Experimental analysis and investigation of thephenomenon of fatigue in the connections of ship

In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclicloading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typicallyproducing striations on some parts of the fracture surface. The crack will continue to grow until itreaches a critical size, which occurs when the stress intensity factor of the crack exceeds the fracturetoughness of the material, producing rapid propagation and typically complete fracture of thestructure. Fatigue cracking is one of the primary damage mechanisms of structural components.Fatigue cracking results from cyclic stresses that are below the ultimate tensile stress, or even theyield stress of the material. The name “fatigue” is based on the concept that a material becomes“tired” and fails at a stress level below the nominal strength of the material. The fact that the originalbulk design strengths are not exceeded and the only warning sign of an impending fracture is oftenjust a tiny crack, makes fatigue damage especially dangerous. Fatigue has traditionally beenassociated with the failure of metal components which led to the term metal fatigue. In the nineteenthcentury, the sudden failing of metal railway axles was thought to be caused by the metal crystallizingbecause of the brittle appearance of the fracture surface, but this has since been disproved. Mostmaterials, such as composites, plastics and ceramics, seem to experience some sort of fatiguerelatedfailure. To aid in predicting the fatigue life of a component, fatigue tests are carried out usingcoupons to measure the rate of crack growth by applying constant amplitude cyclic loading andaveraging the measured growth of a crack over thousands of cycles. However, there are also anumber of special cases that need to be considered where the rate of crack growth is significantlydifferent compared to that obtained from constant amplitude testing. Such as the reduced rate ofgrowth that occurs for small loads near the threshold or after the application of an overload; and theincreased rate of crack growth associated with short cracks or after the application of an underload

کلیدواژه ها:

structural survivability ، experimental method ، crack growth ، fracture ، strain energy