During the past few decades, adhesive bonding technologies have attracted the attention of many researchers and engineers in different fields. Adhesively-bonded joints are more efficient than other types of joints, such as bolted or welding ones, due to their excellent features like having uniform load distribution, lighter weight, lower-cost manufacturing, faster and easier bonding process, and better thermal stability. Optomechanical and aerospace companies, such as TMT International Observatory, NASA, and Raytheon, are extremely interested in learning about the time-dependent behavior of adhesively-bonded joints, where adhesive creep characteristics can drastically affect the performance of the bonded joint over time.

The creep test of materials is one of the most expensive and time-consuming material tests requiring specialized equipment. Due to the complexity of the mechanism of failure in adhesively-bonded joints, the creep behavior of adhesively-bonded joints cannot be studied by a few numbers of creep tests, and it requires a batch of samples. Commercial creep-test machines are mainly designed for the creep test of metals, and they are meant to be only occupied by one specimen for a long time. One can see that occupying commercial creep-test machines for testing adhesively-bonded joints is expensive, and often not feasible. ASTM D2294 is the standard test method that describes the method of analyzing creep properties of adhesives with a suggested apparatus. However, careful analyzing the proposed apparatus reveals two important deficiencies: 1) The contemporary design potentially causes misalignment on the axial force; 2) the load applied on the specimen varies due to the deflection of the loaded spring.

In the first phase of this project, we shall design and prototype a new special apparatus for testing adhesive joints. This advanced and inexpensive device has the feature of running multiple creep tests for a batch of adhesively-bonded joints simultaneously. Its unique designed structure will collect consistent and accurate experimental data, which will be used for the next stage. In the second stage, we will use the theory of nonlocal operators to propose linear constitutive creeps models, instead of common nonlinear ones, to predict the deformation of a bonded joint over time. Then, we will expand the proposed model in an abstracted form, so engineers can easily use them in their simulation software.