The hydrogen absorption characteristics and microstructural evolution of TC21 titanium alloy were investigated by kinetic model analysis, optical microscopy （OM） and X-ray diffraction （XRD）. The results show that ...The hydrogen absorption characteristics and microstructural evolution of TC21 titanium alloy were investigated by kinetic model analysis, optical microscopy （OM） and X-ray diffraction （XRD）. The results show that the hydrogen absorption reaction occurred during the hydrogen absorption process of TC21 titanium alloy can be divided into two different stages according to the hydrogen absorption kinetics. After hydrogenation, the microstructure of TC21 titanium alloy changes obviously. Just a little hydrogen will change the contrast of transformedβphase. The contrast ofα phase darkens when the hydrogen content in TC21 titanium alloy exceeds 0.5% （mass fraction）. The phase/grain boundaries become ambiguous or even vanished, andβ phase becomes the main phase instead ofα phase when the hydrogen content reaches 0.625%. Moreover,α phase disappears when the hydrogen content reaches 1.065%. Additionally, the XRD analysis shows that α＇ martensite and FCCδ hydride appear in the hydrogenated alloy. According to the microstructures and XRD analysis, the schematic diagrams of hydrogen diffusion process in TC21 titanium alloy were established.展开更多
This paper presents the theory,method,and application of performance-based pavement needs assessment at a state level,using the Pennsylvania Interstate System as an example.First,a general framework is presented for t...This paper presents the theory,method,and application of performance-based pavement needs assessment at a state level,using the Pennsylvania Interstate System as an example.First,a general framework is presented for the pavement asset management and a general optimization model is established for the pavement maintenance and rehabilitation needs assessment.Also,the bundling of pavement segments for the project implementation is discussed.Using the examples of Statewide Transportation Improvement Plan and Long Range Transportation Plan for Pennsylvania Interstate System,the application of performance-based pavement needs assessment is demonstrated.It is shown that unconstrained analysis can help decision-makers investigate the real maintenance and rehabilitation needs;financially-constrained analysis can help decision-makers select projects for implementation and examine the corresponding future pavement conditions.Trade-off analysis can help decision-makers investigate the outcomes of different investment levels on pavement maintenance and rehabilitation and make the final decision on the investment level.The proposed case study provides a good example of performance-based pavement needs assessment for developing countries.展开更多
基金Project(51205102)supported by the National Natural Science Foundation of ChinaProject(2012M511401)supported by the Postdoctoral Science Foundation of China
文摘The hydrogen absorption characteristics and microstructural evolution of TC21 titanium alloy were investigated by kinetic model analysis, optical microscopy （OM） and X-ray diffraction （XRD）. The results show that the hydrogen absorption reaction occurred during the hydrogen absorption process of TC21 titanium alloy can be divided into two different stages according to the hydrogen absorption kinetics. After hydrogenation, the microstructure of TC21 titanium alloy changes obviously. Just a little hydrogen will change the contrast of transformedβphase. The contrast ofα phase darkens when the hydrogen content in TC21 titanium alloy exceeds 0.5% （mass fraction）. The phase/grain boundaries become ambiguous or even vanished, andβ phase becomes the main phase instead ofα phase when the hydrogen content reaches 0.625%. Moreover,α phase disappears when the hydrogen content reaches 1.065%. Additionally, the XRD analysis shows that α＇ martensite and FCCδ hydride appear in the hydrogenated alloy. According to the microstructures and XRD analysis, the schematic diagrams of hydrogen diffusion process in TC21 titanium alloy were established.
基金The National Key Research and Development Program of China(No.2018YFB1601202)the Natural Science Foundation of Shaanxi Province(No.2019JM-228)+1 种基金the National Natural Science Foundation of China(No.51308335)the Fundamental Research Funds for the Central Universities of Chang’an University(No.300102218401)
文摘This paper presents the theory,method,and application of performance-based pavement needs assessment at a state level,using the Pennsylvania Interstate System as an example.First,a general framework is presented for the pavement asset management and a general optimization model is established for the pavement maintenance and rehabilitation needs assessment.Also,the bundling of pavement segments for the project implementation is discussed.Using the examples of Statewide Transportation Improvement Plan and Long Range Transportation Plan for Pennsylvania Interstate System,the application of performance-based pavement needs assessment is demonstrated.It is shown that unconstrained analysis can help decision-makers investigate the real maintenance and rehabilitation needs;financially-constrained analysis can help decision-makers select projects for implementation and examine the corresponding future pavement conditions.Trade-off analysis can help decision-makers investigate the outcomes of different investment levels on pavement maintenance and rehabilitation and make the final decision on the investment level.The proposed case study provides a good example of performance-based pavement needs assessment for developing countries.
