GB2492978A - Method for optimising design of fibre reinforced component using models with and without reinforcement - Google Patents

Abstract

A model of the component without reinforcement is prepared (10) and simulated loads are applied to the model (11). Fibre reinforcement is then added to the model in regions of unacceptable stress (12, 13) and simulated loads are then reapplied. The quantity and location of the reinforcement fibres are modified and the steps of re-simulating and modifying (15) are repeated as necessary. Identifying stress of the component may be carried out by finite element analysis. The component may be made from injection moulded polypropylene with glass or carbon fibre reinforcement.

Description

Reinforced Components

Background

The current invention relates to the design and manufacture of composite materials utilising selective reinforcement.

Composite materials are formed of multiple layers of aligned fibres within a matrix material. Fibres within each layer are aligned with each other, and the number of layers and their orientation are selected to provide the required structural properties and to prevent distortion during manufacture and use.

Such composite materials approximate amorphous materials and are often referred to as Quasi Isotropic Laminates.

Such composite components have extremely good strength to weight properties and are therefore very attractive for high-performance applications such as aerospace. However, reinforcing fibres, particularly carbon fibre, are expensive leading to a high cost of manufacture, which may preclude the use of composite technology in lower cost markets.

Summary

Aspects of the invention are set out in the claims.

Description of the drawings

Embodiments of the present invention will now be further described, by way of example, with reference to the drawing, wherein:-Figure 1 shows a flow-chart of a method of designing a composite componet.

Detailed description

The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example.

However, the same or equivalent functions and sequences may be accomplished by different examples.

Figure 1 shows a method of designing a composite component which enables the cost of manufacture to be reduced compared to conventional design utilising layers of parallel fibres.

At block 10 a mathematical model of the component to be formed is composed for use in a finite element stress analysis. The component is defined in an amorphous material without any reinforcement and having material properties worse than the intended manufacture material to enable analysis of stresses.

At block 11 a stress analysis is performed applying the design loads to the model. At block 12 the resulting stress plot is analysed and overloaded regions identified. Directional reinforcement is added to the model in the overloaded regions at block 13 and the process returns to block 12 to re-run the analysis. The reinforcement may comprise fibres running in arbitrary non-parallel directions as required to provide the required strength for the component when loaded according to the component design parameters.

The steps of blocks 12 and 13 are repeated; adding, changing or removing reinforcement at each re-run, until a reinforcement design which achieves the designers objectives is achieved which reduces component stresses to within acceptable limits. The resulting design is a substantially amorphous carrier with a skeleton of reinforcement fibres present only where and in the particular directions required to provide the required performance.

At block 14 the properties of the carrier material are changed to the properties of the actual material to be used in production. For example, a low-cost glass fibre composite may be utilised. At block 15 the analysis is re-run and at block 16 optimisation of the component is performed to minimise material usage (both matrix and reinforcement) and ensure suitable performance.

At block 16 the component is manufactured according to the design using conventional fabrication techniques. For example, a flat form of the glass-fibre may be produced and the shape cut from glass fibre pre-preg material.

The material is laid up in the required layout, and the reinforcement skeleton added using carbon fibre pre-preg. A second layer of glass fibre may be placed over the carbon fibre. The component is then cured. Any conventional fabrication technique may be utilised.

This design technique enables a component to be manufactured principally from low-cost materials such as glass-reinforced polyester resin. Selective, directional, reinforcement utilising high-performance fibres is positioned within, or on, the low-cost materials to provide the required structural properties.

Such components utilise smaller quantities of expensive material than conventional composites as they avoid the use of reinforcement material where it is not providing a benefit to the performance of the component. The removal of unneeded reinforcement reduces cost, weight, and recycling difficulties at the end of the component's life.

In a particular method of manufacture the reinforcement skeleton is formed from polypropylene impregnated fibres which are laid up in an injection moulding tool. Once the tool is closed, the mould is injected with liquid polypropylene, optionally filled with short lengths of fibre. The heat of the liquid polypropylene partially melts the polypropylene of the skeleton material resulting in a contiguous component. This manufacture method allows the use of injection moulding to produce reinforced components. This method of manufacture may also be suitable for manufacturing composite components designed in any way other than that described hereinbefore.

Elements of the above design and fabrication techniques may be combined with elements of any other design and fabrication technique discussed herein or known elsewhere. For example, the materials used may be any material system suitable for the required application. To further improve component performance auxetic materials may be utilised for the reinforcement and/or matrix. Rather than utilising pre-preg materials, dry cloth or fibres may be utilised and infused with the matrix material, for example by utilising a vacuum bag system.

It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. It will further be understood that reference to an' item refers to one or more of those items.

The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any of the methods without departing from the spirit and scope of the subject matter described herein. Aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples without losing the effect sought.

It will be understood that the above description of a preferred embodiment is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments of the invention. Although various embodiments of the invention have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention.