Sun kink

Sun kink refers to a condition that can occur on hot days in rail tracks. The phenomenon is caused by what is properly termed as buckling.

The buckling force in the track due to warming up is a function of the rise in temperature only and is independent of the track length;

The linear thermal expansion due to heating of the track is found using:$\{Delta\; L\; \}\; =\; alpha\_L\; Delta\; T\; L$where
* ΔL = thermal expansion of the rail
* L = length of the rail/track
* α = coefficient of thermal expansion
* ΔT = increase in temperature

According to Hooke's law the extension due to a force (in the rail) is:$Delta\; L\; =\; frac\{F\}\{E\; A\}\; L$where
*ΔL = extension of the rail/track
* F = the force extending a rod, here the induced force in the rail
* E = modulus of elasticity of rail material (steel)
* A = cross section of rail
* L = length of rail

Putting these together gives:$\{frac\{F\}\{E\; A\}\; L\; \}\; =\; alpha\_L\; Delta\; T\; L$or:$F\; =\; E\; A\; alpha\_L\; Delta\; T$

Here E, A and α are all constants, L drops out of the equation, only T is variable.

Accidents

These accidents were deemed to be sun kink-related (more information available at List of rail accidents):
* April 18, 2002 Amtrak Auto-Train derailment, off CSX tracks, near Crescent City, FL.
* July 22, 2002 Amtrak Capitol Limited derails, off CSX tracks, near Kensington, MD.

ee also

* List of rail accidents