NEEP 541 Strength Fall 2003 Jake Blanchard Outline

NEEP 541 – Strength Fall 2003 Jake Blanchard

Outline n Strength n n n Theoretical Effect of dislocations Types of dislocations

Theoretical Strength n n n The strength of a perfect crystal, with no defects, is significantly higher than measured strength This is referred to as theoretical strength Defects, such as dislocations, are the reason for the reduced “real” strength

Theoretical Strength Shear force x b a x

Theoretical Strength

Theoretical Strength n n Steel: G~90 Gpa, max~10 Gpa Yield strength=2 max ~20 Gpa More careful analysis (with realistic potential) gives YS~6 GPa Measured yield strength is 0. 2 -0. 4 GPa

Edge Dislocations

Burgers Vector b

Dislocation Comments n n A dislocation is a one-dimensional defect Bonds between atoms are not in equilibrium (they are distorted - so dislocations possess energy) n n Dislocations move under the influence of external forces Dislocations can be generated by the agglomeration of point defects (interstitials on the extra half-plane or vacancies on the missing half-plane)