S. Panier

PROGRESSIVE WAVINESS DISTORTION: A NEW APPROACH OF HOT SPOTTING IN DISC BRAKES

ABSTRACT This paper deals with the mechanisms of the appearance of hot spots in railway brake disks. From infrared measurements, a classification of hot spots is presented. The most damaging thermal gradients are identified as macroscopic hot spots uniformly distributed on the friction surface. An explanation of the origin of these macroscopic hot spots is presented based on a scenario of progressive distortion of the disk. Three major effects have to be considered: the structural response of the disk and the pads; realistic boundary conditions, both geometric and loading; and the thermoelastoplastic behavior of the material. Finite element simulations based on the proposed model agree with experimental observations.

Strengthening of a Fibre-Matrix Interface: A Novel Method Using Nanoparticles

The surface of carbon fabric (CF) was treated with nanoparticles (NPs) of Ytterbium fluoride (YbF3) (40-80nm size) in various amounts (0, 0.1, 0.3 and 0.5wt%) to improve its wettability with a Polyetherimide (PEI) matrix. The effect of treatment on the fibres of the CF was also studied by adhesion testing and fibre tow tension testing. An improvement in wettability with PEI and a slight reduction in the tensile strength of the CF was observed in these tests. Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATR) indicated the addition of functional groups on the fabric after treatment. Micro- Raman spectroscopy (MRS) showed a slight distortion in the structure of the CF due to the treatment. Increased roughness of the fibre surface and adhesion of NPs on the fibre surface were observed by field emission scanning electron microscopy (FESEM). Composites were developed based on untreated and surface-treated CFs by impregnation techniques. The composites were analysed for interlaminar shear strength (ILSS) and a maximum improvement of 61% was observed for the 0.3% concentration of YbF3, followed by a slight decline in ILSS, indicating that it was the optimum dose.

Infrared characterization of thermal gradients on disc brakes

The heat generated in frictional organs like brakes and clutches induces thermal distortions which may lead to localized contact areas and hot spots developments. Hot spots are high thermal gradients on the rubbing surface. They count among the most dangerous phenomena in frictional organs leading to damage, early failure and unacceptable braking performances such as brake fade or undesirable low frequency vibrations called hot judder. In this paper, an experimental study of hot spots occurrence in railway disc brakes is reported on. The aim of this study was to better classify and to explain the thermal gradients appearance on the surface of the disc. Thermograph measurements with an infrared camera have been carried out on the rubbing surface of brake discs on a full-scale test bench. The infrared system was set to take temperature readings in snap shot mode precisely synchronized with the rotation of the disc. Very short integration time allows reducing drastically haziness of thermal images. Based on thermographs, a classification of hot-spots observed in disc brakes is proposed. A detailed investigation of the most damaging thermal gradients, called macroscopic hot spots (MHS) is given. From these experimental researches, a scenario of hot spots occurrence is suggested step by step. Thanks to infrared measurements at high frequency with high resolution, observations give new highlights on the conditions of hot spots appearance. Comparison of the experimental observations with the theoretical approaches is finally discussed.

Direct Computational Method for Life Prediction of UD Fibre Reinforced Polymers Based-on Plasticity-Damage Simulation

New direct method was developed for fibre reinforced polymers subjected to fatigue loading. Constitutive model is based-on coupled plasticity-damage framework. Microstructure of material is satisfying the periodic conditions. Influence of microstructure has been involved through stress concentration tensor. Plasticity yield surface is described by modified Raghava criterion. Damage of matrix and transverse cracking are governed by quadratic damage surface. Method was examined on the standard example of unidirectional composite plate with carbon-fibre reinforced. Significant reduction of calculation time has been achieved using the direct computational algorithm.