What are the pros and cons of fiberglass body?

Question

Fiberglass is a prominent material for building boats. It's well-tested and durable. Over the years, there have been few attempts to adopt fiberglass as in automotive industry:

• Glasspar G2 - a 1950 car with all-fiberglass body
• Chevrolet Corvette from C1 up to C7 seems to use fiberglass panels in body
• Multiple cars from Lotus, including Elite, Europa, Elan and Espirit used all-fiberglass bodies
• There are numerous kit-cars with fiberglass bodies.

Overall, while fiberglass body is used in the industry, it isn't widely adopted. Why? What are the pros and cons and why cons outweight pros?

Answer 1

I think the main disadvantage of Fibreglass (aka Glass Reinforced Plastic or GRP) is that it cracks and breaks in an impact, rather than deforming and absorbing energy like metal does - so a GRP bodied car would still need an internal crash structure to protect the occupants, removing a lot of the advantages.

British Reliant cars (particularly the Scimitar) in the 1970s had GRP bodywork, and many have been scrapped due to rust in the internal roll-over bars - which are bonded into the bodyshell and to very difficult to repair!

Most use in more recent times has been for individual panels, particularly non load-bearing ones such as roof panels on vans and trucks - where there is another advantage as an unpainted relatively thin GRP panel is semi-translucent, and so allows light into the load-space, as well as it's light weight lowering the centre of gravity of the vehicle.

Answer 2

Pros

• Lightweight.
• Does not rust.
• Does not get dents.

Cons

• Breaks/cracks if bent too much.
• Is not as durable as metal.
• Can deform with heat.

Answer 3

The major reason is probably cost.

Steel panels need expensive tooling to produce them, but once an investment has been made in that tooling the panels can be produced rapidly and cheaply. Drop in a flat sheet of steel and a few seconds later you have a shaped panel.

With GRP the tooling is relatively cheap, but it takes a long time to produce a panel from that tooling. The matting needs to be cut to shape then laid out (most likely by hand), with overlapping areas carefully aligned, all of which is a relatively skilled job. Some sections will need the 'grain' of the matting carefully aligning. Resin can then be added. To minimise weight (and keep it fairly consistent) the panel will then needing bagging up to suck out the excess resin while it cures, all of which takes time.

Carbon fibre is similar but even more time consuming.

If you are making a few hundred panels then the tooling cost savings of GRP outweigh the high labour costs, but once you get to the thousands the labour costs become uneconomical. Hence GRP bodywork tends to be heavily used for limited production vehicles

I suspect another major consideration now for production vehicles is the ability to recycle GRP panels.

Note that even in the 1950s Lotus put in to production a car with a GRP monocoque body shell with no separate chassis.

Answer 4

One thing that most people neglect to mention is UV stability: even with so-called UV inhibitors, any GRP which is left out in the sunlight will begin to deteriorate: the resins will become brittle and the coloured gel-coat top surface will get spider-web like cracks in it and lose colour. I've seen Lotus Europas that look like they're about ready to disintegrate, just because they've been in the sun for a few decades (and this is much harder to fix than rust) GRP has been popular for a number of decades with kit and low-production manufacturers (in the 50's lotus was very much run like a kit-car company in their methodology) so it is good for low production (tooling and setup) costs.

On the other hand, it's much quicker to have a dedicated steel press hammering out panel after panel, usually at a rate of one or more a second. Glass usually takes a few hours to set or cure before it can be removed from the mould. so on one hand, you can produce car bodies with minimal setup costs (quite a lot of the moulds I"ve used over the years have been made of wood with a layer of glass and gelcoat to give a nice surface to then take mouldings from) vs. the cost of making steel dies for pressing, but then on the other hand, the daily production of bodies in steel will be much higher, which is what the major manufacturers want.