scholarly journals Analysis of Crack Initiation and Propagation process in Delayed Fracture by FRASTA (Fracture-surface Topography Analysis) Method

1997 ◽  
Vol 83 (8) ◽  
pp. 526-531 ◽  
Author(s):  
Shingo YAMASAKI ◽  
Toshihiko TAKAHASHI ◽  
Takao KOBAYASHI
Keyword(s):  
Fracture Surface ◽  
Crack Initiation ◽  
Surface Topography ◽  
Analysis Method ◽  
Crack Initiation And Propagation ◽  
Propagation Process ◽  
Delayed Fracture ◽  
Initiation And Propagation ◽  
Topography Analysis

Crack Initiation Process for Semi-Circular Notched Plate in Fatigue Test at Elevated Temperature

2008 ◽  
Author(s):  
Bopit Bubphachot ◽  
Osamu Watanabe ◽  
Nobuchika Kawasaki ◽  
Naoto Kasahara
Keyword(s):  
Elevated Temperature ◽  
Crack Initiation ◽  
Fatigue Test ◽  
Video Camera ◽  
Test Results ◽  
Structural Components ◽  
Crack Initiation And Propagation ◽  
Propagation Process ◽  
Initiation Process ◽  
Initiation And Propagation

Crack initiation and propagation process of fatigue test in semi-circular notched plates at elevated temperature were observed by the CCD video camera. Test specimens are made of SUS304 stainless steel, and temperature is kept to be 550°C, and geometry of semi-circular notched plate specimens are changed by diameter size of the circular hole. Photographs in all cycles were recorded to investigate crack initiation process in structural components having stress concentration and obtain number of cycle of crack initiation (Nc). The test results were compared with predictions by Stress Redistribution Locus (SRL) method and Neuber’s rule’s method.

Fatigue Crack Growth Behavior of Threaded Pipe Couplings

2011 ◽  
Author(s):  
Jeroen Van Wittenberghe ◽  
Patrick De Baets ◽  
Wim De Waele
Keyword(s):  
Fatigue Crack ◽  
Fracture Surface ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Behavior ◽  
Crack Opening ◽  
Bending Test ◽  
Crack Initiation And Propagation ◽  
Accurate Knowledge ◽  
Initiation And Propagation

Threaded couplings are used in various applications to connect steel pipes. To maintain a secure connection, such couplings are preloaded and during service additional dynamic loads can act on the connections. The coupling’s threads act as stress raisers, initiating fatigue cracks, which can cause the connection to fail in time. Accurate knowledge of the fatigue behavior, taking into account crack initiation and propagation is necessary to understand the fatigue mechanisms involved. In this study, the fatigue behavior of tapered couplings with NPT threads is studied. This is done by analyzing the results of an experimental four-point bending test. The fatigue crack propagation is monitored using an optical dynamic 3D displacement measurement device and LVDTs to measure the crack opening. At certain times during the test, the load ratio is changed to apply a number of beach marking cycles. This way a fine line is marked in the fracture surface. These marked crack shapes are used as input for a finite element model. The measured deflection and crack opening are compared to the results of the numerical simulations. Using this methodology a distinction is made between fatigue crack initiation and propagation. By analyzing the fracture surface it was observed that once the crack is initiated, it propagates over a wide segment of the pipe’s circumference and subsequently rapidly penetrates the wall of the pipe. The observed crack growth rates are confirmed by a fracture mechanics analysis. Since the appearing long shallow crack is difficult to detect at an early stage the importance is demonstrated of accurate knowledge of the fatigue behavior of threaded connections in order to define acceptable flaw sizes and inspection intervals.

Three Dimensional Fractography of Extruded Age-Hardened Al Alloys Subjected to Fatigue Tests

2018 ◽  
Vol 940 ◽  
pp. 89-93
Author(s):  
Yuzo Nakamura ◽  
Ryuichi Iwamoto ◽  
Yuta Kurigeno ◽  
Hiroki Kamibayashi ◽  
Kohji Kariya ◽  
...  
Keyword(s):  
Fracture Surface ◽  
Crack Initiation ◽  
Three Dimensional ◽  
Fatigue Tests ◽  
Al Alloys ◽  
Metal Fatigue ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation ◽  
The Difference ◽  
Insight Into

Observation of fracture surface in metal fatigue is one of the most significant procedures to get insight into the cause and mechanism of crack initiation and propagation. In the present study, age-hardened 2017-T4 and 7075-T6 Al alloys having the extrusion texture were fatigue tested in low and high humidities, and their fracture surfaces were examined using a three dimensional (3D) surface analyzer. In addition to the microscopic observations conducted, it is shown that these 3D analyses provide important information on the difference in crack propagation depending on the stress level and environment.

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