Crash Energy Absorption Research Articles

Evolution of a new geometric profile for an ideal tube inversion for crash energy absorption

Circular tubes under axial load undergoing deformation through inversion phenamena are referred to as invertubes. Inversion phenomena controls high initial peak crush force which is a fundamental requirement of an energy absorbing structure in road vehicles and helps in achieving nearly 100% stroke and crush force efficiencies. This rare combination of these three features offers a good potential for invertubes to be an ideal choice for impact crash energy absorption. Researchers have always attempted to predict inversion forces in invertubes in terms of geometrical and material parameters through empirical relations; and often ignored the geometric imperfections on plastic deformation and their influence on the inversion process. Limited knowledge exist on inversion using stainless steel SS304 material. In this paper, series of attempts are made to evolve a new invertube profile with SS304 material to achieve desirable inversion charecterisitics for an ideal energy absorption. In this process, the effect of geometric parameters and their imperfections that contribute to effective inversion of invertubes have been studied in detail through FEA and experiments. A new invertube profile has been proposed that addresses anamolies in existing literature and inversion characteristics of this profile have been validated experimentally in a quasi-static environment.

Effect of Pretreatment on Interface Stability and Morphology of Ni/Al Hybrid Foams by in situ Microcantilever Fracture Experiment

Ni/Al hybrid foams are a new class of innovative cellular composite materials consisting of open-cell aluminium (Al) foams electrochemically coated with nanocrystalline nickel (Ni). They may be used for lightweight construction elements or as crash energy absorbers. The Ni coating strengthens the Al foam achieving an up to ten times higher energy absorption capacities compared to the Al basis foam. Cellular materials such as foams provide a strong structure-property relationship as the macroscopic material properties strongly depend on the strut geometry and the material properties of the individual struts. The interface stability between the coating and the substrate foam is the dominant contribution in the strengthening mechanism of Ni/Al hybrid foams. Hence, micromechanical characterization is an important task for the design of components made of Ni/Al hybrid foams. A strong interface corresponds to a shear-stiff connection between substrate foam and coating, whereas a soft interface allows sliding between the two phases and hence reduces the buckling stiffness of individual foam struts resulting in lower strength and energy absorption capacity of the macroscopic foam. An increased critical energy release rate for interface cracking was revealed by in situ microcantilever bending tests prepared by focused ion beam (FIB) during bending tests in the scanning electron microscope (SEM) after the chemical pretreatment of the base foam.

Development of Crash Energy Absorption Structure and its Processing Method

Development of Crash Energy Absorption Structure and its Processing Method

Crashworthiness performance and microstructural characteristics of foam-filled thin-walled tubes under diverse strain rate

The implementation of Aluminum Alloy Foam (AAF) has made an impact in automobile and aerospace applications where crash energy absorption, vibration and sound damping and weight reduction is obligatory. The AAF is an emerging lightweight material providing high strength and stiffness at relatively low density. This research is carried out to quantify the energy absorption of mild steel reinforced AAF having empty mild steel and foam-filled tubes for different strain rates and geometry parameters. The AAF used in the current study is AlSi10Mg foam of densities 0.45, 0.65, 0.85 g/cm3, which is produced using melt route process. The circular, square and rectangular geometries were tested at strain rates of 0.1, 1, 10 mm/s. From the obtained compressive stress-strain curves Specific Energy Absorption (SEA), Total Energy Absorption (TEA), plateau stress of the empty and filled sections were determined, which were then evaluated. AAF was assessed by both light and electron microscopy. Field Emission Scanning Electron Microscope (FESEM) and Analysis of Variance (ANOVA) technique was employed to investigate the highest contributing factor in energy absorption. It was observed that foam filled tube can absorb more energy than empty tubes before reaching densification point.

Thermographic investigation of strain rate effects in Al foams and Ni/Al hybrid foams

Open-cell metal foams are biomimetic open-porous materials mimicking the construction elements of bones. Based on their special porous microstructure, they are used as lightweight construction elements and for crash energy absorbers. Ni/Al hybrid foams are aluminium (Al) foams electrochemically coated with nanocrystalline nickel (Ni) leading to enhanced strength and energy absorption capacity. A robust understanding and knowledge of the deformation behaviour under different strain rates are essential to design crash absorbers made of foams. The present contribution is focused on the investigation of strain rate effects and is furthermore a pioneering work dealing with a full thermomechanical characterisation of the deformation behaviour in Al foams and Ni/Al hybrid foams by a combination of digital image correlation for measuring local strain fields and infrared thermography for measuring local temperature fields during the deformation process.

Effect of Different Intercritical Annealing Treatments without and with Overaging on the Mechanical Material Behavior

In the last decade, press‐hardening of manganese‐boron steels for the manufacturing of safety‐relevant components has become a well‐established industrial process. Thereby, very high strengths are achieved with pure martensitic microstructures. However, in certain areas of the car body structure more ductile components are necessary to absorb crash energy. For tailoring the material properties, two‐ or multiphase microstructures can be induced by rolling and heat treatment processes. The press‐hardening steel 22MnB5 which is employed in the present study, is used to manufacture three different ferritic‐martensitic microstructures. These different materials are characterized by classical mechanical models, based on experimental results. For the mechanical description of the initial yield stress depending on the stress state of different multiphase steels, the Hill model is calibrated. The elastic limit and the kinematic hardening of three various heat treatment conditions are determined using conventional tensile tests and the Galimel test, respectively. Therefore, the applied mathematical relations are derived and adapted for the performed investigations. The relationship between the load conditions and the proper application of the equations are explained. The resulting microstructures are characterized and the ramifications with respect to their energy absorption capability are discussed.

Crashworthiness characteristics of natural ramie/bio-epoxy composite tubes for energy absorption application

Using metallic materials in automotive structures increases weight, fuel consumption and cost, therefore, certain trends have begun to use lightweight and cheaper materials. Fibre composites are used in automotive applications because they are stiff, lightweight and stronger than bulk material, as well as they have a comparable energy-absorbing capacity to that of metallic materials. The aim of this study is to investigate the potentials in natural ramie/bio-epoxy composite in crash energy absorption applications. Cubic specimens consisted of 12, 24 and 30 plies of ramie/bio-epoxy laminates with 50, 80 and 120 mm long which were prepared by hand layup method. Static axial compression load was then applied and the energy-absorbing capability of the ramie/epoxy composite was evaluated. The crashworthiness characteristics of the composite tubes were evaluated by measuring the average and peak crushing load, specific energy absorption, total absorbed energy and crush force efficiency in quasi-static axial compression. The failure mode and behaviour of the tubes were investigated by taking photographs and recording the load–displacement curves during the test accomplishment. The test results indicated that natural ramie/bio-epoxy composite tube has the great potential to be used as an effective energy-absorbing device.

Energy absorption design study of subway vehicles based on a scaled equivalent model test

To obtain the characteristics of collision energy absorption and improve the passive safety of subway vehicles, the energy absorption design of subway vehicles was studied based on a one-seventh-scale model crash test. A full-size three-dimensional model of a subway vehicle was established using the multibody dynamics software MADYMO. The simulation results of the dynamics model were scaled down according to the similarity coefficients. By comparing the simulation results with the scaled model test results, the maximum error of deformation was 2.10 and 4.35% for the head car and the maximum deforming middle car, respectively, and the energy absorption error was found to be 8.75 and 5.70% for the head car and the maximum deforming middle car, respectively. The results indicate that the collision dynamics model of subway vehicles is relatively accurate. Next, based on this dynamics model, a full factorial experiment was designed to study the effects of the marshalling, mass and crushing tube’s plastic deformation platform force on the energy absorption of subway vehicles. The calculation results were fitted by multiple linear regression functions. Finally, the authors obtained the crash energy absorption formulas for the subway head car with an accuracy of 98.42% and for the maximum deforming middle car with an accuracy of 95.31%. These formulas can be applied to the preliminary design of subway vehicles and offer guiding significance for the parameter design of subway vehicles’ energy-absorbing devices.

A concept of smart multiaxial impact damper made of vacuum packed particles

The conceptual design of smart crash energy absorber made of Vacuum Packed Particles (VPP) is presented in this work. This structure is composed of granular material inside a plastomer sleeve. The absorber can change the flexural stiffness and as a result the amount of dissipated energy depending on the impact conditions. The special properties of the granular structure create the possibility of various applications as different working modes can be used. When the pressure inside is equal or higher than atmospheric pressure the system behaves similarly to a liquid, otherwise it has properties similar to viscoplastic solid. The physical properties of the structure may be rapidly changed by adjusting the pressure inside the system. Due to these properties Vacuum Packed Particles is considered to be a smart material.

Development of new reverse twist type crash energy absorbing structure

Development of new reverse twist type crash energy absorbing structure

Design of a half cut side member structure for optimal car crash energy absorption characteristics

Design of a half cut side member structure for optimal car crash energy absorption characteristics

Design of a half cut side member structure for optimal car crash energy absorption characteristics

The front side members of a car play a vital role in energy absorption for improved occupant safety during a crash. The response of side members with a half cut structure was examined with a parameter study. The structural design variables were the number of edges of the polygonal cross section, the spot welding spacing, and the thickness of the thin-walled side member structure. An optimal design method for the half cut side member was developed to maximise the absorbed energy by applying a response surface optimisation method. An objective function was used to maximise the energy absorbed by the side member structure. The mass of the optimal side member was constrained to be less than an allowed value.

Pop-up assembly of 3D structures actuated by heat shrinkable polymers

Folding 2D sheets into desired 3D structures is a promising fabrication technique that can find a wide range of applications. Compressive buckling provides an attractive strategy to actuate the folding and can be applied to a broad range of materials. Here a new and simple method is reported to achieve controlled compressive buckling, which is actuated by a heat shrinkable polymer sheet. The buckling deformation is localized at the pre-defined creases in the 2D sheet, resulting in sharp folding. Two approaches are developed to actuate the transformation, which follow similar geometric rules. In the first approach, the 2D precursor is pushed from outside, which leads to a 3D structure surrounded by the shrunk polymer sheet. Assembled 3D structures include prisms/pyramids with different base shapes, house roof, partial soccer ball, Miura-ori structure and insect wing. In the second approach, the 2D precursor is pulled from inside, which leads to a 3D structure enclosing the shrunk polymer sheet. Prisms/pyramids with different base shapes are assembled. The assembled structures are further tessellated to fabricate cellular structures that can be used as thermal insulator and crash energy absorber. They are also stacked vertically to fabricate complex multilayer structures.

Study of crash energy absorption characteristics of inversion tube on passenger vehicle

This article studied the energy absorption characteristics of the inversion tube and acquired the inversion tube design key dimensions under theoretical conditions by performing formula derivation in the quasi-static and dynamic state based on the working principle of the inversion tube: free inversion. The article further adopted HyperMesh and LS-Dyna to perform simulation and compared the simulation result with the theoretical calculating value for comparison. The design was applied in the full-vehicle model to perform 50km/h front fullwidth crash simulation. The findings showed that the deformation mode of the inversion tube in the full-vehicle crash was consistent with the design mode, and the inversion tube absorbed 33.0% of total energy, thereby conforming to the vehicle safety design requirements.

Improvement of crash energy absorption of 2D braided composite tubes through an innovative chamfer external triggers

Braided composites tubes have been reported to have a great potential in crash energy absorption applications. In this study, an innovative chamfer external trigger was introduced which is different from the traditional chamfer-flat crush-cap to guide the 2D braided tube. To make the material fully destroyed in the impact process, the innovative trigger restricts the space of tube under compression by a semi-circle cavity. A 3D-FE model for impacting processes of thin-walled braided tubes was built to study the effects of geometrical parameters on external trigger guiding tubes. Simulation and analysis of the influence laws of geometrical parameters on the cavity were then carried out. The results show that braided tubes worked with cavity effect can increase the energy absorption efficiency by 53% than traditional crush-cap, and the result and failure mechanism is significantly affected by the ratio of cavity radius of tube thickness(R/t). It is found that as the R/t ratio increases, the amount specimen energy absorption increases sharply then decreases and tend to be stable, while the ratio of peak load to mean load decreases and then increases. These two trends are very instructive for designing effective energy absorption structures using braided tubes with this innovative external trigger

Investigation on energy absorption of natural and hybrid fiber under axial static crushing

Using metallic materials in vehicles structures increases cost and fuel consumption, therefore, the trends start to use cheaper and lite materials. Fibers are used in composites in automotive applications because they are lightweight, stiff, and stronger than bulk material, as well as achieve comparable energy absorption to metallic materials. The aim of this research is to investigate the potential of natural fiber in the applications of crash energy absorption. An experimental procedure (hand layup) was applied to investigate the effect of using jute fiber on crash worthiness parameter of composite material with other types of fibers such as Kevlar and glass fiber reinforced epoxy composite. The work involved fabrication the tubes using three layers, two geometries (circular and square) with three different heights at constant crush speed 1.5 mm/s. The results show that the tubes of jute fiber were ineffective and failed directly, but, replacing one layer of jute fiber by one layer of other types of fibers lead to an enhancement in crash worthiness parameters especially, failure type and crash worthiness parameters. The better results are achieved when using hybrid jute and kevlar, where the energy absorption is enhanced by 17.75% and the specific energy absorption is enhanced by 25.122% in case of circular tube with diameter 50 mm. In case of square tube with side length 50 mm, the results are enhanced by 62.764% for energy absorption and 58.942% for specific energy absorption.

Crash concepts for CFRP transport aircraft – comparison of the traditional bend frame concept versus the developments in a tension absorbers concept

ABSTRACTDue to their inherently brittle behaviour, carbon fibre reinforced plastics (CFRP) structures demand for a specific design to achieve appropriate crash energy absorption compared to classical metallic fuselage designs. In this paper, experimental as well as numerical studies on two different crashworthy designs are presented. The first concept aims to absorb the crash energy by crushing of CFRP components below a reinforced cargo cross beam in combination with further energy absorbing devices in the lower side shell. The feasibility of this concept was in the meantime proven by tests at the coupon and structural element level. An alternative crash concept making use of energy absorption in so-called tension absorbers in the passenger and cargo floor structure was developed and assessed with the focus on a reduction of structural mass in combination with improved concept robustness. This paper provides a summary of the performed research work and discusses the context of the concept development. Details on the individual research tasks can be found in further publications which are given in the references.

Comparing Occupant Injury in Vehicles Equipped with and without Frontal Airbag

Most vehicle structures have been designed to withstand crash impact during an accident. The front area of the vehicle will crumple to absorb crash energy while the passenger compartment remains intact to protect the occupant inside. In addition, restraint system inclusive of airbag and seatbelts has been integrated in vehicles to further enhance the occupant's protection. However, in certain cases, the airbag is removed due to cost saving by car manufacturers. Although the frontal airbags have been removed, the structure remains the same. This can be observed from the crash tests conducted by ASEAN NCAP on two variants of the same car model which are fitted with and without airbags, where the cars obtained two different rating. This case study compares and presents occupant injuries for both variants.

Improved hybrid cellular automata for crashworthiness optimization of thin-walled structures

Thin-walled structures are of great importance in automotive crashworthiness design, because of their high crash energy absorption capability and their high potential for light weighting. To identify the best compromise between these two requirements, numerical optimization is needed. Size and shape optimization is relatively well explored while topology optimization for crash is still an open issue. Hence, this paper proposes an approach based on hybrid cellular automata (HCA) for crashworthiness topology optimization with a special focus on thin-walled structures. First approaches have been published, e.g. Duddeck et al. (Struct Multidiscip Optim 54(3):415---428, 2016), using a simple rule to define the target mass for the inner loop of the HCA. To improve the performance, a modified scheme is proposed here for the outer optimization loop, which is based on a bi-section search with limited length. In the inner loop, hybrid updating rules are used to redistribute the mass and a mass correction technique is proposed to make the real mass converge to the target mass strictly. The efficiency and correctness of the proposed method is compared with LS-OPT for axial crash case. Two different methods of defining the target mass in the outer loop are studied, the proposed bi-section search with limited length shows its advantage in two types of three-point bending crash optimization cases. Another advantage of this method is that it requires no significantly increasing number of evaluations when the number of design variables increases. This is demonstrated by applying this method to a crashworthiness optimization problem with 380 design variables.

Vehicle energy absorbers consisting of foldable cylinders using response surface methodology

In vehicle head-on collision, the side member cannot be collapsed more than 70% of its length because of its bulk. Moreover, its initial peak load is sometimes too high. So the authors have investigated the foldable origami cylinder structure - reversed spiral cylindrical (RSC) for the existing side member. RSC has solved these two problems mentioned above. In this paper, we treat so called crash box which is shorter than the side member. In the shorter length case, it makes much more difficult to solve the two problems mentioned above simultaneously. With using RSC for the crash box, it is requested to achieve that initial peak load is lower; meanwhile the amount of crash energy absorption is equal or higher than the existing energy absorber. In order to response to the difficulties, the authors try to seek an ideal design specification consisted by RSC and a straight cylinder.