Abstract
The effects of grain size on the dynamic tensile fracture (or spall) response were investigated for high purity copper materials by plate-impact experiments. The spall strength estimated from the free surface velocity profile is nearly constant with no significant effect from the grain size. However, differences are observed in the acceleration rate of velocity rebound beyond the minima. This may be attributed to the effect of grain size on the growth rate of damage. Metallographic analyses of the fracture surface show that the characteristic feature of the fracture surface clearly depends on the grain size. In the smaller samples, the fracture surfaces are decorated with large, high-density ductile dimples suggesting that the preferential failure mode is ductile intergranular fracture. In the larger samples, the fracture surfaces have a rock candy appearance with small, brittle, high density dimples as well as large ductile dimples suggesting that the fracture mode is a mix of both brittle intergranular fracture and ductile transgranular fracture.
Highlights
Plate impact experiments and microscopic observations on post-impact recovered samples were used to study the influence of grain size on the dynamic tensile/spall behavior of high purity copper samples
By holding the loading conditions constant, the free surface velocity profiles were studied as a function of grain size
The spall strength estimated from the pullback velocity has no significant effect of the grain size
Summary
Polycrystalline copper plate material with 99.99% purity was subjected to an additional cold-rolling procedure followed by recrystallization to produce a wide range of grain sizes. Samples were annealed in vacuum with furnace cooling at 500 ◦C for 3.5 hours to produce an average grain size of 78 μm, 700 ◦C for 3.0 hours to produce a grain size of 273 μm, and 850 ◦C for 3.0 hours to produce a grain size of 400 m. The grain size was measured using the line intercept method
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