The Plastic Deformation Of Materials Under Impacting Load

This thesis mainly focuses on the plastic deformation of different materials under impact load experimentally.First, using numerical techniques, the effect of a bump on either surface on the thermal elastohydrodynamic lubrication (EHL) in line contact under reciprocating motion is explored. The oil used is assumed to be Ree-Eyring fluid. The results show that, pressure fluctuations and temperature rising will happened when the bump enter contact area, also the film thickness will reduced.Then a testing bed for the present experiments was designed in order to perform the impact experiments. The experiments were fulfilled by imposing the force with the electromagnets and the time relay. Under a constant frequency, a steel ball was hit the plates made of duralumin, lead brass, steel no.45 and UHMW-PE, respectively. Two contact conditions are employed: dry contact and lubricated contact with two oils of different viscosity. The plastic deformation of the plate was measured with two loads and changing impacting times. It was found that, the surface for all materials was damaged greatly, therefore, the depth of the dent increased drastically with the impacting times and the load. Lubrication can effectively reduce the surface damage. The raised shoulder of the dent, i.e., the so-called iridescent ring, is formed because the heat produced during the impact transfers to the vicinity. The iridescent ring is augmented similar when use low viscosity oil under lower impacting times, but shallower under high impacting times. The iridescent ring is augmented with the increase of the load and the viscosity of the lubricant. Under dry contact condition, superfine powder is found inside the dent. The microcrack occurs inside the lubricated dent. The degrees of the superfine powder and the microcrack increase with the impacting times and the load.