# How to Determine Tensile Strength of PMMA Optical Fiber?

I researched the properties of acrylic, or PMMA, and found different results on its mechanical properties. Tensile strength is a material property, but is it affected by shape or size? I’m working on a project that involves the use of PMMA optical fibers. I want to know how much tension different diameters of fiber can handle. Would diameter affect the tensile strength? If so, I would like to know how to calculate the tensile strength of fibers of several diameters ranging from 0.75mm to 2mm. I don’t think the fibers will be subject to much force to break them, but it would be helpful to know what they can handle. Thanks in advance for any helpful answers.

• Since you mentioned the force required to break the fiber, keep in mind that optical fibers already fail in respect to optical properties before actually mechanically breaking, for example too much bending messes with the total reflexion between the layers Feb 27, 2018 at 11:55
• Strength is not directly related to size, but may be indirectly related. Narrow glass fibers are much stronger than bulk glass because they contain fewer and smaller flaws. This is mostly due to processing. A similar effect could conceivably occur for very fine PMMA fibers. As noted, optical failure may occur long before mechanical rupture. Feb 28, 2018 at 21:46

## 1 Answer

Basically, materials have a tensile strength, and a yield strength. The latter describes how much it elongates under stress, the former how much stress it can have before breaking. It is always given in (M)Pa, so force per surface. This means it doesn't matter what shape or size your fibers are, it remains the same. All the material properties remain the same at the same temperature, and before plastic deformation has been made.

The force you can put on it before it breaks, is determined by the surface/cross-section. So two times as much surface, two times as much tensile strength. If you know the cross-sectional area of your fiber, you can hang weights on it until it breaks, divide found force(Newton) by known surface(m2) and you have experimentally determined the tensile strength.