Shear banding in strained semicrystalline polyamide 6 films as revealed by atomic force microscopy: Role of the amorphous phase

Atomic force microscopy (AFM) has been used to visualize the plastic deformation mechanisms that are responsible for the yielding of semicrystalline polymers of low degree of crystallinity (<50%). Indeed, AFM, if operated in suitable conditions, is able to image both the amorphous and the crystalline phases. Polyamide 6 films have been drawn at temperatures T < 160 °C. Postmortem AFM observations show that, at yield, shear bands nucleate and propagate in the amorphous phase. They cross the crystalline lamellae and run over the whole surface of the sample. By crossing the lamellae, they form nanoblocks of uniform size. Neither the size of the nanoblocks nor the angle between the tensile axis and the shear bands can be explained in terms of crystal plasticity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 687–701, 2004     

草间小黑蛛的核型

报道了草间小黑蛛的核型,包括染色体数目、形态结构和性染色体组成．材料采自石家庄市郊区．细胞学数据主要来自对混合胚胎细胞有丝分裂中期的观察．实验结果表明：草间小黑蛛细胞的染色体数是雄体细胞２ｎ＝２４,雌体细胞２ｎ＝２６,性别决定机制为Ｘ１Ｘ２Ｏ系统．Ｘ染色体为全部染色体中最小的和次最小的一个（对）．对其Ｃ－显带标本观察表明,所有染色体均为端或亚端着丝粒染色体,每个染色体都有其特点．     

Ti6Al4V表面HAP/聚乙酸乙烯酯杂化陶瓷膜层的电化学合成

应用电化学共沉积技术制备HAP／聚乙酸乙烯酯杂化陶瓷膜层，XRD、XPS、SEM表征结果指出，由电化学共沉积制备的复合膜层中无机相以HAP为主，有机物含量达4％。HAP陶瓷膜层的表面结构形貌因引入有机高聚物而发生显著改变。力学拉伸实验表明HAP/聚合物陶瓷膜层与金属基体的结合力比单一HAP相有明显提高。     

煤层顶板应力的一种理论计算方法

运用弹性力学复变函数求解带状无限长板的分析方法,给出了适用于煤层顶板应力的解析表达式,利用该式,通过数值积分可以比较方便地得到顶板的应力分布．     

Shear banding in semidilute entangled polymer solutions

Shear banding in semidilute polymer solutions and other soft materials is one of the most intensely debated topics in current rheology. By means of rheo-optical experiments, physical modeling, and numerical simulations, researchers have started to develop a more thorough understanding of this flow instability within the past few years. Nevertheless, much effort is still required to identify the exact microscopic mechanisms leading to shear band formation and to clarify whether the phenomenon is universal for polymers. For this purpose, basic rheological characteristics, such as the appearance of a stress overshoot during start-up of a simple shear flow, have to be revisited and better related to the dynamics of the polymeric network.     

Shear banding in reaction-diffusion models

Shear banding occurs in the flow of complex fluids: various types of shear thinning and shear thickening micelle solutions and liquid crystals. In order to cope with the strongly inhomogeneous interface between the bands, constitutive models used in standard rheology must be supplemented by non-local terms. This leads rather generally to non-linear partial differential equations of the reaction-diffusion type. We use this formalism in order to explain some observed experimental features and as a guide for future research in this field. Received: 17 May 1999/Accepted: 3 August 1999     

Analysis of banding problem in multiple beam scanning system of laser printer

In the slant scanning method of multiple beams a misalignment of the slant angle causes a beam spacing error and pitch irregularities of scan lines called “banding”. This paper evaluates the pitch irregularities and tries to clarify the allowable beam spacing error. The following results are obtained: (1) The maximum spacing error of print lines is proportional to m/(dpi), where m is the number of multiple beams and dpi print dot density. (2) The noticeable limit of periodic variations of print density at low spatial frequency was presumed to be a visibility between 1 and 2% in experiments. (3) The allowable beam spacing error was calculated introducing the human eye spatial frequency response. (4) The banding simulation experiments by laser recording on the photographic paper on the XY stage showed good coincidence with the theoretical evaluations.     

爆炸金属管绝热剪切断裂的细观研究

介绍了正火及调质后45号钢、TC4钛合金和钨合金四种金属管在内部高能炸药加载下,破片宏观剪切断口的细观断裂形貌;观察到这四种金属管不同的细观剪切断裂机制。根据金相研究及物理分析表明,金属材料的热导率越低,晶粒越细,则越容易产生绝热剪切,生成相变带。     

Kink band propagation in layered structures

Confined layered structures in layer-parallel compression exhibit kink band deformation that has an associated severe initial instability. However, once the first kink band forms the system restabilizes and the bands then propagate in two mechanisms: band broadening and band progression. Previous work on triggering the initial instability and band broadening is now extended to include band progression. A new model for this propagation mechanism that successfully accounts for the modulating restabilizing response is presented and quantitative comparisons with the physical experiments yield excellent results.