Question

Beach marks are observed in

• A. Impact failure
• B. Tensile failure
• C. Shear failure
• D. Fatigue failure

Hint:

If you see "beach marks" or "clamshell marks" in a question about material failure, the answer is almost certainly "fatigue". These marks trace the history of the crack growing under cyclic loading.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Fractography is the study of fracture surfaces to determine the cause of failure. Different failure mechanisms (impact, fatigue, etc.) leave distinct characteristic features on the fracture surface.

Step 2: Detailed Explanation:
Let's define the key terms:

• Fatigue Failure: This is failure that occurs under cyclic or fluctuating loads, even if the maximum stress is below the material's ultimate tensile strength. The failure proceeds by the initiation and slow propagation of a crack.

• Beach Marks (or Clamshell Marks): These are macroscopic (visible to the naked eye) markings on a fatigue fracture surface. They appear as concentric lines or arcs that emanate from the crack initiation site. Each mark represents a position of the crack front and is formed during a period of crack arrest or a change in loading conditions (e.g., when a machine is stopped and restarted). They are a definitive sign of fatigue failure.

• Other Failures: itemize

• Impact failure often shows brittle features like cleavage facets or ductile features like dimples, but not beach marks.

• Tensile failure (in a ductile material) typically results in a "cup and cone" fracture surface.

• Shear failure results in surfaces that have slid past one another, often appearing smooth or smeared.
itemize

Step 3: Final Answer:
Beach marks are the classic macroscopic signature of a fatigue failure.