Abstract
Considering that the correct quantification of fatigue damage involves
two load parameters, the available load ratio data on polymeric
materials are analyzed. It is shown that crack growth can be
characterized by two parameters, ΔK and K max, without
the need for any crack closure concept. The crack growth rates, starting
from the threshold can be represented by the L-shaped curves in the ΔK-K
max plane defining two limiting variables, ΔK* and K
max*. Crack growth trajectory maps for various materials
are developed by plotting ΔK* versus K max*, as a
function of crack growth rate. The trajectory defines the crack growth
resistance curve providing a measure of material resistance to
increasing crack tip driving forces.