SEM OBSERVATION OF THE CRAZING FOR POLYPHENYLQUINOXALINE FILMS DURING IN SITU STRETCHING

The crazing of polyphenylquinoxaline (PPQ-E) films during in situ stretching has been observed by SEM. The crazing phenomena and craze morphology of PPQ-E films were interpreted. The strain values at critical crazing and yielding and the craze stability of PPQ-E samples depend on the thermal-dealing condition for the samples. From the point of view of cohesional entanglements and energy absorbed by samples, the experiment results were explained.

A METHOD TO QUANTIFY CRAZING DEFORMATION BY TENSILE TESTS FOR POLYSTYRENE/POLYOLEFIN ELASTOMER IMMISCIBLE BLENDS

A method to quantify crazing deformations by tensile tests for polystyrene （PS） and polyolefin elastomer （POE） blends was investigated. The toughness of PS/POE blends, reflected by the Charpy impact strength, increased with the content of POE. SEM micrographs showed the poor compatibility between PS and POE. In simple tensile tests, it is very easy to achieve the ratio of crazing deformation, i.e. K by measuring the size changes of samples. The K values decreased with increasing the content of POE, and the deformations of PS/POE blends were dominated by crazing. The plots of the change of volume （△V） against longitudinal variation （△I） showed a linear relationship, and the slope of lines decreased with the content of POE. Measuring samples at the tensile velocities of 5 mm/min, 50 mm/min, and 500 mm/min respectively, the K values kept unchanged for each PS/POE blends.

CRAZING IN BLENDS OF SAN RANDOM COPOLYMER AND SAN-g-PBd GRAFT COPOLYMER

Glassy polymers can be substantially toughened by incorporation of rubber particles at a certain volume percentage. The toughness is related to crazing initiated by rubber particles. The blend of styrene-acrylonitrile random copolymer (abbreviated as SAN)and SAN grafted on polybutadiene (abbreviated as SAN-g-PBd; the SAN chain of SAN-g-PBd abbreviated as g-SAN)is one of the most important copolymer alloys. Transmission Electron Microscope (TEM) was employed to determine the relationship between the morphology and crazing of the blend.

Controlled Wettability of Polymers via Environmental Crazing

This work highlights the benefits of environmental crazing for the control over the hydrophilic-lipophilic balance of glassy amorphous and semicrystalline polymers:poly(ethylene terephthalate)(PET)and biodegradable polycaprolactone(PCL).Task-oriented encapsulation of diverse commercial and natural hydrophilic(polyethyleneoxide,polyvinylpyrrolidone,gelatin)and hydrophobic guest additives(perfluoroorgano siloxanes,water-repellent impregnation)into mesoporous host polymer(PET,PCL)matrixes allows targeted control over the wettability of the resultant nanocomposite materials.Depending on the nature of the guest additive,the properties of the modified polymers can be varied from hydrophilic to hydrophobic:contact angle(CA)of PET can be adjusted from 47_(⊥)/38_(||)to 130_(⊥)/117_(||)°(for initial PET,CA=82°)and CA of PCL from 40°to 114°(for initial PCL CA=75°).The unique benefits of environmental crazing for structural modification are related to the universal character of this approach which can be applied to a broad range of polymers and allows preparation of diverse high-performance materials with tunable hydrophilic-lipophilic balance.

Effect of the Nanoparticle Functionalization on the Cavitation and Crazing Process in the Polymer Nanocomposites

The nanoparticle(NP) functionalization is an effective method for enhancing their compatibility with polymer which can influence the fracture property of the polymer nanocomposites(PNCs). This work aims to further understand the cavitation and crazing process, hoping to uncover the fracture mechanism on the molecular level. By adopting a coarse-grained molecular dynamics simulation, the fracture energy of PNCs first increases and then decreases with increasing the NP functionalization degree α while it shows a continuous increase with increasing the interaction εpA between polymer and modified beads. The bond orientation degree is first characterized which is referred to as the elongation. Meanwhile, the stress by polymer chains is gradually reduced with increasing the α or the εpA while that by NPs is enhanced.Furthermore, the percentage of stress by polymer chains first increases and then decreases with increasing the strain while that by NPs shows a contrast trend. Moreover, the number of voids is quantified which first increases and then decreases with increasing the strain which reflects their nucleation and coalescence process. The voids prefer to generate from the polymer-NP interface to the polymer matrix with increasing α o r εpA.As a result, the number of voids first increases and then decreases with increasing α while it continuously declines with the εpA. In summary, our work provides a clear understanding on how the NP functionalization influences the cavitation and crazing process during the fracture process.

An elasto-visco-plastic constitutive model of polypropylene incorporating craze damage behavior and its validation

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.

Failure Mechanism of Laminated Damping Steel Sheet during Tensile-Shearing

The tensile-shear failure zone of the laminated damping steel sheet was investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. It is found that there exists cohesive failure in polymer sandwich and sub-boundary failure between the steel sheet and the polymer. The sub-boundary layer is dominantly polymer material. The tensile-shear failure of the laminated damping steel sheet is a process during which the crazes form, grow up and merge into cracks.

DYNAMIC MECHANICAL RESPONSE OF CRAZES IN POLYSTYRENE

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.

Chinese Learning Craze

“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.

Online Investigation of Optical Properties and Craze Propagation of Drawn Polypropylene Fiber by Using Interferometric Image Analysis

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.

Analyses between Chinese and England Culture through＂Government Office Worker Craze＂

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.

The Nobel Literature Prize Sparks a Mo Yan Craze

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.

Stock Craze Creates Stir in Lhasa

ＳｔｏｃｋＣｒａｚｅＣｒｅａｔｅｓＳｔｉｒｉｎＬｈａｓａ￥ＤＯＪＥＺＨＡＭＤＵＡｆｔｅｒｒｅｃｅｉｖｉｎｇｔｈｅａｐｐｒｏｖａｌａｎｄｓｕｐｐｏｒｔｏｆｔｈｅｐｅｏｐｌｅ＇ｓｇｏｖｅｒｎｍｅｎｔｏｆｔｈｅＴｉｂｅｔＡｕｔｏｎｏｍｏｕｓＲｅｇｉｏｎ，ｔ...

Damage Studies of Brittle-Ductile Transition in PP EPDM Blends

Damage zones of brittle-ductile (B-D) transition in PP/EPDM blends are studied in this paper. The contribution of crazing and shear yielding zones in damage zones to energy dissipation of blends was measured with computer image analysis (CIA) and the transition of shear yielding zone (A_(sh)) with rubber volume fraction (V_f) was also manipulated. Results showed that the B-D transition of impact strength of blends corresponded to the fracture mechanism in PP/EPDM blends, from matrix crazing to matrix shear yielding. In addition, two new parameters, density of energy dissipation for crazing zone (F_(cz)) and for shear yielding zone (F_(sh)), are first obtained in this paper. The value of F_(sh) is about four times larger than that of F_(cz) for PP/EPDM blends, which confirmed that the matrix shear yielding is a more effective way of energy dissipation in blends.

Is the Game of Flattery Compliments Praiseworthy?

There is a new craze among young people—flocking to so-called kuakuaqun, or flattery groups, on the Internet, where they praise one an other, at times even paying to be exaggeratedly complimented.

Cockfighting Craze Lives on in Colombian Villages

文章真精彩！它把我们带到了南美洲西北部的哥伦比亚,在那里观赏了一次斗鸡竞赛。文章可读,原因有四: 描写精致:The referee rings a bell and the two angry birds erplode into thering,colliding(碰撞;抵触)recklessly(鲁莽地;不顾一切地)and exchangingmidair(半空中)kicks with the curved,razor-sharp spikes fastened to their legs。(三个动词可以玩味:explode/collide/exchange) 历史回顾:The stranger,said Don Pedro,tied his mule to a tree,and withoutsaying a word to the wide-eyed locals,challenged the foreman(领班;工头)of theUnited Fruit Company to a cockfight。 科学分析:The roosters fight for the hen。They can live together in peace but ifyou release a hen not a single one of them will remain alive。 冷静观察:At the pit,class divisions melt。Workers pit their roosters againstthose of landowners,greeting each other with handshakes before the fight。】