US Patent 8936439 Radial turbine backface curvature stress reduction

A turbine wheel is disposed about an axis and has a back having a separator disposed thereon, an inner undercut disposed between the separator and the axis, and an outer undercut disposed between the separator and an outer periphery of the back face. The inner undercut is defined by a first radius blending toward the axis and into a first flat section, and further defined by a second radius blending into the first flat section and into the separator.