Question

The minimum resolved shear stress required to initiate slip is known as:

• A. Yield strength
• B. Ultimate tensile strength
• C. Critical resolved shear stress (CRSS)
• D. Fracture toughness

Hint:

Slip starts when shear stress on the slip plane reaches a critical value — that's the CRSS. It’s like the trigger point for plastic flow in crystals.

Answer 1

The Correct Option is C

Slip is the primary mechanism for plastic deformation in crystalline materials, and it occurs when atoms move along specific planes under applied shear stress.
What is CRSS?

• The Critical Resolved Shear Stress (CRSS) is the minimum shear stress (resolved along a slip plane and direction) required to initiate this slip.
• It depends on the material’s internal structure, temperature, and presence of defects.
• CRSS is a material property and is particularly important in single crystals, where deformation begins only when this threshold is exceeded.
• Described by Schmid's Law: \[ \tau = \sigma \cdot \cos \phi \cdot \cos \lambda \] where \( \tau \) is the resolved shear stress, \( \sigma \) is applied stress, \( \phi \) is the angle between load direction and slip plane normal, and \( \lambda \) is the angle between load direction and slip direction.

Why the Other Options Are Incorrect:

• (A) Yield Strength: The overall stress required to cause plastic deformation in a polycrystalline material — not the resolved shear stress on a specific slip system.
• (B) Ultimate Tensile Strength: The maximum stress a material can withstand before necking — unrelated to initial slip.
• (D) Fracture Toughness: Measures a material's resistance to crack propagation — not related to slip initiation.

Thus, the minimum resolved shear stress needed to initiate slip in a crystal is called the Critical Resolved Shear Stress (CRSS).