Key Engineering Materials Vols. 462-463

Abstract: Since the method of performing displacement measurement and stress assessment of material by non-contact comes to capture the spotlight, study of the digital image correlation method which adopted the pattern-matching method for asking for displacement by deformation of a surface speckle pattern has been advanced. When the configuration for an analysis was settled in the rectangle and the square region, the whole-field mesh generation was also possible, but when it became a complicated configuration, the background etc. entered and mesh generation was affected. In order to solve such a problem, even if the object for an analysis was a complicated configuration, it aimed at generating a mesh automatically and obtaining appropriate analysis output in the displacement analysis and stress analysis using the generated mesh. In addition, the validity of the result was verified by the comparison with the finite element method. By this study, the convenience and availability of the digital image correlation method was improved remarkably, and it became clear to become a leading tool in health monitoring.

Abstract: Health assessment of a structure is various. In architecture and civil engineering, a natural frequency is calculated by conducting the frequency analysis of the response waveform of the structure. The natural frequency measurement has been performed with a speedometer, an acceleration sensor and a laser Doppler velocimeter, but possibility of the evaluation of the natural frequency by the digital image correlation method was examined mainly. In the case of the digital image correlation method, if a picture and time are connected, the displacement response of the structure is obtained. Hence, we considered the applicability of it to the vibration phenomenon. We carried out displacement comparison with the finite element method, and then investigated the accuracy of the displacement response waveform. Furthermore, it succeeded in assessment of the natural frequency by the frequency analysis. The health assessment of the structure is possible by using the digital image correlation method and frequency analysis.

Abstract: This paper presents a comparison work between the filtering methods of fatigue strain loadings using the frequency spectrum and the wavelet transform (WT), in which a raw loading signal can be simplified for purpose of simulation. For this reason, the Fast Fourier Transform (FFT) and the Morlet wavelet algorithms were used in order to transform the vibrational fatigue time series into the frequency domain signal, leading to the observation of the frequency characteristics of the signal. To retain high amplitude cycles in the FFT algorithm, a low pass filter technique was applied to remove the high frequency signals with small amplitude that are non-damaging. The departure of high frequency information smoothed the low amplitude cycles at high frequency events in the fatigue signal. The Butterworth filter was selected as the most efficient filter design as it retained most of the fatigue damage and also had the capability to remove 30 % of the original low amplitude cycles. On the other hand, the Morlet wavelet managed to remove 64 % of the original 59 second signal. This wavelet filtering method removed 34 % more than the similar procedure applied through the FFT approach. Hence, this fatigue data summarising algorithm can be used for studying the durability characteristics of automotive components.

Abstract: Dynamic fracture properties of most engineering materials are evaluated using Charpy test. The dynamic responses of the standard Charpy impact machine are experimentally studied using the relevant data acquisition system in order to obtain the impact response. For this reason, strain gauges were connected to the data acquisition set and it was then attached to the striker for the signal collection. The numerical analysis by mean of the finite element method has been used to obtain the findings. The standard Charpy modelling using the aluminium 6061 material was used in order to obtain strain responses on the striker during the impact simulation. A standard Charpy specimen aluminium 6061 was used for the experimental impact testing. A power spectrum density (PSD) approach is then used to convert a signal from the time domain to the frequency domain using the fast Fourier transform (FFT) method. Related parameters on strain signals, power spectrum density (PSD), comparison between experiment and finite element analysis, and the relationship between all the parameters were finally correlated and discussed. It was found that the finite element results are validated to show simulated time histories and its PSD compared with experimental work.

Abstract: The special clamp for fatigue of shaft under bending, torsion, and bending-torsion that used on the fatigue machine is designed and manufactured. The low-cycle fatigue experiments of shaft with annular notch under cantilever bending have been made. Through experiments and analysis, the effects of tip radius, depth and open angle of notch on low cycle fatigue life of shaft with annular notch under cantilever bending are obtained. The method and results will play an important role on the fatigue life prediction and anti-fatigue design.

Abstract: Under the continuing action of temperature stress and load vehicle, the crack in cement stabilized aggregate base can easily reflect up into the asphalt surface layer, affecting driving condition and then affecting the fatigue life of pavement. On the basis of fracture mechanics, taking center crack loaded with uniform tensile stress as study state, methods were derived to calculate the stress intensity factor (abbreviated in the following “SIF”) of the crack at the bottom of asphalt layer using weight function theory and method of Petroski and Achenbach. Through the comparison of different SIFs under different conditions, factors affecting the SIFs such as crack length, load conditions, modulus ratio between base and surface layer and different jointed conditions were studied. To facilitate comparison, taking completely smooth and completely continuous as study boundary conditions. According to calculation results, factors mentioned above all influence the SIF values of the crack at the bottom of asphalt layer greatly, among which jointed condition between base and surface layer has the most important influence. The SIF values of the completely smooth interface is several times that of the completely continuous interface. We can take measures to improve the jointed condition between the asphalt surface layer and the cement stabilized aggregate base thus can reduce reflection crack effectively.

Abstract: A material with perovskite structure, lanthanum strontium cobaltite ferrite, La0.6Sr0.4Co0.2Fe0.8O3- (LSCF6428) has gained attention as a cathode component for intermediate to low temperature solid oxide fuel cells (IT-LTSOFCs). In this study, LSCF6428 films were developed via the electrophoretic deposition (EPD) technique with the use of an aqueous solvent. 1 wt% of LSCF6428 was suspended in deionised water for the preparation of the EPD suspensions. The EPD process at applied voltages of between 3 to 7 V and deposition times of 3 to 10 minutes has been found to be able to deposit LSCF6428 films. Additionally, the use of additives such as starch and polymethyl methacrylate (PMMA) was found to effectively improve the quality of the deposited films. It is concluded that the applied voltage, deposition time and the addition of additives play important roles that affect the morphology and weight of the deposited films.

Abstract: A Finite Element (FE) programme for crack propagation was developed by using a source code written in the FORTRAN language to evaluate the Stress Intensity Factors (SIFs) and to predict the crack propagation trajectory. In this study, a Central Cracked Plate (CCP) with two holes under mixed mode (I & II) loading conditions is considered. Finite Element Analysis (FEA) combined with the concepts of Linear Elastic Fracture Mechanics (LEFM) provides a practical and convenient means to study the fracture and crack growth of the solid materials. The Displacement Extrapolation Technique (DET) is performed on this work in order to compute the stress intensity factors (SIFs) during the crack propagation. Additionally, to validate the capability and the reliability of this developed FE programme, the results of the current study are compared with experimental results from the literature.

Abstract: The indentation method is able for use in determining the fracture properties of materials. In the present work, a source code programme for two-dimensional finite element method has been applied to simulate cracking behaviour during indentation on brittle specimens under static loading conditions. The study also aims to predict the crack propagation trajectories under Linear Elastic Fracture Mechanics (LEFM). The source code is written in FORTRAN language. The FE mesh is generated using an advancing front method, where the generation of the background mesh and the construction of singular elements are also added to this developed programme to realise the fracture analysis. In evaluating the accuracy of the crack path predictions, the results are compared and validated with the sets of experimental data of relevant published research work. Upon comparison, it is proven that this developed source code programme is capable of demonstrating the crack indentation in terms of predicting the crack trajectories as well as the evaluation of the stress intensity factors.

Abstract: A model of notched shaft in which the crack, V-notch, U-notch and arc were described as notch uniformly, was put forward. The stress field near the notch tip of notched shaft was given using quadric coordinate system by selecting an appropriate displacement function at first, and then the stress field in Cartesian co-ordinates system was obtained. The 3-D model was set up and the local stress and strain near the tip of notch was calculated by using finite element software ANSYS, and the effect of notched parameters of shaft on stress was analysed. The results show that there is a small region, in which the effect of the tip radius and depth on the stresses is obviously. The effect of an open angle of notch on stress is very small. The smaller the ratios between the tip radius and depth of notch, the larger the stress concentrations near the tip of notch.