stress-strain curves

"Anjali Pandit" wrote: in message news:e39rh5$fs2$ snipped-for-privacy@oyez.ccc.nottingham.ac.uk...

Region i: Both metal and and polymer are in their elastic range and you're seeing, primarly, the elastic slope of the metal (assuming your metal has modulus >> than the polymer) Region ii: The metal has passed into its yield range but the polymer is still in its elastic or psuedo-elastic range Region iii: Metal strain hardening kicking in and building stress again, polymer may or may not be doing something similar (depends on the polymer) Region iv: Both metal and polymer are in their yield regions and you're headed for ultimate load

Yep. One from the metal and one from the polymer.

I'm making a whole lot of assumptions here about the stress/strain curve of the materials by themselves, relative modulus, %-age of each composite, etc. but anytime you deal with composites you have dissimilar materials so you get some wierd effects due to the different responses of the two materials at equal strain. Typical composites, and yours seems typical in this regard, have one high-modulus low ductility material and one low-modulus high ductility material. As a result, the material characteristics show up in different places during a tensile test of the whole composite. Depending on your testing setup, you might also have some effects due to not transferring the load equally to both parts of the composite from the get-go.

Tom.

stress-strain curve appears to have 2 elastic regions.

then failure.

The weaker material, probably the polymer yields first. Later the stronger material, probably the metal yields.

Clad aluminum shows primary and secondary moduli of elasticity. Clad AL 2024 is an example.

what about the toughness of such material for impact loadings....

That's related to the material's ductility.

but will it also matter on which side od sandwich material the impact load is applied?

The original question was about stress strain curves...when did we switch to impact loads?

Anyway, which side you hit will matter if the impact resistance of the two materials is significantly different.

Tom.

thanks for all the responses,

Im doing some more testing soon, but in discussions with people here it appears to just be machine error

not very exciting im afraid,

Thanks again