Which statement correctly characterizes Mode I and Mode II loading in interlaminar fracture?

Which statement correctly characterizes Mode I and Mode II loading in interlaminar fracture?

• A. Mode I is opening (tensile) mode; Mode II is sliding (in-plane shear) mode.
• B. Mode I is in-plane shear; Mode II is opening.
• C. Mode I is bending; Mode II is torsion.
• D. Mode I is off-axis loading; Mode II is on-axis loading.

Answer: (A)

In fracture mechanics, the two basic loading modes for an interlaminar crack describe how the crack faces move under load. Mode I is the opening or tensile mode: the crack faces are pulled directly apart by a normal stress to the crack plane, causing the faces to separate like mouths opening. Mode II is the sliding or in-plane shear mode: the crack faces slide relative to each other along the plane due to shear stress that lies in the plane of the crack, so there’s no immediate opening. The statement is best because it matches these definitions: Mode I corresponds to opening (tensile) loading, and Mode II corresponds to sliding (in-plane shear) loading along the crack. The other descriptions mix up the nature of the stresses and motions (for example, treating Mode I as in-plane shear or Mode II as opening, or introducing bending/torsion or off-axis/on-axis loading), which do not reflect the standard fracture-mode behavior.

In fracture mechanics, the two basic loading modes for an interlaminar crack describe how the crack faces move under load. Mode I is the opening or tensile mode: the crack faces are pulled directly apart by a normal stress to the crack plane, causing the faces to separate like mouths opening. Mode II is the sliding or in-plane shear mode: the crack faces slide relative to each other along the plane due to shear stress that lies in the plane of the crack, so there’s no immediate opening.

The statement is best because it matches these definitions: Mode I corresponds to opening (tensile) loading, and Mode II corresponds to sliding (in-plane shear) loading along the crack. The other descriptions mix up the nature of the stresses and motions (for example, treating Mode I as in-plane shear or Mode II as opening, or introducing bending/torsion or off-axis/on-axis loading), which do not reflect the standard fracture-mode behavior.