Contribution to Fatigue Striation Phenomenon Analysis by Using Image Processing

Abstract

Since the use of energetic approaches for the prediction of the number at macro-crack initiation in elastomers, a special attention is paid on fatigue crack growth at the microscopic scale. In filled natural rubber, failure surfaces exhibit wrenchings and striations (Le Cam et al., Int J Fatigue 52:82–94, 2013). Both are assumed to be due to strain-induced crystallization (SIC). Only four studies address fatigue striations (Le Cam et al., Int J Fatigue 52:82–94, 2013; Le Cam and Toussaint, Macromolecules 43:4708–4714, 2010; Flamm et al., Int J Fatigue 33:1189–1198, 2011; Muñoz-Mejia, Dissertation, Université Claude Bernard, Lyon I, 2011), while they could provide information of importance to better understand how SIC enables natural rubber to resist the crack growth. As striations are similar to fringe patterns, this study aims at using a phase extraction algorithm from a single fringe pattern to analyse the striation morphology (Robin et al., Appl Opt 44:7261–7269, 2005; Takeda et al., J Opt Sot Am 72:156–160, 1982; Servin et al., Appl Opt 36(19):4540–4548, 1997; Robin et Valle, Appl Opt 43(22):4355–4361, 2004; Valle et al., Strain 46(2):175–183, 2008). This phase extraction methodology is split into three steps. The first one consists in extracting the wrapped phase without orientation. The second step is devoted to the determination of the fringe pattern orientation from a classic unwrapping algorithm. The third and last step consists in using an unwrapping algorithm (Zuo et al., Opt Lasers Eng 85:84–103, 2016; Menese et al., Appl Opt 44(7):1207–1215, 2005) and to compute the difference between the unwrapped phase processed and a plane in order to analyse the evolution of the striation morphology. This methodology has been applied to characterize the striation morphology observed at the failure surface of specimen tested under different fatigue loading conditions.