The Interfacial Structure And Dynamic Evolution Of Steel Cord/Rubber In Radial Tire

In this paper, the effects of sulfur, PN759and cobalt decanoate on the physical mechanical properties, crosslink density, dynamic mechanical properties of vulcanizates and adhesion properties, dynamic fatigue properties, rubber coverage, fracture micromorphology of steel cord/rubber in a carcass recipe were examined by Tensile Tester, Rubber Process Analyzer, Rubber Flex Fatigue Testing Machine, Stereoscopic Zoom Microscope (SZM) and Scanning Electron Microscope(SEM). It were also studied the effects of fatigue-failure factors such as tension deformations, reciprocating strokes, parking time after fatigue, fatigue temperatures, fatigue cycles to adhesion properties of steel cord/rubber, interfacial structure and dynamic evolution. A new test method for the dynamic adhesion of steel cord/rubber was developed according to the real service condition of tire.The surface of pulled-out steel cord appeared exposed point when carcass recipe was without adhesives, so the adhesion failure mainly occurred in interphase. PN759replacing resorcinol slightly improved the static and dynamic adhesion and the probability that adhesion failure occurred in the interphase was similar to that occurring in the rubber phase. Cobalt decanoate could improve the static adhesion and favored the dynamic adhesion stability of rubber/steel cord, so that adhesion failure mainly occurred in rubber phase. Thus, the carcass compound with5-6phr sulfur,2.0phr PN759,2.0phr cobalt decanoate had higher comprehensive properties.SZM images showed rubber coverage appeared screw-like along the vertical direction of steel cord. The adhesion strength increased as the screw-like was more obvious and the screw thread was narrower. The greatest pull-out force corresponded to more uniform and clearer screw-like rubber coverage with narrower screw threads. The dynamic pull-out force of steel cord/rubber decreased with an increase of the tension deformations and reciprocating strokes. The dynamic pull-out force could be recovered after parking, the recovery of adhesion strength mainly occurred at the beginning of parking, and the adhesion strength was highest at32h of parking. Adhesion strength increased with an increase in temperature, and decreased with further increasing temperature. It also can be seen that dynamic pull-out force increased with increasing fatigue cycles, further increasing fatigue cycles could decreased adhesion strength.SEM images showed the surface roughness of fracture rubber torn from the cords increased with fatigue extent, and small particles emerged on the surface after flex fatigue. The particles were filler agglomerates, and the filler agglomerates grew from either filler aggregates or un-dispersed agglomerates during flex fatigue because fillers in rubber, which were stick to steel cord, were subject to high internal stress due to relative motion during flex fatigue and could move around in a wider range resulting in more chances to contact with the adjacent fillers to aggregate bigger particles. This might be explained that microcrack, induced by stress concentration effects of the filler agglomerates, could be the potential point of crack initiation.