Experimental studies on mixed‐mode dynamic fracture behaviour of aluminium alloy plates with narrow U‐notch

Abstract

Mixed‐mode dynamic fracture behaviour of cast aluminium alloy ZL205A thin plates with narrow U‐notch was studied by split Hopkinson tensile bar apparatus. Specimens with different loading angles were designed to realize different fracture modes. The same loading condition was maintained during the tests. Recovery specimens show that crack propagates along the notch direction. Force–elongation relations show that with the loading angle increasing, the fracture force increases while the final elongation decreases. Deformation and fracture process was observed by a high‐speed camera. Displacement distribution around the crack was calculated through digital image correlation technique. Based on the photos and displacement results, initiation time of the crack was derived. Besides, two stress components (normal stress and shear stress) applied on the fracture surface were investigated. Results show that crack initiation stresses at different loading angles satisfy the ellipse equation. Pure mode I and II fracture stresses are 425.3 and 236.7 MPa, respectively. Furthermore, specific fracture energy of different specimens was calculated. The energy data vary with loading angle and located on an approximate upward parabolic curve. From the curve, the minimum specific fracture energy of the thin plate specimen is 42.0 kJ/m2 under loading angle of 76.3°.

Experimental and numerical investigation on the shock characteristics of U-notched ZL205A specimens under dynamic mixed-mode loading

“…And the quantitative data of maximum force f0 and final elongation e0 are listed in Table 5. From Figure 7 and Table 5, it can be drawn a conclusion that the force increases with the loading angle when the elongation decreases as the loading angle increases, which is in good agreement with Wen's study (Wen et al 2016), demonstrating that the mixed loading patterns have a prominent influence on the strength and ductility properties of materials.…”

“…Through a series of traditional SHTB tests, the basic mechanical properties of ZL205A were obtained by Wen et al, listed as Table 2. Similar with the U-notched mixed-mode tensile specimens proposed by Wen et al (2016), the test specimen in this study is also a combination of the Arcan specimen and the SHTB tensile specimen. Differently, considering that the strength properties and the shock characteristics under mixed-mode will be studied rather than the crack initiation nor the fracture behavior, there is no prefabricated fatigue crack in the specimens and two symmetrical U-notches are manufactured.…”

“…In addition, there are some differences between numerical simulation and experiments, that maximum force values are basically consistent but the relative error of final elongation e0 between numerical simulation and experiments increases with the increase of loading angle β. The possible reason maybe is that the failure strain εf, a material parameter, measured in the experiment (Wen et al 2016) is the average strain at failure of the effective part of specimen, which is usually smaller than the true value. Therefore, when the mesh of the effective part of specimen is small enough, the final elongation of the numerical simulation will be smaller than the experimental result because the failure strain εf of the elements is assigned to the value measured in the experiment.…”

“…As presented in Figure 2, different loading patterns of modified Arcan specimen are achieved with different loading angles. The recent experiments done by Wen et al (2016) provide a novel method for dynamic mixed-mode fracture loading. In Wen's study, a series of specimens with different loading angles in conjunction with the Arcan specimen (Fagerholt et al 2010) and the widely used dumbbellshape tensile specimen in SHTB tests are shown in Figure 3.…”

“…In Wen's study, a series of specimens with different loading angles in conjunction with the Arcan specimen (Fagerholt et al 2010) and the widely used dumbbellshape tensile specimen in SHTB tests are shown in Figure 3. Based on the SHTB test platform and these new-style specimens, the strength criterion and dynamic fracture properties of ZL205A material have been studied by Wen et al (2016).…”