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# Mechanical Properties of Engineering Materials

To finalize the material for an engineering product / application, we should have the knowledge of Mechanical properties of materials. The mechanical properties of a material are those which effect the mechanical strength and ability of material to be molded in suitable shape. Some of the typical mechanical properties of a material are listed below-
• Strength
• Toughness
• Hardness
• Hardenability
• Brittleness
• Malleability
• Ductility
• Creep and Slip
• Resilience
• Fatigue

### Strength

It is the property of material which opposes the deformation or breakdown of material in presence of external forces or load. Material which we finalize for our engineering product, must have suitable mechanical strength to be capable to work under different mechanical forces or loads.

### Toughness

It is the ability of material to absorb the energy and gets plastically deformed without fracturing. Its numerical value is determined by the amount of energy per unit volume. It unit is Joule/ m3. Value of tough ness of a material can be determines by stress-strain characteristics of material. For good toughness material should have good strength as well as ductility. For example: brittle materials, having good strength but limited ductility are not tough enough. Conversely, materials having good ductility but low strength are also not tough enough. Therefore, to be tough, material should be capable to withstand with both high stress and strain.

### Hardness

It is the ability of material to resist to permanent shape change due to external stress. There are various measure of hardness – scratch Hardness, indentation hardness and rebound hardness
1. Scratch Hardness Scratch Hardness is the ability of material to oppose the scratch to outer surface layer due to external force.
2. Indentation Hardness It is ability of material to oppose the dent due to punch of external had and sharp object.
3. Rebound Hardness Rebound hardness is also called as dynamic hardness. It is determined by the height of “bounce” of a diamond tipped hammer dropped from a fixed height on the material.

### Hardenability

It is the ability of a material to attain the hardness by heat treatment processing. It is determined by the depth up to which the material becomes hard. The SI unit of hardenability is meter (similar to length). Hardenability of material is inversely proportional to the weld-ability of material.

### Brittleness

Brittleness of a material indicates that how easily it gets fractured when it is subjected to a force or load. When a brittle material is subjected to a stress is observes very less energy and gets fractures without significant strain. Brittleness is converse to ductility of material. Brittleness of material is temperature depended. Some metals which are ductile at normal temperature become brittle at low temperature.

### Malleability

Malleability is property of solid material which indicates that how easily a materials gets deformed under compressive stress. Malleability is often categorized by the ability of material to be formed in the form of a thin sheet by hammering or rolling. This mechanical property is an aspect of plasticity of material. Malleability of material is temperature dependent. With rise of temperature, the malleability of material increases.

### Ductility

Ductility is a property of a solid material which indicates that how easily a materials gets deformed under tensile stress. Ductility is often categorized by the ability of material to get stretched into a wire by pulling or drawing. This mechanical property is also an aspect of plasticity of material and temperature dependent. With rise of temperature, the ductility of material increases.

### Creep and Slip

Creep is the property of material which indicates the tendency of material to move slowly and deform permanently under the influence of external mechanical stress. It results due to long time exposure to large external mechanical stress with in limit of yielding. Creep is more severe in material that are subjected to heat for long time. Slip in material is a plane with high density of atoms.

### Resilience

Resilience is the ability of material to absorb the energy when it is deformed elastically by applying stress and release the energy when stress is removed. Proof resilience is defined as the maximum energy that can be absorbed without permanent deformation. The modulus of resilience is defined as the maximum energy that can be absorbed per unit volume without permanent deformation. It can be determined by integrating the stress-strain cure from zero to elastic limit. Its unit is joule/m3.

### Fatigue

Fatigue is the weakening of material caused by the repeated loading of material. When a material is subjected to cyclic loading, and loading greater than certain threshold value but much below the strength of material (ultimate tensile strength limit or yield stress limit, microscopic cracks begin to form at grain boundaries and interfaces. Eventually the crack reached to a critical size. This crack propagates suddenly and the structure gets fractured. The shape of structure effects the fatigue very much. Square holes and sharp corners lead to elevated stresses where the fatigue crack initiates.

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