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.