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This paper contributes to the Committee on Commonized Aerodynamics Automotive Testing Standards (CAATS) initiative, established by the late Gary Elfstrom. It is collaboratively compiled by automotive wind tunnel users and operators within the Subsonic Aerodynamic Testing Association (SATA). Its specific focus lies in automotive wind tunnel test techniques, encompassing both those relevant to passenger car and race car development. It is part of the comprehensive CAATS series, which addresses not only test techniques but also wind tunnel calibration, uncertainty analysis, and wind tunnel correction methods. The core objective of this paper is to furnish comprehensive guidelines for wind tunnel testing and associated techniques. It begins by elucidating the initial wind tunnel setup and vehicle arrangement within it.

The strong focus on reducing brake drag, driven by a historic ramp-up in global fuel economy and carbon emissions standards, has led to renewed research on brake caliper drag behaviors and how to measure them. However, with the increased knowledge of the range of drag behaviors that a caliper can exhibit comes a particularly vexing problem - how should this complex range of behaviors be represented in the overall road load of the vehicle? What conditions are encountered during coastdown and fuel economy testing, and how should brake drag be measured and represented in these conditions? With the Environmental Protection Agency (amongst other regulating agencies around the world) conducting audit testing, and the requirement that published road load values be repeatable within a specified range during these audits, the importance of answering these questions accurately is elevated. This paper studies these questions, and even offers methodology for addressing them.

A DFSS study identified a new mechanism for clamp load loss in aluminum threads due to thermal cycling. In bolted joints tightened to yield, the difference in thermal expansion between the aluminum and steel threads can result in a loss of clamp load with each thermal cycle. This clamp load loss is significantly greater than the loss that can be explained by creep alone. A math model was created and used to conduct a robust analysis. This analysis led to an understanding of the design factors necessary to reduce the cyclic clamp load loss in the aluminum threads. This understanding was then used to create optimized design solutions that satisfy constraints common to powertrain applications. Estimations of clamp load loss due to thermal cycling from the math model will be presented. The estimates of the model will be compared to observed physical test data. A robust analysis, including S/N and mean effect summary will be presented.

A common occurrence in computer aided design is the need to make changes to an existing CAD model to compensate for shape changes which occur during a manufacturing process. For instance, finite element analysis of die forming or die tryout results may indicate that a stamped panel springs back after the press line operation so that the final shape is different from nominal shape. Springback may be corrected by redesigning the die face so that the stamped panel springs back to the nominal shape. When done manually, this redesign process is often time consuming and expensive. This article presents a computer program, FESHAPE, that reshapes the CAD or finite element mesh models automatically. The method is based on the technique of volume morphing pioneered by Sederberg and Parry [Sederberg 1986] and refined in [Sarraga 2004]. Volume morphing reshapes regions of surfaces or meshes by reshaping volumes containing those regions.

This paper describes the methodology used to design and perform a CFD analysis of a Chevrolet Impala SS Funny Car body. This body was designed for the purpose of making it available for teams to race it in the National Hot Rod Association (NHRA) drag racing series beginning with the 2007 race season. Several challenges were presented in this project: (1) This was the first time a General Motors drag racing body for use in professional classes (Funny Car or otherwise) was ever designed in CAD. (2) The body was originally designed as a 2007 Chevrolet Monte Carlo. After the tooling was completed, changes in Chevrolet’s product lineup required that the body be changed to a 2007 Impala SS. (3) Budget constraints precluded CFD analysis until after the bodies were already being manufactured. There were several teams that raced the new body during the 2007 race season. One of these teams won the Funny Car Driver’s Championship.

A compatibility study was conducted on fluorinated elastomers (FKM and FEPM) in various Automatic Transmission Fluids (ATF). Representative compounds from various FKM families were tested by three major FKM raw material producers - DuPont Performance Elastomers (DPE), Dyneon and Solvay. All involved FKM compounds were tested in a newly released fluid (ATF-A) side-by-side with conventional transmission fluids, at 150°C for various time intervals per ASTM D471. In order to evaluate the fluid compatibility limits, some FKM's were tested as long as 3024 hrs, which is beyond the normal service life of seals. Tensile strength and elongation were monitored as a function of ATF exposure time. The traditional dipolymers and terpolymers showed poor resistance to the new fluid (ATF-A). Both types demonstrated significant decreases in strength and elongation after extended fluid exposure at 150°C.

Development and integration of the cooling system for an automotive vehicle requires a balancing act between several performance and styling objectives. The cooling system needs to provide sufficient air for heat rejection with minimal impact on the aerodynamic drag, styling requirements and other criteria. An optimization of various design parameters is needed to develop a design to meet these objectives in a short amount of time. Increase in the accuracy of the numerical predictions and reduction in the turn-around time has made it possible for Computational Fluid Dynamics (CFD) to be used early in the design phase of the vehicle development. This study shows application of the CFD for robust design of the engine cooling system.

Durability requirements for exhaust materials have resulted in the increased use of stainless steels throughout the exhaust system. The conversion of carbon steel exhaust flanges to stainless steel has occurred on many vehicles. Ferritic stainless steels are commonly used for exhaust flanges. Flange construction methods include stamped sheet steel, thick plate flanges and powder metal designs. Flange material selection criteria may include strength, oxidation resistance, weldability and cold temperature impact resistance. Flange geometry considerations include desired stiffness criteria, flange rotation, gasket/sealing technique and vehicle packaging. Both the material selection and flange geometry are considered in terms of meeting the desired durability and cost. The cyclic oxidation performance of the material is a key consideration when selecting flange materials.

Two thread forming processes, rolling and cutting, were studied for their effects on fatigue in cast aluminum 319-T7. Material was excised from cylinder blocks and tested in rotating-bending fatigue in the form of unnotched and notched specimens. The notched specimens were prepared by either rolling or cutting to replicate threads in production-intent parts. Cut threads exhibited conventional notch behavior for notch sensitive materials. In contrast, plastic deformation induced by rolling created residual compressive stresses in the notch root and significantly improved fatigue strength to the point that most of the rolled specimens broke outside the notch. Fractographic and metallographic investigation showed that cracks at the root of rolled notches were deflected upon initiation. This lengthened their incubation period, which effectively increased fatigue resistance.

The computational fluid dynamics (CFD) based wind tunnel blockage correction method proposed in [1] was extended in the present study to production vehicles with detailed underhood and underbody components, fascia and grills. Three different types of vehicles (sedan, SUV, and pickup truck) were considered in the study. While the previous CFD based wind tunnel blockage correction method was for vehicle aerodynamic drag, the blockage effect on vehicle cooling airflow is also included in the present study, and a CFD based blockage correction method for vehicle cooling airflow is proposed. Comparisons were made between the blockage effects for the production vehicles and the blockage effects for the generic vehicles.

Drop tower axial crush testing was performed on hat section samples of various steel grades ranging in minimum tensile strength from 410 MPa to 1300 MPa. It was demonstrated that the energy absorption capability increases with the tensile strength of the steel. However, steels of very high strength, greater than 980 MPa tensile strength, exhibited a greater tendency for weld button pullout or material fracture, and thus limited energy the absorption capability. The effect of the closeout plate and the yield strength of the steel on energy absorption were also investigated. FEA simulations were performed and correlated to the experimental results. A flow stress based material criterion is introduced based on the analytical approach to compare the crush performance of steels.

4-Post durability test simulations using a nonlinear FEA model have been executed by engineers responsible for structural durability performance and validation. An integrated Body and Chassis, full FEA model has been used. All components of the test load input were screened and only the most damaging events were incorporated in the simulation. These events included the Potholes, Belgian Block Tracks, Chatter Bump Stops, Twist Ditches, and Driveway Ramps. The CAE technology Virtual Proving Ground (eta/VPG®*) was used to model the full system and the 4-Post test fixtures. The nonlinear dynamic FE solver LS-DYNA** was used in this analysis. The fatigue damage of each selected event was calculated separately and then added together according to the test schedule. Due to the lack of stress/strain information from hardware test, only the analyzed fatigue damage results of the baseline model were scaled to correlate with physical test data.

General Motor's Corvette product engineering was given the challenge to find mass reduction opportunities on the painted body panels of the C6 Z06 through the utilization of carbon fiber reinforced composites (CFRC). The successful implementation of a carbon fiber hood on the 2004 C5 Commemorative Edition Z06 Corvette was the springboard for Corvette Team's appetite for a more extensive application of CFRC on the C6 Z06 model. Fenders were identified as the best application for the technology given their location on the front of the vehicle and the amount of mass saved. The C6 Z06 CFRC fenders provide 6kg reduction of vehicle mass as compared to the smaller RRIM fenders used on the Coupe and Convertible models.

Since its very beginning in 1953, Corvette has been a pioneer in light weight material applications. The new 6th generation corvette high performance Z06 model required aggressive weight savings to achieve its performance and fuel economy targets. In addition to aluminum body structure and some carbon fiber components, the decision to use a magnesium front crossmember was identified to help achieve the targets. An overview of the Structural Cast Magnesium Development (SCMD) project will be presented which will provide information on key project tasks. Project focus was to develop the science and technical expertise to manufacture and validate large structural magnesium castings, which provide a weight reduction potential of 35 percent with respect to aluminum. The die cast magnesium cradle is being produced from a Mg-Al-RE alloy, designated AE44, for high temperature creep and strength performance as well as casting ductility requirements.

Computational fluid dynamics (CFD) was used to simulate the flow field over a pickup truck. The simulation was based on a steady state formulation and the focus of the simulation was to assess the capabilities of the currently used CFD tools for vehicle aerodynamic development for pickup trucks. Detailed comparisons were made between the CFD simulations and the existing experiments for a generic pickup truck. It was found that the flow structures obtained from the CFD calculations are very similar to the corresponding measured mean flows. Furthermore, the surface pressure distributions are captured reasonably well by the CFD analysis. Comparison for aerodynamic drags was carried out for both the generic pickup truck and a production pickup truck. Both the simulations and the measurements show the same trends for the drag as the vehicle geometry changes, This suggests that the steady state CFD simulation can be used to aid the aerodynamic development of pickup trucks.

This paper is intended to give a general overview of the key aerodynamic developments for the 2006 Chevrolet Corvette C6 Z06. Significant computational and wind tunnel time were used to develop the 2006 Z06 to provide it with improved high speed stability, increased cooling capability and equivalent drag compared to the 2004 Chevrolet Corvette C5 Z06.

This paper is targeted to engineers who are involved in predicting fatigue life using either the strain-life approach or the stress-life approach. However, more emphasis is given to the strain-life approach, which is commonly used for fatigue life analysis in the ground vehicle industry. It attempts to discuss, modify and extend approaches in fatigue analysis, so they are best suited for structural durability engineers. Fatigue analysis requires the use of material fatigue properties, stress or strain results obtained from finite element analyses or measurements, and load data obtained from multi-body dynamic analysis or road load data acquisition. This paper examines the effects of these variables in predicting fatigue life. Various mean stress corrections, along with their advantages and disadvantages are discussed. Different stress/strain combinations such as signed von Mises, and signed Tresca are examined. Also, advanced methods such as Fatemi-Socie and Bannantine are discussed.

Effects of the wind tunnel blockage in a closed-wall wind tunnel were investigated using computational fluid dynamics (CFD). Flow over three generic vehicle models representing a passenger sedan, a sports utility vehicle (SUV), and a pickup truck was solved. The models were placed in a baseline virtual wind tunnel as well as four additional virtual wind tunnels, each with different size cross-sections, providing different levels of wind tunnel blockage. For each vehicle model, the CFD analysis produced an aerodynamic drag coefficient for the vehicle at the blockage free condition as well as the blockage effect increment for the baseline wind tunnel. A CFD based blockage correction method is proposed. Comparisons of this method to some existing blockage correction methods for closed-wall wind tunnel are also presented.

This paper outlines a newly developed method for predicting the coupled response of structures from their uncoupled forced responses without having to know the forces acting on such structures. It involves computing the forced response of originally uncoupled structures with several mass loadings at a potential coupling point. The response data obtained from such computations is then used to predict the coupled response. The theory for discrete linear systems is outlined in the paper and a numerical example is given to demonstrate the validity, advantages and limitations of the method. The method is primarily devised to obtain coupled response of linear dynamic systems from independent and uncoupled analytical simulations. Its application significantly decreases computation time by reducing the simulation model size and is excellent for “what if” scenarios where a large number of simulations would otherwise be necessary.

A technique which uses Finite Element Analysis (FEA) to derive important parameters involved in SEA (Statistical Energy Analysis) is discussed. Application of the method to a variety of structures has yielded good correlation with experimentally generated results. SEA parameters including Coupling Loss Factors (CLFs), modal densities, and subsystem equivalent masses were obtained. The technique has the advantage of incorporating structural detail to enhance SEA predictions at lower frequencies where global modes are important, and it can be applied early in the design phase since no hardware is required. With this study, SEA is more readily applied to structure-borne noise problems in vehicles.