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c (dimensionless) is the fraction of particles cutting in an idealized manner.
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M (SI unit: kg) is the total mass of eroding particles.
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U (SI unit: m/s) is the magnitude of the incident particle velocity.
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p (SI unit: Pa) is the Vickers hardness of the material.
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m (SI unit: kg) is the mass of an individual particle hitting the surface.
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r (SI unit: m) is the average particle radius.
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I (SI unit: kg m2) is the moment of inertia of an individual particle about its center of mass. For an isotropic sphere, I = 2mr2/5.
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α (SI unit: rad) is the angle of incidence, with α = 0 tangent to the surface and α = π/2 normal to the surface.
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P is a dimensionless parameter, defined as P = K/(1+mr2/I), where K (dimensionless) is the ratio of vertical and horizontal forces acting on the particle.
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