Effects of orientation on the strength of the aluminum alloy 7010-T6 during shock loading: Experiment and simulation

Abstract

The shock response of the aluminum alloy 7010-T6, induced by the technique of plate impact, has been investigated as a function of orientation to the loading axis to the rolling direction. Measurements of the Hugoniot elastic limit (HEL) and spall strength show that the material is stronger in the longitudinal orientation than the short transverse, in keeping with the mechanical properties measured at quasistatic strain rates. Furthermore, a comparison of the HELs to the 0.2% proof stresses suggests that there is a degree of strain-rate sensitivity in the longitudinal orientation, whilst the short transverse appears strain-rate insensitive. Thus, there exists the possibility that strain-rate sensitivity itself is orientation dependent in this alloy. Comparison of the ratios of spall strength according to orientation, to the equivalent quasistatic yield strengths provides further evidence of this hypothesis. A simulation using finite-element modeling has shown that while the model can reproduce the dependency of the HEL on orientation, the degree of success with the spall strength has not been so great.

Constitutive behaviour of anisotropic materials under shock loading

“…This is done by the technique of plate impact, whereby a flat plate of constant thickness and a known material (aluminium alloy 6082-T6 -dural) is impacted onto a target plate made from the test material (AA 7010-T6). The flyer plates are launched using a 75 mm bore, 1 mm long and 50 mm bore, and 5 m long single stage gas gun the Royal Military College of Science (Bourne and Stevens, 2001;Vignjevic et al, 2002). Thick plates of 7010-T6 (50 mm  50 mm  5 mm size) were cut from a single heattreated block, and ground flat and parallel to within 5 optical fringes over 50 mm.…”

“…Gray et al, 2000Gray et al, , 2002Vignjevic et al, 2002). It was shown in an investigation of cold rolled and annealed zirconium (see Gray et al, 2000) that the value of stresses varies in different directions in the quasi-static test and plate impact test.…”

Laser Doppler interferometer based on a solid Fabry–Perot etalon for measurement of surface velocity in shock experiments

“…Despite the fact that velocity signals have not been compared to those measured with a VISAR, the inverse approach shows that they are coherent in amplitude with the approach of Berthe [19]. They show main features that are usually observed in VISAR experiments: back and forth of longitudinal and lateral waves, Hugoniot elastic precursor.…”

“…The most common value is σ HEL = 550 MPa for aluminum [17], but strongly depends on the strain rate and the aluminum grade. For example, for Al 2024, the Hugoniot elastic limit is about 120 MPa [18] while it is 390 MPa [19]for the Al 7010 T6 grade, determined by bar impacts for various impact velocities. It has not been measured for aluminum AA 5754, but can be estimated from free surface velocity measurement by equation (5),…”

“…The calculated Hugoniot elastic limit was 491 MPa, in agreement with that deduced from experiments. From this set of experiments, a pressure versus power density curve was obtained and compared with the analytical model and previous experiments of Berthe [19] and Sollier [20] (figure 7):…”