Microstructure design and toughening mechanisms of bimodal CNT/Al composites via refined explicit FEM

• Increasing coarse grain size has little effect on strength but greatly reduces elongation. • Randomly arranged coarse grains with large aspect ratio reduce strength and elongation. • Coarse grains perpendicular to the stretching direction enhance ductility under uniaxial tension. • Exploration of strength-ductility synergy and interactions between various phases. • This study contributes to the microstructure design of bimodal metal matrix composites . Carbon nanotube/aluminum (CNT/Al) composites are promising materials due to their superior mechanical properties, but the strength-ductility trade-off limits their engineering applications. A refined explicit finite element scheme for bimodal CNT/Al composites is developed, incorporating various components and strengthening mechanisms. The heterostructure toughening strategy is examined based on this scheme. The results show that the size, aspect ratio (AR), and arrangement of coarse grains (CGs) significantly affect the macroscopic properties of the composites: (1) Increasing the size of CGs from 0.6 μm to 2.4 μm reduces elongation from 9.1 % to 4.8 % with minimal change in strength; (2) Increasing the AR of randomly arranged CGs from 1:2 to 1:3 reduces elongation from 8.9 % to 2.3 % and decreases yield strength from 498 MPa to 426 MPa; (3) For composites with CGs of AR 1:2, aligning the long axes of CGs axes perpendicular to the uniaxial tensile direction increases elongation from 4.33 % to 10.06 % compared to a 135-degree orientation. Numerical simulations further reveal the mechanisms of secondary fracture and load-rebalancing phenomena. This work presents heterostructure toughening strategies to enhance the performance of CNT/Al composites.