Abstract:
X-CorTM and K-CorTM are foam based lightweight structural cores reinforced with ZFiber
® rods oriented in a truss pattern. They can generate sandwich structures which
possess strength- and stiffness-to-weight ratios such to compete with aerospace grade
honeycomb constructions. The enhanced tailoring ability to specific design needs, the
flexibility in reinforcement type and arrangement, the variety between closed cell foamfilled
or hollow core configurations for ultimate weight savings or structural
multifunctionality, while utilising manufacturing procedures similar to traditional
honeycomb sandwich structures (low cost out-of-autoclave manufacturing techniques
included) make these novel materials an attractive alternative. The process of their
implementation into current engineering practice requires a parallel comparison with
existing competitor cores and a critical evaluation of their performance, identifying
advantages and disadvantages.
This study represents one of the first attempts to create a rigorous methodology for the
analysis and evaluation of their mechanical behaviour and manufacturing sensitivities.
The balance of out-of-plane properties (shear and compression), fundamental for a
sandwich core material, has been investigated. The material energy absorption capacity
for the aforementioned loading cases, as well as for in-plane crushing was evaluated.
For this purpose, a new quasi-static test for progressive crushing of flat sandwich
laminates was designed successfully. The experimental data gathered validate proposed
analytical models which allowed further deductions on core parameters influence to be
made. Those parameters were the pin insertion angle, pin lay-out, pin density and the
role of the foam. A local-global FE modelling approach for Z-pinned sandwich cores is
also provided and validated for X-CorTM structures. Structural differences between XCorTM
and K-CorTM are at the base of a diverse mechanical response; their performance
is sensitive to the manufacturing process, as it determines the quality of the pin-skin and
pin-adhesive film interfaces. An ‘improved’ manufacturing technique designed for XCorTM
resulted in a sandwich panel able to offer the same mechanical performance of a
Nomex® honeycomb structure for a 25% of weight saving.
