Cohesive cracking

A. Carpinteri et al Cohesive crack model description of ductile to brittle size-scale transition dimensional analysis vs. renormalization group theory. Eng. Fract. Mech. 70(14) 1809-1839 (2003)... 

Ooi, E.T., Yang, Z.J., 2009. Modeling multiple cohesive crack propagation using a finite element-scaled boundary finite element coupled method. Engineering Analysis with Boundary Elements, 33(7) 915-929. 

In this case, cracks run along the interface between two materials due to interactions between the stress field in the adhesive layer and spatial variations in fracture properties. The cracks are not generally free to evolve as mode I cracks, as was the case for cohesive cracks, and mixed-mode fracture concepts (combinations of tension and shear) have to be considered. Mode II or shear components are induced, even in what appear to be nominally mode I loadings, due to differences in moduli about the interface. Again, if the presence of the adhesive layer is being ignored and the adherends are dissimilar, then a crack appears to be adhesive (i.e. an adhesion failure) on the macroscopic scale. 

One might think that an initially straight cohesive crack (Fig. 14) would turn (kink) upon the slightest application of However, it turns out that the elastic mismatch that is contained in Eq. 38 allows a straight crack to continue as such for approximately < 0.1AT,° . To see this, we take the common assumption that cracks in homogeneous materials grow in such a way that the local mode II component /fn = 0. This condition, when substituted into Eq. 38 yields a relationship between the location of the crack (c//z) and the global mode-mix as... 

For materials that exhibit a strain hardening or a rising stress-strain curve response, the stresses are still singular. Hutchinson [18] and Rice and Rosengren [44] demonstrated this for cohesive cracks using a 72-deformation plasticity approach. Under these conditions, the stress field became known as the HRR stresses with... 

Refined constitutive models for continuum elements and cohesive crack interface elements typically include many parameters, which require calibration with data from material tests. Data fi om uniaxial compression tests on concrete cylinders can be used for the calibration of the continuum material models for the concrete, as shown in Fig. 10a, while data from masomy prism tests (uniaxial compression and bond wrench) can be used for the calibration of the constitutive models for the masomy. Interface elements typically include parameters pertaining to mixed-mode fracture, and data from mixedmode fracture tests on concrete or masomy mortar joints need to be used for the calibration (e.g.. 

Koutromanos I, Shing PB (2012) A cohesive crack model to simulate cyclic response of ctmcrete and masonry structures. ACI Structural Journal 109 349-358... 

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