P K Kostazos

Bio: P K Kostazos is an academic researcher from National Technical University of Athens. The author has contributed to research in topics: Finite element method & Crashworthiness. The author has an hindex of 9, co-authored 17 publications receiving 315 citations.

Finite element simulation of the axial collapse of metallic thin-walled tubes with octagonal cross-section

Abstract: The present paper deals with the implementation of the explicit FE Code LS-DYNA to simulate the crash behaviour and energy absorption characteristics of steel thin-walled tubes of octagonal cross-section subjected to axial loading. The collapse procedure is successfully simulated and the obtained numerical results are compared with actual experimental data from small-scale models and useful concluding remarks pertaining to the design requirements of the crushing process are drawn.

The effect of the implementation of circular holes as crush initiators to the crushing characteristics of mild steel square tubes: experimental and numerical simulation

Abstract: During a crash event, significant energy must be absorbed by kinetic energy-dissipating systems through material plastic deformation. Such systems are thin-walled steel tubes installed in specific places of the vehicle body to reduce the amount of forces transferred to occupants to a required safety limit and to minimise the cargo damage. The present paper deals with the improvement of the response characteristics of structural components by embodying geometrical discontinuities in the form of circular holes. These discontinuities play the role of crash initiators, which can affect the axial collapse mode, by ensuring a stable collapse process and decreasing the initial peak load. Results of both experimental and finite element (FE) simulation of square steel tubes with circular discontinuities subjected to quasi-static axial loadings are reported. The tubular test specimens were manufactured from commercially mild steel S355 tubes and were tested under various schemes of discontinuities (hole diameter, location, etc.). The proposed numerical model using the LS-DYNA explicit FE code was validated employing testing results from the axial loading and was found to be in good agreement with the experimental data.

Numerical simulation of thin-walled metallic circular frusta subjected to axial loading

Abstract: Commercial finite element codes, e.g. the explicit code LS-DYNA, have made significant progress. They have been developed and improved to the point of being able to predict the various crash problems, as well as to successfully simulate the collapse of tubular components with a reasonable amount of computer time, allowing such structural crashworthy elements to be designed and analysed without having to build and test expensive prototypes. The present paper is dealing with the implementation of the explicit FE code LS-DYNA to the simulation of the axial crushing performance of steel and aluminium thin-walled circular frusta with a constant nominal axial length and various semi-apical angles and wall-thickness. The obtained numerical results are compared with actual experimental data from small-scale models and useful concluding remarks pertaining to the design requirements of the crushing process are drawn.

Bending of cylindrical steel tubes: numerical modelling

Abstract: Crashworthy structural elements may be subjected to various types of loading, i.e., axial or lateral compression and bending; consequently, extensive theoretical and experimental research work has been carried out exploring the collapse mechanisms that occur under such loading conditions. However, the designer needs theoretical tools ranging from simple analytical calculations to full finite element analysis using nonlinear, large deformation codes. The main objective of the present paper is to apply the explicit FE code LS-DYNA to the simulation of the crash behaviour of thin-walled cylindrical steel tubes subjected to three-point bending test in different positions and directions of the imposed load. The results obtained from the simulation allow us to draw useful conclusions pertaining to the design of the crash behaviour process.

On the crashworthiness performance of thin-walled energy absorbers: Recent advances and future developments

Abstract: Over the past several decades, a noticeable amount of research efforts has been directed to minimising injuries and death to people inside a structure that is subjected to an impact loading. Thin-walled (TW) tubular components have been widely employed in energy absorbing structures to alleviate the detrimental effects of an impact loading during a collision event and thus enhance the crashworthiness performance of a structure. Comprehensive knowledge of the material properties and the structural behaviour of various TW components under various loading conditions is essential for designing an effective energy absorbing system. In this paper, based on a broad survey of the literature, a comprehensive overview of the recent developments in the area of crashworthiness performance of TW tubes is given with a special focus on the topics that emerged in the last ten years such as crashworthiness optimisation design and energy absorbing responses of unconventional TW components including multi-cells tubes, functionally graded thickness tubes and functionally graded foam filled tubes. Due to the huge number of studies that analysed and assessed the energy absorption behaviour of various TW components, this paper presents only a review of the crashworthiness behaviour of the components that can be used in vehicles structures including hollow and foam-filled TW tubes under lateral, axial, oblique and bending loading.

Axial crushing of thin-walled structures with origami patterns

Abstract: Thin-walled tubes are a kind of popular design for the energy absorbing devices. However, when they are subjected to axial loading, there exists a large undesirable initial peak force, followed by fluctuation in the force–displacement curve. In this paper, the origami patterns are introduced to thin-walled tubes to minimize the initial peak and the subsequent fluctuations. Tubes of square, hexagonal and octagonal cross-sections with origami patterns are investigated by finite element analysis. Numerical results show that compared with the conventional tube, the patterned tubes exhibit a lower initial peak force and more uniform crushing load. The critical states are obtained under which the crushing mode follows the initial origami pattern. The parametric study shows the relationship between the pre-folding angle and the initial peak force as well as the mean crushing force for the tubes with different cross-sections. A prototype of the patterned tube is constructed and tested, showing much lower initial peak force and a smooth crushing process which agrees with the numerical results.