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Industry and academia agree that brake squeal is a nonlinear phenomenon. Consequently, using solely linear finite-element (FE) models and assessing the tendency of a brake system to squeal exclusively on the stability of the trivial solution is not appropriate. However, the latter approach - in the brake community known as complex eigenvalue analysis (CEA) - is extensively used in industry. Until now, nonlinear simulation approaches considering existence and stability of periodic solutions are mostly limited to minimal models. Among the variety of reasons for this the complexity of large-scale nonlinear models as well as the identification of nonlinear material and system parameters are crucial. This contribution discusses the relevance of nonlinearities in friction brake noise, vibration, harshness (NVH) and presents a novel simulation approach for brake squeal.

Friction induced vibrations in brakes are a topic of major interest and concern for the automotive industry. The structural vibrations that may occur, as well as the audible noise that can be related to them, may lead to consequences as diverse as driver discomfort, maintenance requirements, and even safety issues. Although friction induced vibrations are known already since the beginnings of friction brake design, a generally accepted consensus on many aspects, like fundamental mechanisms or generic solution approaches, seems still to be debated. The present paper attempts to shed some light on the reasons for these persisting difficulties. A review of the different classes of phenomena appearing is given, which could be understood as an attempt to limit the scope of phenomena considered as friction induced. Research topics and disciplines involved will be identified and a clarification of achievements and unanswered questions will be attempted.