Tensile and compression tests are essential procedures to check the quality of materials. They help us know many parameters about materials. You’ll see many people debating on tensile test vs compression test when it comes to material testing. However, these two testing methods differ from each other.
The tensile test is primarily about the material’s ability to withstand pulling and stretching. Compression testing involves compressing the material to check its properties. These tests are conducted using specific machines. In this article, I’ll discuss tensile and compression testing, highlighting their key differences.
Basic Rundown of Tensile & Compression Test
Tensile and compression tests are similar to some extent. They expose the material to different levels of load or stress. However, tensile testing involves pulling and stretching the material. It is helpful to know the maximum force a material can withstand before permanently deforming. On the other hand, the compression test is primarily concerned with compressing the material.
In this testing, the material is exposed to extensive force or stress. Interestingly, this force does not pull; instead, it pushes, squeezes, and presses. It is helpful to understand how the material will behave when exposed to stress in real-world conditions. These tests give us the exact value of the following parameters:
- Elongation
- Yield Strength
- Fracture Point
- Necking Behavior
- Compressive Strength
Elongation indicates the elasticity of any material. The yield strength helps us know the point at which the material starts to deform permanently. The compressive strength indicates the maximum force a material can withstand without breaking. These tests help determine the material’s maximum strength, after which it fails to withstand further stress.
The tensile tester and compression machines pull and compress the material, respectively. Gradually, the tester (machine) increases the force (stress). The operator notes the behavior of the material. The tester also showed a stress-strain graph. It tells us when the material starts to deform permanently and breaks. The operator notes different parameters during this testing.
Engineers require these parameters before using any material to produce various products. For example, the compression test is used to assess the quality of materials used in bridges and buildings. Engineers don’t use a material if its elongation, compressive strength, and other parameters are unknown.
Differences Between Tensile Test & Compression Test
Both tensile and compression tests help us know different parameters. They describe how a material will behave when exposed to various stress levels. In this way, we can use them by exposing the stress, which is safe to their structure. However, both tensile and compression tests are different from each other. Let’s dive in and discuss all of their key distinctions.
1- Direction of Applied Force
Tensile and compression tests differ in terms of the direction of the applied force. Tensile testing involves applying a force outward. On the other hand, the compression test consists in applying force inward. As you know, the tensile tester pulls the material by both ends. The force direction goes outwards. The compression testing machine applies force toward or inward. It applies stress to the material and checks its behavior. So, the force applied remains towards the material.
2- Type of Stress Produced
Tensile and compressive testing deal with two different types of stresses. The tensile test generates tensile stress. On the other hand, compression tests expose material to compressive stress. It is more about compressing the material.
The tensile stress stretches the material and checks its elasticity. In simple words, this stress elongates material. The particles of the materials occupy more space and move farther apart from each other. The compressive stress pushes, presses, and shortens the material. The material particles in these cases come very close to each other due to compressive stress or force.
3- Equipment Setup
The tensile test is conducted in a universal testing machine (UTM). This comes with two grips. The material or specimen is clamped between these two grips. The operators check the alignment to ensure an accurate reading. Both grips of the machine pull the specimen and apply stress. The operator then notes stress and material behavior.
The machine also records the stress-strain graph, which is very useful. It provides us with different points where materials exhibit distinct behaviors. On the other hand, compression testing machines come with flat plates. The specimen is placed in the machine between these two plates. The plates compress the material by applying force on it.
4- Deformation Behavior
As said earlier, the tensile test stretches the materials by applying force. Therefore, the material becomes thinner as it is stretched. It will become thinner and thinner with the increase of stress. There will be a point when you’ll notice a material undergoing necking.
At this stage, the material will have a fragile cross-section area. Other parts of the material would be less than that neck. Compression testing applies force to compress the material. As a result, the material shortens, and its size will decrease. If the material is brittle, it can even break and shatter.
5- Material Properties Measured
As stated above, both of these testing methods help us know about different parameters. However, each test provides us with different parameters for the materials. The tensile test includes information about the following parameters:
- Yield Strength
- Fracture Point
- Necking Behavior
- Elongation (Ductility)
- Ultimate Tensile Strength (UTS)
- Young’s Modulus (Elastic Modulus)
All these parameters are associated with the stretching of the materials. On the other hand, the compression test also provides us with some parameters. These parameters are primarily concerned with pushing, compressing, and squeezing. Here is the list of those key parameters.
- Compressive Strength
- Elastic Limit in Compression
- Deformation, shortening & Crushing
- Young Modulus of Elasticity (in compression)
Remember, yield strength and compression strength have the same meaning for different behavior. Yield strength is the material force a material bears before it deforms permanently. Similarly, the compressive strength is the maximum stress or force the material faces before crashing or failing.
6- Commonly Tested Materials
Both tests differ in terms of the materials which they test. The tensile test is generally suitable for those materials that are prone to elongate. Upon stress, these materials typically expand and increase in size. Examples of such materials include plastics, polyesters, rubber, and metals, i.e., steel. On the other hand, the compression test does not test such materials.
Instead, it tests those materials which are brittle. It means these brittle can break when subjected to extreme loading. Examples of such materials include ceramics, concrete, bricks, wood, and others. These materials do not elongate when force is applied to them. Instead, they are more likely to crack and break due to load exceeding their limit.
7- Presence of Necking
Necking is a common phenomenon in tensile tests. As you know, ductile materials, upon pulling, expand and elongate. If you continue to draw, the material will reach its ultimate tensile strength. After this stage, you’ll see a necking of material. Some portions of the material will be thinner than the rest. This portion becomes increasingly thin if you continue to pull it.
This thin portion of the material is referred to as a neck. Generally, the material breaks at this thin part (neck). In the compression test, the material undergoes compression, not pulling. So it is pushed, and there happens no necking on the materials. This necking is only typical in many ductile materials such as metals and plastics.
8- Cost and Complexity of Test Setup
The tensile test is generally more costly and complex as compared to its counterpart. The reason is that tensile testing machines are expensive. Moreover, these machines need grips that act as fixtures. It holds and pulls the material from both ends and checks tensile strength.
If the material is not aligned between those fixtures, this test won’t give an accurate result. The tensile tester also utilizes extensometers to measure the material’s elongation. All these aspects make tensile testing a complex and less user-friendly process.
On the flip side, the compression test is straightforward. The machine used in this test comes with two plates. The material is placed between these plates. The plates then compress material from both sides and check its behavior under stress. Moreover, these machines are inexpensive, which makes this testing cost-effective.
Frequently Asked Questions
Is tensile the same as compression?
No. Tensile refers to the elasticity of materials. Tensile testing checks how much elastic a material is under tension. Compression refers to the process of squeezing or pushing a material. This test compresses the material and checks its behavior.
What is the difference between tensile strength and compressive strength?
The tensile strength indicates the maximum stress (pulling) a material can withstand. After this point, the material will deform permanently. Contrarily, compressive strength is the maximum pushing or pressing stress a material can bear. After compressive strength, the material will crack and break.
Can the same machine perform both tensile and compression tests?
Yes, the modern Universal Testing Machine (UTM) comes with both grips and plates. Grips help perform tensile tests. On the other hand, plates present in these machines help execute the compression test. Previously, we relied on two different machines for these tests.
Conclusion
Both compression and tensile tests are widely used across various industries. They differ from one another and are used for testing different types of materials. However, their importance is equal, and engineers consider them vital for their decision-making.
Remember, engineers only choose a material after knowing its strength and capabilities. In this article, I’ve discussed eight key differences between these tests. Remember, tensile testing involves pulling and stretching the materials. The compression test consists of applying pressure to the material and observing its behavior under stress.