Suid is one of the most common taxa among the Pleistocene mammalian fauna in China.However,its phylogenetic taxonomy and evolution are far from clear.The newly recovered suid fossil materials from the Early Pleistocen...Suid is one of the most common taxa among the Pleistocene mammalian fauna in China.However,its phylogenetic taxonomy and evolution are far from clear.The newly recovered suid fossil materials from the Early Pleistocene Shanshenmiaozui site in Nihewan Basin in North China provide new insight into the evolution of its kind in North China.The new materials include partial skulls and mandibles of males,and most of their teeth were preserved in situ.The specimens can be referred to the species Sus lydekkeri,which is the only species of Sus found in North China from the Early Pleistocene.The fossils of the once reported Pleistocene species“Potamochoerus chinhsienensis”should also be provisionally included in the species S.lydekkeri according to its form and size,which at least now excludes it from Potamochoerus.The species S.lydekkeri is very close to the extant species S.scrofa,and even was combined into the latter as a chronological subspecies by some authors,while its larger size,prominent preorbital fossa,backwardly positioned infraorbital foramen,frequently appearing verrucosic type(at least the intermediate type of the male lower canine),and simple crown structures support its validness as an independent species.The Early Pleistocene forms are characterized by a larger size,lower L/W ratio of cheekteeth,both upper and lower M3s having no more than three lobes,and the male lower canine is exclusively of a verrucosic type.Suid fossils are a very good indicator of paleoenvironments and paleoclimate.Both the northern and the southern faunas in China contain suid fossils throughout the Pleistocene Epoch,while the southern fauna has prominently more diversified taxa and more abundant fossil collections;whether that is caused by different origins or by environmental modifications is still not clear.展开更多
Innovative pulsed current-assisted multi-pass rolling tests were conducted on a 12-roll mill during the rolling deformation processing of SUS304 ultra-thin strips.The results show that in the first rolling pass,the ro...Innovative pulsed current-assisted multi-pass rolling tests were conducted on a 12-roll mill during the rolling deformation processing of SUS304 ultra-thin strips.The results show that in the first rolling pass,the rolling reduction rate of a conventionally rolled sample(at room temperature)is 33.8%,which can be increased to 41.5%by pulsed current-assisted rolling,enabling the formation of an ultra-thin strip with a size of 67.3μm in only one rolling pass.After three passes of pulsed current-assisted rolling,the thickness of the ultra-thin strip can be further reduced to 51.7μm.To clearly compare the effects of a pulsed current on the microstructure and mechanical response of the ultra-thin strip,ultra-thin strips with nearly the same thickness reduction were analyzed.It was found that pulsed current can reduce the degree of work-hardening of the rolled samples by promoting dislocation detachment,reducing the density of stacking faults,inhibiting martensitic phase transformation,and shortening the total length of grain boundaries.As a result,the ductility of ultra-thin strips can be effectively restored to approximately 16.3%while maintaining a high tensile strength of 1118 MPa.Therefore,pulsed current-assisted rolling deformation shows great potential for the formation of ultra-thin strips with a combination of high strength and ductility.展开更多
Surface morphology and roughness are important parameters of surface quality of cold-rolled ultra-thin strip steel.In order to study the effect of Si_(3)N_(4) ceramic work rolls on the surface roughness of SUS304 ultr...Surface morphology and roughness are important parameters of surface quality of cold-rolled ultra-thin strip steel.In order to study the effect of Si_(3)N_(4) ceramic work rolls on the surface roughness of SUS304 ultra-thin strip,ABAQUS finite element model calculation,3D laser profilometry,and other methods were adopted based on the physical characteristics of Si_(3)N_(4) ceramic roll and 9Cr2MoV steel roll,like anti-flattening performance and oil wettability.The surface morphology and roughness of SUS304 ultra-thin strip rolled by different material work rolls under oil lubrication conditions were measured.The results showed that under the rolling force of 10 kN,the maximum flattening amount of Si_(3)N_(4) ceramic roll was reduced by 35.14%compared to that of 9Cr2MoV steel roll.The reduction rate of SUS304 ultra-thin strip rolled by ceramic roll was 34.19%,while that rolled by steel roll was only 22%;Si_(3)N_(4) ceramic roll can further increase the number of alternating convex peaks and concave valleys in the rolled thin strip,reduce the profile steepness,reduce surface roughness,and enhance the planarization effect of surface micro-convex bodies,with improving surface quality and surface glossiness.Finally,the mechanism of Si_(3)N_(4) ceramic roll significantly improving the surface roughness of rolled SUS304 ultra-thin strip was proposed.展开更多
文摘Suid is one of the most common taxa among the Pleistocene mammalian fauna in China.However,its phylogenetic taxonomy and evolution are far from clear.The newly recovered suid fossil materials from the Early Pleistocene Shanshenmiaozui site in Nihewan Basin in North China provide new insight into the evolution of its kind in North China.The new materials include partial skulls and mandibles of males,and most of their teeth were preserved in situ.The specimens can be referred to the species Sus lydekkeri,which is the only species of Sus found in North China from the Early Pleistocene.The fossils of the once reported Pleistocene species“Potamochoerus chinhsienensis”should also be provisionally included in the species S.lydekkeri according to its form and size,which at least now excludes it from Potamochoerus.The species S.lydekkeri is very close to the extant species S.scrofa,and even was combined into the latter as a chronological subspecies by some authors,while its larger size,prominent preorbital fossa,backwardly positioned infraorbital foramen,frequently appearing verrucosic type(at least the intermediate type of the male lower canine),and simple crown structures support its validness as an independent species.The Early Pleistocene forms are characterized by a larger size,lower L/W ratio of cheekteeth,both upper and lower M3s having no more than three lobes,and the male lower canine is exclusively of a verrucosic type.Suid fossils are a very good indicator of paleoenvironments and paleoclimate.Both the northern and the southern faunas in China contain suid fossils throughout the Pleistocene Epoch,while the southern fauna has prominently more diversified taxa and more abundant fossil collections;whether that is caused by different origins or by environmental modifications is still not clear.
基金This work was supported by the fund of the National Natural Science Foundation of China(51974196)Major Program of National Natural Science Foundation of China(U22A20188)+1 种基金Science and Technology Innovation Teams of Shanxi Province(202304051001025)Central Government Guides the Special Fund Projects of Local Scientific and Technological Development(YDZX20191400002149).
文摘Innovative pulsed current-assisted multi-pass rolling tests were conducted on a 12-roll mill during the rolling deformation processing of SUS304 ultra-thin strips.The results show that in the first rolling pass,the rolling reduction rate of a conventionally rolled sample(at room temperature)is 33.8%,which can be increased to 41.5%by pulsed current-assisted rolling,enabling the formation of an ultra-thin strip with a size of 67.3μm in only one rolling pass.After three passes of pulsed current-assisted rolling,the thickness of the ultra-thin strip can be further reduced to 51.7μm.To clearly compare the effects of a pulsed current on the microstructure and mechanical response of the ultra-thin strip,ultra-thin strips with nearly the same thickness reduction were analyzed.It was found that pulsed current can reduce the degree of work-hardening of the rolled samples by promoting dislocation detachment,reducing the density of stacking faults,inhibiting martensitic phase transformation,and shortening the total length of grain boundaries.As a result,the ductility of ultra-thin strips can be effectively restored to approximately 16.3%while maintaining a high tensile strength of 1118 MPa.Therefore,pulsed current-assisted rolling deformation shows great potential for the formation of ultra-thin strips with a combination of high strength and ductility.
基金supported by the National Natural Science Foundation of China (No.51974196)the Major Program of National Natural Science Foundation of China (No.U22A20188)Central Government Guides the Special Fund Projects of Local Scientific and Technological Development (YDZX20191400002149).
文摘Surface morphology and roughness are important parameters of surface quality of cold-rolled ultra-thin strip steel.In order to study the effect of Si_(3)N_(4) ceramic work rolls on the surface roughness of SUS304 ultra-thin strip,ABAQUS finite element model calculation,3D laser profilometry,and other methods were adopted based on the physical characteristics of Si_(3)N_(4) ceramic roll and 9Cr2MoV steel roll,like anti-flattening performance and oil wettability.The surface morphology and roughness of SUS304 ultra-thin strip rolled by different material work rolls under oil lubrication conditions were measured.The results showed that under the rolling force of 10 kN,the maximum flattening amount of Si_(3)N_(4) ceramic roll was reduced by 35.14%compared to that of 9Cr2MoV steel roll.The reduction rate of SUS304 ultra-thin strip rolled by ceramic roll was 34.19%,while that rolled by steel roll was only 22%;Si_(3)N_(4) ceramic roll can further increase the number of alternating convex peaks and concave valleys in the rolled thin strip,reduce the profile steepness,reduce surface roughness,and enhance the planarization effect of surface micro-convex bodies,with improving surface quality and surface glossiness.Finally,the mechanism of Si_(3)N_(4) ceramic roll significantly improving the surface roughness of rolled SUS304 ultra-thin strip was proposed.
