Distinguish Mode I and Mode II delamination.

Distinguish Mode I and Mode II delamination.

• A. Mode I is opening (normal) at the interface; Mode II is in-plane shear (sliding) at the interface.
• B. Mode I is in-plane shear; Mode II is opening at the interface.
• C. Mode I is bending; Mode II is torsion at the interface.
• D. Mode I and II are both out-of-plane fracture modes with no shear interaction.

Answer: (A)

In delamination of composites, two fundamental interfacial fracture modes describe how the crack faces move relative to each other. Mode I is opening the interface: the faces separate normal to the crack plane due to normal tensile stress. Mode II is in-plane shear: the faces slide past one another within the plane of the layers, driven by shear stress along the interface. The statement that Mode I is opening at the interface and Mode II is in-plane shear at the interface captures these distinct mechanisms accurately. The other descriptions don’t fit because one reverses the definitions, calling Mode I in-plane shear and Mode II opening; another attributes bending or torsion to the interface, which are not the standard interfacial fracture modes. A claim that both modes are out-of-plane with no shear interaction ignores the actual in-plane shear nature of Mode II.

In delamination of composites, two fundamental interfacial fracture modes describe how the crack faces move relative to each other. Mode I is opening the interface: the faces separate normal to the crack plane due to normal tensile stress. Mode II is in-plane shear: the faces slide past one another within the plane of the layers, driven by shear stress along the interface. The statement that Mode I is opening at the interface and Mode II is in-plane shear at the interface captures these distinct mechanisms accurately.

The other descriptions don’t fit because one reverses the definitions, calling Mode I in-plane shear and Mode II opening; another attributes bending or torsion to the interface, which are not the standard interfacial fracture modes. A claim that both modes are out-of-plane with no shear interaction ignores the actual in-plane shear nature of Mode II.