What are the three main failure modes in composites under in-plane loading?

What are the three main failure modes in composites under in-plane loading?

• A. Fiber buckling, matrix creep, and surface wear.
• B. Fiber waviness, resin bleeding, and fiber misalignment.
• C. Fiber breakage, matrix cracking, and interlaminar delamination.
• D. Interlaminar friction, ply shear, and void collapse.

Answer: (C)

In-plane loading of a laminated composite fails mainly through three mechanisms: fiber breakage, matrix cracking, and interlaminar delamination. The fibers carry most of the load along their length, so when the stress along a fiber reaches its strength, the fiber breaks and local load paths collapse, potentially causing neighboring fibers to bear more load and fail as well. The matrix surrounding the fibers is typically weaker and more brittle in tension or shear; it cracks transverse to the fiber direction when the local stresses exceed its strength, forming cracks that can grow and link with other cracks. Those matrix cracks often reach ply interfaces and promote delamination. Delamination is the separation between adjacent plies caused by weak interfacial bonding and interlaminar stresses; once layers begin to peel apart, the laminate loses stiffness and overall load-carrying capacity even if individual fibers remain intact within their plies. Other listed issues point to manufacturing defects or secondary effects rather than the primary failure modes seen under in-plane loading, so they don’t describe the main failure pathways the way fiber breakage, matrix cracking, and delamination do.

In-plane loading of a laminated composite fails mainly through three mechanisms: fiber breakage, matrix cracking, and interlaminar delamination. The fibers carry most of the load along their length, so when the stress along a fiber reaches its strength, the fiber breaks and local load paths collapse, potentially causing neighboring fibers to bear more load and fail as well. The matrix surrounding the fibers is typically weaker and more brittle in tension or shear; it cracks transverse to the fiber direction when the local stresses exceed its strength, forming cracks that can grow and link with other cracks. Those matrix cracks often reach ply interfaces and promote delamination. Delamination is the separation between adjacent plies caused by weak interfacial bonding and interlaminar stresses; once layers begin to peel apart, the laminate loses stiffness and overall load-carrying capacity even if individual fibers remain intact within their plies.

Other listed issues point to manufacturing defects or secondary effects rather than the primary failure modes seen under in-plane loading, so they don’t describe the main failure pathways the way fiber breakage, matrix cracking, and delamination do.