Cracks in environmental cracking tend to form at right angles to the direction of what property?

• A. Maximum tensile strength
• B. Shear stress
• C. Compressive load
• D. Temperature

Answer: (A)

Crack growth in environmental cracking follows the opening mode (Mode I), which is driven by tensile normal stress across the crack faces. Because the opening force is normal to the crack plane, the crack tends to orient itself so that the maximum tensile stress acts perpendicular to the crack plane. In other words, cracks form at right angles to the direction of the greatest tensile stress.

The other factors don’t set this orientation: shear stress drives a different fracture mode with different crack paths, a compressive load tends to close cracks rather than open them, and temperature affects the rate of environmental reactions but not the geometric direction of crack propagation.