Study of the Life Span of Adhesively Bonded Single Lap Joint Due to Creep

Abstract

Adhesive joints are often used in several areas, including offshore systems and automobiles. The development of suitable models to predict the joint behavior has several challenges, especially due to creep phenomena. The aim of this study is to investigate the creep lifetime of single lap joints considering two different adhesives (epoxy and polyurethane). Long-term tests are performed using a pneumatic creep equipment (PCE). The parameters to the creep model are obtained for each adhesive, where load and life span are related. The models obtained and the times of joints life span are compared with two other adhesives previously studied. The results confirm that the knowledge of the lap shear strength value is just a reference to the designer, however experimental tests in creep for each different adhesive is necessary. The comparison between the joints bonded with two different epoxies shows similar results, what was demonstrated by the similar curves obtained by the models. The comparison between polyurethane adhesives did not show similar behavior in the curves obtained from the models, especially in the time of life span.

Creep behaviour of adhesively bonded joints: A comprehensive review

“…When the creep load reduces from 80% to 70% of the static strength, the time until rupture increases more than 1700 h (more than 200 times longer). In the same sense, Carneiro Neto et al 103 showed that when the creep load decreased by about 10%, the creep life of SLJs extremely increased. Simões et al 104 performed creep tests in SLJs using an acrylic pressure sensitive adhesive at different creep loads (between 30%-80% of the static strength).…”

“…Carneiro Neto et al 31 also observed substantial differences in the creep life of ENF specimens even with slight variations in the applied creep loads. However, this aspect was not verified in SLJs when a polyurethane adhesive was used, 103 as will be detailed in Adhesive type section.…”

“…Some works showed that epoxy adhesives have higher creep life than polyurethanes, when tested at room temperature. 102,103,106 Epoxies were being tested below T g , while polyurethanes were tested above T g , which implies a higher value of deformation for the latter and consequently a lower capacity to bear the strains resulting from the creep phenomena.…”