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IMPACT AND FRACTURE RESISTANT LAMINATES

IP.com Disclosure Number: IPCOM000243484D
Publication Date: 2015-Sep-24
Document File: 4 page(s) / 907K

Publishing Venue

The IP.com Prior Art Database

Abstract

TECHNICAL FIELD

This disclosure relates to improving the impact and fracture resistance of the laminated composites made by resin infusion.

PROBLEM TO BE SOLVED AND PRIOR ART

In general, in-plane laminates are prone to damage due to impact. This damage could be in the form of delamination or dis-bond or interlaminar crack in the laminates due to an external body hitting the laminate.

The figures below show an example of a failure due to impact from a foreign body.

The crack can lead to grow and cause final fracture or it can lead to the reduction in structural stiffness causing excessive deformation of the structure and thus disturbing the aerodynamics. Or, the change in stiffness can cause change in primary load path and hence starts failure in other components which takes over the load.

Impact and fracture resistance in composites are traditionally improved by 3D weaving or introducing a kind of rubber layers in between the laminas or improving the properties of the resins. The 3D weaving has been quite complex process as it needs specific tools and techniques for specific type of structures. And, using a rubber layers between two laminas has also been limited because the properties of the rubber is destroyed at the curing temperature of the composites (120oC and above). However, some useful work has been done in the past in improving the properties of the resins.

DESCRIPTION

The proposed technique introduces chopped fibres in the resin/matrix material so that it changes the mechanics of failure in laminates and thus reducing the chance of delamination or crack growth in the damage prone areas. In general, when an external body impacts the composite laminate, the failure is in shear mode.

Or when bends and corners are loaded, the layers delaminate in tension. These sort of failures can be reduced if we can introduce short fibres along the thickness of the laminates as these fibres changes the mode/ mechanics of failures. When shearing failure initiates, the short fibre obstructs the growth of the crack. And, when tensile failure initiates, the resin has to shear off along the short fibre or pull the short fibre off the matrix.

Now the question is how to introduce these short fibres along the thickness of the laminate in the resin material. The following steps may be used in the commonly used RTM process (Resin infusion is widely used these days for increased production rates of the composites):

(1) Layup few layers of the dry fibres

(2) Sprinkle chopped fibres on it

(3) Layup again few layers of dry fibres

(4) Sprinkle again the chopped fibres on it

(5) Continue till you achieve the required laminate. One can have lower density of chopper fibres at the top and bottom faces of the laminate

(6) Tightly assemble the dry laminate in a mould so that long fibres (UD) are not allowed to move. Pass the high velocity air through the inlet channels. Flow of high velocity of air for a short duration is meant to move the short fibres in the thickness direction of the laminate into the long fibres.

(7) Plug the inlet channel holes. Remove the upper channel assembly. Debulk the laminate, and then carryout the resin infusion as per the standard process.

(8) Debulk after infusion, apply pressure & cure as per the standard process.

The above technique can be implemented in processing laminates at the specific locations which are prone to impact damage like wing lower cover areas close to tyres which are exposed to tyre debris. In addition, the corners and bends will have improved delamination strength if processed through the above technique.

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This is the abbreviated version, containing approximately 52% of the total text.

Page 01 of 4

IMPACT AND FRACTURE RESISTANT LAMINATES

TECHNICAL FIELD

This disclosure relates to improving the impact and fracture resistance of the laminated composites made by resin infusion.

PROBLEM TO BE SOLVED AND PRIOR ART

In general, in-plane laminates are prone to damage due to impact. This damage could be in the form of delamination or dis-bond or interlaminar crack in the laminates due to an external body hitting the laminate.

The figures below show an example of a failure due to impact from a foreign body.


Page 02 of 4

The crack can lead to grow and cause final fracture or it can lead to the reduction in structural stiffness causing excessive deformation of the structure and thus disturbing the aerodynamics. Or, the change in stiffness can cause change in primary load path and hence starts failure in other components which takes over the load.

Impact and fracture resistance in composites are traditionally improved by 3D weaving or introducing a kind of rubber layers in between the laminas or improving the properties of the resins. The 3D weaving has been quite complex process as it needs specific tools and techniques for specific type of structures. And, using a rubber layers between two laminas has also been limited because the properties of the rubber is destroyed at the curing temperature of the composites (120oC and above). However, some useful work has been done in the past in improving the properties of the resins.

DESCRIPTION

The proposed technique introduces chopped fibres in the resin/matrix material so that it changes the mechanics of failure in laminates and thus reducing the chance of delamination or crack growth in the damage prone areas. In general, when an external body impacts the composite laminate, the failure is in shear mode.

Or when bends and corners are loaded, the layers delaminate in tension.


Page 03 of 4

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