The effect of adhesive type on strength of inter-layer joints in fiber metal laminate composites
Andrzej Kubit
Quarterly No. 3, 2017 pages 162-168
DOI:
keywords: FML composites, adhesive joints, shear strength, peel strength, 2024-T3 aluminum alloy, GFRP, adhesive film
abstract The paper presents the results of an experimental study concerning the strength of adhesive joints between the layers of a hybrid fiber metal laminate (FML) composite. The research was conducted on composites composed of aluminum 2024-T3 sheet metal and a glass fiber reinforced polymer (GFRP) prepreg made using the autoclave process. The key factor determining the quality of the layered composites is the high strength adhesive joint between the layers. The article discusses the issue of static inter-layer adhesive joint strength under different directions of loading for various types of adhesives. Shear strength tests for a single-lap joint were performed, as well as the peel strength test using the drum peel test. The strength tests were conducted for the variant that had an inter-layer joint made by epoxy included in the prepreg, while the second variant used an additional layer of adhesive film. The surfaces of the metal layers were prepared in accordance with the methodology used in aerospace production processes. The sheet surfaces were anodized in a sulfuric acid solution and then primed. Surface structure measurements of the sheets were made immediately before the joining process. Each layer was assembled in a clean room. The strength tests of the adhesive joints were conducted in static shearing and peeling conditions at room temperature. The results show that under shear loading the adhesive film lowers the elastic module of the joint and results in a slight increase in strength. However, under normal loading, there was 289.4% increase in the peel strength of the joint with the adhesive film. After the strength tests the surfaces of the destroyed adherends were analyzed using SEM. For the shear strength specimens no significant differences were found, whereas for the specimens subjected to peeling it was shown that cohesive damage was observed for the variant with the adhesive film, while the specimens without adhesive film were characterized by adhesive damage.