The strength of a metal plays an important role in designing products or structural architectures. There are different elements to a metal’s strength, including tensile strength, yield strength, hardness, and density. Tension vs. compression forces can have an effect on the amount of stress or pressure a metal can handle before it fails, which is why it’s important to determine which material’s strength will work best depending on the required application.
Tension vs. Compression Forces: A Quick Guide
Below, we briefly describe tensile and compressive forces in metals, breaking down how each works and the effects they can have on various metals.
Tensile Force in Metals
Whenever a metal stretches, it is under tensile force. Mathematically, tensile stress equals force/area. The maximum stress a metal can handle represents its tensile strength.
Tensile strength can be further divided into two parts:
- Yield Strength: When the metal is subjected to external tensile loading, it will undergo elastic and plastic deformation. The yield strength denotes the tensile force up to which a metal can regain back its original shape once the force is removed.
- Ultimate Tensile Strength: Beyond the yield point, the metal will continue to show plastic deformation until a point before necking takes place. This limit is known as the ultimate tensile strength. In short, it represents the maximum stress a metal can handle without breaking into two pieces.
Compressive Force in Metals
Compressive force represents the maximum compression or pressure a metal can handle without breaking. There is a reduction in the length in comparison to its original measure.
There are six different types of compressive failure modes:
- Buckling: Sudden sideway change in shape under an axial load
- Shearing: Sliding failure along the direction of applied force
- Double barrelling: The formation of two barrels during the compression of high prismatic bodies without external zones
- Barrelling: The generation of a convex surface on the exterior of a cylinder
- Homogeneous compression: No friction is present at the contact surface
- Compressive instability: Failure due to work softening of the metal
A widely accepted test to determine the compressive strength is the Mohs hardness test.
Different Metals Under Tension vs. Compression Forces
The maximum value of compressive strength and tensile strength varies between metals. Some metals show exceptional tensile strength under tension, whereas some metals are good at handling maximum compressive force. Thus, comparing two metals under tension vs. compression forces requires acknowledging the application of the metal in the first place; only then does it become easy to compare it to other metals.
The chart below compares the strength, hardness, and density of different metals:
Steel has higher tensile strength and yield strength than aluminum; however, aluminum is lightweight and offers better resistance to corrosion than steel. Thus, it’s important to study the parameters when considering the application requirements.
Also, a metal can have high tensile strength yet low compressive strength and vice versa. For instance, the compressive strength of cast iron is more than its tensile strength, but for mild steel, it’s the opposite.
Brittle materials, such as cast iron, contain a lot of voids. Under tensile strength, these voids act as notches, resulting in a high propagation of cracks through the material. But under a compressive force, these voids get closed, nullifying any possibility of crack propagation.
On the other hand, in ductile materials, cracks formed under the load are closed easily without propagating through the material. As a result, these are equally strong in tension and compression; however, they tend to fail under shear stress.
The Importance of Understanding Material Strengths
Compression and tensile strengths are very important properties of a metal when it comes to engineering design. In any engineering design, the main objective is to keep the plastic deformation as small as possible. In this regard, Young’s modulus (denoted as E) can be considered a key parameter in the selection process.
Young’s modulus is another way of calculating the degree of deformation of a material under lengthwise tension or compression. It’s defined as the ratio between longitudinal stress and strain. The higher the Young’s modulus, the stiffer the material, and the smaller the elastic deformation for a given applied load.
Now, for example, if we construct a house from a metal with a low Young’s modulus, it will deflect a lot under a compressive load; a stiffer metal would give a more desired response.
Modern vaulting poles are a great example of this. To maximize an athlete’s performance, a vaulting pole should be made up of light materials but should also store elastic strain as the pole bends. Thus, these poles are constructed from fiberglass (E =15 GPa) or a mix of fiberglass and carbon fiber (E =500 GPa).
The Young’s modulus for some of the most commonly used metals is shown below:
|Material||Young’s Modulus (E)|
|Stainless steel (AISI 302)||180|
|Structural steel (ASTM-A 36)||200|
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