Force and Stress and Strain

- Internal Force: When an external force is applied to an object, deformation and resistance occur simultaneously, creating a balance with the external force.

- Stress: The magnitude of internal force per unit area

   1. Normal Stress (also known as Axial Stress): The stress acting perpendicular to the material surface.

        A. Equation: Normal stress = Load, Internal force, External force/Area = P/A [Pa(N/m^2), MPa(N/mm^2)] [1000000Pa = 1000KPa =1MPa]

         B. When a tensile stress is applied and the specimen extends, it is generally marked as (+).

         C. When a compressive stress is applied and the specimen shrinks, it is generally marked as (-).

   2. Shear Stress: The stress that occurs in the tangential direction along the section.  

         A. Equation: Tau = τ = P/A [Pa(N/m^2), MPa(N/mm^2)]

 

 

- Strain: The ratio of deformation of a material due to load.

   1. Longitudinal Strain: The strain caused in the longitudinal direction by a load in the length direction.

         A. Equation: ε = (l'-l)/l = λ/l

   2. Transverse Strain (Compression Strain): The strain caused in the transverse direction by a load in the length direction.

         A. Equation: ε' = (d'-d)/d = δ/l (where d': contracted length, d: horizontal length)

   3. Shear Strain: The strain of an object under the influence of shear stress.