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  • 1.
    Bonnaud, Etienne L.
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Neumeister, Jonas M.
    KTH, Superseded Departments, Solid Mechanics.
    Inertia and damping effects on the damage-dependent burst size distribution of fiber bundles2001In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 290, p. 261-269Article in journal (Refereed)
    Abstract [en]

    Distributions of simultaneous fiber failures—bursts—in loaded fiber bundles are studied considering inertia and damping. Resulting burst size distributions have universal properties: all approach the power law DΔΔ−2.5 for larger burst sizes Δ. Momentary burst size distributions evolve with increasing damage and do not follow power laws but are still universal. Finally, it is briefly outlined how to use distribution progression to assess damage state.

  • 2.
    Bonnaud, Etienne L.
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Neumeister, Jonas M.
    KTH, Superseded Departments, Solid Mechanics.
    Proper Boundary Conditions for Infinitely Layered Orthotropic Media2000In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 67, p. 629-632Article in journal (Refereed)
    Abstract [en]

    A stress analysis of a plane infinitely layered medium subjected to surface loadings is performed using Airy stress functions, integral transforms, and a revised transfer matrix approach. Proper boundary conditions at infinity are for the first time established, which reduces the problem size by one half. Methods and approximations are also presented to enable numerical treatment and to overcome difficulties inherent to such formulations.

  • 3. 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    KTH, Superseded Departments, Solid Mechanics.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    KTH, Superseded Departments, Solid Mechanics.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    KTH, Superseded Departments, Solid Mechanics.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.

  • 4.
    Melin, Niklas
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Neumeister, Jonas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Measuring constitutive shear behavior of orthotropic composites and evaluation of the modified Iosipescu test2006In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 76, no 1-2, p. 106-115Article in journal (Refereed)
    Abstract [en]

    The modified Iosipescu test uses a variable notch opening angle 0, depending on the material anisotropy and orientation, to accomplish even stress- and strain-fields in the test region. Constitutive shear properties can thus be measured more accurately, more completely, and with fewer sources of error. Here more materials and properties were studied, and a 3D optical strain- and displacement-monitoring system was used to evaluate and improve both the modified test and the novel fixture used here. It performed substantially better than the commonly used Wyoming fixture in terms of producing constant through specimen thickness conditions and preventing undesired specimen twisting. Additionally, loading-unloading behavior of two high-performance, essentially unidirectional, fiber composites was investigated to assess stiffness reduction, damage, localization, and irreversible strains. In the present of such, well controlled testing conditions are even more important.

  • 5.
    Melin, Niklas
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Neumeister, Jonas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Sensitivity to specimen imperfections of Ioisipescu shear for composite laminates2007In: 16th International Conference on Composite Materials, ICCM-16: A Giant Step Towards Environmental Awareness: From Green Composites to Aerospace, 2007Conference paper (Other academic)
    Abstract [en]

    The influence of imperfections in specimen geometry is studied for the Ioispescu test. With FE-analyses and experimental verifications, it is found that slight deviations from nominal geometry in the specimen gripping section may cause errors in measured/calculated strain levels by up to 100%, or even more. Unacceptably large errors may occur already for imperfections in the order of 0.01 mm. Most critical is the case when gripping surfaces are tilted towards each other, giving a stubbed conical shape of the cross section. A rhomboidal cross section does not cause as large front-to-back differences but produces uneven, skewed strain profiles. Numerical calculations show the severity of, and sensitivity to, such imperfections for both isotropic materials and orthotropic composites. And experiments with aluminum- and uniaxial carbon fiber composite specimens with controlled geometrical deviations verify, using in-situ strain field monitoring, that the same phenomena occur also in real experiments, and at comparable magnitudes.

  • 6.
    Melin, Niklas
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Neumeister, Jonas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    The influence of specimen clamping and specimen imperfections on the losipescu shear test performance2006Article in journal (Other academic)
  • 7.
    Neumeister, Jonas M.
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Bonnaud, Etienne
    KTH, Superseded Departments, Solid Mechanics.
    Dynamical Effects on the Burst Size Distribution and Universality in Fiber Bundles2001Report (Other academic)
  • 8.
    Neumeister, Jonas M.
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Melin, L. Niklas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Specimen clamping and performance of the Ioisipescu shear tests applied for composite materials2007In: 16th International Conference on Composite Materials, ICCM-16, 2007Conference paper (Refereed)
    Abstract [en]

    Clamping and subsequent loading in shear of Ioispescu specimens is investigated. Combined stresses reach similar, or even higher, levels locally compared the nominal shear stress, both compressive and tensile. Especially for brittle materials, composites, and materials with anisotropic failure modes, these stresses may cause premature failure outside the test region and appropriate clamping levels become important. A clamping ratio (r) between clamping force and peak shear force is introduced, and it is shown that for quasi-isotropic failure modes, the overall lowest detrimental stresses are obtained for about r ∼ 1. It is further shown that loss of contact always occurs in one part of the clamping region unless r is in excess of 2.5-3. Near that loss of contact, high tensile stresses are obtained. Even with moderate r, there will be local plasticity or crushing etc due to high contact pressure near the end of the opposing gripping face. These findings are shown both numerically and experimentally using optical full field strain measurements.

  • 9.
    Neumeister, Jonas
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Melin, Niklas
    KTH, Superseded Departments, Solid Mechanics.
    A modified Iosipescu Test for Anisotropic Composite Panels2004In: 14th Internatonal Conference on Composite Materials, ICCM-14: San Diego, CA: 14 July 2003 through 18 July 2003, 2004, p. 121-129Conference paper (Refereed)
    Abstract [en]

    The Iosipescu (V-notched beam) shear test for in-plane shear properties of composite panels was modified with respect to specimen geometry. The ASTM standard prescribes V notches with 90° opening angle, while the resulting stress field in the test region strongly depends on the material anisotropy. Thus, the test performance depends on actual material properties and material orientation relative to the test region. A variable notch opening angle was proposed to accomodate both material anisotropy and orientation.

  • 10.
    Neumeister, Jonas
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Melin, Niklas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Specimen Clamping and Performance of the Iosipescu Shear Test Applied for Composite Materials2007In: 16th International Conference on Composite Materials, ICCM-16: A Giant Step Towards Environmental Awareness: From Green Composites to Aerospace, 2007Conference paper (Other academic)
    Abstract [en]

    Clamping and subsequent loading in shear of Ioispescu specimens is investigated. Combined stresses reach similar, or even higher, levels locally compared the nominal shear stress, both compressive and tensile. Especially for brittle materials, composites, and materials with anisotropic failure modes, these stresses may cause premature failure outside the test region and appropriate clamping levels become important. A clamping ratio (r) between clamping force and peak shear force is introduced, and it is shown that for quasi-isotropic failure modes, the overall lowest detrimental stresses are obtained for about r ∼ 1. It is further shown that loss of contact always occurs in one part of the clamping region unless r is in excess of 2.5-3. Near that loss of contact, high tensile stresses are obtained. Even with moderate r, there will be local plasticity or crushing etc due to high contact pressure near the end of the opposing gripping face. These findings are shown both numerically and experimentally using optical full field strain measurements.

  • 11.
    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.

  • 12.
    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.

  • 13.
    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)
  • 14.
    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.

  • 15.
    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)
  • 16.
    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 - 16 of 16
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