How Does Crack Propagation Occur in Materials?

What is crack propagation and fracture in materials?

Crack propagation (and fracture) occurs when _______________ for crack with lowest _______________.

Answer:

Crack propagation (and fracture) occurs when the stress intensity factor for a crack with the lowest critical value is reached.

Crack propagation and fracture in materials occur when the stress intensity factor (SIF) for a crack reaches or exceeds its critical value. The SIF is a measure of the stress concentration at the tip of a crack and is crucial in understanding how cracks propagate through a material.

When an external force or load is applied to a material, it creates stress concentrations near pre-existing cracks or defects within the material. These stress concentrations result in an increase in the SIF at the crack tip. If the SIF surpasses the critical value for that specific crack and material combination, crack propagation initiates. This critical value varies depending on the material's properties, the geometry of the crack, and other factors.

Crack propagation occurs as the crack tip experiences cyclic loading or continued application of stress, causing the crack to extend further into the material. The propagation process can lead to fracture, where the material ultimately fails due to the growth of the crack.