scholarly journals Alternative accelerated and short-term methods for evaluating slow crack growth in polyethylene resins with high crack resistance

2017 ◽  
Vol 62 ◽  
pp. 366-372 ◽  
Author(s):  
Nuria Robledo ◽  
Carlos Domínguez ◽  
Rafael A. García-Muñoz
Keyword(s):  
Crack Resistance ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Short Term ◽  
High Crack ◽  
High Crack Resistance

Increase of crack resistance during slow crack growth in Al2O3 bend specimens

1983 ◽  
Vol 18 (1) ◽  
pp. 265-270 ◽  
Author(s):  
R. Steinbrech ◽  
R. Khehans ◽  
W. Schaarw�chter
Keyword(s):  
Crack Resistance ◽  
Crack Growth ◽  
Slow Crack Growth

Short-Term and Long-Term Mechanical Testing to Evaluate the Effect of Flaws in Butt Fusion Joints in Polyethylene Pipes

2016 ◽  
Author(s):  
Mike Troughton ◽  
Amir Khamsehnezhad
Keyword(s):  
Crack Growth ◽  
Slow Crack Growth ◽  
Short Term ◽  
Acceptance Criteria ◽  
Linear Elastic ◽  
Lack Of Fusion ◽  
Particulate Contamination ◽  
Critical Flaw ◽  
Elastic Fracture

The use of non-destructive examination (NDE) for assessing the quality of butt fusion joints in polyethylene (PE) pipes has been included in the draft Mandatory Appendix XXVI to Section III of the ASME Boiler and Pressure Vessel Code (Rules for construction of Class 3 buried polyethylene pressure piping). However, currently, there are no acceptance criteria for flaws in butt fusion joints in PE pipes. There is an ASME Task Group on flaw evaluation for PE pipe, which is developing a code case using linear elastic fracture mechanics (LEFM) to determine critical flaw sizes. However, the initial experimental crack growth data generated suggests that linear elastic fracture mechanics is not able to adequately describe slow crack growth in PE materials. In addition, this work is only considering planar lack of fusion flaws in the joint; it is not considering other critical flaw types that can occur in butt fusion joints, such as particulate contamination and cold fusion. TWI has developed procedures using mechanical testing to develop flaw acceptance criteria for butt fusion joints in PE pipes. This is based on inserting lack of fusion flaws of known size and particulate contamination flaws of known concentrations into butt fusion joints and determining the effect of these flaws on both the short-term and long-term integrity of the joints. An important aspect of this work is to determine which of the wide array of mechanical tests available for assessing the integrity of butt fusion joints in PE pipes are the most discriminating. This paper describes the procedures developed for inserting simulated flaws into butt fusion joints in PE pipes, the experimental work to compare the results from different standard short-term and long-term tests on flawed and unflawed joints and the procedures developed to determine flaw acceptance criteria. Results have shown that the most discriminating short-term test for butt fusion joints in PE pipes is a tensile test using a waisted specimen, such as those defined in EN 12814-2, EN 12814-7 and ISO 13953, and the most discriminating property is the energy to break the specimen. The most appropriate long-term test for butt fusion joints in PE pipes is the whole pipe tensile creep rupture test, as defined in EN 12814-3; this is the only long-term whole pipe test that consistently generates slow crack growth in the fused joint, even if it contains no flaws.

scholarly journals Structural origin of high crack resistance in sodium aluminoborate glasses

2017 ◽  
Vol 460 ◽  
pp. 54-65 ◽  
Author(s):  
Kacper Januchta ◽  
Randall E. Youngman ◽  
Ashutosh Goel ◽  
Mathieu Bauchy ◽  
Sylwester J. Rzoska ◽  
...  
Keyword(s):  
Crack Resistance ◽  
High Crack ◽  
High Crack Resistance

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.

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