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  • 1
    Electronic Resource
    Electronic Resource
    An enhanced, acoustic emission-based, single-fiber-composite test (1992)
    Springer
    Journal of nondestructive evaluation 11 (1992), S. 251-261 
    Details
    ISSN: 1573-4862
    Keywords: Acoustic emission ; AE source location ; single-fiber-composite ; fragmentation ; interfacial shear strength ; fiber/matrix interface ; size effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In the single-fiber-composite (SFC) test, a fiber imbedded in a matrix is loaded in tension, resulting in a fragmentation of the fiber. In the conventional version of this test, the final fiber fragmentation length distribution is used with a micro-mechanical model to determine the average fiber/matrix interfacial shear stress. In the enhanced version of this test, one also determines the applied stress at each fiber fracture, and from this, one can evaluate the strength of the fiber at short gage lengths. In our measurement system, we utilize an acoustic emission (AE) technique to detect the fiber fractures and to locate the fiber breaks and so determine both the fiber failure stresses as well as the fiber fragmentation lengths while the test is in progress. Critical to the success of this test is a broadband AE system that utilizes point-like AE sensors, procedures for evaluatingin situ, the wavespeed of the first wave arrival and signal processing techniques for determining the arrival time of this signal as precisely as possible for a broad range of wave shapes. Here we describe the application of such an enhanced SFC test procedure to investigate the failure of a Nicalon™ fiber in an epoxy matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566415
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of fibre/matrix interfacial shear strength by an acoustic emission technique (1991)
    Springer
    Journal of materials science 26 (1991), S. 6631-6638 
    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 application of acoustic emission (AE) measurements to locate the sources of fracture of a single high-strength fibre embedded in an epoxy matrix which is loaded in tension is described. From the micromechanical model and the fragment length distribution, interfacial shear strength values were calculated. The technique is demonstrated for small-diameter glass and graphite fibres as well as for fibres which exhibit fibrillar fracture, such as Kevlar and PBZT. Good agreement is found between the mean fragment length values obtained by optical and AE measurements for glass and graphite fibres. Values obtained for interfacial shear strength by the AE technique are comparable with those obtained using other techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02402656
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Ammonia plasma treatment of ultra-high strength polyethylene fibres for improved adhesion to epoxy resin (1992)
    Springer
    Journal of materials science 27 (1992), S. 4625-4632 
    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 A study of the effect of plasma treatments on the mechanical properties and adhesion of ultra-high strength polyethylene fibres to epoxy resin is reported. Fibres were treated with ammonia plasma under various time and power conditions. The fibre/matrix interfacial shear strength was measured using load and fibre pull-out data obtained in a single-fibre pull-out test. The debonding was optically as well as acoustically monitored. Optical birefringence patterns were visible at the fibre debond region. Acoustic emission signals generated from debonding and stick-slip processes were also detected. A more than four-fold increase in the interfacial shear strength was achieved by plasma treating the fibres at the discharging condition of 30 W and 0.5 torr for 1 min. The birefringence patterns showed, qualitatively, that the shear in the matrix around the fibres increased for treated fibres and extended further into the matrix material. Surface topography of the pulled out fibres showed that the failure mode was unchanged by the treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165997
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    On optimal modeling of systems (1973)
    Springer
    Journal of optimization theory and applications 11 (1973), S. 68-83 
    Details
    ISSN: 1573-2878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A procedure, based on Sard's generalized spline, for modeling a linear system by an optimal finite-dimensional system is presented. Error bounds are given and the results are illustrated by means of two examples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00934292
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  • 5
    Electronic Resource
    Electronic Resource
    Strength distribution of Carborundum polycrystalline SiC fibres as derived from the single-fibre-composite test (1994)
    Springer
    Journal of materials science 29 (1994), S. 4718-4728 
    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 single-fibre—composite (s.f.c) test, in which a fibre is embedded in an epoxy matrix and the composite tested in tension, was employed to obtain the statistical strength distribution of Carborundum SiC ceramic fibres over the range of gauge lengths from 0.5 to 20 mm. The raw s.f.c. test data was organized into three independent forms: the number of fibre breaks versus applied stress; the fibre fragment length distribution at the end of the test; and the fibre strength versus fragment length during testing. The data was interpreted using two different models of the fibre/epoxy—matrix interface, and it was found that a constant shear stress model could not self-consistently fit all of the s.f.c. data, whereas an elastic interface model provided good fits to all of the data. The applicability of the elastic interface model was supported by the absence of interfacial debonding and the rough fibre/matrix interface, which promoted mechanical interlocking. The s.f.c. test derived strength of σ0 = 1500 MPa at a gauge length of 20 mm, with a Weibull modulus of m = 9, agreed fairly well with independent tension test results obtained on 254 mm length samples. Obtaining self-consistent fits to all of the manifestations of the s.f.c. data requires careful testing and analysis, but the present work demonstrates that the s.f.c. test can be a powerful tool for the accurate and independent assessment of fibre strengths at small gauge lengths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00356515
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of fibre/matrix interfacial shear strength by an acoustic emission technique (1991)
    Springer
    Journal of materials science 26 (1991), S. 6631-6638 
    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 application of acoustic emission (AE) measurements to locate the sources of fracture of a single high-strength fibre embedded in an epoxy matrix which is loaded in tension is described. From the micromechanical model and the fragment length distribution, interfacial shear strength values were calculated. The technique is demonstrated for small-diameter glass and graphite fibres as well as for fibres which exhibit fibrillar fracture, such as Kevlar and PBZT. Good agreement is found between the mean fragment length values obtained by optical and AE measurements for glass and graphite fibres. Values obtained for interfacial shear strength by the AE technique are comparable with those obtained using other techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00553688
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    A new theory to obtain Weibull fibre strength parameters from a single-fibre composite test (1995)
    Springer
    Journal of materials science 30 (1995), S. 2722-2728 
    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 A theory is developed to obtain the Weibull scale and shape parameters for in situ fibre strength utilizing the data obtained from a single-fibre-composite (SFC) test. It is well known that during the SFC test, the fibre fractures several times along its length at successive weak points that are randomly located. The SFC technique, although most commonly used for measuring the fibre/matrix interfacial shear strength, is an excellent way to determine the fibre flaw spacings and the in situ fibre failure stress at every fracture location. In the present technique, the SFC specimen is partitioned into a relatively large number of small sections of equal length such that each section will have either one or no fibre fracture point. Because all the sections may not include the fibre fracture points because of their random nature, the test data are regarded as “censored data”. In other words, the theory is constructed for the estimation of Weibull parameters that takes into account the censored nature of the data. The Weibull parameters predicted using the present theory are in the same range as those obtained from the single fibre tension tests. For several reasons the values obtained from the SFC test tend to be slightly higher than those obtained from the simple tension tests. However, the in situ fibre strength values obtained using SFC technique may be more realistic and thus may be more useful in modelling composite strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00362158
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  • 8
    Electronic Resource
    Electronic Resource
    Interfacial and mechanical properties of environment-friendly “green” composites made from pineapple fibers and poly(hydroxybutyrate-co-valerate) resin (1999)
    Springer
    Journal of materials science 34 (1999), S. 3709-3719 
    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 Physical and tensile properties of pineapple fibers were characterized. Tensile properties of pineapple fibers, like most natural fibers, showed a large variation. The average interfacial shear strength between the pineapple fiber and poly(hydroxybutyrate-co-valerate) (PHBV) was 8.23 MPa as measured by the microbond technique. Scanning electron microscopy (SEM) photomicrographs of the microbond specimens revealed an adhesive failure of the interface. Fully degradable and environment-friendly “green” composites were prepared by combining pineapple fibers and PHBV with 20 and 30% weight content of fibers placed in a 0°/90°/0° fiber arrangement. Tensile and flexural properties of these “green” composites were compared with different types of wood specimens. Even though tensile and flexural strength and moduli of these “green” composites were lower than those of some wood specimens tested in grain direction, they were significantly higher than those of wood specimens tested in perpendicular to grain direction. Compared to PHBV virgin resin, both tensile and flexural strength and moduli of these “green” composites were significantly higher. SEM photomicrographs of the fracture surface of the “green” composites, in tensile mode, showed partial fiber pull-out indicating weak bonding between the fiber and the matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004659507231
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  • 9
    Electronic Resource
    Electronic Resource
    Modification of mechanical properties of Kevlar fibre by polymer infiltration (1996)
    Springer
    Journal of materials science 31 (1996), S. 1265-1274 
    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 While high-performance organic fibres such as poly (para phenylene benzobisthiazole) and Kevlar possess excellent mechanical properties under axial tension, their strength under compression is generally poor. This study focuses on a polymer infiltration approach to modify the mechanical properties of the Kevlar 49 fibre in tension as well as compression, in which various polymeric resins are infiltrated in an opened fibrillar network of Kevlar single filaments. Opening was achieved using concentrated sulfuric acid, which resulted in a strength loss at high acid concentrations. However, compared to the acid-treated fibre, both the tensile strength and strain-to-failure of the fibres were found to increase after infiltration with epoxy resins and bismaleimide polymers. Polymer infiltration also resulted in a significant improvement in the compressive strength of the Kevlar fibre, with the bismaleimide performing better than the epoxy resins. Plasma modification using ammonia was also used to enhance interfibrillar adhesion by incorporating reactive amine groups on the fibril surface
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00353106
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  • 10
    Electronic Resource
    Electronic Resource
    Investigations of water and high energy radiation interactions in an epoxy (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 29 (1984), S. 311-318 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Differential scanning calorimetry (DSC) and infrared spectroscopy (IR) have been used to study the crosslinked epoxy system tetraglycidyl-4,4′-diaminodiphenyl methane cured with diaminodiphenyl sulfone. Samples cured at various temperatures were soaked in distilled water for extended periods or irradiated with 0.5 Me V electrons and 60Co gamma. DSC results show that the standard-cured (137°C for 2 h and 160°C for 5 h) dry samples have a Tg around 190°C and a large exothermic reaction at about 260°C. The latter is attributed to further reaction of curing agent with the epoxide rings. The exothermic energy is about 124 cal/g for an uncured specimen, 42 cal/g for standard cured specimen, and 20 cal/g for soaked samples containing 4% H2O. The exothermic energy is shown to decrease monotonically with the ionizing radiation dosage. IR results show a reduction in the intensity of the epoxide band as the exothermic energy is decreased.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1984.070290129
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