Stress causes deformation by applying forces that alter an object's shape or size. Essentially, stress is the measure of these internal forces acting within a deformable body. According to our reference, stress is "a quantity that describes the magnitude of forces that cause deformation". The more stress an object is under, the greater the deformation it will experience, provided the material is not at its breaking point.
Understanding Stress and Deformation
Deformation, in the context of material science, refers to any change in the shape or size of an object. This change can be temporary (elastic) or permanent (plastic). Stress, on the other hand, is the internal resistance an object offers to externally applied forces. When these forces are sufficient, they overcome the internal bonds in the material causing it to deform.
Types of Stress and Corresponding Deformation
| Stress Type | Definition | Example of Deformation |
|---|---|---|
| Tensile | Forces pull on an object and cause elongation. | Stretching a rubber band, lengthening a wire when pulled. |
| Compressive | Forces push inward on an object, causing it to shorten or compact. | Squeezing a sponge, the compression of building foundations. |
| Shear | Forces act parallel to a surface, causing layers of the material to slide past each other, leading to angular distortion. | Cutting a deck of cards, twisting a rectangular object. |
| Torsional | Forces act to twist an object, causing a rotational deformation. | Twisting a towel to wring it out. |
How Stress Leads to Deformation
- Force Application: An external force is applied to an object.
- Stress Generation: This external force creates internal stresses within the material. As stated in the reference, "stress is generally defined as force per unit area".
- Material Response: The material responds to the stress. If the stress is below a certain threshold (yield strength), the material will deform elastically and return to its original shape when the stress is removed.
- Deformation: If the stress exceeds the material's yield strength, the deformation becomes plastic, resulting in a permanent change in shape.
Practical Example: Tensile Stress
The reference explains how tensile stress happens: "When forces pull on an object and cause its elongation, like the stretching of an elastic band, we call such stress a tensile stress." Imagine stretching a rubber band. As you pull on both ends, you are applying a force across the area of the band, creating tensile stress. This stress will cause the rubber band to elongate. If you release the force before it reaches its breaking point, the band will return to its original shape because the stress was within the elastic limit. If you pull too hard, the band will permanently stretch or break due to plastic deformation.
Conclusion
Stress, in essence, is the agent that causes deformation by applying forces to an object which changes its form. The nature and magnitude of the stress determine the type and extent of deformation.
