Development of a Multi-Station Creep Machine for Adhesive Joint Testing

Adhesive joints have unique advantages when compared to conventional mechanical joints. Adhesives can undergo creep deformation at room temperature (cold flow) as well as at low stress (well below the yield point of the material), which can lead to considerable reduction in the life expectancy of the bonded structures. Therefore, performing creep tests to determine a material’s expected behavior under certain operational or environmental conditions is of crucial importance. Available commercial creep machines are often designed to test a wide variety of materials and, thus, present suboptimal features for testing specimens with specific characteristics, as is the case of adhesive joints. In this article, a new multi-station creep test machine is proposed and its main subsystems are described, namely the mechanical structure, the pneumatic servo-controlled actuation, the data acquisition, and the command software. The machine is able to run tests at a constant load that can be set from 100 up to 2,800 N, at intervals of 5 N, and a maximum displacement of 250 mm. The three stations can accommodate single lap joints or bulk specimens and allow for totally independent and simultaneous tests, at temperatures ranging from −100°C up to 200°C. The measurement resolution for load and displacement is 0.025 N and 0.025 mm, respectively. Experimental results of creep tests are presented, and the multi-station creep machine behavior is validated by comparison to a reference equipment. The creep machine reveals good performance, with force and displacement repeatability below close to 6 N and 0.25 mm, respectively.