Automotive Panels Research Articles

Reduction of Young’s modulus for a wide range of steel sheet materials and its effect during springback simulation

Springback is among the key issues to be addressed in order to facilitate the application of AHSS in the automotive body. Since numerical simulations have become a standard tool during process design in automotive panel production, advanced material models considering springback-related material properties are increasingly getting into the focus. Next to the Bauschinger-Effect, describing early re-yielding during load reversal, also a reduction of Young’s modulus with increasing plastic strain is depicted in several material models implemented in different FEM codes. Herein, we focus on this Young’s modulus reduction. The initial Young’s modulus as well as its reduction are measured from uniaxial tensile tests with multiple unloading-reloading cycles without load reversal. Results are shown for steel sheet materials ranging from mild steels to AHSS containing retained austenite. Differences of the Young’s modulus decrease among the different steel grades are discussed with respect to their respective microstructure. Material models, depicting the Young’s modulus reduction, are fitted to the obtained data. The consequence of considering this effect during forming simulation is shown for bending-under-tension tests of DP600, representing the largest reduction.

Uticaj obrade otpuštanjem nakon zavarivanja na osobine tačkasto zavarenog spoja dvofaznog čelika DP600

In order to meet the increasing requirements of the automotive industry for material strength grades and performance, the application of advanced highstrength steel automotive panels, represented by dual-phase steel, in lightweight vehicle bodies is increasing. Resistance spot welding is the main joining process for vehicle body manufacturing. How to improve the tensile strength and fatigue performance of dual-phase steel resistance spot welding joints is of great significance to the welding structure of the body. In this paper, resistance spot welding of cold rolled DP600 dual phase steel in the welding current range of 9000A-12000A was carried out. The effects of post-weld tempering treatment on microstructure, microhardness, shearing and fatigue of joints were compared. The results show that the microstructure transformation occurs in the weld nugget area after post-weld tempering, and the tempered martensite appears to reduce the microhardness of the weld nugget area; the nugget diameters, tensile-shear strength and failure energy are all higher than those without tempering treatment; tempering improves the fatigue strength of the spot joints, and regardless of whether the welded joints are tempered, cracks are all generated near the heat affected zone of the joint after fatigue test.

Influence of Sodium Hydroxide (NaOH) Treatment on Mechanical Properties and Morphological Behaviour of Phoenix sp. Fiber/Epoxy Composites

The purpose of this present research work is to assess the static and dynamic mechanical properties of an eco-friendly natural cellulosic fiber (Phoenix sp.) reinforced epoxy composites. The cellulosic fiber was isolated from Phoenix sp. plant petioles, and it was treated with various concentrations of sodium hydroxide (5, 10, 15 and 20%) solution. The impact of treatments on tensile, flexural, impact and dynamic mechanical properties of the fabricated composite was explored and optimized. Moreover, the mechanically tested samples were subjected to morphological analysis to predict the failure mechanisms. The outcomes revealed that the treated fibers had good interfacial bonding with epoxy matrix (confirmed through morphological and single fiber pull-out studies), reduced the failure mechanisms (fiber pull-outs and fiber debonding) and exhibited good static and dynamic mechanical properties of composite materials than untreated fiber composites. It is concluded that composites fabricated using 15% of sodium hydroxide treated fiber could be used to manufacture automotive panels and other lightweight industrial products.

Onesided offsetting and smoothing algorithm for complex 3D trimming curve of trimming insert steel for automotive panels

ABSTRACT Based on the offset of the feature inflection point, the one-sided offsetting and smoothing algorithm of 3D trimming curve is proposed for trimming insert steel of automotive panels. The core of the algorithm is to determine the curve’s 3D offset direction and its feature inflection point. It obtains the offset direction of 3D discrete point by cross-multiplying the trimming direction with the vector of the two adjacent points of the 2D projection of them. Therefore, the offset direction of the 3D curve is not unique, and each discrete point has its own offset direction. To avoid the curve distortion caused by excessive discrete point offset, only by offsetting the feature inflection points, that control the curve shape and trend, to improve the curve smoothness. The 3D feature inflection points in the plane and trimming direction are determined by the abrupt change in curvature and perturbation, so the offset curve maintains the original curve’s characteristics. Self-intersecting defects of the offset curve are eliminated by pre-offsetting the 2D projection points. The target points are obtained by offsetting the feature inflection points and distribution points, and the one-sided offsetting and smoothing curve is obtained by constructing the spline curve.

Intelligent design method and system of trimming block for stamping dies of complex automotive panels

Trimming block is the most important working component of trimming die for automotive panels. Its structure and form are various and complex, resulting in its design quite tedious and time-consuming, which affected the efficiency and quality of die design. Aiming at the three problems of curve offset, surface construction, and flange uncertainty, an intelligent design method based on parameters and sketch driven is proposed to realize the rapid and intelligent design of trimming block. According to the curve offset criterion of trimming block, a 3D curve offset method based on the feature inflection point is proposed, which considers the characteristics of curve from offset direction, curvature, and perturbation, and meets the requirement of minimum offset distance, to maintain the shape following of initial curve. The offset spline curve ensures the minimum offset distance and its trend with the original curve. Combined with the group concept, it introduces a segmented surface construction method for trimming block surfaces based on non-uniform rational B-spline mesh surface and supplemented by filling surface, which can well track the tendency of trimming curve and meet the G1 continuity conditions between adjacent surfaces. It presents an interactive sketch to solve the diversity and uncertainty of flange, which can free to draw the 2D outline of any flange. Finally, the whole design process of trimming block is serialized by parameters and sketch driving to achieve the fully automated intelligent design method, which is integrated into the NX software, and an intelligent design system of trimming block is developed as a submodule in the modular design of the trimming die. The design example of the fender trimming block shows that the system can control the error well and guarantee the success of the onetime design. The designed trimming block has a smooth blade surface, a smooth transition, and excellent structural strength, which can significantly improve design quality and efficiency.

Multifunctional sandwich panel design with lithium-ion polymer batteries

This paper investigates the mechanical properties of lithium-ion polymer (LiPo) batteries and their subsequent use in the design of multifunctional sandwich panels for automotive applications. Shear properties, flexural properties and compression properties of prismatic pouch LiPo batteries are determined experimentally through a hole-punch test, a three-point bending test and an in-plane compression test, respectively. This study is the first to characterize the shear properties of a lithium-ion battery, which are critical in sandwich panel design. The mechanical properties of the batteries obtained are then applied to existing analytical models of multifunctional sandwich panels consisting of carbon fibre composite facesheets and LiPo battery cores, which are currently being considered for use in automotive panel design. A material selection procedure for a stiffness-limited automotive car door panel subjected to bending shows that a trade-off between mechanical performance and cost can be achieved by using a composite sandwich panel with thin LiPo battery cores or by embedding larger LiPo batteries in lower-density polymer foam cores. The practicality and implementation aspects of using sandwich composites with LiPo battery cores in automotive design are also discussed.

On the modal behaviour of ultralight composite sandwich automotive panels

The effects of vibrations in vehicles range from simple noise and reduced comfort, to decreased performance, from wear and material fatigue to irreversible failures and danger. A study of the dynamic behaviour of reinforced composite panels is here presented, applied to the construction of an ultralight photovoltaic roof in the case of a solar sport car. This is an extreme race prototype where design and materials solutions, as high strength carbon fiber reinforced polymers and sandwich-structured composites, were addressed to optimize the stiffness-to-weight ratio. A modal analysis was performed considering materials anisotropies by a layered-shell finite element model and through-the-thickness integration points with the scope to discretize the multi-layered sandwich structure. Additional aspects, as gravity force and external constrains, were also included. Experimental evidences were used for validating the numerical model and underscored an outstanding accuracy. The same design procedure was finally applied to change the preexisting structural solution achieving an optimized roof that was manufactured, installed and tested.

Mechanical Behavior and Damage of Zinc Coating for Hot Dip Galvanized Steel Sheet DP600

Advanced high strength galvanized steel sheet has been one of the dominant materials of modern automotive panels because of its outstanding mechanical properties and corrosion resistance. The zinc coating thickness of hot dip galvanized steel sheet is only about 10–20 μm, which is a discarded object on the macro level. However, it is obvious to damage and impact on stamping performance. Therefore, this paper takes zinc coating as the research object and builds its mechanical constitutive model based on a nano-indentation test and dimensional analysis theory. We separated the zinc coating from the galvanized steel substrate and constructed a sandwich material model by introducing a cohesive layer to connect the zinc coating and the steel substrate. We obtained the interface binding energy between the zinc coating and the steel substrate through the nano-scratch test. The accuracy of the model is verified by the finite element analysis of hemispherical parts. We used the five-layers element model with 0 thickness cohesive layer to simulate the zinc coating damage of galvanized steel sheet. The hemispherical part drawing experiment is used to verify the feasibility of the finite element analysis results. The results demonstrate that it is more accurate to consider the finite element numerical simulation of the zinc coating, introducing the cohesive element to simulate damage between the coating and the substrate. Drawing depth, stamping force, and the strain of the numerical simulation are closer to the experimental results.

Fatigue strength evaluation of self-piercing riveted joints of AZ31 Mg alloy and cold-rolled steel sheets

Abstract The application of magnesium alloys to automobiles is increasing due to their superior specific strength and specific stiffness. In this study, an upper sheet of AZ31 magnesium alloy and a lower sheet of cold-rolled steel were joined by self-piercing riveting (SPR), a method commonly used to join automotive panels. A cross-shaped specimen was fabricated with a punching force of 35 kN, which exhibited the best joint strength for the SPR joint specimen geometry. Monotonic and fatigue strengths were evaluated using cross-shaped specimens at loading angles of 0°, 45°, and 90°. The load amplitude corresponding to the fatigue endurance limit was assumed to be at 106 cycles, and the fatigue ratios (= fatigue endurance limit/static strength) at the loading angles of 0°, 45°, and 90° are 22%, 13%, and 9%, respectively. For all three loading angle specimens, fatigue cracks initiated at the triple point where the rivet shank, the upper sheet and the lower sheet are in contact with each other, with the cracks propagating through the thickness of the upper sheet and ultimately leading to fracture. The fatigue lifetimes were evaluated through the von-Mises stress, maximum principal stress, and equivalent stress intensity factor. It was found that the fatigue lifetimes could be evaluated most appropriately through the maximum principal stress.

Automatic design for trimming die insert of automotive panel

Trimming inserts with complicated geometric features are widely used in the manufacture of automotive panels. The number of trimming inserts for a typical automotive panel is usually more than 20, even up to 100. The design of trimming inserts is a complex and time-consuming process, which significantly affects the development period and quality of automotive panels. However, the design of trimming insert needs to handle a lot of complex geometrical problems, such as 3D curve offset problems. The current commercial CAD software cannot provide a complete and effective solution to the problem, where a lot of tedious human-intersections are needed. This paper presents a systematic methodology which includes the automation of trimming lines division and trimming inserts design. An automatic-decomposition algorithm is presented to divide the trimming lines into short segments. Then the trimming insert is designed for each divided trimming segment. In order to automate the design of trimming insert, a bulking-fairing algorithm is introduced to fair planar curves to meet physical constraints, and a robust 3D curve offset method is proposed to generating 3D offset curves to overcome the main limitation of existing methods. Lastly, the path-interference-check algorithm is presented to check if the interference occurs during the trimming process. This system is implemented and has applications in industry. Case studies and industrial applications have demonstrated the system’s powerful ability in design trimming inserts of automotive panel, and the efficiency for insert design could be improved by 80% at least.

Development of Hot Stamping for Automotive Panel Parts with Step-shaped Wall

Development of Hot Stamping for Automotive Panel Parts with Step-shaped Wall

Effect of Local Heating on the Mechanical Characteristics of Repaired Automotive Panels

Flame straightening is a technology process used to eliminate deformations. This method relies on local heating of the material to correct geometry or damaged parts. In the local automobile services its main use is for repairs of less critical deformed components. The maximum temperature and thermal gradient, heating time, cooling rate and number of heating cycles affect the mechanical properties since local heating can alter material microstructure. The aim of this research was to determine the mechanical characteristics of thin steel plates repaired by local heating associated with plastic deformation (similar to hot working) and cold straightening (similar to local cold working) for automotive side and door panels made of structural steel. Thin sheet plates, 0.9mm thickness, were deformed by impact and repaired by local heating using the flame and induction heating then plastically deformed while hot as well as straightened without heating. The heat repaired samples were studied by light microscopy to determine microstructure change and samples were tensile tested to determine their mechanical characteristics. Local excessive grain growth generates anisotropy, the assembly behaves as a composite material with regions that show significant plastic deformations while others little or no deformations at al. Without procedures adjusted to each material repairs involving heating are to be avoided, cold working should be employed when replacement is not possible.

Market differentiation threshold and the relationship between corporate social responsibility and corporate financial performance

AbstractThis study assesses the impact of corporate social responsibility (CSR) on corporate financial performance (CFP) by using an innovative threshold estimation technique. We examine whether the CSR effect on CFP is varied with the distinct levels of market differentiation. The empirical analysis is based on a world automotive panel dataset for the period of 2011–2017. We unveil an inverted V‐shaped relationship between CSR and CFP and confirm that the increasing nonparametric regression line up to a certain threshold level indicates a positive effect on CFP, whereas a decreasing line indicates a negative effect. Hence, these findings support the idea that engagement in CSR can boost firm performance by incorporating with market differentiation, since higher firm performance is associated with strong differentiation (i.e., less substitutability), but CSR may not provide large benefits in firms with too high market differentiation.

Investigation on mechanical behavior and plastic damage of AA7075 aluminum alloy by thermal small punch test: Experimental trials, numerical analysis

The hot stamping process has demonstrated its high potential to fabricate complex-shaped automotive panel components with high strength AA7075-T6 (Al-5.37Zn-2.18Mg-1.25Cu) aluminum alloy, which conduces to product customization, cost reduction, and efficiency improvement. However, the damage-induced forming crack at high temperatures is more sensitive to the complicated process parameters. A self-developed thermal small punch test (T-SPT) was introduced to investigate the thermo-mechanical behavior and plastic damage of high-strength AA7075-T6 miniature specimens under elevated temperatures in this research. The mesoscopic damage Gurson-Tvergaard-Needleman (GTN) model was employed to predict the micro-area ductile fracture and to conduct formability prediction. An FEM inverse calibration approach coupled with the response surface method (RSM) and the genetic algorithm was developed to accurately identify the temperature-dependent GTN damage parameters based on a series of uniaxial hot tensile curves. Subsequently, numerical simulations of T-SPT regulated by GTN damage parameters were executed to compare with the experimental results. The effects on the mechanical behavior of critical process factors were further discussed, including the deformation temperature, the loading speed, and the surface friction coefficient. Finally, the GTN damage model was successfully applied to predict the formability and the damage distribution of actual AA7075-T6 B-pillar during the hot forming process. The results reveal that the numerical simulation based upon the GTN model owns high reliability and accuracy within the industrialized hot forming application.

Effect of coiling and annealing temperatures on yield point behavior of low-carbon steel

Low-carbon steel is widely used for household appliance and automotive panel steel because of its excellent plasticity. Unfortunately, yield point phenomena easily appear in the low-carbon steel produced by a continuous annealing process and cause degradation to the surface quality during processing. The effect of the coiling temperature (600–750 °C) and annealing temperature (740–820 °C) on the yield point behavior is studied. Tensile tests show that coiling temperature has a greater effect on yield point elongation (YPE) and aging index (AI) than the annealing temperature. Microstructure observations show that coiling temperature at 750 °C would make the micron-sized carbides appearing at the grain boundary disappear and a number of dispersed nanoscale carbides precipitate in grain interior, corresponding to the highest solid solution carbon content in the matrix of 750 °C coiled sample. The experimental results suggest that AI rather than YPE has a positive relationship with the solid solution carbon content of the low-carbon steel. And YPE has a positive relationship with the upper/lower yield strength.

Evaluation of delamination damage and surface roughness in end milling flax fibre composites

Flax fibre reinforced composites have been very attractive in numerous applications such as wall and automotive panels. With chemical treatments and modifications, their mechanical competent can be at par with the existing synthetic fibre composites. The flax fibre composites are normally fabricated to near-net shape, but very often these composites require a secondary cutting process such as milling to attain final geometrical and dimensional tolerances. Due to the continuous contact of the milling tool on the composite material during cutting process, several undesirable damage such as delamination, matrix cracking, fibre pull-out; existed which may lead to deterioration of their mechanical strength. In this study, parametric effects of milling parameters, namely; feed rate, spindle speed, and number of end mill flutes on delamination damage and surface roughness, were investigated. Taguchi L18 orthogonal array was used to design the experimental plan. Signal to Noise (S/N) ratio and response tables were implemented to analyse the experimental data. It was found that spindle speed and feed rate had equal effects on delamination damage and surface roughness, whereas the number of end mill flute had a marginal influence on the aforementioned machining outputs.

52.4: Toward Longer Lifetime‐‐Elongating the Operation Lifetime of Organic Lighting Emitting Diode by Implementing Novel Driving Method

A novel driving method, different from direct current and alternating current methods, was implemented to alleviate the luminance degradation of OLED device. The current density‐voltage‐luminance characteristics measurement results shown that red, green and blue OLED devices have current efficiency of 50 cd/A, 133.4 cd/A and 5.9 cd/A at the CIE coordinate of (0.685, 0.315), (0.252, 0.718) and (0.142, 0.043), with the electroluminescence emission peaks of 622 nm, 532 nm and 457nm, respectively. Driven by the new driving method, the LT97 of red, green and blue OLED devices were about 1.35, 1.3 and 2 times longer than that of driven by direct current method, at the initial luminance of 9320 cd/m2, 20000 cd/m2 and 1758 cd/m2, respectively. If using this new driving method on our 12.3 inch automotive panel, the estimated LT80 of green and blue sub‐pixel were up to over 10,000 hours while that of the red sub‐pixel is nearly 9,000 hours, which means this new driving method is a promising solution to trade off long‐term stability and high efficiency of full color OLED display.

MATERIALS FOR AUTOMOTIVE INDUSTRY AND THEIR INFLUENCE ON THE DYNAMICS OF A CAR CRASH

<p>The aim of this research was to determine the influence of the metallic materials characteristics on the dynamics of a car crash. Another important aspect is that the metallic parts are sometimes repaired after minor accidents and this fact influence strongly the mechanical characteristics and their influence on the dynamics of a car crash. In this paper, we analyze the mechanical characteristics of thin steel plates repaired by local heating associated with plastic deformation (similar to hot working) and cold straightening (similar to local cold working) for automotive side and door panels made of structural steel. Thin sheet plates, 0.9mm thickness, were deformed by impact and repaired by local heating using the flame and induction heating then plastically deformed while hot as well as straightened without heating. The heat repaired samples were studied by light microscopy to determine microstructure change and samples were tensile tested to determine their mechanical characteristics. Local excessive grain growth generates anisotropy, the assembly behaves as a composite material with regions that show significant plastic deformations while others little or no deformations at all. Without procedures adjusted to each material repairs involving heating are to be avoided, cold working should be employed when replacement is not possible.</p>

Anisotropic time dependent and continuum damage coupled plasticity model: An application for Mg AZ31B

In this work, an anisotropic and time-dependent continuum damage-coupled plasticity model is written under a finite strain formulation in arbitrary coordinate space to describe the mechanical behavior of ductile materials. The model accommodates the simulation of proportional and non-proportional 3D loadings. A phenomenological continuum damage mechanics approach is suggested to model the anisotropic damage in the mechanical behavior, including the post-necking region, up to failure. The mathematical model scheme captures the strain rate effect on the material's mechanical response and precisely approximates the yield stress, ultimate tensile strength, and strain to fracture. This paper also presents an implicit time integration method for the anisotropic time-dependent continuum damage-coupled plasticity model under finite strains. The prediction capability of the proposed model is validated by comparing the numerical results to uniaxial tensile experiments on TRC sheets of Mg AZ31B alloy. Magnesium alloys are the lightest engineering metals and therefore are potential candidates for use in stamped automotive panels. Comparisons between the numerical predictions and the experimental results show fair agreement over a wide range of strain rates and temperatures.

Research on Forming Technology of Automobile Rear Wheel Cover Panels

Based on the basic principles of production process and process design for automotive panels, this project develops the stamping process for automotive rear wheel cover panels, and uses CATIA software to draw out the three-dimensional digital models of parts, and then uses the Autoform software to perform numerical simulation analysis. The software analyzes and calculates the stamping direction, the pressing surface, the process supplementary surface, the blank size, the forming limit diagram of the part, the main strain diagram, and the thickness variation, and finally optimizes the blank holder force, friction coefficient, and blank size. To Get the best punch results.