Differential stress is the difference between the greatest and the least compressive stress experienced by an object. For both the geological and civil engineering convention
In other engineering fields and in physics,
These conventions originated because geologists and civil engineers (especially soil mechanicians) are often concerned with failure in compression, while many other engineers are concerned with failure in tension. A further reason for the second convention is that it allows a positive stress to cause a compressible object to increase in size, making the sign convention self-consistent.
In structural geology, differential stress is used to assess whether tensile or shear failure will occur when a Mohr circle (plotted using