Research On Dynamic,Static Tests And Fatigue Performance Of WJ-7 Ballastless Track Fastener

Non-ballasted track is the track form of most high-speed railway in China because of its good smoothness,durability and stability,which are the foundation of safe operation of trains.The fastener is the main contributor to the elastic and adjustment ability of non-ballasted track.The function of fasteners are to hold the rail on sleepers,bear the load of upper trains,and resist the transverse forces.The fastener plays an important role in a fastener system,but its service life is much lower than the design life.In order to explore the reasons for the failure of the fastener,this paper conducts a series of static load and fatigue tests for the research object with WJ-7 type fastener,and the research contents and conclusions are as follows:(1)The stress distribution of WJ-7 type fastener under different pretension forces is measured by strain electrical measurement.The result shows that the largest stress value of the area is back-end big circle of a fastener,which is the danger region in installing and serving.It is points out that 25 k N is the most reasonable installation pretension force,at the same time,a calculation formula about elastic displacement and clamping force of the fastener,which provides a quantitative reference for the actual installation,is summarized according to the field measurement data.(2)Using MTS 810 Flex Test Material Testing System for WJ-7 type fastener exerts pressure load and displacement load,this article analyses changing rules about the displacement of middle circle and clamping force of a fastener under two load controls.The data shows that under displacement load,the speed of decline in clamping force and increase in displacement of middle circle is faster,and the fatigue life is lower.This kind of loading method is similar to the force condition in actual service,which is basically consistent with the fact that the actual service life of fasteners is less than the design life.(3)The fatigue life of WJ-7 type fastener is obtained by group tests under different stress amplitudes,and draw the S-N curve and under three survival rates of P-S-N curve of the fastener.It is suggested that the lowest fatigue life under 99% survival rate should be regard as a reference service life number.This paper deduces a group of S-N curve calculation formula of the fastener,and get a conservative fatigue limit for ?a1=182Mpa and another radical fatigue limit for?a2=234Mpa.By SWT and Walker equations,the formula of S-N curve of the fastener is modified,and the fatigue life of the fastener is shortened when the modified formula iscalculated under the same stress amplitude.