High Frequency Impact Loading Research Articles

Signal Wrap-Around Free Spectral Element Formulation For Multiply Connected Finite 1-D Waveguides

This paper presents a novel spectral element formulation based on Numerical Laplace Transforms for the wave propagation of multiply connected finite 1-D waveguides, based on the first order shear deformation theory. The present formulation overcomes the severe short-comings of Fourier transform based spectral element formulation which has serious problems associated with the signal wrap-around while analysing finite domain structures. The real part of the Laplace variable which provides damping to the wavenumber solution, is characterized by Wilcox and Wedepohl approaches. The effect of this damping alters the wave dispersion and introduces certain interesting phenomenon that is not seen in the undamped waveguides. Problems involving wave propagation analysis are solved on finite multiply connected waveguides of varied complexity to demonstrate the efficiency of the formulated element. In most of the examples, the presence of signal wrap-around in Fourier domain based spectral element is brought out. With this approach, any large structural network, consisting of 2-D either metallic or composite finite length waveguides, under high frequency impact loading can be analyzed with very low computational cost.

Field experiment and numerical simulation investigation on the mechanical properties of ballast bed with elastic sleepers

Under high-frequency impact loading, the ballast bed is prone to ballast crushing, deterioration, and other adverse effects. The use of elastic sleepers is an effective way to solve this problem. In order to investigate the macro-meso static and dynamic characteristics of the ballast bed with elastic sleepers, field static and dynamic experiments were carried out. A simulation model of the elastic sleeper-ballast bed based on DEM-MFBD coupling is established. The effects of laying elastic sleepers on the mass state, vibration characteristics, and contact relationship of the ballast bed are carefully analyzed. The results show that compared to the ordinary sleeper ballast bed, the lateral resistance and the resistance work of the ballast bed with elastic sleepers are reduced by 18.40% and 18.72%, respectively. The vibration acceleration of the rail and sleeper in the elastic sleeper line increases by 10.07% and 47.91%; while the vibration acceleration of the ballast bed decreases by 18.99%. The maximum energy frequency of the rail, sleeper, and ballast bed all decreases. Under the action of train load, the peak value of dynamic displacement of the elastic sleeper is 23.28% higher than that of the ordinary sleeper. The elastic sleeper can increase the number of contact points on the unit contact area between the bottom of the sleeper and the ballast particles, reduce the average contact force between the ballast particles, and mitigate the vibration impact of the sleeper on the ballast bed.

Study on High-Frequency Fatigue Properties of PVD AlTiN Coating of Cutting Tool

Based on ultrasonic vibration-assisted mode, high-frequency impacting tests with diamond indenter at different amplitudes on AlTiN coating of cutting tool are carried out. The microstructure and morphology are obtained by scanning electron microscopy (SEM) and 3D profiler. The failure mechanism of coating under impact is analyzed. The high frequency fatigue property of the coating is analyzed. The results show that: lateral crack could be seen under impact test; the maximum tensile stress occurs close the edge of the contact zone of impact center; AlTiN coating is easy to emerge the fatigue damage under the high-frequency impact loading, and the adhesion strength of the coating and substrate interface affects the impact fatigue strength of cutting tool coating.

High-Bandwidth AFM-Based Rheology Reveals that Cartilage is Most Sensitive to High Loading Rates at Early Stages of Impairment

Utilizing a newly developed atomic-force-microscopy-based wide-frequency rheology system, we measured the dynamic nanomechanical behavior of normal and glycosaminoglycan (GAG)-depleted cartilage, the latter representing matrix degradation that occurs at the earliest stages of osteoarthritis. We observed unique variations in the frequency-dependent stiffness and hydraulic permeability of cartilage in the 1 Hz-to-10 kHz range, a frequency range that is relevant to joint motions from normal ambulation to high-frequency impact loading. Measurement in this frequency range is well beyond the capabilities of typical commercial atomic force microscopes. We showed that the dynamic modulus of cartilage undergoes a dramatic alteration after GAG loss, even with the collagen network still intact: whereas the magnitude of the dynamic modulus decreased two- to threefold at higher frequencies, the peak frequency of the phase angle of the modulus (representing fluid-solid frictional dissipation) increased 15-fold from 55 Hz in normal cartilage to 800 Hz after GAG depletion. These results, based on a fibril-reinforced poroelastic finite-element model, demonstrated that GAG loss caused a dramatic increase in cartilage hydraulic permeability (up to 25-fold), suggesting that early osteoarthritic cartilage is more vulnerable to higher loading rates than to the conventionally studied “loading magnitude”. Thus, over the wide frequency range of joint motion during daily activities, hydraulic permeability appears the most sensitive marker of early tissue degradation.

THERMOELASTIC WAVE PROPAGATION IN ANISOTROPIC LAYERED MEDIA — A SPECTRAL ELEMENT FORMULATION

The generalized dynamic theory of thermoelasticity is used to investigate the propagation of plane harmonic waves in anisotropic layered media using the Spectral Finite Element Method (SFEM). Two different theories, due to Lord and Shulman (LS model) and Green and Lindsay (GL model), are considered for spectral layer element (SLE) formulation. The element is formulated in the frequency domain and the exact solution of the transformed equation is used as the interpolating polynomial of the unknown variables, which are the mechanical displacements and the thermal field. Consequently, single element captures the essential wave response of a layer of arbitrary thickness, when subjected to high frequency impact loading. This element is used to study the characteristic of the thermal wave, also known as the second sound, using nominal computational resource. The study is directed towards finding the justification of using the non-classical model of thermoelasticity and the effect of different parameters on the overall thermal and mechanical field. Stress state within a layered media with general ply-stacking is studied and the limitation of the classical theory in stress prediction is shown. Thermal wave propagation due to temperature burst and heat flux is captured and their properties are discussed.

Wave propagation in inhomogeneous layered media: solution of forward and inverse problems

Wave propagation in anisotropic inhomogeneous layered media due to high frequency impact loading is studied using a new Spectral Layer Element (SLE). The element can model functionally graded materials (FGM), where the material property variation is assumed to follow an exponential function. The element is exact for a single parameter model which describes both moduli and density variation. This novel element is formulated using the method of partial wave technique (PWT) in conjunction with linear algebraic methodology. The matrix structure of finite element (FE) formulation is retained, which substantially simplifies the modeling of a multi-layered structure. The developed SLE has an exact dynamic stiffness matrix as it uses the exact solution of the governing elastodynamic equation in the frequency domain as its interpolation function. The mass distribution is modeled exactly, and, as a result, the element gives the exact frequency response of each layer. Hence, one element may be as large as one complete layer which results in a system size being very small compared to conventional FE systems. The Fast-Fourier Transform (FFT) and Fourier series are used for the inversion to the time/space domain. The formulated element is further used to study the stress distribution in multi-layered media. As a natural application, Lamb wave propagation in an inhomogeneous plate is studied and the time domain description is obtained. Further, the advantage of the spectral formulation in the solution of inverse problems, namely the force identification and system identification is investigated. Constrained nonlinear optimization technique is used for the material property identification, whereas the transfer function approach is taken for the impact force identification.

A spectrally formulated finite element for wave propagation analysis in layered composite media

Wave propagation in orthotropic layered composite media due to high frequency impact loading is studied using a new spectral layer element (SLE). This novel element is formulated using the method of partial wave techniques (PWT) in conjunction with linear algebraic methodology. The matrix structure of finite element (FE) formulation is retained, which substantially simplifies the modeling of multi-layered structure. The developed SLE has an exact dynamic stiffness matrix, as it uses exact solution to the governing elastodynamic equation in frequency domain as its interpolation function. Due to this, the mass distribution is modeled exactly, and as a result, the element gives exact frequency response of each layer. Hence, one element may be as large as one complete layer and as a result system size is very small compared to conventional FE system sizes. The fast-Fourier transform (FFT) and Fourier series are used for inversion to the time/space domain. The formulated element is further used to study the stress distribution in a multi-layered media. As a natural application, Lamb wave propagation in composite plate is studied for different ply-angle and time domain description is obtained. Further, advantage of the spectral formulation in impulse force identification is demonstrated.

Response of plasma sprayed alumina–titania ceramic composite to high frequency impact loading

The life of mechanical components used for tribological and other applications, where surfaces are exposed to different types of loading, can be significantly enhanced through deposition of ceramic/ceramic composite on the surfaces. Among various spray deposition techniques, plasma spraying is most widely used. However, coatings developed through this technique need to be evaluated for performances under different conditions. The main aim of the present investigation is to study the response of the plasma-sprayed alumina–titania (AT-13) ceramic composites subjected to high frequency impact loading, in both as-sprayed and microwave-treated (post-processed) conditions in terms of indentation scar dimension and acoustic emission (AE) signals emitted by the impulsed material. The significance of AE monitoring for evaluation of critical load and duration for the onset of cracking of spray deposits is illustrated. Results show critical load and duration for the onset of cracking as 10 N and 3 min, respectively, in both cases. Results are discussed with illustrations.

Response of plasma-sprayed alumina–titania ceramic composite to high-frequency impact loading

The life of mechanical components used for tribological and other applications where surfaces are exposed to different types of loading can be significantly enhanced through deposition of ceramic/ceramic composite on the surfaces. Among various spray deposition techniques, plasma spraying is most widely used. However, coatings developed through this technique need to be evaluated for performances under different conditions. The main aim of the present investigation is to study the response of the plasma-sprayed alumina–titania (AT-13) ceramic composites subjected to high-frequency impact loading, in both as-sprayed and microwave-treated (post-processed) conditions in terms of indentation scar dimension and acoustic emission (AE) signals emitted by the impulsed material. The significance of AE monitoring for evaluation of critical load and duration for the onset of spray deposits cracking is illustrated. Results show critical load and duration for the onset of cracking as 10 N and 3 min, respectively, in both cases. Results are discussed with illustrations.

SPECTRAL-ELEMENT-BASED SOLUTIONS FOR WAVE PROPAGATION ANALYSIS OF MULTIPLY CONNECTED UNSYMMETRIC LAMINATED COMPOSITE BEAMS

A spectrally formulated element that has three degrees of freedom (axial motion, transverse motion and rotation) per node for analysis of slender multiply connected composite beams under high-frequency impact loading is presented. The model represents a linear distributed parameter system. The element has an exact dynamic stiffness matrix as it is derived from exact solution to the governing wave equation in frequency domain. The present element can handle any kind of cross-sectional unsymmetry due to ply orientation. The results from the present formulation are compared with the results from a time domain finite element model based on linear axial and cubic transverse displacement field. It is shown that the formulated element is able to predict the reflected and transmitted response accurately through a rigid angle joint for varying joint angles and axial–flexural coupling. Also, the effect of ply-stacking sequence on dynamic response is illustrated. With this approach, a very large composite 2-D beam network can be analyzed under high-frequency impact loading with much smaller system size and lower computational cost compared to time domain finite element method.