A permeability prediction for non-crimp fabrics

A model is proposed to analyse the variation in the permeability of Non–Crimp Fabrics, originating from variations in the internal structure of the material. A geometrical description of the fabric based on the distortion induced by the stitch threads piercing through the fabric is employed. The distortions form channels which are mutually connected. It is assumed that these channels dominate the permeability of the fabric. A network of flow channels is subsequently defined, in which the variations, measured in the dimensions of the distortions, is explicitly accounted for. The variations in the internal structure of the fabric affect the averaged permeability significantly. Moreover, a network rather that a single unit cell is required to predict the averaged permeability and its variation properly. Finally, the spatial distribution of the randomly generated channel dimensions affects the permeability significantly

A permeability prediction for (un)sheared non-crimp fabrics

A permeability prediction model for relaxed and sheared Non-Crimp Fabrics is proposed. The model is based on geometrical features of the fabric. The stitches penetrating the uni-directional plies of the NCF induce distortions of the fibres in the plane of the fabric. These Stitch Yarn induced fibre Distortions (SYD) form flow channels, which determine the permeability of the NCF. The channels are connected to each other in overlap regions, allowing the fluid to flow from one channel to another and finally to impregnate the entire preform. A network of SYD flow channels is created to account for the statistical variations in the dimensions of the SYDs. The system of flow resistances is solved analogously to the solution of the effective resistance of an electrical circuit with parallel and serial resistances. The flow in each of the SYD domains is calculated employing an energy minimisation method. Analysis of different networks, with varying spatial distribution of the dimensions of the flow channels, allows the prediction of the variation in the permeability of an NC

Development of a Damage Quantification Model for Composite Skin-Stiffener Structures

The development of a model-based approach for a damage severity assessment applied on a complex composite skin structure with stiffeners is presented in this paper. Earlier investigations on composite structures with stiffeners revealed that a vibration based structural health monitoring approach, employing the Modal Strain Energy Damage Index (MSE-DI) algorithm can detect and localise delaminations. The next step, performed in the presented part of the research, is to assess the severity of the damage. It is shown that combining results from a fre-quency based analysis and from a modal strain energy based analysis can enhance the quantifica-tion of the severity estimation. This conclusion was drawn by analysing the effect of small masses that were added at a specific location in to mimic a damage, but maintain reversibility of the dam-age. The use of a numerical model to create a virtual test space was found to be valuable for the interpretation of experimental dat

Experimental investigation of the compressibility and permeability of fabric reinforcements : abstract

ABSTRACT: A measurement method for the out-of-plane permeability is presented in this paper. The developed permeameter is capable to measure both compression as well as the out-of-plane permeability. First results show an out-of-plane permeability that is in accordance with values found elsewhere. The compression test needs some more refinement and is not discussed here. The design of the instrument is such that it is relatively easy to change a preform between subsequent tests. A first attempt has been made to measure the viscosity of the test fluid in-line

Vibration based Structural Health Monitoring of a Composite Plate Structure with Multiple Stiffeners

A vibration based damage identification method is investigated experimentally.\ud The dynamic response of an intact and a locally damaged 16–layer unidirectional\ud carbon fibre PEKK reinforced plate structure with two stiffener sections is considered.\ud A forced–vibration set–up, including a laser vibrometer system, is employed\ud to measure the dynamic behaviour. The feasibility of the two–dimensional Modal\ud Strain Energy Damage Index algorithm to detect and localize impact induced defects\ud is demonstrated

Damage identification in composite panels using guided waves

A methodology for the identification of barely visible impact damage using guided waves on a typical aircraft composite structure is implemented. Delaminations and debondings have been introduced in two stiffened panels by means of impact loads