Issue 41

V.M. Machado et alii, Frattura ed Integrità Strutturale, 41 (2017) 236-244; DOI: 10.3221/IGF-ESIS.41.32 236 Focused on Crack Tip Fields On short cracks that depart from elastoplastic notch tips Verônica Miquelin Machado, Jaime Tupiassú Pinho de Castro, Marco Antonio Meggiolaro Pontifical Catholic University of Rio de Janeiro, PUC-Rio, R. Marquês de São Vicente 225, Rio de Janeiro, 22451-900, Brazil vetiksm@gmail.com , jtcastro@puc-rio.br, meggi@puc-rio.br A BSTRACT . The behavior of short cracks that depart from elastoplastic notch tips is modeled to estimate the stresses required to initiate and to propagate cracks in notched structural components, and to evaluate the size of tolerable crack-like defects under general loading conditions. This analysis can model both fatigue and environmentally assisted cracking problems; can evaluate notch sensitivity in both cases; and can as well be used to establish design or acceptance criteria for tolerable non-propagating crack-like defects in such cases. The growth of short cracks is assumed driven by the applied stresses and by the stress gradient ahead the notch tip, and supported by the material resistances to crack initiation and to long crack propagation by fatigue or EAC. In the elastoplastic case, the stress gradient ahead of the notch tip is quantified by a J -field to consider the short crack behavior. The tolerable short crack predictions made by this model are evaluated by suitable fatigue and EAC tests of notched specimens specially designed to start non- propagating cracks from the notch tips, both under elastic and elastoplastic conditions. K EYWORDS . Short cracks; notch sensitivity; fatigue cracking; environmentally assisted cracking; elastoplastic behavior; J-integral. Citation: Machado, V.M., Castro, J.T.P., Meggiolaro, M.A., On short cracks that depart from elastoplastic notch tips, Frattura ed Integrità Strutturale, 41 (2017) 236-244. Received: 28.02.2017 Accepted: 03.05.2017 Published: 01.07.2017 Copyright: © 2017 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION t is well-known that abrupt geometric transitions (like holes, slots, grooves, keyways, shoulders, corners, threads, weld fillets, reinforcements, etc.), generically called notches, can significantly perturb the local stress field around their borders. In particular, notches induce a localized stress concentration factor (SCF) K t   max /  n , where  max is the maximum stress at the notch tip and  n is the nominal stress that would act there if the notch did not disturb the stress field in its vicinity. SCF can be calculated by linear elastic (LE) procedures when such conditions apply around the notch borders, but not if the material yields at the notch tip [1]. It is also well-known that notch-induced effects under fatigue load conditions can be smaller than it would be predicted from K t   n , in particular if K t is high. If this was not so, small sharp scratches would be able to ruin any structural component subjected to fatigue loads. Therefore, notch effects in fatigue are often quantified in practical applications by K f  1  q  ( K t  1 ), where 0  q  1 is the notch sensitivity factor. I