Shearing (physics)

Things can slide past each other.

This sliding can change a shape. It can make a box look tilted.

Some things stay tilted like that. They do not go back. This can happen to metal or sand.

Sometimes the sliding stays in one narrow band. This is how parts of the Earth move.

It is neat to see how things shift.

Shearing happens when parts of a material slide past each other. This sliding is caused by a force called shear stress.

When this happens, the shape of the object changes. This change is called shear strain. Sometimes the object does not go back to its old shape. We call this a plastic shear strain. This happens when the material begins yielding. It stays changed forever.

In some materials, the sliding stays in one thin area. We call this a shear band. In metals or sand, the sliding happens only in that band. The rest of the material just slides along. In brittle things, this can cause a break. This is how plates move on the Earth's crust.

Shearing can also change the size of a material. In soil, this is called volumetric strain. If the volume grows, it is called Reynolds' dilation. If the volume gets smaller, it is called compaction. Scientists use tests to measure how soil shears. They use a direct shear test or a triaxial test.

Caption: A building frame shifts its shape due to shearing.

Shearing is a way that materials change shape. It happens when parallel parts of a material slide past one another. This movement is caused by a force called shear stress. When this happens, the material experiences what is called shear strain. This is different from a change in total volume. Instead, it is a change in the angle of the material.

How does this work in real life? Sometimes the change is just elastic. This means the material can snap back to its old shape. Other times, the material undergoes plastic shear strain. This happens when the material starts yielding. In this case, the change is irreversible. The material will not return to its original shape.

Scientists study how different things react to these forces. In soil mechanics, shearing can change the volume of the soil. This is called volumetric strain. If the volume grows, it is called Reynolds' dilation. If the volume gets smaller, it is called compaction. Experts use specific tools to measure this. They use a direct shear test or a triaxial shear test.

In many materials, the sliding does not happen everywhere. It can move into a narrow area called a shear band. This happens in metals, plastics, and sand. All the sliding occurs inside this thin band. The blocks of material on either side just slide past each other. In brittle materials, this can lead to a fracture. The shearing then happens along that break.

We can see shearing in the world around us. One huge example is plate tectonics. The plates of the Earth's crust slide along fracture zones. You can also see it in buildings. A rectangular frame might shift into a parallelogram shape. This shows how the shape changes under stress.

In the study of continuum mechanics, shearing describes a specific way that materials deform. This process occurs when parallel internal surfaces within a substance slide past one another. This movement is triggered by a force known as shear stress. When this stress is applied, the material experiences what is called shear strain. Unlike volumetric strain, which changes the total size of an object, shear strain changes the internal angles. The specific change in angle resulting from this stress is called the angle of shear.

Scientists distinguish between two main types of shear strain based on how the material reacts. The first type is elastic shear strain. In this state, the material can recover its original shape once the stress is removed. The second type is plastic shear strain, which is a more permanent change. Plastic shear strain occurs when a material begins yielding. This type of deformation is continuous and does not cause the material to fracture immediately. However, it is irreversible, meaning the object will never return to its original shape.

Shearing can also influence the volume of a material, a concept known as volumetric strain. This is especially important in the field of soil mechanics. When shearing causes the volume of soil to increase, the process is called Reynolds' dilation. If the shearing causes the volume of the soil to decrease, it is called compaction. Engineers and scientists use specific methods to measure these changes in soil. They often use a direct shear test or a triaxial shear test to understand these forces.

In many substances, the sliding motion does not spread out evenly across the whole object. Instead, the motion often localizes into a very narrow area called a shear band. This phenomenon is common in metals, plastics, and granular materials like sand or soil. Within a shear band, all the actual sliding happens in that thin layer. The larger blocks of material on either side of the band simply slide past each other without deforming internally. This concentration of movement allows the material to shift quite rapidly.

Brittle materials behave differently during shear localization. In these substances, the localized movement can lead to a fracture. Once a fracture occurs, all subsequent shearing happens along that narrow break. This is a special case of shear localization that results in a clean split. This process is vital to understanding how different structures fail under pressure.

We can see the effects of shearing in massive natural systems like plate tectonics. The large plates of the Earth's crust slide along fracture zones. This movement is a large-scale example of shearing in action. On a smaller scale, you can see shearing in man-made structures. For example, a wood-framed house might experience shear strain. The rectangular sections of the frame may deform into a parallelogram shape.

Engineers also look for a specific point called the shear center when analyzing sections. The shear center is an imaginary point on a cross-section. If a shear force is applied exactly at this point, it will not induce any torsion. Torsion is a twisting force. The shear center is not always the same as the centroid, which is the geometric center. For shapes with one axis of symmetry, the shear center sits on that axis. If a shape has two axes of symmetry, the shear center lies exactly on the centroid.