Rubber Strain Measurements in Bias, Belted-Bias and Radial Ply Tires

Abstract

The two-dimensional state of strain on the inner and outer surfaces of automobile tires operating under straight ahead rolling conditions was experimentally determined for bias (cross-ply), belted-bias and radial ply tires of comparable size. The strain transducer employed was fabricated by embedding a column of liquid mercury in a small billet of silicone rubber. The principle of operation of this gage is similar to that of the conventional bonded electric resistance strain gage used with metals - i.e., a change in resistance of the mercury capillary is linearly related to the strain in the direction of the column. These gages were mounted in three directions at locations from the bead to the crown and the measured strains were used to calculate the maximum tensile, compressive and shearing strains. The de formation characteristics of the different tire constructions were compared at various wheel loads and inflation pressures. The experimental results in dicate that membrane strains predominate in the inflated but otherwise un loaded tire, while bending strains predominate in the region of the contact zone of the rolling tire. The magnitude of the maximum shearing strain is, in general, greater than or equal to the maximum tensile strain. The direction of the maximum shearing strain in a plane tangent to the rubber surface, in general, coincides with the cord direction in the ply closest to the tire surface.