mechanical properties of metals n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Mechanical Properties of Metals PowerPoint Presentation
Download Presentation
Mechanical Properties of Metals

Loading in 2 Seconds...

play fullscreen
1 / 26

Mechanical Properties of Metals - PowerPoint PPT Presentation


  • 244 Views
  • Uploaded on

Mechanical Properties of Metals. Mechanical Properties. Stiffness - Elastic Modulus or Young’s Modulus (MPa) Strength - Yield, Ultimate, Fracture, Proof, Offset Yield. Measured as stress (MPa)

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Mechanical Properties of Metals' - eman


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
mechanical properties
Mechanical Properties
  • Stiffness - Elastic Modulus or Young’s Modulus (MPa)
  • Strength - Yield, Ultimate, Fracture, Proof, Offset Yield. Measured as stress (MPa)
  • Ductility - Measure of ability to deform plastically without fracture - Elongation, Area Reduction, Fracture Strain - (no units or mm/mm)
  • Toughness, Resilience - Measure of ability to absorb energy (J/m3).
  • Hardness - Resistance to indentation/abrasion (Various scales, e.g.; Rockwell, Brinell, Vickers.)
stress and strain
Stress and Strain
  • In a simplistic sense, stress may be thought of as Load/Area.
  • Similarly, strain is the deformation of the component/original length.
  • A stress may be direct, shear, or torsional - leading to corresponding deformations.
  • Stress cannot be measured directly, but deformation can be.
direct stress examples
Direct Stress Examples

Engineering Stress

Engineering Strain

Direct Stress - Tension

Direct Stress - Compression

tension test
Tension Test

Measures P

Extensometer

Measures DL

Typical Universal

Testing Machine

modern materials testing system
Modern Materials Testing System

Hydraulic

Wedge

Grips

Specimen

Extensometer

astm tension test specimen
ASTM Tension Test Specimen

Ao=0.20 in2

2” Gauge Length

Lo

raw data obtained
Raw Data Obtained

Total Elongation

Uniform Deformation

Elongation, DL (mm)

Load, P (kN)

X

Maximum Load, Pmax

Elastic

Deformation

Load, Pf

engineering stress strain curve
Engineering Stress-Strain Curve

Elongation

Sy

0.2% offset

yield stress

Engineering Stress, S=P/Ao

(Ultimate)

E

Su

E

Proportional Limit

Engineering Strain, e = DL/Lo)

duke s quick tip
Duke’s Quick Tip!
  • Express Load in Newtons (N) and Area in mm2 to get Stress in MPa.
  • Mechanical properties of metals are almost always given in MPa or ksi.
  • Imperial units: Load in kips (1000 lbf) & Area as in2 givesStress in ksi (kips/in2)
  • 1000 psi = 1 ksi = 6.89 MPa
hooke s law elastic deformation
Hooke’s Law Elastic Deformation
  • Elastic deformation is not permanent; it means that when the load is removed, the part returns to its original shape and dimensions.
  • For most metals, the elastic region is linear. For some materials, including metals such as cast iron, polymers, and concrete, the elastic region is non-linear.
  • If the behavior is linear elastic, or nearly linear-elastic, Hooke’s Law may be applied:
  • Where E is the modulus of elasticity (MPa)
shear stress and strain
Shear Stress and Strain

Shear Stress

Shear Strain

shear stress, t = Shear Load / Area

shear strain, g = angle of deformation (radians)

shear modulus, G = t /g (elastic region)

elastic properties of materials
Elastic Properties of Materials
  • Poisson’s ratio: When a metal is strained in one direction, there are corresponding strains in all other directions.
  • For a uniaxial tension strain, the lateral strains are constrictive.
  • Conversely, for a uniaxial compressive strain, the lateral strains are expansive.
  • i.e.; the lateral strains are opposite in sign to the axial strain.
  • The ratio of lateral to axial strains is known as Poisson’s ratio, n.
poisson s ratio n
Poisson’s Ratio, n

For most metals,

0.25 < n < 0.35

in the elastic range

Furthermore:

plastic deformation

Elastic Plastic

Elastic Plastic

Elastic Plastic

Plastic Deformation

Sy

Sy

Sy

Stress

0.002

Strain

0.002

0.002

Most Metals - Al, Cu

Clad Al-Alloys

Low carbon Steel

microstructural origins of plasticity
Microstructural Origins of Plasticity
  • Slip, Climb and Slide of atoms in the crystal structure.
  • Slip and Climb occur at Dislocations and Slide occurs at Grain Boundaries.

t

t

elastic and plastic strain
Elastic and Plastic Strain

P

(e,S)

Stress

Total Strain

The 0.2% offset yield stress

is the stress that gives a plastic

(permanent) strain of 0.002.

Strain

Plastic

Elastic

ee

ep

elastic recovery
Elastic Recovery

Loading

Loading

Reloading

Stress

Unloading

Unloading

Strain

Strain

elastic strain

ductility el ar
Ductility - EL% & AR%
  • Elongation
  • Area Reduction

Lo

Ao

Lf

Af

ductile vs brittle materials
Ductile Vs Brittle Materials
  • Only Ductile materials will exhibit necking.
  • Ductile if EL%>8% (approximately)
  • Brittle if EL% < 5% (approximately)

Engineering Stress

Engineering Strain

toughness resilience
Toughness & Resilience
  • Toughness: A measure of the ability of a material to absorb energy without fracture. (J/m3 or N.mm/mm3= MPa)
  • Resilience: A measure of the ability of a material to absorb energy without plastic or permanent deformation.

(J/m3 or N.mm/mm3= MPa)

  • Note: Both are determined as

energy/unit volume

toughness u t
Toughness, Ut

Su

Sy

Engineering Stress, S=P/Ao

Engineering Strain, e = DL/Lo)

resilience u r
Resilience, Ur

Su

Sy

Engineering Stress, S=P/Ao

E

ey

Engineering Strain, e = DL/Lo)

typical mechanical properties
Typical Mechanical Properties

Metals in annealed (soft) condition