A comparison of critical distance methods for fracture prediction

Taylor, David; Kasiri, Saeid

doi:10.1016/j.ijmecsci.2008.02.005

Cited by 21 publications

(7 citation statements)

References 23 publications

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“…However, the TCD is already used in many situations where similar problems occur, for example to predict fracture from cracks in metals (Taylor 2005), where the crack-tip stresses are affected by plasticity, and in quasi-brittle materials such as concrete and bone (Kasiri 2008), which have zones of microdamage near crack tips. More discussion of the applicability and limitations of the TCD can be found in our previous publications (Wiersma and Taylor 2004;Kasiri et al 2007;Kasiri 2008;Taylor and Kasiri 2008). It was shown here that optimum predictions occurred with a critical distance of L ¼ 90 mm, which was the same in two slightly different NiTi materials.…”

Section: Discussionsupporting

confidence: 61%

Can the theory of critical distances predict the failure of shape memory alloys?

Kasiri

Kelly

Taylor

2011

Computer Methods in Biomechanics and Biomedical Engineering

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Components made from shape memory alloys (SMAs) such as nitinol often fail from stress concentrations and defects such as notches and cracks. It is shown here for the first time that these failures can be predicted using the theory of critical distances (TCDs), a method which has previously been used to study fracture and fatigue in other materials. The TCD uses the stress at a certain distance ahead of the notch to predict the failure of the material due to the stress concentration. The critical distance is believed to be a material property which is related to the microstructure of the material. The TCD is simply applied to a linear model of the material without the need to model the complication of its non-linear behaviour. The non-linear behaviour of the material at fracture is represented in the critical stress. The effect of notches and short cracks on the fracture of SMA NiTi was studied by analysing experimental data from the literature. Using a finite element model with elastic material behaviour, it is shown that the TCD can predict the effect of crack length and notch geometry on the critical stress and stress intensity for fracture, with prediction errors of less than 5%. The value of the critical distance obtained for this material was L = 90 μm; this may be related to its grain size. The effects of short cracks on stress intensity were studied. It was shown that the same value of the critical distance (L = 90 μm) could estimate the experimental data for both notches and short cracks.

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Section: Discussionsupporting

confidence: 61%

Can the theory of critical distances predict the failure of shape memory alloys?

Kasiri

Kelly

Taylor

2011

Computer Methods in Biomechanics and Biomedical Engineering

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“…The material properties (bone stiffness and fatigue strength) are typical values taken from the literature; in practice these vary from person to person and from bone to bone. Isotropic elasticity was assumed; this will alter somewhat the local stress distributions around the hole but previous work suggests that it does not have a strong effect on the resulting predictions (Taylor and Kasiri 2008a). Perfect bonding was assumed between the graft material and the bone.…”

Section: Discussionmentioning

confidence: 99%

“…The crucial element in this approach is the definition of a material-dependant length constant known as the critical distance, L. Roughly speaking, this quantifies the scale at which toughening mechanisms operate, and therefore defines the size of the critical volume, close to the defect, in which fracture processes such as crack initiation and propagation occur. There are various ways in which this can be used to predict failure: a detailed description and comparison of these methods has recently been published (Taylor and Kasiri 2008a). The simplest method, and the one which has been shown to give the most accurate predictions in the case of longterm fatigue failure, is known as the point method (PM).…”

Section: The Theory Of Critical Distancesmentioning

confidence: 99%

Predicting the structural integrity of bone defects repaired using bone graft materials

Brazel

Taylor

2009

Computer Methods in Biomechanics and Biomedical Engineering

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Bone defects create stress concentrations which can cause fracture under impact or cyclic loading. Defects are often repaired by filling them with a bone graft material; this will reduce the stress concentration, but not completely, because these materials have lower stiffness than bone. The fracture risk decreases over time as the graft material is replaced by living bone. Many new bone graft materials are being developed, using tissue engineering and other techniques, but currently there is no rational way to compare these materials and predict their effectiveness in repairing a given defect. This paper describes, for the first time, a theoretical model which can be used to predict failure by brittle fracture or fatigue, initiating at the defect. Preliminary results are presented, concentrating on the prediction of stress fracture during the crucial post-operative period. It is shown that the likelihood of fracture is strongly influenced by the shape of the defect as well as its size, and also by the level of post-operative exercise. The most important finding is that bone graft materials can be successful in preventing fracture even when their mechanical properties are greatly inferior to those of bone. Future uses of this technique include pre-clinical assessment of bone replacement materials and pre-operative planning in orthopaedic surgery.

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“…At one level, the cracks, which Taylor and Kasiri (2008) call 'imaginary cracks', clearly seem to be fictions in the same sense as the crack extension and compression stress in the strip yield model: they are often known not to exist, but are introduced to take the place of other types of flaws, which are governed by more difficult to model mechanisms. If we look at imaginary cracks more closely, however, their fictitiousness becomes less apparent.…”

Section: Real and Imaginary Cracksmentioning

confidence: 99%

Finding truth in fictions: identifying non-fictions in imaginary cracks

Purves

2012

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A comparison of critical distance methods for fracture prediction

Cited by 21 publications

References 23 publications

Can the theory of critical distances predict the failure of shape memory alloys?

Can the theory of critical distances predict the failure of shape memory alloys?

Predicting the structural integrity of bone defects repaired using bone graft materials

Finding truth in fictions: identifying non-fictions in imaginary cracks

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