(1) Hourglassing Phenomenon
The reduced integration of linear 8-node solid elements leads to numerical difficulty called hourglassing because the reduced 8-node solid elements tend to be excessively flexible. For example, if two layers of reduced 8-node elements in the thickness direction are used, the computed tip deflection of the beam example in Shear Locking is 5.713 mm, which is much larger than 4.281 mm.
(2) Hourglassing Explained
As a reduced 8-node solid element has only one integration point, the element tends to be overly flexible under the bending moment.
