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Axial splitting of empty and foam-filled circular composite tubes – An experimental study

Rezaei B., Niknejad A., Assaee H., Liaghat G. H.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 3

650--662

EN

This paper studies the effects of polyurethane foam-filler on the axial splitting process of circular composite tubes under the axial quasi-static loading, experimentally. A shear mode of failure in circular composite tubes is initiated by crushing the tube onto a conical die to absorb the energy. The effects of conical die angle, number of fiber fabric layers, resin type and also, diameter and fiber fabric type of the tubes on axial load, energy absorption and specific absorbed energy by the structure are studied. Experimental results show that the polyurethane foam-filler increases energy absorption capability by the tubes. Also, it is found that in the investigated domain, composite tubes with smaller diameters are better energy absorbers, comparing with the composite tubes with larger diameters. Experiments show that foam-filled circular tubes under the axial compression in the splitting process works as good energy dissipater.

2

Absorbed energy by foam-filled quadrangle tubes during the crushing process by considering the interaction effects

Niknejad A., Abedi M. M., Liaghat G. H., Nejad M. Z.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 2

376--391

EN

In this article, some theoretical relations are derived to predict instantaneous crushing force and absorbed energy during initial fold formation in polyurethane foam-filled quadrangle tubes under the axial crushing load. Theoretical analysis is performed based on the energy method. In the theoretical analysis, crushing wavelength is considered as a constant parameter through the process and as a function of column geometrical dimensions. In the analytical calculations, interaction effects between the polyurethane foam and inner wall of quadrangle tubes are considered and a formula is presented to predict absorbed energy by the interaction effects. In the experiment part, some foam-filled specimens were prepared and axially crushed to obtain experimental diagram of crushing force versus axial displacement. Comparison of the theoretical predictions of crushing force and absorbed energy with corresponding experimental results showed a good agreement. Also, it was found that theoretical predictions by considering the interaction effects have a better correlation respect to the experiments.

3

Theoretical and experimental study on the flattening deformation of the rectangular brazen and aluminum columns

Niknejad A., Elahi S. M., Elahi S. A., Elahi S. A.

Archives of Civil and Mechanical Engineering

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2013

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Vol. 13, no. 4

449--464

EN

This paper presents a theoretical and experimental study on lateral compression of square and rectangular metal columns. Some theoretical relations are derived to predict the absorbed energy, the specific absorbed energy and the instantaneous lateral load during the lateral compression. Analytical relations are obtained in two stages: elastic and plastic parts. In the plastic zone, the total absorbed energy by the column is calculated, based on the energy method. Then, an analytical equation is derived to predict the instantaneous lateral load. In the elastic part, the instantaneous load is obtained by linear behavior assumption. To verify the theoretical formulas, some lateral compression tests were carried out on square and rectangular columns and the experimental results are compared with the theoretical predictions, which shows a good agreement. Also, based on the experiments, effects of geometrical dimensions and material properties of the columns on the energy absorption capability are investigated. The results show that the absorbed energy by a column increases proportional to the column length. Also, columns with the thicker wall have the higher specific absorbed energy and so, rectangular columns with the thicker wall are the better energy absorbers during the flattening process. Also, the absorbed energy increases when the length of the column edge along which the load is applied decreases. Also, it is found that the specific absorbed energy by the aluminum columns is higher than the brazen ones and therefore, flattened columns with the high ratio of the flow stress/density are the better energy absorbers.