Single-lap joint creep behaviour of two soft adhesives

Two hot melt pressure sensitive adhesives have been submitted to bonded joint creep tests. An amorphous and a semicrystalline adhesives have been considered for their different microstructures leading to different mechanical behaviors. The adhesives are referred as soft since their glass transition temperatures stand well below the temperatures of applications, resulting in low stiffnesses. The creep of structural joints has been characterized with single-lap joint tests. Two types of adherends were considered either glass or stainless steel. The adherend roughness and the adhesive wettability have been characterized before testing. The significant stiffness contrast between the stiff adherends and the soft adhesives promoted homogeneous simple shear creeps. The amorphous adhesive showed creep behaviors that depend on the type of substrates, showing that the joint viscoelasticity could not be predicted knowing the bulk adhesive viscoelasticity only, unlike for stiff adhesives as recently reported in the literature. Finally, the single-lap joint creep behaviors of both adhesives on the same glass adherends were compared and discussed at the light of their different microstructures inducing different mechanical behaviors.