Mode I, II, III

Mode I, II, and III refer to different ways that cracks can grow or open in materials. Mode I is an opening or tensile mode, where the crack faces are pulled apart directly. Mode II is a sliding or in-plane shear mode, where the crack faces slide past each other in the plane of the crack. Mode III is a tearing or out-of-plane shear mode, where the crack faces slide relative to each other but out of the original plane. Understanding these modes helps engineers analyze how materials might fail under different stress conditions.