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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.

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.

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.

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.

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.

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.