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The main goal here is to optimise the finite element mesh used to predict plasticity induced crack closure (PICC). A numerical
model was developed for a M(T) specimen made of 6016-T4 aluminium alloy. The parameters studied were the size of most
refined region perpendicularly to crack flank (ym) and along propagation direction (xr), the size of finite elements near crack tip
(L1) and the vertical size of refinement close to crack flank (yA/B). A maximum size of about 1.3mm was found for ym, but a
smaller value has a limited impact on PICC. An analytical expression was proposed for xr, dependent on δK and Kmax. An
optimum value seems to exist for L1.
Compressive stresses play an important role on tension-compression fatigue which can be attributed to plasticity induced crack
closure (PICC). The objective here is to study numerically the effect of compressive stresses on PICC and to discuss the
applicability of PICC to explain the effect of negative stress ratios on fatigue crack growth rate. The compression produces
reversed plastic deformation at the crack tip, reducing linearly the crack opening level. The incursion to negative stress ratios
did not produce sudden changes in the behavior of PICC and no saturation with the decrease of minimum load was observed
for δKeff. Crack closure was able to collapse da/dN-δK curves with negative stress ratios, indicating the applicability of the
crack closure concept to explain the effect of negative R. The analysis of crack tip plastic strain range with and without contact
of crack flanks confirmed the validity of crack closure concept.
