Welding residual stress effects on fatigue life of hydraulic support top beam

The present study deals with the consideration of the small-scale effects on the pull-in instability of micro-switches subjected to electrostatic and intermolecular forces in the presence of thermal and residual stress effects. Using Eringen's nonlocal elasticity theory along with the nonlocal Euler---Bernoulli beam model, the equilibrium equation is derived in the presence of thermal and residual stress effects using virtual displacement principle. The static governing equation, which is extremely nonlinear due to the intermolecular and electrostatic attraction forces plus thermal and residual effects, is solved numerically by Galerkin method. The accuracy of the solution is verified by comparing the obtained results with the existing numerical, analytical, and experimental models. Finally, a comprehensive study is carried out to determine the influence of nonlocal parameters on the pull-in instability characteristics of double clamped microbeam in the presence of thermal and residual stresses.

The fatigue strength of welded steels is affected by the applied load mean stress and the residual stress in the vicinity of the weld. The mean stress correction in fatigue design concepts used for welded structures commonly distinguishes between three subjective generalized residual stress conditions, “low, medium, and high” tensile residual stress. This qualitative treatment of residual stress leads to imprecise evaluation of residual stress effects, in particular when compressive residual stress is present or high-strength steels are applied. The objectives of the underlying study are to emphasize the interaction of load mean stress with residual stress and to provide an approach for the combined treatment of those stress components in the nominal stress concept. The principles of mean stress and residual stress effects on fatigue are presented and discussed. Furthermore, the role of residual stress relaxation is emphasized and cyclically stabilized local residual stress is combined with mean stress to effective mean stress. The fatigue design concept of local endurance limits and effective mean stress is introduced for the quantitative evaluation of residual and mean stress effects. Finally, the effective mean stress approach is applied to longitudinal stiffeners made from different steel grades containing various residual stress conditions. It is shown how design S-N curves can be adjusted based on quantitative effective mean stress. Finally, an improved bonus factor concept based on effective mean stress is presented, which allows a mean stress correction under consideration of the residual stress condition.

Estimation of fatigue strength on the spot welded joint is very Important for strength design of spot welded steed sheet structures. In this paper, the effect of residual stress on the fatigue life of resistance spot weldment was studied. Residual stress fields of weldment were calculated by using thermo elastic plastic finite element analysis and equivalent fatigue stress considering residual stress effect was obtained. And then we predicted fatigue life, which included the effect of the residual stresses and the actual loading stresses. The calculation and experimental results were in good agreement. Therefore, the proposed calculated model can be considered to be sufficiently powerful for the prediction of fatigue life.

Effects of nonproportional loading and residual stress on creep crack tip fields

Quantitative evaluation of residual stress and microstructural effects on the surface hardness of machined Ti-6Al-4 V alloy with microscopic characterization techniques

: An overview of the ASTM Symposium on Analytical and Experimental Methods for Residual Stress Effects in Fatigue, held on 20-21 October 1986 in Phoenix, Arizona, is presented. The background and objective for the symposium are described and the technical papers presented at the symposium and published in the proceedings are summarized. The papers are in two general categories: (1) Effects of residual stress near the surface of a specimen or component -- particularly shot peening applications, and (2) Effects of bulk residual stresses--particularly autofrettaged pressure vessels and piping. Residual stress, Fatigue, Pressure vessels, Shot peening, Fatigue life, Springs, Welding, Crack propagation, Aluminum alloys.

Effects of axial and residual stresses on thermoelastic damping in capacitive micro-beam resonators

In this study, a process modeling methodology applied in finite element (FE) analysis has been developed to investigate the evolution of residual stress during and after the CMOS-MEMS process. The MEMS (micro-electromechanical systems) capacitive microphone structure which contains a large membrane for sound sensing is selected to be studied, and it is fabricated using a standard foundry CMOS process. From the FE analysis, the thermal and intrinsic stresses are induced and continuously monitored during the process steps. It is found that the buckling of membrane happens after the post-CMOS micromachining, and it leads to the degradation of microphone performance. The membrane deflection becomes larger as higher compressive stress exists after thin film deposition, and the residual normal stress is the major reason of membrane buckling. Besides, the residual gradient stress effect becomes influential as the constraint of the diaphragm is released. To improve the effective sensing area of membrane, the designed slots near the circumference of membrane are applied. On the other hand, the curling-type deformation due to the residual gradient stress can be controlled by the patterned adding layer. The possible approaches to mitigate the residual stress effects are investigated, and thus the qualified CMOS-MEMS capacitive microphone design can be achieved.

Conventional nondestructive inspection (NDI) technologies do not have the ability to reliably and efficiently measure and quantify the effects of surface and subsurface residual stresses in aerospace structures. As part of a National Science Foundation Small Business Innovative Research (SBIR) program and several commercial projects, Positron has successfully demonstrated the ability to apply Induced Positron Analysis (IPA) in a single measurement to nondestructively quantify shot peen and cold expansion induced residual stress and relaxation effects in single crystal superalloys, steels, titanium and aluminum. IPA has demonstrated the ability to quantitatively measure residual stress effects throughout the operational life-cycle of the structural material -from determining the effectiveness of the initial treatment to tracking the operationally-induced changes over the life of the treated component. Use of IPA to nondestructively quantify surface and subsurface residual stress effects in critical structural, turbine engine, and gearbox materials and components will significantly improve the understanding of the effects of material treatments and operational usage on the durability and fatigue life of critical components at the microscale level.

Residual stress may have a significant effect on the fatigue strength of welded joints. As a non-fluctuating stress, it has an effect similar to that of the mean stress. Recently the International Association of Ship Classification Societies (IACS) has issued Common Structural Rules (CSR) for respectively tankers (IACS 2006a) and bulk carriers (IACS 2006b). The effect of mean stress in fatigue design is taken into account in both sets of rules. However, the treatment is quite different, in particular with regard to residual stress and shakedown effects. In the present paper a comparative study of fatigue design procedures of the IACS rules is reported, with emphasis on residual stress effects. Testing was carried out with longitudinal attachment welds in the as-welded condition. The initial residual stress was measured by a sectioning method using strain gages. Hot spot stress was determined experimentally by strain gauges and numerically by finite element analysis using different types of elements. Fatigue testing was carried out and SN-curves were plotted according to the relevant stress as specified by the rules. In order to investigate the shake-down effect of residual stress, testing was performed for several pre-load conditions which could be taken to represent maximum load levels in a load history. The aim of the study is to contribute towards better understanding of the effect of residual stress and shakedown on fatigue strength of welded joints.

The impact of prior heat stress on subsequent aerobic exercise-heat performance has not been studied. To determine whether prior heat stress degrades subsequent aerobic exercise performance in the heat. Eighteen nonheat acclimated males were trained (four practice trials) on an aerobic exercise performance test in 22 degrees C and then divided into two (n = 8) groups. One group (EUHPH; (.)VO2peak = 44 +/- 7 mL x kg x min(-1)) was tested after 90 min of recovery (in 22 degrees C) from 3 h of intermittent light-intensity (<30% (.)VO2peak) exercise-heat (50 degrees C) stress, where sweat losses were matched with fluid intake (3.5 +/- 0.5 L) to maintain euhydration. The other group (EUH; (.)VO2peak = 45 +/- 5 mL x kg x min(-1)) was tested while euhydrated without prior exercise-heat stress. Aerobic performance was determined from a 30-min cycling preload (50% (.)VO2peak) followed by a 15-min time trial in 40 degrees C. Total work during the 15-min performance time trial in EUH and EUHPH was compared, as were the percent changes from the best practice trials. Volunteers were euhydrated (plasma osmolality < 290 mOsm x kg(-1)) and normothermic before each exercise-heat trial. Heart rate and core temperature were not different (P > 0.05) between groups at any time point during exercise. Total work was not different (P > 0.05) at baseline or between EUH (150.5 +/- 28.3 kJ; 2.0 +/- 0.3 kJ x kg(-1)) and EUHPH (160.3 +/- 24.0 kJ; 1.8 +/- 0.2 kJ x kg(-1)). The percent change in total work relative to baseline was not different (P > 0.05) between EUH (-18.7% +/- 9.2%) and EUHPH (-15.0% +/- 7.8%). If hydration and body temperatures recover, prior exercise-heat stress does not result in a greater degradation in aerobic time trial performance in the heat compared with heat exposure alone.

Residual stress effects on fatigue life prediction using hardness measurements for butt-welded joints made of high strength steels

This paper studies the influence of specimen length on residual stress redistribution and fatigue life in welded cruciform joints made of steel grade S355. It uses numerical methods to simulate the common practice in fatigue testing, where specimens are cut from a larger welded plate assembly. A transient thermo-mechanical finite element model is used to simulate the welding and cutting processes, enabling a detailed analysis of residual stress relaxation due to reduced structural constraints when cutting the specimens. Fatigue life is assessed using linear elastic fracture mechanics, incorporating residual stress effects from the finite element simulations via a mean stress correction. Results show that shorter specimens exhibit reduced residual stress and increased fatigue resistance. For assemblies with a single pass weld, a minimum specimen length of 40 mm is recommended for deriving reliable S–N curves for welded joints in fatigue standards. The findings are in good agreement with experimental data and highlight the importance of specimen size in fatigue testing protocols. • Finite element simulations quantify welding and cutting effects on residual stress. • Cruciform joints cut to a small length have reduced residual stresses. • Fatigue life is assessed using fracture mechanics including residual stress effects. • Cruciform joints cut to a small length have increased fatigue resistance. • We advise specimen lengths ≥ 40 mm for deriving S–N curves of single-pass welds.

Results from fatigue testing of small-scale specimens are widely used to study residual stress effects on fatigue of welded structures. It was observed from a literature that welding distortion may cover residual stress effects due to high-bending stresses from clamping. Here, presented are fatigue test results and results from residual stress measurements from welded longitudinal stiffeners in different residual stress conditions. The axial welding distortion was corrected for all samples by straightening reducing effects from clamping and making residual stress effects visible. It was found that the fatigue strength depends strongly on the stabilized residual stresses, especially at high numbers of load cycles. It could be shown that residual stresses at the weld toe either were far below the yield strength or were degraded mainly at the first load cycle but still have major effects. This was investigated at two stress ratios of R = −1 and R = −3.

The estimation of fatigue strength of spot welded joints is crucial to the strength design of spot welded steel sheet structures. In the present paper, the effect of residual stresses on the fatigue life of resistance spot weldments was studied. Residual stress fields in the weldments were calculated using thermoelastic–plastic finite element analysis and the equivalent fatigue stress considering the residual stress effect was obtained. This was followed by fatigue life predictions, which included the effect of the residual stresses and the actual loading stresses. The calculation and experimental results showed good agreement. Therefore, the proposed calculation model can be considered to be sufficiently powerful for the prediction of fatigue life