ABSTRACTAN EXPERIMENTAL AND THEORETICAL ANALYSIS OF COLD WORKING AND RIVETING IN FIBER METAL LAMINATE MATERIALSByDavid S. BackmanThis research describes the results of an investigation into the behaviour of fiber metal laminate (FML) materials after cold expansion and riveting, using both experimental and theoretical methods with an overall aim of producing a new FML variant optimized for these manufacturing processes. To achieve this aim three primary research objectives have been identified including: 1. Experimentally measure the strains in fiber metal laminates due to both hole cold expansion and riveting. 2. Develop a theoretical model that could be used to analytically predict the strains resulting from hole cold expansion and riveting. 3. Develop and test new variants of FML optimized with regards to cold expansion and riveting. Using digital image correlation techniques, full-field strains were measured on various grades of FML after both hole cold expansion and riveting. The cold expansion results, showed how the residual strain field was dependent on the split sleeve direction with respect to the material orientation and that by changing the orientation of the split sleeve one could significantly reduce the magnitude of the residual strains. The effects of material orthotropy were also evident in the riveted coupons, but less pronounced due to the driven and manufactured heads of the rivet obscuring the region closest to the rivet hole. The results from this static testing suggested that designing a more isotropic fiber metal laminate material could improve performance after cold expansion and riveting. Two different analytical approaches were used in this research. In the first, a closed form solution for the strains resulting from cold expansion and riveting was put forward and corroborated against experimental results. In the second, a classical laminated plate approach was used to develop an analytical tool that could predict the material properties of fiber metal laminates based on the glass fiber orientation and the number of aluminum and of fiber layers. This approach was validated against experimental data and used as a design tool to predict the material properties of a variety of new fiber metal laminate (FML) variants.Static tensile testing of the various FML variants confirmed that FML 4 with a quasi isotropic layup had a constant elastic modulus of approximately 50 GPa, regardless of material direction. Strain measurements made after cold expansion and riveting showed that this quasi-isotropic FML 4 variant had a more uniform residual strain field, which was a significant improvement in this regard over standard FML 4 or FML 3. Fatigue testing showed that overall, cold expansion was effective in extending fatigue life. Such testing with the FML 4 variant showed that although it had a lower fatigue life than standard FML 4 in one material orientation, its overall fatigue life was fairly constant, regardless of material orientation. The results suggest that this FML 4 variant may prove to be a valuable addition to the standard grades of FML currently in use today.
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