Compression force (or compressive force) occurs when a physical force presses inward on an object, causing it to become compacted. In this process, the relative positions of atoms and molecules of the object change. This change can be temporary or permanent depending on the type of material receiving the compressive force. There can also be different results depending on the direction or position on the object that the compressive force is applied.

What Are Some Examples of Compression Force?

Figure 1: Compression Force Applied to an Object on a Solid Surface

Figure 1: Compression Force Applied to an Object on a Solid Surface

Newton's Third Law of Motion states that for every action force, there is an equal opposite reaction force. This is depicted in Figure 1: When compression force is applied to an object resting on a surface, both ends of the object receive the same amount of force.

Figure 2: Compression Force Applied to a Spring

Figure 2: Compression Force Applied to a Spring

Figure 2 shows another common visual example of compression force - the act of pressing two ends of a spring together. As compression force is applied to the spring, the spring's physical shape becomes compacted. When the compression is released, the spring immediately expands outward and back to its normal shape. Depending on how much force is applied, and the malleability of the spring itself, this can be a dynamic reaction.

Figure 3: How Different Types of Materials Can Experience Changes as a Result of Compression Force

Figure 3: How Different Types of Materials Can Experience Changes as a Result of Compression Force

Figure 3 shows how elastic and rigid materials respond differently when put under compression force. In this diagram, both the rubber ball and the cinderblock are put under a significant compressive force, though respond very differently. The rubber ball compresses or shrinks in the direction of the applied force and expands outward radially from its normal spherical shape. As for the brittle cinderblock, the compressive force concentrates on its weakest point, which causes the block to buckle under the force load.

Figure 4: Compression & Tensile Force on a Suspension Bridge

Figure 4: Compression & Tensile Force on a Suspension Bridge

Suspension bridges are an example of a rigid structure that is designed to withstand compression forces over a long distance. As Figure 4 shows, when vehicles drive over the bridge, the columns and beams used to support the bridge experience the compression force. Meanwhile, the anchorages and suspension cables are put under tension. These two facets working together essentially transfer the compressive force load across the entire bridge to maintain a sound, stable driving surface. This is a key principle that allows suspension bridges to cover longer distances than other bridge types.

How is Compression Force Measured?

Compression force is usually captured in Newtons (N); defined as a unit of force that give to a mass of one kilogram an acceleration of 1 meter per second squared (m/s², commonly represented as "a").

N = m * a

Table 1: Approximate Conversion Factors For Alternative Force Units

According to a paper by the Institute of Measurement and Control, a force measurement system is made up of a transducer and associated instrumentation. A transducer is a device that receives a physical stimulus and changes it into another measurable physical quantity through a known relationship. Force transducer is really a chain of several transducers that experiences a change in electrical resistance in response to an applied force.

There are a few common force transducer systems used to capture compression force.

• Load cells are highly accurate methods to capture compression force, yet require significantly more area to function than other alternatives.
• Pressure film products like Prescale Fujifilm are an inexpensive alternative, but they only show a snapshot of compressive force, not its impacts over a stretch of time.
• Tactile force sensors (or piezoresistive force sensors) combined with scanning electronics and software (i.e., the ELF™ System), can be used to measure single-point force and load measurements in real time.
• Pressure mapping technology utilizes a matrix of tactile force sensors, scanning electronics, and software to capture dynamic data on the distribution of compression force.

Why Test For Compression Force?

From a design engineer's perspective, there's a lot to be gained from quantifying how a product, device, or structure responds to compressive forces. Compression force testing can yield important information in a variety of aspects:

• Material selection: In the case of material selection for a product design, a compression force test can be used to help design engineers zero-in on a material optimized to withstand compressive environments.
• Competitive benchmarking: Compression force tests can help design engineers improve features of their product designs by capitalizing on competitor shortcomings.
• Meeting internal or third-party certification standards: Compression force tests can be integrated into certification processes like ISO, ASTM, and others.
• Quality testing: Compression force tests can also be a last line of defense for products, where such a test can help identify potential product defects. This test can also be used to help identify whether something in the manufacturing process needs to be adjusted.

Gain More from Compression Force Testing

A compression force test is only as good as the technology used to capture it. Choosing a tool that can dynamically capture how a compressive force is impacting an object will significantly add value to the testing process.

Pressure mapping systems from Tekscan are highly flexible solutions that can help provide actionable information from all types of compression force tests. Each system consists of ultra-thin tactile force matrix sensors, scanning electronics, and software to generate dynamic test & measurement data. Interested in learning more? Contact us today to discuss your application.