Journal articles: 'Tolerance to fatigue'

1

Li, Guowei, Weijian Mi, Kailiang Lu, and Weiguo Zhang. "Reliability Analysis on Gear Contact Fatigue Strength Considering the Effect of Tolerance." Open Mechanical Engineering Journal 8, no. 1 (December 31, 2014): 630–35. http://dx.doi.org/10.2174/1874155x01408010630.

Full text

Abstract:

Tolerance allocation influences product performance especially for miniature precise assembly device. The purpose of this paper is to explore an approach to optimize manufacturing tolerances by combining the reliability of product performance indicators under actual working condition. The paper describes the principle and ways of tolerance handling in the finite element control equations for the displacement and stress, and then introduces the implementation of Monte-Carlo Finite Element Analysis method. We illustrate this method on a gear-tooth of port-cleaning-equipment gear pump and carry out the reliability analysis on gear contact fatigue strength considering the effect of manufacturing tolerance, and a sensitivity analysis is also performed to identify the key tolerances and improve them in order to attain the expected reliability.

APA, Harvard, Vancouver, ISO, and other styles

2

Zhang, Wenlei, Jian Hu, Hang Yang, Zhigang Suo, and Tongqing Lu. "Fatigue-resistant adhesion II: Swell tolerance." Extreme Mechanics Letters 43 (February 2021): 101182. http://dx.doi.org/10.1016/j.eml.2021.101182.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Jones, R. "Fatigue crack growth and damage tolerance." Fatigue & Fracture of Engineering Materials & Structures 37, no. 5 (February 14, 2014): 463–83. http://dx.doi.org/10.1111/ffe.12155.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Seo, Youngji, Silvia Ravazzani, Hyoyeun Jun, Yan Jin, Alfonsa Butera, Alessandra Mazze, and Bryan Reber. "Unintended Effects of Risk Communication: Impacts of Message Fatigue, Risk Tolerance, and Trust in Public Health Information on Psychological Reactance." Journal of International Crisis and Risk Communication Research 4, no. 3 (October 2021): 517–44. http://dx.doi.org/10.30658/jicrcr.4.3.3.

Full text

Abstract:

How individuals experience unintended effects of risk messages is an understudied area. Focusing on three types of unintended effects (i.e., message fatigue, risk tolerance, and psychological reactance) associated with health risk communication, we conducted an online survey among Italian adults (N = 507) to investigate how perceived message fatigue and risk tolerance might induce psychological reactance and whether trust in public health information might mediate this relationship. Results from mediation models revealed: (a) greater message fatigue and risk tolerance increased psychological reactance; (b) greater message fatigue and risk tolerance led to distrust in government-shared health information; (c) trust in public health information mediated the effects of message fatigue and risk tolerance on psychological reactance. Theoretical and practical implications are discussed.

APA, Harvard, Vancouver, ISO, and other styles

5

Gagnon, Philippe, Didier Saey, Isabelle Vivodtzev, Louis Laviolette, Vincent Mainguy, Julie Milot, Steeve Provencher, and François Maltais. "Impact of preinduced quadriceps fatigue on exercise response in chronic obstructive pulmonary disease and healthy subjects." Journal of Applied Physiology 107, no. 3 (September 2009): 832–40. http://dx.doi.org/10.1152/japplphysiol.91546.2008.

Full text

Abstract:

Exercise intolerance in chronic obstructive pulmonary disease (COPD) results from a complex interaction between central (ventilatory) and peripheral (limb muscles) components of exercise limitation. The purpose of this study was to evaluate the influence of quadriceps muscle fatigue on exercise tolerance and ventilatory response during constant-workrate cycling exercise testing (CWT) in patients with COPD and healthy subjects. Fifteen patients with COPD and nine age-matched healthy subjects performed, 7 days apart, two CWTs up to exhaustion at 80% of their predetermined maximal work capacity. In a randomized order, one test was performed with preinduced quadriceps fatigue and the other in a fresh state. Quadriceps fatigue was produced by electrostimulation-induced contractions and quantified by maximal voluntary contraction and potentiated twitch force (TwQpot). Endurance time and ventilatory response during CWT were compared between fatigued and fresh state. Endurance time significantly decreased in the fatigued state compared with the fresh condition in COPD (356 ± 69 s vs. 294 ± 45 s, P < 0.05) and controls (450 ± 74 s vs. 340 ± 45 s, P < 0.05). Controls showed significantly higher ventilation and end-exercise dyspnea scores in the fatigued condition, whereas, in COPD, fatigue did not influence ventilation or dyspnea during exercise. The degree of ventilatory limitation, as expressed by the V̇e/maximum voluntary ventilation ratio, was similar in both conditions in patients with COPD. We conclude that it is possible to induce quadriceps fatigue by local electrostimulation-induced contractions. Our findings demonstrate that peripheral muscle fatigue is an additional important factor, besides intense dyspnea, that limits exercise tolerance in COPD.

APA, Harvard, Vancouver, ISO, and other styles

6

Fitting, JW. "Respiratory muscle fatigue limiting physical exercise?" European Respiratory Journal 4, no. 1 (January 1, 1991): 103–8. http://dx.doi.org/10.1183/09031936.93.04010103.

Full text

Abstract:

Inspiratory muscle fatigue has been documented during loaded breathing or acute respiratory failure, but its role in exercise limitation is still undetermined. Electromyographic (EMG) signs of diaphragmatic fatigue develop in normal subjects hyperventilating above 70% of maximal voluntary ventilation (MVV), a ventilatory level commonly attained at peak exercise. EMG signs of diaphragmatic fatigue also occur during high power cycling exercise in normal subjects and chronic obstructive pulmonary disease (COPD) patients. However, a loss of respiratory muscle strength has rarely been documented following strenuous physical exercise with techniques independent of the subjects' collaboration. Prior inspiratory muscle fatigue decreases exercise tolerance in normal subjects but its effect is largely unknown in COPD patients. Respiratory muscle rest by negative pressure ventilation was reported to improve exercise tolerance in COPD, but this beneficial effect was not confirmed by controlled studies. The effect of inspiratory muscle training on exercise tolerance is still undefined by existing data, in part because of differences in methods and selection criteria between studies. Although respiratory muscle fatigue may occur during exercise, it is not clearly established whether interventions directed at respiratory muscles may improve exercise tolerance in COPD.

APA, Harvard, Vancouver, ISO, and other styles

7

Shah, Dhaval B., Kaushik M. Patel, and Ruchik D. Trivedi. "Analyzing Hertzian contact stress developed in a double row spherical roller bearing and its effect on fatigue life." Industrial Lubrication and Tribology 68, no. 3 (April 11, 2016): 361–68. http://dx.doi.org/10.1108/ilt-06-2015-0082.

Full text

Abstract:

Purpose The purpose of this paper is to describe a method permitting the creation of a realistic model of spherical roller bearing with the aim of determining contact stress and fatigue life based on dynamic loading conditions. The paper also aims to recognize the effect of tolerance values on contact stress and fatigue life. Motion and load transmission in spherical roller bearing occurs within the assembly by elliptical curved contacting surfaces. The stress produced by the transmitted load would be very high because of least contacting area between these surfaces. Design/methodology/approach The paper describes a methodology to determine contact stress using analytically as well as finite element method for spherical roller bearing. The comparison for the both each approach for contact stress at different loading condition is carried out. Prediction of fatigue life based on dynamic loading conditions for bearing is also determined using finite element model. The effect on induced contact stress and fatigue life by varying tolerances on inner race dimensions have been found out. Findings The paper suggests that the maximum stress produces at the start or end of the contacting arc under static loading condition in spherical roller bearing. The analytical and finite element approach is in good agreement. The fatigue life prediction is useful for selecting loading conditions for various applications of double row spherical roller bearing. Tolerance level at inner ring raceway radius is kept high because of manufacturing constrain of complex curvature geometric shape. Research limitations/implications The present approach does not consider dynamic loading conditions for contact stress analysis. Therefore, researchers are encouraged to analyze the effect of wear, lubrication and other tribological aspects on bearing life. Originality/value The paper includes determination of contact stress and prediction of fatigue life for spherical roller bearing using analytical as well as finite element approach. The tolerance values at inner race are identified as per manufacturing constraint based on contact stress and fatigue life.

APA, Harvard, Vancouver, ISO, and other styles

8

Serge L, Popel. "Condition Of Membranes Of Erythrocytes Of Peripheral Blood Of Elderly People With Chronic Tiredness And Low Level Of Tolerance To Physical Load." Emergency and Nursing Management 1, no. 2 (December 29, 2022): 01–05. http://dx.doi.org/10.58489/2836-2179/008.

Full text

Abstract:

The aim of the work is to study the osmotic stability and morpho-functional features of peripheral blood erythrocytes of patients with chronic fatigue syndrome depending on the level of tolerance to physical load (TPL) and associated risk factors. groups of factors that may be the cause, so the development of measures to eliminate them is an urgent problem today, which requires the development of effective ways to correct chronic fatigue syndrome. It is known that the peripheral part of erythron actively responds to changes that occur in the whole body after the action of various factors, including those factors that lead to chronic fatigue syndrome (CFS). Material and Methods of Research The examination was performed on the basis of the Department of Vascular Neurology of the Central Clinical Hospital of Ivano-Frankivsk. The study involved 30 patients aged 55-65 years (mean age 60.6 + 1.2 years), who were divided into 3 groups: 1 gr. included 10 patients with chronic fatigue syndrome and a high level of exercise tolerance. The 2nd group included 10 patients with chronic fatigue syndrome and the average level of exercise tolerance, the composition of 3 gr. included 10 patients with chronic fatigue syndrome associated cardiovascular pathology (angina pectoris, hypertension) and low exercise tolerance (3 gr.). Results It is established that chronic fatigue syndrome proceeds in 3 phases and has natural stages of development which are characterized by three groups of etiological factors and the corresponding levels of teletransitivity to physical activity, each of which corresponds to a certain erythrocyte profile and level of osmotic stability of erythrocytes which are offered to use as prognostic and diagnostic characteristics. chronic fatigue syndrome. Conclusions The study of the quantitative composition of peripheral blood erythrocytes and hemoglobin, as well as their ratio (color index) in patients with chronic fatigue syndrome on the background of low levels of exercise tolerance revealed a decrease in erythrocytes and hemoglobin by 42% and 25%, respectively, indicating the presence of anemic hypoxia. 2. In conditions of chronic fatigue there is a decrease in osmotic resistance of erythrocytes, as evidenced by a decrease in the number of osmotically stable erythrocytes with a gradual decrease in the concentration of NaCl solution (3.0%; 0.5%; 0.46%; 0.3%). 3. In chronic fatigue there is a deterioration of membranes in peripheral blood erythrocytes, as evidenced by a decrease in their osmotic stability and an increase in the number of irreversibly altered forms of РВЕ, as well as a decrease in peripheral blood erythrocytes, which is closely correlated with decreased tolerance to exercise.

APA, Harvard, Vancouver, ISO, and other styles

9

Fukuoka, Toshiyasu, Kaoru Tsukigase, and Keisuke Kumagai. "Fatigue and Damage Tolerance Substantiation Approach for a Regional Jet." Advanced Materials Research 891-892 (March 2014): 1688–93. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.1688.

Full text

Abstract:

The overview of the fatigue and damage tolerance substantiation approach for a 70-90 seat class regional aircraft named Mitsubishi Regional Jet, which is now under development by Mitsubishi Aircraft Corporation, is presented. To comply with the new regulatory requirement for prevention from widespread fatigue damage, full-scale airplane fatigue test will be performed with simulating actual airplane structural configuration and typical loading spectra expected in service. In addition to widespread fatigue damage, damage tolerance evaluations assuming manufacturing defect or in-service damage are being performed. Hundreds of structural tests from coupon level to sub-component level are to be used to verify the material properties and analysis methodology.

APA, Harvard, Vancouver, ISO, and other styles

10

Nesterenko, Boris G., and Grigory I. Nesterenko. "Fatigue and Damage Tolerance of Aging Airplane Structures." Advanced Materials Research 891-892 (March 2014): 1669–74. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.1669.

Full text

Abstract:

The paper highlights key questions in ensuring safe operation of aging civil\transport aircraft in Russia. Presented is the analysis of current requirements to fatigue, fail-safe and damage tolerance for transport aircraft structures stated in FARs, Advisory Circulars (UAS) and Russian Airworthiness Regulations\ AR IAC Aviation Regulations. The paper gives the design goals and actual service life values\ service years of aging aircraft fleet and data on full-scaled fatigue tests, together with methods and approaches to ensure safe operation of aircraft structures in case of multiple site damages, corrosion and materials degradation for Russian aging fleet.

APA, Harvard, Vancouver, ISO, and other styles

11

Larrosa, N. O., R. Akid, and R. A. Ainsworth. "Corrosion-fatigue: a review of damage tolerance models." International Materials Reviews 63, no. 5 (September 25, 2017): 283–308. http://dx.doi.org/10.1080/09506608.2017.1375644.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Taylor, Bryan J., and Lee M. Romer. "Effect of expiratory muscle fatigue on exercise tolerance and locomotor muscle fatigue in healthy humans." Journal of Applied Physiology 104, no. 5 (May 2008): 1442–51. http://dx.doi.org/10.1152/japplphysiol.00428.2007.

Full text

Abstract:

High-intensity exercise (≥90% of maximal O2 uptake) sustained to the limit of tolerance elicits expiratory muscle fatigue (EMF). We asked whether prior EMF affects subsequent exercise tolerance. Eight male subjects (means ± SD; maximal O2 uptake = 53.5 ± 5.2 ml·kg−1·min−1) cycled at 90% of peak power output to the limit of tolerance with (EMF-EX) and without (CON-EX) prior induction of EMF and for a time equal to that achieved in EMF-EX but without prior induction of EMF (ISO-EX). To induce EMF, subjects breathed against an expiratory flow resistor until task failure (15 breaths/min, 0.7 expiratory duty cycle, 40% of maximal expiratory gastric pressure). Fatigue of abdominal and quadriceps muscles was assessed by measuring the reduction relative to prior baseline values in magnetically evoked gastric twitch pressure (Pgatw) and quadriceps twitch force (Qtw), respectively. The reduction in Pgatw was not different after resistive breathing vs. after CON-EX (−27 ± 5 vs. −26 ± 6%; P = 0.127). Exercise time was reduced by 33 ± 10% in EMF-EX vs. CON-EX (6.85 ± 2.88 vs. 9.90 ± 2.94 min; P < 0.001). Exercise-induced abdominal and quadriceps muscle fatigue was greater after EMF-EX than after ISO-EX (−28 ± 9 vs. −12 ± 5% for Pgatw, P = 0.001; −28 ± 7 vs. −14 ± 6% for Qtw, P = 0.015). Perceptual ratings of dyspnea and leg discomfort (Borg CR10) were higher at 1 and 3 min and at end exercise during EMF-EX vs. during ISO-EX ( P < 0.05). Percent changes in limb fatigue and leg discomfort (EMF-EX vs. ISO-EX) correlated significantly with the change in exercise time. We propose that EMF impaired subsequent exercise tolerance primarily through an increased severity of limb locomotor muscle fatigue and a heightened perception of leg discomfort.

APA, Harvard, Vancouver, ISO, and other styles

13

Shekhter, Alex, Simon A. Barter, Marcus McDonald, and R. Wanhill. "Assessment of Durability and Damage Tolerance of β-Annealed Ti-6Al-4V." Materials Science Forum 654-656 (June 2010): 887–89. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.887.

Full text

Abstract:

-annealed Ti-6Al-4V ELI alloy has a special chemical composition and manufacturing process, intended to optimise its fatigue and fracture properties. This alloy is used in primary fatigue-critical structures of advanced military aircraft, but little has been generally published about its properties, particularly the fatigue and crack growth behaviour under service loading. A test programme has been set up to assess the fatigue durability and damage tolerance properties of the alloy, in the context of the two most relevant analysis methods. The first is strain – life analysis, used to estimate safe lives (durability). The second is fatigue crack growth analysis, used to assess the damage tolerance behaviour. This paper presents preliminary results of the test programme.

APA, Harvard, Vancouver, ISO, and other styles

14

Al-shair, Khaled, Umme Kolsum, Dave Singh, and Jørgen Vestbo. "The Effect of Fatigue and Fatigue Intensity on Exercise Tolerance in Moderate COPD." Lung 194, no. 6 (August 22, 2016): 889–95. http://dx.doi.org/10.1007/s00408-016-9931-y.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Popel, Sergii, Ivan Меlnic, Іhor Churpiy, Przemek Bejga, and Zbigniew Śliwiński. "Condition of membranes of erythrocytes of peripheral blood of elderly people with chronic tiredness and low level of tolerance to physical load." Health, sport, rehabilitation 8, no. 2 (June 21, 2022): 78–89. http://dx.doi.org/10.34142/hsr.2022.08.02.07.

Full text

Abstract:

Purpose: The aim of the work is to study the osmotic stability and morpho-functional features of peripheral blood erythrocytes of patients with chronic fatigue syndrome depending on the level of exercise tolerance and associated risk factors. groups of factors that may be the cause, so the development of measures to eliminate them is an urgent problem today, which requires the development of effective ways to correct chronic fatigue syndrome. It is known that the peripheral part of erythron actively responds to changes that occur in the whole body after the action of various factors, including those factors that lead to chronic fatigue syndrome. Material and methods of research. The examination was performed on the basis of the Department of Vascular Neurology of the Central Clinical Hospital of Ivano-Frankivsk. The study involved 30 patients aged 55-65 years (mean age 60.6 + 1.2 years), who were divided into 3 groups: 1 gr. included 10 patients with chronic fatigue syndrome and a high level of exercise tolerance. The 2nd group included 10 patients with chronic fatigue syndrome and the average level of exercise tolerance, the composition of 3 gr. included 10 patients with chronic fatigue syndrome associated cardiovascular pathology (angina pectoris, hypertension) and low exercise tolerance (3 gr.). Results. It is established that chronic fatigue syndrome proceeds in 3 phases and has natural stages of development which are characterized by three groups of etiological factors and the corresponding levels of teletransitivity to physical activity, each of which corresponds to a certain erythrocyte profile and level of osmotic stability of erythrocytes which are offered to use as prognostic and diagnostic characteristics. chronic fatigue syndrome. Conclusions. The study of the quantitative composition of peripheral blood erythrocytes and hemoglobin, as well as their ratio (color index) in patients with chronic fatigue syndrome on the background of low levels of exercise tolerance revealed a decrease in erythrocytes and hemoglobin by 42% and 25%, respectively, indicating the presence of anemic hypoxia. 2. In conditions of chronic fatigue there is a decrease in osmotic resistance of erythrocytes, as evidenced by a decrease in the number of osmotically stable erythrocytes with a gradual decrease in the concentration of NaCl solution (3.0%; 0.5%; 0.46%; 0.3%). 3. In chronic fatigue there is a deterioration of membranes in peripheral blood erythrocytes, as evidenced by a decrease in their osmotic stability and an increase in the number of irreversibly altered forms of РВЕ, as well as a decrease in peripheral blood erythrocytes, which is closely correlated with decreased tolerance to exercise.

APA, Harvard, Vancouver, ISO, and other styles

16

Nahm, Seung Hoon, Chang Min Suh, Min Woo Jung, Jong Yup Kim, and Chang Hwan Yang. "Application of Damage Tolerance Approach for Turbine Disk Life Extension." International Journal of Modern Physics B 17, no. 08n09 (April 10, 2003): 1916–21. http://dx.doi.org/10.1142/s0217979203019873.

Full text

Abstract:

For gas turbine engines, the safe life methodology has historically been used for fatigue life management of failure critical engine components. The safe retirement limit is necessarily determined by a conservative life evaluation procedure, thereby many components which have a long residual life are discarded. The objective of this study is to introduce the damage tolerant design concept into the life management for aircraft engine component instead of conservative fatigue life methodology which has been used for both design and maintenance. The residual lives of turbine disk component under various temperatures and conditions using creep-fatigue crack initiation and growth data were estimated. As the result of analysis, it was confirmed that retirement for cause concept was applicable to the evaluation of residual life of retired turbine disk which had been designed based on the conventional fatigue life methodology.

APA, Harvard, Vancouver, ISO, and other styles

17

Huangfu, Yong Zhuo, Xu Dong Ren, Liang Ruan, Yong Kang Zhang, and Da Wei Jiang. "Effects of Laser Shock Processing on Fatigue Lives of Heat-Resistant Steel and Estimation of Fatigue Safe Lives." Advanced Materials Research 328-330 (September 2011): 376–79. http://dx.doi.org/10.4028/www.scientific.net/amr.328-330.376.

Full text

Abstract:

Fatigue tensile treatment was performed on 00Cr12 heat-resistant steel specimens which had been treated by laser shock processing (LSP). The unilateral tolerance factor statistical analysis method and the two-dimensional Weibull distribution method were used to predict the values of fatigue safe lives of the specimens respectively. The results indicate that the fatigue lives of 00Cr12 specimens were enhanced greatly after LSP, and improved by 62% compared with the specimens which were not treated by LSP. The unilateral tolerance factor method obtained an exact estimation value of the fatigue safe life; while the two-dimensional Weibull distribution method can get a range of values of fatigue safe lives, the fatigue safe lives of the specimens which after LSP were a range from 116570 to 150230, the average value was 132330. The two-dimensional Weibull distribution method has more engineering applicability and can be used to estimate the fatigue safe lives with fewer experiments.

APA, Harvard, Vancouver, ISO, and other styles

18

Sajith, S., K. S. R. K. Murthy, and P. S. Robi. "Fatigue life prediction under mixed-mode loading using equivalent stress intensity factor models." MATEC Web of Conferences 172 (2018): 03005. http://dx.doi.org/10.1051/matecconf/201817203005.

Full text

Abstract:

Damage tolerance principles are widely used to assess the structural integrity and failure of engineering components. The advances in numerical simulation techniques facilitate the prediction of fatigue life of engineering component, which is essential in damage tolerance design. For the components under mixed mode (I/II) loading, the fatigue crack growth and life is predicted by using a modified form of Paris' law along with the equivalent stress intensity factor (ΔKeq). Numerous ΔKeq models are available for correlating the equivalent stress intensity factor range and the fatigue crack growth rate. The knowledge of proper ΔKeq model is essential for the accurate fatigue life estimation. In this work, the authors numerically assess the performance of ΔKeq models in mixed mode fatigue life prediction with the help of published experimental mixed mode data.

APA, Harvard, Vancouver, ISO, and other styles

19

Abdi, F., Y. Xue, M. Garg, B. Farahmand, J. Housner, and K. Nikbin. "An analysis approach toward FAA certification for damage tolerance of aircraft components." Aeronautical Journal 118, no. 1200 (February 2014): 181–96. http://dx.doi.org/10.1017/s0001924000009064.

Full text

Abstract:

Abstract This paper presents a novel analysis approach by considering multiple crack interaction in achieving FAA certification for durability and damage tolerance of exterior attachment installations on an aircraft fuselage according to FAA policy on Certification by Analysis-Supported-by-Test (CAST). Durability and damage tolerance evaluation of an aircraft component requires assessment of damage initiation and fatigue crack propagations under service loading, which consists of complex loading types, paths and variable amplitudes. Both simulation and service experience showed that multiple cracks developed in the fuselage skin and doublers that are made of wrought aluminum alloys. Progressive failure analysis (PFA) tool was used to simulate the fatigue damage initiation life using a scale-down stress-life property. A virtual crack closure technique (VCCT) was implemented to evaluate fatigue crack growth with interactions between cracks from different parts in a component, which preserves conservativeness. The fatigue crack growth data is obtained uniquely from an analytical extension of fatigue crack growth data of thin aluminum sheet. Fatigue crack growth analysis showed that only a few initiated cracks propagated steadily before a crack became visible under inspection, which was validated by comparison to service history. Eventually one crack became dominate in the fracturing process thereby setting an inspection time. Analysis also showed that fatigue damage state in the components at the designed operational life will not exceed the static safety requirements. Therefore, FAA accepted the damage tolerance analysis and the aircraft retained certification with no need for repair.

APA, Harvard, Vancouver, ISO, and other styles

20

Lee, Fang-Tsai, Tz-Yin Kuo, Shaw-Yih Liou, and Chiang-Ting Chien. "Chronic Rhodiola rosea Extract Supplementation Enforces Exhaustive Swimming Tolerance." American Journal of Chinese Medicine 37, no. 03 (January 2009): 557–72. http://dx.doi.org/10.1142/s0192415x09007053.

Full text

Abstract:

We explored the effects and mechanisms of Rhodiola rosea extract supplementation on swimming-induced fatigue in rats. The concentrations of active components in Rhodiola rosea have been determined by high performance liquid chromatography-mass spectrometer. The Rhodiola rosea extract supplementation in water for 2–4 weeks was evaluated in male Wistar rats with 90-min unloaded swimming exercise and 5% body weight loaded swimming up to fatigue. We measured the fatigue biomarkers, including blood urea nitrogen (BUN), glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT), lactate dehydrogenase (LDH), hepatic glycogen content, the activity of fat metabolism enzymes, sterol regulatory element-binding protein-1 (SREBP-1) and fatty acid synthase (FAS), the tissue oxygen content and ratio of red and white skeletal muscle fibers in rats. Rhodiola rosea significantly increased liver glycogen, SREBP-1, FAS, heat shock protein 70 expression, Bcl-2/Bax ratio and oxygen content before swimming. Rhodiola rosea supplementation significantly increased the swimming time in a dose-dependent manner and reduced swimming-enhanced serum BUN, GOT and GPT levels. The ratio of red and white muscle fibers was not altered after chronic Rhodiola rosea extract supplementation. Chronic Rhodiola rosea supplementation significantly improved exhaustive swimming-induced fatigue by the increased glycogen content, energy supply of lipogenic enzyme expressions and protective defense mechanisms.

APA, Harvard, Vancouver, ISO, and other styles

21

De Iorio, Antonio, Marzio Grasso, F. Penta, and G. P. Pucillo. "Fatigue Crack Growth Simulation in Railway Axles." Key Engineering Materials 488-489 (September 2011): 407–10. http://dx.doi.org/10.4028/www.scientific.net/kem.488-489.407.

Full text

Abstract:

In order to carry out the railway axle design according to the “Damage Tolerance” philosophy, reliable crack-growth models for these kind of components are necessary. Indeed, damage tolerance principles have received more and more attention from railway technical community, thanks to its ambitious task concerning the inspection intervals prevision of railway components subjected to non-stationary loading conditions. In this paper, a simple routine is exposed that is able to calculate the characteristic parameters of the Linear Elastic Fracture Mechanics (LEFM) for a generic cracked mechanical component. Such parameters are then used in a two parameters propagation law to estimate the necessary time for a crack to become critical.

APA, Harvard, Vancouver, ISO, and other styles

22

Bailey, Stephen J., Lee M. Romer, James Kelly, Daryl P. Wilkerson, Fred J. DiMenna, and Andrew M. Jones. "Inspiratory muscle training enhances pulmonary O2 uptake kinetics and high-intensity exercise tolerance in humans." Journal of Applied Physiology 109, no. 2 (August 2010): 457–68. http://dx.doi.org/10.1152/japplphysiol.00077.2010.

Full text

Abstract:

Fatigue of the respiratory muscles during intense exercise might compromise leg blood flow, thereby constraining oxygen uptake (V̇o2) and limiting exercise tolerance. We tested the hypothesis that inspiratory muscle training (IMT) would reduce inspiratory muscle fatigue, speed V̇o2 kinetics and enhance exercise tolerance. Sixteen recreationally active subjects (mean ± SD, age 22 ± 4 yr) were randomly assigned to receive 4 wk of either pressure threshold IMT [30 breaths twice daily at ∼50% of maximum inspiratory pressure (MIP)] or sham treatment (60 breaths once daily at ∼15% of MIP). The subjects completed moderate-, severe- and maximal-intensity “step” exercise transitions on a cycle ergometer before (Pre) and after (Post) the 4-wk intervention period for determination of V̇o2 kinetics and exercise tolerance. There were no significant changes in the physiological variables of interest after Sham. After IMT, baseline MIP was significantly increased (Pre vs. Post: 155 ± 22 vs. 181 ± 21 cmH2O; P < 0.001), and the degree of inspiratory muscle fatigue was reduced after severe- and maximal-intensity exercise. During severe exercise, the V̇o2 slow component was reduced (Pre vs. Post: 0.60 ± 0.20 vs. 0.53 ± 0.24 l/min; P < 0.05) and exercise tolerance was enhanced (Pre vs. Post: 765 ± 249 vs. 1,061 ± 304 s; P < 0.01). Similarly, during maximal exercise, the V̇o2 slow component was reduced (Pre vs. Post: 0.28 ± 0.14 vs. 0.18 ± 0.07 l/min; P < 0.05) and exercise tolerance was enhanced (Pre vs. Post: 177 ± 24 vs. 208 ± 37 s; P < 0.01). Four weeks of IMT, which reduced inspiratory muscle fatigue, resulted in a reduced V̇o2 slow-component amplitude and an improved exercise tolerance during severe- and maximal-intensity exercise. The results indicate that the enhanced exercise tolerance observed after IMT might be related, at least in part, to improved V̇o2 dynamics, presumably as a consequence of increased blood flow to the exercising limbs.

APA, Harvard, Vancouver, ISO, and other styles

23

Ramsey, Carol S., Paul M. Werchan, Wayne M. Isdahl, Joseph Fischer, and John A. Gibbons. "Acceleration Tolerance at Night with Acute Fatigue and Stimulants." Aviation, Space, and Environmental Medicine 79, no. 8 (August 1, 2008): 769–73. http://dx.doi.org/10.3357/asem.1977.2008.

Full text

APA, Harvard, Vancouver, ISO, and other styles

24

Aglan, Heshmat A., and Mahmood Fateh. "Fatigue Damage Tolerance of Bainitic and Pearlitic Rail Steels." International Journal of Damage Mechanics 15, no. 4 (October 2006): 393–410. http://dx.doi.org/10.1177/1056789506060775.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

Wu, Chao, Andrew J. Gunnion, Bernard Chen, and Wenyi Yan. "Fatigue damage tolerance of two tapered composite patch configurations." Composite Structures 134 (December 2015): 654–62. http://dx.doi.org/10.1016/j.compstruct.2015.08.114.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Saweeres, Emad S. B., Jan H. Kuiper, Richard O. Evans, James B. Richardson, and Stephen H. White. "Predicting in vivo Clinical Performance of Anterior Cruciate Ligament Fixation Methods from in Vitro Analysis." American Journal of Sports Medicine 33, no. 5 (May 2005): 666–73. http://dx.doi.org/10.1177/0363546504271203.

Full text

Abstract:

Background Anterior cruciate ligament graft fixations experience cyclic loads in vivo. Present cyclic loading studies testing fixation use “incremental cycling,”“residual strength” protocols, or a combination. Industrial standards, however, rely on fatigue life testing and use tolerance limits to determine guaranteed minimum levels of cycles to failure. Hypothesis Industrial standards of fatigue life and lower tolerance limits provide a more conservative assessment of cycles to failure than do currently used cyclic loading models, and they facilitate interpretation of data toward clinical performance. Study Design Descriptive laboratory study. Methods Fatigue life curves and lower tolerance limits were calculated for porcine patellar tendon graft fixations that were tested to failure in single pulls or cycled to failure at 2 different load levels. A log curve was constructed so that the expected values at other load levels could be calculated. Comparison of a metal and a composite resorbable interference screw design was used as an example. Results Cycles to failure of both screw designs varied widely at each load level. The guaranteed minimum number of cycles calculated by tolerance limits was therefore much lower than the mean cycles to failure at any given load level. For example, at a load of 250 N, the predicted mean life for the composite screw and the metal screw was 2513 and 1490 cycles, respectively, whereas the 80/80 tolerance limits (the value that 80% could be expected to achieve with 80% confidence) were only 63 and 68 cycles, respectively. Small reductions in load level gave very large increases in minimally expected life. Conclusions Fatigue testing of anterior cruciate ligament reconstructions better shows the wide variation between specimens and the large effect of load levels on expected life. Wide scatter makes mean levels overoptimistic and difficult to interpret. Tolerance limits give estimates that are more conservative and facilitate data interpretation. Clinical Relevance A method for testing and analyzing fatigue properties was presented, results of which are more readily interpreted to clinical practice.

APA, Harvard, Vancouver, ISO, and other styles

27

Jiang, Minjin, Rui Liu, Hongliang Sun, Xiaosong Jiang, and Song Chen. "Fatigue properties and crack growth behavior of 7N01 and 6N01 aluminum alloys." Materials Testing 64, no. 3 (March 1, 2022): 339–49. http://dx.doi.org/10.1515/mt-2021-2042.

Full text

Abstract:

Abstract In this study, the fatigue properties, microstructure, and surface damage tolerance of the 6N01 profile, 7N01 profile, and 7N01 plate aluminum alloy were studied. The fatigue test results show that the fatigue limit of the 7N01 profile was the highest and the 7N01 plate was the lowest. More importantly, most fatigue specimens failed in the safe life area provided by the Kitagawa–Takahashi line diagram, which indicates that there is a “short-notch effect” in the fatigue behavior of the pre-cracked aluminum alloys. For the sake of safety, according to the Kitagawa–Takahashi line diagram corrected by the fatigue test results, the effective harmless notch sizes a 0,eff of 6N01 profile, 7N01 profile, 7N01 plate is 23.92, 10.81, 24.32 μm, respectively, and their effective fatigue notch propagation threshold Δk eff,th is 0.81, 0.39, 0.77 MPa m1/2, respectively. These corrected values reestablished the fatigue tolerance of the three materials and provided the critical data reference for the practical application. Combined with this study and the analysis of the literature, it can be concluded that the short-notch effect of the three materials should be related to the microstructure, crack closure mechanism, internal defects.

APA, Harvard, Vancouver, ISO, and other styles

28

Marcora, Samuele M., Walter Staiano, and Victoria Manning. "Mental fatigue impairs physical performance in humans." Journal of Applied Physiology 106, no. 3 (March 2009): 857–64. http://dx.doi.org/10.1152/japplphysiol.91324.2008.

Full text

Abstract:

Mental fatigue is a psychobiological state caused by prolonged periods of demanding cognitive activity. Although the impact of mental fatigue on cognitive and skilled performance is well known, its effect on physical performance has not been thoroughly investigated. In this randomized crossover study, 16 subjects cycled to exhaustion at 80% of their peak power output after 90 min of a demanding cognitive task (mental fatigue) or 90 min of watching emotionally neutral documentaries (control). After experimental treatment, a mood questionnaire revealed a state of mental fatigue ( P = 0.005) that significantly reduced time to exhaustion (640 ± 316 s) compared with the control condition (754 ± 339 s) ( P = 0.003). This negative effect was not mediated by cardiorespiratory and musculoenergetic factors as physiological responses to intense exercise remained largely unaffected. Self-reported success and intrinsic motivation related to the physical task were also unaffected by prior cognitive activity. However, mentally fatigued subjects rated perception of effort during exercise to be significantly higher compared with the control condition ( P = 0.007). As ratings of perceived exertion increased similarly over time in both conditions ( P < 0.001), mentally fatigued subjects reached their maximal level of perceived exertion and disengaged from the physical task earlier than in the control condition. In conclusion, our study provides experimental evidence that mental fatigue limits exercise tolerance in humans through higher perception of effort rather than cardiorespiratory and musculoenergetic mechanisms. Future research in this area should investigate the common neurocognitive resources shared by physical and mental activity.

APA, Harvard, Vancouver, ISO, and other styles

29

Huang, Xiaosong, and Selina Zhao. "Damage tolerance characterization of carbon fiber composites at a component level: A thermoset carbon fiber composite." Journal of Composite Materials 52, no. 1 (March 29, 2017): 37–46. http://dx.doi.org/10.1177/0021998317702435.

Full text

Abstract:

This work focuses on the impact damage evaluation of a carbon fiber-reinforced thermoset composite at a component level (beams) as an effort to develop the service strategies for this class of materials. The beams were impact damaged at a variety of energy levels, and the pulse thermography nondestructive evaluation approach was used to characterize the damaged areas. The damaged beams were subjected to compression tests to evaluate their residual properties. As expected, both the beam maximum load and residual stiffness decreased with the increase in damage size. The damage growth rates under different load levels were investigated in fully reversed torsional fatigue tests. The fatigued beams were also characterized for their residual compression properties, which were then compared with those of the unfatigued beams. The results will be used to develop computer-aided engineering models to predict the residual strength and fatigue life of damaged composite components.

APA, Harvard, Vancouver, ISO, and other styles

30

Wang, Zhijian, Xue Lv, and Jiawei Song. "Tolerance Analysis of Cylindrical Roller Bearing under Combined Radial and Axial Loads." Mathematical Problems in Engineering 2022 (December 7, 2022): 1–7. http://dx.doi.org/10.1155/2022/9233627.

Full text

Abstract:

In order to analyze the influence of tolerance values of key parameters for cylindrical roller bearings under combined axial and radial loads, a coupled model, incorporating a dynamic model of cylindrical roller bearings, contact model, and fatigue life model, is developed to investigate the effect of flange angle, roller-end radius, interval of roller length gauge, and roller profile on contact performance and fatigue life. The results show that the grouping design of flange angle and roller-end radius in the tolerance range was helpful for reducing contact ellipse truncation. The difference of the roller length would change the axial load distribution of the bearings. For the longest roller located in the bottom position, the bigger the difference, the bigger the roller tilt angle and carried-axial load. The (0, +2.5 μm) tolerance range of the crown drop can limit the difference of the fatigue life within 20% in the current analysis.

APA, Harvard, Vancouver, ISO, and other styles

31

Mu, Zhi Tao, Wen Lin Liu, and Ping Jin. "The Crack Growth Life Predictions for High Cycle Dynamic Components." Key Engineering Materials 324-325 (November 2006): 963–66. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.963.

Full text

Abstract:

Using of a safe life approach is necessitated by the small critical crack sizes and rapid crack growth rates resulting from the severe vibratory environment of rotorcraft. However Based on the success of damage tolerance initiative for airframe structure, a crack growth based on damage tolerance approach is being examined for implementation into the design and management of dynamic components. In this paper the crack growth behavior in low cycle fatigue (LCF) and high cycle fatigue (HCF) are compared and the accuracy of several damage tolerance analysis methods in determining the crack growth life from an initial detectable crack size 1.25 mm to 12 mm for a rotorcraft main rotor yoke are investigated. The real rotorcraft materials measured by experiment and the fatigue load mean frequency spectrum based on statistical usage spectrum are adopted. The crack growth equations used in the programs are discussed to provide a basis for understanding the results. The results show that the load less than the safe fatigue limit has an important effect on crack growth life and it is reasonable for the material that the cut-off stress ratio for the threshold stress intensity factor range is set 0.7.

APA, Harvard, Vancouver, ISO, and other styles

32

Ronold, Knut O., and Andreas T. Echtermeyer. "Using Tolerance Bounds for Estimation of Characteristic Fatigue Curves for Composites with Confidence." Safety 8, no. 1 (December 23, 2021): 1. http://dx.doi.org/10.3390/safety8010001.

Full text

Abstract:

Fatigue S–N curves provide the number of stress cycles that result in fatigue failure at stress range S and need to be measured for new engineering materials where data are not as readily available as they are for well-characterized and widely used metals. A simple statistical method for the estimation of characteristic fatigue curves defined in terms of lower-tail quantiles in probability distributions of dependent variables is presented. The method allows for the estimation of such quantiles with a specified confidence level, taking account of the statistical uncertainty caused by a limited number of experimental test results available for the estimation. The traditional general approach for estimating characteristic S–N curves by tolerance bounds is complicated and is not much used by engineers. The presented approach allows for calculating the curves with a simple spreadsheet. The only requirement is that the experimental log S data for the S–N curve are fairly uniformly distributed over a finite logS interval, where S denotes the stress range. Experimental fatigue test programs are often designed such that test data fulfil this assumption. Although developed with fatigue of composite laminates in mind, the presented statistical procedure and the presented associated charts are valid for fatigue curve estimation for any material.

APA, Harvard, Vancouver, ISO, and other styles

33

Townsend, Liam, Adam H. Dyer, Patrick McCluskey, Kate O’Brien, Joanne Dowds, Eamon Laird, Ciaran Bannan, et al. "Investigating the Relationship between Vitamin D and Persistent Symptoms Following SARS-CoV-2 Infection." Nutrients 13, no. 7 (July 15, 2021): 2430. http://dx.doi.org/10.3390/nu13072430.

Full text

Abstract:

The emergence of persistent symptoms following SARS-CoV-2 infection, known as long COVID, is providing a new challenge to healthcare systems. The cardinal features are fatigue and reduced exercise tolerance. Vitamin D is known to have pleotropic effects far beyond bone health and is associated with immune modulation and autoimmunity. We hypothesize that vitamin D levels are associated with persistent symptoms following COVID-19. Herein, we investigate the relationship between vitamin D and fatigue and reduced exercise tolerance, assessed by the Chalder Fatigue Score, six-minute walk test and modified Borg scale. Multivariable linear and logistic regression models were used to evaluate the relationships. A total of 149 patients were recruited at a median of 79 days after COVID-19 illness. The median vitamin D level was 62 nmol/L, with n = 36 (24%) having levels 30–49 nmol/L and n = 14 (9%) with levels <30 nmol/L. Fatigue was common, with n = 86 (58%) meeting the case definition. The median Borg score was 3, while the median distance covered for the walk test was 450 m. No relationship between vitamin D and the measures of ongoing ill-health assessed in the study was found following multivariable regression analysis. These results suggest that persistent fatigue and reduced exercise tolerance following COVID-19 are independent of vitamin D.

APA, Harvard, Vancouver, ISO, and other styles

34

Zalewska, Małgorzata. "Influence of the Fatigue Load Level and the Hole Diameter on the Laminate Structure’s Fatigue Performance." Fatigue of Aircraft Structures 2018, no. 10 (December 1, 2018): 21–30. http://dx.doi.org/10.2478/fas-2018-0002.

Full text

Abstract:

Abstract Damage tolerance of composite aircraft structure is one of the main areas of research, important when a new product is being developed. There are a number of variables, such as damage characteristics (dent depth, delamination area) and loading parameters (load type, amplitude of cyclic loading, load sequence) that need to be investigated experimentally [1]. These tests of composite materials are usually performed at an element level and are carried out in order to validate the analytical model, developed to predict the full-scale component’s behaviour. The paper presents the results of compression testing of the [36/55/9] carbon fibre/epoxy laminate, manufactured with the Automated Fibre Placement technology (AFP) and subjected to static and fatigue loads. The laminate compression loading mode was achieved through sandwich 4-point flexure. At the stage of fatigue testing, two parameters were investigated: the damage size, simulated by the hole diameter and the fatigue load level. Based on the test results, the laminate fatigue load limit equal to 75% of the OHC failure load was evaluated. By collating the static and fatigue tests results, the damage tolerance characteristic of the considered laminate was created.

APA, Harvard, Vancouver, ISO, and other styles

35

KAMAYA, Masayuki. "B115 Damage Tolerance Design for Thermal Fatigue Loading : Crack Growth Behavior under Thermal Fatigue Loading." Proceedings of the National Symposium on Power and Energy Systems 2009.14 (2009): 87–90. http://dx.doi.org/10.1299/jsmepes.2009.14.87.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

Tamaki, Tetsuro, Shuichi Uchiyama, Yoshiyasu Uchiyama, Akira Akatsuka, Roland R. Roy, and V. Reggie Edgerton. "Anabolic steroids increase exercise tolerance." American Journal of Physiology-Endocrinology and Metabolism 280, no. 6 (June 1, 2001): E973—E981. http://dx.doi.org/10.1152/ajpendo.2001.280.6.e973.

Full text

Abstract:

The influence of an anabolic androgenic steroid (AAS) on thymidine and amino acid uptake in rat hindlimb skeletal muscles during 14 days after a single exhaustive bout of weight lifting was determined. Adult male rats were divided randomly into Control or Steroid groups. Nandrolone decanoate was administered to the Steroid group 1 wk before the exercise bout. [3H]thymidine and [14C]leucine labeling were used to determine the serial changes in cellular mitotic activity, amino acid uptake, and myosin synthesis. Serum creatine kinase (CK) activity, used as a measure of muscle damage, increased 30 and 60 min after exercise in both groups. The total amount of weight lifted was higher, whereas CK levels were lower in Steroid than in Control rats. [3H]thymidine uptake peaked 2 days after exercise in both groups and was 90% higher in Control than in Steroid rats, reflecting a higher level of muscle damage. [14C]leucine uptake was ∼80% higher at rest and recovered 33% faster postexercise in Steroid than in Control rats. In a separate group of rats, the in situ isometric mechanical properties of the plantaris muscle were determined. The only significant difference was a higher fatigue resistance in the Steroid compared with the Control group. Combined, these results indicate that AAS treatment 1) ameliorates CK efflux and the uptake of [3H]thymidine and enhances the rate of protein synthesis during recovery after a bout of weight lifting, all being consistent with there being less muscle damage, and 2) enhances in vivo work capacity and the in situ fatigue resistance of a primary plantarflexor muscle.

APA, Harvard, Vancouver, ISO, and other styles

37

Hasani Monfared, Banan, and Alireza Sedaghat. "Experimental investigation of impact damage on repetitive loading tolerance in metal-fiber multilayers." International Journal of Engineering & Technology 8, no. 4 (November 10, 2019): 527. http://dx.doi.org/10.14419/ijet.v8i4.28763.

Full text

Abstract:

Fiber is not sensitive to fatigue in some fiber-metal multilayers. They leave a large part of the load through the cracks and prevent the crack from opening. Due to this prevention, the opening in GLARE is less than that of the metals. Unlike what is observed in metals, concentration factor of crack tip is not fully influenced by increase in crack length. Hence, this study uses the experimental method to examine post-impact fatigue behavior of glass fiber-reinforced metal composites, known as GLARE. The GLARE made in this study was produced by autoclave in three types of GLARE 1.2-3, GLARE 1.2-4 and GLARE 3.2-5 and was exposed to impact test by different forces and then fatigue test with different cycles. The results were studied. The results showed that the first GLARE 1.2-3 specimen was completely pierced after the impact test. The second GLARE 1.2-3 specimen produced fatigue cracks from impact dent in the only aluminum impacted layer. These cracks were then amplified to the edge of the specimen. Both GLARE 1.2-4 specimens showed approximately equal fatigue life. The first GLARE 1.2-4 specimen failed near the radius due to the disturbing cracks in a way that is common in FML specimen. Moreover, both GLARE 1.2-4 specimens exhibited cracking in both aluminum layers. In 1.2-5 GLARE, both specimens showed a decrease in fatigue life and increase in impact energy.

APA, Harvard, Vancouver, ISO, and other styles

38

Shen, C. L., P. H. Wirsching, and G. T. Cashman. "Design Curve to Characterize Fatigue Strength." Journal of Engineering Materials and Technology 118, no. 4 (October 1, 1996): 535–41. http://dx.doi.org/10.1115/1.2805953.

Full text

Abstract:

Fatigue (S-N) data exhibit relatively large scatter. For design purposes, an S-N curve that characterizes fatigue strength is required. This curve should lie on the lower, or safe, side of the data. A method based on a modification of the Owen tolerance interval is proposed. The method is general and can be applied to nonlinear heteroscedastic data having runouts.

APA, Harvard, Vancouver, ISO, and other styles

39

Ma, Yu E., Bao Qi Liu, and Zhen Qiang Zhao. "The Effects of Bonded Retarder on Fatigue Crack Growth in 7085 Aluminium Alloy." Advanced Materials Research 217-218 (March 2011): 1135–40. http://dx.doi.org/10.4028/www.scientific.net/amr.217-218.1135.

Full text

Abstract:

To improve damage tolerance performance, GLARE was used as bonded crack retarders in this paper. Fatigue tests were run with unbonded and bonded samples; then test results between them was compared. Thermal residual stresses had been studied. It was found that bonded crack retarders can improve damage tolerance performance and capability. Thermal residual stresses have a detrimental effect on the fatigue crack growth rates by means of increasing the effective R-ratio applied on the aluminium substrate. Finite element analysis was carried out and the result was in good agreement with the experimental data.

APA, Harvard, Vancouver, ISO, and other styles

40

Lee, WJ, BH Seo, SC Hong, MS Won, and JR Lee. "Real world application of angular scan pulse-echo ultrasonic propagation imager for damage tolerance evaluation of full-scale composite fuselage." Structural Health Monitoring 18, no. 5-6 (February 24, 2019): 1943–52. http://dx.doi.org/10.1177/1475921719831370.

Full text

Abstract:

Composite structures are assertively used for new airframe designs and manufacturing in military aircrafts because of superior strength-to-weight ratios and fatigue resistance. Because the composites have different fatigue failure characteristics compared with metals, it is necessary to develop different approaches for the composite fatigue design and testing. In this study, we propose an in situ damage evaluation technology with high spatial resolution during full-scale fatigue testing of composite aircraft structures. For real composite structure development considering composite fatigue characteristics, full-scale fatigue and damage tolerance tests of the composite fuselage structure were conducted to evaluate the structural characteristics. In the meantime, the laser ultrasonic nondestructive inspection method, called an angular scan pulse-echo ultrasonic propagation imager, which is fully noncontact, real-time, and portable to position it in between the complex test rigs, is used to observe in situ damage growth of the composite. Finally, the verification procedure assisted by the angular scan pulse-echo ultrasonic propagation imager assures no growth of the initial impact damages after lifetime operation and proves the damage tolerance capability of the developed composite fuselage structure.

APA, Harvard, Vancouver, ISO, and other styles

41

Doucet, Jeremy, Xiang Zhang, and Philip E. Irving. "Modelling Fatigue Crack Growth Rates in Aluminium Plates Reinforced by Bonded Fibre-Metal Laminates for Fatigue Life Extension." Advanced Materials Research 891-892 (March 2014): 1803–9. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.1803.

Full text

Abstract:

Aircraft structural design and manufacture is moving towards lighter structures that have extended lives and improved damage tolerance. Hybrid structures are a possible solution to improve damage tolerance. They are a combination of metallic structure locally reinforced with adhesively bonded damage tolerant straps. In the present study a 3D finite element model has been developed with a bond line delamination growing under a fatigue law. A series of fatigue delamination tests on bonded aluminium were performed to provide input data. An iterative model for crack and debonding growth was developed to describe how debonding influence crack stress intensity and crack profile, which in turn influence debonding. The model predicts decrease in stress intensity on the bonded face and an overall retardation of fatigue crack growth rates. The stress intensity factor was predicted to vary through the thickness of the substrate due to the phenomenon of secondary bending and also the bridging effect caused by the presence of the reinforcing strap.

APA, Harvard, Vancouver, ISO, and other styles

42

Blinn, Bastian, Florian Krebs, Maximilian Ley, Christopher Gläßner, Marek Smaga, Jan C. Aurich, Roman Teutsch, and Tilmann Beck. "Influence of the Chemical Composition of the Used Powder on the Fatigue Behavior of Additively Manufactured Materials." Metals 9, no. 12 (November 29, 2019): 1285. http://dx.doi.org/10.3390/met9121285.

Full text

Abstract:

To exploit the whole potential of Additive Manufacturing (AM), a sound knowledge about the mechanical and especially cyclic properties of AM materials as well as their dependency on the process parameters is indispensable. In the presented work, the influence of chemical composition of the used powder on the fatigue behavior of Selectively Laser Melted (SLM) and Laser Deposition Welded (LDW) specimens made of austenitic stainless steel AISI 316L was investigated. Therefore, in each manufacturing process two variations of chemical composition of the used powder were utilized. For qualitative characterization of the materials cyclic deformation behavior, load increase tests (LITs) were performed and further used for the physically based lifetime calculation method (PhyBaLLIT), enabling an efficient determination of stress (S)–number of cycles to failure (Nf) curves (S–Nf), which show excellent correlation to additionally performed constant amplitude tests (CATs). Moreover, instrumented cyclic indentation tests (PhyBaLCHT) were utilized to characterize the materials’ defect tolerance in a comparably short time. All material variants exhibit a high influence of microstructural defects on the fatigue properties. Consequently, for the SLM process a higher fatigue lifetime at lower stress amplitudes could be observed for the batch with a higher defect tolerance, resulting from a more pronounced deformation induced austenite–α’-martensite transformation. In correspondence to that, the batch of LDW material with an increased defect tolerance exhibit a higher fatigue strength. However, the differences in defect tolerance between the LDW batches is only slightly influenced by phase transformation and seems to be mainly governed by differences in hardening potential of the austenitic microstructure. Furthermore, a significantly higher fatigue strength could be observed for SLM material in relation to LDW specimens, because of a refined microstructure and smaller microstructural defects of SLM specimens.

APA, Harvard, Vancouver, ISO, and other styles

43

Gomes, Gilberto, Thiago A. A. Oliveira, and Alvaro M. Delgado Neto. "A new methodology to predict damage tolerance based on compliance via global-local analysis." Frattura ed Integrità Strutturale 15, no. 58 (September 25, 2021): 211–30. http://dx.doi.org/10.3221/igf-esis.58.16.

Full text

Abstract:

Over the years several design philosophies to fatigue developed in order to combine structural safety and economy to manufacturing and operating aircraft process. The safe-life approach, which consists of designing and manufacturing a safe aeronautical structure throughout its useful life, results in factors that oversize the structural elements, preventing the possibility of failure and evidently leading to high design costs. On the other hand, the approach based on the damage tolerance concept, in which it is assumed that the structure, even whether damaged, is able to withstand the actions for which it was designed until the detection of a crack due to fatigue or other defects during its operation. Here, we propose a new methodology to the damage tolerance problem in which two-dimensional global-local analysis at different levels of external requests will be made by means of compliance, aimed at finding a relationship between fatigue life and the Paris constant. Moreover, the BemCracker2D program for simulating two-dimensional crack growth is used. This methodology has been proved to be an efficient and applied alternative in the damage tolerance analysis.

APA, Harvard, Vancouver, ISO, and other styles

44

Blinn, Bastian, David Görzen, Torsten Fischer, Bernd Kuhn, and Tilmann Beck. "Analysis of the Thermomechanical Fatigue Behavior of Fully Ferritic High Chromium Steel Crofer®22 H with Cyclic Indentation Testing." Applied Sciences 10, no. 18 (September 16, 2020): 6461. http://dx.doi.org/10.3390/app10186461.

Full text

Abstract:

The 22 wt.% Cr, fully ferritic stainless steel Crofer®22 H has higher thermomechanical fatigue (TMF)- lifetime compared to advanced ferritic-martensitic P91, which is assumed to be caused by different damage tolerance, leading to differences in crack propagation and failure mechanisms. To analyze this, instrumented cyclic indentation tests (CITs) were used because the material’s cyclic hardening potential—which strongly correlates with damage tolerance, can be determined by analyzing the deformation behavior in CITs. In the presented work, CITs were performed for both materials at specimens loaded for different numbers of TMF-cycles. These investigations show higher damage tolerance for Crofer®22 H and demonstrate changes in damage tolerance during TMF-loading for both materials, which correlates with the cyclic deformation behavior observed in TMF-tests. Furthermore, the results obtained at Crofer®22 H indicate an increase of damage tolerance in the second half of TMF-lifetime, which cannot be observed for P91. Moreover, CITs were performed at Crofer®22 H in the vicinity of a fatigue crack, enabling to locally analyze the damage tolerance. These CITs show differences between crack edges and the crack tip. Conclusively, the presented results demonstrate that CITs can be utilized to analyze TMF-induced changes in damage tolerance.

APA, Harvard, Vancouver, ISO, and other styles

45

Legowo, Dibyo, I. Wayan Susena, and Sharudin Tambunan. "Damage Tolerance Analysis on Repaired Fuselage Skin." Key Engineering Materials 306-308 (March 2006): 265–70. http://dx.doi.org/10.4028/www.scientific.net/kem.306-308.265.

Full text

Abstract:

This paper discussed about the method used by operator to perform damage tolerance analysis for repaired fuselage skin. Skin damage may be caused by accidental damage or fatigue crack. Some element needed for damage tolerance analysis and the method to develop load spectrum will be discussed briefly. Therefore, this paper will describe a case study of damage tolerance analysis on repaired fuselage skin of narrow body jet aircraft.

APA, Harvard, Vancouver, ISO, and other styles

46

Labeas, G., and S. Peppa. "Fatigue Crack Growth Behaviour of Friction Stir Welded Aluminium Alloys." Key Engineering Materials 665 (September 2015): 89–92. http://dx.doi.org/10.4028/www.scientific.net/kem.665.89.

Full text

Abstract:

The effect of Friction Stir Welding joining process on the damage tolerance behaviour of friction stir welded aluminium alloys is experimentally investigated. Fatigue crack propagation tests for different aluminium alloys and welding configurations have been performed. The main conclusion arising from the experimental study is that the damage tolerance behaviour of the welded material is in most cases comparable to the base material. Furthermore, the most critical area of the joint was identified to be the weld interface, i.e. the area between the nugget and the thermo-mechanically affected zone

APA, Harvard, Vancouver, ISO, and other styles

47

Burger, Uli, and Ludovic Rochat. "Aspects of Damage Tolerance and Fatigue of CFRP Structural Components." SAE International Journal of Aerospace 8, no. 2 (September 15, 2015): 292–302. http://dx.doi.org/10.4271/2015-01-2596.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Shi, Pan, and Sankaran Mahadevan. "Damage tolerance approach for probabilistic pitting corrosion fatigue life prediction." Engineering Fracture Mechanics 68, no. 13 (September 2001): 1493–507. http://dx.doi.org/10.1016/s0013-7944(01)00041-8.

Full text

APA, Harvard, Vancouver, ISO, and other styles

49

Aidman, E., and R. Crameri. "Mental effort ratio: Assessing individual differences in subjective fatigue tolerance." Journal of Science and Medicine in Sport 13 (December 2010): e44. http://dx.doi.org/10.1016/j.jsams.2010.10.554.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Nazmy, M., M. Staubli, G. Onofrio, and V. Lupinc. "Surface defect tolerance of a cast TiAl alloy in fatigue." Scripta Materialia 45, no. 7 (October 2001): 787–92. http://dx.doi.org/10.1016/s1359-6462(01)01097-1.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Tolerance to fatigue'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles