The martensitic hot-rolled 0.3 C-6 Mn-1.5 Si(wt%)steel was annealed at 630℃for 24 h to improve its cold rollability,followed by cold rolling and annealing at 670℃for 10 min.The annealing process was designed based o...The martensitic hot-rolled 0.3 C-6 Mn-1.5 Si(wt%)steel was annealed at 630℃for 24 h to improve its cold rollability,followed by cold rolling and annealing at 670℃for 10 min.The annealing process was designed based on the capacities of industrial batch annealing and continuous annealing lines.A duplex submicron austenite and ferrite microstructure and excellent tensile properties were obtained finally,proved the above process is feasible."Austenite memory"was found in the hot-rolled and annealed sample which restricted recrystallization of lath martensite,leading to lath-shaped morphology of austenite and ferrite grains."Austenite memory"disappeared in the cold-rolled and annealed sample due to austenite random nucleation and ferrite recrystallization,resulting in globular microstructure and refinement of both austenite and ferrite grains.The austenite to martensite transformation contributed most of strain hardening during deformation and improved the uniform elongation,but the dislocation strengthening played a decisive role on the yielding behavior.The tensile curves change from continuous to discontinuous yielding as the increase of cold-rolled reduction due to the weakening dislocation strengthening of austenite and ferrite grains related to the morphology change and grain refinement.A method by controlling the cold-rolled reduction is proposed to avoid the Lüders strain.展开更多
Influence of crosslinking on physical properties of low density polyethylene was studied. The results indicated that, at low degrees of crosslinking, the network hardly affects the crystallinity, elastic modulus （E）...Influence of crosslinking on physical properties of low density polyethylene was studied. The results indicated that, at low degrees of crosslinking, the network hardly affects the crystallinity, elastic modulus （E） and yielding stress while it improves the tensile strength and strain at break simultaneously. Tensile strength reaches a maximum of about 24 MPa at 1.5 phr dicumyl peroxide （DCP） then decreases to a constant value of about 18 MPa due to decrease of crystallinity. E reaches its maximum at 0.5 phr DCP corresponding to gel fraction of about 75% without marked change in crystallinity. The crosslinked polyethylene exhibits two yielding processes, and both yielding stresses approximately linearly depend on crystallinity.展开更多
Yielding support is often used in the squeezing tunnel to prevent damage to the lining induced by large deformation of the surrounding rock.Highly Deformable Elements(HDE)which is often installed along the circumferen...Yielding support is often used in the squeezing tunnel to prevent damage to the lining induced by large deformation of the surrounding rock.Highly Deformable Elements(HDE)which is often installed along the circumferential direction of the shotcrete lining is a common type of yielding support.To determine the yield parameters of HDE,the support characteristic of the lining using HDE and the ground pressure considering strain-softening of soft rock were analyzed by an analytical method.The analytical solution showed that when considering the strain-softening of squeezing ground,the ground pressure has a non-zero minimum value.The minimum value of ground stress can be used to determine the constant yield stress of the HDE,and the corresponding deformation of the minimum ground pressure can be used to determine the deformation capacity of the HDE.Based on the variation in the design constant yield stress and yield displacement of HDE with the in-situ stress and the mechanical parameters of the soft rock,equations were proposed for determining of the yield parameters of the HDE.展开更多
Using large strain two dimension axisymmetric elasto plastic finite element method and the modified law of mixture, the effects of thermal residual stresses on the yielding behavior of short fiber reinforced metal mat...Using large strain two dimension axisymmetric elasto plastic finite element method and the modified law of mixture, the effects of thermal residual stresses on the yielding behavior of short fiber reinforced metal matrix composite and their dependencies on the material structure parameters (fiber volume fraction, fiber aspect ratio and fiber end distance) were studied. It is demonstrated that the stress strain partition parameter can be used to describe the stress transfer from the matrix to the fiber. The variation of the second derivation of the stress strain partition parameter can be used to determine the elastic modulus, the proportion limit, the initial and final yield strengths. In the presence of thermal residual stress, these yielding properties are asymmetric and are influenced differently by the material structure parameters under tensile and compressive loadings.展开更多
The fracture behavior for welded joint of new generation fine grained steel SS400 was investigated and assessed on the basis of fitness for purpose philosophy. The actual critical defect sizes for the SS400 base metal...The fracture behavior for welded joint of new generation fine grained steel SS400 was investigated and assessed on the basis of fitness for purpose philosophy. The actual critical defect sizes for the SS400 base metal and its weld HAZ (heat affected zone) defined by the gross yielding criterium have been determined directly by means of wide plate tests. It has been shown that although the HAZ grain growth occurs due to the welding heat, the resistance to fracture is not deteriorated. The deformation behavior of wide plate specimen was also studied by finite, element (FE) analysis. The deformation of weld HAZ is protected by the high strength weld metal, so it is easier to get the general yielding for the welded joint specimen.展开更多
The District of Columbia currently uses the standard pedestrian warning signs and diagonal arrow plaques at a substantial number of uncontrolled crosswalks within the City.However, the widespread use of these measures...The District of Columbia currently uses the standard pedestrian warning signs and diagonal arrow plaques at a substantial number of uncontrolled crosswalks within the City.However, the widespread use of these measures appears to be ineffective in curbing the incidence of pedestrian involved crashes or pedestrian-vehicle conflicts. To compensate for the perceived lack of effectiveness of the standard pedestrian warning sign the District Department of Transportation developed a new side-of-street crossing sign to improve driver compliance based on pedestrian right-of-way laws.This study was aimed at determining the effectiveness(defined as the proportion of drivers approaching a crosswalk who stop or yield the right of way to a pedestrian in the crosswalk) of the experimental side-of-street pedestrian crossing sign compared to the standard sign, with and without rectangular rapid flashing beacons. Effectiveness of the side-of-street pedestrian sign and standard sign were observed at a total of 32 locations in the District over a one-year period using the “control” and “experimental” comparison approach. Video data for each location was obtained from March 2018 through February 2019 during typical weekdays for the morning and afternoon peak periods. The results of the study showed that the experimental signs with RRFBs provided higher driver compliance rates(yielding to pedestrians) compared to the standard signs for both the morning and afternoon peak periods. However, the differences in compliance rates for the experimental and standard signs were not statistically significant at a 95% confidence interval.Further evaluation of the signs is recommended using the “before” and “after” approach in addition to an assessment of crash statistics at the selected locations.展开更多
The drivers’yielding distance to pedestrians at midblock crosswalks affects pedestrians’perceived safety.This distance can be influenced by either crosswalk-related or noncrosswalk.In most cases,crosswalk-related fe...The drivers’yielding distance to pedestrians at midblock crosswalks affects pedestrians’perceived safety.This distance can be influenced by either crosswalk-related or noncrosswalk.In most cases,crosswalk-related features are readily available or easy to collect compared to non-crosswalk features.However,the extent to which crosswalk-related features affect the spatial yielding compliance is not clear.This study evaluated the role of combined crosswalk-related features on drivers’spatial yielding compliance at signalized midblock crosswalks.The study used observational survey data collected from fifteen flash-based signalized midblock crosswalks located in Las Vegas,Nevada.Three logistic regression models,with crosswalk-related features only,non-crosswalk features only,and combined features,were developed and compared.It was revealed that the performance difference between the model with crosswalk-related features only and combined features was insignificant.This study found that the presence of state’s law signs,“PED XING”signs,and placement of rectangular rapid flashing beacons(RRFBs)on the advanced pedestrians crossing signs(APCSs),are significant factors for high spatial yielding compliance.On the contrary,the yield line’s presence at a distance greater than 40 ft from the crosswalk,presence of one stage crossing,and high Annual Average Daily Traffic(AADT)negatively affects the spatial yielding compliance.Moreover,the findings suggest that researchers should be careful about excluding the non-crosswalk features from the analysis.To improve spatial yielding compliance,several recommendations that the city planners and engineers can adopt are provided.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.51722402)by the Fundamental Research Funds for the Central Universities(Grant No.2007012)+1 种基金111 Project(No.B16009)the Liaoning Revitalization Talents Program(No.XLYC1907128)。
文摘The martensitic hot-rolled 0.3 C-6 Mn-1.5 Si(wt%)steel was annealed at 630℃for 24 h to improve its cold rollability,followed by cold rolling and annealing at 670℃for 10 min.The annealing process was designed based on the capacities of industrial batch annealing and continuous annealing lines.A duplex submicron austenite and ferrite microstructure and excellent tensile properties were obtained finally,proved the above process is feasible."Austenite memory"was found in the hot-rolled and annealed sample which restricted recrystallization of lath martensite,leading to lath-shaped morphology of austenite and ferrite grains."Austenite memory"disappeared in the cold-rolled and annealed sample due to austenite random nucleation and ferrite recrystallization,resulting in globular microstructure and refinement of both austenite and ferrite grains.The austenite to martensite transformation contributed most of strain hardening during deformation and improved the uniform elongation,but the dislocation strengthening played a decisive role on the yielding behavior.The tensile curves change from continuous to discontinuous yielding as the increase of cold-rolled reduction due to the weakening dislocation strengthening of austenite and ferrite grains related to the morphology change and grain refinement.A method by controlling the cold-rolled reduction is proposed to avoid the Lüders strain.
基金supported by the National Natural Science Fundation of China(No.51073137)
文摘Influence of crosslinking on physical properties of low density polyethylene was studied. The results indicated that, at low degrees of crosslinking, the network hardly affects the crystallinity, elastic modulus （E） and yielding stress while it improves the tensile strength and strain at break simultaneously. Tensile strength reaches a maximum of about 24 MPa at 1.5 phr dicumyl peroxide （DCP） then decreases to a constant value of about 18 MPa due to decrease of crystallinity. E reaches its maximum at 0.5 phr DCP corresponding to gel fraction of about 75% without marked change in crystallinity. The crosslinked polyethylene exhibits two yielding processes, and both yielding stresses approximately linearly depend on crystallinity.
基金the support of the National Natural Science Foundation of China(Grant Nos.52179113,51991392 and 52279119)the Second Comprehensive Scientific Expedition on the Tibetan Plateau(No.2019QZKK0904)。
文摘Yielding support is often used in the squeezing tunnel to prevent damage to the lining induced by large deformation of the surrounding rock.Highly Deformable Elements(HDE)which is often installed along the circumferential direction of the shotcrete lining is a common type of yielding support.To determine the yield parameters of HDE,the support characteristic of the lining using HDE and the ground pressure considering strain-softening of soft rock were analyzed by an analytical method.The analytical solution showed that when considering the strain-softening of squeezing ground,the ground pressure has a non-zero minimum value.The minimum value of ground stress can be used to determine the constant yield stress of the HDE,and the corresponding deformation of the minimum ground pressure can be used to determine the deformation capacity of the HDE.Based on the variation in the design constant yield stress and yield displacement of HDE with the in-situ stress and the mechanical parameters of the soft rock,equations were proposed for determining of the yield parameters of the HDE.
文摘Using large strain two dimension axisymmetric elasto plastic finite element method and the modified law of mixture, the effects of thermal residual stresses on the yielding behavior of short fiber reinforced metal matrix composite and their dependencies on the material structure parameters (fiber volume fraction, fiber aspect ratio and fiber end distance) were studied. It is demonstrated that the stress strain partition parameter can be used to describe the stress transfer from the matrix to the fiber. The variation of the second derivation of the stress strain partition parameter can be used to determine the elastic modulus, the proportion limit, the initial and final yield strengths. In the presence of thermal residual stress, these yielding properties are asymmetric and are influenced differently by the material structure parameters under tensile and compressive loadings.
基金Supported by FOK YING TUNG Education Foundation and the National Natural Science Foundation of China (Grant No.50275107).
文摘The fracture behavior for welded joint of new generation fine grained steel SS400 was investigated and assessed on the basis of fitness for purpose philosophy. The actual critical defect sizes for the SS400 base metal and its weld HAZ (heat affected zone) defined by the gross yielding criterium have been determined directly by means of wide plate tests. It has been shown that although the HAZ grain growth occurs due to the welding heat, the resistance to fracture is not deteriorated. The deformation behavior of wide plate specimen was also studied by finite, element (FE) analysis. The deformation of weld HAZ is protected by the high strength weld metal, so it is easier to get the general yielding for the welded joint specimen.
基金District Department of Transportation for funding and contributing to this study(Grant ID#:HU-0009253)。
文摘The District of Columbia currently uses the standard pedestrian warning signs and diagonal arrow plaques at a substantial number of uncontrolled crosswalks within the City.However, the widespread use of these measures appears to be ineffective in curbing the incidence of pedestrian involved crashes or pedestrian-vehicle conflicts. To compensate for the perceived lack of effectiveness of the standard pedestrian warning sign the District Department of Transportation developed a new side-of-street crossing sign to improve driver compliance based on pedestrian right-of-way laws.This study was aimed at determining the effectiveness(defined as the proportion of drivers approaching a crosswalk who stop or yield the right of way to a pedestrian in the crosswalk) of the experimental side-of-street pedestrian crossing sign compared to the standard sign, with and without rectangular rapid flashing beacons. Effectiveness of the side-of-street pedestrian sign and standard sign were observed at a total of 32 locations in the District over a one-year period using the “control” and “experimental” comparison approach. Video data for each location was obtained from March 2018 through February 2019 during typical weekdays for the morning and afternoon peak periods. The results of the study showed that the experimental signs with RRFBs provided higher driver compliance rates(yielding to pedestrians) compared to the standard signs for both the morning and afternoon peak periods. However, the differences in compliance rates for the experimental and standard signs were not statistically significant at a 95% confidence interval.Further evaluation of the signs is recommended using the “before” and “after” approach in addition to an assessment of crash statistics at the selected locations.
基金the Department of Civil and Environmental Engineering and Construction at the University of Nevada,Las Vegas,for the financial and material support
文摘The drivers’yielding distance to pedestrians at midblock crosswalks affects pedestrians’perceived safety.This distance can be influenced by either crosswalk-related or noncrosswalk.In most cases,crosswalk-related features are readily available or easy to collect compared to non-crosswalk features.However,the extent to which crosswalk-related features affect the spatial yielding compliance is not clear.This study evaluated the role of combined crosswalk-related features on drivers’spatial yielding compliance at signalized midblock crosswalks.The study used observational survey data collected from fifteen flash-based signalized midblock crosswalks located in Las Vegas,Nevada.Three logistic regression models,with crosswalk-related features only,non-crosswalk features only,and combined features,were developed and compared.It was revealed that the performance difference between the model with crosswalk-related features only and combined features was insignificant.This study found that the presence of state’s law signs,“PED XING”signs,and placement of rectangular rapid flashing beacons(RRFBs)on the advanced pedestrians crossing signs(APCSs),are significant factors for high spatial yielding compliance.On the contrary,the yield line’s presence at a distance greater than 40 ft from the crosswalk,presence of one stage crossing,and high Annual Average Daily Traffic(AADT)negatively affects the spatial yielding compliance.Moreover,the findings suggest that researchers should be careful about excluding the non-crosswalk features from the analysis.To improve spatial yielding compliance,several recommendations that the city planners and engineers can adopt are provided.
