Brittle Fracture — Characteristics and Materials Which statement about brittle fracture in metals is correct?

Introduction / Context:
Brittle fracture is a sudden failure with little or no plastic deformation. It is influenced by temperature, strain rate, microstructure, stress state, and crystallography. Recognizing conditions and materials prone to brittle behavior is vital for safe design and failure prevention.

Given Data / Assumptions:

• Comparison between ductile and brittle fracture features.
• Basic knowledge of crystal structures: BCC, FCC, and HCP.
• Ambient to low-temperature service scenarios considered.

Concept / Approach:
HCP metals (e.g., magnesium, zinc, cadmium, beryllium) have fewer independent slip systems at room temperature, limiting plastic deformation and making brittle behavior more common, especially under triaxial stress states. In contrast, FCC metals (e.g., aluminum, copper) remain ductile to low temperatures, and BCC metals can show a ductile-to-brittle transition at lower temperatures or high strain rates. Brittle fracture typically occurs without much warning or necking and does not produce the classic “cup-and-cone” profile of ductile rupture.

Step-by-Step Solution:
Eliminate options contradicted by fundamentals: high temperature and low strain rate promote ductility, not brittleness (reject a).Note that brittle fracture is often silent and sudden; acoustic emissions are not guaranteed (reject c).Cup-and-cone morphology indicates significant plasticity (ductile); brittle fracture surfaces are granular/cleavage-like (reject d).Recognize HCP materials’ limited slip → brittle tendencies (accept b).

Verification / Alternative check:
Fractography texts show cleavage facets in HCP/brittle failures; ductile failures exhibit dimples and cup-and-cone profiles.

Why Other Options Are Wrong:
(a) Conditions invert the trend; brittleness is favored by low temperature/high strain rate.(c) No universal audible precursor; catastrophic and silent failures are frequent.(d) Cup-and-cone is a hallmark of ductile fracture, not brittle.

Common Pitfalls:
Confusing ductile-to-brittle transition of BCC steels with the inherently limited slip of HCP metals.

Final Answer:
Many metals with hexagonal close packed (H.C.P) crystal structure commonly show brittle fracture