Composite optimisation in motorsport and the consideration of practical manufacturing
Summary
The application of composite materials in Motorsport has become understandably commonplace thanks to the stuctural performance benefits they provide. This couples with the suitability of the low volume production techniques that are commonplace thanks to the structural performance benefits they provide. This coupled with the suitability of the low volume production techniques that are common for pre-preg materials makes them very suitable to the Motorsport arena.
First used in the construction of a Formula 1 car chassis in 1981, carbon fibre composites are now used extensively in almost all aspects of the car’s construction and race teams are able to manufacture extremely complex geometrics as the pursuit of aerodynamic efficiency continues.
With the rise in demand of composite materials structural simulation techniques, particularly the Finite Element Method (FEM) have developed to support the prediction of their stiffness and strength characteristics. In the mid-1990’s tools such as the MSC/Patran and Anaglyph Laminate Tools introduced techniques to predict and model the effect on material properties of the draping of long-fibre composite materials over complex curved geometrics, further improving the accuracy of simulation predictions. Today most of the major Finite Element software providers offer the capability to model composite materials within their standard solver routines and code such as MSC/Nastran, Simulia Abaqus, NX/Nastran and VR&D Genesis provide composite modeller tools to allow the automatic management and calculation of resulting laminate properties based upon pre-defined laminate scehdules.
Over a similar period of time as the growth of composite material usage in Motorsport, simulation based structrual optimisation techniques have developed, with capabilities specifically suited to composite materials evolving in the last 15 years. The presentation will discuss the development and capabilities of these methods and how the techniques are managed to provide manufacturable solutions for composite laminates. The presentation will discuss the application to a comptemporary Formula 1 style chassis and the consideration of certain manufacturing requirements.
1. Determining Ply Placement
When developing a carbon fibre laminate for a Formula 1 car chassis the design must support many different requirements for stiffness and strength based loading. In order to achieve the most mass efficient design to support all of the requirements the design engineer must determine the placement, shape and orientation of plies to make best use of the characteristics of the individual lamina.
Many different optimisation methodologies have been applied to the challenge of developing composite laminates, however, a very suitable and well employed approach is the Finite Element based gradient method. Within this method two key approaches are best suited to the optimisation of composite laminates, which are sizing and topometry; both of which will be discussed further.
Sizing optimisation is the optimisation of specific properties of an FE model which, in the case of composite laminates, are the ply thickness and ply angle. Topometry optimisation is an extension of the sizing method where the optimisation algorithm automatially divides the FE model into 1 property per element or element-group.
2. Applying the Consideration of Manufacturing Rules
Whilst the methods of Topometry and sizing can be theoretically applied to a Formula 1 car chassis the practical applicationrequires careful management of the composite propertry data and effective interpretation into physical discrete plies. Taking the example of a single ply whose thickness contour plot over the chosen structure. In order to achieve the optimised thickness distribution by way of discrete composite plies, layers must be built up of differing ply shapes which, when combined, achieve the desired material thickness.
Further to the basic principles of using the sizing and topometry methods to develop optimum composite laminate definitions practical rules must be incorprated into the optimisation forulation. One key example of these rules is the limitation of the minimum and maximum thickness of a laminate. This may be acheived in several ways, however, a common approach is the creation of equations which calculate the total thickness of a selection of composite plies and then constraints are defined on these equations which calculate the total thickness of a selection of composite plies and then constraints are defined on these equations. The process can also be applied to selections of plies within a laminate in order to ensure a composite laminate does not become dominant with a particular material or orientation or composite fibres.
When performing an optimisation on a structure such as a Formla 1 car chassis, the number of plies and manufacturing rules being considered requires the formulation of very large and complex optimisation problem formulations. Managing these problem formulations and the resulting data that is generated by them becomes a complex task, which is not easily achieved as a manual process. Software tools are therefore required to facilitate the optimisation process and such tools have been developed over the last 15 years to work alongside the standard FE analysis solvers.
One such tool is GRM’s OptiAssist, which has been specifically developed to work with the structural optimisation code VR&D Genesis, whilst also linking with composite analysis data generated from a number of standard composite codes such as Simulia Abaqus, MSC/Patran & Nastran, NX/Nastran and Anaglyph Laminate Tools. The OptiAssist tool has been used within Motorsport and specifically tackle the composite optimisation challenges presented within this sector.
Through toold such as OptiAssist the process of composite optimisation, considering practical manufacturing factors has become a significantly more commonplace practice which, in turn, has allowed engineers to better utilise the inherent benefits available by the effective use of composite materials.
