Applied-load-dependent evolutions of local gross- and net-section stress fields in aluminum and steel lap shear joints are examined in order to identify and define transitions between the frictional and bearing modes of load support. An airframe-type structural geometry is analyzed with an experimentally and numerically validated finite element model. Slip-resistant joints utilize fastener clamping to enhance frictional load support at panel-panel and bolt head-panel interfaces and postpone loading at fastener/panel-hole interfaces (bearing). In this work, nominal clamping strains of 0% and 0.5% are considered. Calculations without and with friction (μ = 0.2 and 0.4) are performed in order to separate effects of mechanical springback and friction on the transitions. The effective clamping is found to be only about one-third the nominal value.

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