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This paper outlines the key elements in a laboratory reliability verification test program for an automotive sub-system. Many of these elements are described in some detail through the various stages of development from prototype concept to production. By means of an actual case study, verification testing of the 1970 Ford Anti-Theft Steering Column, steps required to design tests which yield meaningful information and the rationale used to analyze the results are presented. The steering column on a late model automobile is a complex system which combines several functions and features; steering, shifting, warning devices (turn signal and emergency flashers), ignition switch, anti-theft devices plus several safety features. The effectiveness of the overall verification program is evaluated through the presentation of actual field-feedback results.

Due to several indeterminate factors, the assessment of the durability performance of a vehicle body is traditionally accomplished using test methods. An analytical fatigue life prediction method (four-step durability process) that relies mainly on numerical techniques is described in this paper. The four steps comprising this process include the identification of high stress regions, recognizing the critical load types, determining the critical road events and calculation of fatigue life. In addition to utilizing a general purpose finite element analysis software for the application of the Inertia Relief technique and a previously developed fatigue analysis program, two customized programs have been developed to streamline the process into an integrated, user-friendly tool. The process is demonstrated using a full body, finite element model.

During frontal and rear end type collisions, very large forces will be imparted to the passenger compartment by the collapse of either front or rear structures. NCAP tests conducted by NHTSA involve, among other things, a door openability test after barrier impact. This means that the plastic/irreversible deformations of door openings should be kept to a minimum. Thus, the structural members constituting the door opening must operate during frontal and rear impact near the elastic limit of the material. Increasing the size of a structural member, provided the packaging considerations permit it, may prove to be counter productive, since it may lead to premature local buckling and possible collapse of the member. With the current trend towards lighter vehicles, recourse to heavier gages is also counterproductive and therefore a determination of an optimum compartment structure may require a number of design iterations. In this article, FEA is used to simulate front side door behavior.

Automotive product development requires higher degree of quality upfront engineering, faster CAE turn-around, and integration with other functional requirements. Prediction of potential durability concerns using analytical methods for sheet metal structures subjected to road loads and other customer uses has become very important. A process has been developed to provide design direction based upon peak loads, simultaneous peak loads, and vehicle program analytical or measured loads. It identifies critical loads at each input location and load sets for multiple input locations, filters load time histories, selects critical areas and analyzes for fatigue life. Several case studies have been completed. The results show that the variations are consistent with the accuracies in finite element analysis, road load data acquisition, and fatigue calculation methods.

The change in the resistance of titanium dioxide with oxygen partial pressure is utilized to obtain an air-to-fuel ratio sensor. TiO2 material properties, sensor components and performance characteristics are discussed. Some results of engine dynamometer and vehicle tests of sensor performance and durability are presented.

The paper briefly reviews the current and future needs for automotive electronic packaging technology and the related reliability issues. Reliability approaches based upon physics-of-failure are discussed, and an example is given to illustrate the importance of understanding the root cause of failure and the application of a state-of-the-art approach to life prediction of leadless solder joints under thermal cycling. An introduction is also given to the recent development of the CAIR (Computer Aided Interconnect Reliability) system developed at Ford for reliability prediction of solder interconnects in automotive electronic packaging. The system integrates a number of software modules using a user interface and allows for evaluation of critical design parameters within a short period of time. The system is intended to implement the “prevention mode” into the product design process to meet the increasing reliability demand and to reduce cost and cycle time.

The thermal durability of a large frontal area cordierite ceramic wall-flow filter for light-duty diesel engine is examined under various regeneration conditions. The radial temperature distribution during burner regeneration, obtained by eight different thermocouples at six different axial sections of a 75″ diameter x 8″ long filter, is used together with physical properties of the filter to compute thermal stresses via finite element analysis. The stress-time history of the filter is then compared with the strength and fatigue characteristics of extruded cordierite ceramic monolith. The successful performance of the filter over as many as 1000 regenerations is attributed to three important design parameters, namely unique filter properties, controlled regeneration conditions, and optimum packaging design. The latter induces significant radial and axial compression in the filter thereby enhancing its strength and reducing the operating stresses.

Hierarchical computer systems are an effective way of combining the features of mini- and maxi-computers in automation projects. By distributing the functions in a multi-computer system, the mini-computers can retain the responsiveness and reliability of simple configurations while the more extensive information handling is performed by the larger host computers. This approach overcomes most of the problems found with independent small control systems on one hand and over-extended, centralized computer systems on the other. This philosophy is illustrated with actual applications at Ford Motor Co.

A simple CAE method of predicting the performance of a component during sine testing has been developed and applied to the practical case of an automotive component. The slow frequency sweep rate during a test is represented as a sequence of steady state conditions. Direct frequency response analysis at the limited number of frequencies is conducted and results used as a basis for prediction of fatigue damage using the Palmgren-Miner rule. The total damage during the test is calculated by linear summation of the damage during each frequency interval. This technique is completely general and can be applied even if there are multiple inputs to the component. A simple extension enables application to engine testing and other cases where excitation may be expressed as a Fourier series expansion of periodic excitations.

Finite element methods can be used to simulate a class of variation problems induced by build distortion in the assembly process. The FEM approach was used to study two representative assembly problems: 1) Front fender mounting and resulting distortion due to various fastening sequences; and, 2) Coupe door assembly process and resulting deformation due to clamping and welding of flexible sheet metal parts. FEM is used to generate sensitivities of various process conditions. Correlation with measured Co-ordinate Measuring Machine (CMM) data is shown. The use of FEM to simulate manufacturing/assembly processes in the automotive industry is in it's infancy. As the new methods are developed this capability can be used to study the assembly process and provide guidance in designing more robust parts and assembly processes.

General Motors Powertrain Division has developed a new V-8 engine for Cadillac vehicles in the 1990s. The Northstar engine incorporates the use of aluminum for both the cylinder block and head and other lightweight materials throughout. The valve train incorporates direct acting hydraulic lifters actuating the four valves per cylinder through dual overhead camshafts. The primary focus of the project has been to produce an engine of unquestioned reliability and exceptional value which is pleasing to the customer throughout the range of loads and speeds. The engine was designed with a light weight valve train, low valve overlap and moderate lift, resulting in a very pleasing combination of smooth idle and a broad range of power. The use of analytical methods early in the design stage enabled systems to be engineered to optimize reliability, pleaseability and value by reducing frictional losses, noise, and potential leak paths, while increasing efficiency and ease of manufacture.

Properties of thermoplastic bumpers made of polycarbonate (PC) and polybutylene terephthalate (PBT) blend were evaluated after several years of service in the field. In this study we measured the Izod impact strength, PC molecular weight, and melt flow rate of bumpers collected from various geographical areas in the U.S. Generally, the system had good impact resistance after more than five years of service in the field, retaining most of the original impact strength. There were small changes in PC average molecular-weights and melt flow rates. The results showed that changes depended on both exposure time and the weather conditions of the environment.

The fatigue strength of spot welds in a multi-spot-welded structure is one of the key issues of concern for achieving structural durability and optimum design in automobile industry. In this study, a global-local fatigue life prediction method is proposed to predict the fatigue life of spot welds in multi-spot-welded structures. In this method, the remote stress-strain field away from the spot-welds, calculated from a global coarse finite element model, is assumed to be acceptable, and is used to recover the stress-strain information of the spot-welds. To improve the accuracy of the remote stress-strain field, an “equivalent” spot weld element is also proposed. The method makes it feasible to predict the fatigue life of spot welds without constructing a detailed finite element model for each spot weld. The method will help reduce finite element model size and save time.

This paper considers some aspects of the use of linear elastic FE analysis as a basis for durability calculations. It specifically considers problems that can be treated as quasi-static and describes the use of inertia relief. However, much of the discussion is also applicable to situations that can better be represented as dynamic. It provides guide-lines for FE modelling for durability analyses including the requirements for mesh quality and for load and boundary condition definition. It also describes a novel way of looking at surface stress information, and reviews some of the methods of getting from linear elastic FE stresses and load histories to realistic elastic-plastic stress and strain histories.

This paper describes the design, synthesis-analysis and development of the unique vehicle structure architecture for the fifth generation Chevrolet Corvette, ‘C5’, which starts in the 1997 model year. The innovative structural layout of the ‘C5’ enables torsional rigidity in an open roof vehicle which exceeds that of all current production open roof vehicles by a wide margin. The first structural mode of the ‘C5’ in open roof configuration approaches typical values measured in similar size fixed roof vehicles. Extensive use of CAE and a systems methodology of benchmarking and requirements rolldown were employed to develop the ‘C5’ vehicle architecture. Simple computer models coupled with numerical optimization were used early in the design process to evaluate every design concept and alternative iteration for mass and structural efficiency.

A process for creating a Customer Correlated, Accelerated, Life Test is presented. This process, which results in a model for predicting reliability, has been applied to a cold weather piston scuff problem. In this paper, the authors will discuss development of frequency distributions for customer environmental and operational use, establishment of customer based failure criteria, development of an accelerated test based on degradation, selection of testing strategies, data analyses, and measurement techniques.

A design synthesis approach is used to design and analyze a Resin-Transfer-Molded (RTM) composite floorpan to meet the product requirements and assess the structural performance. The design envelope is based on packaging constraints representative of a production vehicle to ensure a feasible design intent. Finite element analysis of the composite design is used to guide the design and integrate all of the product performance requirements to achieve a feasible design concept. Issues discussed include the design and analysis, design features, composite material tailoring, prototype fabrication, vehicle build, and product validation. Stiffness, strength and durability tests were performed on the floorpan and the fully trimmed vehicle, and all requirements were met.

A stress durability test method that incorporates exposure to a corrosive environment has been used to evaluate the performance of adhesively bonded steel joints. For the systems examined, corrosion exposure is more damaging than exposure to humidity alone. The combination of load and corrosion exposure is substantially more severe than either alone. A method for analysis of the data and comparison of the test results for the evaluation of adhesive bond durability is proposed. The dependence of lifetime on load is defined as , where f is the ratio of applied load to initial, unexposed failure load. The exponent n provides a measure of the degree of acceleration of the interfacial degradation processes by load.

This paper describes some methods for greatly reducing or possibly eliminating subjective tuning of suspension parts for ride and handling. Laptop computers can now be used in the vehicle to guide the tuning process. The same tools can be used to select solutions that reduce sensitivity to production and environmental variations. OBJECTIVE Reduce or eliminate time required for tuning of suspension parts for ride characteristics. Improve the robustness of ride performance relative to variations in ambient temperature and production tolerances. PROBLEM REQUIRING SOLUTION AND METHOD OF APPROACH Traditional development programs for new vehicles include time-consuming subjective ride evaluations. One example is shock absorber tuning. Even if sophisticated models define force-velocity curves, numerous hardware iterations are needed to find valvings that will reproduce the curves. Many evaluation rides are needed to modify the valvings to meet performance targets.

One of the many computer oriented structural programs which utilizes the finite element technique is briefly discussed. Examples are presented to demonstrate the application of this program to actual product engineering structural problems. Correlation between predicted deflections and stresses and those obtained in the laboratory are presented. Computer graphics provide a unique method of visually interrogating input data and displaying output data. Graphs, stress contours, and deflected structures obtained by this method are presented.