Thin ﬁlm and substrate cracking under the inﬂuence of externally applied loads Srinath S. Chakravarthy, Eric H. Jordan * , Wilson K.S. Chiu Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Road, Storrs, CT 06269-3139, USA Received 16 April 2004; received in revised form 17 September 2004; accepted 19 September 2004 Abstract Cracking in thin ﬁlm systems subject to residual tension is examined. The existing solution for the case of a crack tip in the substrate is modiﬁed to provide a solution of greater accuracy. The inﬂuence of external tensile loads on thin ﬁlm and substrate cracking is examined. An approximate superposition scheme is presented for the determination of the energy release rate. Crack arrest is examined and parameters for determining the possibility of crack arrest are pre- sented. For compliant ﬁlms it was found that crack arrest does not occur when the substrate stress has the same mag- nitude as the residual stress. The inﬂuence of externally applied loads on crack channelling and conditions under which channelling will occur in the substrate are presented. Ó 2004 Elsevier Ltd. All rights reserved. 1. Introduction Thin bonded ﬁlms have many diverse applications. The applications range from coatings used in optical ﬁlters, to conductive, insulative and semiconductor coatings used in integrated circuits, to protective coat- ings on metals (anti-corrosion) and on optical ﬁbers (hermetic coatings) [1]. Commonly, hermetically coated optical ﬁbers have ﬁlm coatings with tensile residual stress and are then subjected to external loads such that the fracture under this combined inﬂuence is of interest. The inert strength of the ﬁber is strength of the ﬁber measured in a test in which there no eﬀects of stress corrosion cracking. It has been observed that the presence of the coating reduces the inert strength of the ﬁber [2]. Demand for increased reliability of optical ﬁbers subject to the combined loading has motivated the current eﬀort. 0013-7944/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfracmech.2004.09.006 * Corresponding author. Tel.: +1 860 486 2371; fax: +1 860 486 5088. E-mail address: jordan@engr.uconn.edu (E.H. Jordan). Engineering Fracture Mechanics 72 (2005) 1286–1298 www.elsevier.com/locate/engfracmech