MACHINE LOCKING OF DEGENERATED THIN SHELL ELEMENTS

The degenerated shell element is one of the most efficient elements for analyzing shell structures. However, it is known to result in rather stiff models when used in thin element applications. The phenomena associated with this behavior are known as locking phenomena. This paper analyses the machine locking mechanism developed in thin to very thin Lagrangian and serendipity elements. The machine related locking phenomenon is distinguished from the shear and membrane locking phenomena. A remedy for the pure machine locking problem is developed for the two elements. The proposed remedy is based on the technique of the modified transverse shear modulus. It is also extended to control shear locking. The proposed technique is shown to completely eliminate machine locking. Also, it is shown to effectively alleviate stiffening effects due to the presence of spurious shear strain.