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  • 1. Melin, L G
    et al.
    Neumeister, Jonas
    KTH, Superseded Departments, Solid Mechanics.
    Pettersson, Kaj
    KTH, Superseded Departments, Solid Mechanics.
    Johansson, Hans
    KTH, Superseded Departments, Solid Mechanics.
    Asp, L E
    Evaluation of four composite shear test methods by digital speckle strain mapping and fractographic analysis2000In: Journal of composites technology & research, ISSN 0884-6804, E-ISSN 1945-7537, Vol. 22, no 3, p. 161-172Article in journal (Refereed)
    Abstract [en]

    Four methods to determine composite interlaminar shear strength (ILSS) are evaluated. In particular, the recently devised inclined double-notch shear test (IDNS) is compared with three existing and more established methods: the Iosipescu test, the short three-point bending test (S3PB) and the double-notch compression test (DNC). The uniformity of strain field in the test region in a real test situation-which is the crucial test method quality parameter-is investigated by strain mapping using digital speckle photography. The measured strain fields are compared with FE-calculated strains representing ideal conditions and both known advantages and drawbacks of the different methods are confirmed. The IDNS test produces the most uniform strain fields and also consistently high ILSS values. A fractographic analysis indicates shear separation over a major part of the fracture surfaces of all specimen types; typical shear cusps were found over about 80% of the IDNS fracture surface and in about 50% to 70% in the other specimens. For the Iosipescu tests, failure initiation could be ascribed to initiation in tension at defects. Experimentally determined stress-strain responses in shear exhibit a distinct variation among the different methods. For the best methods, a notable material softening was observed Drier to failure. Observed formation of shear cusps is believed to be the primary cause for this softening of the composite material studied here.

  • 2.
    Pettersson, Kaj B.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    The inclined double notch shear test for determination of interlaminar shear properties of composite laminates2005Doctoral thesis, comprehensive summary (Other scientific)
  • 3.
    Pettersson, Kaj B.
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Neumeister, Jonas M.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Strandberg, Morten
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    V-notched shear specimens for the inclined double notch shear test2007In: Journal of Testing and Evaluation, ISSN 0090-3973, E-ISSN 1945-7553, Vol. 35, no 1, p. 85-94Article in journal (Refereed)
    Abstract [en]

    A numerical study of a modified specimen geometry for the inclined double notch shear (IDNS) test was performed. The test uses the standard double notch compression (DNC) specimen whose geometry was modified by replacing the straight grooves with tilted V notches. Arising stress fields were calculated by use of a BEM scheme. Four different geometry parameters were investigated: relative notch distance, specimen loading, and notch tilt and notch opening angles. Different evaluation criteria to determine optimal specimen and test geometries were studied with respect to effects on stress uniformity and stress concentrations/singularities. No single criterion was found to be obviously superior. Judicious specimen loading enabled cancellation of the significant mode I singularity, whereas a careful specimen design enabled the simultaneous cancellation of both modes I and mode II singularities in most specimens. Singular fields (for mathematically sharp notches) were predominant over distances comparable to the root radii used in practice, and thus not very relevant. Further, the shear stress level arising in the specimen center (and in its major part) was controlled by the specimen inclination, whereas stress concentrations in the notch root vicinity were governed mainly by notch tilt and notch opening angles. Appropriately tilted, but sharper notches seemed to result in the generally most uniform stress fields. For the issues studied, several accurate closed form expressions were presented.

  • 4.
    Pettersson, Kaj
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Neumeister, Jonas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    A tensile setup for the IDNS composite shear test2006In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 37, no 2, p. 229-242Article in journal (Refereed)
    Abstract [en]

    An existing test method, the inclined double notch shear (IDNS-) test, for determination of interlaminar shear properties in thin panels of layered composite materials was developed further. Experimentally observed and unresolved issues with the original IDNS-test setup were addressed. Undesired specimen deformation (and potential instability) is observed at high loads with the original compressive setup, particularly for more compliant materials. Then, testing conditions continuously change throughout a test. Here, a tensile setup which applied a statically determined combination of loads to the doubly notched specimen was used instead. The proper combination of loads minimized the arising stress concentrations at the notch roots while it produced a homogeneous state of true inter-laminar shear stress over the test region. Numerical (FE-) analyses and experimental studies to investigate testing conditions such as: specimen geometry parameters, appropriate loading combinations, and recommendations for optimal test performance in terms of achieved shear strengths and shear strain fields, were performed. In addition to the tensile setup, the possibility to use tilted notches was studied. The tensile IDNS-setup produced more homogeneous fields over the test region, even for short notch distances, further it achieved interlaminar shear strength values in the same range as or even higher than the original setup. Finally, distinctly less specimen deformation was observed with the tensile setup, and thus proper adjustment was much simpler while instability was completely avoided.

  • 5.
    Pettersson, Kaj
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Neumeister, Jonas
    KTH, Superseded Departments, Solid Mechanics.
    Analysis of the IDNS test for composite interlaminar shear propertiesArticle in journal (Other academic)
  • 6.
    Pettersson, Kaj
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Neumeister, Jonas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gamstedt, Kristofer
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Öberg, Hans
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Stiffness reduction, creep, and irreversible strains in fiber composites tested in repeated interlaminar shear2006In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 76, no 1-2, p. 151-161Article in journal (Refereed)
    Abstract [en]

    Interlaminar shear of a unidirectional carbon fiber/epoxy composite was studied experimentally by use of a tensile inclined double notch shear (IDNS-) test-setup. The non-linear constitutive behavior, the degradation and stiffness reduction, under monotonic and repeated loading with successively increasing peak strains were investigated. Shear strains (average values) up to 7-8% prior to failure were observed in the test region together with irreversible strains approaching 2.5% when unloaded. Hysteresis loops of notable width, increasing with higher peak strains, were observed. Several shear moduli measures were investigated. A notable decay in unloading secant moduli (similar to 30-40%) was present. Tangent (re-)loading and unloading moduli could be reliably measured only with a 2 h hold time prior to each load reversal. A quite early drop of > 10% was observed in the elastic reloading tangent modulus, but not for the unloading tangent modulus. To the knowledge of the authors, no previous experiments have achieved global interlaminar shear strain levels of such magnitudes, and moreover, stress levels were higher than obtained with previously established methods. Several mechanisms were deemed to contribute to the overall strains; such were higher elastic-but also higher irreversible shear strains in the epoxy matrix and the fibers; damage within the epoxy; conceivably also in the fibers; appearance of microcracks in epoxy-rich regions; possibly separation of the interfaces, and also notable creep deformation at higher loads. None of these phenomena alone could account for the dominating part of the obtained strains. Matrix cracks (shear hackles) were found post mortem, but could not be confirmed during the test: a different damage mechanism is responsible for the early loss of elastic stiffness. Friction-like processes (sliding, viscosity) contributed substantially to the total strains.

  • 7.
    Pettersson, Kaj
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Neumeister, Jonas
    KTH, Superseded Departments, Solid Mechanics.
    Johansson, Hans
    KTH, Superseded Departments, Solid Mechanics.
    Experimental determination of composite interlaminar shear properties and evaluation of the IDNS Setup.In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050Article in journal (Other academic)
  • 8.
    Pettersson, Kaj
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Neumeister, Jonas
    KTH, Superseded Departments, Solid Mechanics.
    Strandberg, Martin
    KTH, Superseded Departments, Solid Mechanics.
    V-notched shear specimens for the idns test method2001Report (Other academic)
1 - 8 of 8
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