No abstract

The through-thickness residual stress distributions within three large rectilinear aluminium alloy 7449 forgings have been determined using neutron diffraction. The results from two neutron diffraction instruments, ENGIN-X at ISIS, UK and SALSA at ILL, France are reported. Both instruments indicate large magnitude (>250 MPa) tensile residual stresses in the core of the as quenched forging balanced by surface regions stressed in compression (>-200MPa). The other two forgings had been stress relieved by cold compression and had significantly lower residual stress than the as-quenched forging. Increasing the amount of cold compression from 2½% to 4% was found to cause an insignificant difference in the final residual stress distribution. The neutron diffraction results are also compared to measurements made by the new incremental deep hole drilling technique and show good correlation.

The residual stresses in and around riveted joints, formed with an electromagnetic riveter (as used in production of the Airbus A380 wing) have been investigated. Synchrotron X-ray and neutron diffraction were used to assess the stresses introduced into skin panel sections by installation of the fasteners. The stress profiles thus obtained exhibited an annular compressive zone, peaking around 400 MPa, around the fastener hole, balanced by tensile residual stresses (at a maximum of approximately 150 MPa) in the bulk material. The in-plane stress field was found to resemble that expected around a cold expanded hole. An analytical solution for the residual stresses in an autofrettaged tube was compared with the stresses around the rivet, allowing estimation of the pressures applied by the rivet to the fastener hole during rivet placement. These pressures were related to the yield stress of the skin material being riveted. This pressure produces a plastic misfit around the hole that places the rivet/hole interface under significant hoop compression. This compressive region is expected to confer significant advantages in terms of the fatigue lifetime of the riveted joints.

No abstract

The residual stresses around clearance-fit mechanical fasteners have been found to be similar to those around cold expanded holes where compressive hoop stresses close to the fastener hole are balanced by far-field tensile stresses. This compressive zone has been shown to prolong fatigue lifetimes around fastener holes. Constant amplitude fatigue loading was applied to single plate rivet specimens for varying numbers of cycles to investigate the redistribution of these stresses after fatiguing. Synchrotron diffraction was used to map the evolution of the residual stresses around the rivets. Little change in the hoop stress local to the rivets occurred until visible fatigue cracks were observed suggesting that relaxation of these stresses is due to the cracks rather than their cause.