Some of the failure theories work well for the tensile domain but are weak in explaining the compressive behaviour and no failure theory works well for the sandwich composite domain including foam cores, corrugated cores and honeycombs. How can it be explained and what are the solutions?
Respected Sir,
I think that the orientation of the fiber at the at the time of failure plays a dominant role. In compression and due to use of corrugated foam, the fibers have micro buckling . It is here where the theories deviate from the actual behavior of the fibers. That is why tensile failures are more predictable than compression failures.
For the specific structures you are mentioning, geometry and material must be captured simultaneously to be predictive for the failure of composites, particularly those you mentioned. What you measured is at the structural level, but most failure theories are constructed and applied at material level which is not correct. You can try SwiftComp, which is a softwre which bridge the gap between materials and structural analysis, directly compute a structural model out of microstructural details. The code is freely launchable in the cloud at https://cdmhub.org/resources/scstandard.
https://cdmhub.org/resources/scstandard
Failure Criteria for laminated composites are established on two approaches: (a) Failure Criteria without regard to failure modes, and (b) Failure Criteria based on failure modes. The later is the most appropriate, as it takes into consideration; fiber fracture, transverse and shear matrix cracking.
You may wish to read the following article, which can be useful:
What Yehia mentioned are the traditional approaches to deal with composite laminates when each layer is artificially assumed to be homogeneous. However, the so-called failure criteria are curve fitting formulas. And the corresponding strength parameters used to fit a certain stress state will be different from another stress state which means those strength parameters are not intrinic to the material and thus cannot be considered as material properties. That is one source of prediction error.
I find very limited studies on the predictability of sandwich composites failure . Besides, In PMCs, the hygrothermal component , I feel must be included in the failure theories. How can one predict failure for the dry environment alone and what use is it of ? How do we account for the in service failures? Again , there are limited studies on the hygrothermal influence on sandwich composites. In general, there is a severe paucity in the failure theory domain for dry and wet sandwich composites.
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