-StressandStrainStress and Strain - femlab/lecture/introduction_mse/ Stress and Strain Stress, σ:...

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Transcript of -StressandStrainStress and Strain - femlab/lecture/introduction_mse/ Stress and Strain Stress, σ:...

  • Chapter 7. Mechanical PropertiesChapter 7. Mechanical Properties

    - Stress and StrainStress and Strain

  • 7.1 Introduction

    Important Mechanical Properties: strength, hardness, ductility and stiffness

    Load: tensile, compressive, shearp

  • 7.2 Stress and Strain

    Stress, : Force per unit area

    Strain, : Unit deformation. Elastic strain is recoverable; plastic strain is

    permanent.

    0AF

    =

    0

    ll

    llli ==

    00 ll

    F

    0AF

    =

  • Geometric consideration

    +==

    2cos1cos2

    ==2

    cos

    2sin

    ==

    22sincossin

  • Elastic Deformation

    7.3 Stress-Strain behavior

    E= Hooks law E=

    E : modulus of elasticity, or Youngs modulus

    Hook s law

    Metal and ceramics : 45 Gpa ~ 407 Gpa Polymer : 0 007 Gpa ~ 4 GpaPolymer : 0.007 Gpa 4 Gpa

    Atomic scale : small changes in the interatomic spacing and

    the stretching of interatomic bonds

  • dFE

    0rdr

    E

  • Ex 7.1

  • 7.5 Elastic properties of materials

    z

    y

    z

    x

    ==

    : Poissons raio

    )1(2 += GE

    0.25< < 0.5

    In most of metals G 0 4EIn most of metals, G ~ 0.4E

  • Ex 7.2