Impact processes between flexible bodies often lead to local stress concentration and wave propagation of high frequency. Therefore, the modeling of flexible multibody systems involving impact should consider the loca...Impact processes between flexible bodies often lead to local stress concentration and wave propagation of high frequency. Therefore, the modeling of flexible multibody systems involving impact should consider the local plastic deformation and the strict requirements of the spatial discretization. Owing to the nonlinearity of the stiffness matrix, the reduction of the element number is extremely important. For the contact-impact problem, since different regions have different requirements regarding the element size, a new subregion mesh method is proposed to reduce the number of the unnecessary elements. A dynamic model for flexible multibody systems with elastic-plastic contact impact is established based on a floating frame of reference formulation and complete Lagrange incremental nonlinear finite-element method to investigate the effect of the elastic-plastic deformation as well as spatial discretization. Experiments on the impact between two bodies are carried out to validate the correctness of the elastic-plastic model. The proposed formulation is applied to a slider-crank system with elastic-plastic impact.展开更多
Background: Plastic pollution is the accumulation of waste composed of plastic and its derivatives all over the environment. Whether in the form of visible garbage or microparticles, as it slowly degrades, plastic pol...Background: Plastic pollution is the accumulation of waste composed of plastic and its derivatives all over the environment. Whether in the form of visible garbage or microparticles, as it slowly degrades, plastic pollution poses significant threats to terrestrial and aquatic habitats and the wildlife that call them home, whether through ingestion, entanglement or exposure to the chemicals contained in the material. Unfortunately, there is a lack of documentation on the impact of plastic waste on human health in low- and middle-income countries (LMICs). Methods: We searched five electronic databases (PubMed, Embase, Global Health, CINAHL and Web of Science) and gray literature, following the preferred reporting elements for systematic reviews and meta-analyses (PRISMA), for the impact of plastic waste on human health in developing countries. We included quantitative and qualitative studies written in English and French. We assessed the quality of the included articles using the Mixed Methods Appraisal tool (MMAT). Results: A total of 3779 articles were initially identified by searching electronic databases. After eliminating duplicates, 3167 articles were reviewed based on title and abstract, and 26 were selected for full-text review. Only three articles were retained. The three articles dealt with practices likely to lead to oral exposure to plastic chemicals in human health, as well as the level of awareness of participants concerning the possible impact of plastic on human health, namely, the use of plastic baby bottles, the use of microwaves to cook food and reheat precooked food, the use of plastic bottles to store water in the refrigerator, water purifier containers with plastic bodies and plastic lunch boxes, the reuse of plastic bags and the inadequacy of treatment facilities. Conclusion: Plastic waste poses different risks to human health at every stage of its life cycle. Hence, strategies must be adopted to raise public awareness of the dangers of plastic waste to their health. Trial registration: The review protocol is registered in the PROSPERO international prospective register of systematic reviews (ID = CRD42023409087).展开更多
Using the finite element code ANSYS/LS-DYNA, a dynamic finite element modelwith an elastic-linear-kinematic-hardening plastic material is established to analyzeelastic-plastic stresses in the railhead in the impact pr...Using the finite element code ANSYS/LS-DYNA, a dynamic finite element modelwith an elastic-linear-kinematic-hardening plastic material is established to analyzeelastic-plastic stresses in the railhead in the impact process of wheel and rail occurring at thegap of rail joint. The model is based on the discrete elastic support condition of the rails, whichis suitable for the actual situation of wheel/track rolling contact. In the analysis the influencesof axle load, yield stress and tangent modulus of rail material on the stresses and strains areinvestigated in detail. The distribution of stresses and strains in the jointed railhead are given.It is found that the axle load, yield stress and tangent modulus of rail material greatly affect thestresses and strains in the railhead during impacting. The study provides a reliable method anduseful datum for the further research on fatigue and wear of railhead and improving the rail jointmode.展开更多
The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigat...The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigated. Experimental results show that the metal-plastic multilayer composite filled with glass fiber exhibits excellent friction and impact wear properties when using rare earth elements as surface modifier for the surface treatment of glass fiber.展开更多
The friction and wear properties under impact load and dry friction conditions of metal-plastic multilayer composites filled with glass fiber, treated with rare earth elements, were investigated. The worn surfaces wer...The friction and wear properties under impact load and dry friction conditions of metal-plastic multilayer composites filled with glass fiber, treated with rare earth elements, were investigated. The worn surfaces were observed and analyzed by scanning electron microscopy (SEM). It shows that applying rare earth elements surface modifier to treat the glass fiber surface can enhance the interfacial adhesion between the glass fiber and polytetrafluoroethylene (PTFE), as well as promote the interface properties of the composites. This helps to form a uniformly distributed and high adhesive transfer film on the counterface and abate the friction between the composite and the counterface. As a result, the wear of composite is greatly reduced. The composite exhibits excellent friction properties and impact wear-resistance.展开更多
The relationship between the crystal lattice free volume,ΔV,and impact sensitivity,E_(dr),of ten nitramines has been analyzed. It was found that this relationship is not uniquely determined,i. e. it is not given only...The relationship between the crystal lattice free volume,ΔV,and impact sensitivity,E_(dr),of ten nitramines has been analyzed. It was found that this relationship is not uniquely determined,i. e. it is not given only by their own ΔV values but fundamentally by the type and intensity of the intermolecular forces in the nitramine crystals. Also,relationships between the E_(dr)values,on the one hand,and bulk modulus,K,and shear modulus,G,on the other,have been the subject of discussion not only for pure cyclic nitramines but also for their PBXs,bonded by a poly-fluoro binder. The closest linear correlation exists between the E_(dr)values and dimensionless K·G^(-1) ratio which indicates the plasticity range. A similar relationship is valid also for the ΔV values. Relationships of the E_(dr) and / or ΔV values with the shear modulus or to the K·G^(-1) ratio reflect an unusual behavior of ε-HNIW to which the published morphological instability of this particular HNIW version might also be related.展开更多
Static and fatigue tests under compression load were made on impacted AS4/PEEK and T300/913C graphite/epoxy with [45/90/-45/0]5S stacking sequence. The comparison of the damage tolerance assessment for thermosetting a...Static and fatigue tests under compression load were made on impacted AS4/PEEK and T300/913C graphite/epoxy with [45/90/-45/0]5S stacking sequence. The comparison of the damage tolerance assessment for thermosetting and thermoplastic composites shows that thermoplastics are more damage tolerant under compression. Impacted thermoplastic composites have excellent compression-compression fatigue behavior. The damage growth life is only a few percent of their total fatigue life and no regular damage growth can be found. Some design principles for thermosetting composite structures may still be used.展开更多
The dynamic buckling of elasto-plastic cylindrical shells under axial fluid-solid impact is investigated theoretically. A simplified liquid- gas- structure model is given to approximately imitate the problem. The basi...The dynamic buckling of elasto-plastic cylindrical shells under axial fluid-solid impact is investigated theoretically. A simplified liquid- gas- structure model is given to approximately imitate the problem. The basic equation of the structure is derived from a minimum principle in dynamics of elasto-plastic continua at finite deformation, and the flow theory of plasticity is employed. The liquid is incompressible and the gas is compressed adiabatically. A number of numerical results are presented and the characteristics of the buckling behavior under fluid-solid impact are illustrated.展开更多
A simple gravity drop experiment was run to investigate plastic deformation of powder aggregrate sprayed on a hard ball under impact of another free falling hard ball and measure coefficient of restitution and plastic...A simple gravity drop experiment was run to investigate plastic deformation of powder aggregrate sprayed on a hard ball under impact of another free falling hard ball and measure coefficient of restitution and plastic strain of powder aggregate. Experimental results show that coefficient of restitution and plastic strain of powder aggregate increase as the velocity of ball increases and initial height (h 0) of powder aggregate has great effects on plastic deformation of powder aggregate. At a higher initial height (h 0), much of kinetic energy is dissipated is interparticle frictional work and coefficient of restitution is very small. Plastic strain of powder aggregate first increases as h 0 increases until a maximum value and then decreases as h 0 increases.展开更多
The recovery of plastic waste has a positive impact on two fronts: The environment, through waste reduction, and the economy, through its use in road construction. This work involves recycling plastic variants such as...The recovery of plastic waste has a positive impact on two fronts: The environment, through waste reduction, and the economy, through its use in road construction. This work involves recycling plastic variants such as Polypropylene (PP) 50% and LDPE (Low Density Polyethylene) 50% in proportions of 2% to 8%, incorporated into a 0/14 BBSG. The results of the Marshall test gave stability values ranging from 826 to 1523 kg and creep values from 5.5 to 2.45 mm. The Duriez test gave r/R values ranging from 0.769 to 0.786, with water absorption percentages from 2.24% to 0.69%. The PCG test at 80 gyrations gave void percentages ranging from 11.9% to 5.23%. The rutting test gives a rutting depth percentage that drops at 30,000 cycles from 11.5% to 1.3%. This study shows a considerable increase in the mechanical characteristics of asphalt mixes by adding plastic waste.展开更多
为探明覆膜水稻生命周期过程的资源消耗和环境影响,本研究基于2021—2022两年的田间试验对东北地区覆膜水稻进行生命周期评价。结果表明:仅考虑资源消耗、气候变化和环境酸化的情况下,覆PE膜旱直播水稻的环境影响潜值更小,对环境更友好...为探明覆膜水稻生命周期过程的资源消耗和环境影响,本研究基于2021—2022两年的田间试验对东北地区覆膜水稻进行生命周期评价。结果表明:仅考虑资源消耗、气候变化和环境酸化的情况下,覆PE膜旱直播水稻的环境影响潜值更小,对环境更友好。东北地区覆PE膜育秧移栽水稻能源消耗、水资源消耗、气候变化、环境酸化、富营养化和生态毒性6个环境影响指标对应的环境影响潜值分别为14046.40 MJ、957082.47 kg、1663.15 kg CO_(2)-eq、8.70 kg SO_(2)-eq、1.84 kg PO^(3-)_(4)-eq和57.05 kg 1,4-DCB-eq;东北地区覆PE膜旱直播水稻这6个环境影响指标对应的环境影响潜值分别为11990.32 MJ、312102.92 kg、1071.41 kg CO_(2)-eq、6.85 kg SO_(2)-eq、1.88 kg PO^(3-)_(4)-eq和73.75 kg 1,4-DCB-eq。造成资源消耗和气候变化的主要原因是氮肥和燃油的生产及使用,另外地膜生产和滴灌设备的生产也对环境造成了较大的影响。研究表明,水稻清洁生产的关键在于农资产品生产技术的优化和氮肥的合理施用。在两种覆膜水稻栽培方式中,覆膜旱直播水稻造成的环境影响更低,更适合我国农业绿色低碳发展。展开更多
雷电作为自然界一种极端天气的表现形式,常给地基、地面、高耸建筑等造成严重破坏。工程防雷措施依赖于土体雷电冲击特性。现阶段,研究人员大多从电气工程角度探究雷电冲击土体造成的危害,但因学科间的差异与局限,雷电作用下岩土工程与...雷电作为自然界一种极端天气的表现形式,常给地基、地面、高耸建筑等造成严重破坏。工程防雷措施依赖于土体雷电冲击特性。现阶段,研究人员大多从电气工程角度探究雷电冲击土体造成的危害,但因学科间的差异与局限,雷电作用下岩土工程与电气工程的交叉融合方面的研究十分欠缺。本文构建土体雷电冲击模型,基于电弧通道能量平衡方程计算雷电放电产生的冲击波压力,将冲击波压力作为外加荷载作用在土体中,并通过修正Mohr-Coulomb屈服准则考虑动荷载下土体应变硬化,利用土体的理想锁定状态方程(Idealized Locked Equation of State)和动态扩孔方法考虑冲击波非稳态加载,探究雷电冲击下土体的弹塑性界面及应力时程变化规律。研究表明:在雷电冲击下,土体应力随时间变化呈现先陡增后迅速衰减的趋势,应力突变点表明土体此时正处于弹塑性交界面;在应力突变点之前,土体附加应力趋于0,处于弹性状态。任一时刻下,随着逐渐远离雷电冲击点,土体应力呈现迅速衰减的趋势,应力发生突变骤降表明此处土体正处于弹塑性交界面;在突变点之后土体附加应力趋于0,处于弹性状态。土体压缩系数对土体的弹塑性界面变化具有显著影响,随着压缩指标增大,土体塑性区半径逐渐减小;随着土体黏聚力逐渐增大,土体塑性区半径逐渐减小;增大土体弹性模量可以增大土体塑性区半径,但变化幅度相对较小;电流波形对土体塑性区中的应力会产生较大影响,而对土体弹性区影响较小。展开更多
基金supported by the National Natural Science Foundation of China (Grants 11132007, 11272203)
文摘Impact processes between flexible bodies often lead to local stress concentration and wave propagation of high frequency. Therefore, the modeling of flexible multibody systems involving impact should consider the local plastic deformation and the strict requirements of the spatial discretization. Owing to the nonlinearity of the stiffness matrix, the reduction of the element number is extremely important. For the contact-impact problem, since different regions have different requirements regarding the element size, a new subregion mesh method is proposed to reduce the number of the unnecessary elements. A dynamic model for flexible multibody systems with elastic-plastic contact impact is established based on a floating frame of reference formulation and complete Lagrange incremental nonlinear finite-element method to investigate the effect of the elastic-plastic deformation as well as spatial discretization. Experiments on the impact between two bodies are carried out to validate the correctness of the elastic-plastic model. The proposed formulation is applied to a slider-crank system with elastic-plastic impact.
文摘Background: Plastic pollution is the accumulation of waste composed of plastic and its derivatives all over the environment. Whether in the form of visible garbage or microparticles, as it slowly degrades, plastic pollution poses significant threats to terrestrial and aquatic habitats and the wildlife that call them home, whether through ingestion, entanglement or exposure to the chemicals contained in the material. Unfortunately, there is a lack of documentation on the impact of plastic waste on human health in low- and middle-income countries (LMICs). Methods: We searched five electronic databases (PubMed, Embase, Global Health, CINAHL and Web of Science) and gray literature, following the preferred reporting elements for systematic reviews and meta-analyses (PRISMA), for the impact of plastic waste on human health in developing countries. We included quantitative and qualitative studies written in English and French. We assessed the quality of the included articles using the Mixed Methods Appraisal tool (MMAT). Results: A total of 3779 articles were initially identified by searching electronic databases. After eliminating duplicates, 3167 articles were reviewed based on title and abstract, and 26 were selected for full-text review. Only three articles were retained. The three articles dealt with practices likely to lead to oral exposure to plastic chemicals in human health, as well as the level of awareness of participants concerning the possible impact of plastic on human health, namely, the use of plastic baby bottles, the use of microwaves to cook food and reheat precooked food, the use of plastic bottles to store water in the refrigerator, water purifier containers with plastic bodies and plastic lunch boxes, the reuse of plastic bags and the inadequacy of treatment facilities. Conclusion: Plastic waste poses different risks to human health at every stage of its life cycle. Hence, strategies must be adopted to raise public awareness of the dangers of plastic waste to their health. Trial registration: The review protocol is registered in the PROSPERO international prospective register of systematic reviews (ID = CRD42023409087).
基金National Natural Science Foundation of China(No.599355100)Foundation for Excellent PhD Thesis of University of Ministry of Education of China (No.200048)
文摘Using the finite element code ANSYS/LS-DYNA, a dynamic finite element modelwith an elastic-linear-kinematic-hardening plastic material is established to analyzeelastic-plastic stresses in the railhead in the impact process of wheel and rail occurring at thegap of rail joint. The model is based on the discrete elastic support condition of the rails, whichis suitable for the actual situation of wheel/track rolling contact. In the analysis the influencesof axle load, yield stress and tangent modulus of rail material on the stresses and strains areinvestigated in detail. The distribution of stresses and strains in the jointed railhead are given.It is found that the axle load, yield stress and tangent modulus of rail material greatly affect thestresses and strains in the railhead during impacting. The study provides a reliable method anduseful datum for the further research on fatigue and wear of railhead and improving the rail jointmode.
文摘The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigated. Experimental results show that the metal-plastic multilayer composite filled with glass fiber exhibits excellent friction and impact wear properties when using rare earth elements as surface modifier for the surface treatment of glass fiber.
文摘The friction and wear properties under impact load and dry friction conditions of metal-plastic multilayer composites filled with glass fiber, treated with rare earth elements, were investigated. The worn surfaces were observed and analyzed by scanning electron microscopy (SEM). It shows that applying rare earth elements surface modifier to treat the glass fiber surface can enhance the interfacial adhesion between the glass fiber and polytetrafluoroethylene (PTFE), as well as promote the interface properties of the composites. This helps to form a uniformly distributed and high adhesive transfer film on the counterface and abate the friction between the composite and the counterface. As a result, the wear of composite is greatly reduced. The composite exhibits excellent friction properties and impact wear-resistance.
文摘The relationship between the crystal lattice free volume,ΔV,and impact sensitivity,E_(dr),of ten nitramines has been analyzed. It was found that this relationship is not uniquely determined,i. e. it is not given only by their own ΔV values but fundamentally by the type and intensity of the intermolecular forces in the nitramine crystals. Also,relationships between the E_(dr)values,on the one hand,and bulk modulus,K,and shear modulus,G,on the other,have been the subject of discussion not only for pure cyclic nitramines but also for their PBXs,bonded by a poly-fluoro binder. The closest linear correlation exists between the E_(dr)values and dimensionless K·G^(-1) ratio which indicates the plasticity range. A similar relationship is valid also for the ΔV values. Relationships of the E_(dr) and / or ΔV values with the shear modulus or to the K·G^(-1) ratio reflect an unusual behavior of ε-HNIW to which the published morphological instability of this particular HNIW version might also be related.
文摘Static and fatigue tests under compression load were made on impacted AS4/PEEK and T300/913C graphite/epoxy with [45/90/-45/0]5S stacking sequence. The comparison of the damage tolerance assessment for thermosetting and thermoplastic composites shows that thermoplastics are more damage tolerant under compression. Impacted thermoplastic composites have excellent compression-compression fatigue behavior. The damage growth life is only a few percent of their total fatigue life and no regular damage growth can be found. Some design principles for thermosetting composite structures may still be used.
文摘The dynamic buckling of elasto-plastic cylindrical shells under axial fluid-solid impact is investigated theoretically. A simplified liquid- gas- structure model is given to approximately imitate the problem. The basic equation of the structure is derived from a minimum principle in dynamics of elasto-plastic continua at finite deformation, and the flow theory of plasticity is employed. The liquid is incompressible and the gas is compressed adiabatically. A number of numerical results are presented and the characteristics of the buckling behavior under fluid-solid impact are illustrated.
文摘A simple gravity drop experiment was run to investigate plastic deformation of powder aggregrate sprayed on a hard ball under impact of another free falling hard ball and measure coefficient of restitution and plastic strain of powder aggregate. Experimental results show that coefficient of restitution and plastic strain of powder aggregate increase as the velocity of ball increases and initial height (h 0) of powder aggregate has great effects on plastic deformation of powder aggregate. At a higher initial height (h 0), much of kinetic energy is dissipated is interparticle frictional work and coefficient of restitution is very small. Plastic strain of powder aggregate first increases as h 0 increases until a maximum value and then decreases as h 0 increases.
文摘The recovery of plastic waste has a positive impact on two fronts: The environment, through waste reduction, and the economy, through its use in road construction. This work involves recycling plastic variants such as Polypropylene (PP) 50% and LDPE (Low Density Polyethylene) 50% in proportions of 2% to 8%, incorporated into a 0/14 BBSG. The results of the Marshall test gave stability values ranging from 826 to 1523 kg and creep values from 5.5 to 2.45 mm. The Duriez test gave r/R values ranging from 0.769 to 0.786, with water absorption percentages from 2.24% to 0.69%. The PCG test at 80 gyrations gave void percentages ranging from 11.9% to 5.23%. The rutting test gives a rutting depth percentage that drops at 30,000 cycles from 11.5% to 1.3%. This study shows a considerable increase in the mechanical characteristics of asphalt mixes by adding plastic waste.
文摘为探明覆膜水稻生命周期过程的资源消耗和环境影响,本研究基于2021—2022两年的田间试验对东北地区覆膜水稻进行生命周期评价。结果表明:仅考虑资源消耗、气候变化和环境酸化的情况下,覆PE膜旱直播水稻的环境影响潜值更小,对环境更友好。东北地区覆PE膜育秧移栽水稻能源消耗、水资源消耗、气候变化、环境酸化、富营养化和生态毒性6个环境影响指标对应的环境影响潜值分别为14046.40 MJ、957082.47 kg、1663.15 kg CO_(2)-eq、8.70 kg SO_(2)-eq、1.84 kg PO^(3-)_(4)-eq和57.05 kg 1,4-DCB-eq;东北地区覆PE膜旱直播水稻这6个环境影响指标对应的环境影响潜值分别为11990.32 MJ、312102.92 kg、1071.41 kg CO_(2)-eq、6.85 kg SO_(2)-eq、1.88 kg PO^(3-)_(4)-eq和73.75 kg 1,4-DCB-eq。造成资源消耗和气候变化的主要原因是氮肥和燃油的生产及使用,另外地膜生产和滴灌设备的生产也对环境造成了较大的影响。研究表明,水稻清洁生产的关键在于农资产品生产技术的优化和氮肥的合理施用。在两种覆膜水稻栽培方式中,覆膜旱直播水稻造成的环境影响更低,更适合我国农业绿色低碳发展。
文摘雷电作为自然界一种极端天气的表现形式,常给地基、地面、高耸建筑等造成严重破坏。工程防雷措施依赖于土体雷电冲击特性。现阶段,研究人员大多从电气工程角度探究雷电冲击土体造成的危害,但因学科间的差异与局限,雷电作用下岩土工程与电气工程的交叉融合方面的研究十分欠缺。本文构建土体雷电冲击模型,基于电弧通道能量平衡方程计算雷电放电产生的冲击波压力,将冲击波压力作为外加荷载作用在土体中,并通过修正Mohr-Coulomb屈服准则考虑动荷载下土体应变硬化,利用土体的理想锁定状态方程(Idealized Locked Equation of State)和动态扩孔方法考虑冲击波非稳态加载,探究雷电冲击下土体的弹塑性界面及应力时程变化规律。研究表明:在雷电冲击下,土体应力随时间变化呈现先陡增后迅速衰减的趋势,应力突变点表明土体此时正处于弹塑性交界面;在应力突变点之前,土体附加应力趋于0,处于弹性状态。任一时刻下,随着逐渐远离雷电冲击点,土体应力呈现迅速衰减的趋势,应力发生突变骤降表明此处土体正处于弹塑性交界面;在突变点之后土体附加应力趋于0,处于弹性状态。土体压缩系数对土体的弹塑性界面变化具有显著影响,随着压缩指标增大,土体塑性区半径逐渐减小;随着土体黏聚力逐渐增大,土体塑性区半径逐渐减小;增大土体弹性模量可以增大土体塑性区半径,但变化幅度相对较小;电流波形对土体塑性区中的应力会产生较大影响,而对土体弹性区影响较小。
