An elasto-visco-plastic constitutive model incorporating the craze damage behavior was developed for the polypropylene(PP), by using the plastic failure model applied for the concrete, to capture the craze yielding an...An elasto-visco-plastic constitutive model incorporating the craze damage behavior was developed for the polypropylene(PP), by using the plastic failure model applied for the concrete, to capture the craze yielding and stress-whitening phenomena. In addition, the developed constitutive model was implemented into finite element codes in Abaqus to simulate the tensile deformation. The standard uniaxial tensile tests were carried out. The stress-strain curves from the uniaxial tensile tests show that the stress keeps decreasing after yielding and the yield stress rises with the increasing of the strain rate. It is worth noting that the craze damage is more visible with higher strain rate. The stress-whitening can be seen clearly around the fracture. The uniaxial tensile tests using specially designed specimen with circular holes weakening were performed for the validation of the developed model. The simulation results of the tensile deformation of the hole-weakened specimen suggest that the stress-whitening could be attributed to the equivalent visco-plastic strain. By comparing between the simulation analysis and the experimental results, the proposed model can describe the stress whitening phenomenon with good accuracy.展开更多
Dynamic mechanical analysis was used to study the mechanical properties and microstructureof crazes in polystyrene produced in air or in methanol at different temperatures. A new loss peakwas found at about 82℃,which...Dynamic mechanical analysis was used to study the mechanical properties and microstructureof crazes in polystyrene produced in air or in methanol at different temperatures. A new loss peakwas found at about 82℃,which is assigned to glass transition peak of craze fibrils. The decreaseof glass transition temperature of polymer in craze fibrils is due to the high values of surface tovolume ratio. The glass transition temperature ratio of craze fibrils to bulk material （T;/Tg） hasbeen expressed as a function of the fibrils diameter （d）. From T;of craze fibrils,the value of fibrildiameter can be calculated. Annealing the crazed specimen at room temperature makes the fibrilsplastically deform and cause the fibrils to thin slightly,whereas annealing the crazed specimen atthe temperature near T;of the craze fibrils makes the fibrils bundle together.展开更多
Pluta polarizing interference microscope was used to follow the crazing that occur on the surface of stretched polypropylene fibres at different drawing conditions. The samples were stretched until crazing initiated, ...Pluta polarizing interference microscope was used to follow the crazing that occur on the surface of stretched polypropylene fibres at different drawing conditions. The samples were stretched until crazing initiated, and then craze propagation was monitored as a function of drawing speed and test temperature. The effect of craze dimension on their propagation velocity was taken into account. Three-dimensional birefringence profile for crazed polypropylene fibre has been demonstrated to investigate the birefringence of crazed fibre at different test times for fixed drawing speed value. Also the mean birefringence values of crazed polypropylene fibres were calculated and the results showed that, these values increased with the areal craze density. Video images were used to calculate the craze velocity. Optical micrographs and microinterferograms were presented for demonstrations.展开更多
“Have you learned any Chinese today?”has become a“top searched item”worldwide.With the rapid rise of China’s international status and its continuing endeavor to open up to the outside world,Chinese language,which...“Have you learned any Chinese today?”has become a“top searched item”worldwide.With the rapid rise of China’s international status and its continuing endeavor to open up to the outside world,Chinese language,which is imbued with profound Chinese cultural connotations,has come into the global spotlight,and become an important language for international cultural exchanges.展开更多
In recent years, more and more people choose to become civil servants for stability of the work and respect of the society. Civil servants not only have a better treatment, but also a higher social status. However, th...In recent years, more and more people choose to become civil servants for stability of the work and respect of the society. Civil servants not only have a better treatment, but also a higher social status. However, the condition is not true in England. This thesis will demonstrate the current condition of ＂Government Office Worker Craze＂, meanwhile, analyze the reasons of this phenomenon by comparing with England. The thesis will firstly display the advantages and disadvantages of this phenomenon; then demonstrate traditional understanding of the two countries separately to find out common characters; the reason of ＂Government Office Worker Craze ＂ in China by exploring the historical cultures; finally, the thesis shows intersections between the two countries and give proper suggestions.展开更多
正At 19 o'clock, October 11th, Beijing time, the Swedish Academy awarded the 2012 Nobel Prize for Literature to the Chinese writer Mo Yan. Within several hours, Mo Yan's works were struck by the "Nobel ef...正At 19 o'clock, October 11th, Beijing time, the Swedish Academy awarded the 2012 Nobel Prize for Literature to the Chinese writer Mo Yan. Within several hours, Mo Yan's works were struck by the "Nobel effect", sales shooting up in both bookstores and online marts. Some websites also jumped on the bandwagon and put up a reservation service for the new editions.展开更多
基金Project(51275185)supported by the National Natural Science Foundation of China
文摘An elasto-visco-plastic constitutive model incorporating the craze damage behavior was developed for the polypropylene(PP), by using the plastic failure model applied for the concrete, to capture the craze yielding and stress-whitening phenomena. In addition, the developed constitutive model was implemented into finite element codes in Abaqus to simulate the tensile deformation. The standard uniaxial tensile tests were carried out. The stress-strain curves from the uniaxial tensile tests show that the stress keeps decreasing after yielding and the yield stress rises with the increasing of the strain rate. It is worth noting that the craze damage is more visible with higher strain rate. The stress-whitening can be seen clearly around the fracture. The uniaxial tensile tests using specially designed specimen with circular holes weakening were performed for the validation of the developed model. The simulation results of the tensile deformation of the hole-weakened specimen suggest that the stress-whitening could be attributed to the equivalent visco-plastic strain. By comparing between the simulation analysis and the experimental results, the proposed model can describe the stress whitening phenomenon with good accuracy.
文摘Dynamic mechanical analysis was used to study the mechanical properties and microstructureof crazes in polystyrene produced in air or in methanol at different temperatures. A new loss peakwas found at about 82℃,which is assigned to glass transition peak of craze fibrils. The decreaseof glass transition temperature of polymer in craze fibrils is due to the high values of surface tovolume ratio. The glass transition temperature ratio of craze fibrils to bulk material （T;/Tg） hasbeen expressed as a function of the fibrils diameter （d）. From T;of craze fibrils,the value of fibrildiameter can be calculated. Annealing the crazed specimen at room temperature makes the fibrilsplastically deform and cause the fibrils to thin slightly,whereas annealing the crazed specimen atthe temperature near T;of the craze fibrils makes the fibrils bundle together.
文摘Pluta polarizing interference microscope was used to follow the crazing that occur on the surface of stretched polypropylene fibres at different drawing conditions. The samples were stretched until crazing initiated, and then craze propagation was monitored as a function of drawing speed and test temperature. The effect of craze dimension on their propagation velocity was taken into account. Three-dimensional birefringence profile for crazed polypropylene fibre has been demonstrated to investigate the birefringence of crazed fibre at different test times for fixed drawing speed value. Also the mean birefringence values of crazed polypropylene fibres were calculated and the results showed that, these values increased with the areal craze density. Video images were used to calculate the craze velocity. Optical micrographs and microinterferograms were presented for demonstrations.
文摘“Have you learned any Chinese today?”has become a“top searched item”worldwide.With the rapid rise of China’s international status and its continuing endeavor to open up to the outside world,Chinese language,which is imbued with profound Chinese cultural connotations,has come into the global spotlight,and become an important language for international cultural exchanges.
文摘In recent years, more and more people choose to become civil servants for stability of the work and respect of the society. Civil servants not only have a better treatment, but also a higher social status. However, the condition is not true in England. This thesis will demonstrate the current condition of ＂Government Office Worker Craze＂, meanwhile, analyze the reasons of this phenomenon by comparing with England. The thesis will firstly display the advantages and disadvantages of this phenomenon; then demonstrate traditional understanding of the two countries separately to find out common characters; the reason of ＂Government Office Worker Craze ＂ in China by exploring the historical cultures; finally, the thesis shows intersections between the two countries and give proper suggestions.
文摘正At 19 o'clock, October 11th, Beijing time, the Swedish Academy awarded the 2012 Nobel Prize for Literature to the Chinese writer Mo Yan. Within several hours, Mo Yan's works were struck by the "Nobel effect", sales shooting up in both bookstores and online marts. Some websites also jumped on the bandwagon and put up a reservation service for the new editions.
