Examination of the fracture surface by the channeling pattern method in the scanning electron microscope

1986 ◽  
Vol 18 (10) ◽  
pp. 1415-1418 ◽  
Author(s):  
E. A. Voitekhova ◽  
M. S. Konstantinova
Keyword(s):  
Electron Microscope ◽  
Fracture Surface ◽  
Scanning Electron Microscope ◽  
Scanning Electron

Stress Corrosion Cracking in Steam Turbine: Two Case Studies

2017 ◽  
Author(s):  
Vamadevan Gowreesan ◽  
Kirill Grebinnyk
Keyword(s):  
Electron Microscope ◽  
Fracture Surface ◽  
Scanning Electron Microscope ◽  
Stress Corrosion ◽  
Steam Turbine ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Steam Turbines ◽  
Root Section ◽  
Scanning Electron

Stress corrosion cracking in steam turbines had been an old problem though some modern steam turbines have almost eliminated this problem by several methods. The methods include design modification to reduce the stress levels below the threshold stress level for stress corrosion cracking, inducing compressive stress by different means and using pure steam [1, 2]. Some of the older steam turbine discs are prone to stress corrosion cracking. Two cases where such machines experienced stress corrosion cracking in their discs are discussed here. The row 6 disc of an integral steam turbine rotor developed cracks in the root sections. Some of the cracks were mechanically opened for the evaluation. Evaluation of the fracture surfaces with a scanning electron microscope showed evidence of intergranular mode of cracking. Optical microscopy of a cracked root confirmed intergranular mode of cracking. In addition, it showed branching of cracks. Based on these findings, it was concluded that stress corrosion cracking was the reason for the cracks. In addition, finite element analysis was used to calculate the stress distribution in the blade root of the disc. The location of the maximum equivalent stress coincided perfectly with that of the actual crack location in the disc root section. Unfortunately, redesign of the root geometry to minimize the local stress concentration is very difficult due to the size limitation of the blade roots. Small amount of chlorine was identified on the fracture surface and the chlorine could have come from the steam used. The customer was advised to analyze their steam quality and to improve the quality of the steam if needed. The cracked portion was removed from the disc and weld-build up to machine new root sections with the same type of roots. Root section of the row 6 disc of another steam turbine developed failure. This disc had radial entry type blades. Portion of the disc root and some blades were liberated from the disc due to the cracking. The fracture surface had heavy oxide layer on it. Evaluation of the fracture surface with a scanning electron microscope revealed intergranular mode of failure. Energy dispersive spectroscopy analysis of the fracture surface found oxides on the fracture surface. Optical microscopy showed secondary cracking and branched cracking. All these evidences confirmed that the failure occurred due to stress corrosion cracking. In addition, it was suspected that forging was not heat treated properly due to measured lower toughness and different microstructure. The lower toughness was believed to be a result of improper heat treatment rather than that of embrittlement. Methods to mitigate the risk of stress corrosion cracking were proposed.

scholarly journals Fractal Dimension of Fracture Surface in Rock Material after High Temperature

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Z. Z. Zhang
Keyword(s):  
Fractal Dimension ◽  
Electron Microscope ◽  
High Temperature ◽  
Fracture Surface ◽  
Scanning Electron Microscope ◽  
Fractal Dimensions ◽  
Threshold Value ◽  
Fracture Surfaces ◽  
Increasing Temperature ◽  
Scanning Electron

Experiments on granite specimens after different high temperature under uniaxial compression were conducted and the fracture surfaces were observed by scanning electron microscope (SEM). The fractal dimensions of the fracture surfaces with increasing temperature were calculated, respectively. The fractal dimension of fracture surface is between 1.44 and 1.63. Its value approximately goes up exponentially with the increase of temperature. There is a quadratic polynomial relationship between the rockburst tendency and fractal dimension of fracture surface; namely, a fractal dimension threshold can be obtained. Below the threshold value, a positive correlativity shows between rockburst tendency and fractal dimension; when the fractal dimension is greater than the threshold value, it shows an inverse correlativity.

Observation of Fracture Surface of Crushed Particle by Scanning Electron Microscope

1970 ◽  
Vol 34 (9) ◽  
pp. 1006-1006,a1
Author(s):  
Saburo Yashima ◽  
Yoshiteru Kanda ◽  
Shoichi Morohashi
Keyword(s):  
Electron Microscope ◽  
Fracture Surface ◽  
Scanning Electron Microscope ◽  
Scanning Electron

Fractographic Analysis of Fatigue Failures

1975 ◽  
Vol 97 (3) ◽  
pp. 194-205 ◽  
Author(s):  
D. McIntyre
Keyword(s):  
Electron Microscope ◽  
Stress State ◽  
Environmental Factors ◽  
Fracture Surface ◽  
Scanning Electron Microscope ◽  
Crack Growth ◽  
Basic Research ◽  
Growth Characteristics ◽  
Fatigue Failures ◽  
Scanning Electron

Although fractography is usually applied to basic research, it can also be used in studies of machine components which have failed in service or in testing. This paper discusses fractographic methods which can be used to obtain information about the stress state, environmental factors, initiating cause, and crack growth characteristics of fatigue failures. The macroscopic and microscopic fracture surface features of fatigue failures are illustrated with photomacrographs and scanning electron microscope (SEM) fractographs, and the use of SEM fractography in crack growth studies is described.

The Effect of Different Colloidal Silica Binders on Strengths of Corundum-Mullite Castables

2015 ◽  
Vol 1094 ◽  
pp. 127-130
Author(s):  
Wen Jie Yuan ◽  
Qing You Zhu ◽  
Cheng Ji Deng ◽  
Hong Xi Zhu
Keyword(s):  
Electron Microscope ◽  
Fracture Surface ◽  
Scanning Electron Microscope ◽  
Size Distribution ◽  
Colloidal Silica ◽  
Modulus Of Rupture ◽  
Fracture Surfaces ◽  
The Difference ◽  
Slit Island Method ◽  
Scanning Electron

Three kinds of colloidal silica (GS-30, AM and HS-30) were applied as binders to corundum-mullite castables. The apparent porosity and cold modulus of rupture for samples fired at 800 oC and 1000 oC were compared. The fractography of colloidal silica bonded corundum-mullite castables was carried out by slit island method. The microstructure of fracture surface was characterized by scanning electron microscope. The results showed that castables by using imported colloidal silica (AM and HS-30) presented higher strength than those with domestic (GS-30), which was determined by the activity of silica and modified ion. The difference of the size distribution of the salient on the fracture surfaces indicated that the strength of castables was dependent on the bonding among the components.

A Comparison of TEM and SEM Fractography

1970 ◽  
Vol 28 ◽  
pp. 398-399
Author(s):  
James L. Hubbard
Keyword(s):  
Electron Microscope ◽  
Fracture Surface ◽  
Scanning Electron Microscope ◽  
Stress Corrosion ◽  
Surface Features ◽  
Fracture Surfaces ◽  
Mental Picture ◽  
Scanning Electron

For many years now, metallurgists have been using replica techniques for electron micrographic studies of the fracture surfaces of metals. The general features which are indicative of a certain mode of fracture, such as fatigue, overstress, or stress corrosion, have become quite familar in a wide variety of alloys. Although replicas are subject to many artifacts these features are usually recognized as such and disregarded in the analysis of the surface. Also since negative replicas are generally used one must reverse his perspective in order to obtain a true mental picture of the fracture surface.With the scanning electron microscope, micrographs of such samples can now be taken directly with no surface replication or preparation involved. The scanning micrographs, while limited in resolution, present a picture not only true to the surface but with a stereo perspective with which one can relate the surface features to reality.

Prediction of Fracture Toughness of Magnesia-Carbon Bricks Based on Fractography

2018 ◽  
Vol 768 ◽  
pp. 3-7
Author(s):  
Hai Tang ◽  
Guang Wei Guo ◽  
Qing You Zhu ◽  
Wen Jie Yuan
Keyword(s):  
Fracture Toughness ◽  
Electron Microscope ◽  
High Temperature ◽  
Fracture Surface ◽  
Scanning Electron Microscope ◽  
Carbon Content ◽  
Fractal Analysis ◽  
Fracture Mechanism ◽  
Temperature Performance ◽  
Scanning Electron

The introduction of carbon greatly improves the high temperature performance of magnesia bricks. In order to explore the influence of carbon content on the fracture toughness and the fracture mechanism of magnesia-carbon bricks, two different carbon content (10wt% and 14wt%) magnesia-carbon bricks were investigated in this work. The fracture toughness and microstructure were characterized by fractal analysis of fracture surface and scanning electron microscope respectively. The results indicated that the strength of magnesia-carbon bricks was strengthened with the carbon content increasing. It was demonstrated that magnesia-carbon bricks with the higher carbon content presented higher fracture toughness as a consequence of lower apparent porosity and compact bonding between matrix and magnesia aggregates.

Sign in / Sign up

Export Citation Format

Share Document