Finite Elements for Damage & Fracture

Floating Node Method (FNM)

The Floating Node Method (FNM) enriches the finite element definition with all its useful geometrical entities such as nodes, edges and surfaces. Degrees of freedom (DoF) can be allocated to these entities to represent their changes during analysis. It opens up a flexible way of forming "smart" elements - self-partitioning elements tailored for a particular material of interest.

FNM solid element general definition

FNM lamina element - definition and partitioning with respect to a crack

A laminate element formed by FNM

References: 2D floating node method, 3D floating node method, separable cohesive element.

Damage and Failure Predictions for Composites

In-Plane Fracture

FNM can predict the competition between matrix cracking and delamination and the effect of ply thickness on matrix crack saturation density and delamination area (note: red dots are failed integration points).

FNM can predict the large and complex crack networks exhibited in open-hole composite laminates under in-plane loading, including the full-length matrix splits and full-scale delamination.

0-degree open-hole lamina: explosive splittings

Cross-ply open-hole laminate: dense matrix cracks

Reference: 3D floating node method, Open-Hole Tension, Open-Hole Compression

Delamination Migration

Delamination migration is a common fracture event in composite laminates under bending (such as in low-velocity impact). It is a challenging problem for modelling because the critical damage mechanism is matrix crack/delamination interaction. Here, the FNM elements nicely captured the multiple migration events in the laminate.

Reference: my PhD thesis, 2D delamination migration and 3D delamination migration

Fatigue crack propagation

FNM has been successfully combined with other techniques to model fatigue crack propagation in composites. Examples include the combination with the Virtual Crack Closure Technique (VCCT) in collaboration with researchers from National Institute of Aerospace and NASA Langley Research Center, and the combination with the high-cycle fatigue model developed by researchers from Aalborg University.

Reference: FNM with VCCT for fatigue; FNM for high-cycle fatigue

2016-ECCM17-Munich.pdf

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