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This paper demonstrates how the critical strain energy density in the delamination tip vicinity may be used to explain the physics of delamination growth under mixed mode I/II. A theory previously proposed to physically relate mode I and mode II delamination growth is further extended towards describing the onset of mixed mode I/II delamination. Subsequently, data from the literature is used to demonstrate that this new concept of the critical strain energy density approach indeed explains, based on the physics of the problem, the strain energy release rate level at which crack onset occurs. This critical strain energy density for the onset of delamination appears to be independent of the opening mode. This means that, in order to characterize the fracture behaviour of a laminate, fracture tests at only one loading mode are necessary. Because the load level at which the physical delamination onset occurs at the microscopic level is much lower than the traditional engineering definition of macroscopic onset, further work must reveal the relationship between the macroscopically visible delamination onset, and the microscopic onset., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Structural Integrity & Composites

In this paper, by considering the absorbed energy in the fracture process zone and extension of the minimum strain energy density theory for orthotropic materials, a new mixed mode I/II failure criterion was proposed. The applicability of the new criterion, to predict the crack growth in both laminated composites and wood species, was investigated. By defining a suitable damage factor and using the mixed mode I/II micromechanical bridging model, the absorbed energy in the fracture process zone was considered. It caused the new criterion to be more compatible with the nature of the failure phenomena in orthotropic materials, unlike available ones that were conservative. A good agreement was obtained between the fracture limit curves extracted by the present criterion and the available experimental data. The theoretical results were also compared with those of the minimum strain energy density criterion to show the superiority of the newly proposed criterion., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Structural Integrity & Composites

In this study, an innovative depth dependent biphasic transversely isotropic model (DBT) was proposed to study the mechanical behavior of Articular Cartilage (AC). To find a more precise model to address the mechanical behavior of AC, the vital role of collagen fibers in all zones of the AC has been taken into account and depth dependent elasticity mechanical properties of cartilage are calculated as a function of collagen fibers orientation and volume fraction. Material parameters of permeability function were calculated in such a way that the variations of indenter displacement with time predicted by Finite Element Method (FEM) simulation for creep indentation test of the AC sample based on DBT model. In addition, the test was simulated by an isotropic-biphasic model to compare the capabilities of these two models and difference in mechanical behaviors of biphasic-isotropic and depth dependent transversely isotropic materials. According to the calculations, the presence of collagen fibers triggers increasing of stresses in fibers direction and decreasing of stresses perpendicular to fiber direction in the superficial and deep zones of AC. The findings of this study may have implications not only for calculating stress distributions in AC components but also for developing progressive damage model of AC for predicting osteoarthritis cartilage behavior in different cartilage-related diseases.