Question

With reference to steels used in ship building and marine engineering:

(a) Describe EACH of the following types of failure.

(i) Brittle failure

(ii) Ductile failure.

(b) Explain the term ductile to brittle transition stating the factor that determines ductile to brittle transition.

(c) Describe a test to determine the value of brittle fracture of a specimen test piece

Answer 1

Part (a)

(i) Brittle failure refers to the breakage of a material due to a sudden fracture. When a brittle failure occurs, the material breaks suddenly instead of deforming or straining under load. The fracturing or breaking can occur with only a small amount of load, impact force or shock

(ii) Ductile failure is also known as plastic collapse, general yielding or ductile overload, and is the failure mode that occurs when a material is simply loaded to beyond its ultimate tensile strength.

Part (b)

At low temperatures some metals that would be ductile at room temperature become brittle. This is known as a ductile to brittle transition. The ductile to brittle transition temperature is strongly dependant on the composition of the metal. Steel is the most commonly used metal that shows this behaviour.

Part (c)

Charpy V notch test is used to determine the value of brittle fracture of a specimen test piece. The specimen is kept as a simply supported beam in horizontal position and loaded behind the notch by the impact of a heavy swinging pendulum. This is a standardised high strain rate test which determines the amount of energy absorbed by material during fracture. This absorbed energy is a measure of a given materials toughness and acts as a tool to study temperature dependent brittle-ductile transition.

✓ Verified Model Answer (Text Solution)

(i) Brittle failure refers to the breakage of a material due to a sudden fracture. When a brittle failure occurs, the material breaks suddenly instead of deforming or straining under load. The fracturing or breaking can occur with only a small amount of load, impact force or shock