Methods for Measuring Static Strains in Automobile Tires

Abstract

Two methods for measuring strains in an automobile tire by means of x-rays are described and significant results are discussed. The first method was designed to measure tire cord strains resulting from tire ex pansion, inflation, and deflection hy studying the dimensional changes of metat-shadowed cord. The second method was developed to provide a measure of tire carcass strains by following the movement of steel balls located between fahric plies. These techniques provide means for studying cord and tire behavior during tire manufacture as well as during tire inflation and deflection. Both series of strain measurements (with shadowed cord and with steel balls) have shown quantitatively significant extensions and contractions in the cord and carcass of an automobile tire as a consequence of curing, expansion, inflation, and deflection. Specifically, it was found that after inflation nonuniform strains existed along the cords within the same ply from crown to head of a tire. Cord strains from ply to ply were also nonuniform. The cords in the crown were stretched during expansion and curing, while the cords in the sidewall were subjected to appreciable contraction ; dimen sional changes which reflected a characteristic strain pattern within the tire and which originated during expansion and curing were retained in the tire after inflation.