IR Camera Applications

• High-speed IR Thermography for Automotive
  Brake System Studies
  
• Application of Microscopic Tribo-thermography to Study Wear Damage Progression on Coated Surfaces
• Carbon Composites for AIrcraft Brakes using Microscope Lock-in Thermography
  
• New Ball Grid Array (BGA) Inspection Technique

Users and Staff
Ralph B. Dinwiddie, HTML
Kwangjin Mike Lee, Delphi Chassis Systems
Jay Fash, Rena Hecht, and Dale Hatsock, Ford

During the occurrence of these instabilities several localized hot spots will form around the circumferential direction of the brake rotor. Observation of the temperature distribution and the time dependence of these hot spots is a critical factor in analyzing this problem and in developing a fundamental understanding of the problem. Dynamometer tests have been performed to study brake torque variation, which can lead to brake roughness on a vehicle. Various techniques have been employed to observe the thermal distribution around the rotor. Thermal evaluations have been made with state of the art infrared camera technology, as well as single point detectors, to observe the non-uniform temperature distributions. Conventional thermal image cameras are not capable of resolving the hot spots occurring on an operating brake system. Special modifications to a relatively recent technology, thermal imaging, allows observation of the operating brake system and provides confirmation of temperature fields which correlate with torque variation during test.

Results
This effort has demonstrated the feasibility of using a high-speed, snapshot mode infrared camera to investigate the thermo-elastic instability phenomena in automotive brake systems (see Fig. 1). It was found to be advantageous to synchronize the camera with the rotation of the brake disk to allow study of the time evolution of individual hot spots. The high-speed rotation of the brake disk necessitated an exposure time of 0.015 ms to prevent blurring of the image. Time-lapse techniques were employed to limit data file size, while maintaining adequate information on the rate of temperature change and hot region movement.

Nonuniform frictional contacts and their effects on brake judder were investigated in automotive disk brake systems. Extreme localized heating due to a variation of lug nut torque (see Fig. 2), thickness variation and lateral runout were observed. It was uncommon to observe more than two extreme localized hot regions on one side of the brake disk. Often, only one large hot area was observed. Extreme localized heating seems to take precedence over thermo-elastic instability, since when conditions are right for extreme localized heating, thermo-elastic instability is rarely observed at any speed.

Publications

1. Kwangjin Lee and R. B. Dinwiddie, "Conditions of Frictional Contact in Disk Brakes and their Effects on Brake Judder," SAE 98PC-392, 1998
2. Kwangjin Lee and R. B. Dinwiddie IR-based methods for automotive brake system studies," Thermosense XX, SPIE Vol. 3361, ed. John R. Snell, Jr. and Richard N. Wurzback, p66-74, 1998

Application of Microscopic Tribo-thermography to Study Wear Damage Progression on Coated Surfaces

Staff:
Peter J. Blau and Ralph B. Dinwiddie, HTML

Abstract :
Wear of coated surfaces tends to progress through a series of stages in which damage accumulates until the coating fails to protect its substrate. Depending on the coating system and the contact conditions, these stages can sometimes be detected as a series of discrete periods of changing frictional behavior, or they can occur quite rapidly, leading to rapid removal of the coating. A new technique has been developed to capture magnified infrared (IR) images of a selected location on a moving wear surface and to synchronize these cycle-by-cycle images with the instantaneous friction force that occurs at the same location. A pin-on-disk tribometer has been used to demonstrate the principle, but other kinds of test geometries can also be used. Contrast in the IR images derives not only from the surface temperatures but also from the emissivity of surface features. By studying a series of captured and friction-synchronized images, it is possible to observe the detailed progression of wear and the corresponding frictional transitions in a limitless variety of materials. Examples of the stages of failure in a thin oxide film will be used to illustrate the application of microscopic tribo-thermography to coatings research.

Key Features:

• Tribo-Thermography
couples a pin-on-disk system with an infrared camera
• Pin-on-disk system measures the coefficient of friction
• Thermal images are captured during each rotation of the disk
• Machine vision software tools provide the means for measurement of spatial features (i.e., wear path, scallops, debris particles, grain size, etc.)
• The camera is fitted with an infrared microscope attachment
• Magnification is approximately 4X (FPA pixel size = 30 m m)
• Spatial resolution depends on the focus ring position (5.4 to 8.2 m m per pixel)
• The exposure time of the camera must be short enough to prevent image blurring
• T_exp = 200 m s, w = 87 rpm, wear path diameter = 51 mm è Blur < 7.4 m m
• An optical trigger allows the same spot to be imaged during the test
• Overcomes depth-of-field limitations of the microscope lens and misalignment of the specimen disk with the axis of rotation
• Allows study of the evolution of the wear phenomena

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Acknowledgments
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