• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.6
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• pp.775-782
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• 2013

In this study, as a series of studies aimed at investigating the spatial randomness of fatigue crack growth for friction stir welded (FSWed) 7075-T651 aluminum alloy joints, the fatigue crack growth behavior of FSWed 7075-T651 aluminum alloy joints was investigated for LT orientation specimens. Fatigue crack growth tests were conducted under constant stress intensity factor range (SIFR) control for 5 specimens of the FSWed 7075-T651 aluminum alloy, including base metal (BM), heat affected zone (HAZ), and weld metal (WM) specimens. The mean fatigue crack growth rate of WM specimens was found to be the highest, whereas that of HAZ and WM specimens was the lowest. Furthermore, the variability of fatigue crack growth rate was found to be the highest in WM specimens and lowest in BM specimens.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1317-1323
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• 2014

The aim of this paper is to investigate the effects of crack orientation on fatigue crack growth behavior in friction stir welded (FSWed) Al 7075-T651. Fatigue crack growth testing was conducted on compact tension (CT) specimens machined from the friction stir welds and the base metal under constant stress intensity factor range control. Tests were performed with the crack propagating nominally perpendicular to the weld line (termed the TL specimen) and the crack propagating in a parallel direction of the weld line (termed the LT specimen), and with three different constant stress intensity factor ranges. Both these specimen orientations were found to have a considerable effect on the fatigue crack growth behavior. Paris's law was adopted for the analysis of experimental results; the exponent m of the WM-LT specimen was determined to be 3.56, which was the largest value in this experimental conditions.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.67-75
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• 2000

The numerical simulation of Brazilian fracture toughness test is carried out using PFC code and the influence parameters are analyzed such as shape of loading plane, size of Brazilian disc and unit panicle of model, loading angle and loading rate. The flattened Brazilian disc is adopted for applying uniform load. The range of loading angle(2$\alpha$) necessary to induce the tensile crack at disc center and to obtain the load-displacement curve giving the critical load for the stable crack propagation is shown as 20$^{\circ}$~40$^{\circ}$. In condition that the loading angle is 20$^{\circ}$, the mode-I fracture toughness is evaluated almost constant in the range of particle size less than I mm and loading rate less than 0.01 mm/s. This range of influence parameters seems appropriate condition for the tensile crack initiation at disc center and the control of stable crack propagation, which can give the reliance in evaluation of fracture toughness by Brazilian test.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.320-328
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• 2000

The numerical simulation of Brazilian fracture toughness test is carried out using PFC code and the influence parameters are analyzed such as shape of loading plane, size of Brazilian disc and unit particle of model, loading angle and loading rate. The flattened Brazilian disc is adopted for applying uniform load. The range of loading angle(2$\alpha$) necessary to induce the tensile crack at disc center and to obtain the load-displacement curve giving the critical load for the stable crack propagation is shown as 20°∼40°. In condition that the loading angle is 20°, the mode-I fracture toughness is evaluated almost constant in the range of particle size less than 1 mm and loading rate less than 0.01㎜/s. This range of influence parameters seems appropriate condition for the tensile crack initiation at disc center and the control of stable crack propagation, which can give the reliance in evaluation of fracture toughness by Brazilian test.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1109-1116
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• 2013

This study aims to investigate the spatial randomness of fatigue crack growth rate for the friction stir welded (FSWed) 7075-T651 aluminum alloy joints. Our previous fatigue crack growth test data are adopted in this investigation. To clearly understand the spatial randomness of fatigue crack growth rate, fatigue crack growth tests were conducted under constant stress intensity factor range (SIFR) control testing. The experimental data were analyzed for two different materials-base metal (BM) and weld metal (WM)-to investigate the effects of spatial randomness of fatigue crack growth rate and material properties, the friction stir welded (FSWed) 7075-T651 aluminum alloy joints, namely weld metal (WM) and base metal (BM). The results showed that the variability, as evaluated by Weibull statistical analysis, of the WM is higher than that of the BM.