4 research outputs found
Theoretical analysis and pressure distribution of thin-walled metal inverbuckle energy absorbing tubes
This dissertation presents an investigation in the energy
absorbing capacity of thin-walled metal inverbucktubes
loaded in axial compression. It also presents the
inversion-buckling(curling-buckling) behaviour achieved
in both, quasi-static and dynamic loading conditions.
In addition, for the first time, the experimental results
of the pressure or normal stress distribution between the
inside surface of the inverbucktube and die fillet radius
interface are stipulated. These were very successful,
using the pressure transducer method.
Furthermore, a mathematical model has been developed,
based on theory of plasticity and making use of energy
method. This predicts the amount of energy absorbed in the
assumed seperate collapse processes. Results yielded from
the theory, showed good agreement with the experimental
results which had geometry factor within feasibility
boundaries of inverbuckling collapse (6.5 ( 5/2t,, ( 22.5).
The successful prediction of energy absorbed,
inverbuckling load and pressure distribution, not only
proves the validity of the model, but also confirms the
quality of the modelling approach proposed in this
dissertation. Using this mathematical model,
inverbucktubes could be designed, developed and applied
Energy absorption behaviours of CSM-based GFRC plates with hemispherical features
In the present study, the mechanical behaviour of CSM (chopped strand mat)-based GFRC (glass fibre-reinforced composite) plates with single and multiple hemispheres under compressive loads has been investigated both experimentally and numerically. The basic stress-strain behaviours arc identified with quasi-static tests on two-ply coupon laminates and short cylinders, and these are followed up with compressive tests in a UTM (universal testing machine) on single- and multiple-hemisphere plates. The ability of an explicit LS-DYNA solver in predicting the complex material behaviour of composite hemispheres, including failure, is demonstrated. The relevance and scalability of the present class of structural components as `force-multipliers' and `energy-multipliers' have been justified by virtue of findings that as the number of hemispheres in a panel increased from one to four, peak load and average absorbed energy rose by factors of approximately four and six, respectively. The performance of a composite hemisphere has been compared to similar-sized steel and aluminium hemispheres, and the former is found to be of distinctly higher specific energy than the steel specimen. A simulation-based study has also been carried out on a composite 2 x 2-hemisphere panel under impact loads and its behaviour approaching that of an ideal energy absorber has been predicted. In summary, the present investigation has established the efficacy of composite plates with hemispherical force multipliers as potential energy-absorbing countermeasures and the suitability of CAE (computer-aided engineering) for their design
Hexagonal honeycomb cell optimisation by way of meta-model techniques
This paper presents the result of an optimisation study by linear, quadratic, Kriging and radial basis meta-models in order to augment the crashworthiness characteristic of cellular structures. Thin-walled cellular structures (honeycomb) have the ability to absorb impact energy during crashing, thus it is important to enhance the crushing efficiency and optimise the structural reliability. The optimisation carried out in this study is aimed at maximising the energy absorption characteristics using meta-models while considering some limitation on the maximum force as a constraint. Achieving these characteristics is an important factor in crashworthiness analysis, which minimises the damage in dynamic performance. The objective of using various meta-models is to qualify the meta-model in crashworthiness analysis using different point selection schemes and different number of points. The optimisation is performed in two stages; through experimental design methods in which a set of sampling points is selected from design space and polynomial fitting in order to optimise the objective. It is concluded that D-optimal best suits response surface method for model approximation. Kriging performed best by space filling and the best point selection scheme for radial basis surrogate is latin hypercube design. The results show that for optimising the crashworthiness characteristics of honeycomb, Kriging and quadratic response surface (RS) are best, in terms of accuracy and robustness point of view and the radial basis neural network would be the second best. During this optimisation, the RS was combined with detailed geometrically simplified finite element model of honeycomb cell using ANSYS/LS-DYNA, LS-DYNA and LS-opt packages. Approximated functions combined with the finite element analysis were an effective tool to optimise highly non-linear impact problems. This has led to the development of validated algorithm that enabled the development of the optimised solutions