As an adhesive, glue is unmatched in its strength, variety and ubiquity. Students are introduced to glue from the moment they get their first school supplies. An experiment that tests the strength of glue is a common proposal for science projects. If done correctly, such an experiment can be an effective and impressive science project.
How Glue Works
Before you can test the strength of glue, you must first understand how glue works. Glue works by two principles: adhesion and cohesion. Adhesion is the ability of glue to stick to a surface, while cohesion is the ability of glue to stick to itself. A strong glue will have good adhesion and cohesion. Glue fills the tiny molecular gaps in a material, then hardens to stick to the material and itself. The principles of physics that govern the behavior of glue make good background information for a science project.
Designing the Project
All science projects should begin with a question. You could ask which brand of glue is the strongest. You might also ask which glue is the best for adhering different materials, or examine the ability of a particular glue to adhere two different materials. Alternatively, you might decide to test the strength of a glue at different temperatures, or test several glues at extreme temperatures.
Regardless of the question asked, the purpose of the experiment remains the same: to determine the strength of a glue joint. Two surfaces must be joined together with glue, then force must be applied to break the glue joint.
One way to arrange the pieces you plan to glue together is at 90 degrees, like an upside-down "L." Apply the glue in a thin, smooth layer. Spread the glue out so that it covers 100 percent of the surface, as any break in coverage can cause weakness. Once the glue is applied, use a clamp to hold the pieces tightly together as the glue dries. Allow the glue to fully dry before conducting the test. When the glue is dry, place the vertical beam in a vise and suspend a string from the horizontal beam and attach the other end of the string to a small bucket. Add weight to the bucket until the glue joint breaks, then record the weight of the bucket.
There are other ways of conducting this experiment. The pieces glued together may be arranged differently or different methods of applying force to the joint may be used. Many universities have Instron testing machines. These devices electronically measure the amount of force necessary to break a glue joint.
Each glue will most likely hold a different amount of weight. This can be ranked between brands or compared in relation to cost. However, you should note how the glue fails. If adhesion fails, glue will separate from the wood. If cohesion fails, the glue joint will break in the center. Regardless of the experiment you choose, it should be conducted at least twice to ensure accurate results.