Question

A scientist conducted a tensile testing on a specimen and observed plastic deformation including deformation lines clearly. Due to the poor resolution in the optical microscope, however, the scientist could not clearly identify whether the deformation mechanism shown in the figure below was slip or twinning. Therefore, he/she decided to check the surface of the sample one more time after polishing the surface. After 3 hours’ polishing, he/she identified that the deformation lines he/she had observed before disappeared but grain boundaries remained unchanged under optical microscope. Determine whether the following statements are true or false.

(a) The plastic deformation mechanism observed above does not involve change in crystal structure. True ( )? or False ( )?

(b) The plastic deformation mechanism observed above often creates cracking sound due to acoustic waves generated. True ( )? or False ( )?

(c) The plastic deformation mechanism observed above is the most common plastic deformation mechanism. True ( )? or False ( )?

(d) All atoms in the deformed region of this sample experienced identical displacement. True ( )? or False ( )?

(e) The stress required to form this plastic deformation phenomenon is independent on temperature. True ( )? or False ( )?

Answer 1

See explaination

Step-by-step explanation:

The deformation process is slip deformation. Because, if you have observed that after polishing the deformation lines (slip lines) disappeared and the grain boundaries remained unchanged. Under microscope the slip can be visible as lines.

(a): True

Only one portion of the block of atoms move over the another block of atoms. In slip, no change in the internal structure of crystal but change in the shape of crystal.

(b): True

Due to dislocation movements slip deformation can cause cracking sound.

(c): True

Slip mechanism is the mostly observed plastic deformation in the metals. Because slip takes less energy to deformation.

(d): True

During slip deformation, the bonds between atoms broken and the atoms displaced identically and new bonds are formed.

(e): False

Higher the temperature; Easier the dislocation