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Hardware benchmarking of body overall stiffness and joint stiffness of the best-in-class competitive vehicles is a common practice in the automobile industry. However, this process does not provide design insights of competitive body structures, which relate stiffness performance to key architectural designs. To overcome this drawback, a CAD body-in-prime model of a competitive vehicle is developed using laser/optical scanning technology and a corresponding CAE model is built based on the CAD data. A deep-dive structural efficiency study is conducted using this model and “pros” and “cons” of the architectural design of each individual joint and each section of major load-carrying members of this body structure are identified. This analytical benchmarking (or reverse engineering) process enables a company to adopt best-in-class design practices and achieve competitive advantages in vehicle designs.

There are two distinct classes of body CAE models (detailed and concept models) that can be used to support vehicle body design and development. A detailed finite element model achieves computational accuracy by precisely simulating component geometries and assembly interfaces. On the other hand, a concept model simulates stiffness behavior of joints and major load-carrying members (e.g., pillars, rails, rockers, etc.) in a body structure. The former is quite useful for conducting trade-off studies when detailed design drawings become available. The latter is valuable for up-front design direction studies prior to detailed design evolution. In concept models, major load-carrying members are universally represented by cross sectional properties (e.g., area, moments of inertia and torsion constant). The key difference between various kinds of concept models is the representation of body joints.

Liftgate chucking is one of the major squeak and rattle concerns for vehicles with a large body closure opening in the liftgate area. High frequency chucking noise is generated as a result of the contact between the latch and striker of a liftgate. Traditionally, liftgate chucking problems (if present) are found and fixed by using a more robust latch/striker mechanism at a very late design stage that normally results in cost penalties for vehicle programs. Significant effort has been made at Ford in identifying and clarifying up-front drivers or body performance metrics that predominantly influence downstream squeak and rattle sensitivity. Two key body performance metrics (diagonal distortions at the liftgate opening and relative displacement between the latch and striker of a liftgate) are found to affect liftgate chucking sensitivity. The effects of body joint designs on liftgate chucking performance are discussed using these metrics in CAE analyses.

Traditionally, door seals are designed to achieve good wind noise performance, water leakage and door closing effort in a vehicle design and development process. However, very little is known concerning the effect of door seal design on vehicle squeak and rattle performance. An earlier research work at Ford indicates a strong correlation between the diagonal distortions of body closure openings (in a low frequency range 0 - 50 Hz) and overall squeak and rattle performance. Another research at Ford reveals that relative accelerations between door latch and striker in a low frequency region (0 - 50 Hz) correlate well with door chucking performance. The findings of this research work enable engineers to assess squeak and rattle and door chucking performance using vehicle low frequency NVH CAE models at a very early design stage.

Squeak and rattle is one of the major concerns in vehicle design for customer satisfaction. Traditionally squeak and rattle problems are found and fixed at a very late design stage due to lack of up-front CAE prevention and prediction tools. A research work at Ford reveals a correlation between the squeak and rattle performance and diagonal distortions at body closure openings and fastener accelerations in an instrument panel. These findings make it possible to assess squeak and rattle performance implications between different body designs using body-in-prime (B-I-P) and vehicle low frequency noise, vibration and harshness (NVH) CAE models at a very early design stage. This paper is concerned with applications of this squeak and rattle assessment method for up-front body designs prior to a prototype stage.

Squeak and rattle is one of the major concerns in vehicle design for customer satisfaction. Traditionally, squeak and rattle problems are found and fixed at a very late design stage due to lack of up-front CAE prevention and prediction tools. An earlier research work conducted at Ford reveals a correlation between the vehicle overall squeak and rattle performance and the diagonal distortions of body closure openings under a static torsional load. This finding makes it possible to assess squeak and rattle performance implications between different body designs using body-in-prime (B-I-P) and vehicle low frequency noise vibration and harshness (NVH) CAE models at a very early design stage. This paper presents an application of this squeak and rattle assessment method for a design feasibility study concerning a cab structure of a super duty truck for weight reduction using high strength steel and adhesive bonding.

Joint stiffness is a major contributor to the vehicle body overall bending and torsional stiffness which in turn affects the vehicle NVH performance. Each joint consists of spot welds which function as load paths between adjacent sheet metal. Spot welds tend to lose structural integrity as a result of fatigue, loosening, aging, wear and corrosion of parts as a vehicle accumulates mileage. Experimental methods are used to identify potential degradation mechanisms associated with a spot weld. A CAE model which simulates a vehicle body joint generically is used to determine the effects of each individual degradation mode of a spot weld on joint stiffness. A real life B-pillar to roof joint CAE model of a production vehicle is then employed to examine the significance of weld distribution on joint stiffness degradation. The knowledge derived from this study can be used as a guidance in designing vehicle body structures with respect to spot weld distribution.

This paper benchmarks some methods of nondestructive testing for zero and high mileage spot weld quality/integrity and degradation evaluation (pin holes, voids, cracks, fatigue, corrosion, etc.). The methods include X-ray radiography, ultrasonic imaging, ultrasonic pulse/ echo, pulsed infrared or thermography, and laser/TV holographic interferometry imaging. The advantages and limitations of each method are provided with descriptive principles and real test examples. It is found that X-ray radiography combined with ultrasonic echo technique is the most favorable one considering time and cost for the current zero and high mileage spot weld evaluation.

High mileage NVH performance is one of the major concerns in vehicle design for long term customer satisfaction. The current paper is concerned with performance analysis of high mileage vehicles which cover four automobile manufacturers and five vehicle families of the same weight class based on subjective evaluation data. The analysis includes the assessment of five vehicle families from the following aspects: overall and NVH performances, performance by individual attribute, degradation history of each vehicle family, performance variation within each vehicle family. Since the data are statistical in nature, statistical methods are employed, numerically and graphically, in the analysis. The performance categories which exhibit most degradation are identified. The analysis method presented in this paper is applicable to any high mileage vehicle fleet subjective data. The knowledge derived in the study can be used as a guideline in designing vehicles for high mileage NVH robustness.

Elastomeric components are used extensively in the construction of the modern automobile to accommodate relative movement between metal parts, absorb shocks and to provide isolation from undesirable vibrations. Their small-amplitude dynamic stiffness and damping characteristics are the key mechanical properties most influencing vehicle NVH performance. Their large-amplitude static force-deflection characteristics are crucial for vehicle ride and handling performance. On the other hand, when a vehicle is driven on a rough road durability course at a proving ground, all elastomeric components experience large-amplitude dynamic loads. The durability loads transferred through each elastomeric component highly depend on the stiffness and damping characteristics of these components.

Fatigue analysis using finite element models of a full vehicle body structure subjected to proving ground durability loads is a very complex task. The current paper presents an analytical procedure for fatigue life predictions of full body structures based on a time-domain approach. The paper addresses those situations where this kind of analysis is necessary. It also discusses the major factors (e.g., stress equivalencing procedure, cycle counting method, event lumping and load interactions) which affect fatigue life predictions in the procedure. A comparison study is conducted which explores the combination of these factors favorable for realistic fatigue life prediction. The concepts are demonstrated using a body system model of production size.

High mileage NVH performance is one of the major concerns in vehicle design for long term customer satisfaction. Elastomeric components such as suspension bushings function as vibration isolators in a vehicle. High mileage driving tends to cause the degradation of these components which in turn results in the degradation of vehicle overall NVH performance. The present paper presents the application of CAE based robustness methodology to vehicle high mileage degradation with respect to bushing degradation. A unitized vehicle with suspension strut mounts is selected as the project vehicle. Strut mount degradation characteristics, vehicle CAE model and design of experiment are linked together to achieve vehicle response robustness. The concept and methodology arc demonstrated using a tire input which simulates road excitations as a first step toward the development of a more extensive robustness methodology which will cover other excitation conditions.

High mileage NVH performance is one of the major concerns in vehicle design for long term customer satisfaction. Elastomeric components such as suspension bushings, engine mounts and tires function as vibration isolators in a vehicle. High mileage tends to cause the degradation of these components which in turn affects vehicle overall NVH performance. The present paper discusses the characteristics of bushing degradation based on laboratory bushing test data. Vehicle subjective evaluation and CAE modeling methods are used to develop a fundamental understanding of the effects of bushing degradation on vehicle NVH performance. The concept and analysis methodology are demonstrated using the front and rear suspension strut mounts and tire inputs which simulate road excitations but they are valid for other elastomeric components such as engine mounts and excitations. The knowledge derived in the study can be used as a generic guideline in designing vehicles for high mileage NVH robustness.

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.

Traditionally, vehicle durability cracks have been treated to be local problems as a result of poor designs of notches, welds, holes, corners or reinforcements. The problems were usually found and fixed at a late design stage which often resulted in weight and cost penalties for a vehicle program. However, in many instances, the local problems mentioned above are simply the consequence of a poor global design. The global problems can generally be grouped into three categories: stress induced fatigue problems due to excessive global stresses as a result of body structural discontinuities, load induced fatigue problems due to excessive loads input to a body as a result of suspension designs, and vibration induced fatigue problems due to unfavorable structural resonance. The current paper presents a CAE analysis process which can be used at the upfront design stage to assess vehicle durability performances from a global design point of view.

Since road roughness is an important source of vehicle vibration, a system model for NVH analysis requires a tire model which accurately predicts spindle response to road input. Most tire models currently used in the auto industry do not meet this requirement, because they are based on static stiffness of the tire and do not produce realistic response to input at the patch. This paper investigates a new modal tire model with patch input capability as a component within a vehicle system model. Comparisons are also presented between the behavior of the new tire model and a conventional spring model. To validate the performance of the tire model for NVH analysis, simulated vehicle responses to bump input are compared to chassis roll test results. Good correlation between the model prediction and the chassis roll measurements is observed.