Search Results

Advanced High Strength Steels (AHSS) have been implemented in the automotive industry to balance the requirements for vehicle crash safety, emissions, and fuel economy. With lower ductility compared to conventional steels, the fracture behavior of AHSS components has to be considered in vehicle crash simulations to achieve a reliable crashworthiness prediction. Without considering the fracture behavior, component fracture cannot be predicted and subsequently the crash energy absorbed by the fractured component can be over-estimated. In full vehicle simulations, failure to predict component fracture sometimes leads to less predicted intrusion. In this paper, the feasibility of using computer simulations in predicting fracture during crash deformation is studied.

One of the issues in stamping of advanced high strength steels (AHSS) is the stretch bending fracture on a sharp radius (commonly referred to as shear fracture). Shear fracture typically occurs at a strain level below the conventional forming limit curve (FLC). Therefore it is difficult to predict in computer simulations using the FLC as the failure criterion. A modified Mohr-Coulomb (M-C) fracture criterion has been developed to predict shear fracture. The model parameters for several AHSS have been calibrated using various tests including the butter-fly shaped shear test. In this paper, validation simulations are conducted using the modified (M-C) fracture criterion for a dual phase (DP) 780 steel to predict fracture in the stretch forming simulator (SFS) test and the bending under tension (BUT) test. Various deformation fracture modes are analyzed, and the range of usability of the criterion is identified.

This work reports on measurement and analysis of the galvanic interaction between steel self-piercing rivets (SPRs) having several different surface conditions and magnesium alloy substrates under consideration for use in automotive structural assemblies. Rivet surface conditions included uncoated steel, conventional Zn-Sn barrel plating and variations of commercial aluminizing processes, including supplemental layers and sealants. Coating characteristics were assessed using open circuit potential (OCP) measurement, potentiodynamic polarization scanning (PDS), and electrochemical impedance spectroscopy (EIS). The degree of galvanic coupling was determined using zero-resistance ammeter (ZRA) and the scanning vibrating electrode technique (SVET), which also permitted characterization of galvanic current flows in situ.

Thermally sprayed coatings have used in place of iron bore liners in recent aluminum engine blocks. The coatings are steel-based, and are sprayed on the bore wall in the liquid phase. The thermal response of the block structure determines how rapidly coatings can be applied and thus the investment and floor space required for the operation. It is critical not to overheat the block to prevent dimensional errors, metallurgical damage, and thermal stress cracks. This paper describes an innovative finite element procedure for estimating both the substrate temperature and residual stresses in the coating for the thermal spray process. Thin layers of metal at a specified temperature, corresponding to the layers deposited in successive thermal spray torch passes, are applied to the substrate model, generating a heat flux into the block. The thickness, temperature, and application speed of the layers can be varied to simulate different coating cycles.

The Composite Hybrid Automotive Suspension System Innovative Structures (CHASSIS) is a project to develop structural commercial vehicle suspension components in high volume utilising hybrid materials and joining techniques to offer a viable lightweight production alternative to steel. Three components are in scope for the project:- Front Subframe Front Lower Control Arm (FLCA) Rear Deadbeam Axle

To evaluate vehicle crash performance in the early design stages, a reliable fracture model is needed in crash simulations to predict material fracture initiation and propagation. In this paper, a generalized incremental stress state dependent damage model (GISSMO) in LS-DYNA® was calibrated and validated for a 780-MPa third generation advanced high strength steels (AHSS), namely 780 XG3TM steel that combines high strength and ductility. The fracture locus of the 780 XG3TM steel was experimentally characterized under various stress states including uniaxial tension, shear, plane strain and equi-biaxial stretch conditions. A process to calibrate the parameters in the GISSMO model was developed and successfully applied to the 780 XG3TM steel using the fracture test data for these stress states.

The design of components for high temperature, thermal cycling situations has traditionally been a challenging problem because the analysis must compensate for the non-linear behavior of the material. One example for automotive applications is the exhaust manifold, where temperatures may reach 900°C during thermal cycling. Fatigue failure and excessive deformation of these components must be analyzed with thermoviscoplastic models. A Finite Element (FE) model is developed to simulate the material behavior at high temperature, thermal cycling conditions. A specimen of Silicon Molybdenum Nodular Cast Iron (4% Si, 0.8% Mo) is cycled between maximum temperatures of 500°C and 960°C while the stress is measured with respect to time. The model predictions for stress are compared to the experimental results for two rates of thermal cycling. The analysis is conducted with and without creep effects to understand its contribution to the overall strain.

The effect of friction modifiers on the low-speed frictional properties of automatic transmission fluids (ATFs) was investigated by scanning force microscopy (SFM). A clutch lining material was covered by a droplet of test ATF, and a steel tip was scanned over the sample. The scanning speeds were varied from 0.13 to 8.56 mm /sec, and the frictional force was deduced from the torsion of the SFM cantilever. A reduction in dynamic friction due to the addition of the friction modifier was clearly observed over the entire speed range. This indicates that the boundary lubrication mechanism is dominant under this condition, and therefore surface-active friction modifiers can effectively improve the frictional characteristics. The friction reduction was more pronounced at lower sliding speeds. Thus addition of friction modifiers produced a more positive slope in the μ-ν (friction vs. sliding speed) plots, and would contribute to make wet clutch systems less susceptible to shudder vibrations.

This paper describes the process of incorporation of 25% post-industrial recycled sheet molded composite (SMC) material in the 1998 Continental Hood inner. 1998 Continental Hood assembly consists of traditional SMC outer and this recycled hood inner along with three small steel reinforcements. BUDD Plastics collects SMC scraps from their manufacturing plants. The scrap is then processed and made into fillers for production of SMC. Strength of SMC comes from glass fibers and fillers are added to produce the final mix of raw materials. This recycled material is approximately 10% lighter and less stiff than the conventional virgin SMC. This presented unique challenges to the product development team to incorporate this material into a production vehicle in order to obtain the desired goal of reducing land fill and improving the environment.

Control of drum brake squeal is difficult to accomplish. After many trials guided by CAE and previous experience, for a passenger car it was felt that changing the metallurgical characteristics of the drum would lead to improved noise performance. The chemistry of the drum casting material was altered. The carbon equivalent was modified by increasing carbon and silicon content of the castings as well as changing the other materials. The integral hub and drum assembly was tested on two different dynamometers. The results were also verified by finite element complex eigenvalue analysis. Finally the solution was validated through vehicle level testing - Los Angeles City Traffic (LACT). For the structural consideration rotary fatigue was evaluated by CAE comparison followed by test rig confirmation. The higher carbon equivalent material drums successfully eliminated the annoying squeal in customer vehicles.

With the increasing demand for safety, energy saving and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive materials for automobile makers. Welding of AHSS remains one of the technical challenges in the successful application of AHSS in automobile structures, especially when durability of the welded structures is required. In this study, 2.0 mm uncoated DP780 was investigated. GMAW welding parameters for lap joints of this steel were developed in order to obtain different weld geometries defined by weld toe angle, weld leg sizes, and weld penetration. Metallurgical properties of the joints were evaluated using optical microscopy and scanning electron microscopy (SEM). Static and fatigue tests were conducted on the welded joints. Effect of weld geometry and HAZ softening on fatigue performance including fatigue life, crack initiation site and propagation path of the joints will be analyzed.

In this study, fatigue performance of Gas Metal Arc Welded (GMAW) joint for 1.5 mm uncoated DP780 and 1.0 mm and aluminized coated boron (or USIBOR) steel was investigated. Metallurgical properties of DP780 to coated boron steel dissimilar steel lap joints were evaluated using optical microscopy. Microhardness traverse, static and fatigue tests were conducted on these joints. Finite element analysis (FEA) was used to identify the stress distribution of the weld joints with different stack-ups and at same loading conditions. It was found that position of the material (top or bottom in lap joint configuration) had a significant impact on fatigue performance of the dissimilar joint. The amount of heat introduced by welding to coated boron steel is also believed to be important to the fatigue performance of the dissimilar joints. The findings in this study can be used when aluminized boron steel is involved in dissimilar steel and dissimilar thickness GMAW lap joint design.

Because of their excellent crash energy absorption capacity, dual phase (DP) steels are gradually replacing conventional High Strength Low Alloy (HSLA) steels for critical crash components in order to meet the more stringent vehicle crash safety regulations. To achieve optimal axial and bending crush performance using DP steels for crash components designed for crash energy absorption and/or intrusion resistance applications, the cross sections need to be optimized. Correlated crush simulation models were employed for the cross-section study. The models were developed using non-linear finite element code LS-DYNA and correlated to dynamic and quasi-static axial and bending crush tests on hexagonal and octagonal cross-sections made of DP590 steel. Several design concepts were proposed, the axial and bending crush performance in DP780 and DP980 were compared, and the potential mass savings were discussed.

In the last few years, there has been a greater emphasis on using advanced lightweight materials in automotive applications, primarily to realize better fuel economy and cost-effectiveness. In response to the demand for such materials, many new grades of steel are now available that offer a wide variety of mechanical properties and manufacturability indices. The new class of steel, known as Advanced High Strength Steels (AHSS) offer better strength-to-weight ratios than conventional cold rolled steels, and could be utilized to design cost effective structures. The paper will discuss the application of using the AHSS steel in an automotive rear seat frame structure. The items to be discussed include the manufacturability of AHSS, the load transfer method of such structures, joining methods used in such an application, and design challenges of modeling in FEA. Test results of seat structures with a comparative analysis with FEA will be reviewed.

With the increasing demand for safety, energy saving and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive materials for automobile makers. The usage of AHSS materials is projected to grow significantly in the next 5-10 years with new safety and fuel economy regulations. These new materials have significant manufacturing challenges, particularly for welding and stamping. Welding of AHSS remains one of the technical challenges in the successful application of AHSS in automobile structures, especially when durability of the welded structures is required. In this study, 2.0 mm uncoated DP600 and 2.0 mm uncoated boron (heat treated) steel lap joint configuration was investigated. Metallurgical properties of the DP600 to boron steel dissimilar steel lap joints were evaluated using optical microscopy. Static and fatigue tests were conducted on these joints.

Gas Metal Arc Welding (GMAW) is commonly used in the automotive industry for joining heavier gauge mild and High Strength Low Alloy (HSLA) uncoated steels, where it is recognized for its versatility and speed. The only constraints typically encountered relate to fatigue performance of the joint as a result of poor design or manufacturing fit-up. Advanced High Strength Steels (AHSS), now being considered for more and more applications, however, do not offer the same ease of welding and process control is significantly more critical. They differ from mild steels in chemical composition and thermal processing, resulting in a different microstructure; designed with a richer metallurgy to have higher strength at equivalent thickness. As a result, the sensitivity to heat input is greater and the process window in which acceptable welds can be achieved is narrower.

Fuel economy and federal safety regulations are driving automotive companies to use Dual Phase and other Advanced High Strength Steels (AHSS) in vehicle body structures. Joining and assembly plays a crucial role in the selection of these steels. Specifications are available for the resistance spot welding (RSW) of lower strength sheet steels, covering many aspects of the welding process from the stabilization procedure to endurance testing. Currently, specifications in the automotive industry for RSW with AHSS are limited. It is well known that welding of a thickness ratio greater than 1:2 poses a challenge. To utilize thinner gauge AHSS panels on body-in-white, welding schedules to join the thin to thick sheet steel stack-up are needed. Most of the existing published work was conducted on uncoated sheets and welded to the same thickness.

This paper describes a joint project between Ford, the American Iron & Steel Institute, the University of Louisville, and the U. S. Army to reduce the weight of a full size pick-up truck by 25%, while keeping incremental costs to a minimum. Several alternate technologies were evaluated for each system, subsystem, and component of the vehicle and based on analysis of all combinations of these technologies, the solution which yielded the best overall cost and weight balance, while meeting all of the functional requirements, was selected. The major focus of the project was to develop new steel architectures and materials, since this would assure the maintenance of the lowest possible cost, though the study was not restricted to steel alone. The project was successful in meeting all of its targets, and a vehicle was built to demonstrate the feasibility of the various concepts.

Die wear is a significant issue in sheet metal forming particularly for stamping Advanced High-Strength Steels (AHSS) because of their higher strength and microstructure composition. Reliable predictions of the magnitude and distribution of die wear are essential if cost-effective wear-protection strategies are desired in the early stages of tooling development. A die Wear Severity Index (WSI) is introduced in this paper to quantify the magnitude of die wear, which in essence characterizes the frictional energy dissipation per unit area on the die surface throughout the entire forming cycle. It can be readily obtained as part of any finite element simulation of stamping process utilizing incremental solution techniques.

This study compared laser and fine plasma technology for cutting typical electro-galvanized steel and aluminum automotive stampings. Comparisons were made of various aspects of cut quality, accuracy, disturbance of parent material, cycle time, and capital and operating costs. A sensitivity analysis was included to determine how different scenarios would impact the operating costs. It was found that both processes were capable of high quality cuts at 3800mm/min. Capital savings were achievable through the fine plasma system, but careful consideration of the specific application was essential. This work will allow for an advised comparison of options for sheet metal flexible cutting.