The role of friction in the 3ENF and 4ENF delamination tests: an analytical solution

In composite structures, the presence and growth of delamination mechanisms in static or fatigue loading conditions is of paramount interest and the American Society for Testing and Materials (ASTM) has adopted the three-points bend end-notched flexure test (3ENF) as the standard for measurement of mode II toughness. The drawback of the 3ENF test is the unstable crack growth and a modified version of the test, namely the four points bend end-notched flexure test (4ENF), has been proposed. The main advantage of the 4ENF over the 3ENF is that crack growth is stable under displacement control, but it can be strong influenced by the interlaminar frictional effects. The effect of frictional cont…

A coupled plasticity-damage cohesive-frictional interface for low-cycle fatigue analysis

A novel thermodynamically consistent cohesive-frictional model for the analysis of interface degradation and failure under either monotonic quasi-static loading or cyclic loading in low-cycle fatigue problems is proposed. Starting from the definition of a suitable Helmholtz energy density function, a phenomenological interface model is developed in the framework of plasticity and damage mechanics. In particular, a coupled plasticitydamage activation function is defined and employed together the consistent evolution rules to capture the evolution of damage and plasticity under the action of the external loads. Due to the specific features of such threshold and flow rules, the initiation and …

A Cohesive-frictional interface model subjected to mixed complex loading paths

The paper presents a cohesive-frictional interface model based on surface damage mechanics. The proposed model is developed under the assumption that the fracture energies in mode I and in mode II are different values, as shown by several experimental evidences. At difference with the most spread available interface models, only one isotropic interface internalvariable is adopted for the constitutive model. The interface constitutive model is developed in a Thermodynamic consistent framework with an Helmholtz free energy potential and the fulfillment of the thermodynamic principles is obtained enforcing the Clausius-Duhem inequality. The damage/friction activation functions and dissipative …

Hellinger-Reissner variational principle for stress gradient elastic bodies with embedded coherent interfaces

An Hellinger-Reissner (H-R) variational principle is proposed for stress gradient elasticity material models. Stress gradient elasticity is an emerging branch of non-simple constitutive elastic models where the infinitesimal strain tensor is linearly related to the Cauchy stress tensor and to its Laplacian. The H-R principle here proposed is particularized for a solid composed by several sub-domains connected by coherent interfaces, that is interfaces across the which both displacement and traction vectors are continuous. In view of possible stress-based finite element applications, a reduced form of the H-R principle is also proposed in which the field linear momentum balance equations are…

A nonlocal integral approach to elastic-damage interface modelling

A nonlinear finite element approach with cohesive-frictional interfaces for mode II Transverse Crak Tension test insight

In many circumstances structural failure modes are driven by the formation and propagation of fractures. For instance in composite laminate structures one of the most worrying condition is delamination, which is an interlaminar progressive fracture. Fracture toughness is the material mechanical parameters which ensure fracture safe condition and it is also an essential parameter for performing nonlinear structural analysis, no matter if based on Fracture Mechanics or by means of Interface Cohesive theories. It is then of paramount relevance to evaluate the critical fracture energy by means of simple and reliable laboratory tests. Several tests are available for the direct determination of m…