Machine design 2 selection of materials stressing
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Machine design 2 selection of materials, stressing. aim. to introduce the structure of machines, the function, type and load of machine elements and the main methods of designing them Main chapters of this semester: Fits & tolerances Basics of stressing Joints Drive systems 1. Requirements.

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Machine design 2 selection of materials, stressing

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Machine design 2selection of materials, stressing


aim

  • to introduce the structure of machines, the function, type and load of machine elements and the main methods of designing them

  • Main chapters of this semester:

    • Fits & tolerances

    • Basics of stressing

    • Joints

    • Drive systems 1.


Requirements

3 hours weekly (mostly 2 lecture, 1 laboratory)

Attendance and participation are important!

Engineering is not a spectator sport.

(allowed absence four occasions)

Course requirements:

Tests (tolerances, stressing) 10+10 points

Assignments (valve, key joint, coupling) (10+15+15)

Written exam 60 point


machine elements


static elements

joints

frames

springs

(mechanical) drive systems

bearings

shafts

couplings & clutches

drives

vessel systems

pipes

valves

tanks

(technical fluids)

general purpose machine elements


material

DESIGN

money

manufacturing

optimum - opportunism

time, place


aims

  • no failure (surface or volume)

  • no big deformations

  • enough service time


loads

  • mechanical forces, moments…

  • thermal 

  • chemical changing in place/ time

static cyclic dynamic


materials

  • metals

    • ferrous/ non~

      • cast iron

      • steel

        • carbon/ alloy

  • plastics

  • ceramics

  • composite

  • density

  • conductivity

  • elasticity

  • plasticity

  • ductility

  • brittleness

  • toughness (impact)

  • creep


loads & stresses

Stress distribution uniforn/linear

(Mohr, H-M-H)


loss of stability

Buckling

elastic/ plastic


Tensile test

Load  deformation

stress – strain diagrams

ductile – carbon steel

rigid – cast iron


simplifyed material models

elasto-plastic

rigid


test

YS ReH

UTS Rm

UTS

YS

real

eng.


strain hardening


elastic properties

elastic (Young) modulus: E [MPa]

(Hook’s law s = Ee)

shear modulus: G [MPa] (t = Gg)


main static properties

elastic limit Rp0.2

yield strengthReH

ultimate tensile strengthRm

maximal strainA

hardnessHHB…

Charpy (V-notch) testKcu


Influencing factor – (not only) static load

Stress concentration

shape factor

αk > 1


sudden area changes


Influencing factor – dynamic load

 Tényl= d

dynamic load factor

1.1~ 3

Depending on machine type & size (handbooks, measurements, calculations)


Periodic stresses

fatique

propagating crack – final static break

90-95% of all failures!


Wöhler- curve

Rm

  • fatique limit

  • N > 106

load cycles

many factors - stohastic phenomenon


types of varying load

σv

σr

Fatique limits

cycle assymetry ratio

cycle mean stress ratio


constructing Smith- diagram


constructing Smith- diagram


constructing Smith- diagram


constructing Smith- diagram


constructing Smith- diagram


constructing Smith- diagram


constructing Smith- diagram


using Smith-diagram

no failure


Influencing factors – fatique strength

size

surface roughness


notch sensitivity ηk (0.5-1.0 )


Stress concentration factor βk

σaver.

stress conc.

sensitivity

shape


Safety factor (SF; n)

  • load, material…

    allbearsuncertainity

    to be onthesafesideuse SF

    n>1 (1.15 ~ 8-10!)

  • importance of element

  • manufacture

  • material testing

  • calculations


That’all, folks!


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