Papers by Keyword: Crashworthiness

Abstract: Production of the honeycomb or thin walled structures by the selective laser melting of powder is of a great scientific and practical interest. It’s because that such approach allows producing structures practically of any configuration and thickness, unobtainable or very hard to produce by traditional methods. Using the additive technology, the principal difference from the traditional is that the honeycomb structures can be produced practically of any shape, and the method itself is 100% waste-free, because there is no need in supporting structures. The results of the structure investigation of the honeycomb structures with the wall thickness of 80-170 μm and 44 mm height are presented along with the correlation dependencies between samples mass, wall thickness, activation and compression loads.

Abstract: Material characteristics at high strain rates are used for various applications involving high speed loading, one of which is plasticity-based impact energy absorbers. In this paper, experimental result of Split-Hopkinson Pressure Bar (SPHB) test of three common structural steels is reported and discussed. The three materials consist of JIS G3101 SS400, API5L Grade B, and S355JR. The material characteristics are presented in Johnson-Cook constitutive equations, and the corresponding parameters have been found through curve fitting. The results are comparable with those of literatures for other carbon steels, hence the acquired data may enrich the database of constitutive equations for various materials, especially carbon steels. The data can then be used for crashworthiness simulation in the future with the corresponding materials.

Abstract: This paper investigates the crashworthiness of a metallic fuselage section. Crashworthiness can be generally described as the ability of a structure to protect its occupants during an impact event. In this paper, the mechanical behaviour of metallic fuselage structures during the crash is simulated by means of the FE code ABAQUS/Explicit. Two different impact terrains have been considered: impact on a rigid surface and ditching on water. The numerical results, in terms of deformation, energy absorption, equivalent stress evolution, and damage onset and propagation have been assessed and compared.

Abstract: This paper presents the crashworthiness performance of carbon reinforced epoxy laminate tubular structure of three different kind tubes made of 0˚ plies Unidirectionally Arrayed Chopped Strand (UACS) introduced into laminate tube. UACS plies with discontinuous angled slit and slit perpendicular to fiber direction, namely bi-angle slits and staggered slits were used as 0˚ ply, respectively, instead of conventional continuous fiber ply to investigate relationship between crashworthiness capacities and progressive collapse behavior under quasi-static crushing tests. Newly designed laminate tube for crashworthy structure made of 0˚ plies UACS bi-angle slits and staggered slit was succesfully enhanced specific energy absorption by about 9.1% and 4.3% respectively compare to conventional continuous fiber laminate tube. The crushed laminate tubes then were sectioned through the impact point and micro-photograph were taken to show the failure behavior, which include effect of distribution slit on delamination, matrix cracking, curvature size, friction, etc. It is shown that UACS laminate beside of showing excellent formability also become newly auto trigger mechanism to achieve much stable and controllable collapse with much extensive fiber fracture occurred.

Abstract: Crashworthiness is one of the requirements for design of aircraft to ensure the safety of passengers on aircraft. With increasing applications of advanced composite in aircraft structures, study on the crashworthiness of composite fuselage is desirable and important. For this purpose, this paper investigates the influence of composites on crashworthiness of fuselage section. Firstly, model of fuselage section of aircraft is established. Skin, frame, stringer and stiffener are made of the composite T800/QY8911 or GLARE. Then, the crash responses subjected to vertical impact velocity of 9.14m/s are analyzed. The acceleration history is recorded for assessment of the crashworthiness. In addition, the deformation process and failure mode of composite fuselage section are analyzed. Results indicate that the frame made of brittle composite may fracture in the crash process, which leads to serious damage to the fuselage. While the frame with good toughness can maintain the integrity of fuselage, thereby protecting passengers.

Abstract: As the lightest structural metal, magnesium alloys have been attractive to reduce vehicle weight and emissions by lightweight design in the automotive industry. Structural crashworthiness is not a physical property itself, but correlates with the material’s ductility and structural design. Magnesium is known to be a material with lower failure strain than other metallic materials. Therefore the use of magnesium in crash-related areas is more challenging compared to steel and aluminum.In structures with a bending load, as in the case of a bumper or the sill, crash properties can be significant improved by filling profiles with a stabilizing core. In order to evaluate the crashworthiness of this hybrid structure under bending loads, both empty and polyurethane foam-filled rectangular section beams were constructed and tested by using the quasi-static/dynamic three-point bending facilities at German Aerospace Centre (DLR) – Institute of Vehicle Concepts.For structures with axial crash loads the normal buckling mode will lead to a very early fracture of the magnesium part. In collaboration with researchers from the University of Windsor and the University of Waterloo, novel technologies for energy absorption which are based on cutting or peeling mechanisms have been developed and investigated, which allow the use of magnesium in these challenging applications. Results of the joint research will be presented.

Abstract: In this study the influence of natural aging in energy absorbance capacity of 6xxx series extruded profiles after artificial aging is examined by means of optical and scanning electron microscopy, quasi-static compression and tensile tests. Mobile quenched-in vacancies are found to play an important role in aging kinetics and formation of precipitate free zones (PFZs) which govern both the observed fracture modes and the resulting strength of the material signifying their important effect when maximum energy absorbance is desired. It is shown that fracture toughness of naturally aged samples is equivalent or higher compared to that of directly aged samples due to restriction of intergranular cracking.

Abstract: Aluminium sheet metal is nowadays used to fabricate lighter, crashworthy, fuel efficient and environment friendly vehicles. Ductile damage of sheet metals affects significantly the crashworthiness, as it naturally exhibits anisotropic behavior due to the grain orientation. Johnson-Cook (J-C) damage model is widely used in numerical simulation for assessing the failure modeling of crash component in particular at high strain rate. The Johnson-Cook material model available in literature is meant for isotropic material behavior which cannot be used directly for anisotropic behavior of materials. To characterize the plastic anisotropy of the rolled sheet, the modified Johnson-Cook material model should be developed. In this research the combination of experimental work and numerical analysis with clear and simpler calibration strategy for damage model is demonstrated. It aims to reduce laboratory tests using advanced numerical analysis to predict failure in order to save overall cost and development time.

Abstract: Crashworthiness is one of the most important criteria in vehicle market. A good crashworthiness avoids being injury for the passenger. There are many accidents happen every day, the most dangerous collision is in horizontal. It can make the passenger injured or died easily, because the distance from body frame to passenger in cabin is very narrow. Therefore, this study is conducted to explore the behavior of top – hat and double - hat structures subjected to three – point impact bending by using analytical and numerical methods. The length of flange is not effected to bending resistance with the same perimeter of top-hat structure. The mean force of double – hat section is higher than the top – hat so that the capability to absorb energy of double – hat structure is better.

Abstract: Quasi-static/dynamic three-point bending tests were conducted to assess the crash performance of magnesium alloy AZ31B extruded and sheet tubes at the German Aerospace Centre (DLR) – Institute of Vehicle Concepts in Stuttgart. Different foam-filled AZ31B beams with a variation of foam density and thickness were fabricated through several manufacturing processes: cold bending, tungsten inert gas welding, cathodic dip painting and polyurethane foam injection. The experimental results were compared with those from mild steel DC04 tubes. It shows that empty magnesium alloy AZ31B outperforms steel DC04 in terms of specific energy absorption for the empty tubes with equivalent volume when subjected to bending loads. It was found that the foam-filled tubes achieved much higher load carrying capacity and specific energy absorption than the empty tubes. Moreover, there is a tendency showing that a foam-filled beam with a higher foam density reaches higher load carrying capacity, but fractures earlier. The foam-filled AZ31B tube with 0.20 g/cm³ foam obtained the highest specific energy absorption, but this outperformance was weakened due to the earlier fracture. In addition, the numerical simulation utilising material model MAT_124 in LS-DYNA explicit FEA package was performed. The simulation results indicate that using calibrated stress-strain curves and failure parameters, material model MAT_124 yields a general good agreement with the experimental results.