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  • 1
    Electronic Resource
    Electronic Resource
    Electron microscopic investigations of initiation and growth of crazes in polystyrene (1986)
    Springer
    Colloid & polymer science 264 (1986), S. 522-532 
    Details
    ISSN: 1435-1536
    Keywords: Polystyrene ; electron microscopy ; craze structure ; craze nuclei ; growth of crazes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The crazes in polystyrene (PS) were investigated by using a high voltage electron microscope (HVEM, accelerating voltage of 1000 kV). The early stages of the formation and the growth of the crazes were studied in detail. The smallest deformation structures visible are weak domains or microvoids with diameters of 10–15 nm and distances of a few 10 nm between them. They act as craze nuclei and are located in narrow, long “pre-craze” zones. Conclusions are drawn on the processes of initiation and propagation of the crazes; both are based on molecular heterogeneities and on an increasing heterogeneity of deformation. In particular, the transformation of the “closed cell structure” of the voids into the “open cell structure” of the craze fibrils is described. Growth of crazes in thickness definitely occurs by drawing new polymeric material from the craze boundaries into the craze.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01422006
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  • 2
    Electronic Resource
    Electronic Resource
    Electron microscopic investigations of the structure of crazes in polystyrene (1985)
    Springer
    Colloid & polymer science 263 (1985), S. 462-474 
    Details
    ISSN: 1435-1536
    Keywords: Craze structure ; craze elongation ; deformation ; fracture ; polystyrene ; electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The structures of the deformation zones in polystyrene (PS), the so-called crazes, were investigated in detail by electron microscopy. Compared with the conventional transmission electron microscope (TEM) the usage of a high voltage electron microscope (HVEM) with an accelerating voltage of 1000 kV has several advantages: it renders possible the investigation of relatively thick specimens (thicknesses up to and exceeding 5 μm), the performance ofin situ deformation tests, and the application of a special tensile device, producing a defined uniaxial straining state. First, general features of the crazes in PS (pressure-molded samples, solution-cast films) are described, and second, the crazes are precisely characterized by quantitatively measuring the electron micrographs of the crazes. Shape, thickness profile, minimum size, interior structure, and elongation of the crazes are discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01458336
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  • 3
    Electronic Resource
    Electronic Resource
    Discussion of craze formation and growth in amorphous polymers in terms of the multiplicity of glass transition at low temperatures (1989)
    Springer
    Colloid & polymer science 267 (1989), S. 557-567 
    Details
    ISSN: 1435-1536
    Keywords: Amorphouspolymers ; crazeformation ; crazefibrilstructure ; crack ; multiplicity of glasstransition ; confinedflow ; negativepressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A craze, the typical deformation zone in an amorphous polymer, can be divided into a precraze and a proper craze. A better understanding of the two corresponding formation processes is possible in terms of glass transition multiplicity. The precraze is associated with the molecular mobility in the confined flow zone, which is part of the main transition. The proper craze corresponds to the mobility in the flow transition zone (terminal zone for shear). A negative pressure generated by nonuniaxial stress is considered to be important for the maintainance of the molecular mobility in these zones belowT g . The behavior of the zones at negative pressure and low temperatures T〈Tg is considered using a pressure-temperature diagram. The fibril structure of crazes is discussed by a defect diffusion model for the proper glass transition; it is correlated with the sequential physical aging of the corresponding frozen structural defects. Typical mode lengths of the molecular mobilities in the different zones are compared with typical craze parameters. The structure of the craze material is considered to result from confined flow processes which cannot percolate because in the main transition the flow is confined by entanglements, and in the flow transition zone the flow is stopped by releasing the negative pressure due to crack propagation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01410431
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  • 4
    Electronic Resource
    Electronic Resource
    Study of the toughening mechanism of crazing in rubber modified thermoplastics (1992)
    Springer
    Colloid & polymer science 270 (1992), S. 972-981 
    Details
    ISSN: 1435-1536
    Keywords: Crazing ; crazedimensions ; electronmicroscopy ; opticalinterferometry ; rubbertoughening ; thermoplastics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Single crazes in transparent glassy thermoplastics are measured by means of optical interferometry. Applying numerical or analytical methods to measured creaze shapes, also their micromechanics has been evaluated. These data can be transferred to rubber-modified species of the respective thermoplastics to predict craze-governed toughening. Such predictions can be verified by comparison with results of electron microscopic investigations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00655966
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  • 5
    Electronic Resource
    Electronic Resource
    Correlations between molecular weight, morphology and micromechanical deformation processes of polyethylenes (1992)
    Springer
    Colloid & polymer science 270 (1992), S. 627-638 
    Details
    ISSN: 1435-1536
    Keywords: Semicrystalline polymers ; polyethylene ; molecular weight ; morphology ; uniaxial tension ; deformation processes ; locally heterogeneous deformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of molecular weight on morphology and micromechanical deformation processes of polyethylene has been studied by conventional transmission and high-voltage electron microscopy. Fractions with very narrow molecular weight distributions and commercial samples of high-density polyethylene in the range of molecular weight 104 to 1.6·106 have been studied. With increasing molecular weight there is a change in the morphology from sheaf-like structures and banded spherulites, to small bundles of parallel lamellae or randomly distributed lamellae. For molecular weights greater than 105, the thickness of the lamellae increases more slowly than the thickness of the interlamellar, amorphous layers. During uniaxial tension the apparently homogeneous transformation to a c-texture consists, on a microscopic scale, of different deformation steps, including twisting of the lamellae and the breaking up of the lamellae into shorter pieces or microblocks. Often, small regions are visible with a locally larger elongation than in the surrounding regions (locally heterogeneous deformation). The deformation steps are changed by modifications of the mobility of the molecules in the amorphous phase, including deformation at different temperatures (from 20° up to 110°C) and annealing below the melting temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00654039
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  • 6
    Electronic Resource
    Electronic Resource
    Crazes in amorphous polymers I. Variety of the structure of crazes and classification of different types of crazes (1989)
    Springer
    Colloid & polymer science 267 (1989), S. 377-388 
    Details
    ISSN: 1435-1536
    Keywords: Amorphous polymers ; craze structure ; craze classification ; electron microscopy ; mechanical behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In investigating 0.5- to 5 Μm-thick deformed samples in a 1000 kV high-voltage electron microscope, the formation and structure of crazes were studied in different amorphous polymers (PS, SAN, PVC, and the highly radiation-sensitive polymers PMMA and PC). Different craze types were found and classified. There are some types of “true crazes” with a fibrillar structure or rather a homogeneous structure, which have to be distinguished from only “craze-like deformation zones”. A peculiarity was found in PMMA which produces a craze type different in structure from the well-known fibrillated crazes typical of PS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01410182
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  • 7
    Electronic Resource
    Electronic Resource
    Comparative study of size and distribution of lamellar thicknesses and long periods in polyethylene with a shish-kebab structure (1996)
    Springer
    Journal of materials science 31 (1996), S. 4199-4206 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This study contains a combined application of three different techniques for the study of injection moulded polyethylene (PE), showing an oriented shish-kebab structure: small angle X-ray scattering (SAXS), low frequency Raman spectroscopy (LAM) and transmission electron microscopy (TEM), A series of linear PEs and molecular weights in the range 51000–478000 has been investigated and two injection temperatures have been used (T m=144 and 210 °C). SAXS patterns from the highly oriented regions show the presence of either one axial long period (L 1) or two (L 1 and L 2) depending on molecular weight (¯M w) and T m. It is shown that L 1 and L 2 increase with ¯M w up to a given critical molecular weight ¯M c. Above ¯M c, L 1 and L 2 remain constant. Raman results qualitatively confirm the existence of two separate distributions of straight-length chain segments for those samples having molecular weights above the critical value. Shorter segments are shown to be more abundant than the longer ones. In the lowest molecular weight sample, results from SAXS, TEM and Raman spectroscopy seem to be consistent with each other, although in some cases a tilted molecular arrangement within the lamellae has to be invoked. On the other hand, in case of the highest molecular weight sample, the length of the short straight-chain segments derived from Raman spectroscopy agrees well with the double periodicity obtained from SAXS. On the contrary, long periods measured from TEM only correspond to the shorter SAXS periodicity. This result is discussed by assuming the occurrence of crystalline bridges among adjacent lamellae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00356439
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  • 8
    Electronic Resource
    Electronic Resource
    Soft matrix fracture surface as a means to reveal the morphology of multi-phase polymer systems (1990)
    Springer
    Journal of materials science 25 (1990), S. 4549-4554 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract To disclose the interior phase structure of soft polymeric materials, a classical procedure exploits the hardening of a material on freezing, usually, in liquid nitrogen. However, there exist some polymer systems, for which the application of the procedure is not suitable due to low differences in the toughness of the individual components in the frozen state. A new procedure of the fracture surface preparation is described, based on a specific property of polymer materials, namely up to a three-decade difference in the Young modulus below and above the glass transition temperature. According the the procedure, the fracture surface is prepared at a temperature at which the matrix is soft (sufficiently high above the glass transition temperature) and the inclusions are hard (below the glass transition temperature) at the same time. Especially at a low volume fraction of the hard dispersed phase a relatively smooth and distinct fracture surface is obtained, the interpretation of which presents no problems. The method has been successfully tested for several systems, such as, silicon rubber/hard methacrylate copolymer, EPDM rubber/inorganic filler, EPDM rubber/polypropylene, liquid rubber/epoxy, and ABS/ inorganic filler.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581122
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  • 9
    Electronic Resource
    Electronic Resource
    Correlation between craze formation and mechanical behaviour of amorphous polymers (1990)
    Springer
    Journal of materials science 25 (1990), S. 2321-2334 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The formation, growth and fracture of crazes have been studied for several amorphous polymers (PS, PMMA, SAN, NEC, PC). From bulk polymeric materials 0.5 to 5μm thick sections were prepared and investigated after uniaxial deformation or duringin situ deformation in a 1000 kV high voltage electron microscope (HVEM). The use of the HVEM also allows one to study irradiation-sensitive polymers (PMMA and PC). The size of crazes (length and thickness), the shape (opening angle at the craze tip, craze thickness profile), the thickness of a pre-craze zone, the structure of the material inside the craze (fibrillar or more homogeneous), and the degree of deformation were measured. Correlations have been found between the type and the size of crazes and their mechanical properties, particularly fracture toughness and elongation at break. There are notable differences between unannealed and annealed samples (SAN and PC) as well as in the craze formation and in the fracture toughness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00638022
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  • 10
    Electronic Resource
    Electronic Resource
    Mechanical properties of weakly segregated block copolymers Part IV Influence of chain architecture and miscibility on tensile properties of block copolymers (2000)
    Springer
    Journal of materials science 35 (2000), S. 1257-1268 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Different types of weakly segregated block copolymers are investigated with respect to the influence of chain architecture and miscibility on tensile properties. Poly(styrene-b-butylmethacrylate) diblock copolymers (PS-b-PBMA) as well as poly(butylmethacrylate-b-polystyrene-b-butylmethacrylate) triblock copolymers (PBMA-b-PS-b-PBMA) show synergistic effects on tensile properties. The triblock copolymers show a higher tensile strength and stiffness compared to that of the diblock copolymers. In addition, the triblock copolymers exhibit a larger composition range for which the tensile strength exceeds that of the respective homopolymers. In order to investigate the influence of block miscibility on tensile properties, poly(methylmethacrylate-b-butylmethacrylate) diblock copolymers (PMMA-b-PBMA) are compared with PS-b-PBMA diblock copolymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004757008254
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