Fatigue Criterion Research Articles

Multi-objective collaborative assembly line design problem with the optimisation of ergonomics and economics

Manufacturing systems are socio-technical systems, with explicit interactions between humans and technologies in shared workspaces. These shared workspaces could also be called hybrid collaborative manufacturing systems, which involve workers as well as technological equipment and combine the benefits of human workers and new Industry 4.0 technologies, such systems are particularly useful in a context requiring flexibility and adaptability. Furthermore, the new Industry 5.0 approach has the objective to shift toward more human-centric and resilient manufacturing systems. The key problems to solve in the design of collaborative manufacturing systems are the combinatorial assembly line balancing problem and the equipment selection problem. An efficient and sustainable line requires a cost-effective choice of equipment while improving the ergonomics and the safety of workers. Both decisions of balancing workload and the assignment of equipment impact the ergonomics of a collaborative system and present conflicting criteria. To this end, we propose a multi-objective approach, the objectives are the optimisation of the investment costs and the ergonomics with a fatigue and recovery criterion. We propose to linearise the fatigue and recovery to formulate a new Mixed Integer Linear Programming formulation. We developed an exact multi-objective solving algorithm based on the ϵ-constraint to obtain the trade-off between these objectives. We conducted numerical experiments with different instances from the literature with promising results for instances with up to 45 operations. Finally, we discuss insightful managerial conclusions and future research perspectives.

Fatigue life evaluation of automotive mechanical components by using smart design algorithm

AbstractThe aim of this work is to develop a so‐called “smart design” in MATLAB™ environment. The design process consists of an innovative and automatic algorithm aimed at rapidly evaluating the fatigue damage of automotive mechanical components, starting from the load cycle that the component is subjected. In this work, the target component is the front halfshaft of a sport utility vehicle. The algorithm works as follows. A driving cycle has been acquired through an experimental setup consisting of a control unit, a GPS and an OBD port. A mathematical model of the vehicle, based on longitudinal vehicle dynamics, has been developed in Simulink™ environment to evaluate the traction torque at the wheel. A torsional fatigue tests campaign has been carried out on nine front halfshafts of the vehicle to evaluate the torque amplitude–number of cycles curve of the component. The output histories, computed with the rainflow method, have been referred to a load ratio R = −1, according to the experimental fatigue tests, by the application of three different mean stress fatigue criteria: Goodman, Gerber, and Morrow. At the end, cumulative fatigue damage on the component has been evaluated by the application of the Palmgren–Miner rules. The results show that the Goodman criteria, with a fatigue damage value of around 20%, represents the most precautionary criteria for the fatigue design of an automotive component.

Critical distance-based fatigue life evaluation of blunt notch details in steel bridges

Orthotropic steel deck (OSD) is applied on many bridges around the world, but its drawback of being prone to fatigue has been a concern due to the damages observed. Fatigue cracks initiated from the blunt notch details in rib-to-floor beam connections have a different fatigue behavior compared to welded connections and deserve to be investigated further. To study the effect of notch radius on the fatigue performance of blunt notch detail, 27 specimens with different geometries were manufactured and tested with fatigue loads. The fatigue lives of specimens and their crack initiation locations were investigated, and the prediction on the fatigue life of notched specimens based on the theory of critical distance (TCD) was also conducted. For notched specimens made of S355, the predicted fatigue life using the TCD method is in good agreement with the experimental results. Also, it is found that the point method has higher accuracy compared to the line method and the use of one calibration curve of notched specimens could provide enough accuracy compared to the case when two calibration curves of notched specimens are used. By modifying the mathematical description of the stress distribution near the notch root, a new formulation of the critical distance-fatigue life relationship is here proposed and validated with the experimental results.

Carburizing effect-inspired bending fatigue forecasting model for spiral bevel gears

Collaborative optimization considering complex meshing interface physical performance evolution is always an important challenge for designer in recent field of spiral bevel gears. Where, an innovative root bending fatigue life forecasting model is established by considering the root flank carburizing effect for spiral bevel gears. First, root flank carburizing simulation is performed to output carburizing effect evaluations, namely the root flank hardness gradient at different carburizing layers and residual stress distribution. Then, carburizing effect-inspired root bending fatigue life forecasting model was established. Where, finite element method (FEM) based bending stress considering residual stress is determined, and root flank hardness gradient is used to compute S-N curve. Considering tooth flank carburizing effect, root bending fatigue life forecasting is performed by correlating with multiaxial fatigue criterion. Finally, the proposed forecasting model is exercised with an instance aerospace spiral bevel gears to verify the impact of key machine settings on the result root bending fatigue life.

Bottomhole-Assembly Dynamics Software Helps Mitigate Twistoffs While Drilling

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202174, “Mitigating Twistoffs While Drilling With the Help of Bottomhole-Assembly Dynamics Software,” by Mario A. Rivas, SPE, Andres A. Ramirez, and Bader S. Al‑Zahrani, SPE, Saudi Aramco, et al. The paper has not been peer reviewed. _ A major challenge during drilling operations is the occurrence of twistoffs on bottomhole assembly (BHA) components. To overcome this challenge, a study was performed of twistoffs experienced on BHA components. Based on the findings, drilling operations and recommendations were provided to reduce or eliminate twistoffs related to suboptimal drilling parameters. This analysis will help drilling engineers and personnel foresee vibration dysfunctions and act accordingly with the use of BHA dynamics software to optimize drilling parameters before and during drilling. Twistoffs Caused by Drillstring Vibrations Field experience has shown that unwanted drillstring vibrations lead to failures, especially stick/slip (torsional vibrations) that occurs approximately 50% of the time during drilling. Three main types of vibrations can be distinguished: torsional (stick/slip oscillations), axial (bit bouncing), and lateral (whirling motion caused by an imbalanced drillstring). These three types of vibration can occur at any time during drilling. Induced axial vibrations at the bit can lead to lateral vibrations in the drillstring and BHA, and axial and torsional vibrations can be observed at surface. Sometimes the severe axial vibrations close to the bit may not be observed at surface, which may lead to a potential twistoff if drilling parameters are not changed and optimized. Additionally, fatigue failure is intensified with high vibrational loads, specifically at curved well trajectories or in buckled drillstring sections as shown in Fig. 1, where high bending stresses occur. The most critical fatigue damage will happen when the drillstring is in resonance with one of its natural frequencies, resulting in twistoff events at a much lower drillstring component yield strength. The objective of the study described in the complete paper is to pursue an integrated approach considering the use of vibration-analysis software in the design of a BHA to identify safe operating windows for rotary speed and weight on bit (WOB) to prevent buckling and analyze fatigue. BHA Dynamics Resonance occurs when the rotary speed is very close to one of the natural frequencies for torsional vibration (the primary cause of failure), and WOB natural frequency for flexural vibrations of the BHA. When the frequency of any excitation is one of the natural drillstring frequencies, then the drillstring will resonate and vibration levels will be highest. With very high amplitudes, vibrations will accelerate drillstring and BHA fatigue. To estimate the critical rotary speed (resonance frequency), the BHA can be simulated using available BHA dynamics and vibration software. This software can analyze downhole vibrations; its simulations have matched several cases very closely to what the operator has experienced. Three different examples were analyzed and presented in the complete paper. The software uses nonlinear vibration theory to determine drillstring-resonance frequencies.

Determination of the critical defect and fatigue life of high-speed railway axles under variable amplitude loads

High-speed railway axles are suffered from extremely complex variable amplitude (VA) loads during operation. However, in the design codes and operation maintenance of railway axles, most of them are based on the equivalent constant amplitude (CA) load spectrum to perform the fatigue resistance design by using the traditional nominal stress method, and carry out the routine inspection based on running experiments and data. In this paper, an innovative time-domain stepwise fatigue assessment (TSFA) approach has been introduced to include the influence of VA loads on the accumulated damage and fatigue crack propagation. Based on this procedure, the fatigue load spectrum from the multi-body system (MBS) dynamics simulation was integrated into the fatigue damage and remaining lifetime assessment of the axles. The calculation indicates that the safe lifetime of the powered and non-powered axles under the time-domain loading is considerably larger than the design value, which shows that the axle could safely operate until they are retired. However, for an original crack with the morphology ratio of 0.6 propagating to 45.0 mm, the lifetime of the powered and non-powered axle is sharply reduced to 1.32, and 2.07 years, respectively. Compared with the classical nominal stress method, the newly-developed TSFA procedure could produce a more conservative but practical result.

Mesoscopic dynamic characteristics and RCF damage evolution of high-speed transmission gear in wind turbine

For the gears utilized in wind turbines, the main reason leading to malfunction is the crack initiation and propagation under cyclic loading. In the gear engagement process, the fatigue damage accumulates gradually and formulate visible microcrack if the fatigue parameter reaches to specified threshold. In order to simulate the fatigue evolution in wind turbine gears, a mesoscopic model is established, in which the Voronoi tessellation and cohesive elements are integrated, such that the crystal structure and grain boundary can be modeled. The dynamic stress distribution and fatigue evolution phenomenon are then investigated under different working conditions. The loading in the meshing region is simplified as moving load on a semi-infinite plane, so the shear stress distributions for per loading cycle are obtained. Furthermore, bilinear traction-separation law (TSL), Jump-in-Cycles (JIC) loading methodology and multi-axial fatigue criterion are involved to fulfill the damage accumulation simulation. As a result, the initiation location and propagation pattern of the fatigue crack are predicted, and the fatigue life curve is also obtained. Thereafter, the influence of wind speed and lubrication condition on fatigue damage evolution is also discussed. The results have shown that the wind loading mainly influences the magnitude of the maximum shear stress, whereas the contact width will determine the location of the maximum shear stress. When the whole fatigue evolution procedure is finished, the first two cracks initiate at the depth of 0.13 mm and 0.27 mm beneath the surface respectively, and then propagate into the substrate. Through comparative analyses of fatigue life curves, it can be concluded that higher wind speeds and poor lubrication conditions will reduce gear service life significantly.

Asphalt Mixtures and Flexible Pavement Construction Degradation Considering Different Environmental Factors

Water, frost, and road salt are counted as environmental factors. They affect the pavement structure, particularly during the winter or in regions located above sea level. In the article, a literature review related to water, frost, and road salt impacts was performed. The main problem of evaluating asphalt mixture degradation and its influence on pavement fatigue life via environmental factors was stated. Four types of asphalt concrete (AC22) road mixes were prepared for laboratory tests. They differed in production technology and the type of binder applied. One binder content level was tested. To investigate the impact of water, frost, and road salt on mineral-asphalt mixtures utilized in flexible constructions, two proprietary experimental methods were applied. Methods allowed for determining the mixtures’ degradation level using the measured stiffness modulus in the 4-PB-PR test. Based on the obtained results, it was found that both interactions cause a significant decrease in the value of the stiffness modulus. In the article, a degradation ratio was proposed. The ratio expressed the impact of water, frost, and road salt on the stiffness mix variability. Its value was considered for pavement fatigue life based on the AASHTO 2004 fatigue criterion. The article demonstrates that the type of binder used influences the mix’s resistance to water, frost, or road salt impact. The highest resistance was reached by a mixture with highly modified asphalt (hot technology), and the worst was with asphalt WMA (warm technology). It has also been proven that the impact of water, frost, or road salt on pavement fatigue life is significant. The drop was significant, amounting to a few dozen percent. It was stated that environmental impacts (such as water, frost, or road salt) should be considered in asphalt mixture and pavement construction design.

Corrosion effects on the fatigue performance of high-strength bolted friction connections

In this paper, the corrosion effects on the fatigue performance of the friction connections are experimentally and numerically investigated. Fatigue test was conducted on the connections with four corrosion levels, and the failure mode and fracture surfaces were analyzed. Based on the finite element modeling of the connection, the crack initiation life caused by the fretting fatigue was calculated based on several multiaxial fatigue criteria, and the crack propagation life in the complex stress field was predicted using the AFGROW software. The results show that the fatigue life of the friction connections could be significantly reduced by corrosion, and the fatigue failure occurred near the minimum cross-section plane of the inner plates. It was also observed that the fatigue cracks initiated at the fretting wear scar and the corrosion pits at the hole edge for the uncorroded and corroded connections, respectively. The predictions show that the fatigue life prediction method in which the crack initiation and propagation lives are both considered can accurately predict the fatigue behavior of the uncorroded connections under different stress ranges. The fatigue life of the corroded friction connections with a mass loss ratio>7.8% can be estimated by assuming an initial crack at the hole edge in the minimum cross-section plane and ignoring the crack initiation life induced by fretting damage.

An Investigation of the Contact Fatigue Characteristics of an RV Reducer Crankshaft, Considering the Hardness Gradients and Initial Residual Stress.

The crankshaft is one of the core components of a Rotate Vector (RV) reducer. The fatigue life of the RV reducer is severely hindered by fatigue failure on the eccentric cylindrical surface of the crankshaft. The hardness gradients and residual stress in the crankshaft, associated with machining operations, exert an enormous impact on the rolling contact fatigue (RCF). In this work, a finite element method (FEM)-based three-dimensional elasto-plastic contact model is established to calculate the stress-strain field by taking hardness gradients and initial residual stress into account. The RCF characteristics of an RV reducer crankshaft is investigated by applying modified Fatemi-Socie (FS) multiaxial fatigue criterion. The results indicate that initial residual stress plays an influential role in the fatigue damage by altering the distribution of the maximum normal stress near the contact surface. The modified FS fatigue criterion could better consider the effect of initial residual stress and the shear stress, which significantly improves the prediction accuracy of the contact fatigue life model. The contact fatigue performance could be considerably improved by designing appropriate shot peening parameters to obtain optimized residual stress distribution. Therefore, the technique presented may serve as an important guideline for the anti-fatigue design of an RV reducer crankshaft.

Study on fretting fatigue crack initiation of scaled railway axles in consideration of fretting wear

The objective of this study is to investigate the fretting fatigue crack initiation of press-fitted railway axles. Fretting fatigue tests were conducted on scaled railway axles, and the fretting wear and crack at the fretted zone were analyzed. Based on the test results, FE models which take the fretting wear profiles into account were established. And then, three multi-axial fatigue criteria combined with the theory of critical distance were used to evaluate the fretting fatigue crack initiation. The analysis results show that the contact pressure and slip amplitude within the fretted zone are increased with the evolution of fretting wear, and thus produce a gradual increment of frictional shear stress at the inner side of the fretted zone. This finally leads to the fretting fatigue crack initiation of press-fitted axles. The fretting wear would play a more significant role in fretting fatigue initiation of press-fitted axles in the condition of lower applied stresses and higher loading cycles. As compared with the SWT criterion based on the maximum normal stress and elastic strain amplitude, the criteria considering the shear stress as the main controlling parameter (modified Dang Van criterion and McDiarmid criterion) can give a better-predicted result of the fretting fatigue crack initiation for press-fitted axles.

Component Tests and Numerical Investigations to Determine the Lifetime and Failure Behavior of End Stage Blades

Abstract The paper focuses on experimental and numerical fatigue assessment procedures to evaluate the influence of multi-axial stress state caused by high centrifugal forces superimposed with bending loads due to blade vibrations on the lifetime of end stage blades from steam turbines. The experimental investigations on original-sized end stage blades were carried out on a test rig specially developed for high forces and multicomponent force application. This was based on detailed numerical simulations by the MPA University of Stuttgart. During the fractographic postexaminations of the tested blades using magnetic particle inspection, light and scanning electron microscopes, two competing damage mechanisms were identified that occurred at different locations. Numerical investigations by means of elastic–plastic finite element analyses were carried out to estimate the local stress conditions acting in the blade root. The local stresses and strains were postprocessed using the critical plane approach and advanced multi-axial fatigue damage parameters. Due to the high stress gradients at the edge of contact, over-conservative predictions may result if their effects are not taken into account. Based on the critical plane method in conjunction with fatigue damage parameters, an approach taking the stress gradient into consideration was developed to predict the fatigue life of the end stage blades. The approach is verified by the component tests on original-sized blades.

Fatigue lifetime of both plain and notched specimens made of additively manufactured AISI 316L

During last few years, the Additive Manufacturing (AM) technology has increasingly attracted the interest of both industries and researchers. In such a context, the present paper deals with the analysis of specimens made of additively manufactured AISI 316L stainless steel subjected to cyclic loading. More precisely, fatigue tests available in the literature and related to both plain and notched specimens are considered. The fatigue assessment of such specimens is performed by means of an analytical methodology, recently proposed by the present authors, consisting of the joint application of: a multiaxial stress-based fatigue criterion, named Carpinteri et al. criterion, which exploits the concept of the critical plane, and a stress averaging method, named Critical Direction Method, for the determination of the orientation of the critical plane. Satisfactory results are here obtained in terms of fatigue life for AM components, irrespective of both the specimen geometry and the degree of multiaxiality and non-proportionality.

A new approach for the prediction of fatigue life in rolling bearings based on damage accumulation theory considering residual stresses

Today, the service life calculation of rolling bearings is standardized in ISO 281, based on the theory of Lundberg and Palmgren. In the standard calculation method, material properties such as fatigue limit stress were taken into account by introducing the fatigue limit stress proposed by Ioannides and Harris. This standard calculation method provides a reasonable range of fatigue life in good agreement with experimental results under ideal test conditions such as constant external load. However, complex operating conditions of bearings such as varying loads and oscillating motion are not considered. Therefore, there is a need for a new analytical calculation model that can predict the fatigue life of rolling bearings operating under these complex conditions. This makes it possible to advance the application of rolling bearings and optimize their use in machines such as wind turbines. In the proposed approach, the fatigue life is determined based on the Palmgren-Miner linear damage rule, evaluating the subsurface stresses below the rolling contact using the S-N curve according to the fatigue criterion proposed by Lundberg and Palmgren. All rolling contacts that occur in an internal stress cycle due to the internal dynamic behavior during rotating operations are evaluated individually and referred to as partial damage risks. The partial damage risks are accumulated linearly according to the Palmgren-Miner theory to obtain the load cycle to failure. At this time, the loaded volume is assessed along the depth from the contact area to the core of the bearing ring, which makes it possible to indicate the depth position of fatigue occurrence in terms of crack initiation. The material properties such as the fatigue limit stress and the probability of failure are taken from the S-N curve itself. To consider the residual stress, a simple link concept is suggested by using the ratio of the maximum contact pressure to the yield criteria. The proposed approach can be extended to calculate oscillating fatigue life regarding the number of rolling contacts at a given oscillation amplitude. In this study, it can be confirmed that the analytically determined fatigue lifetime according to ISO 281 is still close to the bearing life test result. In addition, it shows that the results obtained using the proposed approach agree well with the calculation results obtained using ISO 281.

Numerical modeling for efficiency and endurance assessment of an indirect mitral annuloplasty device

In recent years, several transcatheter systems have been introduced for treatment of common mitral regurgitation (MR). Such a system that is based on indirect mitral annuloplasty (IMA) is currently indicated for functional MR. Very few clinical studies have been performed to assess the efficiency and durability of such devices, despite their high risk of fracture resulting from ongoing exposure to large cyclic deformations. In this study, numerical models of moderate primary MR were created to test the implantation procedure of a customized IMA device and its sealing efficiency. The ability of the implanted device to reduce systolic leakage was evaluated and affirmed with a model of a more generic device. The long-term durability of the device was tested using a range of Nickel Titanium material properties. Our results demonstrated a considerable reduction in leakage for both the simplified generic device and the more detailed customized device models. The device met different fatigue criteria, confirming its resiliency and safety even after 10 years, even under the harsher conditions of primary MR. This is the first study to assess the performance and fatigue risk of IMA devices for the treatment of more complicated MR conditions. These findings may pave the way for further research to ultimately consider the device in selective cases of PMR.

Effect of severe thermo-oxidative aging on the mechanical behavior and fatigue durability of short glass fiber reinforced PA6/6.6

The work deals with the fatigue lifetime estimation of Short Fiber Reinforced Thermoplastics (SFRP), with a focus on conjugated effects of thermal aging. Two materials containing 35% (V35) and 50% (V50) weight ratio of short glass fibers were aged for 500 h at 200°C in air and compared to the same materials in a Dry-As-Molded (DAM) state. Monotonic and fatigue tests were performed in samples machined out of injected plates and cut along three different orientations to the injection one (0°, 45°, 90°) in order to capture the anisotropy of the skin-core microstructure, classical in injected SFRP.Monotonic tensile tests evidenced the stiffening and embrittlement of the Polyamide matrix reported in the literature, nevertheless with an acuity depending on the matrix ratio and fiber orientation. Stress-controlled fatigue tests were performed at constant amplitude, frequency (10 Hz), temperature (200°C) and stress ratio R = 0.1. The fatigue curves of V35 are more affected by aging than those of the V50 material. The combined results from the mean strain evolutions and SEM observations confirmed that the initiation approach for fatigue lifetime estimation was still valid in aged composites. Several fatigue criteria, among the most recently reported in the literature, were evaluated from this database. The effect of aging on the cyclic evolution of the different Fatigue Indicator Parameters (FIP) involved in the criteria was analyzed preliminarily. For the present fatigue conditions, the best criteria for unaged materials (i.e cyclic creep energy-based ones) were shown to still be the best for aged materials. Finally, the ability to predict fatigue lifetime for aged composites from the identification of the fatigue criterion in the unaged state was evaluated.

Numerical evaluation on fatigue crack growth and life predictions of an FPSO mooring system

This study aims to systematically study the fatigue crack propagation characteristics of the mooring system for a floating production storage and offloading vessel (FPSO) through the fracture mechanics-based approach. The remaining fatigue life of the mooring lines is predicted by a self-integrated program through the simulation of the crack growth behavior. Additionally, parametric studies are performed to investigate the influence of initial crack status (location/size/shape) on mooring crack propagation characteristics. Results illustrate that the remaining fatigue life at the uppermost position of mooring lines at the wave-ward side is similar, which is approximately 178 years longer than that of mooring lines at the wave-back side. Fatigue issues are the severest in the crown region, where the critical fatigue life is about 49% of that in the bend region and 19.9% of that in the straight region. With the increase of the initial crack size and aspect ratio, the remaining fatigue life experiences a remarkable decrease with amplitudes up to 47.8% and 30.1% respectively. The integrated evaluation program is a promising tool for the damage tolerance design of mooring system due to the excellent capability in predicting the remaining fatigue life and charactering the crack growth behavior.

Fatigue characterization analysis of a submerged fishing farm platform through spectral-based fracture mechanics

This study proposes a general direct calculation approach for fatigue crack growth evaluation and life predictions through a spectral-based fracture mechanics method. First, equivalent damage accumulation rates are introduced to describe the crack propagation characteristics under short-term sea states, integrating wave spectrum and fracture mechanics. Subsequently, a general fatigue crack growth program is integrated to realize automatic crack growth, accurate stress intensity factor (SIF) calculation and reliable fatigue life prediction through coupling analysis of meter-scale structures and millimeter-scale cracks. Finally, a parameter study is implemented to explore the influence of wave direction and initial crack size/shape on the fatigue performance of the fishing farm platform. Results indicate that the remaining fatigue life is evidently longer under 90° wave direction than that under 0 and 45°, which can be well characterized through SIF transfer functions. Critical fatigue life decreases with the increase of crack size and aspect ratio with the shortest duration of 12.8 years, demonstrating that residual fatigue life is closely associated with initial crack state. Fatigue failure is more predominant at lower tubular joints with the critical fatigue life ranging from 15 to 30 years, indicating the self-developed program possesses good universality and applicability in dealing with fatigue issues.

Investigating the effect of notch size on critical distance and fatigue limit by coupling the theory of critical distance and finite fracture mechanics

The energy based failure criterion Finite Fracture Mechanics is transformed into a stress based failure criterion and expressed by an effective stress similar with Line Method. After coupling the two criterions, the theoretical critical distance expression is derived based on notch stress distribution, stress intensity factor function and material characteristic length. The effect of notch size and material characteristic length on the critical distance and fatigue limit prediction was analyzed for a group of V-shaped notches. Then, the coupled method was validated by a large number of experimental results. It is revealed that the Line Method and coupled method are the same except that they employ different critical distances. The validity of Line Method was discussed based on the difference of critical distances and fatigue limit predictions between the Line Method and coupled method.

Effects Of A 4-week Neuromuscular Electrical Stimulation Treatment On Skeletal Muscle Endurance In Older Adults

Neuromuscular electrical stimulation (NMES) is often used as a rehabilitative modality and evidence has suggested that high frequency NMES (HF-NMES) may elicit increases in muscle strength. However, little is known regarding the effects of HF-NMES treatment on voluntary skeletal muscle endurance. PURPOSE: The aim of this study was to determine the effect of a 4-week HF-NMES intervention on muscular endurance and changes in neuromuscular activation patterns of the quadriceps during voluntary fatiguing muscle contractions in older adults. METHODS: Seventeen healthy older adults (68.8 ± 1.8 yrs; NMES: n = 12; SHAM: n = 5) completed the study. The NMES group underwent NMES treatment to the quadriceps of each leg 3x/week for 4 weeks at a 60 Hz stimulation frequency. Electrodes were applied to the SHAM group, but no current was delivered. All subjects performed maximal voluntary contractions (MVC) and a knee extension isometric submaximal voluntary fatigue task at 50% MVC until fatigue criteria were met. Surface electromyography (sEMG) of the vastus lateralis (VL) and vastus medialis (VM) muscles were recorded during the fatigue task and quantified for root mean square (RMS) EMG (percent rate of change during the fatigue task) and median frequency (MF) to examine changes in muscle activation. Repeated measures ANOVAs were used to determine differences pre-post NMES for muscular endurance time, MVC, and EMG measures. Statistical significance was set at p < 0.05. RESULTS: MVC increased in the NMES group (117.1 ± 8.7 Nm vs. 127.6 ± 11.1 Nm, p = 0.049; pre- and post-training, respectively) with no changes in SHAM (p = 0.96). No differences were observed pre-post training, respectively for muscular endurance time (NMES: 159.3 ± 20.1 s vs 141.9 ± 21.2 s, p = 0.29; SHAM: 242.2 ± 43.3 s vs 202.9 ± 23.3 s, p = 0.13), RMS EMG rate of change (NMES: VL: 16.6 ± 3.6% vs 18.8 ± 10.4%, p = 0.84; VM: 11.4 ± 2.1% vs 19.6 ± 5.5%, p = 0.15; SHAM: VL: 7.8 ± 1.6% vs 7.1 ± 3.0%, p = 0.81; VM: 7.1 ± 3.3% vs 5.9 ± 2.2%, p = 0.55) and MF EMG (NMES: VL: 77.6 ± 4.1 Hz vs 74.9 ± 3.6 Hz, p = 0.13; VM: 72.5 ± 2.4 Hz vs 72.6 ± 2.2 Hz, p = 0.97; SHAM: VL: 79.3 ± 3.4 Hz vs 80.2 ± 4.9 Hz, p = 0.85; VM: 76.9 ± 3.7 Hz vs 83.9 ± 5.1 Hz, p = 0.12). CONCLUSION: Treatment with HF-NMES did not improve muscle endurance or EMG-related parameters. HF-NMES may not be efficacious when the goal is to improve skeletal muscle endurance.