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Streszczenie:
The present paper is concerned with modelling of fatigue crack initiation and propagation by applying the non-local critical plane model, proposed by Seweryn and Mróz. Using the linear elastic stress field at the front of a crack or sharp notch the damage growth on a physical plane is specified in terms of mean values of stress and strength functions. When the damage zone reaches a critical length, crack growth accompanies damage evolution. The model is applied to study crack propagation under cyclically varying tension compression and the predictions are compared with experimental data. The evolution of the damage zone and crack propagation in the biaxial case is considered next.

Streszczenie:
The present paper is concerned with the modelling of fatigue crack initiation and propagation by applying the non-local critical plane model, proposed by Seweryn and Mróz (1996, 1998). Using the linear elastic stress field at the front of a crack or sharp notch, the damage growth on a physical plane is specified in terms of mean values of the stress and strength function. The model is applied to study crack propagation under cyclically varying tension-compression conditions. The predictions are compared with experimental data.

Słowa kluczowe:
fatigue, damage accumulation, crack propagation

Streszczenie:
The damage accumulation condition expressed in terms of traction components on a physical plane is discussed for both monotonic and cyclic loading conditions. The crack initiation is assumed to correspond to a critical value of damage reached on the physical plane. For singular stress distribution in the front of sharp notch or crack the non-local condition is formulated. The proposed condition is applied to predict damage distribution within the representative element for cyclic loading conditions. The rosette diagrams are constructed for visualization of damage distribution. The prediction of crack initiation for multiaxial fatigue loading is provided. The second- and fourth-order damage tensors in order to describe damage distribution within the element, and the associated compliance variation are introduced.

Streszczenie:
Plane structural elements with sharp wedge-shaped notches are considered and the conditions for crack initiation are discussed. The use of the Griffith energy condition would require the assumption of pre-existence of a plane crack emanating from the notch vertex at specified direction. To avoid this assumption, a nonlocal crack initiation and propagation condition proposed by Seweryn and Mróz is applied to study crack initiation. This condition is expressed in terms of normal and tangential traction components acting on a physical plane segment of specified dimension. Mixed-mode conditions are considered for which both critical load value and crack orientation are predicted. The generalized stress intensity factors at the notch tip are determined by applying finite elements accounting for stress singularity. A special device was constructed in order to generate mixed-mode loading conditions in a tensile machine. The experimental program was executed in order to verify predictions of critical load variation and crack orientation for plane notched specimens of polymethyl metacrylate. Experimental data provide satisfactory agreement with model predictions. - See more at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)0733-9399(1997)123%3A6(535)#sthash.M6SKEj2w.dpuf

Streszczenie:
A non-local stress condition for crack initiation and propagation is proposed and applied to several particular cases, such as plate with wedge-shaped notch, elliptical hole and hyperbolic notch. Brittle failure initiation for notched elements under complex loading (Modes I and II) is studied in detail. A value of critical load and crack orientation is predicted from the non-local condition, which is applicable to both regular and singular stress concentrations.

Streszczenie:
A non-local crack propagation and damage evolution criteria were discussed in detail by the authors in [13-15] and applied to predict crack initiation from sharp notches and damage accumulation for complex cyclic loading programs. In the present paper the non-local condition is applied to the case of a cracked body subjected to compression and shear tractions inducing frictional slip and dilatancy at crack interfaces. The crack propagation directions with critical loading conditions are obtained taking into account the crack asperity interaction and dilatancy induced by slip. The material strength and compliance variation can be predicted from the model.

Streszczenie:
The damage accumulation condition expressed in terms of traction components on a physical plane is considered for both monotonic and cyclic loading conditions. The crack initiation is assumed to correspond to a critical value of damage parameter on a maximum damage plane. A non-local condition is formulated for singular stress or strain regimes. The model is applied to predict damage distribution within the element for cyclic loading condition; in particular for combined torsion and bending. The damage tensors are introduced to describe the predicted damage distribution.