Elastic and Plastic Deformation in Compression

Steps:

• Initial compression reduces length from L to 0.6L, showing total deformation.
• Upon unloading, length recovers to 0.8L, indicating elastic recovery of 0.2L (from 0.6L to 0.8L).
• Remaining change from L to 0.8L (0.2L permanent) shows plastic deformation.
• Thus, total deformation at 0.6L combines elastic (recoverable) and plastic (permanent) parts.

Why A is correct:

• Deformation is both elastic (recovers 0.2L) and plastic (permanent 0.2L shortening), per definitions of recoverable vs. irreversible strain.

Why the others are wrong:

• B: Ignores permanent 0.2L change, which is plastic.
• C: Ignores 0.2L recovery, which is elastic.
• D: Deformation exists and fits both categories.

Final answer: A