Increases in fatigue life caused by the introduction of rest periods

1972 ◽  
Vol 7 (1) ◽  
pp. 69-73 ◽  
Author(s):  
K J Miller ◽  
D J Hatter
Keyword(s):  
Fatigue Life ◽  
Laboratory Tests ◽  
Rest Period ◽  
Critical Value ◽  
Rest Periods ◽  
Fatigue Data

Fatigue data are usually derived from uninterrupted laboratory tests although the data may be required for conditions in which components are infrequently cycled. This paper discusses tests that involve rest periods to simulate infrequent cycling. The introduction of rest periods always causes an increase in endurance which approaches a maximum of approximately 100 per cent at a critical value of rest. The total rest period appears to be a more important parameter than either the number of rest periods or the position in the lifetime at which rests may be taken.

Effect of Healing on Fatigue Law Parameters of Asphalt Binders

2012 ◽  
Vol 2293 (1) ◽  
pp. 96-105 ◽  
Author(s):  
Arianna Stimilli ◽  
Cassie Hintz ◽  
Zhijun Li ◽  
Raul Velasquez ◽  
Hussain U. Bahia
Keyword(s):  
Fatigue Life ◽  
Asphalt Binder ◽  
Rest Period ◽  
Power Laws ◽  
Asphalt Binders ◽  
Traffic Loading ◽  
Damage Level ◽  
Rest Periods ◽  
Pavement Structure ◽  
Number Of Cycles

Asphalt binder has the ability to self-heal during rest periods when repetitive loading is applied. Studying the effect of rest on fatigue law parameters provides useful insight into the healing capabilities of asphalt binders. Currently, standard testing and analysis procedures to quantify asphalt binder healing capability are limited and difficult to implement in practice. Fatigue is known to depend on both traffic loading and pavement structure. Power law relations (e.g., Nf = Aγ−B) are commonly used for fatigue analysis of pavement materials. Power laws are used to estimate fatigue life (i.e., number of cycles to failure, Nf) as a function of load amplitude (e.g., strain, γ), which is a reflection of the pavement structure. In this study, testing consisted of strain-controlled time sweeps in the dynamic shear rheometer with a single rest period inserted at a specified damage level. With the selected test, the effect of healing on the relationship between fatigue life and strain was investigated. Nine neat and modified binders were tested. Healing testing was conducted at multiple age levels and strains. Healing that resulted from a single rest period had an insignificant effect on fatigue performance compared with modification and oxidative aging. Although this paper highlights the challenges of using few rest periods to predict healing potential, preliminary results of testing with multiple rest periods show the importance of healing. Further investigation is needed to verify the effect of multiple rest periods on binder fatigue.

Influence of a zero-load rest period in elevated-temperature fatigue

1976 ◽  
Vol 11 (4) ◽  
pp. 235-239 ◽  
Author(s):  
K J Miller ◽  
W J Plumbridge
Keyword(s):  
Laboratory Tests ◽  
High Strain ◽  
Preliminary Investigation ◽  
Rest Period ◽  
Cyclic Softening ◽  
Strain Ageing ◽  
Maximum Lifetime ◽  
Rest Periods ◽  
Dominant Process ◽  
Period Duration

A preliminary investigation of the influence of rest periods on Stage I crack growth has been performed on a 2½ per cent Ni Cr Mo steel by testing cylindrical specimens under high-strain reversed torsion conditions at 20, 100, 200, 300 and 400°C. Increases in lifetime of up to 100 per cent are observed, and their magnitude is a function of temperature and the rest-period duration, with maximum lifetime occurring at 300°C and a total rest period of 20 hours. Strain ageing is cited as the dominant process, which explains the dependence of optimum lifetime conditions on both temperature and total rest period duration. Since components are frequently rested and/or subjected to variable strain-rate conditions over a range of temperatures, it is suggested that results obtained from uninterrupted laboratory tests may be conservative unless overageing occurs leading to cyclic softening.

Morphophysiological studies of the shoot apex. I. Recurrent growth flushes and their relationship with structural changes in the growing apex of Callistemon viminalis

1968 ◽  
Vol 46 (10) ◽  
pp. 1287-1295 ◽  
Author(s):  
A. N. Purohit ◽  
K. K. Nanda
Keyword(s):  
Structural Changes ◽  
Rest Period ◽  
Growth Cycle ◽  
Active Period ◽  
Active Growth ◽  
Histological Changes ◽  
Floral Buds ◽  
Rest Periods ◽  
Number Of Leaves ◽  
Callistemon Viminalis

The annual growth cycle of Callistemon viminalis consists of three phases: (1) a reproductive phase that continues till the end of February; (2) a vegetative phase that lasts from the end of February till the end of August; and (3) a long dormant phase which lasts till the end of December. The cycle exhibits four growth flushes with alternating periods of active growth and rest. The duration of the successive rest periods increases, leading eventually to the onset of the long dormant phase.The growing apex exhibits more or less similar histological changes in different growth flushes. An increase in divisional activity of the cells of flanking meristem, accompanied by a decline in the elongation of cells of pith rib meristem, characterizes the rest period. During the active period of growth, the cells of the pith rib meristem elongate but the activity of the flanking meristem decreases. The number of leaves produced in each growth flush, therefore, is dependent upon the duration of the preceding rest period, and their size and nature on the duration of active growth. In growth flush 1 the cells of the rib meristem show elongation twice during the active period corresponding with the separation of floral buds and of foliage leaves respectively. In the long dormant phase, on the other hand, the cells of the flanking meristem show high divisional activity twice, first during September when new leaf primordia are initiated, and again during November when floral buds are initiated. Events of great significance thus occur during the long dormant phase. The reproductive development is characterized by a marked increase in the rate of cell division in the flanking meristem accompanied by cessation of growth, the features that characterize the rest period as well.

scholarly journals Structural characteristics and chemical composition of andropogon grass pasture managed under different defoliation intensities and rest periods

2017 ◽  
Vol 18 (4) ◽  
pp. 492-504
Author(s):  
Clésio dos Santos Costa ◽  
Rosane Cláudia Rodrigues ◽  
Francisco Naysson de Sousa Santos ◽  
Ricardo Alves Araújo ◽  
Giovanne Oliveira Costa Sousa ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Linear Trend ◽  
Structural Characteristics ◽  
Rest Period ◽  
Matter Content ◽  
Neutral Detergent Fiber ◽  
Dry Matter Content ◽  
Linear Effect ◽  
Rest Periods ◽  
Dry Biomass

SUMMARY This study aimed to evaluate the agronomic, structural traits and chemical composition of andropogon grass subjected to different defoliation intensities and rest periods. Two defoliation intensities (15 and 30 cm) and four rest periods (25; 35, 45 and 55 days) were evaluated in a factorial completely randomized design, with four replications. The rest period promoted a linear decreasing effect (P <0.05) on the dry biomass of leaf blades in the two defoliation intensities. The dry biomass of stems showed an increasing linear effect (P <0.05) according to the rest periods in the two defoliation intensities. Production was recorded at 2427.71; 2907.39; 3325.72 and 3749.45 kg ha−1 for the periods of 25; 35; 45 and 55 days, respectively. The dry matter content showed an increasing linear effect (P <0.05) as a function of the rest periods evaluated in the two defoliation intensities. The rest period indicated a decreasing linear trend (P <0.05) for the crude protein content in the two defoliation intensities. A decrease of 0.9 and 0.7 g kg−1 was verified for each day of the rest period. For each additional day in the rest period, there was an increase of 1.2 and 1.5 g kg−1 DM in the neutral detergent fiber content at intensities of 15 and 30 cm. The andropogon grass pasture managed with a 25-day rest period and defoliation intensity of 30 cm showed high leaf/stem ratio and good nutritional value.

scholarly journals Pengaruh Waktu Istirahat Berbeda Sebelum Proses Pemotongan Terhadap Respon Suhu Permukaan Tubuh Sapi Brahman Cross

2021 ◽  
Vol 2 (1) ◽  
pp. 27-32
Author(s):  
M. Adhyatma ◽  
Gayuh Syaikhullah ◽  
Himmatul Khasanah
Keyword(s):  
Surface Temperature ◽  
Body Surface ◽  
Rest Period ◽  
The Body ◽  
Surface Temperature Change ◽  
Rest Periods ◽  
Randomized Design ◽  
Humidity Index ◽  
Body Surface Temperature ◽  
Data Collections

his study aims to assess the physiological response through body surface temperature of Brahman Cross beef by giving different rest periods. This study used 24 Brahman Cross cattle in several slaughterhouses in West Java. Observation of microclimatic conditions includes temperature, humidity, THI (temperature-humidity index). Data collections of livestock body surface temperature was carried out when the cattle arrive at the slaughterhouse, while they are in the holding pen and the restraining box. Comparative tests were carried out on the surface temperature of cows under different conditions using a completely randomized design (CRD). This study showed that the body surface temperature was still in the normal range, between 30.89-36.75 °C. Analysis of variance showed that different rest periods had a significant effect  (P <0.05) on body surface temperature change in the eye area in the three pre-cutting stages. Providing a 24 hours rest period resulted in lower stress response in livestock.

Changes in hormonal concentrations after different heavy-resistance exercise protocols in women

1993 ◽  
Vol 75 (2) ◽  
pp. 594-604 ◽  
Author(s):  
W. J. Kraemer ◽  
S. J. Fleck ◽  
J. E. Dziados ◽  
E. A. Harman ◽  
L. J. Marchitelli ◽  
...  
Keyword(s):  
Menstrual Cycle ◽  
Rest Period ◽  
Follicular Phase ◽  
Total Testosterone ◽  
Factor I ◽  
Rest Periods ◽  
Early Follicular Phase ◽  
In Series ◽  
Heavy Resistance Exercise ◽  
Blood Variables

Nine eumenorrheic women (age 24.11 +/- 4.28 yr) performed each of six randomly assigned heavy-resistance protocols (HREPs) on separate days during the early follicular phase of the menstrual cycle. The HREPs consisted of two series [series 1 (strength, S) and series 2 (hypertrophy, H)] of three protocols, each using identically ordered exercises controlled for load [5 vs. 10 repetitions maximum (RM)], rest period length (1 vs. 3 min), and total work (J) within each three-protocol series. Blood measures were determined pre-, mid- (after 4 of 8 exercises), and postexercise (0, 5, 15, 30, 60, 90, 120 min and 24 and 48 h). In series 1, a significant (P < 0.05) reduction in growth hormone (GH) was observed at 90 min postexercise for all three protocols. In series 2, the 10-RM protocol with 1-min rest periods (H10/1) produced significant increases above rest in GH concentrations at 0, 5, and 15 min postexercise, and the H10/1 and H5/1 protocols demonstrated significant reductions at 90 and 120 min postexercise. Cortisol demonstrated significant increases in response to the S10/3 protocol at 0 min, to the H10/1 protocol at midexercise and at 0 and 5 min postexercise, and to the H5/1 protocol at 5 and 15 min postexercise. No significant changes were observed in total insulin-like growth factor I, total testosterone, urea, or creatinine for any of the HREPs. Significant elevations in whole blood lactate and ammonia along with significant reductions in blood glucose were observed. Hormonal and metabolic blood variables measured in the early follicular phase of the menstrual cycle varied in response to different HREPs. The most dramatic increases above resting concentrations were observed with the H10/1 protocol, indicating that the more glycolytic HREPs may stimulate greater GH and cortisol increases.

The Effect of Self-Paced and Prescribed Interset Rest Strategies on Performance in Strength Training

2019 ◽  
Vol 14 (7) ◽  
pp. 980-986
Author(s):  
Peter Ibbott ◽  
Nick Ball ◽  
Marijke Welvaert ◽  
Kevin G. Thompson
Keyword(s):  
Strength Training ◽  
Perceived Exertion ◽  
Mechanical Performance ◽  
Rest Period ◽  
Rating Of Perceived Exertion ◽  
Subjective Rating ◽  
Male Athletes ◽  
Rest Periods ◽  
Pacing Strategies ◽  
Feasible Alternative

Purpose: To assess pacing strategies using prescribed and self-selected interset rest periods and their influence on performance in strength-trained athletes. Methods: A total of 16 strength-trained male athletes completed 3 randomized heavy strength-training sessions (5 sets and 5 repetitions) with different interset rest periods. The interset rest periods were 3 min (3MIN), 5 min (5MIN), and self-selected (SS). Mechanical (power, velocity, work, and displacement), surface electromyography (sEMG), and subjective (rating of perceived exertion) and readiness-to-lift data were recorded for each set. Results: SS-condition interset rest periods increased from sets 1 to 4 (from 207.52 to 277.71 s; P = .01). No differences in mechanical performance were shown between the different interset rest-period conditions. Power output (210 W; 8.03%) and velocity (0.03 m·s−1; 6.73%) decreased as sets progressed for all conditions (P < .001) from set 1 to set 5. No differences in sEMG activity between conditions were shown; however, vastus medialis sEMG decreased as the sets progressed for each condition (1.75%; P = .005). All conditions showed increases in rating of perceived exertion as sets progressed (set 1 = 6.1, set 5 = 7.9; P < .001). Participants reported greater readiness to lift in the 5MIN condition (7.81) than in the 3MIN (7.09) and SS (7.20) conditions (P < .001). Conclusions: Self-selecting interset rest periods does not significantly change performance compared with 3MIN and 5MIN conditions. Given the opportunity, athletes will vary their interset rest periods to complete multiple sets of heavy strength training. Self-selection of interset rest periods may be a feasible alternative to prescribed interset rest periods.

scholarly journals Temporary Relocation during Rest Periods: Relocation Stress and Other Factors Influence Hair Cortisol Concentrations in Horses

Animals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 642
Author(s):  
Jaume Gardela ◽  
Annaïs Carbajal ◽  
Oriol Tallo-Parra ◽  
Sergi Olvera-Maneu ◽  
Manuel Álvarez-Rodríguez ◽  
...  
Keyword(s):  
Hair Growth ◽  
Sudden Change ◽  
Rest Period ◽  
Seasonal Effect ◽  
Hair Cortisol ◽  
Sample Collection ◽  
Rest Periods ◽  
Sport Competition ◽  
Autumn And Winter ◽  
The Relationship

Horse transportation for temporary relocation during rest periods is a common and widespread practice among horse owners, either from sport competition or working tasks. This study aimed to determine the effect of a relocation period and the multiple factors associated with a rest period on hair cortisol concentrations (HCCs) in horses. Additionally, this study reports the seasonal effect on HCCs and hair growth over a year. Thirteen police horses, Pure Spanish stallions of various ages (5–13 y), were selected to participate in this study. Hair sample collection was carried out approximately every 30 d for seven months (Study 1) and a year (Study 2). Cortisol determinations were performed by enzyme immunoassay. Interestingly, Study 1 revealed that relocated horses (n = 4) exhibited elevated HCCs compared with control horses (n = 4) after the relocation period (p < 0.05). Study 2 (n = 5) showed higher HCCs during summer compared with autumn and winter, and higher hair growth rates in winter compared with the other seasons (p < 0.05). Relocated horses had higher HCCs, suggesting a change in their welfare status, probably related to the sudden change in their surrounding conditions. However, these results should be interpreted cautiously due to the low sample size used. The nature of the relationship between HCCs and horse welfare needs to be further examined.

Proposal of Fatigue Life Equations for Carbon and Low-Alloy Steels and Austenitic Stainless Steels as a Function of Tensile Strength

2013 ◽  
Author(s):  
Hiroshi Kanasaki ◽  
Makoto Higuchi ◽  
Seiji Asada ◽  
Munehiro Yasuda ◽  
Takehiko Sera
Keyword(s):  
Tensile Strength ◽  
Fatigue Life ◽  
Stainless Steels ◽  
Room Temperature ◽  
Austenitic Stainless Steels ◽  
Low Alloy Steels ◽  
Strength Based ◽  
Fatigue Data ◽  
Current Design ◽  
Alloy Steels

Fatigue life equations for carbon & low-alloy steels and also austenitic stainless steels are proposed as a function of their tensile strength based on large number of fatigue data tested in air at RT to high temperature. The proposed equations give a very good estimation of fatigue life for the steels of varying tensile strength. These results indicate that the current design fatigue curves may be overly conservative at the tensile strength level of 550 MPa for carbon & low-alloy steels. As for austenitic stainless steels, the proposed fatigue life equation is applicable at room temperature to 430 °C and gives more accurate prediction compared to the previously proposed equation which is not function of temperature and tensile strength.

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