STRESSES AND DEFORMATION OF COMPRESSED ELASTOMERIC

The sealing capability of an elastomeric O-ring seal depends upon the contact stresses that develop between the O-ring and the surfaces with which it comes into contact. It has been suggested in the literature that leakage will occur when the pressure differential across the seal just exceeds the initial (or static) peak contact stress. The stresses that develop in compressed O-rings, in common cases of restrained and unrestrained geometries (grooved and ungrooved), are investigated using the finite element method. The analysis includes material hyperelasticity and axisymmetry. Contact stress profiles, and peak contact stresses are plotted versus squeeze, up to 32 percent. The contact width, which is the length of the O-ring that touches the retaining surfaces when viewed from the cross-section, is also determined. Expressions are derived empirically to predict the peak contact stress and the contact width. These expressions are also compared to those obtained by other researchers (who assumed plain strain conditions) and conclusions to their validity are drawn. NOMENCLATURE b = contact width S = compressive stress d = wire diameter x * = displacement D = nominal (mean) diameter x = radial coordinate Ddef = deformed mean diameter X = radial distance from O-ring center E = modulus of elasticity y = axial coordinate h = deformed O-ring thickness Y = axial distance from O-ring center l = groove width * = normalized squeeze (i.e., fractional q = chord diameter compression) Q = normalized chord diameter, q/d *ij = equivalent normalized squeez