Page 17 - ConnectorSupplier.com 2019 How-to-Specify E-Book

The Arrhenius equation:
in which k is the rate constant, T is the absolute temperature in kelvin, A is the pre-exponential factor (a constant for each chemical reaction), Ea is the activation energy for the reaction (in the same units as R*T), and R is the universal gas constant, provides a formula for the temperature dependence of reaction rates.1 For Arrhenius- type reaction behavior, it can be estimated that the reaction rate doubles for each 10° increase in temperature. Therefore, a 25° increase would increase the rate by a factor of 6 (22.5) and a 125° increase would increase the reaction rate by a factor of 6,000. By this logic, it is safe to assume that components that barely function at the upper temperature limits of consumer applications would rapidly degrade in more demanding environments.
Table II details the temperature profile for the automotive market segment. The anticipated underhood temperatures of 150°C or 200°C have not been realized using standard designs and wiring technology. Maximum peak temperatures of 125°C have been recorded, albeit with considerably lower steady-state temperatures, and newer designs and wiring technology will significantly increase these peak temperatures. Mechatronics is the placement of electronic controls directly on an electromechanical device (e.g., on-engine, on-transmission, wheel-based, and exhaust stream). These various devices are interconnected via a common bus. While engine and transmission controls will experience anticipated peak temperatures, wheel and brake controls will exceed these limits by 50°C to 100°C.
Table II: Temperature profiles for various applications within the automotive market segment.
Thermal effects are cumulative, so the net effect of several short-term exposures is equal to a single exposure for the equivalent amount of time. In order to design and qualify parts for elevated-temperature applications, the thermal profile must be understood. It is important to know, for instance, whether the exposure will be more or less isothermal, as is the case for geothermal walls, or whether there will be a distribution of temperatures akin to automotive demands. Knowledge of the thermal distribution will lead to a reliable test plan.
Connector Failure Modes and Effects
There are two failure modes associated with thermal exposure. The first is a loss of normal contact force, which can result from thermal expansion effects between the spring material and the plastic housing, reduced strength
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