2010-02-08 Chapter 06 Mechanical Properties of Metals

2010-02-08 Chapter 06 Mechanical Properties of Metals -...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
ISSUES TO ADDRESS. .. Stress and strain : What are they and why are they used instead of load and deformation? Elastic behavior: When loads are small, how much deformation occurs? What materials deform least? Plastic behavior: At what point do dislocations cause permanent deformation? What materials are most resistant to permanent deformation? 1 Toughness and ductility : What are they and how do we measure them? CHAPTER 6: MECHANICAL PROPERTIES
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Tensile (Pulling) Compression (Pushing) Elongation or, extension Compression or, contraction TYPES OF FORCES/LOADS (I) Tensile and compressive forces are normal (perpendicular) to the cross sectional area. Change in dimension is referred as deformation. Tension – elongation Compression – contraction
Background image of page 2
Shear Angular deformation Shear forces are parallel to the cross sectional area. TYPES OF FORCES/LOADS (II)
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
F δ bonds stretch return to initial 2 1. Initial 2. Small load 3. Unload Elastic means reversible ! F δ Linear- elastic Non-Linear- elastic ELASTIC DEFORMATION
Background image of page 4
1. Initial 2. Small load 3. Unload Plastic means permanent ! planes still sheared F δ elastic + plastic bonds stretch & planes shear δ plastic PLASTIC DEFORMATION (METALS) F δ linear elastic linear elastic δ plastic Elastic strain recovery
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
HOW DO WE MEASURE MAX. CAPACITY OF THE MATERIAL BEFORE IT FRACTURES (BREAKS)? Can we measure that capacity in terms of force/load? NO. F1 F2 For same material, Rod with larger diameter will take more load before breaking. F2 >F1. It doesn’t mean larger diameter rod is stronger! Let F1 & F2 be loads required to break the rod made of same material. 1 2
Background image of page 6
CONCEPT OF STRESS If we compute quantities and in earlier example, then these quantities are equal. It is called “Ultimate Strength of the Material” i.e. max. capacity of the material before it breaks. Therefore, it is convenient to define the term called “Stress”. Stress is ‘force’ divided by ‘area on which force is acting’. When the stress reaches the maximum value, the material breaks (fractures). The corresponding stress is called “Ultimate Strength of the Material”. 1 A 1 F 2 A 2 F A F = σ
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
ULTIMATE STRENGTHS Tensile load – ‘Ultimate tensile strength’ (UTS) or, ‘Tensile strength (TS)’, σ ut Compressive load – ‘Ultimate compressive strength (UCS) or, “Compressive strength’, σ uc Shear load – ‘Ultimate shear strength’ (USS) or, ‘Shear strength’, τ u In this course we ONLY deal with tensile loads so we will refer TS simply as σ u instead of σ ut
Background image of page 8
Simple tension: cable o σ = F A A o = cross sectional Area (when unloaded) F F σ σ Ski lift (photo courtesy P.M. Anderson) Canyon Bridge, Los Alamos, NM Simple compression: o σ = F A (photo courtesy P.M. Anderson) ENGINEERING STRESS When original area is considered for calculation, stress is called ‘engineering stress’.
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Bi-axial tension: Hydrostatic compression: Fish under water
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 41

2010-02-08 Chapter 06 Mechanical Properties of Metals -...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online