Comparative study of elastic properties measurement techniques during plastic deformation of aluminum, magnesium, and titanium alloys: application to springback simulation

Reliable determination of the elastic moduli of metals can be quite demanding, especially as the apparent elastic modulus of metals is known to decrease with deformation. Traditionally, this dependence on plastic strain has been investigated through various tensile tests, but discrepancies persist across the different approaches. Here we compare several tensile test-based evaluation protocols based on loading-unloading experiments to measure the change in elastic moduli of the light metal alloys AZ31B, EN AW-6082, and Ti-6Al-4V during tensile deformation. Additionally, the initial Young's modulus determination via tensile testing, three-point-bending experiments, contact-free laser ultrasonic zero-group-velocity plate resonance, and piezoelectric contact ultrasonic time-of-flight measurements were compared. The results reveal non-negligible differences in the strain-dependency of elastic moduli between the determination techniques. Additionally, the laser ultrasound measurements demonstrate an improved accuracy and repeatability for the determination of the initial elastic moduli of light metal sheets. The benefit of considering the reduction of the elastic moduli in finite element springback simulation of three-point-bending tests is demonstrated and the use of the chord modulus is found to be generally most appropriate.