Chip control in metal cutting: In machining of metals, chips tend to break primarily because of which material or process characteristic?

Introduction / Context:
Chip formation governs surface finish, tool life, and safety. Chips may be continuous, segmented, or discontinuous. Knowing why chips break helps in selecting cutting parameters, chip breakers, and tool materials.

Given Data / Assumptions:

• Orthogonal cutting with a sharp tool.
• Work materials showing strain hardening (work hardening) under plastic deformation.
• Moderate cutting speeds where thermal softening does not dominate.

Concept / Approach:
As the chip forms and flows up the rake face, it undergoes severe plastic strain and cyclic bending over the tool/chip breaker. Many alloys exhibit strain hardening: their flow stress rises with plastic strain. This promotes periodic fracture of the chip root or along shear bands, creating segmented or broken chips.

Step-by-Step Solution:

Verification / Alternative check:
Metallographic examination of chips shows shear localization bands and higher hardness compared to the parent material, confirming work hardening.

Why Other Options Are Wrong:

• Toughness: Greater toughness resists fracture, encouraging continuous chips.
• Ductility: High ductility favors long continuous chips rather than breakage.
• Elasticity: Elastic effects are recovered and small; breakage is a plastic deformation/fracture phenomenon.
• Perfect lubrication: Reduces friction and heat; it does not inherently cause chip breakage.

Common Pitfalls:
Assuming brittle materials are the only source of chip breakage; even ductile alloys can produce segmented chips due to work hardening and thermal effects at certain speeds.

Final Answer:
Work hardening of the work material