Creep behavior of soft adhesives

Single-lap joint creep behaviour of two soft adhesives

We have submitted two hot melt pressure sensitive adhesives (HMPSA) to bonded joint creep tests. While glassy state adhesives such as epoxys are often studied in the literature, data on soft adhesives that are in the rubbery state are scarce. These adhesives have applications such as sealing letters, gluing garnment or diapers… We have therefore submitted two HMPSA varying in their microstructures, one being semi-crystalline while the second one being amorphous, to single lap-joint creep tests. Two different substrates (or adherends) were used for the joint, glass and stainless steel. Our experimental results showed that the viscoelasticity of the joint is very much dependent of the type of adherend. As a consequence, despite the rigid characteristic of the adherends compared to the adhesives, the viscoelasticity of the joint cannot be predicted by simply knowing the viscoelasticity of the adhesives. Note that recent work from the literature and cited in our contribution seems to show the contrary for stiff (glassy) adhesives.
Moreover, it was observed that the mechanical behavior at large stretch of the adhesive has a significant impact on the creep behavior. The semi-crystalline adhesives showed viscoplastic behavior with necking at large strain, which induces quick catastrophic failure of the joint during the creep test once the strain becomes large.
Details on this study conducted by E. Ernault may be found here : Single-lap joint creep behavior of two soft adhesives

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