are we laying our lamina and just stacking them and not fully understanding the strength possible
with composites?
have any of you been able to examine your own products after failure or damage ?
 i know this link i have is oriented towards aircraft, but some of it is also basic composites
fabrication as well. i am trying to work out the cost and labor end of how to make a good strong
part for automotive uses. waste is bad,this stuff is far too expensive to waste any of it.
so more exploration for me for my fabric stack-
i do think attention to the orientation of the layers is worth looking into.
 i am unsure how this could effect out parts, but just stacking lamina at 0 and 90 sounds
like it could be damaged easier from impact. 0/90 and then alternating to 45 degrees seems to make
the stack quasi-isotropic.(strength in all directions of the lamina).
and then there is delamination damage,and that comes from impact damage ,and sometimes it is a built in defect
of the process.(hence the MUST BE THOROUGHLY MIXED nature of your resins)
holes drilled for bolts ,screws or rivets and holes cut for access etc all weaken the laminate. and dont slack off
when you make and trim and dress your edges of the panels, as delamination at an edge from impact damage
is easier to start, and you may not be able to detect this damage and repair it while doing the other repairs.heat
and water/rain exposure also effect the strength of our panels. IE for kayaks.
 so my thoughts on damage of say a bonnet? well my own thoughts would to be to build a stronger part
if the cost is not significant. and if it is damaged, i'd rather the repair be smaller than if it were stacked at 0 and 90 and
the damage runs along the 0 or 90 plane. worst case is i dont want the vehicle occupants hurt from flying delaminated
parts or even bystanders either. if it cracks, delaminates,collapses, or otherwise breaks down i want it to stay together.
so i am not a doomsayer here, i was just reading up on how things are made and designed.
Laminate Design Principles



thanks for reading my ramblings


Scott

CarbonFiberCreations

Some good composite theory in those links.

However, in practice that level of design is usually overkill for most DIY projects. The extra cost of the waste and wider fabric needed for doing a 45 degree layer for a relatively small increase in stiffness usually isnt worth it when, for example, a foam core will achieve even better stiffness for a quarter of the cost of that additional carbon layer.

Sure for more specialised applications then its fine to use all the advanced principles - that is what they are for, to achieve the best strength etc.

Not withstanding that, it is useful to understand how and why your part behaves in the way it does.

An interesting point touched on is splintering and people getting hurt in a crash.  Depending on where you live and the jurisdictions applying to you, that could be a legal minefield.  Modified cars are a grey area in law for many countries, especially when it comes to modifying "safety related" componants.

Now in most definitions you'd be hard pushed to consider most bodywork as "safety related" componants however in our increasingly "risk averse" (read it "cotton wool" if your older like me) society then things like pedestrian safety are taking a greater and greater impact on car design legislation to the extent that many new cars designs are quite heavily influenced by it, eg lower further back engine, higher bonnet line, pedestrian airbags, pedestrian crumple zone panels etc etc etc.

Now personally i think its going too far, if we pander to safety too much we will be driving around in blocks of soft foam or further still cars will be banned full stop for being dangerous......

Why not just teach people to look before they cross the road and follow the highway code when driving? oh yeah we do teach people these things but they are often too stupid or too arrogant to follow them - hence avoidable crashes.

But thats just my view of it in europe where often legislation and burocracy seems to be put in place instead of people using some common sense....

You may have different views or be forced to subscribe to the safety culture more than I am.  

You can lesson the chances of splintering etc by adding an aramid or diolen based fabric in your layup.  The panel may be mashed beyond recognition, but it will remain largely intact with significantly reduced splintering.

Beyond simple principles like that, you are entering into the realms of having your parts crash tested to see if they are at least as good as the OEM parts.  That is an incredibly expensive and drawn out process beyond most of our means.


So that leaves us with having to make a choice as what is acceptable to us either personally or in a legal sense.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant