6 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS NON-AUTOCLAVE PROCESSING OF SANDWICH STRUCTURES: THE ROLE OF PREPREG THROUGH THICKNESS AIR PERMEABILITY

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Vacuum-bag processing of sandwich structures: role of honeycomb pressure level on skin-core adhesion and skin quality

Non-autoclave processing of honeycomb sandwich structures generally leads to poor compaction and high porosity of the skins, along with a decreased skin-core adhesion. The pressure level inside the honeycomb cells plays an important role and is controlled by the permeability to air of the skins. In this work, an initial range of skin permeability to air was explored by perforating the prepregs and adhesive layer selectively. The role of the resulting pressure inside the honeycomb on skin?core adhesion and skin quality was evaluated. Prepreg air permeability was found to control skin-core adhesion through the pressure in the honeycomb and potential outgassing of the adhesive layer. An optimal range of initial pressure inside the honeycomb was found to be 40?70 kPa. A universal process window was proposed to determine the time frame of vacuum application leading to an optimal initial honeycomb pressure level

Non-autoclave processing of sandwich structures: the role of prepreg through thickness air permeability

Non-autoclave processing of honeycomb sandwich structures generally leads to poor compaction and high porosity of the skins along with a decreased skin-core adhesion. Air permeability of the skins, a critical parameter of low pressure processing, is often increased by perforating the prepregs in a patterned way, before curing of the second skin. This procedure, frequently designated as "spiking", provides an air path for the honeycomb cells voiding. Prepreg through thickness air permeability was characterised at room temperature and its evolution monitored during cure. Several spiking configurations were tested and their role on skin-core adhesion and skin quality was evaluated. Prepreg air permeability controls skin-core bonding through the pressure drop in the honeycomb cells and potential outgassing of the adhesive layer. An optimal range of skin permeability was found to be between 5×10-14 cm2 and 3×10-12 cm2, which corresponds to a range of 200-600 mbar of air pressure in the honeycomb

Non-autoclave processing of honeycomb sandwich structures: Skin through thickness air permeability during cure

In non-autoclave processing of sandwich structures, the pressure level inside the honeycomb becomes a critical process parameter, which depends on the permeability to air of the upper skin. In this work, prepreg and adhesive permeabilities were determined separately and in combination through a falling pressure method. We showed that a range of initial skin through thickness air permeability could be achieved by perforating the prepreg plies, the adhesive layer or a combination of both. A corresponding range of achievable pressure was measured inside the honeycomb. The change in the through thickness permeability with time during the cure cycle was determined for each of the studied cases. The adhesive layer was identified as the element that most reduces the initial through thickness air permeability in skin manufacturing