1,721,014 research outputs found
Fatigue behaviour and life assessment of composite laminates under multiaxial loadings
No full textA thorough analysis of fatigue of composite laminates under multiaxial loading is presented. A large body of experimental data taken from the literature is examined to delineate the influence on the fatigue strength of factors such as biaxiality ratios and off-axis and out-of-phase angles. The data are found to clearly suggest that the ply-level shear biaxiality ratio, defined as the ratio of the shear stress amplitude to the largest normal stress amplitude, is the governing factor. The multiaxial fatigue criteria are examined next. The empirical method proposed by Ellyin and co-workers, based on the assumed log-linear fatigue life relationship, is compared with data. The Tsai-Hill and Smith-Pascoe quadratic polynomial criteria are also scrutinised. Finally, a mechanisms-based approach to multiaxial fatigue is outlined and proposed as the way to developing a reliable life prediction methodology
Fatigue behaviour and life assessment of composites under multiaxial loadings
No full textA thorough analysis of fatigue of composite laminates under multiaxial loading is presented. A large body of experimental data taken from the literature is examined to delineate the influence on the fatigue strength of factors such as biaxiality ratios and off-axis and out-of-phase angles. The data are found to clearly suggest that the ply-level shear biaxiality ratio, defined as the ratio of the shear stress amplitude to the largest normal stress amplitude, is the governing factor. The multiaxial fatigue criteria are examined next. The empirical method proposed by Ellyin and co-workers, based on the assumed log-linear fatigue life relationship, is compared with data. The Tsai–Hill and Smith–Pascoe quadratic polynomial criteria are also scrutinised. Finally, a mechanisms-based approach to multiaxial fatigue is outlined and proposed as the way to developing a reliable life prediction methodology
Effect of microstructure on initiation of delamination in cross ply laminates from a transverse crack
No full textTransverse crack propagating towards a cross-ply interface is investigated in this study. The non-uniform fiber distribution near ply interface is modelled explicitly in order to study the effect of microstructure on crack path and initiation of delamination. The growth of fiber/matrix interfacial debond and debond kinking out of interface are analyzed based on a combination of energy and stress-based approach, which is convenient in predicting matrix crack path. Kinking of transverse crack tip when it approaches ply interface is investigated using an energy-based approach. It is found that predicted matrix crack path and crack tip kinking behavior near interface is strongly influenced by the local microstructure. The obtained results indicate that an induced symmetrical delamination, i.e., interface cracks of equal length on either side of the transverse ply crack, as often assumed in modeling studies, is not always a favorable damage mode
Crack deflection near a ply interface in a composite laminate
No full textThe deflection of a matrix crack near 0°/90° interface in a cross-ply laminate was studied numerically. In the finite element (FE) model, an initial matrix crack was introduced in the 90° layers away from the 0°/90° interface. The initial matrix crack could be initiated either at the middle of 90° layer or at one side of 0°/90° interface. The 0° layers and a part of the initial matrix crack were modeled using homogenized layer properties to simplify the model. The nonuniformly distributed fibers were modeled explicitly close to the 0°/90° interface in order to study the influence of this nonuniformity on the crack deflection process. The Energy Release Rate (ERR) of debond crack tip was calculated using Virtual Crack Closure Technique (VCCT) to study the debond growth. Maximum principal stress was then adopted to access the debond crack kinking qualitatively. It's found that when a macro-size matrix crack forms and propagate towards ply interface, the subsequent debonding and debond cracking process in nearby intact fiber shows some distinct differences compared to the same processes at single isolated fiber without considering the interaction with nearby debonded fiber and existing matrix crack. Meanwhile, present analysis shows clear influence of microstructures on the crack deflection process by affecting the fiber/matrix debonding and debond kinking processes
Mode I Strain Energy Release Rate in composite laminates in the presence of voids
No full textThe paper presents a methodology for evaluating the effects of voids on the fracture behaviour of woven
fabric composites. The particular model studied consists of a double cantilever beam (DCB) in which
voids are placed ahead of the crack tip and the Mode I Strain Energy Release Rate (SERR) is calculated.
The standard beam-on-elastic-foundation theory is modified to account for shear compliance and material
orthotropy, and the new formulation is used to evaluate the deformed shape, elastic deformation
energy and SERR. The presence of the voids is simulated as an unsupported zone in the elastic-foundation.
The validation of the new analytical model, in terms of the deformed shapes and SERR values, is successfully
carried out by suitable 2D finite element (FE) analyses. The effect of size, location and shape of
the voids is investigated by a parametric study that showed that the enhancement of SERR increases with
the size of the voids and the proximity to the crack tip and that elongated (elliptical) voids are more critical
than the circular voids. Finally, the influence of more complex void distributions on the fracture
toughness is evaluated by FE analysis
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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