High Frequency Loading Research Articles

Microstructural evolution of wear-resistant FeCrB and FeCrNiCoB coating alloys during high-energy mechanical attrition

Mechanical milling/attrition provides a convenient scope of simulating the microstructural changes encountered by wear-resistant coating alloys subjected to deformation under high frequency and high-intensity impact loading or accelerated wear condition. In the present study, the microstructural evolution of two commercial coating materials, FeCrB (Armacor M) and FeCrNiCoB (Armacor C), in the course of low- and high-intensity mechanical attrition, was monitored by X-ray diffraction and high-resolution transmission electron microscopy. While low-intensity milling leads to marginal grain refinement but no change in phase-aggregate in FeCrB, similar mechanical attrition causes boride precipitation in FeCrNiCoB alloy powder. On the other hand, attrition in high-intensity mill leads to formation of a nanocrystalline extended solid solution of ferrite in FeCrB and nanocrystalline two-phase mixture of boride and austenite in FeCrNiCoB, respectively. Furthermore, continued milling seems to produce partial solid-state amorphization, particularly in FeCrB. On isothermal heating, the milled powders (both FeCrB and FeCrNiCoB) develop identical two-phase nanocrystalline aggregate signifying large-scale solute redistribution and nearly the same level of metastability of the deformed microstructure. Thus, it is concluded that the microstructure and hence wear resistance of FeCrB and FeCrNiCoB coatings is likely to undergo significant changes during high load and high strain rate impact or wear condition.

Electromyographical study on muscle fatigue in repetitive forearm tasks

The purpose of this study was to examine whether repetitive muscle tasks in low weight load might influence the fatigue of forearm muscles, and to identify ergonomic risk factors of forearm muscle fatigue in these tasks. Sixteen healthy male volunteers performed eight wrist extensions in different frequency, weight and angle loads while being instructed to keep a dominant upper limb posture as constant as possible. Surface electromyograph (sEMG) was recorded from right extensors digitorium (ED), flexor carpi radialis (FCR), flexor carpi ulnaris (FCU) and extensor carpi ulnaris (ECU) during the task performance. Our results showed that mean power frequency (MPF) and median frequency (MF) values of ED, FCR and FCU were significantly lower (P<0.05) at high frequency load level than at low load level. However, MPF and MF values of ED were significantly lower (P<0.01) in higher load groups of frequency, angle and weight than in lower load groups. These results indicated that the fatigue of muscles varied in the same task, and the number-one risk factor of ECU, ED and FCR was angle load.

Computational Investigations of Small Deploying Tabs and Flaps for Aerodynamic Load Control

The cost of wind-generated electricity can be reduced by mitigating fatigue loads acting on the blades of wind turbine rotors. One way to accomplish this is with active aerodynamic load control devices that supplement the load control obtainable with current full-span pitch control. Techniques to actively mitigate blade loads that are being considered include individual blade pitch control, trailing-edge flaps, and other much smaller trailing-edge devices such as microtabs and microflaps. The focus of this paper is on the latter aerodynamic devices, their time-dependent effect on sectional lift, drag, and pitching moment, and their effectiveness in mitigating high frequency loads on the wind turbine. Although these small devices show promise for this application, significant challenges must be overcome before they can be demonstrated to be a viable, cost-effective technology.

Characteristics of accelerated lifetime behavior of polycarbonate under athermal and high loading frequency conditions

An accelerated lifetime testing (ALT) technique has been developed to determine the long-term fatigue life over millions of cycles for glassy polymers. Dumbbell shaped specimens made of carbon-filled polycarbonate (PC) were tested under fatigue based on the stress–lifetime approach ( S– N curve). Fatigue-induced localized yield-like deformation is considered as the defect leading to fatigue, and its evolution behavior is characterized by a modified energy activation model in which temperature and frequency are considered as fatigue acceleration factors. This model allows the reduced time concept to account for effects of different temperatures and frequencies in short-term fatigue data to determine long-term fatigue life through the use of time–temperature and time–frequency superpositions that are applicable under high frequency and athermal conditions. The experimental results show that the application of the reduced time model can be a possible method for ALT of time-dependent polymeric materials.

Viscoelasticity of biological materials – measurement and practical impact on biomedicine

Mechanical behavior of biological structures under dynamic loading generally depends on elastic as well as viscous properties of biological materials. The significance of "viscous" parameters in real situations remains to be elucidated. Behavior of rheological models consisting of a combination of inertial body and two Voigt's bodies were described mathematically with respect to inverse problem solution, and behavior in impulse and harmonic loadings was analyzed. Samples of walls of porcine and human aorta thoracica in transverse direction and samples of human bone (caput femoris, substantia compacta) were measured. Deformation responses of human skin in vivo were also measured. Values of elastic moduli of porcine aorta walls were in the interval from 10(2)kPa to 10(3) kPa, values of viscous coefficients were in the interval from 10(2) Pa.s to 10(3) Pa.s. The value of shear stress moduli of human caput femoris, substantia compacta range from 52.7 to 161.1 MPa, and viscous coefficients were in the interval from 27.3 to 98.9 kPa.s. The role of viscous coefficients is significant for relatively high loading frequencies - in our materials above 8 Hz in aorta walls and 5 Hz for bones. In bones, the viscosity reduced maximum deformation corresponding to short rectangular stress.

0941 多孔質弾性論による骨梁内間質液流れの理論的検討(S05-3 生体のシミュレーション・モデリング・計測(3),S05 生体のシミュレーション・モデリング・計測)

Interstitial fluid flow in the lacuna-canalicular system induced by bone matrix deformation is considered to play an important role in adaptive bone remodeling. Evidences from recent researches have lead to the hypothesis that osteocytes sense interstitial fluid shear stresses acting on the membranes of their osteocytic processes. In this report, we present an analytical solution of interstitial fluid pressure in a trabecula which has been modeled as a two-dimensional poroelastic material under cyclic axial loading. The solution contains steady-state response and transient response, which depend on nondimensional loading frequency Ω. Our results suggest that: (1) in the steady state, high loading frequency causes a steep fluid pressure gradient near trabecular surfaces; (2) the transient response appears when phase-shift between applied load and fluid pressure is remarkable enough to accelerate the rate of change in fluid pressure.

Fatigue behavior of calcium carbonate filled polypropylene under high frequency loading

Fatigue behavior of polyproylenes filled with three different percentages of CaCO 3 (0%, 20%, and 40%) was investigated in this study. Specimens were produced by injection molding. Tensile properties were also evaluated. Tensile–tensile cyclic loading was applied using MTS 810 test apparatus at different frequencies of 23 and 50 Hz. Effects of cyclic frequency and filler content were examined to their fatigue behavior. S–N diagrams were obtained also with normalization of stress amplitudes with respect to their tensile strengths. Besides that temperature rise curves were presented. It is reported that filler content influences the fatigue performance. Increasing the filler content reduces the fatigue performance of PP from pure to PP40, respectively, if normalization effects are not included. The situation differs if normalization effects are included. Results show that fatigue failure mode occurs with thermal fatigue failure mechanism at both frequencies with necking of specimens and it is excessive at higher frequencies and amplitudes.

Effect of loading frequency on fatigue life and dissipated energy of structural plywood under panel shear load

Wood-based panels are subjected to cyclic panel shear load caused by wind and seismic forces in such an application as the sheathing of bearing walls. The fatigue behavior of structural plywood under panel shear load with two different loading frequencies was examined. Pulsating panel shear load with a triangular waveform and loading frequency of 0.5 or 5 Hz was applied to the plywood specimens. Stress−strain hysteresis loops were measured throughout the fatigue tests. Fatigue life was highly dependent on loading frequency at more than 0.5 stress level. The deterioration of mechanical property and damage accumulation in plywood specimen was observed to be slower at higher loading frequency at more than 0.5 stress level. Analyses based on energy loss suggest that panel shear load with higher loading frequency causes less damage to the plywood specimen during one loading cycle at higher stress level, and that the fatigue damage accumulation causing failure might be dependent on stress level although it seems to be unaffected by loading frequency. Based on these results, a new fatigue failure model for plywood specimen was qualitatively developed by combining Weibull’s weakest link model and Daniels’ fiber bundle model.

A Novel Method to Evaluate the Influence of Hydrogen on Fatigue Properties of High Strength Steels

Abstract In rolling contact fatigue, hydrogen is believed to contribute to early flaking failures under some conditions. Hydrogen diffuses quickly in steels, even at room temperature, thus resulting in its dissipation into the surrounding atmosphere. This condition presents a uniquely difficult challenge for evaluating the intrinsic fatigue properties related to hydrogen embrittlement. In order to compensate for this, we employed ultrasonic fatigue testing at a loading frequency of 20 kHz, because a high loading frequency offsets the rapid hydrogen loss. In this report, the fatigue properties of hydrogen pre-charged JIS-SUJ2 (SAE52100 equivalent) were assessed. The amount of hydrogen was quantitatively measured by thermal desorption analysis. The diffusion coefficient of hydrogen was determined via electrochemical hydrogen permeation testing. These results indicate that the magnitude of fatigue strength reduction is directly proportional to the diffusible hydrogen content. Included with this report is our proposed method for evaluating fatigue strength related to hydrogen embrittlement.

Numerical study on the creep damage development in circumferential notched specimens under cyclic loading

Numerical calculations with Kachanov–Rabotnov damage law have been performed to study the creep damage development of circumferential notched specimens under cyclic loading. The emphasis was placed on the roles of specimen geometry and loading. The results show that the distributions of creep stress and damage are different under cyclic loading from that under a constant amplitude load. Different specimen has different damage distribution. The development of creep damage in the minimum cross-section varies reasonably with the notch radius. The evolution of creep damage is clearly affected by the mean load, loading cycle (frequency) and ratio. With the other two factors unchanged, each of the following three factors, larger mean load, higher loading frequency and smaller loading ratio, can cause the damage to develop faster.

422 超音波疲労試験による強度評価 : 低速負荷状態への適用性と高速負荷状態での疲労特性について(超音波疲労,学術講演)

422 超音波疲労試験による強度評価 : 低速負荷状態への適用性と高速負荷状態での疲労特性について(超音波疲労,学術講演)

Characterisation and wear properties of industrially produced nanoscaled CrN/NbN multilayer coating

Present work deals with morphological, microstructural, compositional and tribological characterisation of nanoscaled multilayer CrN/NbN coating produced by an industrial process presently in development phase. This coating has been applied on steel ring components used in textile plants subjected to contact erosion wear, at high frequency and low load, between the external surface of a ring and a bar where friction coefficient and corrosion resistance are critical. Nanoscaled multilayer structures usually show both high hardness and better wear resistance, correlated with grain refinement, coherency strain hardening, inhibition of dislocation motion, together with an excellent corrosion resistance due to the interruption of coating columnar pinholes and to the combined metal element effect. In order to obtain multilayer structure a non-conventional technique has been set up, consisting of triggering alternatively on Cr or Nb cathodes with appropriate time constant so as to obtain couple of layers of about 5 nm each. In order to satisfy industrial requirements, the process was optimised using a commercially available Cathodic Arc PVD equipment, routinely used to produce conventional CrN coatings. Microstructural and compositional properties were investigated and reported hereby. Low angle X-ray diffraction, Optical and Atomic Force Microscopy, Electron Probe Microscopy (SEM, TEM, SAD, EDS) and Focussed Ion Beam techniques has been used. Defects were also investigated, particularly microdroplets (shape, dimension, density, clustering and other process-sensitive features). Mechanical and tribological properties were characterized by micro and nano hardness measurements, scratch test, ball on ring, ball-cratering and residual stresses evaluation with X-ray diffraction (XRD) sin 2 ψ method. Multilayer coating shows higher H/E ratio, a clear tendency to delaminate during fracture and a different size distribution of microdroplets. As a consequence, CrN/NbN coating results in a lower wear rate with respect to the CrN coating (up to 30%) but only if a normal force dominated stress is applied. Finally, performances results (e.g. wear rate and degradation behaviour) obtained by operating in line two different sets of components (respectively CrN and CrN/NbN coated) are presented; lifetime of industrially produced multilayer coated components has been elongated from 9 to 11 months.

Accceleration of Fatigue Tests of Polymer Composite Materials by Using High-Frequency Loadings

The possibility of using high-frequency loading in fatigue tests of polymer composite materials is discussed. A review of studies on the use of high-frequency loading of organic-, carbon-, and glass-fiber-reinforced plastics is presented. The results obtained are compared with those found in conventional low-frequency loadings. A rig for fatigue tests of rigid materials at loading frequencies to 500 Hz is described, and results for an LM-L1 unidirectional glass-fiber plastic in loadings with frequencies of 17 and 400 Hz are given. These results confirm that it is possible to accelerate the fatigue testing of polymer composite materials by considerably increasing the loading frequency. The necessary condition for using this method is an intense cooling of specimens to prevent them from vibration heating.

On the influence of crack closure on strength estimates of wood

Three well-known duration of load models (Gerhard, Barrett/Foschi, DVM) are considered in this note with respect to their ability to predict lifetime of wood subjected to harmonically varying loads. The result obtained is that they practically predict the same lifetime—which for low frequency loading can be considered approximately true. For higher frequencies, however, this result can be far too overestimated. The reason is that the models considered do not take into account the effect of the crack closure phenomenon (which are the main mechanisms of energy dissipation causing fatigue failure in metals). It is suggested that any of the simple models can be used in practice when low frequency load variations are considered. The DVM model, however, should be preferred because of its ability to predict residual strength, and because of its ‘build in’ flexibility with respect to wood quality and ambient climatic conditions. For high frequency load histories more refined models are required. The extended DVM model, recently developed by the author, is suggested as such a model—especially because it has the potentials of being further developed to consider arbitrary load variations (such as earthquakes). Finally, the widely spread concept of estimating long-term strength by multiplying short time strength with a codified factor (so-called k MOD factor) is discussed. It is concluded that the k MOD -method can be justified in practice with low frequency load variations. When high frequency load histories or unexpected peak loads are considered, the k MOD -method may cause considerably overestimated lifetimes.

Rest insertion combined with high-frequency loading enhances osteogenesis

Mechanical loading can significantly affect skeletal adaptation. High-frequency loading can be a potent osteogenic stimulus. Additionally, insertion of rest periods between consecutive loading bouts can be a potent osteogenic stimulus. Thus we investigated whether the insertion of rest-periods between short-term high-frequency loading bouts would augment adaptation in the mature murine skeleton. Right tibiae of skeletally mature (16 wk) female C57BL/6 mice were loaded in cantilever bending at peak of 800 microepsilon, 30 Hz, 5 days/wk for 3 wk. Left tibiae were the contralateral control condition. Mice were randomly assigned into one of two groups: continuous high-frequency (CT) stimulation for 100 s (n = 9), or 1-s pulses of high-frequency stimuli followed by 10 s of rest (RI) for 100 s (n = 9). Calcein labels were administered on days 1 and 21; label incorporation was used to histomorphometrically assess periosteal and endosteal indexes of adaptation. Periosteal surface referent bone formation rate (pBFR/BS) was significantly enhanced in CT (>88%) and RI (>126%) loaded tibiae, relative to control tibiae. Furthermore, RI tibiae had significantly greater pBFR/BS, relative to CT tibiae (>72%). The endosteal surface was not as sensitive to mechanical loading as the periosteal surface. Thus short-term high-frequency loading significantly elevated pBFR/BS, relative to control tibiae. Furthermore, despite the 10-fold reduction in cycle number, the insertion of rest periods between bouts of high-frequency stimuli significantly augmented pBFR/BS, relative to tibiae loaded continually. Optimization of osteogenesis in response to mechanical loading may underpin the development of nonpharmacological regiments designed to increase bone strength in individuals with compromised bone structures.

Effect of Frequency on Giga-Cycle Fatigue Properties for Ti-6Al-4V Alloy

The effect of frequency on giga-cycle fatigue properties was investigated for 900-MPa-class Ti-6 Al-4 V alloy of three heats (heat A-C) with smoothed specimen and with 0.3 mm-hole-notched specimens. Fatigue tests were carried out at frequencies of 120 Hz, 600 Hz and 20 kHz, using electromagnetic resonance, high-speed servohydraulic and ultrasonic fatigue testing machines, respectively. Heats A and B developed internal fractures, and in that case, frequency effects were negligible. On the other hands, heat C revealed only surface fracture. In this case, high frequency tests showed higher fatigue strength, i.e. frequency effects were not negligible. The tests using notched specimens hardly not revealed frequency effects regardless of the heats. The frequency effect observed in the cases of surface fracture were considered to relate to the delay of local plastic deformation reacting to the high frequency loading, since the temperature increase of specimens were successfully suppressed. The delay of plastic deformation was found to be reduced in the notched specimens, because of stress concentration and limitation of plastic deformation zone. In turn, the significant conclusion of this research was that the high frequency tests could be applicable not only to internal fracture but also to notched problem, while those were not to surface fracture of smoothed specimens.

Mechanotransduction in the cortical bone is most efficient at loading frequencies of 5–10 Hz

A dose-response relationship has been shown between loading frequency and cortical bone adaptation for frequencies of up to 10 Hz, and is presumed to persist with further increases in frequency. Studies herein aimed to investigate cortical bone adaptation to loading frequencies of 1, 5, 10, 20 and 30 Hz. Two studies were performed in adult C57BL/6 mice using the ulna axial compression-loading model. In the first study, the histomorphometric response of the ulna was studied when loaded for 120 cycles day −1 for 3 days at one of the five frequencies and one of two load magnitudes (1.5 or 2.0 N). In the second study, the changes in ulna geometry and mechanical properties were studied following loading for 5 min day −1, 3 days week −1 for 4 weeks at one of the five frequencies and one of two load magnitudes (1.0 or 1.6 N). Preliminary strain gauge measurements showed that frequency had no effect on mechanical strain per unit load. In study 1, loading frequency significantly influenced bone adaptation when loading at 2.0 N, with loading at 10 Hz resulting in significantly greater adaptation than with loading at other frequencies. In study 2, loading frequency significantly influenced the change in geometry when loading at 1.6 N, with loading at 5, 10 or 30 Hz resulting in significantly greater change than with loading at 1 Hz. Loading at 5 Hz also resulted in significantly greater change than with loading at 20 Hz. No frequency effect was found on any of the mechanical properties at either load. Overall, we found cortical bone adaptation to mechanical loading to increase with increasing loading frequency up to 5–10 Hz and to plateau with frequencies beyond 10 Hz. The mechanism for this nonlinear frequency response is not known; however, based on strain gauge measurements, we do not believe it resulted from dampening associated with high frequency loading through the flexed carpal joint. The obtained findings may relate to the mechanism of mechanotransduction within the bone. This requires further investigation.

A new super convergent thin walled composite beam element for analysis of box beam structures

In this paper, a new composite thin wall beam element of arbitrary cross-section with open or closed contour is developed. The formulation incorporates the effect of elastic coupling, restrained warping, transverse shear deformation associated with thin walled composite structures. A first order shear deformation theory is considered with the beam deformation expressed in terms of axial, spanwise and chordwise bending, corresponding shears and twist. The formulated locking free element uses higher order interpolating polynomial obtained by solving static part of the coupled governing differential equations. The formulated element has super convergent properties as it gives the exact elemental stiffness matrix. Static and free vibration analyses are performed for various beam configuration and compared with experimental and numerical results available in current literature. Good correlation is observed in all cases with extremely small system size. The formulated element is used to study the wave propagation behavior in box beams subjected to high frequency loading such as impact. Simultaneous existence of various propagating modes are graphically captured. Here the effect of transverse shear on wave propagation characteristics in axial and transverse directions are investigated for different ply layup sequences.

Effect of dynamic hydrostatic pressure on rabbit intervertebral disc cells

The pathogenesis of vibration-induced disorders of intervertebral disc at the cellular level is largely unknown. The objective of this study was to establish a method to investigate the ranges of constructive and destructive hydrostatic loading frequencies and amplitudes in preventing or inducing extracellular disc matrix degradation. Using a hydraulic chamber, normal rabbit intervertebral disc cells were tested under dynamic hydrostatic loading. Monolayer cultures of disc outer annulus cells and 3-dimensional (3-D) alginate cultures of disc nucleus pulposus cells were tested. Effects of different loading amplitudes (3-D culture, 0–3 MPa; monolayer, 0–1.7 MPa) and frequencies (1–20 Hz) on disc collagen and protein metabolism were investigated by measuring 3H-proline-labeled proteins associated with the cells in the extracellular matrix and release of 3H-proline-labeled molecules into culture medium. High frequency and high amplitude hydrostatic stress stimulated collagen synthesis in cultures of outer annulus cells whereas the lower amplitude and frequency hydrostatic stress had little effect. For the same loading duration and repetition, neither treatment significantly affected the relative amount of protein released from the cell layers, indicating that protein degradation and stability were unaffected. In the 3-D nucleus culture, higher amplitude and frequency increased synthesis rate and lowered degradation. In this case, loading amplitude had a stronger influence on cell response than that of loading frequency. Considering the ranges of loading amplitude and frequency used in this study, short-term application of high loading amplitudes and frequencies was beneficial in stimulation of protein synthesis and reduction of protein degradation.

Rheological evaluation of ethylene vinyl acetate polymer modified bitumens

The morphological, thermal and fundamental rheological characteristics of ethylene vinyl acetate (EVA) copolymer modified bitumens are studied in this paper. Nine plastomeric EVA polymer modified bitumens (PMBs) have been produced by laboratory mixing bitumen from three sources with an EVA copolymer at three polymer contents. The morphology, thermal properties and rheological characteristics of the EVA PMBs have been analysed using fluorescent microscopy, differential scanning calorometry and dynamic mechanical analysis using a dynamic shear rheometer, respectively. The results of the investigation indicate that EVA polymer modification increases binder stiffness and elasticity at high service temperatures and low loading frequencies with the degree of modification being a function of bitumen source, bitumen–polymer compatibility and polymer concentration. Filler type modification is evident at low temperatures, temperatures above the melting temperature of the semi-crystalline EVA copolymer and for those modified binders that do not exhibit a dominant polymer network.