Elastic-plastic behavior of coldworked holes

Abstract

The objective of this paper is to describe a four-stage analytical procedure used to determine the crack-growth response for coldworked open holes, and holes filled with neat- and interference-fit fasteners. The methodology utilizes an elastic-plast ic finite element analysis program to determine residual stress states. A crack-growth procedure, modified to include the residual stresses, is used to evaluate the coldworking process. Consideration is given to the effects of various degrees of coldworking, interference levels, short-edge margins, and magnitudes of compressive overloads on the residual stresses. For those conditions involving compressive overloads applied to coldworked neat- and interference-fit fasteners, further consideration is given to the effects of slip vs no-slip condition's at the fastener-sheet interface. A comparison of results between analysis and test data is presented for the crack-growth response of coldworked open-hole specimens. Nomenclature - crack length = diameter of hole prior to coldworking = expanded diameter of hole = residual diameter of hole (after coldworking) = diameter of fastener = edge distance from hole center = material constant, Eq. (2) = vector of constraint forces, Eq. (4) = measure of coldwork (percentage), Eq. (3) = stiffness matrices, Eqs. (4) and (5), respectively = stress intensity factors, Eqs. (1) and (2) = residual stress distribution, Eq. (2) = vector of forces for remote loads, Eq. (7) = plastic residual load vector, Eqs. (4) and (5), respectively - stress ratio (min/max) = vector of independent nodal displacements, Eq. (4) = vector of residual nodal displacements, Eq. (5) = distance along crackline, Eq. (2) = range of stress intensity = displacement profile along crack surface, Eq. (2)