Preventing Specimen Slippage: Quick Tips for Testing

[00:10]: Specimen slippage is a common challenge in tensile testing. In this video, we'll break down what slippage is, how to recognize it, and the simple steps you can take to prevent it.

[00:20]: Slippage happens when your tensile grips fail to maintain sufficient hold on a specimen, causing it to slowly slide out as the crosshead loads. On the stress strain curve, this usually appears as a jagged, sawtooth pattern.

[00:33]: In some cases, you may also see signs of slippage directly on the specimen tabs.

[00:38]: Slippage can occur for many reasons, but the three most common are: insufficient gripping force, incorrect jaw face selection, and a lack of friction between the specimen and the jaw faces.

[00:49]: The first step is figuring out what's behind the slippage so you can apply the right solution.

[00:55]: If the slippage is caused by low gripping force, the solution is simple: Increase the clamping pressure. This could mean tightening manual grips further or increasing the pressure on pneumatic or hydraulic grips.

[01:06]: Just be careful not to over-tighten. Too much pressure can damage the specimen and compromise your test results.

[01:12]: Since manual grips rely on operator strength, pneumatic or hydraulic grips can often be a more reliable option, as they provide consistent and adjustable gripping pressure.

[01:22]: If you've eliminated gripping force as the source of slippage, the next thing to look at is the jaw face selection. The wrong jaw faces can allow slippage to occur even when your gripping pressure is set correctly.

[01:34]: For rigid materials like plastics or metals, serrated jaw faces typically work best because they create the friction needed to hold the specimen securely. Using smooth or rubber-coated faces on these materials often isn't enough, making slippage more likely.

[01:49]: The final factor to consider is the condition of your jaw faces. Even with the right gripping force and jaw face type, worn or dirty faces can reduce friction and lead to slippage.

[02:00]: Regularly inspect your jaw faces for wear, and clean them according to your user manual. If you're testing common materials like metals, plastics, or composites, a quick pass with a wire brush is often enough to remove buildup and restore proper gripping performance.

[02:15]: While every testing setup is a little different, applying these fundamentals will help you prevent specimen slippage and ensure consistent, reliable results.

[02:23]: For additional support, contact your local Instron® Sales Engineer or visit instron.com, and make sure to subscribe to our YouTube channel for more testing tips. Thanks for watching!