Mechanical Properties of a Material

Mechanical properties of material defines material behavior under load conditions such as tension, compression and shear forces. These properties help in the selection of material during product and process design. For example to draw wire. We select a material with high ductility. This article covers the following mechanical properties of a material. We suggest you also read this article on Factor of Safety in mechanical engineering.

  • Strength
  • Stiffness
  • Hardness
  • Elasticity
  • Plasticity
  • Toughness
  • Ductility
  • Malleability
  • Machinability
  • Resilence
  • Creep
  • Fatique
Strength of a Material

Strength of a material is a very important term used during product design. It is the property of material that resist any change in material when external force is applied. External force results in internal mechanical stresses in a material. And internal mechanical stress causes mechanical strain in the material. 

This curve represents the relation between stress and strain produced in a material when load is applied.
Stress Strain Diagram for Ductile Material

As shown above, Strength of a material can be defined under a stress strain diagram for a material. Following types of material strengths are used during product design.

Yield Strength

Till yield point, a material exhibits an elastic behavior. At this point a material can handle maximum tensile strength before permanent deformation.

Ultimate Strength

Ultimate strength of a material is the maximum amount of external force a material can bear before failure.

Fracture Strength

Fracture strength is the maximum strength of a material on the stress-strain curve at which failure occurs.

Stiffness
This Image indicates stiffness on stress strain curve
Material Stiffness on Stress and Strain

Stiffness defines the ability of a material to resist elastic deformation when load is applied. Modulus of elasticity in the stress-Strain curve measures the stiffness of a material. 

For example, To ensure small deformation in a part. We need to select material with high stiffness or higher young modulus. Steel has higher stiffness than rubber.

Hardness of a Material

Hardness of a material defines the localized permanent surface deformation of a material when external force is applied. Higher the hardness of a material. Higher will be the external force required to deform material. It looks similar to stiffness, But it’s not correct.

Hardness of a material also controls a material’s resistance to wear, scratch resistance and machinability. Material hardness can be increased using various heat treatment processes. For example diamond is the hardest material used to cut other hard materials.

Hardness of a material is defined by a number. Following Tests are used to determine a material hardness. 

  • Rockwell Hardness Test.
  • Vickers Hardness Test.
  • Brinell Hardness Test.
  • Shore Scleroscope.
Toughness
This image shows toughness of a material under stress strain curve.

Toughness helps in resisting high impact or sudden load on a part. Mathematically toughness is the energy absorbed per unit volume upto material fracture points. 

Area under the stress-strain curve till the fracture point is known as the toughness of a material. Tough materials are used where part has to bear high impact load such as a hammer.

Elasticity

Elasticity in a material helps a part in regaining its original shape when the external forces are removed. In a stress-strain curve till yield strength a material behaves as elastic material. For example, steel has more elasticity compared to rubber. Area under the stress-strain curve till the yield point is known as the elastic region of the material.

Plasticity

Plasticity of a material helps in retaining the existing position of a material even after the removal of external force. In a Stress Strain Diagram a material exhibits plastic behavior after yield point. Plasticity of a material is used during sheet metal bending, forging and deep drawing operations.

Ductility

Ductility of a material is used to draw the material into wires by the application of tensile force. A ductile material should have good strength and plastic behavior. For example, steel, copper and aluminum materials are used to draw wires.

Malleability

Malleability property of a material is used in converting a material into thin sheets. For example, steel, aluminum and copper sheets are formed by passing them through rolling mills.

Machinability

Machinability property of a material defines how easily a material can be cut. For example, aluminum is relatively easy to machine compared to stainless steel. Therefore aluminum has good machinability compared to stainless steel.

Resilience of a Material

Resilience defines the ability of material to absorb energy and resist shock. Mathematically resilience of a material is the amount of energy absorbed per unit volume within its elastic limit.

For example, spring steel has high resilience compared to aluminum. Therefore spring steels are used to manufacture springs.

Creep Resistance

Creep resistance in a material defines a material ability to permanently deform when continuous load is applied. This property of a material is used in applications where continuous stress is applied to a part for prolonged time.

Fatigue in a Material

Fatigue in a material occurs due to repetitive cyclic loading. It results in progressive or localized damages in a part or cracks. For example, Gears in a gearbox and springs in suspension systems are subjected to continuous loading.

Commonly Asked Questions on Materials

Mechanical properties of a material are used during the selection of a material for required application.

For example , why don’t we manufacture car roofs or doors in plastic or glass? Because glass is very fragile and it can not bear loads acting on it. We come to this conclusion by looking at mechanical properties of glass and plastic materials.

Mechanical properties (such as elasticity, hardness, ductility etc) defines the behaviors of a material under loading conditions.

Whereas physical properties define the characteristics of a material. For example conductivity, resistivity, melting point, specific heat and Density are physical properties of a material.

A material mechanical properties depends on:

  1. Arrangement of grain structure inside material.
  2. Composition of a material (such as carbon, silicon, magnesium etc)

Therefore mechanical properties of a material can be modified either by changing its grain structure (Heat Treatment Process) or by modifying its chemical composition. 

To sum up, mechanical properties of a material are very important parameters in the selection of a material for a given application. Mechanical properties of a material are available in the simulation tool material library. Users can use these properties for the selection of material. We suggest you also read this article on the role of simulation in product design.

I will keep adding more information in mechanical properties of materials. Please add your suggestions, comments or questions on mechanical properties of materials in the comment box.

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