1,720,979 research outputs found
Concepts for bridged mode II delamination cracks
No full textLimiting cases and length scales are detailed for Mode II delamination cracks bridged by through-thickness reinforcement. Analytical results are found for two limits: a steady-state configuration indicative of noncatastrophic failure and a small-scale bridging configuration indicative of catastrophic failure. General large-scale bridging conditions are studied numerically using bending theory for anisotropic plates. The effects of the mechanical properties of the laminate and the reinforcement, notch length, and plate thickness on the transition between the two limiting configurations, notch sensitivity and mechanical behavior are analyzed. All of these effects can be expressed succinctly in terms of a few length scales which are material-structure parameters involving the plate thickness. (C) 1999 Elsevier Science Ltd. All rights reserved
Mode II delamination cracks in laminate composites with through-thickness reinforcement
No full textAnalytical results are found for the limiting configurations of a mode II delamination crack in a laminate composite beam with through-thickness reinforcement. Crack growth under more general large-scale bridging conditions is studied by a numerical model based on a bending theory for anisotropic plates. The effects of the mechanical and geometrical properties of the laminate and of the bridging mechanism developed by the reinforcement on the mode of failure are studied
Towards Standardization for Through-Thickness Reinforcement of Laminates
No full textThrough-thickness reinforcement in the form of stitching, short fibrous or metallic rods (z-pins), or woven or braided tows suppresses delamination and may well offer a cost-effective approach to durable laminated structures. The through-thickness reinforcement acts as a crack bridging mechanism, with benefits of crack arrest or total suppression. However, certifying through-thickness reinforcement for delamination resistance has been impeded because delamination cracks do not behave according to Linear Elastic Fracture Mechanics (LEFM) in these composites. The bridging mechanism may act over quite long crack lengths, leading to so-called large scale bridging problems. Structural optimisation and the correct prediction of delamination, stiffness loss, and ultimate failure can therefore emerge only from correct fracture mechanics, which is not traditional LEFM, but involves fracture concepts that are new to most of the design community. Progress towards standardised design methods for these systems will be reviewed, including advances in modeling, the design of standard experiments, and the challenge of educating a generation of designers in simple but sound design practices
Bridged delamination cracks in curved beams and mixed-mode bending specimens
No full textTheoretical approaches based on bridged-crack models and plate/beam theory have proved to be effective in the modeling of Mode I and Mode II delaminations in composite laminates reinforced through the thickness. This paper deals with some aspects of the modeling of Mixed Mode delaminations. Two typical mixed mode problems are considered: the curved beam in bending (C specimen) and the Mixed-Mode Bending specimen (MMB) reinforced through the thickness
Interlaminar fracture of laminates with through-thickness reinforcement
No full textThe influence of through-thickness reinforcement on Mode II delamination fracture in composite laminates is investigated. The bridging traction law, which characterizes the toughening mechanisms due to the through-thickness reinforcement, is deduced from crack profile measurements in End Notched Flexure specimens. The problem is solved through an inverse formulation of a bridged-crack model based on bending theory for anisotropic plates
Beam theory and weight function methods for mode I delamination with large scale bridging
No full textA nonlinear fracture mechanics model is formulated for analysis of mode I delamination of orthotropic
double cantilever beam specimens in the presence of large scale bridging conditions. The problem is solved
using a nonlinear integral equation approach in terms of stress intensity factors at the crack tip. An
approximate weight function is proposed and validated numerically for a pair of concentrated forces acting
on the surfaces of the delamination. The model accounts for the presence of regions of contact along the
wake of the crack, which may form due to the action of the bridging mechanisms. The influence of the
orthotropy of the material on the fracture behavior is investigated and the validity of approximated solutions
based on beam theory is checked
Designing dynamic tests to assess rate dependence in large-scale crack bridging
No full textA numerical study is used to design test geometries and loading histories that can probe the mode II bridging effect of through-thickness reinforcement in composite laminates loaded at high strain rates. Rate-dependence in the assumed cohesive law of a cohesive fracture model causes large enough changes to calibrate the law, if tests are properly selected to vary the crack sliding displacement rate
Small fatigue cracks in laminates with through-thickness reinforcement
No full textSmallness in cracks is determined by the size of the domain over which nonlinear processes occur. In fiber-reinforced composites, diverse nonlinear processes arise, including those intrinsic to the matrix and those associated with crack shielding phenomena on a much larger scale. The length scales characterizing these processes will be reviewed here. In laminates containing through-thickness reinforcement such as stitched or woven fiber tows or short rods, the scales associated with smallness in fatigue delamination cracks can be very large (~ 100 mm). Thus in analyzing structures containing such cracks, the usual approaches to fracture predictions are inadequate. The path to correct modeling will be discussed and an engineering approach to fatigue life prediction outlined
The science and engineering of delamination suppression
No full textBasic research issues and engineering challenges are discussed for delamination cracks in laminates that are reinforced through the thickness. A fairly complete picture is now available of the mechanisms of deformation of through-thickness reinforcement in mixed mode loading, with some insight into fatigue and dynamic loading effects. A growing body of work on delamination fracture in the presence of large bridging zones indicates a viable approach to the engineering problems of creating uncomplicated design methods and processes of certification. Some fracture concepts are required that are beyond the traditional body of engineering fracture mechanics
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