What are the CIF susceptibility factors?

• A. High tensile stresses, low constraints, planar discontinuity normal to primary stresses
• B. Low tensile stresses, high constraints, planar discontinuity normal to primary stresses
• C. High tensile stresses, high constraints, planar discontinuity parallel to primary stresses
• D. High tensile stresses, high constraints, planar discontinuity normal to primary stresses

Answer: (D)

Crack initiation and growth under load are most likely when three conditions line up: strong tensile loading, restricted surroundings, and a flaw plane oriented to open under that load. High tensile stresses push the material into a opening-mode crack situation, increasing the driving force at the crack tip. High constraint around the flaw tip makes the stress state more triaxial and reduces the ability of the material to blunt the crack, which tends to accelerate crack growth and raise the likelihood of failure. A planar discontinuity that is normal (perpendicular) to the primary tensile stresses aligns with the direction that produces maximum opening at the crack plane, so the stress intensity driving the crack tip is largest.

When all three are present—high tensile stresses, high constraints, and the flaw oriented perpendicular to the main tension—the conditions are most favorable for CIF, meaning the crack is most susceptible to initiation and propagation. If any one of these factors is reduced (lower tensile load, less constraint, or a flaw oriented parallel to the stress), the driving force for cracking decreases and susceptibility drops.