1 Stress in a loaded deformable material body assumed as a continuum. 2 Axial stress in a prismatic bar axially loaded. The stress or force distribution in the cross section of the bar is not necessarily uniform. 4 Shear stress in simple stress and strain pdf prismatic bar.
These internal forces are a reaction to the external forces applied on the body that cause it to separate, compress or slide. Stress is the average force per unit area that a particle of a body exerts on an adjacent particle, across an imaginary surface that separates them. F is the force and A is the surface area. So, these internal forces are distributed continually within the volume of the material body. Some models of continuum mechanics treat force as something that can change. Other models look at the deformation of matter and solid bodies, because the characteristics of matter and solids are three dimensional. Each approach can give different results.
Classical models of continuum mechanics assume an average force and do not properly include “geometrical factors”. The geometry of the body can be important to how stress is shared out and how energy builds up during the application of the external force. The volume of the material stays constant. When equal and opposite forces are applied on a body, then the stress due to this force is called tensile stress. Therefore in a uniaxial material the length increases in the tensile stress direction and the other two directions will decrease in size. All real objects occupy three-dimensional space. However, if two dimensions are very large or very small compared to the others, the object may be modelled as one-dimensional.
One-dimensional objects include a piece of wire loaded at the ends and viewed from the side, and a metal sheet loaded on the face and viewed up close and through the cross section. Practical Stress Analysis in Engineering Design”. 3rd edition, CRC Press, 634 pages. Volume 1 of Advanced series in engineering science. You can change this page.