Residual stress in 7449 aluminium alloy forgings

Application of multiple analysis methods in optimising complex residual stress characterisation

“…Therefore the selection of a stress-free d 0 sample is critical in obtaining a reliable residual stress result using the neutron diffraction technique. Robinson et al [19] by re-analysing stress-free d 0 sample obtained a higher ND measured residual stresses which correlated better with their FEA predictions. Figures 16 and 17 show respectively a comparison of L and LT residual stress distributions measured using different techniques including the ND technique, the conventional DHD technique and the incremental DHD technique.…”

“…For the same sample two different residual stress distributions are obtained. Two possible explanations for the discrepancy include (i) the effect of stressfree (d 0 ) reference sample; a cube extracted from the corner of the block was used as the reference sample and was unable to account for any microstructural variation [19] and (ii) natural ageing of the specimen at room temperature; the measurement using the SALSA instrument was at a later date. Figure 14 compares the ENGIN-X measured residual stress distributions with corresponding initial FEA predicted.…”

Through Thickness Residual Stress and Microstructural Mapping of AA7085-T7452 Die Forging

“…The surface and subsurface compressive residual stresses in an as-quenched (before stress relief treatment) aluminium alloy forgings have been reported to be in the range -200 MPa -250 MPa [4]. The mechanical stress relief treatment by cold compression (forgings) or stretching (rolled plate) that follows, aims to relieve (or reduce) the severity of the bulk residual stresses existed in the asquenched state in the component.…”

“…The mechanical stress relief treatment by cold compression (forgings) or stretching (rolled plate) that follows, aims to relieve (or reduce) the severity of the bulk residual stresses existed in the asquenched state in the component. However, cold compression stress relief in die forged components do not always fully relieve the complex 3 D bulk residual stresses, and the unrelieved residual stresses may be of sufficient magnitude to cause distortion in machined components [4][5][6]. Moreover, the three dimensional residual stress distribution in the stress relieved aluminium die forging varied…”

“…The presence of process related bulk residual stresses results in: a) part distortion during machining which is a cost driver and b) high degree of scatter and/or variability in fatigue crack growth rate [2], which is a performance driver affecting the durability and damage tolerance of the component. The residual stresses in an aluminium 7050-T7452 forged block that caused distortion during machining was reported to be a major cost driver for a commercial aircraft manufacturer, as a result of excess manufacturing time, schedule overruns, and part rejection and scrapped material [3].The surface and subsurface compressive residual stresses in an as-quenched (before stress relief treatment) aluminium alloy forgings have been reported to be in the range -200 MPa -250 MPa [4]. The mechanical stress relief treatment by cold compression (forgings) or stretching (rolled plate) that follows, aims to relieve (or reduce) the severity of the bulk residual stresses existed in the asquenched state in the component.…”