Fatigue Threshold Research Articles

Fracture mechanics‐based criteria for fatigue fracture of rolling bearings under the influence of defects

AbstractFatigue tests were carried out on real bearings with various types of artificial defects on their outer‐ring raceways. Finite element analysis (FEM) revealed that the stress intensity factor (SIF) ranges and stress ratios were complex and variable, depending on the gap fittings between the outer rings and housings, as well as on the sizes of the initial defects, both of which influenced the fatigue thresholds of the bearings. In order to establish a comprehensive evaluation of fatigue limits under several combinations of bearing geometries and defect sizes, fatigue crack‐growth thresholds were also measured at different stress ratios by focusing on crack‐closure behaviour. Based on all of the analytical and experimental results, fracture mechanics‐based criteria were proposed for the assessment of fatigue fracture in rolling bearings.

Fatigue Response of Cold-Rolled Type-304 Stainless Steel Foil

This study presents the fatigue response of 304 stainless steel foil, cold-rolled to a thickness of 3.2 μm with 87 percent cold work at orientations of 0, 45, and 90 degrees to the direction of rolling. Fatigue specimens were fabricated by laminating a supportive layer of 20-μm polyimide film to one side of the foil and patterning 242 crack initiation features by photolithographic process. Progression of fatigue damage was determined through electrical resistance measurement. The fatigue response was demonstrated to be largely affected by anisotropy existing between the rolling direction and the off-axis orientations. Fatigue cracks that traveled in a direction parallel to the elongated grains (cyclic loads applied at 90-degree orientation to foil rolling direction) had the most fatigue response (undesirable characteristic). The construction of the specimens with thin foil supported by a film backing contributed to high fatigue threshold.

Perceived Consumption of a High-Dose Caffeine Drink Delays Neuromuscular Fatigue.

Elhaj, HM, Imam, O, Page, BW, Vitale, JM, and Malek, MH. Perceived consumption of a high-dose caffeine drink delays neuromuscular fatigue. J Strength Cond Res 36(5): 1185-1190, 2022-The placebo effect is a concept in which a desired outcome arises, mainly from the belief that the treatment (i.e., supplement or drug) was beneficial although no active ingredient was given. The results of studies related to the placebo effect primarily examine functional performance. What remains unanswered, however, is whether these changes in performance are associated with neuromuscular alterations in the exercised muscles. The purpose of the study, therefore, was to determine the influence of the placebo effect on the physical working capacity fatigue threshold (PWCFT) for a continuous exercise paradigm. To achieve this aim, subjects were told that they were participating in a study to determine the dosage response (low or high) of caffeine on neuromuscular fatigue when in fact no caffeine was given during the experiment. We hypothesized that the perceived consumption of the high-dose caffeine drink would result in a higher PWCFT than the perceived consumption of the low-dose caffeine drink and placebo. Secondarily, we hypothesized that the perceived consumption of the high-dose caffeine drink would result in a higher power output than the perceived consumption of the placebo. Nine healthy college-aged men (mean ± SEM: age, 25.7 ± 1.3 years; body mass, 84.4 ± 3.1 kg; and height: 1.82 ± 0.02 m) volunteered to be in the study. For each of the visits, subjects were given an 8 oz. bottle of water with dissolved crystal light. After the drink was consumed, subjects rested in the laboratory for 1 hour before performing the incremental single-leg knee-extensor ergometry. Immediately after the termination of the incremental single-leg knee-extensor ergometry, the subject was asked which caffeine dose (placebo, low, or high) they believed they consumed for that visit. There were no significant mean differences for maximal power output for the 3 perceived conditions (placebo: 62 ± 3, low-dose caffeine: 62 ± 4, and high-dose caffeine: 65 ± 3 W). When the subjects perceived consuming the high-dose caffeine drink, there were significant mean differences (all p-values < 0.01), for PWCFT, between the other conditions (mean ± SEM: placebo: 23 ± 3 W, low-dose caffeine: 26 ± 2 W, and high-dose caffeine: 42 ± 3 W). This corresponded to a significant mean difference (all p-values < 0.01) when the PWCFT was presented as a percentage of the maximal power output (mean ± SEM: placebo: 37 ± 5%, low-dose caffeine: 42 ± 3%, and high-dose caffeine: 64 ± 3%). The application of our results may indicate that the subject's expectancy, to caffeine consumption, plays a critical role in delaying the onset of neuromuscular fatigue despite not receiving any caffeine in their drinks.

Rehabilitation Effects of Fatigue-Controlled Treadmill Training After Stroke: A Rat Model Study.

Background: Traditional rehabilitation with uniformed intensity would ignore individual tolerance and introduce the second injury to stroke survivors due to overloaded training. However, effective control of the training intensity of different stroke survivors is still lacking. The purpose of the study was to investigate the rehabilitative effects of electromyography (EMG)-based fatigue-controlled treadmill training on rat stroke model.Methods: Sprague–Dawley rats after intracerebral hemorrhage and EMG electrode implantation surgeries were randomly distributed into three groups: the control group (CTRL, n = 11), forced training group (FOR-T, n = 11), and fatigue-controlled training group (FAT-C, n = 11). The rehabilitation interventions were delivered every day from day 2 to day 14 post-stroke. No training was delivered to the CTRL group. The rats in the FOR-T group were forced to run on the treadmill without rest. The fatigue level was monitored in the FAT-C group through the drop rate of EMG mean power frequency, and rest was applied to the rats when the fatigue level exceeded the moderate fatigue threshold. The speed and accumulated running duration were comparable in the FAT-C and the FOR-T groups. Daily evaluation of the motor functions was performed using the modified Neurological Severity Score. Running symmetry was investigated by the symmetry index of EMG bursts collected from both hind limbs during training. The expression level of neurofilament-light in the striatum was measured to evaluate the neuroplasticity.Results: The FAT-C group showed significantly lower modified Neurological Severity Score compared with the FOR-T (P ≤ 0.003) and CTRL (P ≤ 0.003) groups. The FAT-C group showed a significant increase in the symmetry of hind limbs since day 7 (P = 0.000), whereas the FOR-T group did not (P = 0.349). The FAT-C group showed a higher concentration of neurofilament-light compared to the CTRL group (P = 0.005) in the unaffected striatum and the FOR-T group (P = 0.021) in the affected striatum.Conclusion: The treadmill training with moderate fatigue level controlled was more effective in motor restoration than forced training. The fatigue-controlled physical training also demonstrated positive effects in the striatum neuroplasticity. This study indicated that protocol with individual fatigue-controlled training should be considered in both animal and clinical studies for better stroke rehabilitation.

Effects of Curcumin and Fenugreek Soluble Fiber on the Physical Working Capacity at the Fatigue Threshold, Peak Oxygen Consumption, and Time to Exhaustion

Herrick, LP, Goh, J, Menke, W, Campbell, MS, Fleenor, BS, Abel, MG, and Bergstrom, HC. Effects of curcumin and fenugreek soluble fiber on the physical working capacity at the fatigue threshold, peak oxygen consumption, and time to exhaustion. J Strength Cond Res 34(12): 3346-3355, 2020-The purpose of this study was to examine the effects of curcumin in combination with fenugreek soluble fiber (CUR + FEN) or fenugreek soluble fiber alone (FEN) on the neuromuscular fatigue threshold (PWCFT), peak oxygen consumption (V˙o2peak), and time to exhaustion (Tlim) on a graded exercise test (GXT), in untrained subjects. The PWCFT estimates the highest power output that can be maintained without evidence of neuromuscular fatigue. Forty-seven untrained, college-aged subjects were randomly assigned to one of 3 supplementation groups; placebo (PLA, n = 15), CUR + FEN (500 mg·d, n = 18), or FEN (300 mg·d, n = 14). The subjects completed a maximal GXT on a cycle ergometer to determine the PWCFT, V˙o2peak, and Tlim before (PRE) and after (POST) 28 days of daily supplementation. Surface electromyographic signals were recorded from a bipolar electrode arrangement on the vastus lateralis of the right leg during each test. Separate one-way analysis of covariances were used to determine if there were between-group differences for adjusted POST-PWCFT, POST-V˙o2peak, and POST-Tlim values, covaried for the respective PRE-test scores. The adjusted POST-PWCFT for the CUR + FEN group (mean ± SD: 196 ± 58 W) was greater (p = 0.016) than the PLA group (168 ± 49 W) but the FEN group (185 ± 32 W) was not different from the CUR + FEN or PLA groups (p > 0.05). There were no differences for adjusted POST-V˙o2peak (p = 0.612) or POST-Tlim (p = 0.508) among the groups. These findings suggested curcumin combined with fenugreek soluble fiber might delay neuromuscular fatigue.

Brief Behavioral Therapy and Bupropion for Sleep and Fatigue in Young Adults With Crohn’s Disease: An Exploratory Open Trial Study

Background/AimsSleep disturbances and fatigue are common symptoms amongst patients with Crohn’s disease (CD). The aim of this study was to test the feasibility and effects of a pragmatic, stepped-care intervention for the treatment of poor sleep quality and fatigue in adolescents and young adults with CD. MethodsThis study is a two-phase open trial exploring interventions for sleep and fatigue. After the initial comprehensive assessment which included quantitative measures and an interview to evaluate sleep and physical and mental health, the 12-week intervention consisted of two sequential steps: 1) a brief behavioral therapy for sleep in inflammatory bowel disease (IBD) (BBTS-I; 4 weeks) and 2) adding the psychotropic medication, bupropion sustained release (BUP-SR; 8 weeks), for the subset of subjects continuing to experience fatigue. Results232 CD patients (median age=24, median sex=female) were approached over 18 months, of whom 112 screened positive on the Pittsburgh Sleep Quality Index (PSQI) and multi-dimensional fatigue inventory (MFI), with 68 CD patients completing the more comprehensive baseline assessment. Of the 68 patients, 52 participated in Phase I of the BBTS-I intervention. Following 4-weeks of the BBTS-I, there were significant improvements in sleep quality (p < .001) and fatigue (p < .001). As part of Phase II, of the 52 patients who met fatigue threshold criteria, 33 patients participated in the BUP-SR+BBTS-I arm while 19 participated in the BBTS-I only intervention group. After 8 weeks of Phase II, both intervention groups saw significant further improvement in sleep, fatigue, anxiety and depressive symptoms, but without significant differences between the two intervention groups. ConclusionsA stepped-care approach shows that we can improve sleep disturbance with BBTS-I in CD patients, but fatigue only partially improves. For a subset of patients who chose to add BUP-SR to their behavioral therapy, fatigue improves further but not to a statistically significant effect compared to behavioral therapy alone.

Effects of texture on the functional and structural fatigue of a NiTi shape memory alloy

The effects of crystallographic texture on the fatigue performance of superelastic NiTi sheet were investigated to assess the evolution of plastic deformation and transformation stress (functional fatigue) and the resistance to crack growth (structural fatigue). During uniaxial cycling, about twice as much plasticity accumulated for tensile specimens aligned in the rolling direction (RD) of the NiTi sheet compared to those in the transverse direction (TD). Fatigue experiments on compact tension specimens also showed a 25% lower fatigue threshold and twice the fatigue crack growth rate when loaded in the RD than in the TD. These macroscopic findings correlated with the microscopic observations of crack-tip displacements, where the crack tip opened at a lower stress intensity (K≈0.9 MPam) when loaded in the RD than in the TD (≈1.5 MPam). The dissimilar crack growth rates highlight the strong orientation-dependent mechanisms of plasticity, transformation, and twinning on both functional and structural fatigue. Although the RD had a larger transformation strain that might suggest an enhanced deformation accommodation, under stress-controlled cycling the TD was more resistant to plastic slip, leading to more reversible transformation. Assuming other microstructural aspects are held fixed (composition, grain size, and precipitates), these results suggest that tension along the textures akin to that of the TD (i.e., with a higher density of [100] and lower density of [111] and [110]) is beneficial to fatigue performance during stress-limited cycling.

Fatigue crack growth behavior of laser powder bed fusion additive manufactured Ti-6Al-4V: Roles of post heat treatment and build orientation

Effects of build orientation (0°, 45°, 90°) and post heat treatments (hot isostatic pressing 820 °C, 950 °C or annealing 1020 °C) on the fatigue crack growth rates (FCGRs) of Ti-6Al-4V fabricated by laser powder bed fusion were examined. Coarser α′/α lath thicknesses resulted in slower FCGRs and higher fatigue thresholds while texture and build orientation had little influence. Fatigue thresholds were defined by the ability to transfer slip from one α′/α lath to another, with a minor role of roughness induced crack closure. The transition away from microstructure sensitive FCG occurred where the packet/colony size equaled the cyclic plastic zone size.

Effects of cryogenic temperature and grain size on fatigue-crack propagation in the medium-entropy CrCoNi alloy

CrCoNi-based high-entropy alloys have demonstrated outstanding mechanical properties, particularly at cryogenic temperatures. Here we investigate the fatigue-crack propagation properties of the equiatomic, single-phase, face-centered cubic, medium-entropy alloy (MEA), CrCoNi, that displays exceptional strength, ductility and toughness, all of which are enhanced at cryogenic temperatures. Fatigue-crack growth is examined, at a load ratio of 0.1 over a wide range of growth rates, from ~10−11 to >10−7 m/cycle, at room (293 K) and cryogenic (198 K, 77 K) temperatures for two grain sizes (~7 and 68 µm), with emphasis on near-threshold behavior. We find that the ΔKth fatigue thresholds are increased with decreasing temperature and increasing grain size: from 5.7 MPa√m at 293 K to 8 MPa√m at 77 K in the fine-grained alloy, and from 9.4 MPa√m at 293 K to 13.7 MPa√m at 77 K in the coarse-grained alloy. Mechanistically, transgranular cracking at 293 K transitions to a mixture of intergranular and transgranular at cryogenic temperatures, where the increased propensity of nano-twins appears to inhibit growth rates by deflecting the crack path. However, the main factor affecting near-threshold behavior is roughness-induced crack closure from interference between the crack flanks, which is enhanced by the rougher fracture surfaces at low temperatures, particularly in the coarser-grained microstructure. Fatigue-crack propagation behavior in CrCoNi is comparable to nickel-based superalloys but is superior to that of the high-entropy CrMnFeCoNi (Cantor) alloy and many high-strength steels, making the CrCoNi alloy an excellent candidate material for safety-critical applications, particularly involving low temperatures.

Effect of pearlite interlamellar spacing on fatigue property of a wheel steel

AbstractDifferent pearlite interlamellar spacings of 0.54 % carbon (C) wheel steel were obtained by heat treatment, and the influence of interlamellar spacing on fatigue behavior of the steel was studied through conducting the staircase method fatigue testing and decreasing/increasing stress intensity factor range (ΔK) fatigue crack growth tests. The results indicate that the fatigue endurance limit and fatigue threshold with smaller interlamellar spacing are higher than those with larger one, which can be well explained by dislocation slipping theory. Furthermore, the fatigue crack growth rates in the near‐threshold and Paris regions were found to reduce with decreasing the interlamellar spacing. The decreased growth rate is attributed to the deflected crack path induced crack closure effect, as evidenced by fatigue steps on the fatigue fracture surface. The present results show how to enhance the fatigue property of wheel steel through refining the pearlite interlamellar spacing.

Upper limb movement characteristics of children and youth with dyskinetic cerebral palsy – A sensor approach

People with spinal cord injury (SCI) may have their paralyzed muscles activated through functional electrical stimulation (FES). This neuromodulation technique has been used frequently to assist in controlling the movement of neuroprostheses. Electroencephalography (EEG) is able to trigger FES from the motor imagery captured through movements intentions. This research presents an isometric neuromuscular control system of the quadriceps muscle activated by EEG. Additionally, the detection of neuromuscular fatigue through the mechanomyography (MMG) technique is proposed, which is used to shut-off the system. A pilot study was performed on a chronic 42-year-old paraplegic (no voluntary contraction below the spinal cord injury level T8) volunteer. To do so, the training procedure for EEG signals was divided into the calibration and feedback phases. In the first one, four EEG channels and the Linear Discriminant Analysis (LDA) classifier were used to classify between motor imagery of the right leg and remain at rest. The maximum accuracy obtained during this stage was 77%. In the feedback phase, the volunteer was able to activate FES through brain–computer interface (BCI) in two tests (defined as Test 1 and Test 2) with the same procedure in different days. The closed-loop force control was tested with the setpoint of 2 kgf and 2.5 kgf and proved to be stable on both tests, successfully turning off the FES using the fatigue threshold from the MMG signal, being the main contribution of this work.

Training induced fatigability assessed by sEMG in Pre-Olympic ice-skaters

The aim of this study was to investigate the size of the change and asymmetry in fatigability of gluteus maximus muscles during endurance training in short-track. The research has taken into account the position of athletes during skating and the problem of fatigue and pain in these muscles. The research covered involved eight female athletes of the Polish National Team in short track, which had been prepared to the Olympic Games in PyeongChang. The surface electromyography (sEMG) system was used to measure fatigue of right and left gluteus maximus muscles, in the modified Biering–Sorensen test. The test was conducted five times during the training: before training, after warmup, and after each of 3 series of the endurance training. Comparing the mean frequency of the surface electromyography power spectrum of the test, statistically significant reduction of the average frequency value of the right muscle from 55.61 ± 7.08 to 48.64 ± 4.48 Hz and left muscle from 58.78 ± 4.98 to 53.18 ± 4.62 Hz was reported, which prove the muscle fatigue. In subsequent series tests, the sEMG signal frequency of begin decrease more than the end of the each measurement, which determines the fatigue threshold. The size of the d Cohen effect in fatigue drops along with subsequent five tests during the training. Skaters has higher frequency reduction of the right lower limb, which indicates its greater fatigue during skateing. The fatigue and asymmetry in muscle observed in short-track has implications for training and performance.

Stretchable hydrogels with low hysteresis and anti-fatigue fracture based on polyprotein cross-linkers

Hydrogel-based devices are widely used as flexible electronics, biosensors, soft robots, and intelligent human-machine interfaces. In these applications, high stretchability, low hysteresis, and anti-fatigue fracture are essential but can be rarely met in the same hydrogels simultaneously. Here, we demonstrate a hydrogel design using tandem-repeat proteins as the cross-linkers and random coiled polymers as the percolating network. Such a design allows the polyprotein cross-linkers only to experience considerable forces at the fracture zone and unfold to prevent crack propagation. Thus, we are able to decouple the hysteresis-toughness correlation and create hydrogels of high stretchability (~1100%), low hysteresis (< 5%), and high fracture toughness (~900 J m−2). Moreover, the hydrogels show a high fatigue threshold of ~126 J m−2 and can undergo 5000 load-unload cycles up to 500% strain without noticeable mechanical changes. Our study provides a general route to decouple network elasticity and local mechanical response in synthetic hydrogels.

A new fatigue reliability analysis method for steel bridges based on peridynamic theory

A fatigue reliability model based on the peridynamic (PD) theory was proposed to analyze the fatigue performance of steel bridges in this study. Different from previous methods based on classical continuum mechanics, the PD model does not require additional criteria to guide the growth of crack or damage. In particular, the influence of fatigue threshold value was considered in a systematic formula, and the response surface method was utilized to analyze fatigue failure probability. The proposed model was applied to complex fatigue phenomena such as spontaneous crack nucleation, crack branching, and fatigue failure under biaxial cyclic loadings where fatigue crack paths interact in complicated ways. The fatigue crack growth pattern, fatigue life, and fatigue reliability of specimens considering the biaxial or uniaxial fatigue loadings were analyzed. The accuracy of the fatigue model was verified through a series of comparisons with the experimental, analytical, and FEM results. The effectiveness of the proposed method was also demonstrated in the application to the fatigue reliability analysis of the Ting Kau Bridge.

Fracture and fatigue behaviour of a laser additive manufactured Zr-based bulk metallic glass

Laser additive manufacturing of bulk metallic glass (BMG) provides an effective bypassing of the critical casting thickness constraints that limit the size of components that can be produced; however, open questions remain regarding the resulting mechanical properties. In this work, a Zr-based BMG known as AMZ4 with composition Zr59.3Cu28.8Nb1.5Al10.4 was printed using a laser powder bed fusion (LPBF) technique. Micro X-ray computed tomography results together with electron microscopy imaging revealed porous processing defects in LPBF produced AMZ4 that led to a loss in tensile strength. Fatigue crack growth studies revealed a fatigue threshold, ΔKth., of ∼1.33 MPa√m and a Paris law exponent of m = 1.14, which are relatively low values for metallic materials. A KIC fracture toughness of 24−29 MPa√m was found for the LPBF BMG samples, which is much lower than the KQ of 97−138 MPa√m and KJIC of 158−253 MPa√m measured for the cast alloy with the same composition. The lower fracture toughness of the laser processed AMZ4 was attributed to ∼7.5× higher dissolved oxygen in the structure when compared to the cast AMZ4. Despite the higher level of oxygen, the formation of oxide nanocrystals was not observed by transmission electron microscopy. Oxygen induced toughness loss was confirmed by dissolving elevated concentrations of oxygen into cast AMZ4 rods, which led to a reduction in bending ductility and changes in the short-range order of the glass structure, as revealed by synchrotron X-ray diffraction.

An engineering estimation of fatigue thresholds from a microstructural size and Vickers hardness: application to wrought and additively manufactured metals

A novel empirical bi-parametric model based on the Vickers hardness HV and a microstructural length parameter, l, is proposed to estimate the fully-reversed threshold-Stress Intensity Factor for long cracks. The model was calibrated on fatigue data of wrought alloys taken from the literature and then extended to additively manufactured (AMed) metals. Experimental results, generated from testing AMed maraging steel 300 specimens containing natural defects as well as taken from the literature, were compared successfully with the estimation based on the El-Haddad model defined solely on the basis of the HV and l.

A 'fatigue threshold' during incremental exercise was identified (and then forgotten) 100 years ago.

A 'fatigue threshold' during incremental exercise was identified (and then forgotten) 100 years ago.

Fatigue-resistant adhesion I. Long-chain polymers as elastic dissipaters

Tough adhesion is often achieved by using inelastic dissipaters. However, inelastic dissipaters fail to enhance adhesion under cyclic loads. Here we achieve fatigue-resistant adhesion by using a particularly simple kind of elastic dissipater: long-chain polymers. Each polymer chain is elastic before rupture. When a single covalent bond of the chain breaks, the elastic energy stored in the entire chain dissipates, amplifying the adhesion energy by the number of links on the chain. So far as the adherends provide the stiffness of an adhered sample, the adhesive can be made of polymer chains of extremely long length. As a proof of concept, we use polyacrylamide hydrogels to adhere two pieces of polyester cloth through topological entanglement. We find that both the adhesion energy and fatigue threshold increase with the polymer chain length and can reach 1400 J/m2 and 300 J/m2, respectively. The measured fatigue threshold of adhesion is linearly proportional to the square root of the chain length, in agreement with the Lake–Thomas model. This fatigue-resistant design can be extended to a variety of adhesion topologies for different adherends and adhesives.

Exploring the Impact of Fatigue in Progressive Multiple Sclerosis: A Mixed-Methods Analysis

BackgroundPatient-focused literature on fatigue in progressive forms of multiple sclerosis (MS) is sparse. This study aimed to explore progressive MS patients’ experiences of fatigue. MethodsAdult patients in the United States with primary progressive MS (n=21) and secondary progressive MS (n=23), recruited from research panels, completed the following PRO measures: Patient Global Impression of Severity (Fatigue) (PGI-F); Fatigue Scale of Motor and Cognitive Functions (FSMC); Modified Fatigue Impact Scale (MFIS); Patient Health Questionnaire, two-item version (PHQ-2); and Patient Determined Disease Steps (PDDS). Patients subsequently participated in a 45-minute semistructured telephone interview and were asked to describe their MS symptoms and to comment on how MS affected their day-to-day lives. More detailed questions followed on the nature of their fatigue, including symptoms, impacts, frequency, and bothersomeness. ResultsPatients’ mean age was 52.5 years, mean time since diagnosis was 14.7 years, and 81.8% were female. 79.5% of patients were unemployed and/or receiving disability benefits. Of all spontaneously reported MS symptoms, fatigue was the most common (n=38, 86.4%), followed by ambulation problems (n=31, 70.5%) and muscle weakness (n=25, 56.8%). Patients used the words “tired,” “exhausted,” “wiped out,” and having “little or no energy” to describe their fatigue. More patients rated fatigue as their “most troubling symptom” (n=17, 38.6%) compared with other MS-related symptoms. Half of patients reported feeling constantly fatigued, and more than 90% reported experiencing fatigue at least daily. The top three most frequently reported negative impacts of fatigue were social functioning, emotional well-being, and cognitive functioning (all >80%). Patients described themselves as “homebodies,” as fatigue limited their social interactions with friends and family and impacted the types of activities they could participate in. Patients attributed their inability to think clearly or focus for long periods of time to their fatigue. Patients also reported experiencing depression and anxiety because of their fatigue, which would often have further negative effects on their relationships with friends and family. On the fatigue PRO measures, mean (standard deviation) scores were 75.2 (14.7) on the FSMC and 55.0 (15.2) on the MFIS. Most participants scored in the “high” fatigue category on the FSMC (84.1%) and above the clinically significant fatigue threshold (86.4%). MFIS and FSMC total scores correlated with PGI-F (polyserial correlations r=0.74 and r=0.62, both p<0.01) and PHQ-2 (r=0.56 and r=0.57, both p<0.01), but not with PDDS (r=0.09 and r=0.02, both p>0.05). ConclusionsFatigue is a common, troublesome, and disabling symptom which has a profound impact on patients’ daily lives, as evidenced by qualitative analyses and high scores on established fatigue measures observed in this sample. These findings provide insights into the burden of fatigue and can inform its measurement in both clinical and research settings. Treatments that improve the symptoms of fatigue or prevent exacerbations are needed for patients with progressive MS.

Application of strain-life fatigue-corrosion model for fillet-welded connections of sign support structures

Fatigue-related corrosion is a complex phenomenon that induces damage accumulation and electrochemical deterioration throughout the service life of the structure. This article presents a previously proposed and modified strain-life Smith–Watson–Topper corrosion model for details on fillet-welded connection of highway sign support structures. To evaluate the degree of corrosion activity, hot-dip galvanized, weathering, and low-carbon steel are investigated with respect to chemical compositions, material properties, and the corresponding corrosion resistance indices. The existing fatigue testing data were analyzed and used to evaluate fatigue resistance under various corrosion environments. A modified Smith–Watson–Topper corrosion model is further utilized to determine acceptable constant amplitude fatigue thresholds for the American Association of State Highway and Transportation Officials fatigue limits under each corrosion category. It was found that low constant amplitude fatigue threshold values were observed for ASTM A588, A595, and A572 steels in locations with corrosion categories exposed to severe corrosive environments. Under these conditions, hot-dip galvanization or other surface treatments of the steel components of the sign supports are recommended to achieve higher constant amplitude fatigue threshold values.