Residual Fatigue Research Articles

Surface crack growth in metallic pipes reinforced with Fibre-Reinforced Polymers subjected to cyclic loads: An analytical approach

This paper introduces a novel analytical approach aimed at predicting the growth of surface cracks in metallic pipes reinforced with Fibre-Reinforced Polymers (FRPs) subjected to cyclic bending and/or tension loads. The primary objective of this study is to develop a comprehensive analytical model that accounts for multiple factors influencing crack growth, namely stress reduction, crack-bridging effect, stiffness degradation, and fatigue damage of the FRP-to-metal interface simultaneously. By considering these simultaneous effects, our proposed approach enables accurate evaluations of the stress intensity factors (SIFs) at both the surface point and the deepest point of a surface crack. To facilitate practical implementation, we have developed an in-house program that automates crack growth rate and residual fatigue life predictions. The proposed analytical method has been validated through a series of comparisons with experimental data and finite element results, demonstrating its accuracy in estimating fatigue lives. The key novelties of this research lie in the holistic consideration of multiple dominating and influencing factors, the achievement of precise SIF evaluations, and the development of an automated prediction tool for practical applications. Overall, our findings confirm the suitability of the proposed analytical approach for predicting crack growth and provide valuable insights for guiding the design of FRP reinforcement in surface-cracked metallic pipes. This work contributes to advancing the understanding of crack growth behaviour in FRP-reinforced metallic pipes and opens new possibilities for the safe and efficient design of such structures.

Experimental study of the strengthening effect: A novel fatigue life prediction method for variable amplitude loads

AbstractThe strengthening effect of low‐amplitude loading at elevated temperatures was investigated experimentally. A powder metallurgy nickel‐based superalloy FGH96 was preloaded with different cycle numbers and stress levels, and the residual fatigue life was tested under subsequent high‐amplitude loads. The results show that when the number of preloading cycles is in a specific range, the residual fatigue life is higher than that of the virgin specimen under the same load. A novel damage accumulation model was proposed to incorporate the strengthening effect into the life prediction framework. The proposed model was validated using experimental results for various materials in the literature. The mechanism of the strengthening effect of FGH96 was discussed based on electron backscatter diffraction (EBSD) analysis.

Effect of ultrasonic impact treatment on welding residual stress and fatigue resistance of doubly-welded rib-to-deck joints in OSD

Innovative doubly-welded rib-to-deck joints (DRJ) have been developed to enhance the fatigue life of orthotropic steel decks (OSD) used in steel bridges. However, the welding process and welding residual stress (WRS) distribution of DRJ are more complicated than those of conventional single-side welded rib-to-deck joints. To release WRS and improve the fatigue resistance of DRJ, ultrasonic impact treatment (UIT) and fatigue tests were performed in this study. The effect of the UIT process on the WRS distribution and fatigue resistance of the DRJ was investigated. Furthermore, the welding processes of the DRJ and UIT were simulated using the finite element method and validated against the relevant measurements. Subsequently, they were used to investigate the effect of the UIT process on the WRS distribution and represent the mechanism of fatigue failure of the DRJ. Compared with the as-welded specimens without UIT, the fatigue strength of the DRJ increased by more than 60%, and the UIT process altered the dominant fatigue failure mode of the DRJ. The fatigue crack, caused by a UIT-induced fold defect, tends to initiate at the bottom of the impact pit. Owing to the UIT process, the adverse tensile WRS in the weld toe is eliminated, and beneficial compressive residual stress is introduced, leading to an improvement in the fatigue strength of the DRJ.

Study on fatigue damage evolution and model prediction of asphalt pavement in the end-stage of service

Through the use of the material test system (MTS), bending fatigue tests are conducted in this work in order to investigate the attenuation law of fatigue performance of asphalt pavement in the end-stage of service. Response surface methodology (RSM) is used to analyze the effects of strain, frequency, and temperature on the asphalt surface layer's initial stiffness, fatigue life, phase angle, and cumulative dissipated energy when there is a 50 % reduction in the initial stiffness. Through multi-factor coupling analysis, the optimal combination is found and verified by the MTS-810 test system. Based on this, the data of the initial stiffness declining to 20 % was used for analysis on the AC-13C asphalt surface mixture of the APT full-size test road in the laboratory. At 15 °C and 10 Hz, the evolution law of the flexural stiffness, the residual stiffness, phase angle, and cumulative dissipated energy of the asphalt mixture was investigated. Analysis of the asphalt mixture's damage evolution under the single stage of loading and various strain levels revealed changes in the fatigue cracking crack. Beam specimens were made from asphalt mixture field test beams of AC-13C (laboratory accelerated pavement test road), AC-20C, and AC-25C (Ji-Qing expressway) to conduct four-point bending fatigue test (4PB). According to the constant strain fatigue prediction equation, and the residual fatigue life of prediction localized model was established. The results show that the influence of frequency and temperature on the initial stiffness and phase angle is more significant than strain, and the influence of strain on number of fatigue is more significant. The flexural stiffness of the asphalt mixture shows an obvious S-curve, and larger the tensile strain at the bottom of the asphalt layer, shorter the time needed to reach the termination condition, that is, the faster the fatigue failure occurs. When the damage termination condition is reached, under the strain level of 200–300 με, 60 % of the number of loading produce about 35–40 % damage, and the remaining 20 % of the number of loading lead to 10–20 % damage.

Evaluation of the residual fatigue lifetime of a semi-elliptical crack of a Low-Alloy steel pressure vessel under High-Pressure gaseous hydrogen

The demand for broadening fatigue crack growth behavior has increased owing to the extended use of hydrogen gas as an energy carrier, and it is known that high-pressure hydrogen has a major effect on fatigue crack growth behavior. In this study, the effect of high-pressure hydrogen on an SA-372 Grade J steel pressure vessel was analyzed using fatigue crack growth testing, fracture toughness testing, and finite element analysis. A test was performed to compare the fatigue crack growth of SA-372 Grade J steel in ambient air and 99-MPa hydrogen environments. The test results, including the identified degradation of fracture toughness and the presence of hydrogen inflection in the fatigue crack growth rate, were used in the finite element analysis to analyze the fatigue crack growth behavior under various loading and environmental conditions. The residual fatigue life was evaluated considering the morphological evolution of the crack during growth, the initial aspect ratio, and the initial crack-to-depth ratio.

Thickness and weld orientation effects on fatigue crack growth after a single tensile overload

Numerical calculations were performed to investigate the effects of thickness and weld orientation on welding residual stress (WRS) and fatigue life after a single tensile overload (OL) using a centrally-cracked steel specimen. First, welding simulations were carried out to predict WRS due to the change in thickness and weld orientation. The WRS was then considered in elastic-plastic crack growth calculations in addition to the single tensile OL. A rigorous discussion was conducted to explain the effects of thickness and weld orientation on the state of the local stress ahead of the crack tip, crack driving force, and fatigue life.

The relationship between mental fatigue, depression, and cognition in Graves' disease.

Mental fatigue, depression, anxiety, and cognitive complaints are common in Graves' disease (GD). Our aims were to assess the relationship between these variables in patients with GD during both hyperthyroidism and a long stable euthyroidism. A prospective longitudinal case-control study where 65 premenopausal women diagnosed with GD and 65 matched controls were assessed twice with 15 months in between. The first visit for patients was in overt hyperthyroidism and the second after treatment. During the hyperthyroid phase, mental fatigue, depression, and anxiety were significantly increased for GD patients compared to controls (all P < 0.001). Among GD patients, 89% reported mental fatigue and among controls 14%. No difference in cognitive tests was found. After 15 months, significant improvements for GD patients after treatment were found for the items of mental fatigue, depression, and anxiety (all P < 0.001), but these were unchanged in controls. GD patients reported residual mental fatigue (38%), 23% without depression, and 15% mental fatigue combined with depression. Self-reported cognitive complaints were pronounced while cognitive tests did not reveal any deficiencies. Mental fatigue and emotional distress are common in the hyperthyroid phase. These improve with treatment but are still more common in GD patients after 15 months of therapy than in controls. The residual mental fatigue is shown to be a phenomenon distinct from depression in this study. This indicates the importance of assessing mental fatigue in GD patients and underlines the need for rehabilitation and healthcare support as fatigue will have consequences for work ability.

Numerical and experimental investigation of the effect of cold extrusion process on residual stress and fatigue life of internal thread of high-strength steel

Numerical and experimental investigation of the effect of cold extrusion process on residual stress and fatigue life of internal thread of high-strength steel

A calculation method for residual stress of cold expanded hole based on measured springback

Cold expansion can improve the fatigue life of bearing hole by introducing compressive residual stress. However, there is yet difficulty to measure the stress of hole wall because of the geometry and device limitations. In this study, a calculation method of residual stress based on the experimental-theoretical method is proposed by considering the circumferential symmetry of cold expansion. Stress and displacement are analyzed in the loading and unloading stages, and the measured springback is used in the unloading stage. The residual stress accuracy of the proposed method is significantly better than that of the classical elastic–plastic theory. Moreover, the effects of interference, expansion cycles and expansion speed on surface integrity and fatigue life are analyzed. It is found that interference is the most influencing parameter in coad expansion process, and there is a saturation effect of interference on improving the residual stress and fatigue life of bearing holes.

Effects of muscle fatigue on exercise-induced hamstring muscle damage: a three-armed randomized controlled trial

PurposeHamstring injuries in soccer reportedly increase towards the end of the matches’ halves as well as with increased match frequency in combination with short rest periods, possibly due to acute or residual fatigue. Therefore, this study aimed to investigate the effects of acute and residual muscle fatigue on exercise-induced hamstring muscle damage.MethodsA three-armed randomized-controlled trial, including 24 resistance-trained males, was performed allocating subjects to either a training group with acute muscle fatigue + eccentric exercise (AF/ECC); residual muscle fatigue + eccentric exercise (RF/ECC) or a control group with only eccentric exercise (ECC). Muscle stiffness, thickness, contractility, peak torque, range of motion, pain perception, and creatine kinase were assessed as muscle damage markers pre, post, 1 h post, and on the consecutive three days.ResultsSignificant group × time interactions were revealed for muscle thickness (p = 0.02) and muscle contractility parameters radial displacement (Dm) and contraction velocity (Vc) (both p = 0.01), with larger changes in the ECC group (partial η2 = 0.4). Peak torque dropped by an average of 22% in all groups; stiffness only changed in the RF/ECC group (p = 0.04). Muscle work during the damage protocol was lower for AF/ECC than for ECC and RF/ECC (p = 0.005).ConclusionHamstring muscle damage was comparable between the three groups. However, the AF/ECC group resulted in the same amount of muscle damage while accumulating significantly less muscle work during the protocol of the damage exercise.Trial registrationThis study was preregistered in the international trial registration platform (WHO; registration number: DRKS00025243).

Evaluation of residual stress reproducibility and orientation dependent fatigue crack growth in powder bed fusion stainless steel

The complex thermal gradients of additive manufacturing (AM) result in residual stress and distinctive grain morphologies that influence mechanical performance and contribute to concern regarding the fatigue properties of AM parts. In this study, residual stress, microstructure, and fatigue crack growth rate (FCGR) results were compared in AM Type 304L stainless steel produced by laser powder bed fusion (PBF) on different systems using similar process parameters. Residual stress measured in the build direction was remarkably consistent in all PBF builds. Backscatter electron large area images revealed similar grain morphologies in the different builds, all of which exhibited elongated grains in the build direction and inhomogeneous grain size and shape. Fatigue crack growth investigated both parallel and perpendicular to the build direction revealed higher measured crack growth rates in the near-threshold regime in both orientations of the PBF material compared to wrought material. The difference in near-threshold fatigue crack growth rates is attributed primarily to the influence of processing-induced residual stress quantified by the residual stress intensity factor. These values revealed consistent FCGR effects in each orientation across specimens extracted from different builds and were then used to reveal a convergence of the corrected FCGR data of all PBF and wrought specimens.

Fatigue life of unified riveted superstructures designed by Transmostproject with the introduction of increased axle loads

The article presents a study of the residual fatigue life of superstructures during the introduction of trains with increased axial loads on bridges with riveted superstructures, designed in the fifties of the last century. Unified metal superstructures have been in relatively heavy duty conditions for more than 60 years. During lcontinuous operation, processes occur in elements and joints that lead to the appearance and development of various damages and varying degree failures of hazard, so it is necessary to decide on the further operation of old bridge spans and their replacement. When determining the fatigue life, the linear addition hypothesis of fatigue damage accumulation was used, taking into account the increase in stresses with the introduction of increased axial loads. As a critical measure of damage, providing a given reliability, the value obtained from the calculation results of several hundred cracks in riveted superstructures of older design standards was adopted. The increase in load from the installation of a ballastless bridge floor is taken into account. To determine the residual fatigue life, fatigue data is used depending on the concentration of stresses magnitude in the attachments of the main truss elements. For a more accurate determination of the rivet joints operation stage, the author carried out a wear-out calculation through operation period. The introduction of heavier train loads will lead to an increase in the accumulation of fatigue damage in the elements. If weak rivets in attachments are found during inspection, they must be replaced with high-strength bolts to increase fatigue life. The author obtained that the residual fatigue life of the span structures designed by Transmostproekt has not yet been fully exhausted even with the introduction of heavy trains with a wagon axle load of 27–30 tons.

1005 The hunt for solutions to daytime sleepiness in the setting of treated obstructive sleep apnea

Abstract Introduction There is a possible association between OSA and vitamin D deficiency (Neighbors 2018). Vitamin D deficiency is associated with fatigue and excessive daytime sleepiness (EDS) (Bouloukaki 2022). Vitamin D deficiency might play a role in the residual fatigue or sleepiness seen in some patients with treated OSA. Report of case(s) We present a 28 year old female with RLS, anxiety and mild OSA with persistent daytime fatigue and sleepiness despite optimal treatment of OSA. She was evaluated for OSA via a HST due to symptoms of snoring, overnight awakenings, non-restorative sleep, and EDS (Epworth Sleepiness Scale (ESS) of 11/24). The HST revealed mild OSA (REI 4% of 11). Bloodwork revealed a ferritin of 31 ng/mL. She was treated with autoPAP 5-15 cm and daily ferrous sulfate 325 mg. At follow-up she reported significant improvement in her RLS. Repeat ferritin level was 59 ng/ml and continued iron supplementation was recommended. Despite 98% (40/41 days) compliance and effective treatment of OSA with residual AHI of 0.9, she continued to report persistent daytime fatigue and EDS. Given the residual symptoms we checked a vitamin D level which was reduced at 7 ng/mL (21-100 ng/mL). Conclusion We identified in the sleep medicine literature a case report of a 28 yo patient with EDS who had significant improvement in symptoms after her vitamin D deficiency (5.9 ng/mL) was treated. This woman had improvement in her ESS from 10/24 to 1/24 (McCarty 2010). This patient, however, did not have OSA which was the case with our patient. This report speculated that a possible mechanism for clinical improvement could include enhanced sleep quality due to resolution of hypovitaminosis D-associated non-inflammatory myopathy, or a possible immunomodulatory effect of vitamin D decreasing central nervous system homeostatic sleep pressure. Residual fatigue and EDS in the treatment of OSA may have multiple causes for which a comprehensive approach can help identify and treat the underlying cause. Support (if any) Vitamin D and obstructive sleep apnea: a systematic review and meta-analysis(Neighbors 2018) Vitamin D levels in primary care patients: correlations with clinical, seasonal, and quality-of-life parameters(Bouloukaki 2022) Resolution of Hypersomnia Following Identification and Treatment of Vitamin D Deficiency(McCarty 2010)

Interface of resilience with other related concepts in physiological and psychosocial/spiritual domains.

Interface of resilience with other related concepts in physiological and psychosocial/spiritual domains.

Investigation on fatigue failure of split-sleeve cold expansion holes of 7075-T651 aluminum alloy

7075-T6 is widely used in the manufacture of aircraft structural components, the majority of which are joined and assembled through hole structures. However, the geometric discontinuity near the fastener holes facilitates stress concentration and makes the joints susceptible to crack nucleation and fatigue failure. It is essential to improve the fatigue resistance of the hole structure. In this paper, the factors affecting the split-sleeve cold expansion on the fatigue behavior of fastener holes of 7075-T651 are investigated based on the compressive residual stress, microstructure, surface roughness, and fatigue fracture. Results revealed that cold expansion causes sub-grain refinement near the hole wall, which increases the surface micro-hardness and favors inhibition of crack growth. Grain refinement, plastic deformation on the surface of the holes, and residual compressive stress produced by the cold expansion process all work together to extend the fatigue life of the hole structure. The constituent particles and microstructure after expansion are important factors affecting fatigue performance, higher level of Fe content could result in the formation of a large number of iron-bearing particles leading to the acceleration of the failure of the workpiece.

Post-impact Fatigue Performance of 2198-T8 Aluminum-Lithium Alloy Sheet with Pre-crack

Abstract The fatigue test with the digital image correlation system is applied to 2198-T8 aluminum-lithium alloy sheets with preset cracks and impact dents. The influence of different inserts and impact energies on residual fatigue life and failure behavior is analyzed. The results show that the shape of inserts is the main factor of the residual fatigue life at the same impact energy following the order: U-shaped &amp;gt; hemispherical &amp;gt; conical. Moreover the fatigue life decreases with the increase of impact energy. The hemispherical and U-shaped inserts cause local hardening at low impact energy 5 J, resulting in a maximum increase in fatigue life of 12.09 %. In the initial stages of fatigue failure, high strain areas are always around the preset crack where the propagations initiate. There is a multi-axial loading area around the impact dent in the middle stage. Its fatigue crack propagation mode is type I+III, resulting in a deceleration period.

Discussion on Fatigue Life Analysis Methods for Connecting Bolts of the Top Cover of Water Pump Turbines

Under the joint action of dynamic and static loads, the connecting bolts of the top cover of the pump turbine are prone to cumulative damage in local areas such as threads, resulting in cracks or development, and fatigue fracture may occur in severe cases, which will cause serious safety accidents. Therefore, it is necessary to carry out accurate fatigue life estimation analysis for connecting bolts, which has always been a hot spot and difficulty in the industry. This paper introduces several commonly used fatigue life analysis methods of parts, combined with the force characteristics and structural characteristics of the connecting bolts of the top cover, and analyzes and discusses the fatigue life analysis methods suitable for the top cover bolts. Finally, it is believed that the application of stress-strain field strength method can better describe the actual state of the bolt danger area, and the current damage state has an influence on the amount of damage generated by further loading, and the fatigue life analysis of connecting bolts can be combined with the stress-strain field strength method and variable damage linear cumulative damage theory, and the fatigue life and residual fatigue life can be estimated in the design stage or after the phased service of the bolt.

Influence of distortion ratio on distortion-induced fatigue behavior of steel girder bridges

The physical fatigue test and a new proposed research methodology called the digital fatigue test are used to investigate distortion-induced fatigue performance at web gap regions in steel girder bridges. Digital fatigue test based on the extended finite element method can combine factors such as residual welding stress, initial defects, and fatigue action, to simulate the propagation of mixed-mode cracks. Physical and digital fatigue test results show fatigue strength decreases significantly with increasing distortion ratio, which is the ratio of the minimum and maximum distortion at web gaps. When distortion ratio and nominal stress ratio increased from 0.2 to 0.5, the fatigue strength of 60 mm horizontal gusset plate–vertical​ stiffener web gap and 40 mm vertical stiffener web gap decreases by 43% and 50%, respectively.

Femtosecond Laser Shock Peening Residual Stress and Fatigue Life of Additive Manufactured AlSi10Mg

Femtosecond Laser Shock Peening Residual Stress and Fatigue Life of Additive Manufactured AlSi10Mg

Effects of high-energy laser peening followed by pre-hot corrosion on stress relaxation, microhardness, and fatigue life and strength of single-crystal nickel CMSX-4® superalloy

This study investigated the stress relaxation and fatigue life and strength of laser-peened single-crystal nickel superalloy specimens compared to unpeened and shot-peened specimens following hot corrosion exposure and then fatigue testing. The specimens were treated by conventional laser peening and a new cyclic laser peening plus thermal microstructure engineering process. The latter treatment supports the benefit of a unique process involving application of layers of laser peening using high energy with large footprint spots combined with interspersed cyclic annealing. Stress measurements by slitting showed the plastic penetration depth of laser peening exceeded shot peening by a factor of 24. Unpeened and peened specimens were exposed to sulphate corrosives at 700 °C for 300 h and then fatigue tested. Tests of five non-laser-peened specimens all failed in low-cycle fatigue regime, whereas three identically tested laser-peened specimens all achieved multi-million-cycle runout without failure, indicating fully consistent large benefit for life by laser peening. Additional tests also showed fatigue strength improvement of 2:1 by laser peening. Residual stress measurements post hot-corrosion exposure and fatigue testing showed notable 5 mm depth retention of residual eigenstress in a laser-peened specimen.