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The friction performance of a Disc Brake Pad is even more required to present stable mu behavior in various environmental conditions such as different temperature and humidity. Interaction between compositional variables (raw materials) and environmental conditions cannot be revealed by a simplistic approach without taking into account their mutual interactions. Thereby is necessary a "crossed" design able to combine mixture components with environmental factors. This paper reports the mu behavior of a commercial Brake Pad Formulation in two different environmental conditions (winter condition, e.g., low humidity, and summer condition, e.g., high humidity) through a Combined Design of Experiment. The design was defined by the variation of three mixture components (Al₂O₃, Graphite and Sulfides) of the Brake Pad Formula according to a Response Surface Method (RSM). The μ behavior has been evaluated on a full-scale dynamometric bench test (AK-Master) with climatic control.

Brake pad material formulation and disc microstructure/composition plays a mutual role during wear test due to the third body layer (TBL) formation and its relative evolution due to temperature change. Nevertheless these ones could influence corrosion behavior. In this study we investigated the effect of rotors characteristics on wear and sticking behavior. Rotor and brake pad microstructure were analysed with optical, metallographic and scanning electron microscope to understand the surface and TBL evolution (using different thermal preconditioning) taking into consideration also the copper role during the different wear stages. During this preliminary study we were able to find out different copper smear morphologies depending on test conditions and rotors features.

An adhesion phenomenon between brake pad and rotor frequently appears as a result of prolonged static exposure to corrosive environments. In these highly oxidative conditions, electrochemical reactions occur on the gray cast iron brake rotor surface to produce iron oxide(s), which can then penetrate the brake pad surface porosity, causing adhesion of the brake pad(s) to the rotor. In some instances the shear load necessary to detach the brake pad from the rotor is sufficiently high and becomes a real issue in the field. The corrosive mechanisms and magnitude of material interactions involved in this issue are very complex. These complexities are in part due to the heterogeneity of the rotor and friction material compositions, but also brake geometry, loading conditions, and environmental variations are large contributing factors.