Nik Abdullah Nik Mohamed

In-plane Tensile Behavior of Shape Memory Alloy Honeycombs with Positive and Negative Poisson’s Ratio

This work illustrates the manufacturing and tensile testing of a novel concept of honeycomb structures with hexagonal and auxetic (negative Poissons ratio) topology, made of shape memory alloy core material. The honeycombs are manufactured using Nitinol ribbons having 6.40 mm of width and 0.2 mm of thickness. The ribbons were inserted in a special dye using cyanoacrilate to bond the longitudinal strips of the unit cells. Tensile tests at room temperature (full martensite) were performed on the honeycombs. Finite element models of the honeycomb assemblies under tensile loading have been developed using nonlinear beam elements from a commercial code. Good agreement is observed between numerical nonlinear simulations and the experimental results.

Shape memory alloys honeycomb: design and properties

This work illustrates the design, manufacturing and tensile testing of a novel concept of honeycomb structure made of shape memory alloy (SMA) core material. The honeycomb is manufactured using SMA Nitinol ribbons inserted in a special dye and using cyanoacrilate to bond the longitudinal strips of the unit cells. Analytical and Numerical FE models of the ribbons are developed to predict the homogenized properties and the overall tensile test behavior of the honeycomb sample. Good agreement is observed between numerical nonlinear simulations and experimental results carried out at room temperature (martensite phase).

Viscoelastic material models in peridynamics

In this paper we propose a new viscoelastic material model within the framework of the nonlocal peridynamic formulation of continuum mechanics. Using Fourier- and Laplace-transforms we derive integral-representation formulas using a Greens function approach for both local and nonlocal viscoelasticity. As an example we calculate the local and nonlocal response of an infinite viscoelastic bar impacted by a point load. We show both analytically and numerically that local viscoelasticity is recovered in the limit as the peridynamic lengthscales become small.

On the crushing behavior of foam-filled composite tubes under compressive loading

The present papers determine the effect of composite pultrusion square tubes E-glass polyester empty and polymeric foam-filled subjected to axial compressive loading. The specimens of square composite pultrusion were compressed experimentally under axial loadings to examine the effect of empty and polymeric foam-filled with different wall-thickness. The wall-thickness was used in this study were 2.1 and 2.4 mm. During the experimental observation, three characteristic crushing stages were identified as initial peak load, progressive crushing and compaction zone stages. The composite pultrusion square tube profile were analyzed and investigated in terms of crashworthiness parameters to meet the improvement of structural material widely used in automobile, aerospace and marine applications. Result obtained from experimental analysis such that initial peak load, mean load, energy absorption and specific energy absorption versus displacement curves were compared for each specimen. Results showed that the tubes energy absorption was affected significantly by different tube profile. It is also found that the polymeric foam-filled exhibit superb crashworthy structure on specific absorbed energy and the amount of initial peak load, mean load and absorbed energy recorded higher than the empty tube profiles.

A Preliminary Study on the Sound Absorption of Date Palm Fibers

In this study sound absorption properties of a single layer date palm fiber has been investigated. Experimental measurements were carried out using impedance tube at the acoustic lab, Faculty of Engineering, Universiti Kebangsaan Malaysia. A constant thickness sample was considered in this study.The results show that the values of absorption coefficient are small at low frequencies, rising with increasing frequency but exhibiting a significant peak. The low density of the sample is reflected in the overall sound absorption performance of the date palm fiber. An improvement in the sound absorption in the lower frequency range was achieved by backing the sample with air gap of different thicknesses of 10 mm, 20 mm and 30 mm. The increase in the air gap thickness moved the peaks toward lower frequencies and improved the low frequencies absorption. However, that increase coincided with reduction of absorption in medium frequency range and reduction in the absorption peak. A linear relationship was found between sound absorption peaks and the air gap thickness. The performance of the date palm fiber can be improved by increasing the density of the sample, using different sample thicknesses and adding perforated plates to the date palm fiber panel.

Effects of electromagnetic absorption toward a human head due to variation of its dielectric properties at 900 and 1900 MHz with different antenna substrates

Abstract The aim of this paper is to analyze the effects of electromagnetic (EM) energy absorption at 900 and 1900 MHz when the human head’s dielectric properties are varied. This radiation is measured in terms of specific absorption rate (SAR). The characteristics of the helical antenna and its substrates with variation of the human head dielectric properties were simulated via the finite-difference time domain (FDTD) method using the CST Microwave studio. The human head dielectric properties are manipulated by increasing and decreasing 10% and 20% of each dielectric property. In this study, SAR values increase with increase of the human head’s conductivity, while increase of permittivity and densities decreases it. A helical antenna with a substrate of FR4 resulted in higher SAR values in all frequencies. The head SAR values are higher in the upper frequency exposures. The helical antenna with a substrate of Rogers RO3006 (loss free) was found to be the best-tested substrate, which contributed toward much lower SAR values in all GSM frequency bands.

Modeling of Flywheel Hybrid Powertrain to Optimize Energy Consumption in Mechanical Hybrid Motorcycle

The creation of internal combustion engine is a significant milestone in power engineering world which simplified high mechanical energy demand jobs like moving vehicle and machinery. Even though the internal combustion engine gives lot of advantages, however, this type of engine is incapable to convert the heat energy from fuel combustion to the mechanical energy efficiently. Small capacity engine e.g. motorcycle engine having the power conversion efficiency between 25-30%. Therefore, alternative power source is required to support the internal combustion engine in order to increase the overall system efficiency. These phenomena give encouragement to implement the hybridization process. This is to increase the system efficiency in transferring power to the wheel. Hybridization processes e.g. flywheel as secondary power source can increase power transfer efficiency between 30%-80%. Hence, the purpose of this research is to develop the mathematical model of the power transfer efficiency of flywheel hybrid motorcycle by using back trace simulation method. This model will record the amount of energy use in acceleration phase of the driving cycle. Subsequently, the efficiency ratio of motorcycle power transfer is calculated and comparison of those ratios between the conventional motorcycle and the hybrid motorcycle is made. The outstanding results show that the hybrid motorcycle is capable to conserve the energy used up to 36% compare to the conventional motorcycle that wasted energy up to 200%. As a conclusion, flywheel as the secondary power source is capable to supply enough energy to propel the motorcycle forward.

Hybrid Finite-Discrete Element Simulation of Crack Propagation under Mixed Mode Loading Condition

This paper describes the numerical modeling based on combination of finite element method (FEM) and discrete element method (DEM) has been employed to simulate crack propagation under mixed mode loading. The work demonstrates the ability of combination finitediscrete element method to simulate the crack propagation that is usually performed through, what is termed, transition from continua to discontinua process. Crack propagation trajectory under selected loading angles (30o & 60o) are presented. The result obtained using the proposed model compare well with experimental result.

The Implementation of Inter-Element Model for Crack Growth Simulation

The implementation of inter-element model to simulate crack propagation by using finite element analysis with adaptive mesh is presented. An adaptive finite element mesh is applied to analyze two-dimension elastoplastic fracture during crack propagation. Displacement control approach and updated Lagrangean strategy are used to solve the non-linearity in geometry, material and boundary for plane stress crack problem. In the finite element analysis, remeshing process is based on stress error norm coupled with h-version mesh refinement to find an optimal mesh. The crack is modeled by splitting crack tip node and automatic remeshing calculated for each step of crack growth. Crack has been modeled to propagate through the inter-element in the mesh. The crack is free to propagates without predetermine path direction. Maximum principal normal stress criterion is used as the direction criteria. Several examples are presented to show the results of the implementation.

Assessment of specific absorption rate reduction in human head using metamaterial

Abstract In this paper, the specific absorption rate (SAR) reduction in human head with metamaterial attachment is calculated. The finite-difference time-domain (FDTD) method has been used to evaluate the SAR in an anatomically correct model of the human head. We designed the double-negative metamaterials by placing periodic array arrangement of split ring resonators (SRRs). By properly designing and tuning the structural parameters of SRRS, the effective medium parameters can be made negative at 900 and 1800 MHz band, as presented in this paper. Experimental results show that, with presence of resonators, SAR reduction in the human head is achievable. These results can provide useful insight into the design of safety-compliant mobile communication equipment.