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This two-part article presents the results of experimental and numerical work on the crushing characteristics of square tubes, with blast-induced imperfections, subjected to axial load. In Part I, the experimental studies are presented. The approach in the studies involves creating imperfections on opposite sides at midlength of a square tube by means of localized blast loads to create three types of imperfections; nontouching domes, rebound domes, and capped domes. These imperfections change the geometry and the material properties in the midsection of the tubes and hence affect the crushing characteristics. While the blast-induced imperfections enhance the energy absorption characteristics of the tubes they also affect the lobe formation process. In Part II, the finite element package ABAQUS/EXPLICIT v6.5-6 is used to construct a 1/2 symmetry model by means of shell and continuum elements to simulate the tube response to the localized blast loads followed by dynamic axial loading in the form of a rigid mass impacting at a specified initial velocity. The hydrodynamic code AUTODYN is used to characterize the localized blast pressure time and spatial history. The predictions show satisfactory correlation with experiments for both crushed shapes and crushed distance. [DOI: 10.1115/1.3005977] Keywords: square tubes, imperfections, blast load, energy absorption

This two-part paper presents the results of experimental and numerical work on the crushing characteristics of square tubes, with blast-induced imperfections, subjected to axial load. In Part I, the experimental studies are presented. The approach in the studies involves creating imperfections on opposite sides at midlength of a square tube by means of localized blast loads to create three types of imperfections: nontouching domes, rebound domes, and capped domes. These imperfections change the geometry and the material properties in the midsection of the tubes and hence affect the crushing characteristics. While the blast-induced imperfections enhance the energy absorption characteristics of the tubes they also affect the lobe formation process. In Part II, the finite element package ABAQUS/EXPLICIT v6.5-6 is used to construct a 1/2 symmetry model by means of shell and continuum elements to simulate the tube response to the localized blast loads followed by dynamic axial loading in the form of a rigid mass impacting at a specified initial velocity. The hydrodynamic code AUTODYN is used to characterize the localized blast pressure time and spatial history. The predictions show satisfactory correlation with experiments for both crushed shapes and crushed distance. [DOI: 10.1115/1.3005980] Keywords: square tubes, imperfections, blast load, energy absorption

This paper is Part II of a two-part article and presents the results of numerical simulations conducted to investigate the energy absorption characteristics of square tubes subjected to dynamic axial loading. Part I reports the experimental results of both quasistatic and dynamic tests. The validated model is used to study the crushing characteristics of tubes with multiple induced circular hole discontinuities using the finite element package ABAQUS/EXPLICIT version 6.4-6. Holes of diameter 17 mm are used as crush initiators, which are laterally drilled into the tube wall to form opposing hole pairs. Holes of diameters 12.5 mm and 25 mm are also used to assess the effects of hole diameter on energy absorption. Two hole spacing configurations are investigated, one in which the hole pairs are placed at regular intervals of 50 mm along the tube wall and another in which the hole pairs are spaced symmetrically along the tube length. Holes are also drilled on either two or all four opposing tube walls. The number of holes is varied from 2 to 10. The results indicate that the introduction of the holes decreases the initial peak force. However, an increase in the number of holes, beyond two holes, does not further significantly decrease the initial peak force. A study of the crushing history of the tubes reveals that crushing is initiated at the location of the holes. The results also indicate that the type of hole spacing determines how crushing is initiated at the hole locations. The model satisfactorily predicts the resultant collapse shapes but overpredicts the crushed distance. [DOI: 10.1115/1.3114967] Keywords: square tubes, imperfections, multiple circular cut-outs, energy absorption

This two-part article reports the results of experimental and numerical works conducted on the energy absorption characteristics of thin-walled square tubes with multiple circular hole discontinuities. Part 1 presents the experimental tests in which dynamic and quasistatic axial crushings are performed. The mild steel tubes are 350 mm in length, 50 mm wide, and 1.5 mm thick. Circular hole discontinuities, 17 mm in diameter, are laterally drilled on two or all four opposing walls of the tube to form opposing hole pairs. The total number of holes varies from 2 to 10. The results indicate that the introduction of holes decreases the initial peak force but an increase in the number of holes beyond 2 holes per side does not further significantly decrease the initial peak force. The findings show that strategic positioning of holes triggers progressive collapse hence improving energy absorption. The results also indicate that the presence of holes may at times disrupt the formation of lobes thus compromising the energy absorption capacity of the tube. In Part 11, the finite element package ABAQUS/EXPLICIT version 6.4-6 is used to model the dynamic axial crushing of the tubes and to investigate the action of the holes during dynamic loading at an impact velocity of 8 m/s. [DOI: 10.1115/1.3114971] Keywords: square tubes, imperfections, multiple hole cut-outs, energy absorption