How Do The Interfacial Shear Stresses And Micro-crack Propagation In A Carbon Fiber Reinforced Polymer (CFRP) Composite With A Hybrid Epoxy-resin Matrix, Subjected To A Combination Of Thermal Cycling And Mechanical Loading, Affect The Degradation Of The Interlaminar Fracture Toughness In The Presence Of Moisture Absorption?

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The degradation of interlaminar fracture toughness in a carbon fiber reinforced polymer (CFRP) composite with a hybrid epoxy-resin matrix, subjected to thermal cycling, mechanical loading, and moisture absorption, can be understood through the following mechanisms:

  1. Thermal Cycling and Mechanical Loading:

    • Thermal cycling induces thermal stresses due to differential expansion rates between the carbon fibers and the epoxy matrix, leading to interfacial shear stresses.
    • Mechanical loading, especially cyclic, exacerbates these stresses, initiating micro-cracks in the matrix and at the fiber-matrix interface.

  2. Micro-Crack Propagation:

    • Initiated micro-cracks propagate under continued loading, compromising the composite's integrity. Moisture absorption accelerates this propagation by weakening the matrix and interfaces.

  3. Moisture Absorption:

    • Moisture seeps into the composite, softening the epoxy matrix and reducing its load transfer efficiency. It also penetrates micro-cracks, increasing stress intensity and facilitating crack growth.

  4. Hybrid Epoxy Matrix:

    • The hybrid matrix may offer varied resistance to moisture and adhesion properties. Components with lower moisture resistance can degrade faster, affecting overall toughness.

  5. Interface Degradation:

    • Moisture weakens fiber-matrix adhesion, making the interface more susceptible to debonding under stress.

  6. Cumulative Effect:

    • Combined thermal, mechanical, and environmental factors lead to reduced interlaminar fracture toughness, as less energy is required for delamination due to compromised interfaces and matrix.

In conclusion, the interplay of thermal cycling, mechanical loading, and moisture absorption leads to a progressive degradation of the CFRP composite's interlaminar fracture toughness, primarily through stress-induced damage and environmental weakening.