What is Compressive Strength of Plastics | The Complete Guide

What is Compressive Strength In Plastics?

Compressive strength or compression strength means the ability of a material to resist loads reducing size, which is contrary to tensile strength resisting loads leading to elongation. Compressive strength and tensile strength can be calculated separately. In a nutshell, compressive strength in plastics is all about materials being pushed together, and tensile strength is about materials being pulled apart.

ASTM D65 is the standard test for analyzing compressive strength in the United States. Some materials start to deform once the compressive strength yield point is exceeded (Some materials fracture at their limit). However, when a certain stress limit is exceeded, clasping occurs to prevent breakage, but that can cause a hurried and inconsistent change in the material’s compressive strength.

The clasping is peculiar to the compression test and is highly influenced by the elastic modulus of the material and the strain of the sample. Overstressing, which leads to fracturing of the sample, is called Ultimate compressive strength.

Compressive strength (MPa) is often analyzed on a Universal Testing Machine, and the measurement can also vary depending on the environment and specific testing methods.

The Testing Method – 

When a sample is placed on a machine in such a way it extends, it is said to be tension, and if the sample is shortened and compressed, it is said to be compressed.

On an atomic level, the atoms, when in compression mode, are forced together. The atoms in a solid-state are always in the run for finding an equilibrium position and distance between other atoms; raised forces within the sample counter both tension and compression. That makes the phenomenon occurring at the atomic level similar to each other.

As mentioned earlier, compressive stress will shorten the sample with a negative strain. Over-compression can amplify the sample leading to clasping or buckling.

Let’s see a table with compressive yield strength and compressive modulus of all the mainstream plastic materials.

Difference Between Compressive Strength and Compressive Modulus – 

The basic difference between them can be attributed to the compression yield strength, a unit for measuring a material’s stress. On the other hand, compressive modulus represents both stress and strain.

Compressive strength is an alarm point for any plastic material being compressed before it fractures. Compressive modulus provides a reliable ratio of compressive stress and strain.

Engaging Read – Mechanical Properties of Plastic Materials | The Definitive Guide

FAQs – 

1. What is the difference between flexural strength and bending strength?

Ans. The difference is usually classified with the type of material being tested. A flexure test is conducted to test the bending strength of brittle material. On the other hand, a bend test is designed to measure the crack resistance of a ductile material.

2. How do you calculate bending strength?

Ans. We have to do some math – Let’s take F as a force applied, L as the length of the sample, W as the width of the sample, and D as the depth of the sample. To get the bending strength, multiply force with the length of the sample and then multiply it by 3.

3. What is Modulus Strength?

Ans. Modulus strength means a force of a specific elongation value. It is expressed by units MPa and psi.

4. What is the difference between flexural strength and compressive strength?

Ans. Tensile strength means the ability of materials to withstand bending, and flexural strength is the ability to resist rupture. The simplest way to find a material’s flexural strength is by raising its compressive strength to 2/3 power and multiplying it by 2.3.

5. How crucial is Young’s Modulus?

Ans. Young’s Modulus is one of the most important factors when using a material for any application. It can determine the behavior of a material when subjected to force. Whatever we see around us, such as buildings, flyovers, roads, and any other structure, are built around the same concept of force.

Final Thoughts – 

That was my take on compressive strength in plastics. Figuring out the right compressive and strength and compressive modulus can help analyze the right applications for each material.

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