In this paper, the orientation of grains which adjacent to a developed opening crack was investigated by EBSD. A definition of θ has been came up with which represents the angle between the principal stress plane and each plane of the grains. Smaller θ means easier to crack. It gave a good explanation of the crack propagation throughout the grains. It also revealed that propagation path is along with the plane. This finding will give a prediction of tear properties and help us understanding the cracking mechanism and the behavior of tearing.
High strength and high toughness aluminum alloys such as 2024 is the key materials of aviation industry. It should have good durability while under severe environment. Not only the strength but also fracture toughness plays an important role in application. Not until A.A. Griffith did people realize that the fracture can happen even under a load significantly less than the yield range if the surface is scratched [
A notched 2024-T39 aluminum sheet with a thickness of 0.3 mm was torn, which polished by 180#, 320#, 600#, 800#, 1000#, 1200#, 1500# rough sand paper and 800#, 1000# fine sand paper before tearing. Loading stopped before the crack went edge opposite to the notch. The specimens for tearing are thin enough for tearing it easily, as well as minimize the influence of inner grains that can’t observe. It treated by annealing of 200˚C, 1 h to release the residual stress. Twin-jet electro polishing was conducted before EBSD. EBSD data was acquired in FEI Helios Nanolab 600i with a step length of 6 μm.
In order to measure how the orientation influence the crack propagation, the Euler angles and the
The crack resistance can be identified quantitatively by calculating the angle between all symmetrically equivalent
The θ of each
It can be seen that the grain B has minor θ of 37.10 degrees compared to the 40.56 of the neighbor grain D. High angle of θ prevented the grains from being cut though by crack. It also can inhibit the crack propagation. The calculating of θ successfully revealed that the
By testing the grains orientation, resistance level of crack propagation can be
estimated. Furthermore, when using the appropriate processing method to change the grains orientation, tear properties as well as fracture toughness can be improved.
If only the crack is along
Euler angles | Miller indices | θ (Angle between | ||||||
---|---|---|---|---|---|---|---|---|
111 | ||||||||
Grain A | 289.140 | 38.773 | 70.21 | 66.49 | 43.32 | 50.51 | 60.63 | |
Grain B | 102.842 | 39.348 | 277.39 | 62.87 | 50.59 | 37.10 | 72.94 | |
Grain C | 49.646 | 27.581 | 294.75 | 61.19 | 53.51 | 75.61 | 34.10 | |
Grain D | 143.167 | 23.512 | 221.12 | 61.08 | 69.27 | 50.94 | 40.56 | |
Grain E | 330.275 | 11.894 | 26.38 | 44.88 | 59.87 | 50.84 | 64.86 |
It’s all know that the close-packed plane of f.c.c. metal is
It can be inferred from above, when crack come across the grain boundary and the orientation of the grain in front of the crack tip is different; the crack propagation will also be different. As is shown in
The θ of
A definition of θ explained the crack propagation path of tearing, which has a lot
to do with the grain orientation. If a grain’s
This work is supported by the Major State Research Program of China (Project No. 2016YFB0300901) and the Chinese National Science Foundation (Project No. 51375503).
Hu, C. (2017) On the Relation of Grain Orientation and Opening Crack of an Al-Cu-Mg Sheet. Engineering, 9, 510-516. https://doi.org/10.4236/eng.2017.95031