No description available.

No description available.

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.

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The main aim of this project was to examine the effects of introducing hierarchy into honeycombs and determining the variables that preside over the global response of the structure. Specifically to understand how the in and out-of-plane elastic and non-linear plastic properties of honeycombs were affected by hierarchy. Analytical analysis of hierarchical honeycombs has been used to explain and predict the response of finite element simulations validated by experimental investigations. The early stage of the investigation focused on finding if the elastic modulus could be maintained or improved on an equal density basis due to the introduction of hierarchy. It is clear that honeycombs are sensitive to hierarchical sub-structures, particularly the fraction of mass shared between the super-and sub-structures. Introduction of an additional level of hierarchy without reducing performance is difficult, but was possible by functional grading. Another original result was that it was determined when the sub-structure could be assumed to be a continuum of the super-structure. Meaning the material properties from a single unit sub-cell could be used as the constituent material properties of the super-structure, as in previous work by (Lakes 1993) and (Carpinteri et al 2009) for example. Work investigating the in-plane, non-linear plastic response of hierarchical honeycombs showed that the introduction of hierarchy into honeycombs can have the effect of delaying the onset of elastic buckling, which is a common failure mechanism for low relative density structures. As such it was possible to achieve a marked increase in the recoverable energy absorbed by hierarchical honeycombs prior to elastic buckling or plastic yield. The potential benefits are less apparent in higher relative density structures due to the onset of plasticity becoming the first mode of failure. The out-of-plane properties also investigated showed no increase in the elastic properties due to the introduction of hierarchy, but showed a marked increase in the out-of-plane elastic buckling stress of 60% when compared to a conventional hexagonal honeycomb of the same relative density.