Keywords: composites, Hooke's law, fibre angle, MATLAB, composite design, micromechanical analysis.

Composites have the disadvantage of tedious design processes [1]. Conventional methods for designing composite structures involve the use of Hooke's law for two-dimensional unidirectional composites. Equations have been developed and are available from various texts [2,3,4]. These equations are limited to flat unidirectional laminates.

The calculation procedure for this conventional approach is quite laborious to follow and very tedious. A computer program was developed in MATLAB to perform the computations automatically. The inputs are the material properties, material limits, number of fibre layers, and the fibre orientation and thickness of each layer. The output of the program is the global and local stresses and strains of each layer. These stresses are then compared with allowable values and, if they exceed these limits, the entire process needs to be repeated with new inputs. This program was tested against manually calculated examples in the various texts [2,3] and the results were exactly comparable to the manual computations.

In the above program the number of layers and the fibre orientation needs to be known. However these will not be known when commencing the design stage. Therefore the above program was adapted to create a second program. The number of inputs was reduced to the material properties, material limits and applied loading conditions. The outputs of this program are the number of layers and the fibre angle of each layer. These outputs were input into the conventional program in order to verify the results. In each case the resulting composite structure did not fail.

Another program based on the micromechanical analysis of composites was developed. This program determines the material properties of a composite from the properties of its constituent components. The aim of this program is to assist the user to build a database of properties of composite materials. When using the above programs, a composite may be chosen from a list rather than having each property being input manually.

The use of these programs will greatly reduce the design time as the numerous computations are completed in a fraction of the time that it would take if done manually.

1

S.K. Mazumdar, "Composite Manufacturing: Materials, Product, and Process Engineering", CRC Press LLC, USA, 2002.

2

A.K. Kaw, "Mechanics of Composite Materials", CRC Press LLC, Florida, USA, 1997.

3

C.T. Herakovich, "Mechanics of Fibrous Materials", John Wiley & Sons Inc., USA, 1998.

4

R.M. Christensen, "Mechanics of Composite Materials", Dover Publications, Mineola, New York, 2005.

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