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For the surgical technique, see Microfracture surgery. Fracture mechanics is the field of mechanics concerned with the study of the propagation of cracks in materials. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the material’s resistance to fracture. In modern materials science, fracture mechanics is an important tool used to improve the performance of mechanical components.
It applies the physics of stress and strain behavior of materials, in particular the theories of elasticity and plasticity, to the microscopic crystallographic defects found in real materials in order to predict the macroscopic mechanical behavior of those bodies. Fractography is widely used with fracture mechanics to understand the causes of failures and also verify the theoretical failure predictions with real life failures. The prediction of crack growth is at the heart of the damage tolerance mechanical design discipline. The processes of material manufacture, processing, machining, and forming may introduce flaws in a finished mechanical component.
Arising from the manufacturing process, interior and surface flaws are found in all metal structures. Not all such flaws are unstable under service conditions. Despite these inherent flaws, it is possible to achieve through damage tolerance analysis the safe operation of a structure.
Fracture mechanics as a subject for critical study has barely been around for a century and thus is relatively new. What is the strength of the component as a function of crack size? What crack size can be tolerated under service loading, i. How long does it take for a crack to grow from a certain initial size, for example the minimum detectable crack size, to the maximum permissible crack size?
During the period available for crack detection how often should the structure be inspected for cracks? Fracture mechanics was developed during World War I by English aeronautical engineer, A. Griffith, to explain the failure of brittle materials. A theory was needed to reconcile these conflicting observations.
Also, experiments on glass fibers that Griffith himself conducted suggested that the fracture stress increases as the fiber diameter decreases. Hence the uniaxial tensile strength, which had been used extensively to predict material failure before Griffith, could not be a specimen-independent material property. Griffith suggested that the low fracture strength observed in experiments, as well as the size-dependence of strength, was due to the presence of microscopic flaws in the bulk material. To verify the flaw hypothesis, Griffith introduced an artificial flaw in his experimental glass specimens.