Stress and strain
Simple Stresses and Strains
Stress
• No engineering material is perfectly rigid and hence, when a material is subjected to external load, it undergoes deformation.
• While undergoing deformation, the particles of the material offer a resisting force (internal force). When this resisting force equals applied load the equilibrium condition exists and hence the deformation stops.
• These internal forces maintain the externally applied forces in equilibrium.
Contd…
• Stress = internal resisting force / resisting cross sectional area = R/ A
• The internal force resisting the deformation per unit area is called as stress or intensity of stress. • SI unit for stress: N/m2
• Also designated as a pascal (Pa) Pa = N/m2
Contd…
• gigapascal, 1GPa = 1×109 N/m2 = 1×103 MPa=
1×103 N/mm2
• kilopascal, 1kPa = 1000 N/m2
• megapascal, 1 MPa= 1×106 N/m2 =
1×106N/(106 mm2) = 1 N/mm2
• 1 MPa= 1 N/mm2
Direct or Normal Stress: Intensity of resisting force perpendicular to or normal to the section is called the normal stress. Normal stress may be tensile or compressive. Tensile stress: stresses that cause pulling on the surface of the section, (particles of the materials tend to pull apart causing extension in the direction of force)
Compressive stress: stresses that cause pushing on the surface of the section, (particles of the materials tend to push together causing shortening in the direction of force)
Strain
• If a bar is subjected to a direct load, and hence a stress, the bar will changes in length. If the bar has an original length L and change in length by an amount δL, the linear strain produced is defined as,
Linear strain, ε=Original length (L) / Change in length (δL )
• Strain is a dimensionless quantity.
Stress- Strain curve for mild steel
• Elastic limit : It is the stress beyond which the material will not return to its original shape when unloaded but will retain a permanent deformation called permanent
Stress
• No engineering material is perfectly rigid and hence, when a material is subjected to external load, it undergoes deformation.
• While undergoing deformation, the particles of the material offer a resisting force (internal force). When this resisting force equals applied load the equilibrium condition exists and hence the deformation stops.
• These internal forces maintain the externally applied forces in equilibrium.
Contd…
• Stress = internal resisting force / resisting cross sectional area = R/ A
• The internal force resisting the deformation per unit area is called as stress or intensity of stress. • SI unit for stress: N/m2
• Also designated as a pascal (Pa) Pa = N/m2
Contd…
• gigapascal, 1GPa = 1×109 N/m2 = 1×103 MPa=
1×103 N/mm2
• kilopascal, 1kPa = 1000 N/m2
• megapascal, 1 MPa= 1×106 N/m2 =
1×106N/(106 mm2) = 1 N/mm2
• 1 MPa= 1 N/mm2
Direct or Normal Stress: Intensity of resisting force perpendicular to or normal to the section is called the normal stress. Normal stress may be tensile or compressive. Tensile stress: stresses that cause pulling on the surface of the section, (particles of the materials tend to pull apart causing extension in the direction of force)
Compressive stress: stresses that cause pushing on the surface of the section, (particles of the materials tend to push together causing shortening in the direction of force)
Strain
• If a bar is subjected to a direct load, and hence a stress, the bar will changes in length. If the bar has an original length L and change in length by an amount δL, the linear strain produced is defined as,
Linear strain, ε=Original length (L) / Change in length (δL )
• Strain is a dimensionless quantity.
Stress- Strain curve for mild steel
• Elastic limit : It is the stress beyond which the material will not return to its original shape when unloaded but will retain a permanent deformation called permanent