Brittle failure is more likely under which conditions?

• A. High temps, low load rates and rigid constraints
• B. Cold temps, low load rates and flexible constraints
• C. Cold temps, high load rates and rigid constraints
• D. Cold temps, high load rates and flexible constraints

Answer: (C)

Brittle failure happens when a material can’t deform plastically to relieve stresses, so cracks grow quickly without significant plastic work. Cold temperatures reduce toughness and promote embrittlement, making cracks easier to initiate and propagate. A high loading rate leaves little time for microscopic mechanisms that would blunt or blunt-bridge cracks, so the stress intensity at crack tips rises rapidly. Rigid constraints stop the material from redistributing load and permit higher local stresses at flaws, further encouraging brittle fracture. Put together, cold temperature, rapid loading, and rigid constraints create the conditions most prone to brittle failure, which is why this option is the best fit. In contrast, warmer temperatures, slower loading, or more flexible constraints generally allow more ductility and stress redistribution, reducing brittleness.