# Surface pressure

Surface pressure is the force per contact area between two solids , i.e. a compressive stress . If two solid bodies are pressed against each other with a force , a normal load distribution occurs in the contact area between the bodies , which is referred to as surface pressure. It is usually given in the unit of the surface pressure Pascal (1 Pa = 1 N / m 2 or 1 MPa = 1 N / mm 2 ). ${\ displaystyle F}$ In contrast to pressure , the surface pressure is not isotropic , that is, it has - like a stress  - a direction and it is not necessarily constant over the contact surface; In addition to the amount of force  and the material properties, the surface contours of the bodies involved are decisive for the load distribution over the contact area and for the size and shape of the contact area. ${\ displaystyle F}$ ## calculation

For linear-elastic materials, the surface pressure is usually calculated on the basis of half-space theory ; the Hertzian pressure equations can be used for special, simple bodies . More complex body geometries or non-linear materials require the use of other calculation methods, e.g. B. the numerical calculation using finite element methods or related processes.

Under the effect of the surface pressure, a characteristic stress distribution is established in the bodies involved. The tension maximum is not on the body surface, but inside the body. This is a major cause of pitting formation in technical components (gear wheels, roller bearings, etc.).

In the construction, materials are often selected according to the permissible surface pressure, the following applies:

${\ displaystyle p \ leq p _ {\ mathrm {perm}}}$ .

Where and from the table of materials is the force that acts on the surface and is called the interface pressure. ${\ displaystyle p = {\ frac {F} {A}}}$ ${\ displaystyle p _ {\ mathrm {perm}}}$ ${\ displaystyle F}$ ${\ displaystyle A}$ ${\ displaystyle p _ {\ mathrm {perm}}}$ ## Examples

Surface pressure occurs z. B. on