There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plast...There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.展开更多
Microplastics pollution has received growing attention worldwide in recent years.However,data on microplastics in the freshwater environment are still limited,especially in high-latitude nature reserves in Northern Ch...Microplastics pollution has received growing attention worldwide in recent years.However,data on microplastics in the freshwater environment are still limited,especially in high-latitude nature reserves in Northern China.The first study on microplastic pollution in the Liaohe River Reserve in Northern China is reported here,and mesoplastics were also incorporated.Surface water and sediment samples were collected from 32 sites along the nature reserve.The abundance,type,shape,color,and size of micro-and mesoplastics were measured using density extraction,optical microscopy,and FTIR spectroscopy.The data showed that diverse micro-and mesoplastics were found widespread in the 32 sites,and the average abundance of these plastics was 0.11±0.0410^(–2) items/L in surface water and 62.29±54.30 items/kg in sediment.Moreover,70%and 66%were smaller than 2000μm in surface water and sediment,respectively.Fiber accounted for 91.86%in surface water and 43.48%in sediment,indicating that the major source of micro-and mesoplastics in the Liaohe River Reserve may be domestic sewage and aquaculture.A total of 16 and 27 polymers were identified in surface water and sediment,respectively,and mostly consisted of rayon,polyester,polystyrene,and poly(ethylene terephthalate).Moreover,both the risk index and the pollution load index demonstrated a low risk of micro-and mesoplastics in surface water and sediment in the Liaohe River Reserve.展开更多
基金the Research Committee of The Hong Kong Polytechnic University and the Innovation Technology Commission of The Hong Kong SAR Government for their financial support of the Hong Kong Partner State Key Laboratory of Ultra-Precision Machining Technology
文摘There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.
基金supported by the Capacity-building Projects by the Beijing Academy of Agriculture and Forestry Sciences(KJCX20190405,KJCX20210430,KJCX20200422),and Beijing Outstanding Talents Cultivation Youth Backbone Project。
文摘Microplastics pollution has received growing attention worldwide in recent years.However,data on microplastics in the freshwater environment are still limited,especially in high-latitude nature reserves in Northern China.The first study on microplastic pollution in the Liaohe River Reserve in Northern China is reported here,and mesoplastics were also incorporated.Surface water and sediment samples were collected from 32 sites along the nature reserve.The abundance,type,shape,color,and size of micro-and mesoplastics were measured using density extraction,optical microscopy,and FTIR spectroscopy.The data showed that diverse micro-and mesoplastics were found widespread in the 32 sites,and the average abundance of these plastics was 0.11±0.0410^(–2) items/L in surface water and 62.29±54.30 items/kg in sediment.Moreover,70%and 66%were smaller than 2000μm in surface water and sediment,respectively.Fiber accounted for 91.86%in surface water and 43.48%in sediment,indicating that the major source of micro-and mesoplastics in the Liaohe River Reserve may be domestic sewage and aquaculture.A total of 16 and 27 polymers were identified in surface water and sediment,respectively,and mostly consisted of rayon,polyester,polystyrene,and poly(ethylene terephthalate).Moreover,both the risk index and the pollution load index demonstrated a low risk of micro-and mesoplastics in surface water and sediment in the Liaohe River Reserve.
