Material Properties

Metallic engineering materials are classified as either ductile or brittle materials.

Ductile materials 

A ductile material is one having relatively large tensile strains up to the point of rupture.

Ductile materials have a well-defined elastic region with linear stress- strain relationship, yield point, strain-harden and necking before the point of rupture in stress strain curve. 

Example: structural steel, Copper, Brass and aluminum etc.

Brittle materials

A brittle material has a relatively small strain up to the point of rupture.
A material is brittle if, when subjected to stress, it breaks with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength.
Brittle materials do not have a well-defined yield point, and do not strain-harden. Therefore, the ultimate strength and breaking strength are the same.
Example: Glass, Cast iron and Concrete etc.

Malleability

Malleability is a physical property of metals that defines their ability to be hammered, pressed, or rolled into thin sheets without breaking. 

In other words, it is the property of a metal to deform under compression and take on a new shape. When a piece of hot iron is hammered it takes the shape of a sheet. The property is not seen in non-metals.

Examples: Gold, iron, aluminium, copper, silver, and lead.Gold and silver are highly malleable.

Hardness 

Hardness is a measure of the material property to resist indentation,abrasion and wear. 

It is a material's ability to withstand friction, essentially abrasion resistance, is known as hardness. 

Hardness is quantified by hardness scale such as Rockwell and Brinell hardness scale that measure indentation /penetration under a load. 

Hardness and Strength correlate well because both properties are related to inter-molecular bonding. A high-strength material is typically resistant to wear and abrasion.

Modulus of Resilience

The resilience of the material is its ability to absorb energy without creating a permanent distortion. The maximum strain energy stored within elastic limit per unit volume is called Modulus of resilience.

It is the work done on a unit volume of material as the force is gradually increased from O to Y, in N⋅m/m3. This may be calculated as the area under the stress-strain curve from the origin O to up to the elastic limit Y (the shaded area in the above figure).

Modulus of Toughness

The toughness of a material is its ability to absorb energy without causing it to break.

Modulus of toughness is the work done on a unit volume of material as the force is gradually increased upto rupture, in N⋅m/m3. 

This may be calculated as the area under the entire stress-strain curve as Shown in figure.

Fatigue 

The repeated application of stress typically produced by an oscillating load such as vibration. 

Example: Sources of ship vibration are engine, propeller and waves. 

The resistance to maximum stress decreases as the number of loading cycles increases.

Endurance limit

The fatigue limit, also known as the endurance limit or fatigue strength, is the stress level below which an infinite number of loading cycles can be applied to a material without causing fatigue failure. Ferrous alloys and titanium alloys have a distinct limit.