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The strength, toughness, and fatigue crack growth (FCG) resistance of high‐strength steels are the key performance indexes concerned in the material selection of engineering components. It is considered that the FCG resistance of high‐strength steels can be optimized by simultaneous strengthening and toughening. In order to make clear whether the above view is correct or not, the strength–toughness combination and FCG resistance of AISI 4340 steel under different heat treatments are investigated and compared with those of 18Ni maraging steel in the present study. Meanwhile, the major fatigue damage mechanism of the AISI 4340 steel is analyzed and discussed. It is found that the FCG resistance of AISI 4340 steel enhances rapidly at first and then remains approximately the same with the decrement of strength (the improvement of toughness). Moreover, it is detected that simultaneously upgrading the strength and toughness of high‐strength steels cannot improve the FCG resistance. Finally, it is believed that the microscopic fatigue damage mechanism is the major factor determining the FCG resistance rather than the macroscopic strength–toughness combination, and the factors affecting the FCG resistance of AISI 4340 steel are mainly the pre‐existing dislocations and carbide precipitates. [ABSTRACT FROM AUTHOR]

Herein, the high‐cycle fatigue behaviors of 18Ni maraging steel with different tensile strength in the stress ratio range from 0.1 to 0.5 are investigated, and compared with those at the stress ratio of −1. It is found that the relationship between the fatigue strength at the stress ratios of −1 and 0.1 and tensile strength is nonmonotonic, while the fatigue strength at the stress ratio of 0.5 improves as the tensile strength heightens. The tensile strength corresponding to the optimal fatigue strength state would change with the variation of the stress ratio, which is related to the alteration of key factors affecting the fatigue damage. Moreover, it is found that the Walker equation: σaR = σ−1 ⋅ [(1 − R)/2]β gives reasonable results for the influence of stress ratio on the fatigue strength of 18Ni maraging steel. [ABSTRACT FROM AUTHOR]

To explore the micro-mechanism for the size effect of the mechanical behavior of metallic crystals, the tensile and fatigue behavior of [ABSTRACT FROM AUTHOR]

The microstructures of Veined rapa whelk shell were characterized, and a series of compression tests were carried out on the shell with the compressive loading direction making different angles (0°, 30°, 60° and 90°) with the shell spiral lines. Weibull analysis of the experiment results shows that the compressive strength is generally the highest for the sample with 0°-orientation but the lowest for that with 60°-orientation, which means that the strength shows an obvious anisotropy and the strongest orientation represents the direction parallel to the spiral lines of the shell. Such a phenomenon is closely related to the distinctive microscopic arrangements of different-order aragonite lamellae. The interfaces of different-level lamellae in the adjacent macro-layers yield effects on the mechanical behavior of the shell in a coordinated fashion. [ABSTRACT FROM AUTHOR]

The microstructures and mechanical properties of Clinocardium californiense shell were investigated in relation to the different parts of shell. It is found that the shell can be divided into three parts, that is, the dorsal side, body part, and marginal side based on the variation of microstructures along the longitudinal cross section. Specifically, all areas exhibit a cross-lamellar structure on the dorsal side, and a hierarchical structure comprising three layers including inner (with a cross-lamellar structure), middle (with a complex cross-lamellar structure), and outer (with a prismatic structure) layers was observed on the body part, whereas on the marginal side, the orientation of aragonite sheets shows an obvious deflection. The structural architecture, the dimensions of different-order lamellae in the same kind of structure and the orientation between the indenting direction and aragonite sheet all contribute to the unique mechanical properties of this shell. It is also found that a low value of the ratio of hardness-to-Young's modulus ( H/ E) corresponds to an improved indentation toughness. The middle layer with the densest and most complicated structure on the body part shows the lowest H/ E ratio and the highest hardness and Young's modulus. [ABSTRACT FROM AUTHOR]