నైరూప్య

Strength and Fatigue of Natural and Artificial Materials

Alexander Berlin

Material strength is a complex concept that includes the material resistance to various types of loading. Often the improvement of strength in one type of load leads to deterioration in the other. For example, the ordinary window glass is quite durable material under the pseudo-static slow loading, but it is easily broken upon impact. In solid mechanics, there are conceptions of the static strength and fracture toughness characterizing resistance to the crack growing in a material. The glass has very low fracture toughness: A crack propagates easily in it. Metals can possess both high strength and high fracture toughness. These characteristics are largely determined by the possibility of dislocations movement. The easier the dislocations move, the lower the static strength, but the higher the fracture toughness, the harder the crack propagates. Therefore, the introduction of special additives impeding the movement of the dislocations (for example, carbon in iron) leads to an increase in the static strength, but also to rising in brittleness and facilitating the crack propagation.