1,721,004 research outputs found
A novel Finite Fracture Mechanics approach to assess the lifetime of notched components
Full text linkA generalized Paris' law for fatigue crack growth
No full textAn extension of the celebrated Paris law for crack propagation is given to take into account some of the deviations from the power-law regime in a simple manner using the Wohler SN curve of the material, suggesting a more general "unified law". In particular, using recent proposals by the first author, the stress intensity factor K(a) is replaced with a suitable mean over a material/structural parameter length scale Delta a, the "fracture quantum". In practice, for a Griffith crack, this is seen to correspond to increasing the effective crack length of Delta a, similarly to the Dugdale strip-yield models. However, instead of including explicitly information on cyclic plastic yield, short-crack behavior, crack closure, and all other detailed information needed to eventually explain the SN curve of the material, we include directly the SN curve constants as material property. The idea comes as a natural extension of the recent successful proposals by the first author to the static failure and to the infinite life envelopes. Here, we suggest a dependence of this fracture "quantum" on the applied stress range level such that the correct convergence towards the Wohler-like regime is obtained. Hence, the final law includes both Wohler's and Paris' material constants, and can be seen as either a generalized Wohler's SN curve law in the presence of a crack or a generalized Paris' law for cracks of any size. (c) 2006 Elsevier Ltd. All rights reserved
Comparison between two nonlocal criteria: A case study on pressurized holes
Full text linkTwo nonlocal approaches are applied to the borehole geometry, i.e. a circular hole in an infinite elastic medium subjected to internal pressure. The former approach lays in the framework of Gradient Elasticity (GE), which results nonlocal in the strict sense, being based on a nonlocal constitutive relationship. Changing the stress field as the geometry (i.e., the radius of the hole) varies, the related stress concentration factor can be thought as the critical failure parameter. The latter approach is the Finite Fracture Mechanics (FFM), well-consolidated in the framework of brittle fracture. Whereas the model belongs to classical linear elasticity, it reveals nonlocal in a loose sense: the failure condition is no more punctual, but achieved when two average requirements on the stress and the energy ahead of the notch tip are simultaneously fulfilled. Τhe two approaches, although different, present some similarities, both involving a characteristic length. It will be shown that the GE and FFM predictions are in excellent agreement when the two lengths are properly defined
Non-local criteria for the borehole problem: Gradient Elasticity versus Finite Fracture Mechanics
Full text linkTwo nonlocal approaches are applied to the borehole geometry, herein simply modelled as a circular hole in an infinite elastic medium, subjected to remote biaxial loading and/or internal pressure. The former approach lies within the framework of Gradient Elasticity (GE). Its characteristic is nonlocal in the elastic material behaviour and local in the failure criterion, hence simply related to the stress concentration factor. The latter approach is the Finite Fracture Mechanics (FFM), a well-consolidated model within the framework of brittle fracture. Its characteristic is local in the elastic material behaviour and non-local in the fracture criterion, since crack onset occurs when two (stress and energy) conditions in front of the stress concentration point are simultaneously met. Although the two approaches have a completely different origin, they present some similarities, both involving a characteristic length. Notably, they lead to almost identical critical load predictions as far as the two internal lengths are properly related. A comparison with experimental data available in the literature is also provided
Cohesive Crack Models and Finite Fracture Mechanics analytical solutions for FRP-concrete single-lap shear test: An overview
Full text linkIn the present paper we review and compare several analytical models describing the single-lap shear test, which is the most common test to determine the bonding behaviour between a strengthening FRP plates and the concrete substrate. The models are one-dimensional and formulated under the assumption that debonding occurs as a pure mode II cracking process throughout a zero-thickness interface between the FRP strip and the brittle substrate. As such, they are all amenable of an analytical treatment. The FRP-concrete interface is described by at most three parameters among the interfacial fracture energy, the tensile strength and the elastic stiffness. Particularly, we compare the effective bond length estimates provided by different models and compare them with the ones present in Design Codes. Finally, a comparison with experimental data sets available in the Scientific Literature is also given
Finite fracture mechanics and cohesive crack model: Weight functions vs. cohesive laws
Full text linkThe present work represents the prosecution of a previous paper [Short cracks and V-notches: Finite Frac- ture Mechanics vs. Cohesive Crack Model (2016). P. Cornetti, A. Sapora, A. Carpinteri. Engineering Fracture Mechanics 168:2–12] aiming to corroborate the use of Finite Fracture Mechanics by showing that its fail- ure load estimates are very close to the ones provided by the well-established Cohesive Crack Model. While the above paper focused only on the Dugdale cohesive law and the original Finite Fracture Me- chanics approach, here we consider generic cohesive laws of power law type and propose an extension of Finite Fracture Mechanics based on stress weight functions. We argue that excellent agreement be- tween the models is found provided proper correspondence rules between the shape of the cohesive laws and of the weight functions are given. As a test bench for this conjecture, we choose the Griffith crack geometry, where we are able to achieve the solutions in a semi-analytical way for both the models. Finally, we show that similar results can be obtained also by varying the domain of the weight function while keeping fixed its shape
Mode I fatigue limit of notched structures: A deeper insight into Finite Fracture Mechanics
Full text linkIn the present contribution, the coupled stress-energy criterion of Finite Fracture Mechanics (FFM) is applied to assess the fatigue limit of structures weakened by sharp V- and U-notches and subjected to mode I loading conditions. The FFM is a critical-distance-based approach whose implementation requires the knowledge of two material properties, namely the plain material fatigue limit and the threshold value of the stress intensity factor (SIF) range for the fatigue crack growth of long cracks. However, the FFM critical distance is a structural parameter, being a function not only of the material but also of the geometry of the notched component. Experimental notch fatigue results taken from the literature and referred to a variety of materials and geometrical configurations are compared with FFM theoretical estimations, obtained through simple semi-analytical relationships. The case of semi-circular edge notches is also dealt with
Finite Fracture Mechanics extension to dynamic loading scenarios
Full text linkThe coupled criterion of Finite Fracture Mechanics (FFM) has already been successfully applied to assess the brittle failure initiation in cracked and notched structures subjected to quasi-static loading conditions. The FFM originality lies in addressing failure onset through the simultaneous fulfilment of a stress requirement and the energy balance, both computed over a finite distance ahead of the stress raiser. Accordingly, this length results to be a structural parameter, thus able to interact with the geometry under investigation. This work aims at extending the FFM failure criterion to dynamic loadings. To this end, the general requisites of a proper dynamic failure criterion are first shortlisted. The novel Dynamic extension of FFM (DFFM) is then put forward assuming the existence of a material time interval that is related to the coalescence period of microcracks upon macroscopic failure. On this basis, the DFFM model is investigated in case a one-to-one relation between the external solicitation and both the dynamic stress field and energy release rate holds true. Under such a condition, the DFFM is also validated against suitable experimental data on rock materials from the literature and proven to properly catch the increase of the failure load as the loading rate rises, thus proving to be a novel technique suitable for modelling the rate dependence of failure initiation in brittle and quasi-brittle materials
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