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6. Mechanical Properties

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Presentation on theme: "6. Mechanical Properties"— Presentation transcript:

1 6. Mechanical Properties
Forms of Mechanical Loading compression tension shear torsion

2 6. Mechanical Properties
Stress-Strain Behaviour Linearelastic Deformation Robert Hooke:

3 6. Mechanical Properties
Stress-Strain Behaviour Nonlinearelastic Deformation

4 6. Mechanical Properties
Force-Separation-Curve

5 6. Mechanical Properties
Potentielle Energie Anziehungskräfte Abstoßungskräfte Kraft Kernabstand Abs-k. Anz-k. K K-abst.

6 6. Mechanical Properties
Influence of Temperature

7 6. Mechanical Properties
Tensile Properties of Metals(1) Streck- grenzen- effekt Lüders-Dehnung cV - Konz. gleitfähiger Versetzg b – Burgersvektor V - Abgleitgschwindigkeit

8 6. Mechanical Properties
Deformation Mechanisms for Metals Basic Concepts of Dislocations(3) Video Versetzungsbewegung (Blasenmodell)

9 6. Mechanical Properties
Deformation Mechanisms for Metals Characteristics of Dislocations(1)

10 6. Mechanical Properties
Tensile Properties of Metals(3)

11 6. Mechanical Properties

12 6. Mechanical Properties

13 6. Mechanical Properties
Deformation Mechanisms for Metals Basic Concepts of Dislocations(1)

14 6. Mechanical Properties
Deformation Mechanisms for Metals Basic Concepts of Dislocations(2)

15 6. Mechanical Properties
Deformation Mechanisms for Metals Basic Concepts of Dislocations(3) Video Versetzungsbewegung (Blasenmodell)

16 6. Mechanical Properties
Effect of Temperature

17 6. Mechanical Properties
Tensile Properties of Metals(2)

18 6. Mechanical Properties
True Stress-Strain-Curve

19 6. Mechanical Properties
Mechanical Behaviour of Ceramics(1)

20 6. Mechanical Properties
Mechanical Behaviour of Ceramics(2)

21 6. Mechanical Properties
Mechanical Behaviour of Polymers(1) spröde plastisch hoch elastisch C-C H-Brücken Van der Waals

22 6. Mechanical Properties
Mechanical Behaviour of Polymers(2) Polymethylmetacrylate PMMA (Plexiglas) E-Modul sinkt mit steigender T Duktilität steigt mit steigender T

23 6. Mechanical Properties
Tensile Properties of Metals(2)

24 6. Mechanical Properties
Slip in Single Crystals Geometrical Relationships

25 6. Mechanical Properties
Slip in Single Crystals Geometrical Relationships

26 6. Mechanical Properties
Example Video Gleitlinienbildung

27 6. Mechanical Properties
Slip Systems in the fcc-Lattice

28 6. Mechanical Properties
Slip Systems in the bcc-Lattice(1)

29 6. Mechanical Properties
Slip Systems in the bcc-Lattice(2)

30 6. Mechanical Properties
Slip Systems in the bcc-Lattice(3)

31 6. Mechanical Properties
Slip Systems in the hcp-Lattice(3) {1000}-[1120] →1 plane, 3 directions {1010}-[1120] →3 planes, 1 direction {1011}-[1120] →6 planes, 1 direction Only few possible slip systems!

32 6. Mechanical Properties
Slip Systems

33 6. Mechanical Properties
Anwendung in TWIP-Stählen => Hohe Verformung + Festigkeit Deformation twinning Twin Matrix

34 Hochleistungswerkstoff Stahl – eine faszinierende Vielfalt
Streckgrenze [MPa] Verformbarkeit

35 6. Mechanical Properties
Deformation: Slip vs. Twinning Slip Twinning Atomic movement Lattice orientation Atoms move fractional atomic spacing. Microscopic appearance Thin lines Wide bands or broad lines No change in lattice orientation. The steps are only visible on the surface of the crystal and can be removed by polishing. After polishing there is no evidence of slip. Lattice orientation changes. Surface polishing will not destroy the evidence of twinning.

36 6. Mechanical Properties
What is the maximum shear-stress ?

37 6. Mechanical Properties
The shear-stress-law of Schmid Winkel zwischen Zug- und Gleitrichtung kristallographische Gleitebene definiert A Kristallographische Gleitrichtung definiert Fg Schmid-Faktor

38 6. Mechanical Properties
Dislocation Sources - The Frank-Read Source ·b Critical radius: R=lo/2 lo: dislocation length

39 6. Mechanical Properties
Plastic Deformation of Polycrystalline Materials (Cu) Cu-Polykristall Verschiedene Orientierungen der Gleitsysteme

40 6. Mechanical Properties
Plastic Deformation of Polycrystalline Materials Requirement of five independent slip systems to realize any plastic deformation in polycrystals (Compatibility of deformation)

41 6. Mechanical Properties
Plastic deformation: Single vs. polycrystal Increase due to: Manifold of grain orientations in polycrystals Grain Boundaries!!! Why such an increase of strength?

42 6. Mechanical Properties
Plastic deformation Characteristics of Dislocations

43 6. Mechanical Properties
Plastic deformation Characteristics of Dislocations

44 6. Mechanical Properties
Plastic Deformation of Polycrystalline Materials Grains with the highest Schmid-factor deform first. yield stress (= Streckgrenze) is reached when deformation of all grains occurs any plastic deformation of polycrystalline materials needs activation of 5 independent slip systems (Compatibility of deformation) The role of Grain size

45 6. Mechanical Properties
The Relation of Hall-Petch

46 6. Mechanical Properties
Solid solution hardening Alloying causes hardening effects due to three types of interactions between the dislocations and the alloyed atoms: Parelastic interaction  distortion of the lattice; change in the lattice parameter a Dielastic interaction  different shear modulus G of alloyed atoms compared to that of the matrix atoms chemical interaction

47 6. Mechanical Properties
Work Hardening Property Degree of Deformation

48 6. Mechanical Properties
Dispersion and precipitation hardening The Fine-Kelly-Mechanism The Orowan-Mechanism shear-modulus particle diameter surface energy Volume fraction of particles Burgers-vector particle distance

49 6. Mechanical Properties
Texture hardening Strengthening effect due to: bad orientation between applied stress and „slip system“ morphological texture (Hall-Petch!!) Loading in direction A shows an enhanced yield stress compared to direction B B A

50 6. Mechanical Properties
Mechanisms to enhance strength Plastic deformation - at lower temperatures (no recyrstallization) grain refinement – Hall Petch solid solution hardening – solubility and lattice distortion dispersion hardening – input of highly dispers particles precipitation hardening – creation of particles (solubility) texture hardening (morphology, orientation and slip systems,


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