Curved weak interfaces present promising advantages to be implemented as crack arrestors in structures designed under the tolerant-design principles. Among other advantages, they neither add extra weight nor affect significantly to the global stiffness of the structural element, in contrast with other crack arrestors. To be employed as crack arrestor, it is key that the interface can deviate the crack. If the crack penetrates across the interface, the effect of the weak interface as crack arrestor is canceled. In view of this, this work studies how to set the interface parameters to promote the crack deviation along the interface. In particular, following the dimensional analysis of the problem, the effect of three significant dimensionless parameters is studied: interface to bulk fracture toughness, interface to bulk tensile strength and the interface curvature radius normalized with the material characteristic length. The study is carried out using the Coupled Criterion of the Finite Fracture Mechanics.
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Themes: Finite Fracture Mechanics: Theoretical Aspects, Numerical Procedures, and Experimental Applications
FINITE FRACTURE MECHANICS VERSUS PHASE FIELD: A CASE STUDY ON THE CRACK ONSET FROM CIRCULAR HOLES UNDER BIAXIAL LOADING CONDITIONS
The phenomenon of brittle crack onset stemming from a circular hole embodied in a biaxially loaded infinite plate is herein investigated. Three different approaches are used to determine the biaxial safety domains: Finite Fracture Mechanics, Cohesive Zone Model and Phase Field. In particular, the original formulation of Finite Fracture Mechanics (FFM) proves to be consistently more optimistic than its averaged-stress variant (FFM-avg); likewise, both agree in predicting the existence of a region in the loading space where failure is governed by the energy condition. Besides, failure predictions according to Dugdale’s Cohesive Zone Model (CZM) prove to be fairly close to those by FFM, whereas the differences between CZM and FFM-avg result more noticeable. Lastly, the Phase Field model of fracture is implemented paying special attention to the choice of the energy decomposition, being herein implemented two relevant options: No-Decomposition and No-Tension decomposition. In particular, the latter showcases reasonable agreement with FFM (and CZM), thus rendering it a solid contender for its use in applications in which combined tension-compression stress states appear, such as in the dynamic failure of brittle materials.
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MECHANICS OF THE INTERACTION OF TWO PARALLEL, SIMULTANEOUSLY GROWING CRACKS USING LEFM
Experiments and numerical simulations studied the mechanics of two interacting colinear and offset cracks. Quasi-static experiments were carried out on acrylic sheets to determine the crack growth direction in the specimens with double parallel cracks or a single crack. The Finite Element Method (FEM) was adopted to calculate stress intensity factors at the crack tips. The interaction and influence of crack growth and direction of propagation with various geometries of cracks and their positions were discussed. This interaction is observed through a change in the propagation directions of crack tips. As the cracks grow, the SIF at the crack tip continuously increases. When the cracks are very close, SIF sharply increases for the colinear case. Crack growth behavior is observed, and the stress intensity factor is calculated at each step of crack growth for both cracks. The interaction effect on the crack path during propagation in simulation is predicted by the Maximum Tangential Stress (MTS) criterion. Some experiments are conducted to validate the analysis results. Comparisons are also made with experiments conducted under this study.
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THE THEORY OF CRITICAL DISTANCES TO MODEL THE STATIC STRENGTH OF ADDITIVELY MANUFACTURED CONCRETE/POLYMERS CONTAINING MANUFACTURING DEFECTS/VOIDS [Keynote]
The present paper deals with the use of the Theory of Critical Distances to model the detrimental effect of manufacturing defects and voids in 3D-printed concrete/polymers subjected to static loading. The validity and robustness of the proposed approach is assessed against a large number of experimental results that were generated by testing 3D-printed specimens of both concrete and polylactide (PLA) containing manufacturing defects/voids. The sound agreement between experiments and predictive model makes it evident that the Theory of Critical Distances is not only a reliable design approach, but also a powerful tool suitable for guiding and informing effectively the additive manufacturing process.
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SINGULAR ELASTIC SOLUTIONS IN CORNERS AND CRACKS WITH SPRING BOUNDARY CONDITIONS WITH VARYING STIFFNESS [Keynote]
Singular elastic solutions in corners and cracks with spring boundary conditions with varying spring stiffness are studied. First, a novel analytic procedure is developed for the antiplane strain case. Then, some general observations obtained are checked for the plane strain case by using a FEM code. Finally, applications of these observations in a suitable computational implementation of the Coupled Criterion of Finite Fracture Mechanics are discussed.
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