Stress is the result of forces acting in specified element parallel or perpendicular to the sliced plane of element. The force perpendicular to the plane is called normal force and generates normal stress. Meanwhile, the force parallel to the plane is called shear force and produce shear stress. Both of them are shown in the following equation:
σ = P / A and τ = V / A
Where:
σ = normal stress
τ = shear stress
P = normal force
V = shear force
A = plane area
The external force which is given on the element will cause internal reaction force that called as deformation. Deformation can be a change in geometry and dimension. Deformation that occurs on a unit length is called strain and can be shown in the following equation:
ε = (l – lo) / lo
Where:
ε = strain
lo = length before deformation
l = length after deformation
Tensile test on specimen material can be carried out to determine the strength of material against forces. This specimen is slowly pulled until failure (fracture). Tensile force and length specimen is always measured continuously during tensile test.
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| Figure 1: Specimen of Tensile Test |
Based on the result of test, can observed and get conclusion of properties of material which show relationship between stress and strain. This linear relationship is expressed in Hooke Law as shown in the following equation:
E = σ / ε
Analysis and diagram of stress and strain in mild steel and brittle steel can be seen in stress analysis in piping system.