Simulation goes on the transfer list.(Software)

UNTIL quite recently, if you wanted to know how an idea or a design would work out, there was only one option. You had to make it and try it out. If you could not make the real thing, you had to make the best approximation you could manage or afford. Then you had to try to allow for the inaccuracies in your model. You could play safe but if you worked at the cutting edge of design, you risked catastrophe.

No one worked closer to the edge than the cathedral builders. Sadly their designs could and did fall down. Some of what we see today was created by designers who learned from those disastrous experiences. Only the greatest or the bravest designers could transcend these limitations. Brunel's railway bridge at Maidenhead has the flattest brick arches in the world. Even today it looks inconceivable that it can stand and indeed its collapse was confidently predicted over 160 years ago. But Brunel got it right. This is fine if you are a genius but what about the rest of us?

Two things have come to our rescue; science and computing. Science has enabled us to understand materials, structures and processes. Computing has allowed us to use that knowledge in everyday design, without having scientists and mathematicians on call. What emerged was simulation software; the virtual experiment. We can now know, with a fail degree of certainty, whether our ideas will work. We can know that quickly and we can know it cheaply. Simulation works, from the most practical situations to the most esoteric.

Apparently one reason why nations agreed to a nuclear test ban treaty is that much of the development work could still go on by simulation.

Simulation of course has made its way into plastics processing where it received a cautious but lasting welcome. Plastics processing is a natural candidate for simulation. The materials are complex and the processes are costly. So much so that the whole thing was long regarded as an art rather than a science-based proposition, and it was this as much as anything that made simulation difficult for many people to accept. It is here now but bow far has it penetrated? For most people, simulation means injection moulding but what about the other plastics processes? There is software for simulating extrusion, thermoforming and blow moulding but after that? This month we look at one of the lesser known areas--resin transfer moulding.

Resin transfer moulding, or RTM, is a closed mould process. Reinforcing fabrics or fibres are clamped in the mould--they may be preformed to the mould shape or pressed into shape by the mould closing--and are then injected under pressure with a resin. The impregnated reinforcement is then cured to create the finished article.

The process has more than enough complexity to justify simulation. Resin injection can be under pressure or vacuum assisted, the process can be hot or cold, the mould shape can be complex, the material, form and orientation of reinforcements is almost limitless, and many types of resin can be used including epoxies, polyesters, ...