Fauziah Mat

Impact Response of Thin-Walled Tubes: A Prospective Review

Thin-walled structures have been widely used in various structural applications asimpact energy absorbing devices. During an impact situation, thin-walled tubesdemonstrate excellent capability in absorbing greater energy through plastic deformation. In this paper, a review of thin-walled tubes as collapsible energy absorbers is presented.As a mean of improving the impact energy absorption of thin-walled tubes, the influence of geometrical parameters such as length, diameter and wall thickness on the response of thin-walled tubes under compression axial loading are briefly discussed. Several design improvements proposed by previous researchers are also presented. The scope of this review is mainly focus on axial deformation under quasi-static and dynamic compressive loading. Other deformations, such as lateral indentation, inversion and splitting are considered beyond the scope of this paper. This review is intended to assist the future development of thin-walled tubes as efficient energy absorbing elements.

Hydrothermal effects on the burst strength of impacted glass fiber/epoxy composite pipes

Abstract The effects of hydrothermal aging and low velocity impact loading on E-glass fiber/epoxy composite pipes subjected to a continuous internal pressure were experimentally investigated in this paper. The pipes were manufactured by the commonly adopted filament winding method, which is consisting of six antisymmetric layers with (±55°)3 winding angles. Then, they were immersed in tap water at intervals of 500, 1000 and 1500 h. Low velocity impact tests were performed at three different energy levels (5, 7.5 and 10 J), followed by internal pressure testing. The results showed that both impact energy levels and water immersion time have significantly affected the burst strength of the pipe. It also indicated that the peak force and displacement increased with the increase of impact energy. During the burst pressure tests, weepage and eruption failures were observed.

Experimental and Numerical Analysis of Foam-Filled Aluminum Conical Tubes Subjected to Oblique Impact Loading

Abstract This study aims to investigate the response of AA6061-T6 conical tubes under oblique impact loading, for variations in filler density and tube material by using experimentally validated model. Good correlations between the numerical and experimental results were observed. The initial peak force and dynamic force increase from AA6061-T6 to carbon steel tubes and further increase with increasing filler density, leading to increased energy absorption capacity. Conversely, the initial peak force and dynamic force of empty and foam-filled AA6061-T6 conical tubes decrease with the introduction of oblique loading as the load angle increases from 0° to 20°, leading to reduced energy absorption capacity. Carbon steel is relatively more advantageous compared with AA6061-T6 in terms of energy absorption, whereas AA6061-T6 is comparable with carbon steel because of its lower initial peak force.

Spectral Density Analysis: Theta Wave as Mental Stress Indicator

This paper aims to investigate the correlation between mental tasks and the emanated theta and alpha brain waves. Electroencephalogram (EEG) signal is a highly random, complex and non linear in nature. The analysis of Electroencephalogram remains problematic due to the limited understanding of the signal origin. In spite of these shortcomings, the EEG is valuable tool to evaluate the overall cerebral activity. Advanced signal processing technique is required to extract hidden features carried by the signal. These features are useful to determine the mental state condition. Analysis was carried out using five adult right handed subjects, healthy and non smokers. Subjects were asked to perform mental arithmetic (MA) task in a period of time to induce the mental stress. To ensure the subjects performed all the MA tasks with full effort, a honorarium was given for every correct response. Using Burg’s Method, power spectral density (PSD) were extracted from the emanate brain signal. Statistical analysis using correlation was performed and a positive relationship (r=0.625, p<0.05) has been observed between the highest PSD theta waves to the mental stress condition.

Improved Model for Impact of Viscoplastic Bodies

This study proposes an improved viscoplastic impact model that calculates impact response for direct impact between two compact bodies. The proposed model employs spring and viscous elements that represent the energy loss due to plastic deformation and stress wave propagation, respectively. The impact response is calculated by solving differential equations through analytical and numerical methods. This model can accurately predict impact response for low, moderate and high impact speeds.

Classification of materials by modal analysis and neural network

Modal analysis is the study of dynamic characteristic of structures induced by vibrational excitation. Under modal excitation, three important parameters namely natural frequency, damping ratio and mode shape associated with the structural properties are acquired. These modal parameters are used as the extracted features for classification on artificial neural network. This paper presents an experimental investigation of two different kinds of materials by implementation of modal analysis along with the integration of neural network for materials classification. The experimental modal analysis is done using the LMS instruments and software where Fast Fourier Transform (FFT) and Frequency Response Function (FRF) are used to extract the mentioned modal parameters. The extracted parameters are used as the classification process feature of the neural network. Multi-layer Perceptron (MLP) is used as the mapping model of the network. The technique adopted for the system is the Levenberg-Marquadt (LM) and Scaled Conjugate Gradient (SCG) Backpropagation technique.

Fracture Behavior of Intermetallic Compound (IMC) of Solder Joints Based on Finite Elements’ Simulation Result

The development of microelectronic industry has made solder joints failure a major reliability issue. From literature, many researchers have identified that intermetallic compounds (IMC) layer contribute greatly to the fracture of solder joint. This paper presents a finite element modeling of solder butt joints IMC layer failure based on displacement extrapolation method (DEM). Conceptual study on single edge crack of IMC solder joints is presented. A FE analytical model is proposed to be used in difference range of crack length to understand the fracture behavior of solder joint of IMC layer. The simulation results show that soldering material become less tough if greater crack length is present in the joint. It also seen that the thicker IMC has slightly reduced the stress intensity factor on the crack tip but the change from solder to IMC layer decrease the solder joint fracture toughness.

Influence of ceramic dental crown coating substrate thickness ratio on strain energy release rate

This paper presents the analysis of coating substrate thickness ratio effect on the crown coating fracture behaviour. The bi-layer material is examined under four point bending with pre-crack at the bottom of the core material by using finite element. Three different coating thickness of core/substrate was tested which is 1:1, 1:2 and 2:1. The fracture parameters are analysed based on bilayer and homogenous elastic interaction. The result shows that the ratio thickness of core/veneer provided a significant effect on energy release rate.

Effect of meshing element on J-integral value for homogenous crown fracture behavior

This paper presents the meshing strategy schemes to solve the inconsistency of J-integral value for stress intensity factor (SIF) evaluation using finite element (FE) analysis. The effect of meshing element types on homogenous crown fracture behavior is investigated using developed ANSYS APDL code. For simplicity of the analysis, complex geometry of the dental crown was simplified into four point bending model. Two-dimensional FE single edge notch four-point bending model on In-Ceram Alumina was implemented in this study. A series of convergence analysis was performed to reveal the effect of various element types and combination quadrilateral and triangular elements on J-Integral for 10 contours. The meshing region was divided by two; non-critical part was set as global region and the critical part which is the pre-cracked area was set as local region. The effect of meshing size and combination of meshing shape were observed. For validation, the results of SIF through FE analysis using J-Integral have bee...

Influence of local meshing size on stress intensity factor of orthopedic lag screw

Linear elastic fracture mechanics (LEFM) concept is generally used to study the influence of crack on the performance of structures. In order to study the LEFM concept on damaged structure, the usage of finite element analysis software is implemented to do the simulation of the structure. Mesh generation is one of the most crucial procedures in finite element method. For the structure that crack or damaged, it is very important to determine the accurate local meshing size at the crack tip of the crack itself in order to get the accurate value of stress intensity factor, KI. Pre crack will be introduced to the lag screw based on the von mises’ stress result that had been performed in previous research. This paper shows the influence of local mesh arrangement on numerical value of the stress intensity factor, KI obtained by the displacement method. This study aims to simulate the effect of local meshing which is the singularity region on stress intensity factor, KI to the critical point of failure in screw....