“…When using this type of formulation, two main difficulties arise: the first is the continuity conditions that must be guaranteed by the density functions, and the second is the need to perform the integration of strongly singular and hypersingular kernels that come up after differentiating the classical ones. A number of approaches have been proposed to deal with both difficulties (among others, see [30] and [5]), in particular relating to the choice of the elements and collocation procedure to be used [10,12,21,24,32,46] and concerning the implementation of regularization techniques or non-singular formulations [9,12,33,42]. Other ways of dealing with the hypersingular integrals have been proposed in [19,29] and [43], while in [25] and [26] an indirect approach to evaluate these integrals for the plane-strain cases in 2D problems has been adopted.…”