Study on Crush Tube Geometric Cross sections and Topology for Axial Crashworthiness

Crush tubes are used as crash impact energy absorbing structure (EAS) and are located in the frontal compartment of road vehicles. Ideal crashworthiness of an EAS mandates that the equivalent decelerations due to impact forces should to be ≤ 20g; and crush force and stroke efficiencies should tend to unity. It is understood from the literature that no single geometric cross-section shape exhibits a near-ideal crashworthiness; and most EAS members exhibit a high initial peak crush force which is detrimental to the occupant safety, and moderate stroke and crush force efficiencies leading to a compromise in the total energy absorbed. In this paper, finite element analysis (FEA) methodology is formulated and experimentally validated for axial crush of a crush tube of SS304 material with circular cross section.  Subsequently, plastic deformation phenomenon and folding patterns in relation to crush force behaviour of crush tubes with various basic cross-sections of polygonal geometric shapes from triangle to octagon and circle are extensively studied through FEA. Further, two new geometric cross-section profiles with combination of basic shapes are proposed to combine the merits of different basic shapes. The crashworthiness of all basic cross-sections including the two proposed cross-section profiles is assessed based on standard parameters. The proposed new geometries may form a basis for the development of new EAS configurations for enhanced crashworthiness

Response of a Thin Flat Scored Metallic Disc Under Pressure Impulse

This paper presents the large deformation, and failure response of a thin flat scored metallic disc (FSMD) subjected to a pressure impulse as experienced in a break-away disc or an explosion vent. The response of this thin FSMD is numerically simulated for a loading rate and validated with an experiment, where a good agreement is found on plastic strains, burst pressure, and deformation pattern. The loading rate and several geometric parameters of FSMD significantly influence its response. Therefore, the influence of loading rate ( P& ), score depth and width-todisc thickness ratio (t 1 /t and b/t), diameter-to-disc thickness ratio (D/t), score length-to-disc radius ratio (l/R), score pattern, and score geometry on the deformation and failure response of the thin FSMD is thoroughly investigated. The studies demonstrate that 1) the failure initiation point shifts from disc centre to between 1/5th and 1/3rd radius for loading rates ≤ 25 MPa/s; 2) the responses such as burst pressure, burst time, central deflection, and equivalent strain are i) sensitive to the loading rates up to 100 MPa/s, ii) sensitive to score’s depth, only up to 0.6t and insensitive to score’s width, iii) significantly unaffected for the number of scores N > 8, iv) stabilised for l/R > 0.5 and D/t > 250, v) almost the same for semi-circular, rectangular and triangular score geometries, and vi) very minimal for the number of scores N = 3; and 3) the failure do not initiate and propagate along all scores for N > 4 in the disc