The issue of fracture toughness of beryllium

There are residual thermal stresses (RTS) in any polycrystalline beryllium. The destruction of the plane of the basis was blocked by the RTS. The stress relaxation was in a top of the growing cracks and the strength of material reduced.
It is difficult for the establishing a fatique crack. The dimensionless deviation of the mechanical properties from ideal (model) named the uniformity coefficient of the structure. The calculated coefficient uniformity and fracture toughness for the hot pressed beryllium was compared. The maximum ($\mathrm{fc} = 0.8$) is on the dependenсе.
Large inclusions and dispersions of grain size exist at heterogeneous structure ($\mathrm{fc} < 0.5$) such as T-56 material. There are not elements that can stop the developing of cracks in homogeneous structure ($\mathrm{fc} = 1$). It is the casting beryllium.
The increasing homogeneity of the structure for improving efficiency of articles of beryllium leads to reduction of fracture toughness.