Kanninen, M.F.: A finite element calculation of stress intensity factor by a modified crack closure integral. Eng. Fract. Mech. 9, 931-938
ABSTRACT An efficient technique for evaluating stress intensity factors is presented. The method, based on the crack closure integral, can be used with a constant strain finite element stress analysis and a coarse grid. The technique also permits evaluation of both Mode I and Mode II stress intensity factors from the results of a single analysis. Example computations are performed for a double cantilever beam test specimen, a finite width strip with a central crack, and a pin loaded circular hole with radial cracks. Close agreement between numerical results given by this approach and reference solutions were found in all cases.
- SourceAvailable from: Debasish Roy
[Show abstract] [Hide abstract]
- "While the first one broadly works within the classical fracture mechanics setting, the second poses the problem as one in damage mechanics, softening plasticity, or a combination of the two . The first approach, which employs classical fracture mechanics, uses stress-based criteria to predict delamination initiation  , and techniques based on linear elastic fracture mechanics (LEFM) such as virtual crack closure technique (VCCT)     , J-integral method , virtual crack extension , or stiffness derivative  to model delamination propagation. However, finite element (FE) implementations of the LEFM techniques are fraught with difficulties, especially as the simulation of delamination growth may require complex moving mesh techniques . "
ABSTRACT: A micropolar cohesive damage model for delamination of composites is proposed. The main idea is to embed micropolarity, which brings an additional layer of kinematics through the micro-rotation degrees of freedom within a continuum model to account for the micro-structural effects during delamination. The resulting cohesive model, describing the modified traction separation law, includes micro-rotational jumps in addition to displacement jumps across the interface. The incorporation of micro-rotation requires the model to be supplemented with physically relevant material length scale parameters, whose effects during delamination of modes I and II are brought forth using numerical simulations appropriately supported by experimental evidences.Composite Structures 04/2015; DOI:10.1016/j.compstruct.2015.05.026 · 3.32 Impact Factor
[Show abstract] [Hide abstract]
- "Increased computational processing power and understanding of composite failure has enabled the development of finite element modelling techniques that can simulate damage growth within composite structures. Numerical analysis techniques include the Virtual Crack Closure Technique (Rybicki and Kanninen, 1977; Krueger, 2004) and the use of interface elements, which are specialised finite elements placed along potential failure planes and used to simulate crack growth (Camanho et al., 2003; Jiang et al., 2007; Hallett, 2007). A key advantage of interface elements is that they can encompass both strength based damage initiation criteria and fracture based crack propagation criteria. "
ABSTRACT: Tidal stream turbine blades must withstand both extreme one-off loads and severe fatigue loads during their 20–25 year required lifetimes in harsh marine environments. This necessitates the use of high-strength fibre reinforced composite materials to provide the required stiffness, strength and fatigue life, as well as resistance to corrosion, whilst minimising the mass of material required for blade construction and allowing its geometric form to provide the required hydrodynamic performance. Although composites provide superior performance to metals, potential failure mechanisms are more complicated and difficult to predict. A dominant failure mechanism is interfacial failure (delamination) between the composite layers (plies). This paper demonstrates how the development of numerical techniques for modelling the growth of interfacial cracks can aid the design process, allowing the effects on crack growth from potential manufacturing defects and the effect of stacking sequence of composite plies to be analysed. This can ultimately lead to reduced design safety margins and a reduction in the mass of material required for blade manufacture, essential for reducing lifecycle costs. Although the examples provided in this article are specific to tidal turbine blades, the analysis techniques are applicable to all composite structures where fatigue delamination is a primary failure concern.Ocean Engineering 03/2015; 96. DOI:10.1016/j.oceaneng.2014.12.025 · 1.34 Impact Factor
[Show abstract] [Hide abstract]
- "This has led to several testing standards for characterizing delamination under quasi-static and cyclic loading conditions   . Analysis methods have been developed based on linear elastic fracture mechanics and utilize the measurements of fracture toughnesses obtained from these standardized tests as the criterion for delamination growth  . Combined, these experimental and analytical efforts have led to significant advances towards a practical means for assessing the damage tolerance of composite structures from a fracture mechanics perspective. "
ABSTRACT: The transition of delamination growth between different ply interfaces in composite tape laminates, known as migration, was investigated experimentally. The test method used promotes delamination growth initially along a 0/θ ply interface, which eventually migrates to a neighbouring θ/0 ply interface. Specimens with θ = 60° and 75° were tested. Migration occurs in two main stages: (1) the initial 0/θ interface delamination turns, transforming into intraply cracks that grow through the θ plies; this process occurs at multiple locations across the width of a specimen, (2) one or more of these cracks growing through the θ plies reaches and turns into the θ/0 ply interface, where it continues to grow as a delamination. A correlation was established between these experimental observations and the shear stress sign at the delamination front, obtained by finite element analyses.Composites Part A Applied Science and Manufacturing 02/2015; 73C:20-34. DOI:10.1016/j.compositesa.2015.02.018 · 3.01 Impact Factor