glass/ carbon to epoxy/ resin ratios?

PVC has low tensile stiffness. Epoxy can be stiff but very brittle; less brittle epoxy is not so stiff

As I understand it (sorts of), part of the way that a fibre/resin composite gains stiffness is that the resins bind the fibres together. When the laminate is then loaded in flexure, the fibres are constrained with respect to one another. The Fibres on the outside of the bend become loaded in tension. If there was no resin, they would simply slide against the fibres to the inside of the bend. Because they can't, and because glass and carbon have good tensile modulus, the bending is resisted.

 


Edited by foaminatthedeck

Originally posted by JimC ass resin

Whats this? ok so although the ratio will affect the stiffness and failure type. So how about using say PVC strands with epoxy. The PVC would allow flex while the epoxy is nice and stiff. What restricts which material 'takes the strain' and which deforms?

It's not that the epoxy (or other resin) itself is stiff. It's the composite of the epoxy and fibre that is stiff.carbon fibres are, as mentioned, not that stiff in dry form. Glass fibres similarly.

epoxy fibres have high tensile stiffness (modulus), but the resin matrix works with the fibres to create higher flexural stiffness.

Generally speaking, as you go to higher laminate technologies, you decrease the resin content. Wet layup tends have a lot of resin, then infusion techniques, whilst pre-pregs can be 35% or less resin by weight- note that this is a general trend, and not absolute. It's very hard to decrease resin content in wet layup and infusion.

There's other factors at play- expensive prepregs can use expensive tougheners in the resin matrix system, which dramatically improve the ability to withstand flexure and impact without damage.

Lasers though- aren't they chopped strand glass polyester? There's a heck of a lot could be done to improve both their stiffness and fatigue performance, even without making them lighter or (out of the box) faster.