Some formulas for the crack opening stress level

van der Linden, 1979, NLR test results as a data base to be used in a check of crack propagation prediction models. A Garteur activity, NLR TR 79121 Elber, 1971, The significance of crack closure, ASTM STP, 486, 230 Schijve, 1979, The stress ratio effect on fatigue crack growth in 2024-T3 Alclad and the relation to crack closure Newman, 1976, A finite-element analysis of fatigue crack closure. Mechanics of crack growth, ASTM STP, 590, 281 de Koning, 1980, A simple crack closure model for prediction of fatigue crack growth rates under variable amplitude loading, NLR MP 80006