A comparative study of strain- and stress-based failure prediction methods in single-point incremental forming of Al/Ti two-layer sheets considering different strain paths

In this study, the effect of the rolling process on the mechanical and metallurgical properties of a two-layer Al and Ti sample was investigated. First, the two-layer samples were produced through the rolling process. The effects of the parameters, including vertical step, feed rate, tool diameter, and layer arrangement, were then experimentally investigated using the single-point incremental forming (SPIF) process in four different strain directions. The results showed that in the strain path with a cone geometry featuring a Ti-Al layer arrangement (where titanium is in contact with the tool and aluminum forms the outer layer), the highest formability was observed compared to other samples. Additionally, the simulation process for SPIF was investigated to study the prediction of failure due to the stress effect on formed samples. The simulation process was performed for four strain paths, and the prediction accuracy of stress and strain methods in predicting fracture strain was compared with the experimental method. The results showed that second derivative thinning (SDT) has the highest accuracy in predicting failure for geometries with high strain rates, and the second derivative of the maximum principal stress (SDPS) has the highest accuracy in predicting failure for geometries with high stress. Additionally, to investigate the effect of rolling on the metallurgical properties, the study of intermetallic phases and the depth of penetration of the layers was conducted. The results showed that in the penetration zone, intermetallic phases, specifically Al₅Ti₃, were formed in the two-layer samples.