Advanced fragmentation stage of oxide coating on polymer substrate under biaxial tension

Image analysis of microscopic crack patterns applied to thermal fatigue heat-checking of high temperature tool steels

“…For example, the crack patterns appearing in the glaze of ceramics (Bohn et al, 2005), in thin films prepared by sol-gel process (Bockmeyer and Löbmann, 2007), and in oxide coatings on polymer substrate under biaxial tension (Andersons and Leterrier, 2005) present a quite similar aspect and development to those observed on our specimens.…”

“…Moreover, this evaluation is rather subjective, since the results can vary from an observer to another. More recently, quantitative investigations have been proposed using image analysis software to evaluate the "crack density" (Andersons and Leterrier, 2005;Bockmeyer and Löbmann, 2007;Jean et al, 1999;Lemoine et al, 1986;Maillot et al, 2005;Wu and Xu, 2002). These methods constitute a more precise tool to qualify the damage rate.…”

“…This approach, which leads also to represent the irregularity of the crack pattern by a global coefficient, generally requires different scales of observation of the same pattern, and is furthermore difficult to interpret. Some geometrical aspects, like the fragment area (Andersons and Leterrier, 2005), the crack segments length (Lemoine et al, 1986;Velde, 1999), or the orientation of the crack segments (Lemoine et al, 1986), have been in addition examined in different works.…”

Mechanics of fragmentation of crocodile skin and other thin films

“…It is found that both α = 1 and 7 lead to smaller fragments with more uniform ( L max / L = 1.9 and 1.8, for α = 1 and 7, respectively, where L max is the maximum length and L is the average length of all the fragments) and symmetric distribution of the fragment length than α = 2.4 which contains fragments much larger than the rest ( L max / L = 2.5). The result obtained for α = 1 quantitatively agrees with the experimental observation for oxide coating, which is taken as a linear-elastic material, as L max / L = 1.65 ~ 1.8 is obtained for this material under different applied strains12. These results agree with what we observe for crocodile skin and other thin films (Fig.…”

Evaluation of interfacial stress transfer efficiency by coating fragmentation test

“…The interfacial shear stress was taken as a power function of the shear strain, s $ c m , where m < 1 models a softening interface and m = 1, naturally, corresponds to linear stress transfer. However, comparison of the slope of fragmentation diagrams at high uniaxial (Handge, 2000) and biaxial (Andersons and Leterrier, 2005) strains to the corresponding theoretical relations still yielded the estimate of m close to 1 for a number of SiO x /polymer systems. This suggests that, despite the local interfacial yielding and damage, the common linear shear-lag model relations Eqs.…”