Experimental study of bond strength between core and composite layers under tensile and shear loads in different methods of fabricating nucleate composite structures

Honeycombs cores are widely used in nucleate composite structures. One of the important issues in using cores, especially honeycombs, is to ensure proper connection between the layers on both sides of the structure to the core; Because improper connection will lead to separating the layer from the core. The purpose of this study is to investigate and propose the most suitable method for making composite parts with honeycomb core under ASTM C273 and ASTM C297 standards. As a result, it was concluded that the most appropriate way to make a composite piece with honeycomb core is a two-step fabrication method. This is because in the two-stage method, using a vacuum device, after creating a vacuum in the part, the resin rises to the walls of the core and the connection between the core and the layers is established well. The area of connection of the core with the layers in the two-stage method is twice as large as the single-stage method and the manual construction method. So that out of 30 samples that were used for each of the three mentioned construction methods, in the two-stage method, this separation occurred in the honeycomb core itself in 28 samples out of 30 samples, which indicates the suitability of this method. (Separation is acceptable with more than 90%). However, in the one-step method and the manual method, 18 out of 30 samples and also 9 out of 30 core samples failed in the core area under the tensile and shear test, respectively.