Shear strain vs shear elongation

Scuff- Here is the diagram of the terms Barry has meticulously explained.

 

Those graphs also illustrate a very important characteristic: toughness. That is represented by the area under the curve. Toughness is the amount of energy a material can absorb before it breaks. SAN (Core-Cell) is the best from that aspect.

 

Also called tenacity.

 

Is Gurit pvc omitted?

I have used the Gurit Pvc80 and the Gurit M80 interchangeably is why I ask.

 

Maybe it wasn't available at the time of test or maybe the test is not brand specific. The table is just to guide you in the choice and you can see at a glance where the chosen material property fits.

 

I am sort of assuming the Gurit PVC is similar to the other cross linked pvcs as it has elongation at break at 19%. Is this a correct assumption based on the chart data?

I have long wondered the big difference between pvc and san as it was not immediately clear to the uninformed me. I used pvc80 and m80 interchangeably above the waterline; especially now nearer the end of the build. Thanks to all. Catamaran cabin (to be painted white). Green is pvc and yellow is san

 

Attached are the differences between the two and they are extremely large
M80 Shear elongation at break 58% vs H80 19%

As RX stated, the graph was provided to see the differences between various types of material. Within each type of material, for example, the shear elongation for the H series goes from 4 to 35% depending on the H series material and the Shear E goes from 20% to 58% in the M series.

Tensile strength almost double between the M and H and so on

This information is available off the Gurit.com site

 

No worry FG. That graph came as a sidebar to the main article. The main article is about impact resistance of the cored laminate when subjected to concentrated load such as a steel ball. The SAN corecell came out a winner with the balsa (higher strength) showing delamination of the skin, and the others showing crushing of the foam and breaks at the laminate.

You don't need to analyze superstructure for impact resistance. Not practical. Only the bottom shell.

 

I have those charts sort of memorized Barry. The M and the PVC are all I am using. The M is all my main hulls. I only bought pvc for the cabin, but as it turned out, I decided to hand laminate the deck shoes; so I used pvc ftmp on deck shoes. And I had extra san now for the cabin and not enough pvc. The reason was I did not realize I was gonna hand lay the deck shoes and my pvc was not holed for vac..which made it a perfect candidate for hand laminating deck..yada yada, details an amateur messes up buying materials that are all special order...

Anyhow, hope you all enjoyed the anecdotal interjection.

my cabin also uses 12mm ply core and one inch plascore...boat name might be 'at the core of it'. (No)

 

rx as per the composite graph Specifically SAN Corecell

This type of curve is quite similar to say steel in tension.
BUT the first drop after the first apex is the beginning of permanent deformation, non-elastic strain, the next rise is often the result of work hardening up to next apex and then a sudden drop as the rate of necking increases
Ie fast drop in minimum cross sectional area and hence a fast increase in stress at that point

We see this SIMILARITY in many ductile materials

I would have not thought that a foam composite would exhibit these characteristics. I would appreciate any insight as to the apex, valley etc for a composite.
Thanks

 

Indeed it is. The foam behaves like metal. Cured resin or "Neat resin" curve also behaves in a similar way when tension is applied.
Image #1 is typical graph of a medium strength high elongation resin which behave like metal. Regular epoxy behaves in a similar way but with a much reduced elongation as shown in image #2.

I formulated this graph to predict the strength of a laminate with a given fiber and matrix combination. Note that I am after usable strength, the one within the area of the modulus, not the elongation at failure.

There are two equations really, the tensile/compressive strength and the shear strength. The shear strength is the one resisted by the core. Given that I can predict the tensile/compressive strength of a laminate (which is the skin of the core), I can investigate the shear of the core. As you can see from the image #3, the stresses on the skins are plotted first, then the shear is plotted. It is much easier when doing a tabulated graph of a layer by layer analysis of a beam in deflection. I just segregate the "skin of the cored laminate" from the core and use the shear formula to see if I am exceeding the parameter constraint of the material(s). It can also be done using the first principle, whichever you are comfortable with.

Given your analytical mind, you would want to know more. An in depth analysis and formulas are given in Marine Composites by Eric Green and associates. I believe it is downloadable. I have the two versions hard copy. Lloyds also give a formula for sizing a core and includes the modulus of the skin as a factor.