Mohd Khir Mohd Nor

Plane-Stress Analysis of the New Stress Tensor Decomposition

The accuracy and reliability of the new stress tensor decomposition to capture the plasticity behaviour of orthotropic materials under plane-stress conditions was examined in this paper. No experiment was required to perform this work. Therefore, the suitable, published paper which provides a relevant test result and sufficient material properties to characterise the new stress tensor decomposition, was used. This new stress tensor decomposition was used to presents a new yield criterion for orthotropic sheet metals under plane-stress conditions in this work. This was done by assuming the yield surface to be circular in the new deviatoric plane. The predictions of the new effectice stress expression were then compared with the experimental data of 6000 series aluminium alloy sheet (A6XXX-T4) and Al-killed cold-rolled steel sheet SPCE. The predicted new yield surfaces are in good agreement with respect to the experimental data for two materials (A6XXX-T4 and SPCE).

Modelling of Shockwave Propagation in Orthotropic Materials

Modelling of shockwave propagation in orthotropic materials requires an appropriate description of material behaviour within elastic and plastic regimes. To deal with this issues, a finite strain constitutive model for orthotropic materials was developed within a consistent thermodynamic framework of irreversible process in this paper. The important features of this material model are the multiplicative decomposition of the deformation gradient and a Mandel stress tensor combined with the new stress tensor decomposition generalised for orthotropic materials. The elastic free energy function and the yield function are defined within an invariant theory by means of the introduction of the structural tensors. The plastic behaviour is characterised within the associative plasticity framework using the Hills yield criterion. The complexity was further extended by coupling the formulation with the equation of state (EOS) to control the response of the material to shock loading. This material model which was developed and integrated in the isoclinic configuration provides a unique treatment for elastic and plastic anisotropy. The effects of elastic anisotropy are taken into account through the stress tensor decomposition and plastic anisotropy through yield surface defined in the generalized deviatoric plane perpendicular to the generalised pressure. To test its ability to describe shockwave propagation, the new material model was implemented into the LLNL-DYNA3D code. The results generated by the proposed material model were compared against the experimental Plate Impact test data of Aluminium Alloy 7010. A good agreement between experimental and simulation was obtained for two principal directions of material orthotropy.

Effects of Temperature and Strain Rate on Commercial Aluminum Alloy AA5083

Superplastic forming, SPF is a special metalworking process that allows sheets of metal alloys such as aluminum to be stretched to lengths over ten times. Nowdays, only a few aluminium alloys can meet the specific requirement of SPF manufacturing process and not much data available to represent their mechanical behaviour. In order to deal with this issue, this research project is conducted to investigate the characteristics of commercial aluminum alloy, AA5083 when tested at different strain rates and temperatures. These parameters play a crucial roles in the design and manufacturing processes of military, automotive and aerospace structures. Equally, the effects must be considered in the constitutive model development to accurately capture the deformation behaviour of such materials. The specimens were prepared according to 12.5mm gauge length standard. The Uniaxial Tensile Tests were carried out at various strain rate from 4.167 x10-1 s-1 to 4.167 x10-5 s-1 over a wide temperature range from ambient to 95°C. The experimental data shows that increasing strain rate increases flow stress, while increasing temperature decrease flow stress. This is leads to important conclusion that material AA5083 exhibits strain rate and temperature sensitivite, and suit with the SPF operating condition.

Rollover Analysis of Heavy Vehicle Bus

Rollover is motor vehicle accident that occurs when vehicle is tipping over onto its side or roof. Due to its fatality rate, the Malaysian government reinforced an Economic Commission for Europe of the United Nations (UN/ECE) Regulation no. 66 (R66) upon bus construction. This is to prevent the catastrophic consequences of rollover accidents. The R66 regulation provides an option of certification based on full-scale vehicle testing that maitaning the survival space. Therefore research that contribute to the development of safe transportation vehicle under rollover is really important. The physical prototype of rollover test can be simplified using simulation model. Using this motivation, the characteristic of heavy vehicle rolleover is investigated in this paper. The simulation was performed using ANSYS simulation tool and simplified by locating the position of the bus in unstable equilibriumm, just before it hit the ground. Another method is to perform a quasi-static loading test. The quasi-static simulation test was performed using impact load that directed towards the side of beam around the centre of frame body. The dynamic response due to rollover impact was determined using an Explicit Dynamic Analysis in ANSYS. The stress maximum stress first developed around the impact area before lag the stress stream to the opposite side. It can be observed that the maximum stress point is located at the middle structure of impact side. After few times of impact, the maximum stress starts to changes to the opposite side. Quasi-static simulation result in higher total deformation on impact side area. It also indicates high maximum stress point around the middle structure.

Effect of Rotating Mold Speed on Microstructure of Al LM6 Hollow Cylinder Fabricated Using Centrifugal Method

Al LM6 hollow cylinder is fabricated using horizontal centrifugal casting which produce a very fine grain on the outer surface of the structure. In this study, the effect of motor speed and pouring temperature on the microstructure of Al LM6 hollow cylinder is determined. The speed of the motor used during casting are 1300rpm, 1500rpm and 1700rpm and the pouring temperature are 690°C, 710°C and 725°C. The Al LM6 hollow cylinder is produced by pouring the molten Al LM6 into a cylindrical casting mold which is connected with a shaft and it is rotated by motor until it is solidified. Then, the cross-section is observed using OM and SEM/EDS. From the microstructure observation, the distributions of Si are more concentrated at the inner parts and the size of Si is bigger at the inner parts. The result shows that the Si particles at the inner part which is fabricated at the highest motor speed (1700rpm) have the most Si particles compared with the Si particles that are casted with other motor speeds.

Modelling Dynamic Behaviour and Spall Failure of Aluminium Alloy AA7010

A finite strain constitutive model to predict the dynamic deformation behaviour of Aluminium Alloy 7010 including shockwaves and spall failure is developed in this work. The important feature of this newly hyperelastic-plastic constitutive formulation is a new Mandel stress tensor formulated using new generalized orthotropic pressure. This tensor is combined with a shock equation of state (EOS) and Grady spall failure. The Hills yield criterion is adopted to characterize plastic orthotropy by means of the evolving structural tensors that is defined in the isoclinic configuration. This material model was developed and integration into elastic and plastic parts. The elastic anisotropy is taken into account through the newly stress tensor decomposition of a generalized orthotropic pressure. Plastic anisotropy is considered through yield surface and an isotropic hardening defined in a unique alignment of deviatoric plane within the stress space. To test its ability to describe shockwave propagation and spall failure, the new material model was implemented into the LLNL-DYNA3D code of UTHMs. The capability of this newly constitutive model were compared against published experimental data of Plate Impact Test at 234m/s, 450m/s and 895m/s impact velocities. A good agreement is obtained between experimental and simulation in each test.

Deflection of elastic beam with SMA wires eccentrically inserted

This research is intended to investigate the ability of shape memory alloys (SMA), through its activation, in generating loads to control beam deflection. An elastic beam is formed by sandwiching eccentrically SMA wires between two elastic plates. SMA wires are activated by electrical current from the power supply. Laser displacement meter (LDM) is used to measures deflection of sample. Results show that the deflection of the beam is dependent on the temperature change. The temperature-deflection response also shows the existence of hysteresis.

Numerical modelling of steel tubes under oblique crushing forces

This paper presents the numerical assessment of crushing responses of elliptical tubes under crushing forces. Based on the literature survey, tremendous amount of works on the axial crushing behaviour can be found. However, the studies on the oblique crushing responses are rarely found. Therefore, this work investigates numerically the elliptical tubes under compressions. The numerical model of the tubes are developed using ANSYS finite element program. Two important parameters are used such as elliptical ratios and oblique angles. The tubes are compressed quasi-statically and the force-displacement curves are extracted. Then, the area under the curves are calculated and it is represented the performances of energy absorptions. It is found numerically that the introductions of oblique angles during the crushing processes decrease the crushing performances. However, the elliptical-shaped tubes capable to enhance the energy absorption capabilities. On the other hand, the elliptical-shaped tubes produced the enhancement on the energy absorption capabilities.

Torsion vehicle model test for automotive vehicle

Torsion vehicle model test of Simple Structural Surfaces (SSS) model for automotive vehicle sedan is proposed in this paper to demonstrate the importance of providing continuous load path within the vehicle structures. The proposed approach is relatively easy to understand as compared to Finite Element Method (FEM). The results prove that the proposed vehicle model test is capable to show that a satisfactory load paths can five a sufficient structural stiffness within the vehicle structure. It is clearly observed that the global torsion stiffness reduces significantly when only one panel is removed from the complete SSS model. The results also five a food agreement with respect to the theoretical hypothesis as the structure is less stiff in torsion in an open section condition. The SSS model and the corresponding torsion test is obviously useful to give an overview of vehicle structural integrity. It can be potentially integrated with FEM to speed up the design process of automotive vehicle.

Nonlinear analysis of collapse mechanism in superstructure vehicle

The EU directive 2001/85/EC is an official European text which describes the specifications for “single deck class II and III vehicles” required to be approved by the regulation UN/ECE no.66 (R66). To prevent the catastrophic consequences by occupant during an accident, the Malaysian government has reinforced the same regulation upon superstructure construction. This paper discusses collapse mechanism analysis of a superstructure vehicle using a Crash D nonlinear analysis computer program based on this regulation. The analysis starts by hand calculation to define the required energy absorption by the chosen structure. Simple calculations were then performed to define the weakest collapse mechanism after undesirable collapse modes are eliminated. There are few factors highlighted in this work to pass the regulation. Using the selected cross section, Crash D simulation showed a good result. Generally, the deformation is linearly correlates to the energy absorption for the structure with low stiffness. Failu...