Automotive Safety Components Research Articles

Numerical Study of an Automotive Crash Box in Carbon Fiber Reinforced Polymer Material Using Chang Failure Criteria

This paper discusses novel numerical techniques for studying the damage to automotive safety components in carbon fiber reinforced polymer (CFRP) deployed in the automotive industry to protect passengers, high voltage batteries and powertrains from rear impacts. The idea proposed in the manuscript is to use Newmark’s methodology with the FEM for the numerical description of the explicit dynamic model of the components facing the standard impactor, following the Euro NCAP protocol. Using an explicit dynamic Radioss rear crash box, we have successfully demonstrated normal behavior for CFRP materials, where the value of kinetic energy is close to the theoretical value. Moreover, the simulation provides a behavior consistent with previous successful studies because the maximum dynamic time is the same as the total damage (0.10 ms).

Improvement of HCF life of automotive safety components considering a novel design of wheel alignment based on a Hybrid multibody dynamic, finite element, and data mining techniques

The main aim of the present study is to improve the High-Cycle Fatigue (HCF) life of automotive safety components subjected to multi-input random non-proportional loading. A case study was conducted on the automotive knuckle as one of the high-critical mechanical components of the suspension and steering systems. The steering knuckle is subjected to the highest road- and steering-induced random loads that are exerted on several points (i.e., joints of knuckle with lower control arm, steering linkage, and Macpherson strut). Moreover, incorrect adjustment of wheel angles increases the intensity of road loads. In this regard, previous studies have shown that wheel angles affect the service time of this component. In the present study, the authors attempted to present a novel design of wheel alignment to reduce the intensity of 3D stress components, and subsequently, to increase the fatigue life of the steering knuckle. To this end, a Hybrid multibody dynamic, finite element, and data mining techniques was used. Accordingly, different load histories extracted through Multi-Body Dynamics (MBD) analysis of a full vehicle model were applied on various joints of this component. Next, a transient dynamic analysis was performed, and the time histories of 3D stress fields were obtained in the critical zone. The fatigue life of the component was predicted using the Critical Plane Method (CPM) via employing the Rain-flow cycle counting technique and Miner-Palmgren damage accumulation rule. Finally, the results of Taguchi Sensitivity Analysis (TSA) were used to investigate the effect of wheel primary angles, including Camber and Toe, on the fatigue life of the cast iron knuckle. Moreover, Response Surface Method (RSM) was utilized to optimize the wheel alignment, and the cyclic lifetime of the component was compared under the pre- and post-optimization process. The results reveal that knuckle life improves by 33.66% using the optimum settings of wheel alignment.

Lightweight scheme selection for automotive safety structures using a quantifiable multi-objective approach

Abstract The main objective of this paper is to propose a quantifiable multi-objective evaluation approach method to rationalize the subjective evaluation in the selection of lightweight scheme for automotive safety components, which can be applied in the selection of materials and structures in lightweight design of automobiles and other products. The proposed method combines intuitionistic fuzzy number theory, entropy method and Technique for Order Preference by Similarity to Ideal Solutions (TOPSIS) to deal with uncertainty in the decision-making process. Intuitionistic fuzzy number theory was used to quantifies the subjective evaluation of decision makers. Entropy method and fuzzy logic theory were utilized to objectively weight the criteria and decision makers, and The TOPSIS method is used to assess the pros and cons of alternatives. To assess and validate the effectiveness of the proposed method, three automotive bumper systems using different materials and structures, namely, high strength steel (HSS), polymer composite-metal hybrid (PMH), and glass fiber-reinforced aluminum laminates (GLARE) were taken as example, some qualitative criteria including recyclability and easy manufacturability as well as several quantitative criteria such as the weight, cost, crash safety (energy absorption, peak impact force and maximum deflection), were considered and balanced. According to the findings, the evaluation results of the proposed method are consistent with the evaluation results of the existing VIKOR method and TOPSIS method, which verifies the correctness of the proposed method. In addition, from the perspective of sensitivity analysis results and method principles, it is proved that the proposed method is superior to the other two methods in robustness and efficiency.

Investigation of Fatigue Strength and Life Prediction for Automotive Safety Components of V-Notched and Un-notched Specimen Part I: Utilization of Waste Materials into Raw Materials

This paper deals with a design of industrial cast-parts and mainly focuses on fatigue life influenced by organic and inorganic particles at different stress levels over a wide range spectrum, which is evaluated and compared. The fracture mechanisms and fatigue strength of V-notch and un-notch specimens are described. The notch factor and notch sensitivity factors have been studied. Porosity is the main factor for crack growth, and it reduces with the addition of waste particles. This combination receives a lot of attention due to its low cost and environmental safety. The micro-/macro-cracks and fracture surface are revealed using SEM and OM analysis.

A new algorithm for fatigue life assessment of automotive safety components based on the probabilistic approach: The case of the steering knuckle

In the present paper, the author has attempted to examine fatigue life of automotive safety components under axial variable amplitude loading conditions. To this end, the time components of stress tensor in the critical area of the knuckle and Liu-Zenner criterion were used to calculate the time history of equivalent stress. Then, the probability distribution function (PDF) of stress was extracted by applying the stress level counting technique. The Fourier curve fitting method was employed in order to formulate the PDF. Subsequently, the fatigue life of the component was estimated using the probabilistic approach. Finally, the results of the higher order of Fourier curve fitting and different counting ranges were compared with the experimental results. Thus, the best algorithm for precisely determining fatigue life of automotive components was obtained.

Effect of organic and inorganic reinforced particulates for fatigue behaviour of Al–Si7–Mg0.3 hybrid composite: V-notched and un-notched specimen experiments with microstructural constituents

The design of industrial cast parts Al–7Si–0.3Mg alloy is widely used as structural components of aircraft and automotive safety components. The investigation mainly focuses on fatigue life influenced by organic and inorganic particles with different weight fractions measured at different stress levels over a wide range spectrum of three different materials which are evaluated and compared. The notch and un-notch specimens of these materials are described fatigue strength and crack mechanism using high cycle fatigue. According to Basquin constants, fatigue notch factor and notch sensitivity factor were studied. The A356/7.5% rice husk ash-7.5% fly ash hybrid composite increases fatigue strength of 30% and lower the fatigue notch factor to 25% compared to the matrix alloy. Porosity is the main factor for estimation of fatigue life. The micro-/macro-cracks and fracture surface are revealed under the SEM and optical microscope analysis.

Microstructural and Mechanical Study of Press Hardening of Thick Boron Steel Sheet

Press hardening has become a staple in the production of automotive safety components, due to the combination of high mechanical properties and form complexity it offers. However, the use of press hardened components has not spread to the truck industry despite the advantages it confers, namely affordable weight reduction without the use of exotic materials, would be extremely attractive for this sector.The main reason for this is that application of press hardened components in trucks implies adapting the process to the manufacture of thick sheet metal. This introduces an additional layer of complexity, mainly due to the thermal gradients inside the material resulting in though-thickness differences in austenitization and cooling, potentially resulting in complex microstructure and gradient of mechanical properties.This work presents a preliminary study on the press hardening of thick boron steel sheet. First of all, the evolution of the sheet metal during austenitization is studied by means of dilatometry tests and by analysing the effect of furnace dwell time on grain size. Afterwards, material cooled using different cooling strategies, and therefore different effective cooling rates, is studied in terms of microstructure and mechanical properties. Initial results from finite element simulation are compared to experimental results, focusing on the phase composition in through thickness direction.Results show that industrial-equivalent cooling conditions do not lead to gradient microstructures, even in extreme scenarios involving asymmetrical cooling.

Multiaxial fatigue assessment for automotive safety components of cast aluminium EN AC-42000 T6 (G-AlSi7Mg0.3 T6) under constant and variable amplitude loading

EN AC-42000 T6 (A 356 T6) is the most frequently used cast aluminium alloy for automotive safety components. Under non-proportional normal and shear stresses, fatigue life is increased in contrast to ductile steels where life is reduced. This behaviour is caused by the low ductility of this alloy (e<10%) compared to structural steels suggesting the application of the Normal (Principal) Stress Hypothesis (NSH). Under multiaxial constant and variable amplitudes without and with mean stresses, the NSH was able to deliver, for most cases, conservative but non-exaggerated results. Fatigue lives under spectrum loadings were estimated by the application of the modified Palmgren-Miner Hypothesis using the allowable damage sum Dal=0.3.

Multiaxial fatigue of cast aluminium EN AC-42000 T6 (G-AlSi7Mg0.3 T6) for automotive safety components under constant and variable amplitude loading

Regarding the fatigue behaviour of EN AC-42000 T6 (A 356 T6), which is the most frequently used cast aluminium alloy for automotive safety components, especially under non-proportional constant and variable normal and shear stress amplitudes with changing principal stress directions, a poor level of knowledge was available. The reported investigations show that, under non-proportional normal and shear stresses, fatigue life is increased in contrast to ductile steels where life is reduced due to changing principal stress directions. This behaviour caused by the low ductility of this alloy (e < 10%) compared to quenched and tempered steels suggests the application of the Normal (Principal) Stress Hypothesis (NSH). For all of the investigated stress states under multiaxial constant and variable (Gaussian spectrum) amplitudes without and with mean stresses, the NSH was able to depict the life increase by the non-proportionality and delivered, for most cases, conservative but non-exaggerated results.

Concept Validation for Selective Heating and Press Hardening of Automotive Safety Components with Tailored Properties

A new strategy termed selective heating and press hardening, for hot stamping of boron steel parts with tailored properties is proposed in this paper. Feasibility studies were carried out through a specially designed experimental programme. The main aim was to validate the strategy and demonstrate its potential for structural optimisation. In the work, a lab-scale demonstrator part was designed, and relevant manufacturing and property-assessment processes were defined. A heating technique and selective-heating rigs were designed to enable certain microstructural distributions in blanks to be obtained. A hot stamping tool set was designed for forming and quenching the parts. Demonstrator parts of full martensite phase, full initial phase, and differentially graded microstructures have been formed with high dimensional quality. Hardness testing and three point bending tests were conducted to assess the microstructure distribution and load bearing performance of the as-formed parts, respectively. The feasibility of the concept has been validated by the testing results.

Influence of the edge rounding process on the behaviour of blanked parts: numerical predictions with experimental correlation

Blanking of sheet metal is an important forming process in the automotive industry for the manufacture of mechanical components. The final component shape, obtained at the end of bending or deep-drawing processes, often has sharp edges due to the blanking operation. Concerning passenger safety components, like seat belt anchors, rounding of the edges by punching is necessary to avoid cutting the belt material. In addition to removing the sharp edges, the punching results in work hardening of the material in the rounded zones which results in an increase in the local resistance of the material. In this study, a high-strength low-alloy steel (HSLA S500MC) has been tested with the aim of quantifying the blanking and edge rounding operations. The mechanical behaviour of test specimens is investigated by means of tensile tests and the material is characterised in terms of Vickers micro-hardness. Numerical simulations of the edge rounding process are developed using previously identified material behaviour laws. The residual stress fields are characterised and compared to experimental results. This is done so that numerical simulation can be done in the future to prediction the in-service behaviour of the component. Specimens with rounded edges are compared to specimens that were not submitted to the rounding operation. It is shown that Edge Rounding by Punching improves the component resistance, therefore justifying the use of this process in the manufacture of automotive safety components.

Experimental and Numerical Studies of Edge Rounding Process in HSLA Steels Sheet Metal

Blanking of sheet-metal is an important forming process in the automotive industry for the manufacture of mechanical components. The final component shape, obtained at the end of bending or deep-drawing processes, often has sharp edges due to the blanking operation. Edge Rounding by Punching (E.R.P.) of safety components is necessary to avoid cutting the belt material. In addition to removing the sharp edges, the punching results in work hardening of the material in the rounded zones which results in an increase in the local resistance of the material. In this study, a High Strength Low Alloy steel (HSLA S500MC) is tested with the aim of analysing the residuals fields in the chaining of blanking and edge rounding processes. The mechanical behaviour of the sheet material is investigated by means of tensile tests and Vickers micro-hardness measurements. Numerical simulations are performed using a ductile damage criterion. The experimental residual stress fields are characterised and compared to numerical results, in view of predicting the in-service behaviour of the component. Specimens with rounded edges are compared to specimens that were not submitted to the rounding operation. It is shown that (E.R.P.) improves the component resistance, therefore justifying the use of this process in the manufacture of automotive safety components.

Experimental and Numerical Evaluation of the Heat Transfer Coefficient in Press Hardening

When producing thin ultra high strength steel components with the press hardening process, it is essential that the final component achieves desirable material properties. This applies in particular to passive automotive safety components where it is of great importance to accurately predict the final component properties early in the product development process. The transfer of heat is a key process that affects the evolution of the mechanical properties in the product and it is essential that the thermal contact conditions between the blank and tool are properly described in the forming simulations. In this study an experimental setup is developed combined with an elementary inverse simulation approach to predict the interfacial heat transfer coefficient (IHTC) when the hot blank and cold tool are in mechanical contact. Different process conditions such as contact pressure and blank material (22MnB5 and Usibor 1500P) are investigated. In the inverse simulation, a thermo-mechanical coupled simulation model is used with a thermo-elastic-plastic constitutive model including effects from changes in the microstructure during quenching. The results from simulations give the variations of the heat transfer coefficient in time for best match to experimental results. It is found that the pressure dependence for the two materials is different and the heat transfer coefficient is varying during quenching. This information together with further testing will be used as a base in a future model of the heat transfer coefficient influence at different conditions in press hardening process.