Accident damage assessment

All damage to the body is covered by the following

categories:

Highly stressed

Moderately stressed

Lightly stressed.

Figure 16.34Final inspection of the completed

Lotus Elan (Lotus Engineering)

16.9 Repair of reinforced composite bodies

The repair of reinforced composite bodies and component

panels is not difficult, and unless major damage

has been sustained it can quite readily be carried

out by a competent body repair shop. If the correct

materials and tools are used and operations are carried

out in the correct sequence, repair is usually considerably

easier than to a metal body damaged in an

accident of similar severity. The equipment required

is simple, the only two items not generally found in

the average workshop being a split washer roller and

a graduated measuring cylinder. Power tools can

speed preparation, but hand tools will be just as effective.

Much of the success of the repair depends on the

correct preparation of the resin mix. If polyester resin

is supplied from a manufacturer, the correct proportions

of resin, catalyst and accelerator will be stipulated.

In calculating the amount of resin required for

the repair, first weigh the cut patches of chopped

Reinforced composite materials 563

On that definition depends the original construction

and therefore the repair method to be employed.

As a general rule there should be a bonded joint

wherever two panels touch, or wherever they close

on important points. It is usually possible to check

these bonds both visually and physically for fractures

and breaks. Ascertain the cause of damage

and the direction of impact and examine all panels

or bonds which may have been affected.

A front-end impact, for example, may easily

cause the bonds at the bulkhead to split without the

defect being easily visible. To facilitate a closer

examination, it may be necessary to remove parts

and mechanical components to determine the extent

of the damage. When determining the replacement

underbody sections and panels to be ordered, make

sure the new underbody section and panels will be

attached to firm composite materials: avoid badly

crazed areas and badly burnt areas.

Fire damage is the most difficult to assess, but

generally only the obviously burnt or charred sections

will need to be replaced or reinforced.

After a moderate or severe accident, checks

should be carried out on the A- and B-posts, chassis

datum points, and suspension and wheel alignment.

Accident repair

For repair purposes, accidents may be defined as

Front section

Centre section

Rear section.

This definition determines the original construction

and therefore the repair method employed.

Resin and gel mix

The panels on GRP vehicles are manufactured using

different types of materials. Therefore, when carrying

out repair, the type of resin and gel mixes used will

depend on the original materials used in manufacture.

Superficial defect repairs

Pin holes or air voids Either drill or rout out so

as to leave a larger hole with near vertical walls, or

enlarge by gouging or picking out. Then fill the

holes with polyester stopper or filler.

Surface crazing There are various causes of surface

crazing, but most results from sharp impacts or accidental

damage. During an accident some panels may

flex sufficiently to cause the surface to craze without

immediate apparent damage to the painted surface.

The crazing may not work its way through the paint

surface for some weeks, so it may be necessary when

assessing accident damage to carefully examine all

panels, particularly near cracks or split bonds. In

case of doubt it may be possible to promote the

appearance of the crazing by applying gentle heat.

Surface crazing itself generally stops at the first

layer of glass fibre and is consequently not structurally

serious. However, the extensive crazing near

damaged areas should be taken as an indication of

over-stressing and the panel should be reinforced or

replaced. It is not possible to remedy crazing by

simply resurfacing with a further layer of resin.

Replacement sections and panels

Where the repair of a damaged vehicle calls for

replacement sections and panels, they may be

obtained in most cases direct from the manufacturer

of the vehicle under repair.

Where severe damage has been sustained, the

damaged section or panel may be cut away, and a

replacement section or panel grafted in. Before cutting

away any damaged section, or before ordering

replacements, the repairer should ascertain the proposed

method of repair and the positioning of joint

lines. Determine a method of correct positioning of

replacement panels and sections such as B-posts,

A-posts, or any prominent feature from which measurements

can be made, and scribe these clearly on to

the section which is to be used. Use a marker to

define the lines on which it is proposed to cut the

section or panel. Study these lines to see that any

damaged section or panel removed will allow adequate

pick-up points on the replacement section to

ensure it can be accurately positioned, and that the

proposed outline transverses longitudinal, lateral

and horizontal definition points to assist easy lining

up of the new section or panel in all three planes.

Repair of a damaged wing

1 Investigate the damaged area to find its extent.

A powerful lamp held on the reverse side of the

panel helps. Damage then shows as a dark or

light patch depending on the colour of the car.

All road dirt, grit and moisture must be cleaned

from the area of repair to allow effective adhesion

of the new material (Figure 16.35).

564Repair of Vehicle Bodies

2 Decide on the most effective way of repairing

the damage, bearing in mind ease of access and

the degree of surface finish required.

3 Cut away the damaged area surrounding the

point of impact, ensuring that the cut is taken

into sound, undamaged laminate (Figure 16.36).

4 Finish preparation of area to be repaired by sanding

or filing a scarf edge to the laminate. Cut the

scarf with the slope on the opposite face to that

Figure 16.35Damage area on composite body

Figure 16.36Removing damaged laminate

Figure 16.38Applying release medium and

temporary moulds

Figure 16.37Scarfing the laminate

from which work will be carried out. This assists

in locking the repair in place (Figure 16.37).

5 Temporary moulds are prepared, usually in

metal, but before fixing these in place a layer of

cellophane is applied to the working area to

prevent adhesion of the repair to the mould.

Wax polish and polythene sheet are other suitable

release media (Figure 16.38).

Reinforced composite materials 565

6 The temporary moulds can be held in place

with self-adhesive tape, by wedging, or by

packing to a curve with struts and wadding.

7 Prepare the resin and, if working from the

inside of the laminate, first paint the temporary

moulds with a gel coat of activated resin and

allow this to cure.

8 Cut patches of chopped strand mat to fit the

area of repair. Two or more layers will be

required, and as work proceeds they should be

made larger to bond well to the original laminate

surrounding the repair (Figure 16.39).