Experimental assessment of mixed-mode partition theories for generally laminated composite beams (original) (raw)
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Mixed-mode partition theories for one-dimensional delamination in laminated composite beams
2012
Completely analytical theories are presented for the mixed-mode partitioning of one-dimensional delamination in laminated composite beams. The work builds on previous research by the authors on one-dimensional fractures in layered isotropic beams. The partition theories are developed within the contexts of both Euler and Timoshenko beam theories. Two sets of orthogonal pairs of pure modes are found and used to partition mixed modes. Approximate ‘averaged partition rules’ are also established for 2D elasticity. The beam partition theories and averaged rules are extensively validated against numerical simulations using the finite element method (FEM). The contact behavior of double cantilever beams (DCBs) is also investigated. Two types of contact exist: crack tip running contact, which results in a region of pure mode II; and point contact at the DCB tip, which can result in either in mixed modes or pure mode II.
2014
A powerful method for partitioning mixed-mode fractures on rigid interfaces in laminated unidirectional double cantilever beams (DCBs) is developed by taking 2D elasticity into consideration in a novel way. Pure modes based on 2D elasticity are obtained by introducing correction factors into the beam-theory-based mechanical conditions. These 2D-elasticity-based pure modes are then used to derive a 2D-elasticity-based partition theory for mixed-mode fractures. Excellent agreement is observed between the present partition theory and Suo and Hutchinson’s partition theory [1]. Furthermore, the method that is developed in this work has a stronger capability for solving more complex mixed-mode partition problems, for example, in the bimaterial case. [1] Suo Z, Hutchinson JW. Interface crack between two elastic layers. International Journal of Fracture Mechanics 1990;43:1–18.
Engineering Fracture Mechanics, 1998
The interlaminar fracture behavior of a unidirectionally glass ®ber reinforced composite under the full range of in-plane loading conditions has been investigated. Loading conditions from pure mode I through various mixed mode I/II ratios up to pure mode II have been generated by the aid of the proposed compound version of the CTS (compact tension shear) specimen. From the experimentally measured critical loads, the mode I, mode II and the various mixed mode I/II critical energy release rates at crack initiation have been determined by the aid of the ®nite element method and the modi®ed virtual crack closure integral method. Based on these results the parameters for a fracture criterion for the composite under consideration have been determined. # Engineering Fracture Mechanics 61 (1998) 325±342 0013-7944/98/$ -see front matter # 1998 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 3 -7 9 4 4 ( 9 8 ) 0 0 0 6 8 -X PERGAMON fracture behaviour of composite materials. The double cantilever beam (DCB) and the end notched¯exure (ENF) specimens have been employed for mode I and mode II tests, respectively. Also for the mixed mode tests, mostly beam type specimens were used in order to obtain mixed mode I/II critical energy release rates.
Partition of mixed-mode fractures in 2D elastic orthotropic laminated beams under general loading
Composite Structures, 2016
An analytical method for partitioning mixed-mode fractures on rigid interfaces in orthotropic laminated double cantilever beams (DCBs) under through-thickness shear forces, in addition to bending moments and axial forces, is developed by extending recent work by the authors (Harvey et al., 2014). First, two pure through-thickness-shear-force modes (one pure mode I and one pure mode II) are discovered by extending the authors’ mixed-mode partition theory for Timoshenko beams. Partition of mixed-mode fractures under pure through-thickness shear forces is then achieved by using these two pure modes in conjunction with two thickness ratio-dependent correction factors: (1) a shear correction factor, and (2) a pure-mode-II energy release rate (ERR) correction factor. Both correction factors closely follow an elegant normal distribution around a symmetric DCB geometry. The principle of orthogonality between all pure mode I and all pure mode II fracture modes is then used to complete the mixed-mode fracture partition theory for a general loading condition, including bending moments, axial forces, and through-thickness shear forces. Excellent agreement is observed between the present analytical partition theory and numerical results from finite element method (FEM) simulations.
2020
This paper reports the authors' recent work on mixed-mode fracture in fiber-reinforced laminated composite beams and plates. The work considers the so-called one-dimensional fracture which propagates in one-dimension and consists of only mode I and mode II fracture modes. Fracture interfaces are assumed to be either rigidly or cohesively bonded. Analytical theories are developed within the contexts of both classical and first-order shear deformable laminated composite theories. When a rigid interface is assumed for brittle fracture, there are two sets of orthogonal pure modes in classical theory, and there is only one set of orthogonal pure modes in shear-deformable theory. A mixed-mode fracture is partitioned by using these orthogonal pure modes. The classical and shear deformable partitions can be regarded as either lower or upper bound partitions for 2D elasticity, and hence approximate 2D elasticity partition theories are developed by 'averaging' the classical and...
Tehnicki vjesnik-Technical Gazette, 2015
Original scientific paper Delamination (fracture) tests have been numerically investigated using various cohesive zone properties. The test utilises asymmetric and symmetric double cantilever beam specimens loaded with bending moment. Energy release rate contributions from mode I and mode II fracture are calculated using a global and local approach. Mode-mixities results are presented and analysed. The numerical partitioning results for different configurations are compared to two analytical partitioning theories, namely, after Williams and after Hutchinson and Suo. Opposite to these theories, partitioning is observed to be dependent on cohesive zone properties.
Modeling of delamination propagation in composite laminated beam structures
AIP Conference Proceedings, 2012
A numerical method is developed to predict delamination propagation in composite laminated beam structures under lateral and axial loads. Full geometrical nonlinearity is included in the development of beam elements and the interfaces are modeled with imaginary interface springs. The one step crack closure technique, a contact algorithm and tensor symmetrization are employed in the formulation. It is found that asymmetric composite beam elements suffer from membrane locking and this is completely solved in the work. Also, the mode partitioning results are different to those from the existing mode partition theory. A new theory is developed which shows the flaw in the existing theory and demonstrates the validity of the imaginary interface spring model. In general, excellent agreement with existing numerical and experimental results is observed.
Characterization of Delamination Fracture Surfaces Under Mixed Mode Loading
Delamination is an important mode of failure on laminated composite materials and the characterization of this failure mode is a subject of research. Mode I, mode II, mode III and mixed-mode I+II fracture toughness were obtained using the double cantilever beam test (mode I), the end notch flexure test (mode II), the original and the modified edge crack torsion test (mode III) and the mixed-mode bending test (mixed-mode I+II) respectively. Fracture surfaces obtained during mode III interlaminar fracture toughness of glass/epoxy composites have been also studied using the original and the modified edge crack torsion test geometry. Results were compared with delaminating surfaces obtained during tests of mode I, mode II and mixed-mode I+II. In the original ECT test the hackle marks appears only in the side of the loading pin. In the modified ECT test the hackle marks appears in both sides of the sample and slightly less well defined and smoother fracture features in the middle of the ...
A new mixed mode I/II failure criterion for laminated composites considering fracture process zone
Theoretical and Applied Fracture Mechanics
In this paper, by considering the absorbed energy in the fracture process zone and extension of the minimum strain energy density theory for orthotropic materials, a new mixed mode I/II failure criterion was proposed. The applicability of the new criterion, to predict the crack growth in both laminated composites and wood species, was investigated. By defining a suitable damage factor and using the mixed mode I/II micromechanical bridging model, the absorbed energy in the fracture process zone was considered. It caused the new criterion to be more compatible with the nature of the failure phenomena in orthotropic materials, unlike available ones that were conservative. A good agreement was obtained between the fracture limit curves extracted by the present criterion and the available experimental data. The theoretical results were also compared with those of the minimum strain energy density criterion to show the superiority of the newly proposed criterion.
A Testing Procedure for Mixed Mode Delamination of Composite Materials
A mixed-mode delamination test procedure was developed combining mode I, double cantilever beam (DCB) and mode II, end-notch fixture (ENF) loading on a split unidirectional laminate. The test is based on the standard D6671 of ASTM international ìStandard test method for mixed mode I ñ mode II interlaminar fracture toughness of unidirectional fibre reinforced polymer matrix compositesî. By loading with a lever, a single applied load simultaneously produces mode I and mode II bending loads on the specimen. The mixed-mode bending test (MMB) was demonstrated using a quasi-isotropic laminate [(-45, 90, 45, 0)4]s made of unidirectional carbon fibre reinforced epoxy. The mode I and mode II components of strain energy release rate GI and GII, respectively were obtained for a wide range of GI/GII ratios. The initial delamination is in the midplane of the laminate.