Compression Set： Definition, How it Works, and Understanding the Graph

In materials science, a compression set refers to an important parameter that describes how much deformation or height loss a material experiences after being subjected to a particular compressive force for a given time. It is a measurement of how well a material can recover to its initial shape. A compression set is a key factor in the choice of printing materials in 3D printing. 

To determine the compression set, the material is typically subjected to a specific compressive load for a predetermined amount of time. The resulting deformation or loss of height is then measured. A compression set graph offers insight into the material's propensity to hold its shape under compression over time. This article will discuss what a compression set is, examine how it works, and provide an understanding of the compression set graph.

What Is Compression Set?

A compression set is a measurement of how permanently a material is altered after being compressed for some time and then released. The amount of the material's original thickness or height that is still compressed after a certain amount of time is expressed as a percentage. A common test procedure for calculating the compression sets of rubber and rubber-like materials is ASTM D395. 

Knowing the compression set is crucial in applications where the material is continuously compressed, such as gaskets, seals, and O-rings. A compression set is also relevant to situations where the material is expected to regain its original form following compression, such as in springs and shock absorbers. A high compression set indicates that the material will not be able to maintain its shape and functionality over time, which can lead to failure or decreased performance.

How Does a Compression Set Work?

In a compression test, a sample of the material is compressed and held for a predetermined amount of time while being subjected to a specific load. The percentage of deformation that remains is calculated after the material has been allowed to recover for a predetermined amount of time. A compression set is a measurement that determines whether a material is suitable for uses that need reliable and consistent compression resistance.

How To Understand the Compression Set Graph?

The following (example) guidelines should be followed in order to understand the compression set graph:

1. Look for the key material being studied, in this case, silicone rubber.
2. Keep in mind that it differs from other elastomers in that its elastic behavior only modifies marginally with temperature change.
3. The y-axis, which represents the percentage of the compression set, should be noted.
4. Pay attention to the x-axis, which represents the range of temperatures in Celsius.
5. Pay close attention to the different graph lines that show the silicone rubber's compression set after a 24-hour period of compression at various temperatures. By selecting a point on the x-axis that corresponds to a particular temperature and projecting a line to the curve, these lines can be created. A line from the curve needs to be projected to the y-axis to obtain the compression set.
6. Keep in mind that the elastic behavior of silicone rubber reduces as the temperature rises because its compression set also rises—though slightly.
7. The rate of change in the compression set as the temperature rises can be seen if the slope at different points on the graph is drawn.
8. Examine the various lines on the graph to determine how temperature impacts the silicone rubber's compression set.

To ensure the material will function as expected over time, for instance, if silicone rubber is being used in a high-temperature environment, the compression set may need to be considered. Figure 1 below is an example of a compression set graph: