Front Side Rail Research Articles

Effect of geometric irregularities induced during manufacturing of a crash-box on its crashworthiness performance

Imperfections associated with the geometric features of any component are inevitable during its fabrication and some of those can even have a drastic impact on its functionalities. One such case arises while fabricating one of the essential passive safety devices in an automobile called as 'thin-walled collapsible energy absorbers'. Thin-walled collapsible energy absorbers also known as crash-boxes are the tubular shell structures located in between the bumper and front side rails of an automobile. Crash-boxes collapse in a stable progressive manner to absorb kinetic energy of an external impact to protect the occupants during an accident. Tubular crash-boxes are generally manufactured by extrusion. Geometric imperfections in the form of irregularities in the shell thickness may be induced during extrusion of the crash-boxes. The present study aims to gauge the effects of irregularities present in the thickness of the extruded crash-box on it’s crashworthiness performance, numerically. Cylindrical aluminium alloy tubes are modelled as crash-boxes using ABAQUS/Explicit. The irregularities in the thickness of the tubular crash-box are modelled with the help of three different imperfect models. In every imperfect model, maximum variation in the thickness is kept within the tolerance value, provided by the standards DIN EN-755-9. The quasi-static axial collapse of these ‘imperfect’ cylindrical tubes is simulated and their crashworthiness performance indicators are compared with those of an ‘ideal’ circular crash-box. It is seen that the energy absorption and the mean crushing force reduced drastically due to these shell thickness irregularities in comparison to the ideal model. It is also observed that the mode of collapse of the circular tube changed from axi-symmetric concertina mode to the diamond mode due to irregularities in their thickness. Such significant change in the crashworthiness performance of crash-box may lead to a huge disaster in terms of human lives. Hence, crash-boxes should be fabricated carefully with more tight geometric and dimensional tolerances.

Design optimization of the S-frame to improve crashworthiness

In this paper, the S-frames, the front side rail structures of automobile, were investigated for crashworthiness. Various cross-sections including regular polygon, non-convex polygon and multi-cell with inner stiffener sections were investigated in terms of energy absorption of S-frames. It was determined through extensive numerical simulation that a multi-cell S-frame with double vertical internal stiffeners can absorb more energy than the other configurations. Shape optimization was also carried out to improve energy absorption of the S-frame with a rectangular section. The center composite design of experiment and the sequential response surface method (SRSM) were adopted to construct the approximate design sub-problem, which was then solved by the feasible direction method. An innovative double S-frame was obtained from the optimal result. The optimum configuration of the S-frame was crushed numerically and more plastic hinges as well as shear zones were observed during the crush process. The energy absorption efficiency of the structure with the optimal configuration was improved compared to the initial configuration.

Crashworthiness Study of S-Rail Behavior

In this study, a different design aspect of a simplified front side rail structure of an automobile body (S- Rail) from the point of view of crashworthiness parameters which are crushed energy absorption and force response and also weight efficiency is studied. Various orientations of cross section design and various material replacements have been applied to investigate their effects. The specific energy absorption (i.e. Energy absorption per unit weight) is taken as a measure of the performance of a structure. Effect of different cross section with model cross section horizontally ‘hat – type’ model (shape 5) given greatest energy absorbed. This model then being analyzed with different material such as mild steel, aluminum, Hastelloy X alloy and Fiberglass Polyamide (PA – 66). Hastelloy X alloy result the highest increment in ability to absorbed energy during collision. The consideration of various cross sections and the best material selection of replacement then been discussed and compared for suitability from the aspect of crashworthiness, safety of passengers, weight efficiency and cost to automobile industry.

A Contrastive Analysis of the Crashworthiness between 22MnB5 and DP590 Front Bumper Inner Plates

The front bumper inner plate was researched based on contrastive analysis of the crashworthiness considering using 22MnB5, a typical hot forming AHSS (Advanced High Strength Steel) and DP590, a kind of general high strength steel. In this paper, we contrasted energy absorption, section force, and maximum displacement of the two different front bumper systems in low-speed collision. The analysis shows the front bumper inner plate using hot forming AHSS can improve the crashworthiness of automobiles and make it more balanced and reasonable to transfer collision energy and force. As a result, the maximum displacement of the front bumper system decreases and other parts such as front side rails can be safer. Thus, using hot forming AHSS in designing a front bumper inner plate can improve the passive safety of automobiles.

Study on Accuracy Improvement of Vehicle Crash Simulation Considering Stamping Effects

It is general preferable to consider stamping effects of sheet metal forming for vehicle crash simulation nowadays. However, the present approaches for stamping simulation and coupling forming results to crash finite element model require massive pre-works. To overcome these difficulties, an inverse method for rapid and simple stamping simulation using HYCRASH is introduced, where crashworthiness analysis of front side rail under frontal crash was used as an example in this study. A detailed stamping simulation by AUTOFORM is used for comparison, also accompanied with the one without stamping effects. Through comparison of stamping results and frontal crashworthiness performance, it is concluded that effective plastic strain makes more contribution on simulation accuracy than thickness reduction, and HYCRASH shows an attractive approach for stamping analysis than AUTOFORM coupled in crash simulation in the context of computational cost.

Finite element analysis of collapse of front side rails with new types of crush initiators

Today’s vehicles are designed with lighter weight to increase performance and to lower fuel consumption, while at the same time meeting the demands of safety requirements. Reducing the cross-section of structural elements to achieve weight reduction can lead to adverse effects on passive safety of the vehicle. In such cases, necessary design modifications must be created to overcome the adverse effects. For this purpose, front rail columns with crush initiators are used in the front zone of cars. These shock-absorbing elements act as energy consuming devices that convert impact energy (kinetic energy) into plastic deformation energy. Simulation of this energy conversion phenomenon is the subject of this paper. The primary objective of this study is to computationally determine how various crush initiators can reduce the maximum crushing force and how different types of structural modifications affect the observed folding form. The ribs near the crash area are placed in two rows and four different configurations on all facing sides of the column in order to decrease reaction forces and absorb more kinetic energy. These structures are analyzed under axially loaded crushing forces using the explicit nonlinear finite element analysis solver ANSYS/LS-DYNA.

Lightweight Design of Automotive Front Side Rail Based on Robust Optimisation

Nowadays, both conventional automobiles and new energy cars require urgently the lightweight design to realise energy economy and environmental protection in a long run. The weight reduction of body structure plays a rather important role in decreasing the weight of full vehicle. In the real engineering problems, the variation in sheet gauge, geometrical size and material parameters, caused by environmental factors and other uncertainties, may affect the structural performances of body parts. Therefore, the lightweight design without considering this kind of tolerance may result in the loss of feasibility and reliability in engineering application. In this work, based on robust optimisation method, the study on the front side rail lightweight design is performed. The response surface method (RSM), coupled with design of experiment (DOE) technique, is employed to create the approximate functions of structural performances. The robust optimisation and deterministic optimisation formulations are constructed, respectively, for comparison. The solutions are obtained by using the sequential quadratic programming (SQP) algorithm. The lightweight design, considering the impact of the tolerance of sheet gauge, mechanical parameters of material and structural performances, is still guaranteed to be reliable when structural random varieties are present. The weight reduction achieved by using robust optimisation reached 29.96%.

Lightweight design of automotive front side rails with TWB concept

Due to the continuous tightening of various regulations for conserving energy and protecting the environment, the weight reduction of and automobile body becomes an increasingly important issue. In order to reduce the weight of an automobile, we have brought forward a method of replacing the simple structure with the tailor-welded blank (TWB), in which a design process is appropriately defined for a front side rail. Focusing on the thickness determination of TWB, we have deduced the constraint inequalities of strength, bending stiffness, and torsion stiffness to prevent the thickness from decreasing unboundedly due to the lightweight requirement, thus reducing the weight of the front side rail satisfying the design demands of these three factors. The full-width frontal impact simulation of the whole car after redesign in the front side rails has been performed to verify vital performances such as deformation mode, energy absorption, and acceleration.

Study on Structural Lightweight Design of Automotive Front Side Rail Based on Response Surface Method

Nowadays, vehicle lightweight design is a main topic in automotive industry. Crashworthiness, which is the most important performance of a full vehicle, must be always satisfied in the study on body lightweight design. This paper presents research, from the point of view of safety, of structural lightweight design of the front side rail of a passenger car. The response surface method is used to create mathematical models that represent the relationship between structural sheet thicknesses and absorbed energy of the entire structure in the frontal crash simulation, and the relationship between structural sheet thicknesses and the mass of the entire structure. Then an optimization process is performed, and the structural mass and original absorbed energy are defined as objective and constraint functions, respectively. Minimum mass and structural sheet thicknesses are obtained with the satisfaction of original absorbed energy of the front side rail structure. The weight reduction of the front side rail is 26.95%.

Two materials S-frame representation for improving crashworthiness and lightening

In this paper, different designs of a simplified front side rail structure of an automobile body (S-frame) from the point of view of crashworthiness and weight efficiency is studied. Various possible models of S-frame is presented and characteristics of each models are compared and discussed. It is shown that a hybrid S-frame made of steel and aluminum shows better characteristics from the point of view of passenger safety and weight efficiency.

Effect of the cross-sectional shape of hat-type cross-sections on crash resistance of an “S”-frame

This paper addresses a design aspect of a front side rail structure of an automobile body from the point of view of weight efficiency and crush energy absorption. Various orientations of the cross-section and ways of reinforcing the cross-section by an internal stiffening member are investigated. The specific energy absorption (i.e. energy absorption per unit weight) is taken as a measure of the performance of a structure. Also the advantages of reinforcing the side rail by means of aluminum foam filling are assessed. It is shown through extensive numerical simulation using nonlinear finite element code PAM–CRASH, that the model with a diagonally positioned internal stiffener and suitable triggering dents can absorb up to 200% more energy than the typical double-hat/double-cell profile member. At the same time there is a 3 fold increase in the specific energy absorption. By using the concept of aluminum foam-filling with 3 MPa foam, the specific energy absorption increases by a factor of 2.84.

Analysis of crash response of aluminium foam-filled front side rail of a passenger car

The objective of this paper is to gain an understanding of the reinforcing effect by aluminium foam-filling for the front side rail and subframe structure of a passenger car. The reinforcing effect by aluminium foam-filling on two major collapsing modes, axial compression and bending, is studied. The front rail is divided into axial collapse and a bending collapse parts, and the crush response of each is investigated by varying wall thickness and the aluminium foam strength. The effect of the anisotropy of aluminium foam on the crush response of the front side rail structure is also studied by varying the orientation of aluminium foam. The sensitivity analysis of wall thickness and aluminium foam strength on the energy absorption and the specific energy absorption is made in axial compression and bending collapse. A summary of optimisation process of aluminium foam-filled front rail structure is given as a design example. The optimum design with regard to weight efficiency and crash energy absorption is determined using “Design of Experiment” and “Response Surface Method”.