Shear stress occurs on a plane where force is measured. Normal stress occurs when a component is under tension or compression. Shear stress is parallel to the stress plane and can cause mechanical failure if it exceeds the material’s limit.
A shear plane is the plane where shear stress occurs. Like normal stress, shear stress is a measure of force per unit area. At any given point in a structure, there are many possible planes that can be defined to measure stress. Consequently, whichever plane contains the area in question is the cutting plane. The cut plane is useful for engineers analyzing internal stresses in structures.
Stress has the same units as pressure: force times area. Normal stress occurs when a component is put under tension or compression. If a metal rod is stretched vertically, an internal stress will tend to resist further deformation. This stress will occur in the horizontal cross sections of the bar. The stress is called normal because it is directed at right angles or normal to the horizontal stress planes.
Shear stress is similar to normal stress in that it has the same units. The direction of the stress, however, is parallel to its stress plane. This type of stress could result from the application of a different set of forces to the same metal bar; that is, if someone held the bottom of the bar steady while trying to move the top of the bar to the right. The resulting internal stress is called shear stress, because parts of the bar are trying to slide, or shear, across each other.
Under these loading conditions, stresses in a horizontal plane located in the center of the bar would be horizontally directed shear stresses. The bottom of the bar would try to move to the left; would submit forces to the left in a horizontal shear plane. The top of the bar would try to move to the right; would subject forces to the right in the same shear plane.
Shear plane analysis is important to prevent mechanical failure of a structure. Every material has a limit on how much stress it can handle. This limit is a property of the material itself, rather than the shape of the object. For example, two rubber bands could be made in different sizes but from the same material. The larger one can take more force before breaking, but only because it has more cross-sectional area to distribute the force; the internal stress will be the same at failure for both sizes.
Likewise, components can fail due to excessive shear stress. If a component fails under shear stress, parts of it will literally slide over each other. Old metal bolts, for example, usually fail like this. The shear stress limit, as with normal stress, is a material property.
Protect your devices with Threat Protection by NordVPN
