E. Y. Kuo

Finite Element Concept Models for Vehicle Architecture Assessment and Optimization

There are two distinct classes of finite element models that can be used to support vehicle body design and development. The most familiar of these is the detailed body model, which achieves computational accuracy by precisely simulating component geometries and assembly interfaces. This model type is quite useful for conducting trade-off studies after detail drawings become available. The second class is an architecture concept model that simulates the basic layout and general structural behavior of major load-carrying members (e.g., pillars, rails, rockers, etc.) and joints in the body. Such modes are valuable for design direction studies in the earliest phases of the vehicle development process. This paper presents a generic process for building architecture concept models that include a mathematical representation of the major body joints derived from existing CAE models. The difficulties involved with such joint representation are discussed, and the concept model NVH results are compared with those from a detailed body model. Although the discussion is based on a specific joint representation model, the conclusions are generic and applicable to other joint representations of the same nature.

A TIME-DOMAIN FATIGUE LIFE PREDICTION METHOD FOR VEHICLE BODY STRUCTURES

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 timedomain 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.

The Effect of Seal Stiffness on Door Chucking and Squeak and Rattle Performance

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. This paper is concerned with a sensitivity study of door chucking and squeak and rattle performance with respect to door seal stiffness using two performance metrics (diagonal distortions at closure openings and relative accelerations between latch & striker) mentioned above. It is found that door chucking performance improves with the increase of seal stiffness monotonically. Whereas overall squeak and rattle performance is dictated by match boxing modes of doors and liftgate that are in turn affected by seal stiffness. No special trend is observed in terms of squeak and rattle sensitivity with respect to seal stiffness.

Major compliance joint modelling survey for automotive body structures

There are two distinct classes of vehicle body CAE abstractions that can be used to support vehicle body design and development, detailed models and concept models. 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 behaviour of joints and major load-carrying members (e.g. pillars, rails, rockers, etc.) in a body structure. The main difference between various kinds of concept models is the representation of body joints. Joints are important components of the auto body because they affect significantly, and in some cases, they even dominate, the static and dynamic behaviour of a model. This paper reviews generic characteristics of two typical joint representation methods: a superelement elastic representation and tri-spring representation. The benefits of using a tri-spring representation over a superelement elastic representation are discussed.

Development of Squeak and Rattle Countermeasures Through Up-Front Designs

Squeak and rattle are one of the major quality concerns in vehicle design for customer satisfaction. Squeak is a high frequency noise due to local parts in frictional contact and rattle a high frequency noise due to impact contact. Traditionally, problems are found and fixed locally using countermeasures such as anti-squeak coatings, flocked tapes or foams, etc. These fixes are generally applied at a relatively late design stage and result in cost and weight penalties. Extensive research at Ford indicates that squeak and rattle performance depends on not only local designs but also global ones. This paper discusses generic root causes of squeak and rattle problems and development of squeak and rattle counter measures through up-front designs in contrast to traditional downstream “find & fix” approaches.