Inspection of unstable elements
Introduction
Fracture mechanics is a branch of the mechanics of deformable solids concerned with the study of the structural stability of materials, considering the formation and propagation of cracks or defects in materials and analyzing stress conditions with the stress concentration due to said defects.
It uses analytical methods derived from other branches of mechanics and materials science to study the mechanisms of formation and propagation of defects, and experimental methods related to solid mechanics to determine the relative resistance of the material to fracture.
Fracture mechanics allows us to improve product design, as well as manufacturing and inspection processes to control the propagation of defects that could lead to the failure of their components, but without the need to use unjustified safety coefficients. It applies the theories of elasticity "Elasticity (solid mechanics)") and plasticity "Plasticity (solid mechanics)"), to the microscopic crystallographic defects of materials to predict macroscopic mechanical fracture in bodies. Fractography is highly used in fracture mechanics to understand the causes of failure and verifies theoretical predictions by identifying actual failures.
History
Griffith energy ratio
Fracture Mechanics began to be developed during the First World War by the English aeronautical engineer Alan Arnold Griffith to explain the failure of brittle materials.[1] Griffith's work was motivated by two apparently contradictory facts:
• - The stress necessary for glass fracture is approximately 100 MPa.
• - The theoretical stress to break the atomic bonds of the glass was approximately 10,000 MPa.
A theory was needed that would reconcile these two contradictory facts. Furthermore, the experiments on glass fibers, which Griffith himself carried out, showed that the breaking stress increased when the diameter of the fiber was smaller. Therefore uniaxial tensile strength, which had been used extensively to predict material failure, could not be an independent property of the material. Griffith suggested that the low fracture resistance observed in the experiments, as well as the size-dependent resistance, was due to the presence of small microscopic breaks in the bulk of the material.