scholarly journals Effects of Initial Crack Length and Specimen Thickness on Fracture Toughness of Compact Bone.

1999 ◽  
Vol 42 (3) ◽  
pp. 532-538 ◽  
Author(s):  
Yuji TANABE ◽  
William BONFIELD
Keyword(s):  
Fracture Toughness ◽  
Crack Length ◽  
Compact Bone ◽  
Initial Crack ◽  
Specimen Thickness ◽  
Initial Crack Length

Measurement of the fracture toughness of CVD-grown ZnS using a miniaturized disk-bend test

1991 ◽  
Vol 6 (9) ◽  
pp. 1950-1957 ◽  
Author(s):  
Jimin Zhang ◽  
Alan J. Ardell
Keyword(s):  
Fracture Toughness ◽  
Crack Length ◽  
Graphical Method ◽  
Chemical Vapor ◽  
Initial Crack ◽  
Initial Crack Length ◽  
Small Disk ◽  
Apparent Fracture Toughness ◽  
Bending Mode ◽  
Good Agreement

Novel apparatus and methodology have been developed for measuring the fracture toughness of ceramics using small disk-shaped samples 3 mm in diameter. The method involves the Vickers indentation of specimens ranging in thickness from 300 to 700 μm, and testing them in a ring-on-ring bending mode. Experiments on ZnS grown by chemical vapor deposition (CVD) have been used to evaluate the technique. The apparent fracture toughness of this material increases with crack length (R-curve behavior). This behavior is analyzed using established equations in conjunction with a new graphical method that obviates the need for measuring the apparent toughness of samples containing very large cracks. The fracture toughness at “infinite” crack length, 0.86 ± 0.08 MPa · m1/2, is in very good agreement with the values obtained by conventional methods. The effect of sample size on the accuracy of the results is thoroughly discussed. The thickness, t, of the sample should exceed by a factor of ten the initial crack length produced by the indentation. Also, since samples are tested at various indentation loads, P, the ratio of their thicknesses should be chosen to satisfy the condition t ∝ P2/3. The importance of several parameters in the design of the apparatus is also discussed.

Initial crack length on the interlaminar fracture of woven carbon/epoxy laminates

2015 ◽  
Vol 16 (4) ◽  
pp. 894-901 ◽  
Author(s):  
P. N. B. Reis ◽  
J. A. M. Ferreira ◽  
F. V. Antunes ◽  
J. D. M. Costa
Keyword(s):  
Crack Length ◽  
Initial Crack ◽  
Initial Crack Length ◽  
Interlaminar Fracture

A finite element model on effects of impact load and cavitation on fatigue crack propagation in mechanical bileaflet aortic heart valve

2008 ◽  
Vol 222 (7) ◽  
pp. 1115-1125 ◽  
Author(s):  
H Mohammadi ◽  
R J Klassen ◽  
W-K Wan
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Crack Length ◽  
Heart Valve ◽  
Heart Valves ◽  
Element Model ◽  
Initial Crack ◽  
Initial Crack Length ◽  
Element Approach ◽  
The Impact

Pyrolytic carbon mechanical heart valves (MHVs) are widely used to replace dysfunctional and failed heart valves. As the human heart beats around 40 million times per year, fatigue is the prime mechanism of mechanical failure. In this study, a finite element approach is implemented to develop a model for fatigue analysis of MHVs due to the impact force between the leaflet and the stent and cavitation in the aortic position. A two-step method to predict crack propagation in the leaflets of MHVs has been developed. Stress intensity factors (SIFs) are computed at a small initiated crack located on the leaflet edge (the worst case) using the boundary element method (BEM). Static analysis of the crack is performed to analyse the stress distribution around the front crack zone when the crack is opened; this is followed by a dynamic crack analysis to consider crack propagation using the finite element approach. Two factors are taken into account in the calculation of the SIFs: first, the effect of microjet formation due to cavitation in the vicinity of leaflets, resulting in water hammer pressure; second, the effect of the impact force between the leaflet and the stent of the MHVs, both in the closing phase. The critical initial crack length, the SIFs, the water hammer pressure, and the maximum jet velocity due to cavitation have been calculated. With an initial crack length of 35 μm, the fatigue life of the heart valve is greater than 60 years (i.e. about 2.2×109 cycles) and, with an initial crack length of 170 μm, the fatigue life of the heart valve would be around 2.5 years (i.e. about 9.1×107 cycles). For an initial crack length greater than 170 μm, there is catastrophic failure and fatigue cracking no longer occurs. A finite element model of fatigue analysis using Patran command language (PCL custom code) in MSC software can be used to evaluate the useful lifespan of MHVs. Similar methodologies can be extended to other medical devices under cyclic loads.

Tearing behavior of membrane coated fabrics based on the DIC method under the effect of initial crack length

2019 ◽  
Vol 61 (1) ◽  
pp. 41-48
Author(s):  
Zhou-Lian Zheng ◽  
Yuan Tian ◽  
Dong Li ◽  
Chang-Jiang Liu
Keyword(s):  
Crack Length ◽  
Initial Crack ◽  
Initial Crack Length ◽  
Coated Fabrics

Predicting the Initial Crack Length in a Solid Propellant

2001 ◽  
Author(s):  
C. T. Liu ◽  
Y. G. Kwon ◽  
T. L. Hendrickson
Keyword(s):  
Crack Length ◽  
Solid Propellant ◽  
Initial Crack ◽  
Initial Crack Length
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