Various micro-mechanical and micro-structural influences on fatigue crack growth resistance of the material have been investigated over the years. It is widely recognized that resistance to fatigue crack growth can be...Various micro-mechanical and micro-structural influences on fatigue crack growth resistance of the material have been investigated over the years. It is widely recognized that resistance to fatigue crack growth can be differentiated into ‘intrinsic＇ and ‘extrinsic＇. The separation of intrinsic and extrinsic crack growth resistance has constituted a major theme of fatigue research in the last 30 years, with the concept of crack closure or crack tip shielding being used to rationalize a wide range of micro-structural and mechanical influences on fatigue crack growth behavior. An accurately quantitative understanding of intrinsic and extrinsic effects on crack growth is essential to directed alloy design for improved fatigue resistance, and/or improved structural service life. This paper presents a compliance-based crack closure measurement method and a multi-mechanism based analytical model for the separation of intrinsic and extrinsic material fatigue resistance, with application in characterizing the fatigue performance of two high strength damage tolerant airframe AI alloys.展开更多
The nanoparticle transportation and Brownian diffusion in planar jet flow is simulated via large eddy simulation in this work. To thorough compare the Brownian diffusion with different particle size, we computed three...The nanoparticle transportation and Brownian diffusion in planar jet flow is simulated via large eddy simulation in this work. To thorough compare the Brownian diffusion with different particle size, we computed three particle diameter dp = 1 nm, 10 nm and 50 nm in one simulation process simultaneously. The numerical results showed that at the flow de- veloping stage, the particle mass concentration pattern develops as the flow vorticity develops. The distribution is nearly uniform at the lower reaches of the nozzle exit. When the jet flow is developing on, vortexes always carry the particle from upstream to downstream, from the central axis region to the outer mixing layer of jet. At the front of the jet flow, particles distribute more homogeneous for they have more residence time to diffuse from higher concentration region to the lower concentration region. The time averaged particle concentration distribution patterns are similar to Gaussian distribution form. The maximum concentration contributed by diffusion is present at the mixing layer near the nozzle exit. The farther away from the nozzle exit in the cross-stream direction, the smaller the concentration is. The maximum concentration contributed by diffusion is several orders smaller than that contributed by flow convection.展开更多
文摘Various micro-mechanical and micro-structural influences on fatigue crack growth resistance of the material have been investigated over the years. It is widely recognized that resistance to fatigue crack growth can be differentiated into ‘intrinsic＇ and ‘extrinsic＇. The separation of intrinsic and extrinsic crack growth resistance has constituted a major theme of fatigue research in the last 30 years, with the concept of crack closure or crack tip shielding being used to rationalize a wide range of micro-structural and mechanical influences on fatigue crack growth behavior. An accurately quantitative understanding of intrinsic and extrinsic effects on crack growth is essential to directed alloy design for improved fatigue resistance, and/or improved structural service life. This paper presents a compliance-based crack closure measurement method and a multi-mechanism based analytical model for the separation of intrinsic and extrinsic material fatigue resistance, with application in characterizing the fatigue performance of two high strength damage tolerant airframe AI alloys.
文摘The nanoparticle transportation and Brownian diffusion in planar jet flow is simulated via large eddy simulation in this work. To thorough compare the Brownian diffusion with different particle size, we computed three particle diameter dp = 1 nm, 10 nm and 50 nm in one simulation process simultaneously. The numerical results showed that at the flow de- veloping stage, the particle mass concentration pattern develops as the flow vorticity develops. The distribution is nearly uniform at the lower reaches of the nozzle exit. When the jet flow is developing on, vortexes always carry the particle from upstream to downstream, from the central axis region to the outer mixing layer of jet. At the front of the jet flow, particles distribute more homogeneous for they have more residence time to diffuse from higher concentration region to the lower concentration region. The time averaged particle concentration distribution patterns are similar to Gaussian distribution form. The maximum concentration contributed by diffusion is present at the mixing layer near the nozzle exit. The farther away from the nozzle exit in the cross-stream direction, the smaller the concentration is. The maximum concentration contributed by diffusion is several orders smaller than that contributed by flow convection.
