Characteristics or properties of sheet metals

CHARACTERISTICS OR PROPERTIES OF SHEET METALS

1. Strength:

The strength of a sheet metal is the property of resistance to external loads or stresses while not causing the structural damage. The following types of strengths in the sheet metals normally are often measured:

a) Tensile strength:

Tensile strength is the ability of a metal to resist being pulled apart by opposing forces acting in a straight line. The tensile test is the one most often used to measure the strength of metals.

b) Shear strength:

Shear strength is the ability of a material to resist being fractured by opposing forces acting in a straight line but not in the same plane.

c) Compressive strength:

Compressive strength is the ability of a material to withstand pressures acting on a given plane.

2. Elongation:

It is the capability of the sheet metal to stretch without necking and failure. A specimen subjected to tension undergoes uniform elongation. When the load is exceeded, the ultimate tensile strength, the specimen begins to neck.

3. Elasticity:

Elasticity is the ability of material to return to its original size, shape and dimensions after being deformed. Also, the property of regaining the original dimensions upon removal of the external load is known as elasticity. The elastic limit is the point at which the permanent deformation begins. The yield point is the point at which a definite deformation occurs with little or no increase in load.

4. Modulus of elasticity:

The modulus of elasticity is the ratio of the internal stress to the strain produced. It expresses the stiffness of a material.

5. Ductility:

Ductility is the capacity of a material to be drawn or stretched under tension loading and permanently deformed without rupture or fracture.

6. Malleability:

Malleability is the property of a metal to be deformed or compressed permanently without rupture or fracture.

7. Plasticity:

Plasticity is the ability of a metal to be deformed extensively without rupture.

8. Toughness:

Toughness is a combination of high strength and medium ductility. Toughness is the ability of a material or metal to resist the fracture after the damage has begun.

9. Hardness:

Hardness is the ability of a material to resist penetration and wear by another material. 

10. Brittleness:

Brittleness is the property of breaking the material without visible permanent deformation. It is the reverse of toughness.

11. Corrosive resistance:

Corrosive resistance is the resistance to eating away or wearing by the atmosphere, moisture or other agents such as acid.

12. Anisotropy

Since most sheets used as blanks are formed by rolling, they have anisotropic properties (different yield strength along different directions). It is obtained during the thermo- mechanical processing.

13. Springback:

The tendency of the metal that tries to resume its original position causing a decrease in bend angle is known as springback. The springback varies from 0.5° to 5o for steel. Greater springback is caused by a larger bend radius.

Springback depends on the following factors:

1. Material type

2. Thickness

3. Hardness

4. Bend radius.

14. Wrinkling:

It is the formation of wrinkles in deep drawing operations in sheet metal material, generally in the wall or flange of the part. It is caused by compressive stresses in the plane of the sheet. It can be objectionable or can be useful in imparting the stiffness to parts.

15. Grain size:

It determines the surface roughness on a stretched sheet metal. It affects both mechanical properties and surface appearance. Smaller is the grain size, stronger will be the metal.

16. Dent resistance of sheet metals:

Dents caused by dynamic forces from moving objects that hit the sheet metal. Dynamic yield stress instead of static yield stress should be the significant strength parameter for the determination of dent resistance.

17. Residual stress:

It is caused by non-uniform deformation during forming and it causes the part distortion when sectioned and leads to stress-corrosion cracking which can be reduced or eliminated by stress relieving.