Armor steels become harder and harder. Unfortunately this increase of strength induces brittleness, and fracture occurs during penetration of projectiles. The purpose of the present paper is to study the dynamic fracture of a very high strength 0.5% C martensitic armor steel (UTS=2300 MPa, K_(Ic)=50 MPa√m) showing a ductile fracture mode while the crack aspect is brittle. The fracture toughness at crack initiation, K_(Ic), and at crack arrest, K_(Ia), have been measured with a new ring specimen geometry and compared to the values obtained with conventional CT specimens. This geometry has never been used before on specimens showing a ductile fracture mode. The results show that K_(Ia) is independent of the crack velocity over the range between 0.1 and 500 m/s.
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机译：装甲钢越来越硬。不幸的是，强度的增加会导致脆性，并且在弹丸穿透期间会发生断裂。本文的目的是研究强度很高的0.5％C马氏体装甲钢（UTS = 2300 MPa，K_（Ic）= 50MPa√m）的动态断裂，显示出韧性的断裂模式，而裂纹方面则是脆性的。用新的环形试样几何形状测量了裂纹萌生时的断裂韧度K_（Ic）和裂纹止裂时的韧度K_（Ia），并将其与常规CT试样获得的值进行了比较。以前从未在显示出韧性断裂模式的试样上使用过这种几何形状。结果表明，K_（Ia）在0.1至500 m / s的范围内与裂纹速度无关。
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