Which statement best describes the significance of G_IC and G_IIC in delamination?

Which statement best describes the significance of G_IC and G_IIC in delamination?

• A. They are the densities of the laminate.
• B. They are the critical energy release rates for mode I and mode II; if G exceeds these values, delamination grows.
• C. They are the tensile strengths of the fiber.
• D. They are the thermal expansion coefficients.

Answer: (B)

Delamination growth in composites is governed by fracture mechanics: a crack between layers will propagate when the energy available to drive that growth exceeds the material’s resistance. G_IC and G_IIC are the critical energy release rates for the two basic delamination loading modes. G_IC is the threshold for mode I, the opening (perpendicular) mode, and G_IIC is the threshold for mode II, the in-plane shear mode. They quantify how much energy is required to advance the crack under those specific loadings. If the actual energy release rate, G, for the crack under the given loading exceeds the corresponding critical value, the delamination tends to grow. In practice, delamination can involve a mix of mode I and mode II, but the essential idea remains: surpassing these toughness values means crack growth is energetically favorable. These are not densities, tensile strengths of fibers, or thermal expansion coefficients; they specifically measure resistance to crack growth under opening and shear.

Delamination growth in composites is governed by fracture mechanics: a crack between layers will propagate when the energy available to drive that growth exceeds the material’s resistance. G_IC and G_IIC are the critical energy release rates for the two basic delamination loading modes. G_IC is the threshold for mode I, the opening (perpendicular) mode, and G_IIC is the threshold for mode II, the in-plane shear mode. They quantify how much energy is required to advance the crack under those specific loadings. If the actual energy release rate, G, for the crack under the given loading exceeds the corresponding critical value, the delamination tends to grow. In practice, delamination can involve a mix of mode I and mode II, but the essential idea remains: surpassing these toughness values means crack growth is energetically favorable. These are not densities, tensile strengths of fibers, or thermal expansion coefficients; they specifically measure resistance to crack growth under opening and shear.