Some 260 have a very clear running crack and some break straight across. Why?
In materials with uniform properties in all directions, cracks like to extend perpendicular to the maximum applied tensile stress. In a 260, we have two tensile stresses which are perpendicular to each other. But remember that hoop stress is always twice the magnitude of the axial stress. Since these are “principal stresses” (no shear stresses), it turns out that the hoop stress will always be the maximum stress. In an ideal world then, cracks will start at a flaw, then turn so that they run perpendicular to the maximum stress which means they really want to run axially. However, this isn’t an ideal world, and latex does not have uniform properties in all directions when inflated….
