Function Of Test Frequency Research Articles

Effect of cycling frequency and self-heating on fatigue behavior of reinforced and unreinforced thermoplastic polymers

An experimental study was conducted to evaluate the effect of frequency and self-heating on fatigue behavior of two unreinforced and two short glass fiber reinforced thermoplastic polymers. Load-controlled fatigue tests were conducted under fully reversed (R = −1) and R = 0.1 conditions with specimens loaded in either longitudinal or transverse direction to the mold flow direction. Effect of frequency on fatigue life was evaluated at 23 and 125°C and for a range of frequencies between 0.063 and 20 Hz. Incremental step frequency tests were also performed at different stress ratios and stress levels. Surface temperature rise was found to be material, frequency, and stress level dependent. Three energy-based models were applied to the incremental step frequency data and relationships were developed for each material to estimate surface temperature rise as a function of test frequency and stress level. Relationships were also developed to assess critical frequency for the unreinforced thermoplastics at a given stress level above which surface temperature does not stabilize. POLYM. COMPOS., 55:2355–2367, 2015. © 2015 Society of Plastics Engineers

Estimation of Corrosion Fatigue-Crack Growth through Frequency Shedding Method

Abstract Corrosion fatigue-crack growth characteristics are important for the design of marine and off-shore structures. Design of critical components requires data on fatigue-crack growth rate at very low frequencies of the order of 10−2 to 10−3 Hz. Experiments at low frequencies pose practical difficulties of enormous test duration. To address this, it is proposed to estimate corrosion crack growth characteristics using a frequency shedding method where the frequency is shed with crack advance using an exponential law. Fatigue-crack growth rate tests have been conducted on Ni–Mn–Cr steel at a constant ΔK range of 18 MPa√m (lower Paris regime) under lab air conditions as well as 3.5 % NaCl solution. Crack growth rate data plotted as a function of test frequency presents a straight-line trend in log–log scale for a frequency range of 1–0.1 Hz; however, there is a change in trend when the frequencies are dropped further, which could be due to domination of corrosion mechanism. To understand the role of crack closure, crack closure estimates were obtained at periodic intervals of crack length and the effective stress intensity graphs suggest acceleration in crack growth rate due to corrosion as the frequency is reduced.

Investigation of Load Control Errors for Spectrum Fatigue Testing at High Frequencies

Abstract Ultra-high cycle fatigue (gigacycle) tests have shown that a true fatigue endurance limit does not exist for most metallic materials used in high cycle applications. These findings have significant implications for rotorcraft dynamic structural components that have traditionally been designed using endurance limit, stress-life methods. Unfortunately, the gigacycle fatigue test results generated to date cannot be easily applied to rotorcraft component design, because the interaction of different crack nucleating mechanisms under variable amplitude loading is not well understood, and must be studied using spectrum fatigue tests carried out to very long lives. To quantify the effect of spectrum load control errors on the rate of fatigue damage accumulation for a standard servo-hydraulic fatigue test machine, a damage ratio parameter for crack initiation is calculated using the high cycle fatigue portion of the Coffin-Manson strain-life curve with rainflow cycle counting. The fatigue damage parameter allows the level of controller error to be assessed as a function of test frequency, peak load levels, and test spectrum complexity. Also, different command feedback compensation schemes are tested to determine the range of control error that can be expected for a given set of test parameters. A sensitivity study was performed on the command signal response errors as a function of changes in the slope of the mean damage curve beyond 106 cycles. The test results demonstrate that rotorcraft spectrum fatigue tests can be performed at frequencies up to 150 Hz with a level of nominal damage accumulation error less that 1 % under most conditions. When electrical measurement system error is accounted for, the damage accumulation error is less than 2 % under most conditions. The results also show that it is important to consider the shape of the stress-life curves in the gigacycle fatigue range when performing spectrum tests out to long fatigue lives.

WE‐E‐BRA‐05: Reducing the Frequency of Linac Output Check: A Statistical Model of Linac Output Fluctuation Based On a 3 Year History to Evaluate New Tolerances as a Function of Test Frequency for 12 Linear Accelerators

Purpose: The study is based on a formalism to model the fluctuation of 12 linac outputs during a 3 year period. From a semi‐empirical statistical model and TG‐40 recommendations, a QA program is built from calculated action levels as a function of test frequency and time‐dependant probability distributions. Method and Materials: The linac output data is analyzed to fit a statistical model taking into account a systematic and a random component in the daily fluctuation. A 3 year history of daily output measurements totalizing 71 independent energies of photons and electrons is used to evaluate the parameters in each model. Action levels are calculated as a function of test frequency from obtained models based on tolerances defined in TG‐40. A confidence level of 95% is used to define the QA program such that machine output is kept within given limits, the latter being obtained by fitting tolerance functions with TG‐40 action levels. Measurement uncertainties are taken into account in the model and Gaussian statistics are used in the formalism. Results: Comparison between models and data history are in agreement with Gaussian statistics. For each linac and energy, tolerance functions are obtained from data history and new action levels are used with reduced test frequency. The tolerance of 2% recommended by TG‐40 for monthly output constancy check is reduced to values ranging from 1.2% to 1.8% for a test frequency of two months. Linac calibration frequency is reassessed to values ranging from 4 to 12 months. Conclusion: While daily check should be kept constant to prevent unpredictable variations, the frequency of output check can be reduced using new action levels based on a program‐defined limit and confidence level. Probability distributions can be used to evaluate linac calibration frequency based on machine stability. The model can be extended to other linac parameters.

Hydrogen Accumulation during Fatigue Deformation of Al-Mg-Si Base Alloys

Hydrogen accumulation during fatigue of bake-hardened Al-Mg-Si alloys was investigated by means of hydrogen microprint technique. As a result of S-N curve relation as a function of testing frequency, effect of environmental hydrogen on fatigue properties was not clearly identified. Based on the low cycle fatigue test with 60MPa stress amplitude, it was revealed that hydrogen was preferentially accumulated on slip lines and that distribution of hydrogen emission was changed in the crack propagation direction. Hydrogen was preferentially accumulated at the coarse slip lines near the fatigue cracks where the separation of slip planes was observed in the fracture surface. On the other hand, hydrogen was observed on the slip lines arranged like steps where the fatigue striations were formed in the fracture surface. At near the final fracture area where the finer slip lines were formed on specimen surface, hydrogen was arranged on each slip lines formed by multiple slips. Morphology of hydrogen accumulation on slip lines was not changed when the testing frequency was changed from 2Hz to 15Hz.

Ａｌ‐Ｍｇ‐Ｓｉ合金の疲労破壊に伴う水素集積の可視化

Hydrogen accumulation during fatigue of a bake-hardened Al–Mg–Si alloy was investigated by means of hydrogen microprint technique. As a result of S–N curve relation as a function of testing frequency, effect of environmental hydrogen on fatigue properties was not clearly identified. Based on the low cycle fatigue test with 60 MPa stress amplitude, it was revealed that hydrogen was accumulated on slip bands and that distribution of hydrogen emission was changed in the crack propagation direction. Hydrogen was preferentially accumulated at the coarse slip bands near the fatigue crack where the separation of slip planes was observed in the fracture surface. On the other hand, hydrogen was observed on the slip lines arranged like steps where the fatigue striations were formed in the fracture surface. At near the final fracture area where the fine slip bands were formed on specimen surface, hydrogen was arranged on each slip bands formed by multiple slips.

Comparisons of experimental measurements and a theoretical model for specimen self-heating during fatigue of type 316 LN stainless steel

The Type 316 stainless steel is being considered as a candidate target-container material for the spallation neutron source (SNS) being built at the Oak Ridge National Laboratory. Satisfactory behavior under fatigue loading is a requirement for the target container. Stress-controlled fatigue experiments were performed on the 316 stainless steel at 0.2 and 10 Hz with an R ratio of −1, where R=σ min./σ max.; σ min. and σ max. are the minimum and maximum applied stresses, respectively. At R=−1, a large specimen-temperature increase at 10 Hz was observed, which approached approximately 350 °C at a stress amplitude of 263 MPa, and affected fatigue lives. The specimen temperature at 0.2 Hz was about room temperature. The fatigue lives at 10 Hz were found to be shorter than those at 0.2 Hz. Different specimen temperatures were achieved by varying test frequencies. Significant differences in fatigue lives as a function of test frequency were observed with shorter fatigue lives at higher frequencies. The higher specimen temperature at 10 than at 0.2 Hz reduced the fatigue life at 10 Hz. A model based on the dissipation energy of the specimen during fatigue tests was developed to explain the fatigue-life result and predict the specimen-temperature evolution.

Initial permeability studies of Ni–Zn ferrites prepared by flash combustion technique

The initial permeability ( μ i) and relative loss factor (tan δ/ μ i) of Ni–Zn ferrite of composition Ni 0.8Zn 0.2Fe 2O 4 prepared by the non-conventional flash combustion technique are studied and reported. The ferrite powder prepared by this technique was calcined at 900 °C and the uniaxially pressed samples were sintered at various temperatures 1150, 1250 and 1350 °C. The initial permeability and the relative loss factor have been studied as the function of testing frequency and temperature. It is observed that the Ni–Zn ferrites prepared by this technique have the initial permeability from 16 to 20 in the frequency range 1 kHZ to 13 MHz and the relative loss factor of 10 3–10 4 in the frequency range 100 kHZ to 13 MHz. The initial permeability increases from room temperature to 300 °C. The relative loss factor is of the order of 10 −2. The results obtained are better when compared with ferrites prepared by the conventional ceramic method. This is attributed to better purity, controlled microstructure and chemical homogeneity achievable by the flash combustion method. Low relative loss factor makes these ferrites particularly useful as inductor and transformer materials for high frequency applications.

New data on the short-term effects of tone exposure

Three experiments studied the short-term effects of moderate- and high-level tone exposures on threshold and loudness. Experiment 1 measured temporary threshold and loudness shifts (TTS and TLS) due to a 1000-Hz exposure at a moderate level (65 dB SPL) as a function of exposure duration. Whereas there was no significant TTS, TLS was as high as 11 dB and recovered rapidly. TLS was significantly larger for the highest test levels. TTS and TLS were practically independent of exposure duration. Experiment 2 measured TTS and TLS as a function of test frequency following exposures to 500-, 1000-, or 3000-Hz tones at 65 dB SPL. The frequency patterns of TLS were established at test levels of 20-60 phons. TLS and TTS had similar frequency patterns with a maximum at the exposure frequency, but TLS patterns were higher and more extended than those of TTS. In experiment 3, subjects were exposed to a 1000-Hz tone at a high level (90 dB SPL). Frequency patterns for TTS or TLS at a 60-dB test level were measured repeatedly during 5 1/2 min after the end of exposure. Two short-term effects were observed immediately after the exposure: (1) a slight TTS (4.5 dB) at the exposure frequency which disappeared 2 to 3 min later; and (2) a large TLS (9 dB) which extended over the whole range of test frequencies, recovered rapidly, and had disappeared by 330 s after exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Temporal resolution within the upper ‘‘accessory excitation’’ region for maskers with fluctuating envelopes.

During Zwicker’s numerous investigations of the time structure of masking, he observed that envelope masking period patterns were larger for frequencies above the masker (in the upper ‘‘accessory excitation’’ region) than for frequencies near the masker (in the ‘‘main excitation’’ region). For example, the peak-to-trough ratio of the masking period pattern for a 4-Hz 100% amplitude-modulated masker was only 12 dB when the probe tone was within the main excitation region, at 1000 Hz, while the ratio was as large as 36 dB when the probe tone was within the accessory excitation region, at 3200 Hz [E. Zwicker, Acustica 36, 113–120 (1976)]. In the present research, masking at the peak and within the trough of 500-Hz amplitude-modulated maskers was investigated as a function of test frequency and masker level for modulation frequencies from 4 to 128 Hz in normal-hearing and hearing-impaired ears. Peak and trough masked thresholds were measured using amplitude-modulated signals with phasic and antiphasic envelopes. The results from normal-hearing ears confirm Zwicker’s finding that temporal resolution can be up to three times better in the upper accessory excitation region than in the main excitation region. Masking during envelope peaks remains constant while masking during envelope troughs increases with modulation frequency. This finding, and the slopes of the growth of masking, support Zwicker’s interpretation that masking during the envelope peaks and troughs are associated with simultaneous and nonsimultaneous masking, respectively. Peak-to-trough ratios in the upper accessory region are considerably reduced in hearing-impaired ears, which has important implications for processing speech signals in the presence of maskers with fluctuating envelopes. [Work supported by NIDCD.]

The quantitative relation between sensory cell loss and hearing thresholds

On the basis of experimental data obtained from 420 noise-exposed animals (chinchilla), the amount of sensory cell loss has been quantitatively related to the amount of permanent threshold shift at eight audiometric test frequencies between 0.125 and 16 kHz. The noise exposures, which varied extensively in spectrum, intensity and duration, produced permanent threshold shifts that ranged from 0 to 70 dB across a broad range of test frequencies. These data show: (1) consistent outer hair cell losses with less than 5 dB permanent threshold shifts (PTS) across all the test frequencies; (2) the first approximately 30 dB of PTS is established by losses of primarily outer hair cells; (3) in regions of the cochlea that transduce frequencies higher than or equal to 2 kHz, the three rows of outer hair cells show the same degree of loss for a given PTS, while in the 0.5 to 1.0 kHz region of the cochlea, the third row of outer hair cells (OHC) consistently shows less loss than do rows one and two; (4) appreciable inner hair cell (IHC) loss does not begin to appear until PTS exceeds approximately 30 dB; (5) in the virtual absence of OHC, hearing thresholds are least sensitive to IHC loss in the octave band centered at 4 kHz, i.e., the 4 kHz region can be as functional as other areas of the cochlea in spite of a greater amount of damage. The quantitative relation between cell loss and PTS varies as a function of test frequency in an orderly fashion.

ON THE NUCLEATION OF FATIGUE CRACKS IN PURE POLYCRYSTALLINE ?-IRON

— This paper presents the results of an investigation of fatigue crack initiation in pure polycrystalline α-iron as a function of testing frequency (0.01–1000 Hz). Three distinct types of fatigue crack initiation mechanisms were identified: (i) At low frequencies, <0.5 Hz, cracks were observed to nucleate at intrusions, extrusions and grain boundaries. However over the frequency range studied the cracks at the intrusions and extrusions were not associated with the final fatigue failure. The results suggest that in pure iron frequencies <0.01 Hz are required for fatigue failure to be initiated at intrusions and extrusions. (ii) At frequencies ≤0.01 Hz at high strain amplitudes, cracks nucleated at the intersection of grain boundaries with the free surface as a result of the incompatable deformation of surface grains. The subsequent propagation of these cracks resulted in fatigue failure. (iii) Tests performed at low strain amplitude at 5 Hz and 1000 Hz initiated surface grain boundary cracking without any significant associated change of grain shape. The results of the present investigation indicate that fatigue failure in pure iron alloys (at frequencies >0.01 Hz) is initiated not at intrusions and extrusions but at grain boundaries.

Effect of Environment on Fatigue and Creep Crack Growth in Inconel X-750 at Elevated Temperature

The fatigue crack growth rates (FCGR) of Inconel X-750 were measured in air and in vacuum at 25 °C and 650 °C as a function of test frequency. The wave shape was triangular and the frequency varied from 10 Hz to 0.01 Hz. The creep crack growth rates (CCGR) were also measured on single edge notch specimens at 650 °C in air and in purified argon. For a givenAK, the FCGR increases when temperature increases and frequency decreases. At low frequency the FCGR approach the creep crack growth rates. The mode of fracture changes from transgranular at 10 Hz to intergranular at 0.01 Hz. The effect of air environment is to accelerate the transition from transgranular to intergranular fracture modes with decreasing frequency. The role of oxidation in accelerating crack growth rate in fatigue and in creep is discussed in detail.

Tonal Consonance and Critical Bandwidth

Firstly, theories are reviewed on the explanation of tonal consonance as the singular nature of tone intervals with frequency ratios corresponding with small integer numbers. An evaluation of these explanations in the light of some experimental studies supports the hypothesis, as promoted by von Helmholtz, that the difference between consonant and dissonant intervals is related to beats of adjacent partials. This relation was studied more fully by experiments in which subjects had to judge simple-tone intervals as a function of test frequency and interval width. The results may be considered as a modification of von Helmholtz's conception and indicate that, as a function of frequency, the transition range between consonant and dissonant intervals is related to critical bandwidth. Simple-tone intervals are evaluated as consonant for frequency differences exceeding this bandwidth. whereas the most dissonant intervals correspond with frequency differences of about a quarter of this bandwidth. On the base of these results, some properties of consonant intervals consisting of complex tones are explained. To answer the question whether critical bandwidth also plays a rôle in music, the chords of two compositions (parts of a trio sonata of J. S. Bach and of a string quartet of A. Dvořák) were analyzed by computing interval distributions as a function of frequency and number of harmonics taken into account. The results strongly suggest that, indeed, critical bandwidth plays an important rôle in music: for a number of harmonics representative for musical instruments, the “density” of simultaneous partials alters as a function of frequency in the same way as critical bandwidth does.