What Does Shear Strength Mean?
The shear strength of a material is defined as its ability to resist forces that cause the material's internal structure to slide against itself. The shear strength of a material can be measured in either the vertical or horizontal direction. For example, if the force causes the object's layers to slide in the horizontal direction, the material will exhibit horizontal shear strength. Conversely, if the force causes the layers of the material to slide in the vertical direction, the material will exhibit vertical shear strength.
To better understand shear strength, consider lifting a horizontal stack of books by pressing them on both extreme ends (each hand acting as a support). The compressive force induced by squeezing the stack of books generates a frictional force between the books. This friction is a vertical force that keeps the books from sliding against each other and falling apart.
This same principle applies to solid objects. Suppose the vertical (or horizontal) force is greater than the shear strength of the material. In that case, the object can experience shear failure, where the object separates into two or more sliding parts. For example, a force applied to a building’s I-beam can cause a shear failure that separates the I-beam into two parts as they slide against each other due to a vertical load.
The shear strength of an object can be heavily influenced by corrosion. Corrosion is a deteriorative process that diminishes the thickness of metal components. Thinning due to corrosion can reduce a component's cross-sectional area, thus, reducing its shear strength.
If the corroded section is subjected to loads that exceed its reduced shear capacity, shear failure can occur, which can lead to catastrophic overall structural failure.