Qasim Hussain Shah

Modeling large deformation and failure of expanded polystyrene crushable foam using LS-DYNA

In the initial phase of the research work, quasistatic compression tests were conducted on the expanded polystyrene (EPS) crushable foam for material characterisation at lowstrain rates (8.3×10-3 ∼ 8.3×10-2 s-1) to obtain the stress strain curves. The resulting stress strain curves are compared well with the ones found in the literature. Numerical analysis of compression tests was carried out to validate them against experimental results. Additionally gravity-driven drop tests were carried out using a long rod projectile with semispherical end that penetrated into the EPS foam block. Long rod projectile drop tests were simulated in LS-DYNA by using suggested parameter enhancements that were able to compute the material damage and failure response precisely. The material parameters adjustment for successful modelling has been reported.

Optimisation of vehicle front-end geometry for adult and pediatric pedestrian protection

This study proposes a method of achieving an optimised vehicle front-end profile for improved protection for both adult and child pedestrian groups, which at the same time is able to avoid designs that may cause Run-over scenarios. A hybrid model of a seven-parameter vehicle front-end geometry and a pedestrian dummy is used. Latin Hypercube sampling is utilised to generate a Plan of Experiments for the adult and child pedestrian cases. Head injury criteria results from the simulations that are tabulated as the response functions. The radial basis function method is used to obtain mathematical models for the response functions. Optimised front-end geometries are obtained using the Genetic Algorithm method. The optimised vehicle front-end profile for the adult pedestrian is shown to be different from that of the optimised profile for the child pedestrian, and optimised profiles are shown to be not mutually applicable for safety. Furthermore, Run-over scenario is observed in child pedestrian optimised profiles, where its occurrence invalidates the optimisation. A simple weighting method is used to optimise the geometry for both adult and child pedestrian groups. The Run-over occurrences are mapped using Logistic Regression and is subsequently used as a constraint for optimisation. The final optimised model is shown to achieve a safe vehicle front-end profile which equally caters for both adult and child pedestrians while simultaneously avoiding Run-over scenarios.

Sintering and Properties of Dense Manganese-Doped Calcium Phosphate Bioceramics Prepared Using Sol-Gel Derived Nanopowders

Dense manganese-doped biphasic calcium phosphate (Mn-BCP) ceramics were fabricated via uniaxial pressing using the sol-gel derived powders. The compacted discs were sintered in ambient atmosphere with temperatures ranging from 800°C to 1400°C. Manganese (Mn) level was varied in the range of 0.6, 1.9, 4.3, and 11.9 mol%, and its effect on physical and mechanical properties of the dense samples were investigated. All dense samples have been proved to show HA and β-TCP phases only. Mn doping has shifted the onset of the sintering temperature of the BCP, leading to the improved densification of BCP ceramics. The relative density also increased with sintering temperature. Considerable grain growth has been observed for Mn-doped BCP samples when compared to the undoped BCP. Furthermore, 11.9 mol% Mn-doped BCP dense samples showed the maximum hardness of 6.66 GPa compared to 2.89 GPa for the undoped BCP. The incorporation of Mn was also found to be beneficial in enhancing the fracture toughness of BCP throughout the temperature range employed. This study has shown that Mn doping was effective in improving the sintering properties of BCP without affecting the phase stability.

Parametric study for head injury criteria response of three-year olds in a child restraint system in oblique and lateral intrusive side impact

A parametric study is undertaken to ascertain the sensitivity of the child restraint system (CRS) design, with respect to oblique side impact at standard velocities in consideration of intrusion. A hybrid model is constructed using a combination of both finite elements and multi-body ellipsoids where a three-year-old Hybrid III child dummy is placed inside a CRS and restrained with a harness system. A prescribed structural motion simulation of a side-impact crash is carried out based on experimental data. Validation is performed and the model is shown to be acceptable for common standard injury responses as well as being greatly economical in terms of computational processing time. A plan of experiments is prepared based on the Latin hypercube sampling for six parameters involving two different crash velocities. The head injury criterion (HIC) is considered as the response in this study. The model is adapted for intrusion and oblique impact. Response surface models are shown to be suitable for the mathematical modelling of the problem and Students t-test is used to assess the parameter sensitivity both qualitatively and quantitatively. Most of the parameters are seen to have greater significance for wider principle direction of force (PDOF) angles above 60°. In general, a gradual decrease in significance is observed for parameters with increasing impact velocity, with the notable exception of the impact angle. The impact angle is shown to most notably affect the HIC especially from PDOF angles 45°–75°, identified as the critical impact angle range. The far side shoulder harness slack parameter is also found to be significant in reducing the HIC.

Dense manganese doped biphasic calcium phosphate for load bearing bone implants

Dense pure biphasic calcium phosphate (BCP) and Mn-doped BCP ceramics were fabricated via uniaxial pressing using the sol-gel derived powders. The compacted discs were sintered in air atmosphere with temperatures ranging from 1000 °C to 1400 °C. All powders have been proved to show HA and β-TCP phases only. Manganese doping improves the densification in the BCP structure as the relative density increased with Mn doping and also sintering temperature. Considerable grain growth has been observed at 1300 °C for Mn-doped BCP samples compared to the pure BCP. 15 mol% Mn showed the maximum hardness value of 6.66 GPa at 1400 °C compared to pure BCP of only 2.89 GPa. Similarly, the Mn-doped BCP has superior fracture toughness where it attained maximum values of 1.05 MPam1/2 at 1400 °C compared to 0.72 MPam1/2 at 1300 °C of pure BCP. In a nutshell, Mn doping has successfully brought improvement in the mechanical properties of the BCP.

Fabrication and Sintering Behavior of Zinc-Doped Biphasic Calcium Phosphate Bioceramics

Dense bioceramics with improved mechanical properties have been prepared using sol–gel derived zinc doped biphasic calcium phosphate (BCP) powders. Zinc concentration was varied in the range of 0,1, 2, 4, 5, 10, and 15 mol%. The compaction of the powders followed by sintering provided the dense ceramics. The effects of zinc concentration doped and sintering temperature on phase stability and mechanical characteristics were examined. The presence of Zn changed the phase of dense BCP, leading to improved mechanical properties. Zn free BCP attained the highest density of only 92.6% after 1400°C sintering, equally achieved by 4 mol% Zn-doped BCP at a lower temperature of 1200°C. It is presumed that the steady increase in the compact density up to 4 mol% zinc incorporation was contributed by progressive consolidation in the BCP structure, but the density dropped again from 5 mol% until 15 mol% due to low density β-tricalcium phosphate phase formation. This study showed that Zn doping was effective in producing high strength dense BCP with 3.40 GPa hardness and 1.43 MPa · m1/2 fracture toughness.

Failure Prediction in Bulk Metal Forming Process

An important concern in metal forming is whether the desired deformation can be accomplished without defects in the final product. Various ductile fracture criteria have been developed and experimentally verified for a limited number of cases of metal forming processes. These criteria are highly dependent on the geometry of the workpiece and cannot be utilized for complicated shapes without experimental verification. However, experimental work is a resource hungry process. This paper proposes the ability of finite element analysis (FEA) software such as LS-DYNA to pinpoint the crack-like flaws in bulk metal forming products. Two different approaches named as arbitrary Lagrangian-Eulerian (ALE) and smooth particle hydrodynamics (SPH) formulations were adopted. The results of the simulations agree well with the experimental work and a comparison between the two formulations has been carried out. Both approximation methods successfully predicted the flow of workpiece material (plastic deformation). However ALE method was able to pinpoint the location of the flaws.

Lateral Side Impact Crash Simulation of Restrained 3 Year Old Child

Motor vehicle crashes have become the leading cause of death for children in many developed countries and the trend is on the rise in Malaysia. Child anatomy and physiology necessitates a separate restraints system to be implemented during vehicle travel. Although approximately twice as many crashes with a child fatality are frontal compared to lateral, it is shown that side impacts are nearly twice as likely to result in a child fatality as frontal impacts. Due to the complexity and the highly non-linear nature of vehicle crash affecting occupants, much work still remains to be looked into. This is especially so in the study of injury mechanisms towards efforts of improving CRS design as well as vehicle parameters that may offer more effective and robust injury mitigation. The study here presents a methodology which outlines the development and testing of a simulation model where a 3 year old child, restrained in a CRS within a vehicle, is subjected to lateral side impact by a bullet vehicle. A combined environment of both Finite Element as well as Multi-body is used for the model development. A HYBRID III dummy model is used to represent the child while an FE model is used for the CRS model. A hybrid modelling method is utilized for the belt harness system. The model and simulation conditions are set based on the global FMVSS standard. Head injury criterion and Neck injury criterion are primarily considered in the model assessment. Model development as well as validation steps are presented with discussion of the model’s salient features for greater insights in the study of injury mechanisms.

Injury analysis validation of a deformable vehicle front end model

In the event of an impact with an automobile, pedestrians suffer multiple impacts with the bumper, hood and the windscreen. The characteristics of a vehicles front end and structural stiffness have a significant influence on the kinematics and injury risk of the pedestrians body regions, in a vehicle-to-pedestrian collision. In this present study, the injury risk of the pedestrian is investigated in an impact with a deformable vehicle front end model for the purpose of validating the developed model. A simplified vehicle front end model consisting of a multi body windscreen and a finite element cowl, hood and bumper is developed. The MADYMO human pedestrian multi body dummy model is impacted by the vehicle front end model at the speed of 40 km/h. The injuryto the various body segments namely the head, neck, sternum, lumbar, femur and tibia is obtained. The simulation values are compared to the experimental values for verification of the vehicle front end model.

Finite element analysis of a composite crash box subjected to low velocity impact

In this work, finite element analyses using LS-DYNA had been carried out to investigate the energy absorption capability of a composite crash box. The analysed design incorporates grooves to the cross sectional shape and E-Glass/Epoxy as design material. The effects of groove depth, ridge lines, plane width, material properties, wall thickness and fibre orientation had been quantitatively analysed and found to significantly enhance the energy absorption capability of the crash box.