Bonded (glued) insulated rail joints are widely used in continuously welded railroad track. These joints frequently develop problems in which the epoxy debonds from the fishing surfaces of the rail and joint bars, leadingto problems such as pull-aparts and electrical failures. Insulated joint problems can be disruptive to railroad operations, and may in some cases increase the risk of train derailments. This paper describes the results of computer modeling of the effects of epoxy debonding on the stresses and strains in a bonded insulated joint subjected to longitudinal forces. The primary goal of this research is to identify measurable changes in the joint's strain distribution that correlate with the extent of debonding, to serve as the basis of a non-destructive monitoring and evaluation technique. The results of the modeling show that, under thermal tensile loads, strains at the center of the outer surface of the joint bar tend to increase as debonding begins near the endpost. The strain at this point tends to stabilize after the debonding reaches the innermost bolt hole. Strain at a point between the outermost and middle bolt holes starts off relatively stable, but increases after debonding passes the innermost bolt hole. Strains in the event of a pull-apart depend on the friction parameters chosen for the ruptured epoxy. In all cases, results suggest that any increase in debonding causes an increase in the elastic relative displacement of the railends under load.
Samenvatting