Which method uses existing crack size and stress intensity to predict the critical crack length?

• A. Fracture mechanics
• B. Fatigue life analysis
• C. Load rating
• D. Dynamic analysis

Answer: (A)

Predicting when an existing crack becomes critical by relating crack size to the applied load through fracture mechanics. In this approach, you calculate the stress intensity factor for the current crack, K_I = Y sigma sqrt(pi a), where a is the crack length and sigma is the applied stress. When K_I reaches the material’s fracture toughness K_IC, failure becomes imminent. Solving for the critical crack length a_c under that load shows how large the crack would have to grow to reach instability. This method directly uses both the existing crack size and the stress intensity to forecast whether the crack will propagate to a dangerous length, which is the essence of fracture mechanics. Fatigue life analysis looks at cycles to failure under varying loads, load rating assesses safe load capacities, and dynamic analysis studies time-varying responses—none of which directly predict a critical crack length from the current crack size and stress intensity.