The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Richard E. Robertson - One of the best experts on this subject based on the ideXlab platform.
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The effect of fiber orientation on the toughening of short fiber-reinforced polymers
Journal of Applied Polymer Science, 2003Co-Authors: David A. Norman, Richard E. RobertsonAbstract:The effect of fiber orientation on the tough- ening of polymers by short glass fibers generally below their critical length was investigated using specimens with either well-aligned or randomly oriented fibers. The fibers were aligned by an electric field in a photopolymerizable mono- mer, which was polymerized while the field was still being applied. These materials were Fractured with the aligned fibers in three orientations with respect to the crack Plane and propagation direction. Specimens with fibers aligned normal to the Fracture Plane were the most tough, those with randomly oriented fibers were less tough, and those with fibers aligned within the Fracture Plane were the least tough. The Fracture behaviors compared favorably with predictions based on observed processes accounting for fiber orienta- tion. The processes considered were fiber pull-out (includ- ing snubbing), fiber breakage, fiber-matrix debonding, and localized matrix-yielding adjacent to fibers bridging the frac- ture Plane. Fibers not quite perpendicular to the Fracture Plane provided the greatest toughening; these fibers pulled out completely and gave a significant contribution from snubbing. Fibers at higher angles provided less toughening, involving nearly equal contributions from pull-out, break- age, and debonding. Fibers within the Fracture Plane pro- vided the least toughening, involving debonding alone. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2740 -2751, 2003
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Rigid-particle toughening of glassy polymers
Polymer, 2003Co-Authors: David A. Norman, Richard E. RobertsonAbstract:The nature of the toughening of glassy polymers by rigid particles was investigated by using aligned assemblages of spherical glass particles. The particles were aligned by an electric field in a photopolymerizable monomer, which was polymerized while the field was still being applied. These materials were Fractured with the aligned particle strings in three orientations with respect to the crack Plane and propagation direction. The Fracture toughness and Fracture energy of these and of random arrangements of particles (formed without the electric field) were all higher than of the matrix alone. The increases were compared with predictions from processes on or in the immediate vicinity of the Fracture Plane and from those away from the Fracture Plane. The increases were inconsistent with those predicted by on-Fracture Plane processes as represented by crack pinning and bowing. But the increases did correlate with the size of the process zones, which could extend more than 100 μm away from the Fracture Plane. Detailed calculations showed that the increase in Fracture energy arose almost completely from off-Fracture Plane processes of particle-matrix debonding and the accompanying local inelastic deformation of the matrix around the particles.
A.k.m. Kais Bin Zaman - One of the best experts on this subject based on the ideXlab platform.
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Modeling of energy absorption of short fiber composite considering interfacial properties of fiber/matrix
Journal of Materials Processing Technology, 2006Co-Authors: A.k.m. Masud, A.k.m. Kais Bin ZamanAbstract:Abstract A generalized mathematical model of energy absorption of randomly oriented short fiber composite is developed on the basis of result of single-fiber pull-out test and some assumptions obtained from experimental investigation of the Fracture of the composite of Aramid short fiber. Concept of the pull-out test is incorporated to the model, such that the fibers intersecting a Fracture Plane (where the Fracture of composite occurs) would pull out or Fracture like single-fiber pull-out test. The energy contribution of each fiber in the Fracture Plane is calculated for different embedded length and orientation to estimate the total Fracture energy. According to the model, it is found that energy absorption depends upon the intrinsic properties of the fiber and matrix, volume fraction, critical embedded length of the fiber, fiber length and orientation of the fibers in the matrix. Analytical results obtained by the model are compared with the experimental results of Aramid short fiber composite.
Michael May - One of the best experts on this subject based on the ideXlab platform.
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The effect of strain rate on the orientation of the Fracture Plane in a unidirectional polymer matrix composite under transverse compression loading
Composites Part A: Applied Science and Manufacturing, 2020Co-Authors: Michael May, Noah Ledford, Matti Isakov, Philipp Hahn, Hanna Paul, Sumito NagasawaAbstract:Abstract Transverse compression tests on a unidirectional composite were performed under quasi-static and high-rate loading conditions using servo-hydraulic machines as well as a direct impact Hopkinson bar. Aside the expected increase of compressive strength with increasing loading rate, a change of Fracture Plane orientation was observed. For quasi-static loading conditions, the Fracture angle was 54.5°, for high rate-loading conditions this increased to 65°. Assuming a Mohr-Coulomb type of Fracture for unidirectional composites under transverse compression loading, the change of Fracture Plane orientation indicates a rate dependency of the internal friction angle ϕ , which has not previously been reported for composite materials.
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3D modeling of Fracture in brittle isotropic materials using a novel algorithm for the determination of the Fracture Plane orientation and crack surface area
Finite Elements in Analysis and Design, 2012Co-Authors: Michael May, Sebastian Kilchert, Stefan HiermaierAbstract:A user defined material model for simulation of brittle Fracture in isotropic materials was implemented into the explicit FE code Abaqus/Explicit. The model uses a methodology for calculating the orientation of the Fracture Plane in isotropic materials in 3D space using an analytical approach. Knowing the orientation of the Fracture Plane, the cross-sectional area of the Fracture surface can in a hexagonal element can be calculated. Regularization is then achieved using the size of the Fracture Plane. The model is first tested on single-element tests and then applied to more complex test cases such as a short bar with chevron notch or micromechanical analyses of composite materials. The numerical predictions correlate well with experimental evidence from the literature
Sumito Nagasawa - One of the best experts on this subject based on the ideXlab platform.
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The effect of strain rate on the orientation of the Fracture Plane in a unidirectional polymer matrix composite under transverse compression loading
Composites Part A: Applied Science and Manufacturing, 2020Co-Authors: Michael May, Noah Ledford, Matti Isakov, Philipp Hahn, Hanna Paul, Sumito NagasawaAbstract:Abstract Transverse compression tests on a unidirectional composite were performed under quasi-static and high-rate loading conditions using servo-hydraulic machines as well as a direct impact Hopkinson bar. Aside the expected increase of compressive strength with increasing loading rate, a change of Fracture Plane orientation was observed. For quasi-static loading conditions, the Fracture angle was 54.5°, for high rate-loading conditions this increased to 65°. Assuming a Mohr-Coulomb type of Fracture for unidirectional composites under transverse compression loading, the change of Fracture Plane orientation indicates a rate dependency of the internal friction angle ϕ , which has not previously been reported for composite materials.
Ewald Macha - One of the best experts on this subject based on the ideXlab platform.
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verification of fatigue critical Plane position according to variance and damage accumulation methods under multiaxial loading
International Journal of Fatigue, 2014Co-Authors: Zbigniew Marciniak, Dariusz Rozumek, Ewald MachaAbstract:Abstract The paper presents a comparison of Fracture Plane position gained from experimental tests of specimens under multiaxial loading and theoretical ones from calculation according to variance and damage accumulation methods. In the variance method it is assumed that the Plane in which the maximum variance of the equivalent stress appears is critical for a material and the fatigue Fracture should be expected in this Plane. In the damage accumulation method the fatigue critical Plane is assumed to be the Plane which suffered the greatest damage during service loading. For both methods the equivalent stress is calculated according to the multiaxial fatigue failure criteria of (i) maximum normal stresses, (ii) maximum shear stresses as well as (iii) maximum normal and shear stresses in the critical Plane.
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Fatigue Fracture Planes and the Critical Plane Orientations in Multiaxial Fatigue Failure Criteria
2013Co-Authors: Aleksander Karolczuk, Ewald MachaAbstract:This paper deals with the problem of the critical Plane determination formultiaxial fatigue failure criteria. Experimental results from multiaxial proportional,non-proportional cyclic loading and variable-amplitude bending and torsion were usedto determine the macroscopic Fracture Plane orientations and the fatigue lives. Someknown multiaxial critical Plane criteria were verified based on the Fracture Planeorientations and experimental fatigue lives. It was concluded that frequently the criticaland Fracture Plane orientations do not coincide. However, the morphology of FracturePlanes is a key for an appropriate choice of the fatigue failure criterion for the fatiguelife estimation.
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Expected position of the fatigue Fracture Plane by using the weighted mean principal Euler angles
International Journal of Fracture, 2002Co-Authors: Andrea Carpinteri, Aleksander Karolczuk, Ewald Macha, Sabrina VantadoriAbstract:The expected principal stress axes under multiaxial fatigue loading are determined by averaging the instantaneous Euler angles through suitable weight functions. Then, the Fracture Plane position is derived from such expected principal stress directions. Three weight functions based on stress parameters are discussed by comparing theoretical predictions with available test results related to six metallic materials under proportional and non-proportional loading. The fatigue Fracture Plane position under multiaxial loading may be established on the basis of the averaged direction of the maximum principal stress, with such a direction deduced by employing proper weight functions.
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Critical Fracture Plane Under Multiaxial Random Loading by Means of Euler Angles Averaging
Multiaxial Fatigue and Fracture, 1999Co-Authors: Andrea Carpinteril, Ewald Macha, Roberto Brighenti, Andrea SpagnoliAbstract:ABSTRACT Several authors have experimentally observed that the position of the fatigue Fracture Plane strongly depends on the directions of the principal stresses or strains. The expected principal stress directions under multiaxial random loading are obtained herein by averaging the instantaneous values of the three Euler angles through some suitable weight functions, in order to take into account the main factors influencing the fatigue Fracture behaviour. Then the correlation between such theoretical principal directions and the experimental Fracture Plane is examined for some biaxial random fatigue tests.
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Comparison of Variance and Damage Indicator Methods for Prediction of the Fracture Plane Orientation in Multiaxial Fatigue
Multiaxial Fatigue and Fracture, 1999Co-Authors: W. Będkowski, Ewald Macha, Bastien Weber, Jean-louis RobertAbstract:ABSTRACT Two methods that enable prediction of the Fracture Plane orientation are presented and compared in this paper. The first one is a statistical approach, which is based on the variance of an equivalent stress. It is assumed that the Fracture Plane is the one where the variance of a linear combination of the shear and normal stresses acting on this Plane is maximum. The second one uses the so-called damage indicator of a multiaxial fatigue criterion, which is based on the research of the critical Plane. The formulation of the criterion involves shear and normal stress amplitudes and mean normal stress. The Fracture Plane is the critical Plane; That is to say the one where the damage indicator is the highest. A comparison of the two methods against experimental results is made for biaxial cyclic and random stress states.
