Fig. 1. (a) Geometry and dimension of hourglass-shaped specimen for in-situ interrupted tensile tests. The scans are performed on the specimen flat side (dashed rectangle). (b) SEM images showing area of interest viz. Location 1 and Location 2 with respect to micro-indents on specimen surface. The load-displacement curves for in-situ interrupted tension test along (c) RD and (d) TD. The drops in the curves marked with letters ⅰ (Ⅰ), ⅱ (Ⅱ), ⅲ (Ⅲ), ⅳ (Ⅳ), ⅴ (Ⅴ) and ⅵ (Ⅵ) are when the tests are interrupted for SEM imaging. Final stage of failure for (e) RD tension and (f) TD tension.

Fig. 2. A sequence of in-situ SEM images of (a) micro-hardness indent location 1 (1000× magnification) and (b) micro-hardness indent location 2 (2000× magnification) under RD tension, when interrupted at sequential points ⅰ, ⅱ, ⅲ, ⅳ, ⅴ and ⅵ marked in the load-displacement curve.

Fig. 3. A sequence of in-situ SEM images of (a) micro-hardness indent location 1 (1000× magnification) and (b) micro-hardness indent location 2 (2000× magnification) under TD tension, when interrupted at sequential points Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ and Ⅵ marked in the load-displacement curve.

Fig. 4. (a) The comparisons of load-displacement curves for in-situ SEM tensile test along RD and TD. The in-situ SEM observation of the slip system in RD and TD tension, when applied displacements are (b) 0.7 mm and (c) 1.1 mm.

Fig. 5. SEM images (top) and μ-DIC equivalent Mises strain maps overlapping with microstructures for in-situ SEM tensile tests along (a) RD and (b) TD.

Fig. 6. (a) SEM-EDS images of 7075-O alloy with related elemental mapping results. (b) SEM-EBSD map showing second-phase particles.

Fig. 7. Schematic diagram of reconstruction 3D micro-scale RVE model with real distribution of particles based on FIB-SEM technique by using AVIZO software.

Fig. 8. Reconstructed 3D RVE models with particles by using Analysis Filter module in AVIZO by ignoring the small ones based on particles’ volumes.

Fig. 9. Illustration of the mesh generated for the RVE case 7 and examples of three main kinds of particle in the RVE model, each meshed by a set of tetrahedral elements.

Fig. 10. Illustration of a three-phase heterogeneous material used in the micro-scale RVE case 6 for computational analysis: Al matrix (phase 1) with real distribution of second-phase particles (phase 2) and interface between particle and matrix (phase 3).

Fig. 11. (a) Experimental plastic stress-plastic strain curve of the AA7075-O alloy and Holloman fitting of the data. (b) Bilinear constitutive model for mixed modes involving mode-I and shear modes.

Fig. 12. Schematic diagrams of the uniaxial tension boundary condition applied on the RVE case 8.

Fig. 13. The contours plots of Von Mises stress in Al matrix at tensile strain of 40% in X (RD) direction for: (a) RVE model without any particles (matrix only). (b) RVE case 1. (c) RVE case 4 and (d) RVE case 7.

Fig. 14. (a) µ-DIC equivalent strain map and (b) RVE case 7 equivalent strain maps in the regions of high strain and low strain highlighted in red and yellow, respectively. (c) Comparing strain evolution at high local strain in shear bands and low local strain away from the slip bands between µ-DIC experimental result and RVE modeling result.

Fig. 15. The contours plots of Von Mises stress in Al matrix at ε=40% for RVE case 7 subjected to (a) Y-TD and (b) Z-ND tension.

Fig. 16. (a) Comparison of stress-strain/strain-hardening curves between computational prediction for only matrix model as well as RVE cases 1,4,7,9 and experiment result under X-RD tension. (b) Comparison of stress-strain/strain-hardening curves between computational prediction of RVE case 7 under X-RD, Y-TD and Z-ND tension and experiment result.

Fig. 17. Parametric studies of the cohesive element parameters by changing interfacial properties of various particle/matrix interfaces and a comparison of RVE model (X-RD tension loading) and experimental stress-strain curve of material; (a) identical interface properties of irregularly-shaped Al3Fe/matrix interface and elliptic-shaped MgZn2/matrix interface for RVE case 1, (b, c) different irregularly-shaped Al3Fe/matrix and elliptic-shaped MgZn2/matrix interface properties for RVE case 1, and (d) different irregularly-shaped Al3Fe/matrix, elliptic-shaped MgZn2/matrix, and needlelike-shaped CuAl2/matrix interface properties for RVE case 7.

Fig. 18. The interfacial failure initiation and propagation of the cohesive element parameters, where Points A and B are marked in the strain-stress curves in Fig. 17(a). X-axis is the loading direction.

Fig. 19. The interfacial failure initiation and propagation of the cohesive element parameters, where Points C and D are marked in the strain-stress curves in Fig. 17(b). X-axis is the loading direction.

Fig. 20. The interfacial failure initiation and propagation of the cohesive element parameters, where Points E and F are marked in the strain-stress curves in Fig. 17(c). X-axis is the loading direction.

Fig. 21. The interfacial failure initiation and propagation of the cohesive element parameters, where Points G, H and I are marked in the strain-stress curves in Fig. 17(d). X-axis is the loading direction.

Fig. 22. Comparison of stress-strain/strain-hardening curves between with interfacial failure and without interfacial failure for (a) RVE case 1 and (b) RVE case 7.

Fig. 23. Interfacial failure mechanisms of the particle-reinforced AA7075-O sheet subjected to X-RD.

Fig. 24. Interfacial failure mechanisms of the particle-reinforced AA7075-O sheet subjected to Y-TD.

Fig. 25. Interfacial failure mechanisms of the particle-reinforced AA7075-O sheet subjected to Z-ND.

Fig. 26. A comparison of strain-stress/strain-hardening curves of the RVE case 5 subjected to X-RD, Y-TD and Z-ND tension.