Elongation : What is it and Why Does it Matter?

Have you ever seen this spec listed on a material data sheet? 

“Elongation at Break %”

To understand it, and realize why it’s important in adhesives, let’s first tackle two definitions.

• “Ductility” is a measure of a material's ability to undergo significant deformation before rupture or breaking.
• “Elongation at Break” is a measurement that shows how much a material can be stretched — as a percentage of its original dimensions — before it breaks. This is also referred to as percent elongation, which is a measurement of the amount a material will plastically and elastically deform up to fracture. The material's final length is compared with its original length to determine the percent elongation and the material's ductility

The ductility of material means a lot. A material with high ductility means it’s more likely to deform (but not break!). Low ductility indicates that it’s brittle and will fracture easily under a tensile load. 

Elongation at break also called “fracture strain” or “tensile elongation at break” is the percentage increase in length that material will achieve before breaking. How is elongation measured? Most often using test method ASTM D412, a common test for strip samples of rubber and elastomers. Elongation is important in components that absorb energy before deforming plastically (think crash barriers and car bumpers). High elongation to failure is important for "plastic hinges" (think gate or door hinges where stretching is not an option.

Short story: A higher percent elongation usually indicates a better quality material when combined with good tensile strength.

What Does Elongation Have To Do With Adhesives?

OK, so elongation at break is the ratio between initial length and increased length after breakage at a controlled temperature. Speaking of temperature, the ductility of a material depends on its chemical composition, which is important when selecting materials subjected to extreme cold or heat.

This affects many masking applications, for instance, so the elongation needs to be good in order for the adhesive to withstand the cold. Similarly, if the adhesive can stretch while it’s being applied to a surface, it helps the applicator to be able to mask small corners. These tough to reach spots are important to mask so they don’t get exposed during the painting process.

A Case Study In Elongation

Strouse supplies Ford with pressure-sensitive automotive adhesives for some things you might expect:

• Part mounting and attachment
• Prevent buzz, squeak, and rattle (BSR)
• Mask vehicles during the paint process using high temperature and fine line masking tapes
• Protect surfaces during assembly and shipment with protective films

Here’s the fun (and unexpected) part. Ford uses Strouse tapes on their clay, full-scale prototypes when designing cars. Designers often stretch tape along the contours of the body to create the design they want and indicate changes that need to be made.

Tape is perfect for the design team at Ford because it’s easy to handle, can quickly be placed, and it’s repositionable. In addition to being stretched, tape can form to the shapes and curves on the body of a sports car. That type of precision can’t be replicated by using your hands to mold or a knife to carve the clay prototype.

It’s a form of communication when designing and developing the body of a new vehicle. This method has been used since the beginning of car modeling, and it is still used today, even with advanced technology of 3D modeling on computers.

The flexibility of the adhesive tape gives designers the freedom to communicate their ideas instantly. That’s elongation in action!

What About Tensile Strength?

The tensile strength of a material is how much pulling stress (or tensile stress) a material can take before failing (breaking, deformation, etc.).

As the pulling stress reaches, and then passes, the tensile strength, the material fractures or breaks. However, when any stress less than tensile strength is removed from a material, it returns to its original shape and size, either completely or nearly completely.

Testing a material’s tensile strength provides information about its ductility as well as strength. Because it’s a destructive test, it shows how much force a material can take before failing, so tensile strength is an important part of elongation.

Instead of being stated in a percentage (like elongation), tensile strength is measured in units of pounds per square inch (psi).

How will elongation in adhesives affect your next project? When you’re ready to start designing, contact us first. Strouse provides more than tape.

Speaking of getting started, if you’re worried about choosing the wrong partner (and making a costly mistake), review our checklist, Choosing The Right Converter. It’s a simple quick-read that can prevent a lot of headaches. Just click the image below now.