This action usually begins on the top side shortly after the elastic limit is reached and extends downward, sometimes almost reaching the neutral plane before complete failure occurs.

Frequently two or more failures develop at about the same time.
~Horizontal shear failure,~ in which the upper and lower portions of the beam slide along each other for a portion of their length either at one or at both ends (see Fig.

17, No.

6), is fairly common in air-dry material and in green material when the ratio of the height of the beam to the span is relatively large.

It is not common in small clear specimens.