Choosing Test Methods for Adhesive Selection

When and why is testing important for adhesive selection?

Say you’re tasked with creating a new product design or improving or changing an existing product. Say there are also features of the design that rely on adhesives. How do you know if the adhesive you plan to use is up to the task?

Maybe you’ve read all the data and literature available on the adhesive or used an interactive selection guide. Maybe you’re using a “tried and true” adhesive you and your company have been using for years. Maybe you trust the recommendation from your supplier or distributor. Maybe everything will work out just fine? Maybe, maybe not. Unfortunately, you won’t know for certain until the new or improved product is launched out into the world.

If there are important safety, performance, or quality aspects of the product that rely on adhesives, testing might be a wise move. Testing the adhesive as part of the commercialization process can help reduce risks and uncertainty. Generating a set of test data during commercialization can also be valuable when and if quality or warranty issues occur; the tests become a tool for troubleshooting and can help identify or rule out root causes.

Furthermore, technical data sheets typically contain statements or language indicating that it is the user’s responsibility to determine suitability for use. Testing becomes an important part of due diligence during product commercialization.

What to test for?

Perhaps the end user, customer, or client has expectations or requirements about how a part or product will perform. If so, this can be helpful in determining exactly what needs to be tested for and how to test it.

If not, it will be up to your team to build a plan defining what to test for and how to test it as part of normal validation or verification activities. The “what to test for” can be determined using tools such as failure mode and effects analysis for the design or manufacturing process (DFMEA or PFMEA) used in making the product. Depending on the specifics, some aspects of the adhesive performance or adhesive application might be of concern. If the probability or consequences of a failure related to those concerns are high enough, testing might be called for in the design verification plan (DVP) and might be performed regularly during production as part of the product quality control plan.

Once you know what areas of concern your team has, you can start to build your adhesive testing plan.

How to test?

How many different tests are needed? Which specific tests do you run? What relation do these tests have to product performance? Do you test coupons, test components, or test the entire product? This is where the challenge of developing a thorough but timely and representative but practical plan becomes important for success.

The areas of concern identified earlier in the design process will determine how many different tests are needed. If you’re working with an experienced team or have well defined requirements, the “how” of the testing might be clear. If not, this is where a good understanding of existing test methods, what results the test methods provide, and the relationship of those results to expected performance is key. This skill often takes time to master.

A good place to start when choosing test methods for general industrial applications is ASTM D6465. This standard helps you identify standard test methods that are generally recognized as relating to particular areas of concern for adhesive properties or performance. A major benefit to running standard test methods is that they can be performed under controlled conditions and this can allow you to draw conclusions about performance without confounding variables. A potential downside is that some standard test methods are not representative of use and might be milder or harsher than expected for your product. Each application has its own unique requirements and it is up to you to determine if a particular test method will provide the data you need for your test plan.

Searching for adhesive test methods among the different standards organizations can be helpful.

Choosing the best form for test specimens, such as coupons, components, or product, depends on many factors. Some tests might require a specific specimen geometry which could require coupon testing. Early in commercialization, components and product might not be available for testing and would make coupon testing the default. Another factor to consider is that coupon testing might be helpful in screening multiple adhesives or bonding process conditions before components or prototypes are built. This might save your team the pain of learning about a material compatibility issue later in the commercialization process. Evaluating components or product sometimes carries the limitation that quantitative analysis of joint strength is only effective with specific joint designs and with specialized tools and test fixtures.

Where to test?

If you plan on performing qualitative tests using the product or components and have the time and resources to document the results, testing could likely be done on your shop floor.

If your company has access to a well equipped characterization lab (e.g., load frames, rheometers, thermal analysis equipment), and you have time and resources to test according to the standards or methods of choice, testing can be done in-house.

If you don’t have access to the necessary test equipment, there are many third-party test labs who can help. Capabilities, quality, lead times, and prices vary, so it is best to inquire with more than one lab and keep these tips for choosing a materials testing laboratory in mind.

Conclusions

Building a test plan for adhesive selection can be an important step toward commercialization of your product. It lays out the road ahead for testing and frees you up to focus on other areas of the project. Thanks for reading and good luck!

If you have questions about how to choose the right adhesive or how to develop and execute your own test plan for your application, contact Digital Glissade to schedule a consultation.