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  • Artikel: DFG Deutsche Nationallizenzen  (3)
  • Hopkinson bar  (2)
  • 72.40  (1)
  • Epon 828  (1)
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  • Artikel: DFG Deutsche Nationallizenzen  (3)
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  • 1
    ISSN: 1432-0630
    Schlagwort(e): 72.40
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Deep-level transient spectroscopy and thermally stimulated capacitance measurements were used to investigate the properties of deep traps in Si-dopedn-Al x Ga1−xAl layers grown by molecular beam epitaxy. Two electron traps at electron emission activation energies of 0.44 and 0.57 eV have been detected. Both traps were studied in detail and found to be the origin of the persistent-photo-conductivity phenomenon in this material. The nature of both traps is the same as of the DX center in liquid phase epitaxial material reported by Lang et al. The electron capture cross-sections areσ n 1 =σ n 2=8.3×10−22cm2 atT=205K. Activation energies ofE σ 1= 0.33eV andE σ 2=0.37eV at temperatures higher than 125 K were determined by DLTS measurements and by direct measurements of the capture transient. In order to allow for the variation of the free-electron concentration during the capture process, a new method for the evaluation of the electron capture crosssection was developed.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Experimental mechanics 40 (2000), S. 1-6 
    ISSN: 1741-2765
    Schlagwort(e): Soft materials ; Hopkinson bar ; quartz crystal ; dynamic behavior ; high strain rate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A dynamic experimental technique that is three orders of magnitude as sensitive in stress measurement as a conventional split Hopkinson pressure bar (SHPB) has been developed. Experimental results show that this new method is effective and reliable for determining the dynamic compressive stress-strain responses of materials with low mechanical impedance and low compressive strengths, such as elastomeric materials and foams at high strain rates. The technique is based on a conventional SHPB. Instead of a surface strain gage mounted on the transmission bar, a piezoelectric force transducer was embedded in the middle of the transmission bar of a high-strength aluminum alloy to directly measure the weakly transmitted force profile from a soft specimen. In addition, a pulse-shape technique was used for increasing the rise time of the incident pulse to ensure stress equilibrium and homogeneous deformation in the low-impedance and low-strength specimen.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of time-dependent materials 2 (1998), S. 103-111 
    ISSN: 1573-2738
    Schlagwort(e): dynamic response ; Epon 828 ; T-403 ; epoxy ; high-strain rate test ; Hopkinson bar ; material modeling ; strain-rate effects
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The uniaxial compressive mechanical response of an epoxy, Epon 828/T-403, was experimentally, measured over a strain-rate range of 1.1 × 10-4 to 5.2 × 103 s-1. A modified split Hopkinson pressure bar was employed to apply dynamic compressive loading over a very short time of ∼ 0.2 millisecond, whereas an MTS was used to conduct quasi-static experiments at a duration of 0.2 to 2,000 seconds to determine strain-rate sensitivity. The experimental results show that the compressive strength of the epoxy increases with increasing strain rate until adiabatic heating offsets the strain-rate hardening. A constitutive model based on the Johnson–Cook model was constructed to describe the stress-strain behavior of the epoxy at the strain rates tested. A Ludwig equation was modified to model the stress-strain behavior at a reference strain rate, which included elastic deformation, a yield-like peak, and a strain-softening region. A hyperbolic tangent function provided a good description of the strain-rate effect. The material constants in this proposed model were determined using the experimental results.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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