Dynamic fracture in a semicrystalline biobased polymer: an analysis of the fracture surface

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ORIGINAL PAPER

Dynamic fracture in a semicrystalline biobased polymer: an analysis of the fracture surface Jean-Benoît Kopp

· Jeremie Girardot

Received: 4 June 2020 / Accepted: 5 September 2020 © Springer Nature B.V. 2020

Abstract The fracture behaviour of a semi-crystalline bio-based polymer was studied. Dynamic fracture tests on strip band specimens were carried out. Fracture surfaces were observed at different scales by optical and electron microscopy to describe cracking scenarios. Crack initiation, propagation and arrest zones were described. Three distinct zones are highlighted in the initiation and propagation zone: a zone with conical markings, a mist zone and a hackle zone. The conical mark zone shows a variation in the size and density of the conical marks along the propagation path. This is synonymous with local speed variation. Microcracks at the origin of the conical marks in the initiation zone seem to develop from the nucleus of the spherulites. In the propagation zone with complex roughness, the direction of the microcracks and their cracking planes are highly variable. Their propagation directions are disturbed by the heterogeneities of the material. They branch or bifurcate at the level of the spherulites. In the arrest zone, the microcracks developed upstream continue to propagate in different directions. The surface created is increasingly smoother as the energy release rate decreases. It is shown that the local velocity of the crack varies in contrast to the macroscopic speed. A J.-B. Kopp (B) · J. Girardot Arts et Metiers Institute of Technology, Université de Bordeaux, CNRS, INRA, INP, I2M, HESAM Université, Esplanade des Arts et Métiers, 33400 Talence, France e-mail: [email protected] J. Girardot e-mail: [email protected]

specific setup allowing to estimate the minimum fracture energy of the material in order to maintain the rapid propagation of the crack is proposed for materials with antagonistic behaviour: ductile at initiation and brittle in propagation. Keywords Dynamic fracture · Rapid crack propagation · Fracture surface analysis · Semi-crystalline · Polymer 1 Introduction There are numerous studies in the literature on the fracture behaviour of materials and structures (Beguelin et al. 1997, 1998; Yoffe 1951; Broberg 1960; Freund 1972; Cros et al. 2000; Irwin et al. 1979; Sheng and Zhao 2000; Rosakis and Zehnder 1985; Ponson and Bonamy 2010; Fineberg and Bouchbinder 2015; Lebihain et al. 2020; Le Barbenchon et al. 2020; Ravi-Chandar 1998; Sharon and Fineberg 1999). Approaches in the analysis of the mechanism vary widely depending on the point of view. Experimenters tend to replicate the mechanism more or less rigorously in the laboratory (Fond and Schirrer 2001; Kopp et al. 2018; Ravi-Chandar and Knauss 1984a; Kolvin et al. 2017). They describe it with ever more sophisticated tools and sometimes different interests. Some are interested in crack initiation (Bisoffi-Sauve et al. 2019; Rittel and Maigre 1996), some in crack propagation (Kopp et al. 2018; Fond and Sc