Fatigue frequency

AK = A a (dynamic correction not needed at conventional fatigue frequencies)... 

Cyclic loads were applied to the specimens using a hydraulic feedback load system which could be either load-, stroke-, or strain-controlled. Sinusoidal and linear-ramp waveforms were generally used. Fatigue frequencies were varied from 0.1 to 15 Hz. Unless otherwise stated, mechanical property data were obtained at a fatigue frequency of 10 Hz. 

Initially, by defining key-words aiming at limiting the search to the rather specific theme under study, focusing on words such as, Eye blink , EEG , Blink , Artifact , Rate , Fatigue , Frequency , Blink frequency , Video , Image capture , Environmental conditions , Mental load , Temperature , Relative Humidity , which in groups in the databases with the appropriate Boolean operator AND . This way a total... 

In addition hysteresis heating occurs in the strained craze material. Both effects combine to give rise to a distinct frequency sensitivity of A for a variety of materials such as PC and PMMA [219, 220], and PPO, PVC, PA 66, PC, PVDF, and PSU [220]. As has been noted by Skibo et al. [220] the frequency sensitivity varies with temperature. It reaches a maximum at that temperature where the external (fatigue) frequency corresponds to the internal segmental jump frequency (of the jS-relaxation process). 

Fatigue tests were performed under load control mode on a Schenck horizontal fatigue testing machine with hydraulic grips and a maximum load capacity of 25 kN. Tension-tension constant amplitude fatigue tests were carried out at three stress levels 60% a , 70% Cu and 80% a at two different stress ratios R = 0.1 and R = 0.5. The test frequency was kept constant (f = 3 Hz) for all the tests. 

An important aspect of the mechanical properties of fibers concerns their response to time dependent deformations. Fibers are frequently subjected to conditions of loading and unloading at various frequencies and strains, and it is important to know their response to these dynamic conditions. In this connection the fatigue properties of textile fibers are of particular importance, and have been studied extensively in cycHc tension (23). The results have been interpreted in terms of molecular processes. The mechanical and other properties of fibers have been reviewed extensively (20,24—27). 

Bellows can vibrate, both from internal fluid flow and externally imposed mechanical vibrations. Internal flow liner sleeves prevent flow-induced resonance, which produces bellows fatigue failure in minutes at high flow velocities. Mechanically induced resonant vibration is avoided by a bellows with a natural frequency far away from the forcing frequency, if known. Multiple-ply bellows are less susceptible to vibration failure because of the damping effect of interply friction. 

The operating schedule of a gas turbine produces low-frequency thermal fatigue. The number of starts per hours of operating time directly affects the hfe of the hot sections (combustor, turbine nozzles, and blades). The life reduction effect of the number of starts on a combustor liner could be as high as 230 hours/start and on the turbine nozzles as high as 180 hours/start. The effect of full load trips can be nearly 2-3 times as great ... 

Variable nozzles produce a series of jets of gas entering the rotor, and these impulses add up to form a frequency equal to the blade-passing frequency the number of revolutions per second multiplied by the number of nozzle vanes, which is of the order of thousands of cycles per second. Frequently the rotor will resonate at this frequency, and if it does, it will be fatigued and crack and break up thus these frequencies must be avoided, and the manufac turer should be asked to supply information to the customer on this subject. 

Perhaps the most important stress factor affecting corrosion fatigue is the frequency of the cyclic stress. Since corrosion is an essential component of the failure mechanism and since corrosion processes typically require time for the interaction between the metal and its environment, the corrosion-fatigue life of a metal depends on the frequency of the cyclic stress. Relatively low-stress frequencies permit adequate time for corrosion to occur high-stress frequencies may not allow sufficient time for the corrosion processes necessary for corrosion... 

The operating schedule of a gas turbine produces a low-frequency thermal fatigue. The number of starts per hours of operating time directly affects the blade life. Table 11-1 shows fewer starts per operating time increases turbine life. 

Another important factor in the selection of a lead alloy is fatigue strength, which may arise from high-frequency vibration from pumps and stirrers or from differential expansion from heat and cooling cycles. The marked increase of fatigue strength obtained by alloying with copper, silver and tellurium can be seen from Table 3.25. 

This represents the locus of all the combinations of Ca and Om which cause fatigue failure in a particular number of cycles, N. For plastics the picture is slightly different from that observed in metals. Over the region WX the behaviour is similar in that as the mean stress increases, the stress amplitude must be decreased to cause failure in the same number of cycles. Over the region YZ, however, the mean stress is so large that creep rupture failures are dominant. Point Z may be obtained from creep rupture data at a time equal to that necessary to give (V cycles at the test frequency. It should be realised that, depending on the level of mean stress, different phenomena may be the cause of failure. 

A uPVC rod of diameter 12 mm is subjected to an eccentric axial force at a distance of 3 ttun from the centre of the cross-section. If the force varies sinusoidally from — F to f at a frequency of 10 Hz, calculate the value of F so that fatigue failure will not occur in 10 cycles. Assume a safety factor of 2.5 and use the creep rupture and fatigue characteristics described in the previous question. Thermal softening effects may be ignored at the stress levels involved. 

The links between levels of exposure and inconvenience caused by ventilation noise are described in an investigation carried out on office workers.- Technical measurements and analyses of the ventilation noise at 155 typical office workplaces were in this study combined with assessments by the office workers of the level of disturbance that they experienced, the effect on working performance, fatigue, stress-related pain, and headaches. The average noise level was about 40 dB(A) at two of the workplaces, while it was about 35 dB(A) at two others. It emerged from rhe narrow-band analyses that the sound pressure levels of rhe infrasound were not in any event of an order that this type of sound frequencies (below 20 Hz) could contribute to any disturbance effects. Any steps taken to counter the sound frequencies of the ventilation noise under 50 Hz, i.e., the point of btersection between the threshold curve of auditory perception and the spectral level distribution curve of... 

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