication. The residual tensile stresses produced after welding are known to worsen the corrosion and mechanical properties of welds. However, these properties can be improved by introducing near surface residual compressive stress by shot peening. When compared to the traditional shot peening treatment, the surface roughness that results from multiple shot peening with varying ball sizes and intensities can be significantly reduced. In the present work, Ti-6Al-4V plates were welded using conventional GTAW technique. Six different combinations of multiple shot peening treatments were applied to the welded specimens. Surface morphology and surface roughness were analysed. Surface residual stresses measurement were performed using by X-ray stress analyzer. Domain size and microstrain were measured using X-ray diffraction technique. Micro-hardness measurements were made along the weld thickness. Corrosion studies were carried out using potentiodynamic polarization test in 3.5% NaCl solution. The SP4 parameter comes out to have the best combination among all the multiple shot peened samples. It results in lowered surface roughness, higher compressive residual stress, better grain refinement, increased surface hardness, and enhanced corrosion resistance.

Abstract: Recently, researchers have developed the method as a harmless the crack by the surface modification. For the purpose of contributing to reliability improvement of the A6061-T6 structure by harmless method, the following research was carried out: The tensile residual stress of friction stir welding was added by shot peening, resulting in a more significant compressive residual stress than that of the base metal. The effect of the surface crack aspect ratio on the maximum harmless crack depth (a_hml) of A6061-T6 was evaluated for residual stress distribution. The detectable depth was evaluated in the relationship between a_hml and the maximum detectable crack depth (a_NDI) by non-destructive inspection (NDI).

Abstract: This paper presents a finite element modeling procedure to determine of crack growth behaviour of butt welded joints under the subject of load for mode I. This paper presents a computation procedure to determine the ratio of fatigue crack growth in butt welded plates for mode I fracture mechanics loading conditions. The presence of residual stresses in welded structures can significantly affect the material’s resistance to fatigue under cyclic loading. The presence of tensile residual stresses adversely affects the fatigue crack growth rate increased it. Change of microstructure and hardening material as a result of the welding process also has a negative impact on the growth of the crack. Accurate prediction and reliable assessment of the residual stress are important for the structural integrity and residual life assessment of welded parts design. Although there are several techniques for the determination of residual stresses, the finite element method (FEM) is one of the most convenient and useful. This paper presents a finite element modeling procedure to determine of crack growth behaviour of butt welded joints under tensile load for mode I. Keywords: Welding, Residual stress, Residual life, Crack growth, FEM, Butt welded joint