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  • Electronic Resource  (5)
  • 2005-2009  (5)
  • 1830-1839
  • 2008  (5)
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  • Electronic Resource  (5)
  • Book  (2)
Years
  • 2005-2009  (5)
  • 1830-1839
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  • 1
    Electronic Resource
    Electronic Resource
    Fracture of Quasi-Brittle Materials like Concrete under Compressive Loading (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Advanced materials research Vol. 41-42 (Apr. 2008), p. 207-214 
    Details
    ISSN: 1662-8985
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Fracture under compression is one of the most commonly studied properties of geomaterialslike concrete and rock, in particular since these materials reach their best performance incompression. The fracture process is however rather complex due to the heterogeneous structures ofsaid materials. Over the years fundemental studies of fracture under compression have led to amuch improved insight in the details of the fracture process depending on the actual composition ofthe material. Fracture can be described by means of a 4-stage fracture model, which included asmost important aspects pre-peak cracking, which is stable and can be arrested by stiffer and strongerelements in the material structure, and post-peak cracking [1]. The latter macroscopic cracks arebasically un-stable and can only be arrested by measures at a structural scale, such as applyingconfining stress or by using positive geometries. The material structure cannot assist in the arrest ofthe large energetic cracks other than locally affecting the crack path. In the paper an overview isgiven of the fracture process in compression. Recently we embarked on studying compressivefracture using a simpler material structure, namely foamed hardened cement paste [2]. Stiffaggregates that are normally included in normal concrete have been left-out; instead a larger thanusual quantity of large pores is brought into the material, even up to 80%. Studying fractureprocesses in this simpler material system ultimately allows for a better understanding of the detailsof the pre-peak cracking process, which is considered more important than the post-peak processsince it defines strength
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/40/transtech_doi~10.4028%252Fwww.scientific.net%252FAMR.41-42.207.pdf
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of Mechanical Milling on the Microstructure and Hydrogen Interaction of Both Mm-Ni and MmNi5-Ni Mixtures (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 570 (Feb. 2008), p. 72-77 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Mechanical milling (MM) and a combination of MM and temperature heating wereused to synthesize the intermetallic MmNi5 and a MmNi5-Ni mixture, respectively. Theprocess evolution with time was analyzed by scanning electron microscopy (SEM) and X-raydiffraction (XRD). SEM was used to characterize size and morphology of particles in order toreveal the governing mechanisms during the milling of each system. X-ray diffraction (XRD)was utilized to determine strain and crystallite size changes introduced by milling. The effectsof integrated milling time on the sorption properties of the MmNi5-Ni mixture were analyzed.Results were correlated to defects introduced into microstructure. A comparison of the finalcharacteristics of alloys obtained in each case is also shown
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/18/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.570.72.pdf
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructure and Mechanical Properties Affecting Crack Growth Behaviour in AA6060 Produced by Equal-Channel Angular Extrusion (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 815-820 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Crack growth in AA6060 after two and eight equal-channel angular extrusions (ECAE),showing a bimodal microstructure and a homogenous ultrafine-grained microstructure, respectively,are compared to the coarse grained counterpart. Furthermore, an optimized condition, obtained bycombining one ECA-extrusion and a subsequent short aging treatment is included. Fatigue crackgrowth behaviour in the near-threshold regime and the region of stable crack growth is investigatedand related to microstructural features such as grain size, grain size distribution, grain boundarycharacteristics and ductility. Micrographs of crack propagation surfaces reveal information on crackpropagation features such as crack path deflection and give an insight to the underlyingmicrostructure. Instrumented Charpy impact tests are performed to investigate crack initiation andpropagation under impact conditions. Due to the recovery of ductility during the post-ECAE heattreatment, the optimized condition shows improved fatigue crack properties and higher energyconsumption in Charpy impact tests, when compared to the as-processed conditions without heattreatment
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.815.pdf
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Ultimate Strength of a Tungsten Heavy Alloy after Severe Plastic Deformation at Quasi-Static and Dynamic Loading (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 405-410 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A tungsten heavy alloy (92%W, Ni-Co matrix) is subjected to severe plastic deformation(SPD) by high pressure torsion (HPT) at room temperature up to equivalent strains of 0.7, 5.3, 10.7and 14.3. The microstructure and the mechanical properties are investigated by cylindricalcompression samples at quasi-static and dynamic loading. The harder spherical W particles arehomogeneously deformed within the softer matrix, becoming ellipsoidal at medium strains andbanded at high strains without shear localization or fracture. Results of quasi-static loading showthat the strength is approaching a limiting value at strains of ~10. At this strain for the matrix a grainsize of ~80 nm and for W a cell size of ~250 nm was observed, suggesting strain concentration onthe matrix. The initial yield stress of 945 MPa for the coarse-grained condition is increased therebyto an ultimate value of 3500 MPa, while a peak stress of ~3600 MPa is reached. Such remarkablystrength has never been reported before for pure W or W-based composites. The strain hardeningcapacity as well as the strain rate sensitivity is reduced drastically, promoting the early formation of(adiabatic) shear bands
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.405.pdf
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Combining Equal-Channel Angular Extrusion (ECAE) and Heat Treatment for Achieving High Strength and Moderate Ductility in an Al-Cu Alloy (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 685-690 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The effect of equal-channel angular extrusion (ECAE) on mechanical properties of anAA2017 produced by powder metallurgy is investigated. Special attention is given to the influenceof heat treatment, processing temperature and backpressure on the workability for achieving highstrength and moderate ductility. This is of special interest, since it is often reported that Al-Cualloys have low ductility and therefore are prone to cracking during severe plastic deformation. It isshown that ECAE at high temperatures (〉220°C) does not necessitate backpressure to ensurehomogeneous deformation but leads to a significant sacrifice in strength due to in-situ precipitation.Thus, most of the extrusions are done at considerably low temperatures. Performing roomtemperature-extrusion is most effective in achieving high strengths but also requires highbackpressures. Due to severe strain hardening during processing, the strength increase is combinedwith a reduction in ductility. Recently it was reported that a post-ECAE aging of pre-ECAE solutiontreated material is effective in enhancing the ductility of aluminium alloys. This approach wassuccessfully transferred to the current alloy. A high-temperature, short-time aging after only oneextrusion, for example, doubles the failure strain to a value of ~13%. Compared to the naturallyaged condition with coarse grains that serves as reference (T4), an increase of 15 % in yield stress(YS) was obtained while retaining the ultimate tensile stress (UTS). Another effective approach isthe combination of a pre-ECAE solution treatment with subsequent under-aging prior to ECAE. It isshown that performing ECAE at medium temperatures (160-180°C) enables a better workability andadditionally gives higher strengths and better ductility compared to the processing in the waterquenched condition. A remarkable YS of 530 MPa and an UTS of 580 MPa combined with amoderate failure strain of 11.6 % were achieved
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.685.pdf
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    Paper (German National Licenses)
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