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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of polymer research 2 (1995), S. 163-170 
    ISSN: 1572-8935
    Keywords: Polyurethane/Urea ; Reaction injection molding ; Impact fracture ; Fracture mechanisms ; Charpy test ; Double-notch four-point-bend
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The impact fracture behavior of commercially available reaction injection molding (RIM) polyurethane/urea (PUR) systems was investigated using a novel double-notch four-point-bend charpy impact (DN-4PB-CI) test, followed by microscopy investigations. It is found that the PUU matrix is capable of large scale plastic deformation under mode-I DN-4PB-CI fracture. However, when mica filler is added, the PUU matrix begins to fail in a brittle manner. No sign of matrix plastic flow is observed. Furthermore, since mica filler is flake-like in shape, the orientation of mica, which can be strongly influenced by the processing condition as well as processing direction, appears to affect the Charpy impact fracture toughness of the mica-filled PUU system. The present work intends to give the first investigation of its kind on fracture mechanisms study of the PUU-RIM systmes under impact conditions. Approaches for making impact damage-tolerant PUU-RIM systems are discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of polymer research 1 (1994), S. 205-209 
    ISSN: 1572-8935
    Keywords: Chlor-alkali membrane ; Fatigue fracture behavior ; Fracture mechanics ; da/dN vs. ΔK
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The fatigue fracture behavior of chlor-alkali monolayer membranes is investigated under a condition similar to the membrane electrolysis cell service environment, i.e., at 86°C in brine solution. The linear elastic fracture mechanics (LEFM) approach, i.e., da/dN vs. AK, is implemented in this study. It is found that the fatigue crack propagation behavior of the chlor-alkali membranes can be successfully characterized via the LEFM technique. The fatigue fracture surfaces of the membranes are also investigated using stereo-optical microscopy and are found to show typical fatigue striation patterns. Detailed experimental procedures for preparing and testing of the membranes are presented.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 28 (1993), S. 2975-2980 
    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 double-notch four-point-bend technique (DN-4PB) is developed to study the fracture mechanisms of multiphase polymers. This technique is found to be effective for an unambiguous determination of the fracture mechanisms and the sequence of toughening events of polymer alloys when fracture occurs. The DN-4PB technique is also found to be especially useful for situations where the quantity of the test material is limited and the testing rate is high. The present study demonstrates the usefulness of the DN-4PB technique in a variety of polymeric systems and testing conditions. Requirements for which the DN-4PB technique becomes useful are also addressed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 28 (1993), S. 6381-6391 
    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 fracture behaviour of two toughened epoxy composite systems was investigated using various microscopy techniques. The Mode I delamination fracture toughness,G IC, Mode II delamination fracture toughness;G IIC, and compression after impact (CAI) strength of these model composite systems were also measured. Under Mode I fracture, it was found that these composites exhibit nearly identical toughening mechanisms to those of the rubber-modified neat resins. The composites differ primarily in having smaller damage zones than the neat resin equivalents. Under Mode II fracture, the typical hackles were found to initiate from inside the resin-rich interlaminar region due to the presence of the toughener particles. The CAI strength, based on the present study as well as the work conducted by others, appeared to be related to, but not necessarily strongly dependent on, the interlaminarG IC andG IIC, the thickness of the interlaminar resin-rich region, and the type of the interlaminar toughener particles. Approaches for improving theG IC,G IIC, and CAI strength of high-performance toughened composites are discussed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 12 (1993), S. 1463-1466 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1435-1536
    Keywords: Rubber modification ; low crosslink density highT g epoxy ; toughening mechanisms ; double-notch four-point-bend ; fatigue fracture
    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 fracture behavior of a core-shell rubber (CSR) modified cross-linkable epoxy thermoplastic (CET) system, which exhibits high rigidity, highT g, and low crosslink density characteristics, is examined. The toughening mechanisms in this modified CET system are found to be cavitation of the CSR particles, followed by formation of extended shear banding around the advancing crack. With an addition of only 5 wt.% CSR, the modified CET possesses a greater than five-fold increase in fracture toughness (G IC) as well as greatly improved fatigue crack propagation resistance properties, with respect to those of the neat resin equivalents. The fracture mechanisms observed under static loading and under fatigue cyclic loading are compared and discussed.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 274 (1996), S. 342-349 
    ISSN: 1435-1536
    Keywords: Rigid-rigid polymer toughening concept ; high performance epoxy ; toughening mechanisms ; rigid core-shell particle ; microcracking
    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 fracture mechanisms of a high performance epoxy system modified with two types of preformed rigid core-shell particles (RCSP) were investigated. The use of the preformed RCSP anables the control of the dispersion of the toughener phase in the epoxy, which, in turn, allows the mechanical properties of the modified epoxy to be optimized. The toughening effect via the RCSP modification is found to be as good as that via the core-shell rubber modification. The moduli andT g of these RCSP-modified epoxies are virtually unaltered via the RCSP modification, when compared with the neat epoxy resin equivalent. The toughening mechanisms in these toughened systems appear to be predominantly crack deflection, crack bifurcation, and microcracking. Approaches for effective toughening of high performance polymers via rigid polymers are discussed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 26 (1991), S. 3449-3456 
    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 Toughening mechanisms of a polyamide 6,6/polyphenylene oxide alloy containing an elastomer tested under a slow rate, an impact rate, and a low temperature have been investigated using various microscopy techniques. It is found that the toughening mechanisms of the alloy may change from crazing/shear yielding, to crack bridging/crazing, and to transparticle failure, depending on the testing conditions. Except for the low temperature high strain rate testing condition and in the plane stress region of the crack, the crazing mechanism has been observed in all the conditions we studied. When the testing rate is high, the shear yielding mechanism is suppressed; multiple crazing and particle bridging mechanisms appear to dominate.
    Type of Medium: Electronic Resource
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  • 9
    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 mechanical behaviours of unoriented, poured resin castings based on formulated blends containing the diglycidyl ether of 4,4′-dihydroxy-α-methylstilbene monomer are studied. It is found that the mechanical and fracture behaviours of these liquid crystalline epoxy (LCE) blends vary significantly. In general, the LCE blends possess much higher fracture toughness and fatigue crack resistance than conventional epoxy resins. At low temperatures (−40°C), the KIC values of the LCE blends are slightly higher than those measured at room temperature. The common fracture mechanisms observed in the ductile LCE blends are crack segmentation, crack branching, crack bridging and crack blunting. The fracture surfaces of the tougher LCE blends only exhibit limited ductile drawing (furrow pattern) at the slow crack growth region; no signs of shear lips on the edges of the starter crack region are observed. The optical microscopy and transmission electron microscopy work suggests that orientation and/or transformation toughening may be the source for such high fracture toughness of the LCE blends. The possible cause(s) of the unusual fracture behaviour of the LCEs is discussed. Approaches for making high performance LCE blends are also addressed.
    Type of Medium: Electronic Resource
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  • 10
    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 fracture behaviours of the pour-cast, unoriented diglycidyl ether of 4,4′-dihydroxy-α-methylstilbene/sulphanilamide liquid crystalline epoxies (LCE) cured at various temperature steps are investigated. It is found that, depending on how the LCE is cured, the liquid crystalline (LC) domain size varies dramatically. These, in turn, affect how the LCEs fracture. The operative toughening mechanisms in the toughest LCE are studied in detail and found to include the formation of numerous segmented, unlinked microcracks in front of the main crack. When the crack opens up, the matrix material between the segmented microcracks acts as a bridge between the opening crack planes. Furthermore, crack bifurcation appears to take place when the segmented cracks are eventually linked with the main crack. This entire fracture process accounts for the high fracture toughness (GIC=580 J m-2) of this particular LCE with respect to conventional epoxies (GIC=180 J m-2). The relationship between the LCE morphology and the corresponding fracture mechanisms is discussed.
    Type of Medium: Electronic Resource
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