Fatigue Data Research Articles

Influence of High-Strength, Low-Alloy Steel on Fatigue Life at a Non-Load-Bearing Transverse Welded Attachment

<div>This study investigated the influence of high-strength low-alloy steel on the fatigue life of a load-bearing member with a non-load-bearing transverse welded attachment (T-joint). It compared high cycle fatigue data to two fatigue design codes, namely BS 7608 and Eurocode EN 1993-1-9. Different base and filler material combinations of varying material strengths were investigated, resulting in a total of three different specimen configurations. Two material combinations had a high-strength steel (Strenx<sup>®</sup> 700 MC D) for the base material, with one combination having a matched filler material and the other having an undermatched filler material. The third material combination had a lower-strength steel (S 355 JR AR) for the base material, with a matched filler material. Tensile tests were performed to confirm the base material mechanical properties and weld quality of the manufactured specimens. The investigation showed that there was no significant benefit to using high-strength steel as the base material for a fatigue loaded T-joint with a non-load-bearing welded attachments.</div>

Isothermal and thermo-mechanical fatigue-crack-growth analysis of XH73M nickel alloy

In service-power engineering and aviation, gas-turbine engine structures are operated at elevated temperatures and under extensive variable mechanical loading, which is classified as thermomechanical fatigue (TMF). This coupling effect leads to flaw initiation and growth in components fabricated from thermally resistant nickel-based alloys. This paper presents experimental crack-growth data for isothermal pure fatigue, in-phase and out-of-phase TMF conditions. A crack-growth testing method is developed using inductive heating/forced convective cooling and direct crack-tip opening displacement techniques. The crack-growth experimental results are interpreted based on finite element analyses of the stress–strain rate fields at the crack tip under TMF conditions. Therefore, multi-physics numerical calculations are employed for the interaction of the heat loss from magnetic-field eddy currents with forced convective air cooling through a computer fluid dynamics model, which presents a nonuniform mechanical elastic–plastic stress distribution. Consequently, the dependence of the new nonlinear stress intensity factors on the crack length are obtained for each of the isothermal and thermomechanical cyclic deformation conditions. The polycrystalline XH73M nickel-based alloy tests performed show that, from the crack-growth acceleration viewpoint, the following order of arrangement of fatigue fracture diagrams is formed: isothermal pure fatigue, in-phase TMF, out-of-phase TMF, and isothermal pure fatigue at T = 400 °C and T = 23 °C. The differences and corresponding conclusions based on the interpretation of the experimental results of the crack growth rate characteristics at elevated temperatures in terms of elastic and nonlinear fracture resistance parameters are discussed.

Improved maximum likelihood method for P-S-N curve fitting method with small number specimens and application in T-welded joint

In fatigue data analysis, fitting accurate P-S-N curve is problematic if only a small number of specimen is available, especially to evaluate the relationship between the stress level and the standard deviation. This paper proposes a sample information reconstruction method that can effectively solve this problem. Based on this method and the life equivalent principle, a new maximum likelihood method (which is abbreviated to improved maximum likelihood method) is proposed for P-S-N curve fitting. T-joint specimens of Q450NQR1 steel were fabricated and tested, then the P-S-N curves was fitted by the improved maximum likelihood method, least square method, maximum likelihood method, standard BS7608 and standard IIW. Finally, P-S-N curves by three methods and two standards are compared and analyzed. The results show that the relevant parameters of the P-S-N curve with 99.9% survival probability fitted by the improved maximum likelihood method are similar to those in the two standards, and it is indicated that the improved maximum likelihood method is a better way for P-S-N curve fitting with the small number of fatigue test specimens.

The effect of welding deformation on the equivalent structural stress of dissimilar girth welded joint

Weld distortion refers to the phenomenon of shrinkage around the weld seam and warping of the outer weldment edges. This leads to a deviation from the original straight force transfer path in the joint, resulting in higher stress concentration. The weld root's stress concentrations can cause significant fatigue issues in dissimilar girth welded joints. However, previous evaluation methods have generally overlooked the impact of the welding process on fatigue assessment. To address this gap, this paper proposes integrating welding deformation into the fatigue life calculation process for welded joints made of G20Mn5 cast steel. In this study, a welding calculation program was developed to accurately simulate joint deformation using a two-curvature conical heat source model. Subsequently, high-frequency fatigue test data from scaled specimens of four types of joints were analyzed. The original equivalent structural stress fatigue data were corrected by taking into account the initial condition of weld deformation. This correction resulted in a reduction in the scatter of the fatigue data. Furthermore, the study also analyzed the welding deformation differences and the dispersion of stress concentration in scaled specimens caused by welding inhomogeneity.

Field-based longitudinal evaluation of multimodal worker fatigue assessments in offshore shiftwork

Fatigue in offshore environments is a critical safety hazard, yet the utility of daily fatigue assessments has not been longitudinally examined in these environments. The aim of this exploratory longitudinal field study across two drillships in the Gulf of Mexico was to determine the changes in subjective, performance-based, and physiological fatigue measures over time across different shift types (day, night, and swing) and to identify correlations between these multimodal fatigue assessments. Repeated measures correlation analyses of daily fatigue data from seventy offshore workers revealed that while total sleep time remained unaffected by time on rig, workers’ performances on the psychomotor vigilance test (PVT) deteriorated over time across all shift types. Several correlations between the various multimodal measures were consistent with the extant literature on worker fatigue symptoms and perceptual and physiological manifestations. These findings emphasize the utility of PVT and single item self-reports to capture worker fatigue in offshore shiftwork.

Fatigue performance assessment of thick TIG-Dressing cruciform welded joints made by Q355D structural steel

TIG-Dressing treatment is often used for steel welded joints in construction machinery manufacturing as an effective and reliable method for post-weld fatigue strength improvement. This paper investigates the fatigue performance of thick Q355D cruciform joints in heavy load-carrying steel structures under different TIG-Dressing treatments. Two TIG-Dressing treatments for the full-penetration welded joints were used for fatigue tests considering filling metal during this post-welded processing. Experimental tests studied the fatigue strength of TIG-Dressing cruciform welded joints of Q355D structural steel. The geometric parameters and relevant statistical analyses were performed by actual 3D optical measurement. Moreover, the stress concentration factors are calculated according to the actual geometrics of the welded joint. On the other hand, the effective notch stress and hot spot stress methods were employed to evaluate the fatigue data of Load-Carrying Welded joints (LCWJs) under different notch radius. The collected fatigue data from the literature was compared with the tested data by the above methods. The results show that the fatigue strength of LCWJs under TIG-Dressing processing without filler metal is higher than those under the same TIG-Dressing treatment with filler metal. The effective notch stress method with a fictitious notch radius r = rtrue + 1 mm (rtrue is the actual notch radius at weld toe) could obtain smaller scatter bands for the tested fatigue data.

Gym training muscle fatigue monitoring using EMG myoware and arduino with envelope and sliding window methods

<p><span>Muscles are an important organ in the movement of the body's skeleton to carry out sports activities. Measurement of muscle activity during the exercise process can be done using electromyography (EMG). This research uses Myoware muscle sensor (AT-04-001) which is integrated with Arduino Uno and Xbee to monitor biceps brachii muscle fatigue wirelessly. Fatigue data processing is carried out objectively using the envelope and sliding window method and subjectively verbally from the respondents. From this study, it was found that muscle fatigue can be measured using the method objectively when there is an increase in EMG amplitude with a window size of 5 s. The indication of biceps brachii muscle fatigue for the right arm is stronger to withstand the load during exercise with the average duration of the measurement of the right arm is 41.87 s from 69.67 s; 53.53 s from 98.90 s and 76.87 s from 98.80 s with the ratio of the left arm tending to fatigue more quickly is 23.53 s from 42.13 s; 41.87 s from 51.60 s and 23.53 s from 44.73 s.</span></p>

Surface treatments for polyetheretherketone (Peek): Effects on the bond strength to a resin cement and on the fatigue performance of a bonded glass-ceramic

ObjectiveTo evaluate the effect of distinct surface treatments on Peek (polyetheretherketone) adhesion to the resin cement and the mechanical fatigue behavior of lithium disilicate adhesively bonded to it. Materials and methodsPeek slices embedded in plastic rings with self-curing acrylic resin were randomized into 4 groups for adhesion testing, considering the following surface treatment factors: Ctrl (just cleaned with 78 % isopropyl alcohol); Grinding (4219F diamond bur - 46 μm grain size); Air abrasion (45 μm aluminum oxide for 10 s); Sulfuric acid (acid etching for 30 s). All slices received a layer of adhesive agent; resin composite cylinder specimens (Ø = 3 mm; h = 3 mm) were produced and bonded onto the Peek slices using a dual resin cement for the shear bond strength tests (n = 20) through the wire-loop technique. Next, disc-shaped specimens of Peek (Ø = 10 mm; thickness: 2 mm) and lithium disilicate (LD) (Ø = 10 mm; thickness: 1 mm) were produced for the fatigue tests (n = 20) and paired. The LD was treated (5 % hydrofluoric acid for 20 s + silane agent) and adhesively bonded (with dual resin cement) onto Peek (treated with the previously mentioned surface treatments). The fatigue tests were performed with a step-stress approach (20 Hz; 10,000 cycles/step; initial load: 100 N; step-size: 50 N). Roughness, contact angle, topography and fractographic analysis were performed. The adhesive data was analyzed by one-way ANOVA and Tukey post-hoc tests, while the fatigue data were subjected to survival analysis (Kaplan Meier and Mantel-cox post hoc tests). ResultsOnly the air abrasion surface treatment was able to improve the bond strength between Peek and resin cement (p < 0.05); the Grinding and Sulfuric acid groups were similar to the Ctrl. All surface treatments promoted similar fatigue performance. ConclusionAir abrasion promoted increased bond strength between Peek and resin cement, having no detrimental effect on fatigue behavior. Overall, the mechanical behavior under fatigue of a lithium disilicate glass-ceramic was not influenced by the Peek substrate surface treatments.

Risk volume effect in very high cycle fatigue of 304L stainless steel

Risk volume can be considered as a volume where the crack will initiate with the highest probability. Thus, it is a serious issue considering the specific geometry of the samples for ultrasonic loading. Also, the distribution of the stresses within the risk volume represents important information for fatigue behaviour prediction and description. The risk volume for 304L stainless austenitic steel samples with different geometry was numerically analysed and correlated to the results of the ultrasonic fatigue experiments. Obtained fatigue data and the evolution of the microstructure related to the calculated risk volume sizes. The formation of slip marks corresponded to the calculated stress distribution within the risk volume. The differences in the calculated sizes of the risk volume for different sample geometries were reflected in changes in the microstructure of the material and in the measured fatigue lifetimes. Obtained results can partially explain observed differences in the fatigue properties when comparing ultrasonic fatigue testing with conventional methods.

Biomechanical comparison of titanium alloy additively manufactured and conventionally manufactured plate-screw constructs

ABSTRACTAimTo biomechanically compare the bending stiffness, strength, and cyclic fatigue of titanium additively manufactured (AM) and conventionally manufactured (CM) limited contact plates (LCP) of equivalent dimensions using plate-screw constructs.MethodsTwenty-four 1.5/2.0-mm plate constructs (CM: n = 12; AM: n = 12) were placed under 4-point bending conditions. Data were collected during quasi-static single cycle to failure and cyclic fatigue testing until implants plastically deformed or failed. Bending stiffness, bending structural stiffness, and bending strength were determined from load–displacement curves. Fatigue life was determined as number of cycles to failure. Median test variables for each method were compared using the Wilcoxon rank sum test within each group. Fatigue data was also analysed by the Kaplan–Meier estimator of survival function.ResultsThere was no evidence for a difference in bending stiffness and bending structural stiffness between AM and CM constructs. However, AM constructs exhibited greater bending strength (median 3.07 (min 3.0, max 3.4) Nm) under quasi-static 4-point bending than the CM constructs (median 2.57 (min 2.5, max 2.6) Nm, p = 0.006). Number of cycles to failure under dynamic 4-point bending was higher for the CM constructs (median 164,272 (min 73,557, max 250,000) cycles) than the AM constructs (median 18,704 (min 14,427, max 33,228) cycles; p = 0.02). Survival analysis showed that 50% of AM plates failed by 18,842 cycles, while 50% CM plates failed by 78,543 cycles.Conclusion and clinical relevanceAdditively manufactured titanium implants, printed to replicate a conventional titanium orthopaedic plate, were more prone to failure in a shorter fatigue period despite being stronger in single cycle to failure. Patient-specific implants made using this process may be brittle and therefore not comparable to CM orthopaedic implants. Careful selection of their use on a case/patient-specific basis is recommended.

A re-assessment of Ti-685 as a dwell sensitive titanium alloy and a definition for engineering relevant dwell behaviour

It is believed that the near-α titanium alloy Ti-685 was the first to demonstrate dwell sensitive fatigue behaviour whilst under engineering service as a gas turbine fan disc material. New fatigue data, micro-textural characterisation and fractography from a recent study which utilised remnant Ti-685 specimens originally manufactured for previous laboratory campaigns based at Swansea dating back to the late 1980s are now reported. In isolation, the present results failed to demonstrate a significant dwell effect in either aligned or basketweave microstructural variants. On this occasion, the limited sensitivity to dwell loading was explained by the combination of heat treatment artifacts and selection of a relatively small test specimen geometry. However, the present data were also reviewed in the context of the wider fatigue database generated by multiple studies over the past fifty years. In combination, stress-life (SN) curves defined the magnitude in applied peak stress necessary to demonstrate a dwell effect in this alloy. Ultimately, this facilitated a fundamental definition of dwell sensitivity that is relevant to the engineering community.

A probabilistic stress-life model supported by weakest link principle and highly-stressed volume/surface area concepts

This article introduces a probabilistic fatigue model that combines the principles of the weakest link theory with the highly-stressed volume (HSV) or highly-stressed surface area (HSSA) concepts to estimate stress-life (P-S-N) curves for both unnotched (smooth) and notched large-scale specimens, for any prescribed failure probability. By incorporating probabilistic models, P-S-N curves corresponding to lower probabilities of failure can be obtained. The integration of HSV or HSSA with the weakest link principle enhances the estimation of fatigue strength for real elements or components, which often require testing with reduced-size specimens. The proposed model is verified by experimental fatigue data from the literature, specifically involving unnotched and notched cylindrical specimens subjected to different constant amplitude loadings. The results demonstrate the robustness and effectiveness of the model in estimating characteristic P-S-N curves at lower probabilities of failure.

The length parameter for gigacycle fatigue life predictions of notched specimens made of 304L steel

In this paper, the fatigue data of smooth and notched specimens are evaluated using the method based on the theory of critical distances. This method is suitable for predictions of the fatigue lifetime of notched specimens using the axial stress distributions, the length parameter, and experimental data measured on smooth specimens. The critical length parameter lcr is determined from the relationship between two fatigue curves (one generated by testing smooth specimens and the other generated by testing specimens with a model notch). Experimental fatigue data are obtained using an ultrasonic fatigue pulsator at a frequency of 20 kHz and a load stress ratio R = −1. The paper describes the dependence of the critical length parameter for different notch radii on the number of cycles to fracture, as well as on the applied stress amplitude. The obtained results prove the possibility of using the critical length parameter for fatigue life prediction of notched specimens.

Dual order-reduced Gaussian process emulators (DORGP) for quantifying high-dimensional uncertain crack growth using limited and noisy data

This paper proposes a novel data driven scheme, called dual order-reduced Gaussian Process emulators (DORGP), for efficiently quantifying the high-dimensional uncertain crack growth using limited and noisy data. Firstly, we freshly construct the dual order-reduced spaces that decouple and draw the features among the high-dimensional raw inputs (i.e., material/load uncertainties) and raw outputs (i.e., stress intensity factor and cracks) obtained by isogeometric boundary element simulator, respectively. Secondly, Gaussian Process emulators are built to map the features of the input to the features of the output in the constructed dual order-reduced spaces. Consequently, given new uncertain parameters, the proposed scheme can accurately predict the features with limited and noisy data, and project them back to the high-dimensional space quantifying the complex fatigue crack growth, including the mean value and confidence interval. Numerical examples are provided to validate the efficacy of the proposed approach, including both material and load uncertainties having or without noise. The results demonstrate that the DORGP are highly efficient, with time consumption ranging from 1/4000 to 1/10000 of that required for numerical simulations, and accurate, with relative errors of less than 1%. Furthermore, the approach delivers probabilistic predictions using only a small dataset of samples (e.g., 25), significantly reducing the burden of collecting expensive fatigue data.

Bayesian model averaging for probabilistic S-N curves with probability distribution model form uncertainty

Reliability analysis of engineering components or structures heavily relies on accurately estimating the fatigue properties of materials. However, significant uncertainty exists regarding the distribution form and value in fatigue data, posing significant challenges in constructing a robust probability fatigue model. To address this challenge, we propose a Bayesian model averaging (BMA) method to incorporate model form uncertainty into the estimation of the probability density of fatigue life. The performance of BMA was verified through numerical experiments using both simulated and experimental data. The results highlight the robustness and reliability of BMA compared to individual models, as it effectively incorporates model form uncertainty. The proposed BMA model offers a general framework for developing probabilistic fatigue models with high robustness and accuracy in their predictions. This model contributes to advancing the field of reliability analysis by addressing the challenges posed by uncertainty and enhancing the understanding of fatigue properties for engineering components and structures.

Experimental scatter of the fatigue response of additively manufactured components: a statistical method based on the Profile Likelihood

The fatigue response of additively manufactured (AM) specimens is mainly driven by manufacturing defects, like pores and lack of fusion defects, which are mainly responsible for the large variability of fatigue data in the S–N plot. The analysis of the results of AM tests can be therefore complex: for example, the influence of a specific factor, e.g. the building direction, can be concealed by the experimental variability. Accordingly, appropriate statistical methodologies should be employed to safely and properly analyze the results of fatigue tests on AM specimens. In the present paper, a statistical methodology for the analysis of the AM fatigue test results is proposed. The approach is based on shifting the experimental failures to a reference number of cycles starting from the estimated P–S–N curves. The experimental variability of the fatigue strength at the reference number of cycles is also considered by estimating the profile likelihood function. This methodology has been validated with literature datasets and has proven its effectiveness in dealing with the experimental scatter typical of AM fatigue test results.

Data-driven approach to very high cycle fatigue life prediction

The research on life prediction for mechanical structures in very high cycle fatigue regime is pivotal to improve structure service, but it can be costly and time-consuming to collect fatigue data. In response, the data-driven approach of machine learning emerged as a solution to data insufficiency. In this work, after extracting a small dataset of GCr15 bearing steel subjected to very high cycle fatigue tests from open literature, the Z-parameter model was applied to obtain extended datasets to establish models driven by support vector machine, artificial neural network, and Z-parameter based physics-informed neural network, respectively. With training on extended datasets and the original data as test set, fatigue life prediction for GCr15 steel was carried out and evaluated between these models. Results showed that the physics-informed neural network calibrated by Z-parameter model trained on a larger dataset featured more accurate and reliable prediction than other models did, which demonstrated effectiveness of Z-parameter in data extension and model construction as priori physics knowledge for a data-driven approach. Looking into the future, Z-parameter model deserves more attention to its employment in life prediction for more engineering materials and structures serving in the very high cycle fatigue regime.

Experimental and numerical investigation on fatigue behaviors of Q690D butt welds

With the improvement of steel production technology, different grades of high-strength steel have been developed and widely applied in engineering, however the fatigue properties of high-strength steel need to be further studied. In this research, regarding the fatigue properties of Q690D high strength steel butt welds, experimental investigation and numerical simulation were carried out. Experimental investigations of Q690D high strength steel butt welds were performed, and properties including the basic mechanical behaviors, metallographic structure, fatigue crack growth rate and fatigue performance were obtained. The fatigue test results were compared with fatigue data from existing studies of butt welds and the Eurocode3 fatigue design S-N curve. The fatigue life prediction was performed and the fatigue crack propagation process was simulated based on the platform combining ABAQUS and Franc3D. The results show that the tested butt-welded joints specimen includes more initial defects, its fatigue properties are comparable to those of 355 MPa grade steel butt-welded joints, and the fatigue resistance advantages of high strength steels are not obvious. The simulated results are in good agreement with the fatigue test results, indicating the proposed simulation method is applicable in the fatigue life assessment of engineering structures with known initial defects. The proposed simulation method provided a numerical analysis approach to the fatigue assessment of engineering structures, thereby reducing the cost of fatigue tests and bringing significant economic and social benefits.

Influence of physiological, psychological and environmental factors on passenger ship seafarer fatigue in real navigation environment

The occurrence of passenger ship accidents can easily cause a large number of casualties. Seafarers of deck department on passenger ships are prone to fatigue in complex navigation environment and work tasks, thus causing water traffic accidents. To investigate the relationship between physiological, psychological, environmental factors and fatigue, electrocardiogram (ECG), electroencephalogram (EEG) and subjective fatigue (KSS) data of 24 seafarers were collected in real navigation environment. The time domain characteristics MRR, SDNN, RMSSD and frequency domain characteristics LF, HF, LF/HF were extracted from ECG. Welch’s method was used to extract the power in different EEG sub-bands from a one-channel EEG acquisition headset. By analyzing the influential factors of seafarer fatigue through significance analysis and correlation analysis, it is indicated that the perceived stress, safety behavior, health condition and the number of passengers can have an impact on fatigue. Different waters and different time will also affect the seafarer’s physiological fatigue. In addition, the ordinal logistic regression model based on multi-source physiological signals shows that age, ECG indexes, EEG indexes and ship departure interval can be used to predict the fatigue levels of seafarers with an accuracy of 81.13 %.

Evaluation of the influence of mean stress on the fatigue behavior of notched and smooth medium carbon steel components through an energetic local approach

AbstractIn the present paper, the influence of the mean stress on the fatigue behavior of smooth and notched medium carbon steel components (C45 grade) is investigated through conventional and more advanced design methodologies. Original experimental data are provided for two notched specimen geometries and three different high load ratios (R = {0.7, 0.8, 0.9}). To assess the effect of the mean stress in a larger range, the bulk of fatigue data has been widened through more than 150 tests on C45 steel drawn from literature. The considered experimental data ranged between a load ratio of −2 and 0.9. The mean stress effect has been assessed in a first attempt through well‐established literature models resulting in a data correlation characterized by a large scatter. Finally, an attempt to uniquely consider both geometrical and load ratio effects has been performed through a numerical application of the strain energy density (SED) method. Elevated load ratios (R ≥ 0.7) prove to be highly detrimental for C45 steel with a fatigue life reduction of up to 3 orders of magnitude; however, this effect can be considered with a sufficient degree of accuracy through the SED method.