scholarly journals Subcritical Crack Growth in MnZn Ferrites

1997 ◽  
Vol 07 (C1) ◽  
pp. C1-263-C1-264
Author(s):  
M. Donners ◽  
L. Dortmans ◽  
G. de With ◽  
M. de Graaf
Keyword(s):  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Mnzn Ferrites

Modelling of Subcritical Crack Growth in MnZn Ferrites

1997 ◽  
Vol 132-136 ◽  
pp. 714-717 ◽  
Author(s):  
M. Donners ◽  
L. Dortmans ◽  
G. de With ◽  
M. de Graaf
Keyword(s):  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Mnzn Ferrites

Minima in the strength of MnZn ferrites

2001 ◽  
Vol 16 (12) ◽  
pp. 3575-3582 ◽  
Author(s):  
M. A. H. Donners ◽  
L. J. M. G. Dortmans ◽  
G. de With ◽  
M. J. M. de Graaf
Keyword(s):  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Dissociative Adsorption ◽  
Adsorption Model ◽  
Mnzn Ferrite ◽  
Adsorption Mechanisms ◽  
Hydroxyl Ion ◽  
Kinetic Effects ◽  
Reaction With Water ◽  
Mnzn Ferrites

Like many other oxides, MnZn ferrite shows a considerably decreased strength in a humid environment. Conventionally one explains this behavior by subcritical crack growth, i.e., a kinetic effect affecting the oxygen–metal bond breaking rate at the crack tip via a reaction with water. The dissociation of water in a proton and hydroxyl ion is considered as crucial. However, it appears that also other gases have a detrimental effect on the strength. In this paper the effect of H2O, H2S, NH3, NO, and CO on the strength of MnZn ferrite have been studied experimentally. For water a clear minimum in strength occurs at relative low partial pressure. For the other gases the data also indicate a minimum. An adsorption model taking into account the presence of competitive adsorption mechanisms, involving dissociative and nondissociative adsorption of the adsorbate and the (non)dissociative adsorption of the ever present N2, is presented. This model can explain the experimentally observed features well. Although kinetic effects induce subcritical crack growth in MnZn ferrites, it is concluded that adsorption is an important strength lowering effect for MnZn ferrite when exposed to active gases.

Adsorption and Kinetic Effects on Crack Growth in MnZn Ferrites

2000 ◽  
Vol 15 (6) ◽  
pp. 1377-1388 ◽  
Author(s):  
M. A. H. Donners ◽  
L. J. M. G. Dortmans ◽  
G. de With
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Loading Rate ◽  
Crack Growth Behavior ◽  
Mnzn Ferrite ◽  
Strength Behavior ◽  
Kinetic Effects ◽  
Mnzn Ferrites ◽  
Double Torsion

The variation of the fracture toughness of MnZn ferrite ceramics with varying loading rate and humidity was determined with the aid of the single edge notched beam (SENB) test. A strong decrease with increasing humidity and decreasing loading rate was observed. A model for subcritical crack growth incorporating kinetic and adsorption effects was formulated to analyze the data. The value of the adsorptioncontrolled fracture toughness was determined independently by double torsion experiments and agreed favorably with the values as determined from the SENB data using the model. The strength of the material was determined, and analysis showed a strength behavior similar to the fracture toughness behavior, as predicted by the model. The analysis presented can be used to assess the subcritical crack growth behavior using a limited number of SENB specimens.

scholarly journals Subcritical crack growth in MnZn ferrites with a bimodal defect distribution

1997 ◽  
Vol 17 (13) ◽  
pp. 1591-1596 ◽  
Author(s):  
M. Donners ◽  
L. Dortmans ◽  
G. de With ◽  
M. de Graaf
Keyword(s):  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Defect Distribution ◽  
Mnzn Ferrites

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

Subcritical Crack Growth and Long-Term Strength in Rock and High-Strength and Ultra Low-Permeability Concrete

2009 ◽  
Vol 58 (6) ◽  
pp. 525-532 ◽  
Author(s):  
Yoshitaka NARA ◽  
Masafumi TAKADA ◽  
Daisuke MORI ◽  
Hitoshi OWADA ◽  
Tetsuro YONEDA ◽  
...  
Keyword(s):  
Crack Growth ◽  
Subcritical Crack Growth ◽  
High Strength ◽  
Low Permeability ◽  
Term Strength

Subcritical crack growth and in vitro lifetime prediction of resin composites with different filler distributions

2012 ◽  
Vol 28 (9) ◽  
pp. 985-995 ◽  
Author(s):  
Bárbara P. Ornaghi ◽  
Marcia M. Meier ◽  
Vinícius Rosa ◽  
Paulo F. Cesar ◽  
Ulrich Lohbauer ◽  
...  
Keyword(s):  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Lifetime Prediction ◽  
Resin Composites
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