1.22657!lecture1introductionandfailuremechanisms[1]

8/12/2019 1.22657!lecture1introductionandfailuremechanisms[1]

1/20


2/20

3

Atlas Copco Tools- LTV angle nut runners

4

Atlas Copco Toolsnut runner

motor

avstngningsventil koppling

utgende axel planetvxlar pinion-

axel

vinkelvxelhus

clutch

pinion

shaft

closing valve

motor exit shaftplanetary gears

bevel gear housing


3/20

5

Monte Carlo simulation

L

W

P

6

Dimensioning of conical gears withthe AGMA standard


4/20

7

Dimensioning of the pinion shaft

8

Modeling and simulation


5/20

9

Surface fatigue

Maximum shear stress

Pitting

Flaking

Yielding

Spalling

Vermelding onderdeel organisatie10

Introduction1 Reliability engineering

2 Failure modes of machineelements3 Fatigue failure prediction andprevention


6/20

11

Failure analysis

12

DN 13 sep 2007

Slitage orsak till SAS-haveriSlitage fick en bult att lossna. Det var orsaken tillproblemen med landningsstllet nr ett SAS-flygplan avmodellen Dash-8 Q400 tvingades ndlanda i lborg isndags, enligt en preliminr rapport frn den danskahaverikommission, rapporterar nyhetsbyrn Ritzau.


7/20

13

The allowable pressure in slidingcontacts between metals is limitedby seizure

Steel cast iron 510 MPa, =0.120.18Steel - CuSn or CuAl alloys 1020MPa, =0.120.18

In screw joints contact pressuresup to 100 MPa are common, butthe sliding motion is limited to onesingle move. Zinc plated to prevent

corrosion and seizure.

1) You need to know how stuff fails

2) You need to know the measures

that can be taken to prevent failures.

How to improve operating reliability?

14

Shear fractureDuctile fracture

Fatigue fracture

How stuff failsHow to prevent failure

Thread stripping Check steel grade of the nut

Ductile fracture Check preload

Fatigue fracture Check joint stiffness


8/20

15

Failure modes of machine elements

Yielding

(Shear, ductile fraction by tension)Fatigue fracture(drive shaft, gear teeth)Wear(abrasive wear, adhesive, corrosion)

Friction(jamming, stick-slip)

Wear mechanisms / failure analysis

16

Fatigue failure


9/20

17

Wear mechanisms

Dry sliding metal to metal contactsalways showadhesive wear.Dry sliding polymer to metalcontacts showabrasive wear.

18

Zinc plated to preventcorrosion and seizure.


10/20

19

Two bodyabrasive wear

Three bodyabrasive wear

20

Adhesive wear(Galling)


11/20

21

22

Wear mechanismsStainless steel bushingin contact with a polymerbearing has completely wornthrough in short time!Corrosion wear


12/20

23

24

Wear mechanisms

Hertzian contact

Surface fatigue

Maximum shear stress


13/20

25

26

Wear mechanisms Adhesivescuffing, galling, cold welding, seizure, smearing

Abrasive

ploughing, polishing wear, grinding, scratchingCorrosionthermo chemical wear, oxidative wearSurface fatiguepitting, spalling, flaking

Motion related: fretting , false Brinelling


14/20

27

How rolling bearings fail?

Adhesivescuffing, galling, cold welding, seizure, smearing

Abrasiveploughing, polishing wear, grinding, scratchingCorrosionthermo chemical wear, oxidative wear

Surface fatiguepitting, spalling, flaking


Flaking

28

Failure mode classification forbearing damage


15/20


16/20

31

Angivna prestandabegrnsande fenomen r:Wear = ntningScoring = repbildningSpalling = gropbildning eller ytutmattning

Breakage = kuggbrott.

32

How cams failYielding

Adhesive wear Surface fatigue

Abrasive wear

Spalling

Yielding

Galling

Pitting Spalling

Mild abrasive wear


17/20

33

How journal bearings fail

Adhesivescuffing, galling, cold welding, seizure, smearing

Abrasiveploughing, polishing wear, grinding, scratchingCorrosionthermo chemical wear, oxidative wearSurface fatiguepitting, spalling, flaking


Scuffing

Scuffing

34

How journal bearings fail

Fatigue fractured Crankshaft

Fatigue fractured surface with band shaped progression marks


18/20

35

How shaft-hub connections failFatigue fracture

36

How transmission chains failFatigue fracture

Abrasive wear Corrosive wear

Yielding

Abrasive wear

Fatigue fracture

Corrosion

Yielding

Fatigue fractureformed without deformation


19/20

37

How rail-wheel systems fail Abrasive wear Adhesive wear Fatigue fractureYielding

Fracture initiated by surface fatigue

Yielding

38

Friction determines the life ofclutches


20/20

39

Friction change with running time

Summary About 80% of all machine failures are of Tribology

nature Adhesive wear, abrasive wear corrosion wear Fatigue wear Variation in friction result in unpredictable preload Stick slip may cause uncontrolled motion, noise Radial play caused high cyclic loading

Design for lifetime performance and reliability

Failure modes of machine elements

Documents

1.22657!lecture1introductionandfailuremechanisms[1]