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.

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.

scholarly journals Related Rule Study of Subcritical Crack Growth and Threshold Values in Transversely Isotropic Slates

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Gang Ma ◽  
Jiangteng Li ◽  
Huiwen Wang
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Transversely Isotropic ◽  
Relaxation Method ◽  
Threshold Values ◽  
Load Relaxation ◽  
Bedding Angle ◽  
Constant Displacement ◽  
Double Torsion

Elastic parameters and the subcritical crack growth of different bedding angle slate specimens were studied using uniaxial compression testing and the double torsion constant displacement load relaxation method using SANS and MTS Insight machines. To study the relations of the mode-I stress intensity factor K I versus the subcritical crack growth velocity V , the fracture toughness K I C , the stagnation speed, and the threshold values, the double torsion constant displacement load relaxation method was carried out. The related rules between the bedding angles (β) and the uniaxial compressive strength, fracture toughness, and threshold values were investigated. Experimental results show that the uniaxial compression, the fracture toughness, and the threshold value curves move to the bottom then increase with the increase of the β angle. In addition, its fracture toughness is minimal when the β angle of the slates is 45°, and crack initiation and crack propagation are generated under load, which can lead to the failure of the slate. lg K I - lg V relations of transversely isotropic slates measured by this method are in accordance with linear rules, which is in good agreement with the Charles theory. The range of K 0 / K I C for these different bedding angle slates is from 0.511 to 0.789. The test results would provide the basis for studying seepage and time-dependency of rock engineering stability.

scholarly journals Time-dependent behavior of subcritical crack growth for rock plate: Experimental and numerical study

2018 ◽  
Vol 14 (11) ◽  
pp. 155014771881201 ◽  
Author(s):  
Haiping Yuan ◽  
Feng Wang ◽  
Yan Liu ◽  
Hanbing Bian ◽  
Wen Chen ◽  
...  
Keyword(s):  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Torsion Test ◽  
Time Dependent ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Crack Growth Behavior ◽  
Dependent Behavior ◽  
Double Torsion

Time-dependent behavior of subcritical crack growth is one of the main characteristics in rocks. The double-torsion test is commonly used to study the slow crack growth behavior of brittle and quasi-brittle materials. However, double-torsion specimen is difficult to processing, the process of the laboratory test is irreversible, and the current numerical simulation is difficult to consider the time-dependent behavior, and so on. In view of all above problems, an idealized particle model was built, and the crack was identified in this article, based on the theory of particle flow. The numerical model was built using Particle Flow Code in 3 Dimensions, and the macromechanical and micromechanical parameters of the model were calibrated. The process of the macroscopic crack propagation and its evolution were analyzed. The intrinsic relations with the load, the displacement, and the time were established. The results show that the Particle Flow Code in 3 Dimensions can reproduce the time-dependent behavior of subcritical crack growth in double-torsion test. And, the peak and the law of the curves are in good agreement with the laboratory test results. Therefore, the Particle Flow Code in 3 Dimensions numerical simulation can be used as a new effective method to reveal the slow crack growth behavior, to get the relevant parameters such as V, KI, and KIC, and to build the relationship between V and KI. The results of this article will have some reference value for the simulation and application of double-torsion test.

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