Tuesday, July 17, 2007
Core Infusion: Got Grooves?
The fatigue properties of composite sandwich core materials can be compromised when modified with grooves, perforations, or scores for the infusion process. The use of an Infusion Flow Reinforcement on both sides of the core can reduce or eliminate the use of grooves, perforations, or scores, while increasing the bond strength at the lamina.
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4 comments:
It seems to me that the elimination of grooves would have two additional benefits: (i) a reduction of weight given less resin-rich area and (ii) material cost reduction due to use of less resin.
How does core density factor into this matter?
Looking at the change in core density when going from a plain core to one that has been modified for infusion forms an important basis for determining the affect of filling the core with resin. Using Airex C70.75 5lbs/ft^3 foam as an example, the plain core has a shear strength of 175 psi and a shear modulus of 4.35 ksi. If we then double cut the core and infuse it with a vinylester, the shear strength of the resulting foam/resin core is 167.71 psi and the shear modulus is 5.13 ksi, but the core density is now 10.30 lbs/ft^3.
So, in order to fairly determine if the resin has affected the shear value of the core we need to look at a plain core of equivalent density. While plain Airex C70.130 is 2.2 lbs/ft^3 lighter at 8.1 lbs/ft^3, its as close as we can get in the Airex line. With a shear strength of 330 psi and a shear modulus of 6.85 ksi it’s quite apparent that the resin in the infusion core has significantly degraded the cores properties.
A 1" core will absorb more resin than a 3/4" core if they both have cuts. This information needs to be considered as well. The thicker the core the more resin it will absorb.
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