Q1: Internal cracks in drawn bars are due to

ANS:A - secondary tensile stresses.

Internal cracks in drawn bars are typically due to internal tensile stresses, specifically secondary tensile stresses. Explanation:

• When a metal bar is subjected to the drawing process (where it is pulled through a die to reduce its diameter), it undergoes plastic deformation, causing the metal to elongate and reduce in diameter.
• During this process, internal stresses are induced within the metal due to the uneven deformation and material flow. These internal stresses can become tensile in nature, particularly in regions where the metal experiences significant stretching or reduction in cross-sectional area.
• Secondary tensile stresses refer to stresses that are perpendicular to the primary direction of applied load. In the context of drawing, secondary tensile stresses can develop in regions where the metal undergoes changes in shape or direction.
• These internal tensile stresses can exceed the material's strength and lead to the initiation and propagation of cracks within the drawn bar. These cracks may propagate internally, leading to the formation of internal cracks within the drawn bar.
• While temperature gradients and heating of dies and grips may affect the overall drawing process, they are not typically the primary cause of internal cracks in drawn bars.
• Internal compressive residual stresses, if present, would generally inhibit the formation of cracks rather than cause them.