University:
McMaster University
Course:
MATLS 2H04 | Introduction to Materials Engineering
Academic year:

2023
Views:

427

Pages:

2
Author:

Sabrina S.

Plastic Failure 9.3 Introduction to Strengthening Mechanisms Plastic Failure permanent and non-recoverable failure to avoid plastic failure. decrease the stress in o material select a high yield strength material engineer the current material using strengthening mechanisms yield stress = stress at which the material starts to deform plastically (Lo some materials have a clear point where the material yields (diagram on right)) for other materials, need to use the proof stress to define the transition from elastic to plastic point P is where plastic deformation starts to occur, but this is difficult to accurately define in real experimental data yield strength is estimated by taking the slope of the linear region of the stress-strain curve & than offsetting this at the 0.2% strain point on the y-axis, the intersection point between this straight line & the experimental stress-strain curve defines the yield strength (ry) plastic deformation in metals is due to dislocation motion introducing features wwo a material that impedes or stops dislocation motion will f the yield strength Strengthening Mechanisms will examine each one using Aluminium solid solution work hardening precipitation hardening grain size refinement Properties: Low density (2.7 g/cm³ as compared to 7.9 g/cm³ for steel) High electrical conductivity High thermal conductivity Resistance to corrosion Melting point (660°C) Mechanical Properties FCC crystal structure gives Aluminium high ductility Low yield strength (7-11 MPa) Solid Solution Strengthening impurity atoms are added to the parent matrix either interstitially or substitutionally Impurity Atomic % Yield strength (MPa) Mn 0.5 20 Cu 1.0 15 Mg 2.2 30 Work Hardening A high density of dislocations are introduced to the ductile metal, which Res the yield strength Commonly done by cold rolling Al alloy number Annealed Work-hardened 1100 35 145 3005 65 185 5456 140 370 Експортувати в Таблиці Precipitation Hardening (AKA. age hardening) Strength & hardness of some metal alloys may be increased by the formation of small uniformly dispersed particles within the original matrix 3 steps Solid solution treatment Quenching aging The precipitates act as obstacles to dislocation motion which Res yield strength Not every alloy can be precipitation hardened Grain Size Refinement Hall-Petch eq: σy = σo + ky * d^-0.5 d = grain diameter Decreasing the grain size, increases the yield strength A fine-grained material is stronger than a coarse-grained material because a fine-grained material has more grain boundaries to impede dislocation motion 9.4 Work Hardening Ductility Yield strength is the stress at the point when the material transitions from elastic to plastic deformation Ductility is an amount of plastic deformation that has been sustained at fracture Ductility is an important parameter to consider when we need to fabricate a component Metal forming processes involve subjecting a component to a large amount of strain Eg rolling of sheets, forging, wire drawing, extrusion