Which Adhesive Tests Hold Up in the Real World?

Exponent Senior Managing Scientist Christopher White, Ph.D., and colleagues from Virginia Tech have co-authored a chapter titled "Durability and Accelerated Characterization of Adhesive Bonds," in the second edition of Advances in Structural Adhesive Bonding, a book released through the Woodhead Publishing Series in Materials.

For adhesive bonds, hundreds of national, industry, and company-specific joint tests are available, but in any product case, only a few laboratory tests will be relevant or suitable for developing design data. So how should testing engineers choose a laboratory test to determine the reliability of a bonded structure?

Accelerated short-term environmental testing offers a way for product designers to extrapolate long-term structural durability and reliability providing the short-term accelerated testing correlates to long-term observed performance. Accelerated testing is also a practical alternative to spending years evaluating an adhesive bond against a specific load condition and real-world environments.

As a result, an accelerated test chamber can represent an extreme condition of one damage driver (humidity, temperature, cyclic frequency, concentration level, etc.) so that degradation effects that occur over years in real-world conditions can be observed in days under laboratory settings. 

Using illustrations and figures of ASTM testing apparatuses, the chapter also explains how tests based on the time-temperature superposition principle (TTSP) produce the most relevant results for assessing environmental-induced aging, although product designers should remain aware of multiple degradation mechanisms that may work on adhesive bonds simultaneously.

From the publication: "Of the existing techniques for accelerated testing of adhesives, TTSP and the related time-temperature-stress superposition and time-temperature-diluent concentration superposition have the best grounding in polymer physics and are relatively simple to employ."