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This paper discusses an analytical technique for computing the failure rate of steel springs used in automotive part applications. Preliminary computations may be performed and used to predict spring failure rates quickly at a very early stage of a product development cycle and to establish program reliability impact before commitment. The analytical method is essentially a combination of various existing procedures that are logically sequenced to compute a spring probability of failure under various operational conditions. Fatigue life of a mechanical component can be computed from its S-N curve. For steels, the S-N curve can be approximated by formulae which describe the fatigue life as a function of its endurance limit and its alternating stress. Most springs in service are preloaded and the actual stress fluctuates about a mean level. In order to compute an equivalent alternating stress with zero mean, an analytical method based on the Goodman Diagram is used.

Adhesive bonding technology is rapidly gaining acceptance as an alternative to spot welding. This technology is helping automobile manufacturers reduce vehicle weight by letting them use lighter but stronger advanced high strength steels (AHSS's). This can make cars safer and more fuel efficient at the same time. The other benefits of this technology include its flexibility, ability to join dissimilar materials, distribute stress uniformly, provide sealing characteristics and sound dampening, and provide a moisture barrier, thus minimizing the chance for corrosion. The lap shear work reported in the late 1980s and early 1990s has led to the prevalent perception that the galvannealed (GA) coating can delaminate from the steels, resulting in poor joint performance. However, the above work was carried out on steels used primarily in automobile outer body panels.

Over the last five years, the automotive industry has experienced a trend towards niche performance vehicles equipped with high-output powertrains. These high performance vehicles also demand higher output braking systems. One method used to provide enhanced pedal feel and fade performance is to equip vehicles with higher apparent friction linings. The challenge then becomes how to design and manufacture these brake systems without high-frequency disc brake squeal and without paying a significant mass penalty. One alternative is to design disc brake rotors with increased damping. There are several options for increasing rotor damping. The classical approach is to increase the rotor's cast iron carbon content, thus increasing the internal material damping of the rotor. However, this methodology provides only a small increase in rotor damping. Alternatively, the rotor damping can be increased by introducing friction, sometimes referred to as Coulomb damping.

Casting, machining and structural simulations were completed on a V8 engine block made in Compacted Graphite Iron (CGI) for use in a racing application. The casting and machining simulations generated maps of predicted tensile strength and residual stress in the block. These strength and stress maps were exported to a finite element structural model of the machined part. Assembly and operating loads were applied, and stresses due to these loads were determined. High cycle fatigue analysis was completed, and three sets of safety factors were calculated using the following conditions: uniform properties and no residual stress, predicted properties and no residual stress, and predicted properties plus residual stress.

An innovative seat back design for fold down split-rear seat backs has been developed for application in SUV’s, MPV’s and hatchbacks. The all-thermoplastic seat back design meets US and European government regulations such as, the FMVSS 210, 207 in the US, and ECE 17 (luggage retention) in Europe. It is also expected to meet the newly introduced FMVSS 225 (child seat belt tether load) requirement. Currently application of the blow molded seat back is limited to sedans where the seat belt anchor loads are transmitted to a steel package shelf. For applications where the seat-belt anchor loads are transmitted to the seat back, hefty steel frame and reinforcements are required which add weight and cost to the seat back. The same is true for seats that need to comply with the European luggage retention requirement.

The Auto/Steel Partnership established the Light Truck Frame Project Group in 1996 with two objectives: (a) to develop materials, design and fabrication knowledge that would enable the frames on North American OEM (original equipment manufacturer) light trucks to be reduced in weight, and (b) to improve corrosion resistance of frames on these vehicles, thereby allowing a reduction in the thickness of the components and a reduction in frame weight. To address the issues relating to corrosion, a subgroup of the Light Truck Frame Project Group was formed. The group comprised representatives from the North American automotive companies, test laboratories, frame manufacturers, and steel producers. As part of a comprehensive test program, the Corrosion Subgroup has completed tests on frame coatings. Using coated panels of a low carbon hot rolled and pickled steel sheet and two types of accelerated cyclic corrosion tests, seven frame coatings were tested for corrosion performance.

The bulge test in hydroforming is a simple fundamental experiment used to obtain basic knowledge in tube expansion. The results can be used to assist design and manufacturing of hydroformed automotive parts. It also can be used to develop a failure criterion for tubes in hydroforming. For these purposes, a section of a long unsupported tube with fixed ends was simulated numerically to obtain the mechanical states of the tube subjected to internal pressure. Steel and aluminum tubes are used. For the bulge tests, the internal pressure reaches a maximum and then decreases in value without failure while the stress, strain and volume of the tube keep increasing. A failure criterion for the bursting of a tube is proposed based on the stress-strain curve of the material.

Modular front-end carriers to pre-assemble front-end components such as cooling systems, lights, and bumper beam have been in production in different vehicles for several years. Compression molded or overmolded steel/plastic carriers have traditionally been used. The present paper explains the design, material options, and engineering optimization of a composite front-end carrier, which utilizes long glass fiber injection moldable resins and adhesively bonded steel reinforcements. Experimental evaluation of prototypes shows the system met the functional performance requirements at minimum weight.

Fundamental differences exist between sheet metal forming and hydroforming processes. Sheet metal forming is basically a one step metal fabrication process. Almost all plastic deformation of an originally flat blank is introduced when the punch is moved normal to a clamped sheet metal. Hydroforming, however, consists of multiple steps of tube making, pre-bending, crushing, pressurization, etc. Each of the above mentioned steps can introduce permanent plastic deformations. The forming limit diagram obtained for sheet metal forming may or may not be used in hydroforming evaluations. A failure criterion is proposed for predicting bursting failures in tube hydroforming. The tube material's stress-strain curve, obtainable from uniaxial tensile test and subjected to some postulations under large stress/strain states, is used in judging the failure.

Advanced high strength steels (AHSS) are becoming major enablers for vehicle light weighting in the automotive industry. Crash resistant and fracture-toughened structural adhesives have shown potential to improve vehicle stiffness, noise, vibration, and harshness (NVH), and crashworthiness. They provide weight reduction opportunity while maintaining crash performance or weight increase avoidance while meeting the increasing crash requirement. Unfortunately, the adhesive bonding of galvanneal (GA)-coated steels has generally yielded adhesive failures with the GA coating peeling from the steel substrate resulting in poor bond strength. A limited study conducted by ArcelorMittal and Dow Automotive in 2008 showed that GA-coated AHSS exhibited cohesive failure, and good bond strength and crash performance. In order to confirm the reliable performance, a project focusing on the consistency of the adhesive bond performance of GA-coated steels of 590 MPa strength level was initiated.

An extensive investigation was conducted to assess the influence of steel sheet surface finish (i.e. topography or “texture”) on painted surface appearance. Ten sets of steel panels representing a variety of shot blast, EDT, laser, and bright surface textures were painted simultaneously using advanced solvent-based luxury vehicle paint systems. Paint appearance was measured using a relatively new Autospect instrument and also in terms of conventional Distinctness of Reflected Image (DOI). The results are discussed in detail with respect to 1) the influence of different steel surface textures on paint appearance, 2) the evolution of surface topography during painting, and 3) the implications of this work.

Surface friction is an important characteristic which influences the formability of sheet steel products. Numerous friction tests have been developed, and many previous investigations have reported effects of surface characteristics, coatings, lubrication, etc., on formability. Recently, increased attention has been focussed on reducing friction via the application of solid film lubricants or special surface post-treatments such as phosphates, metallics/intermetallics, etc. This paper presents the results of selected laboratory evaluations conducted using a variety of steels and surface treatments. Formability was measured using Limiting Dome Height and Drawbead Simulator friction testing, along with Limiting Draw Ratio testing in one instance. The examples highlight some potential opportunities which may be considered for improving formability in industrial stamping operations.

A design of experiments is used to study the effect of laser weld parameters on formability of welded blanks for two different material combinations of cold rolled (bare) steel to cold rolled steel and cold rolled steel to hot dipped galvanized steel. Critical weld parameters influencing the formability of welded blanks are identified and the optimum weld set-up condition is obtained based on formability performance and consistency of formability for laser welded blanks. The results are applied to an automotive body side frame. The robustness of welded blank production is also assessed and the final welded set-up condition for the body side frame is obtained based on both the formability of welded blanks and the robustness of welded blank production. The body side frame is successfully made from the welded blanks with this final weld set-up condition.

A rear full overlap car-to-car high speed impact simulation using the DYNA3D Finite Element Software was performed to examine the crush mode for rear structure of a vehicle and to observe the effect of rear bumper system in order to maintain the fuel system integrity. The study was conducted first for two different bumper system configurations, namely: (1) validating the model for struck vehicle with steel rear bumper system, (2) simulating rear end collision with composite rear bumper system attached to the rear rails of struck vehicle. Later a third simulation of the model was conducted with a viable design modification to the composite bumper system for improved crashworthiness. It was identified that a more comprehensive FEA model of the bullet car including front end structure, powertrain components, cooling system and other components which constitute the load paths should be incorporated in the analysis to obtain more meaningful correlation and crashworthiness prediction.

Galvannealed sheet steel is gaining acceptance by automotive manufacturers due to its combination of properties and cost. Galvanneal can be produced by several processes including the most common method termed the “hot” line hot dip coating process, but also using “flux” line hot dip coating application. Similarly, several types of phosphate coatings: Zn, Zn-Ni, and Zn-Ni-Mn phosphates can be applied to these materials prior to painting to enhance paint adhesion and painted corrosion resistance. This manuscript reports the affects of commercial phosphate type and galvanneal type (based on production method and properties) on the corrosion performance of galvanneal. In addition, painted corrosion performance of galvanneal is compared to painted corrosion performance of electroplated zinc. The manuscript also describes the use of electrochemical methods as one alternative to conventional test methods resulting in substantial time savings.

Corrosion resistance has been the major impetus toward increased use of galvanneal and other coated sheet products by the automotive industry. Galvanneal has the additional advantages of good weldability, due to the iron in the coating, and a higher surface porosity which leads to better paint adhesion. The porosity of the galvanneal surface, however, could also lead to reduced cleanability. This paper reports the effects of pretreatment variables on galvanneal phosphatability and resulting painted corrosion performance. The studies showed that the rust preventative oil applied and the alkaline cleaner used to clean samples prior to phosphating had significant effects on carbon residuals after cleaning. The painted corrosion performance of galvanneal panels with various levels of residual carbon showed a much smaller effect within a given cyclic test. The studies also indicated significant differences in performance depending on the type of cyclic test performed.

Galvanneal powdering was examined on a stabilized ultra low carbon steel substrate as a function of strain state using cup drawing and in-plane stretching experiments to simulate deformations encountered in production stampings. Significant powdering was encountered in drawing while minimal powdering occurred in in-plane stretching. Powdering was measured at specific locations and correlated with strains in those locations. A powdering map was generated in strain space using the experimental data. A few measurements of powdering on selected regions of an automotive stamped part are reported.

A program was initiated to determine corrosion performance of coated sheet products. The program examined the performance of galvannealed, hot-dip galvanized and electroplated zinc coated steel sheet in a variety of cyclic laboratory corrosion tests. Both perforation and cosmetic corrosion susceptibility were evaluated. Materials were pretreated using immersion and spray phosphate systems and were also prepared without a phosphate pretreatment. Results of these studies will be presented in this paper.

Automotive demands for increased service life and use of flexible fuel blends of alcohol and gasoline have propelled the development of new materials for automotive fuel systems. Traditional fuel system materials, i.e., bare or prepainted terne coated steel sheet, which do not meet the new requirements are being replaced with prepainted zinc-nickel coated steel sheet. Automotive fuel tanks and fuel system components made from the new prepainted zinc-nickel steel sheet offer increased service life and compatibility with the entire range of flexible fuel blends. This paper describes the results of several laboratory corrosion studies which examined the environmental corrosion performance and the fuel compatibility of prepainted zinc-nickel coated steel as a function of several system properties. Performance is compared to prepainted terne, prepainted hot dip tin, and prepainted galvanneal.

Casting technology developmentshave led to a manufacturing process that allows the casting of thin wall (2-3mm) heat resistant ferritic stainless steel exhaust manifolds which can replace stamped and tubular weldments as well as iron castings where temperature requirements are increased. This casting process combines the thin wall and clean metal benefits of the counter gravity, vacuum-assist casting process using thin, light-weight bonded sand molds supported by vacuum-ridgidized sand. This combination is called the LSVAC (Loose Sand Vacuum Assisted Casting) process, a patented process. This process will significantly contribute to the growth of near-net shape steellstainless steel castings for automotive and allied industries. For exhaust manifolds, a modified grade of ferritic stainless steel with good oxidation resistance to 950°C in high dew point synthetic exhaust gas atmospheres was developed.