In this paper we discuss locking and robustness of the finite element method for a model circular arch problem. It is shown that in the primal variable (i.e., the standard displacement formulation), the p-version is free from locking and uniformly robust with order p −k and hence exhibits optimal rate of convergence. On the other hand, the h-version shows locking of order h −2 , and is uniformly robust with order h p−2 for p > 2 which explains the fact that the quadratic element for some circular arch problems suffers from locking for thin arches in computational experience. If mixed method is used, both the h-version and the p-version are free from locking. Furthermore, the mixed method even converges uniformly with an optimal rate for the stress. Classification (1991): 65N30, 73K05, 73V05
Mathematics Subject