Angle of repose

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For the Wallace Stegner novel, see Angle of Repose (novel).

The angle of repose is an engineering property of granular materials. When bulk granular materials are poured onto a horizontal surface, a conical pile will form. The angle between the edge of the pile and the horizontal surface is known as the angle of repose and is related to the density, surface area, and coefficient of friction of the material. Material with a low angle of repose forms flatter piles than material with a high angle of repose.

[edit] Applications of theory

This property is sometimes used in the design of equipment for the processing of particulate solids. For example, it may be used to design an appropriate hopper or silo to store the material. It can also be used to size a conveyor belt for transporting the material. It can also be used in determining whether or not a slope will likely collapse. It is also crucial in determining the correct calculus of stability in vessels.

[edit] Measurement

There are numerous methods for measuring angle of repose and each produces slightly different results. Results are also sensitive to the exact methodology of the experimenter. As a result, data from different labs is not always comparable.

An alternative measurement, useful for many of the same purposes, is testing with a shear cell.