The chart below schematically shows the interactive approach taken by CAFS researchers to study brakes . The approach brings various expertise and technologies to bear on a somewhat complex problem. Our research team prides itself in its adaptation and development of technologies and methods, including these areas:

• Mechanical Properties – Nanoindentation (modulus, stiffness, and hardness)
• Thermal Properties – diffusivity, DSC, DTA, TGA, and expansion
• Thermodynamics and kinetics data and theory
• Topography – AFM and contact profilometry
• Data Analysis and Modeling
• Statistics (probability based sampling and assessment)
• Structure and Chemistry via (FE)SEM, (S)TEM, EDX, XRD, Synchrotron, XRF, GC-MS, FTIR, AFM, XPS
• Modified evaluation procedures; emphasis on energy dissipation rate (power)

The research equipment for each of the areas indicated in the chart above is as follows:

Mechanical Properties Characterization
• Static measurements under tension, compression, flexure using Instron Multiproperty System
• Dynamic measurements of elastic and bulk moduli using Grindosonic Tester.
Thermal Properties Characterization
DSC (RT up to 1500 ^oC, vacuum, gasses, air)
TGA (RT up to 1700 ^oC, vacuum, gasses, air)
Dilatometer (RT up to 1600 ^oC, vacuum, gasses, air)
Flash Thermal Diffusivity - RT (air) up to 2000 ^oC (vacuum or inert gasses)
density measurements (helium pycnometry or mineral spirits immersion)
Surface Topography Characterization
• Contact Stylus Profilometer
• Atomic Force Microscopy
Structure and Chemistry Characterization
• White and Polarized Light Microscopy
• Scanning Electron Microscopy (variable pressure) with EDX
• Transmission Electron Microscopy with EDX
• X-ray Diffraction, Synchrotron, Grazing Angle
• FTIR, XPS, AES
Friction Properties Characterization
• Pin on Disc Apparatus
• Friction Assessment and Screening Test (FAST)
• Subscale Aircraft Dynamometer
• Full Scale Automotive Dynamometer

Let’s look at some brake materials…
Brake rotors are typically cast iron Brake pads fall into three categories: semi-metallic (SM), non-asbestos organic (NAO), and hybrid. Here are some images that reveal the construction of these materials.

Examining Brake Performance Brake performance includes not only the safety issue of how the friction coefficient changes under conditions, but also how the materials wear under various conditions, the noise that is generated, and the impact on the environment (particulate and noise pollution). Brake noise is the number one consumer complaint in the brake industry and responsible for most warranty returns. It’s hard to correlate performance and bulk material composition or bulk material properties or the properties of individual components. As we seek answers, we are guided to look in detail at the friction layer that is developed on both materials at the friction interface. This friction layer is very different (compositionally and often structurally) than the bulk materials.

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