Deformation is a change of the dimensions and in some case shape of a body due to an applied external force. The deformation at any point is completely determined by six components of the linear deformation, εx, εy, εz, and the angular deformation, γxy, γyz, γzx. These components characterize linear and angular changes of the elemental parallelepiped at this point. Linear deformation is a ratio: εx = Δdx/dx; εy = Δdy/dy; εz = Δdz/dz it is considered positive for tension and negative for compression. Angular deformation is considered positive (negative) if a right angle becomes acute (obtuse). The relative volume change is ε = εx+ εy+ εz.