Process-Induced Stresses and Deformations of Hobe Block During Shrinkage and Cooling

Aluminum honeycomb cores are usually formed after assembling of a block of roll foil, its gluing and stretching into the hexagonal cell. In the process of the block formation, shrinkage stresses and deformations arise on the faces of honeycomb cells because of adhesive shrinkage and effect of the temperature field. Such stresses and deformations lead to a significant decrease in the mechanical characteristics of the honeycomb core and sandwich structures based on it. For the hobe block, we performed finite-element modeling of its stress-strain behavior, arising because of adhesive shrinkage and significant difference in the coefficients of linear thermal expansion of adhesive and foil, and identified the main reason for the occurrence of the technological camber of honeycomb core faces having a large impact on their stability during loading. The method of analysis of this type of honeycomb cell defect has been developed. Our findings allow making the quantitative assessment of the technological camber of honeycomb faces and giving the reasonable recommendations to standardize its tolerance band. The recommendations provide the fixed level of shrinkage deformations and the corresponding coefficient of linear thermal expansion at different moulding temperatures. It is shown that by choosing adhesives with less shrinkage and lower coefficient of linear thermal expansion of material of the adhesive being cured at relatively low temperatures, tolerance band for the relative technological camber can be regulated within 0…1.4. Results of the work allow solving a number of new problems in the technology of assembling honeycomb structures for the various classes of equipment.