This research aims to correlate the macroscopic fracture phenomenon with its microscopic fracture mechanism for an advanced high-strength steel (AHSS) TRIP 780 sheet by applying a combined experimental-numerical approach. Six specimens with different shapes were tensioned to fracture and the main deformation areas of specimens were subjected to stress states ranging from lower to higher stress triaxiality. The final fracture surface feature for each specimen was obtained to characterize the macroscopic fracture modes at different stress states. The scanning electron microscope (SEM) fractographies of fracture surfaces were detected to reveal the microscopic fracture mechanisms. The stress triaxiality evolution was applied to correlate of fracture mode and fracture mechanism by comparing the macroscopic fracture features as well as micro-defect changes. An increase of stress triaxiality leads to voids extension and then results in a voids-dominant fracture. The micro-shear-slip tends to appear in the stress triaxiality level lower than that of pure shear stress state. The fracture behavior of a practice deformation process was the result of interplay between shear-slip fracture and void-dominant fracture. The unified relationship between average void sizes and stress triaxiality was obtained. The void growth was predicted by the Rice–Tracey model with higher precision.
In this manuscript, the graphite/resin composite plates were prepared via a facile ball milling strategy. The needle coke (NC) as a conductive additive was studied on effects of treated by ball milling on the electrical conductivity, mechanical property of the composite plates. All the characterizations showed that after ball milling, the NC particles have smaller particle size, and more uniform particle size distribution, which enhanced the interfacial adhesion between particles and resin. Due to the difference in shape and size between the auxiliary conductive filler and flake graphite, the addition of NC particles can easily fill the gap between flake‐like graphite and phenolic resin. The uniform distribution of these fillers improves the cross‐linking density, and the conductive path was added between the flake‐like graphite and the resin, which improved the electric conductivity of composit plate from 26.32 S cm−1 to 149.23 S cm−1. Such a prominent performance was attributed to the synergistic effects between the uniformly incorporated NC and the graphite/resin composite adhesive system.
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