Influence Of Cycling Frequency Research Articles

Very high cycle fatigue properties of short glass fiber reinforced polyetheretherketone (PEEK)

The fatigue properties of 14 wt-% short glass fiber reinforced polyetheretherketone (PEEK–GF14) have been investigated in the high and very high cycle fatigue (VHCF) regime. Experiments were performed at a load ratio of –1 with servohydraulic and electrodynamic equipment at cycling frequency 10–20 Hz, and with ultrasonic equipment at 19 kHz. A new specimen geometry has been developed that allows ultrasonic tests up to high stress amplitudes. The same specimen shape was used in both testing series to exclude size effects, which enabled to focus on the influence of cycling frequency and testing technique. Ultrasonic fatigue testing with intermittent loading served to avoid heating of specimens. The S-N curves measured at 10–20 Hz and 19 kHz show a similar slope exponent (i.e., 10 % deviation). Mean S-N curve determined with ultrasonic equipment is shifted to slightly lower stress amplitudes, which may be attributed to statistical scatter. PEEK–GF14 does not show a fatigue limit and failures still occurred above 109 cycles. The VHCF strength of PEEK-GF14 is approximately two times higher compared with unreinforced PEEK. Fractographic investigations revealed fiber fracture and, less frequently, fiber pull-out.

Very High Cycle Fatigue Data Acquisition Using High-Accuracy Ultrasonic Fatigue Testing Equipment

Abstract Fatigue testing at ultrasonic frequency is a powerful method for rapid generation of high and very high cycle fatigue data. High accuracy of cyclic loading is the basis for reproducible test results, which can be obtained with closed-loop control of vibration amplitude and resonance frequency. Self-heating of test specimens can be suppressed by intermittent (pulse-pause) loading. In the present work, the high-accuracy ultrasonic fatigue testing equipment developed at the University of Natural Resources and Life Science, Vienna (BOKU) is described, and systematic investigations are presented that demonstrate the effects of cycling frequency, specimen size, and intermittent loading. Data obtained with additively manufactured (AMed) austenitic stainless steel 316L at 19 kHz are compared with electromagnetic resonation test results measured at 90 Hz. No influence of cycling frequency on fatigue lifetimes and fatigue limit was found when specimens of comparable size were used for tests at 19 kHz and 90 Hz. In contrast, the use of as-built specimens with smaller testing volume resulted in an increase in cyclic strength, demonstrating a size effect on fatigue properties. Polishing the surfaces of AMed specimens increased the fatigue limit by a factor of two. Furthermore, ultrasonic fatigue tests with intermittent loading and four different pulse lengths as well as continuous cycling were performed. The tests were conducted with wrought aluminum alloy 7075-T651 and with specimens containing small artificial surface defects. Similar lifetimes were measured in all testing series. Moreover, the same fatigue limit is found for all pulse lengths and for continuous cycling. This demonstrates that pulsed loading is a most suitable method to avoid specimen heating at ultrasonic frequency and that there is no influence on measured fatigue properties if ultrasonic loading is appropriately controlled. Measurement artifacts could be identified and avoided by measuring and recording all load amplitudes during ultrasonic fatigue tests.

Influence of cycling frequency and testing volume on the VHCF properties of 18Ni maraging steel

Fatigue properties of nitrided 18Ni maraging steel sheets under cyclic tension loading were investigated at cycling frequency 95 Hz by using a resonance tester and at 20 kHz using ultrasonic fatigue testing equipment. High and very high cycle fatigue (VHCF) tests have been performed with two specimen shapes with distinctly different stressed volumes. Fatigue cracks started at internal aluminate or Zr(N,C) inclusions. Inclusions are considered as initial cracks, and fatigue lifetimes as the numbers of cycles necessary to propagate the cracks to fracture. Specimen size effect is explained with volume influence on statistical distribution of inclusion sizes. Comparable mean lifetimes for the same specimen shape and similar dependence of lifetimes on stress intensity factor range were found at 95 Hz and 20 kHz, which indicates the absence of frequency effects in maraging steel.

The Influence of Cycling Frequency to Response Loading in Fatigue Tests for Sandwich Beam with Viscoelastic Core

In 3-point bending fatigue experiments of sandwich plate with visoelastic core and steel faceplates, it is found that response loading of specimen is very sensitive to cycling frequency. From fatigue test, different loading response of sandwich beam obtained in various cycling frequencies. Based on viscoelastic theory, responses of deformation of sandwich plate in cyclic square load wave are calculated. And an explanation of influences of cycling frequency is elaborated.

Fatigue Fracture in VNS-25 Stainless Steel

The paper covers the experimental study of the influence of cycling frequency ranging from 20 Hz to 10 kHz and the cycle asymmetry on the crack growth resistance of VNS-25 stainless steel. It is demonstrated that as the cycling frequency is raised, the crack growth rate decreases monotonically, while threshold values of the stress intensity factor ΔKth grow. The latter is due to the fact that at high cycling frequencies the plastic deformation processes remain incomplete and the contribution of the fracture mechanisms that facilitate greater energy intensity of fatigue crack growth processes becomes more significant. A comparison of ΔKth and fatigue life values as a function of cycling frequency for smooth and notched specimens demonstrates that if represented in relative coordinates these functions are described by a common relationship. This allows a quantitative assessment of the effect of the strain cycling rate on the above-mentioned properties of a material from the results of tests of one type only. It has been found that the values ΔKth in asymmetrical loading cycles are related to those in symmetrical cycles, as well as to a coefficient of material's sensitivity to the static component, and linearly depend on the load ratio.

Influence of cycle frequency, muscle strain and muscle length on work and power production of rainbow trout (Oncorhynchus mykiss) ventricular muscle

This study investigates the effects of cycle frequency, strain and length on work and power output of isolated rainbow trout (Oncorhynchus mykiss) ventricular preparations using the work loop technique. These effects are discussed in the context of the whole heart using analogies with heart rate, stroke volume and end-diastolic volume. Power output was dependent on cycle frequency, increasing threefold beween 0.3 and 1.1 Hz. The frequency for maximum power output was approximately 1.1 Hz, corresponding to the frequency for maximum power in perfused heart experiments. The length for maximum work production (Lopt) was found to be the same as the length for maximum isometric force production (Lmax). The decline in net work at lengths greater than Lopt/Lmax was attributed to an increase in passive work (the work done on an unstimulated muscle) or to hysteresis and to a large increase in lengthening work. The strain yielding maximum work decreased with increasing frequency. This is discussed in the context of the decline in stroke volume observed at increased heart rates in vivo. Muscle strain in intact hearts paced at 0.3 Hz was +/-11.9 % (23.8 % peak to peak), a value similar to the optimum strain at 0.3 Hz in vitro (+/-12 %).

Influence of cycling frequency on cyclic creep characteristics of nickel base single-crystal superalloy

The static and the cyclic creep load-controlled tests of the nickel base single-crystal superalloy, CMSX 3 have been studied. In this study, two different testing procedures of cyclic creep were carried out under specific loading schedules defined by the stress amplitude, the stress range, stress ratio, and cycling frequency. The different cycling frequencies for two cycling hold periods were investigated to influence the creep/fatigue behaviour of the alloy. The influence of these variables was evaluated through the deformation behaviour and the fracture life data. It is concluded that the additional fatigue stress component superimposed onto creep stress component is of great significance influencing the deformation process and fracture life and accelerating the creep strain rate for chosen types of testing.

The Influence of the Cycle Frequency and Wave Shape on the Fatigue Life of Leaded Chip Carrier Printed Wiring Board Interconnections

This study employed different cycle frequencies, to determine the influence of cycle frequency on the fatigue life of leaded chip carrier printed wiring board (LCC/PWB) interconnections. Real LCC/PWB interconnections were mechanically cycled at 35°C or 125°C. The cycle frequency was varied by varying the ramp loading and unloading rates or by introducing hold times. Tests were run with equal hold times at the maximum and minimum displacements or only at the maximum displacement. The use of slower ramp cycling or the introduction in the hold times increased the plastic displacement and this decreased the fatigue life. This plastic displacement increase was corrected for, to unveil the underlying material response. The corrected data was similar to that observed in previous tests on simple, single, solder joints, where the plastic strain was kept constant while the cycle frequency was reduced. At 125°C there was a small influence of wave shape, with maximum displacement hold time tests showing the shortest fatigue lives and symmetric (maximum and minimum) hold time tests showing the longest fatigue lives. The fatigue lives of the tests run with ramp cycling were intermediate. This wave shape effect is relatively small, especially compared to the large overall influence of the cycle frequency.

Fatigue of 60/40 Solder

Plastic strain versus fatigue life data are presented for tests run at -- 50, 35, 125, and 150°C. It was found that these data could be correlated by the Coffin-Manson fatigue law, with an exponent of approximately 0.5 for the tests run at -35°C to 125°C. At 150°C the exponent was reduced to 0.37. These results were obtained for plastic strain limited tests. Different results are obtained when total strain limits are employed. This difference is discussed. The influence of cycling frequency and temperature changes are also discussed. A model is presented which describes the influence of plastic strain and cycling frequency. Corrections to the model predicted fatigue life, which account for temperature changes, cycling waveshape, and joint geometries, are also discussed.