Experimental and crystal plasticity finite element study of slip-induced free surface roughening of aluminum sheet in uniaxial tensile deformation

• Free surface roughening was continuously evaluated on the same dogbone-shaped specimen by applying precise uniaxial tension followed by EBSD measurements, and compared directly with CPFEM. • A CPFEM model incorporating the actual grain morphology obtained from EBSD was developed, enabling rigorous one-to-one validation with the experiments • Going beyond the conventional “textbook” factors such as the Schmid factor and slip direction, the study quantitatively identified the role of grain–grain interactions across boundaries as a critical mechanism driving additional roughening. • The study further provided the first quantitative evidence of non-slip-related surface roughening, where the observed ND displacement cannot be explained by slip activity alone. Free surface roughening of a pure aluminum sheet was investigated through experiments and crystal plasticity finite element method (CPFEM) to clarify the role of slip deformation and grain interactions. Roughness evolution and slip lines during uniaxial tensile deformation were continuously observed, and grain orientations were measured by EBSD. The Schmid factor was calculated by assuming that the applied uniaxial tension also acted on each grain. A CPFEM model replicating the actual grain morphology and orientation distribution was developed, enabling rigorous one-to-one comparison with the experiments. The results showed that, in most grains, the slip system with the maximum Schmid factor was dominant in both the experiment and CPFEM. A larger Schmid factor or a slip direction more inclined toward the negative ND tended to cause greater subsidence. In some grains, however, interactions with neighboring grains of relatively large Schmid factor promoted the activation of non-primary slip systems, producing concave depths comparable to adjacent grains. Most importantly, we provided the first quantitative evidence of non-slip-related surface roughening, where the observed ND displacement cannot be explained by slip components alone. These findings establish a more comprehensive mechanistic framework for understanding and controlling surface roughening in sheet metals.