core shear strength calc.

1Msq panel with 40mm core (0.5 MPa shear) and 1200gsm fiberglass skins. What's the failure mode, the skins or the core? and loading? tks

 

It might be useful if you supply some more details about your project?
What type / size of boat (I presume it is a boat?) are you building?
Re the above panel, is it representative of what a section through the hull is like?

 

The fiberglass is triaxial. (omnidirectional)
The loading is at the center.
Shear modulus 8MPa.

Let's assume failure along the bond-line will not happen.
Failure is also large deflection, without actual fracture of the core or the fiberglass but we ignore this too. (but will this be considered a failure of core shear?)

Brain storming, trying to understand trade-offs for most effective use of materials vs weight. tks.

 

This is engineering. You need to specify the panel size and the triaxial fiber orientation. Is it 0/45/90. What resin are you using and what is you target glass content?

 

Thanks RX, 1Msq, the rest standard, 72GPa modulus at 55%fiber/45%resin = 40GPa?

 

Guess if we plot a graph of increasing loads, the defection will be small then show an infection point where the rate of defection increases more rapidly. At this point the panel has effectively failed. Will it be more advantageous to increase Shear value or Skin thickness, ie. which one has failed?

 

Styrofoam has too low a Shear value to be any good with 1000gsm of Skins, but say if we had a surfboard and 200gsm Skins then it works... Regards of loads or weight (Shear requirement inverse with core thickness, it seems, for a given load) there is a balance of Shear value to Skin. This is what I'm trying to workout, a practical guide to this. Shear is some fraction of Skin, not a rule but a range, not as cookbook but to tell if a laminate is bias and then based on weights and cost, what might be a good trade-off to make.

 

Is this for a distributed load, point load (puncture), sustained or impact load, torsion, tension, compression, torsion, combinations, etc.? Each will give you a different value and failure mode.

 

Point sustained load but not puncture, Normal to panel. Tks

 

What is the compression strength of the core?

 

600 KPa, tks

 

What is the shear strength of the resin used?

 

Thanks Rx, 71 MPa strength,

 

Hi, MST3000, may I propose a basic ISO12215 ply-by-ply analysis ? There is quite a lot of coefficient that are introduced in this standard, so the mechanical properties differ from those your are willing to use for this analysis. The Classical Lamination Theory will give more adequate results, authorizing the use of ultimate values but since I make a living from this, its use is quite out of scope of this forum. If we stay with the ply-by-ply analysis of the ISO standard :

- mechanical properties of the laminates with additionnal coefficients including the manufacturing process [Infusion], its level of quality [Low No measurements or checking on fibre mass content. Volume content is taken according to the minimum values of the standard] and the method of analysis [Ply-by-ply]. Fiber content by mass is 45%
- No values for tri-axial are included in the standard. Without calculating them by CLT, I've based my calculations with a laminate schedule [0,+-45]. Commercial triaxial fabrics can also be [0,+-60], [-45,90,+45]
- the ultimate pressure is applied on the whole panel, rather than a a local force at the center. The bending moment and the shear force on the edge take into account the aspect-ratio of the panel.








Ultimate pressure : 54.8KPa. Mode of failure : Shear of the core



Hope this could be usefull. Feel free to contact me if more details are requires to estimate the more advantageous in your particular case. We can easily establish abacus for you to be able to determine the best compositions compatible with your manufacturing process, according to strenght or weight requirements.

 

That value will be much higher than for a point load as the OP asked for though. I am not too clear on his statement that it is "Point sustained load but not puncture, Normal to panel." The failure mode may be for the core or the laminate. Unless he means that the core must fail before puncturing.