Component engineering (MF2010)

Transcription

1 Component engineering (MF2010) Lecture 1 Course introduction Failure mechanisms MF2010@md.kth.se 1 Component engineering, 6 hp Advanced level Compulsory for the specialization Machine Design Selectable för M4,P4,T4 Component dimensioning Function, reliability, failure mechanisms, efficiency Monte Carlo simulations, gear standard, FEM, modeling 2 1

2 Atlas Copco Tools - LTV angle nut runners 3 Atlas Copco Tools nut runner motor planetary planetväxlar gears utgående exit shaft axel pinion- shaft axel avstängningsventil closing valve koppling clutch bevel vinkelväxelhus gear housing 4 2

3 Monte Carlo simulation P W α L 5 Dimensioning of conical gears with the AGMA standard 6 3

4 Dimensioning of the pinion shaft 7 Modeling and simulation 8 4

5 Pitting Yielding Surface fatigue Flaking Maximum shear stress Spalling 9 Introduction 1 Reliability engineering 2 Failure modes of machine elements 3 Fatigue failure prediction and prevention Vermelding onderdeel organisatie 10 5

6 Failure analysis 11 DN 13 sep 2007 Slitage orsak till SAS-haveri Slitage fick en bult att lossna. Det var orsaken till problemen med landningsstället när ett SAS-flygplan av modellen Dash-8 Q400 tvingades nödlanda i Ålborg i söndags, enligt en preliminär rapport från den danska haverikommission, rapporterar nyhetsbyrån Ritzau. 12 6

7 How to improve operating reliability? 1) You need to know how stuff fails. The allowable pressure in sliding contacts between metals is limited by seizure 2) You need to know the measures Steel that can cast be iron taken 5 10 to prevent MPa, failures. μ= In screw joints contact pressures up to 100 MPa are common, but the sliding motion is limited to one single move. Steel - CuSn or CuAl alloys MPa, μ= Zinc plated to prevent corrosion and seizure. 13 Shear fracture Ductile fracture Fatigue fracture How stuff fails How to prevent failure Fatigue fracture Check joint stiffness Thread stripping Check steel grade of the nut Ductile fracture Check preload 14 7

8 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 15 Fatigue failure 16 8

9 Wear mechanisms Dry sliding metal to metal contacts always show adhesive wear. Dry sliding polymer to metal contacts show abrasive wear. 17 Zinc plated to prevent corrosion and seizure. 18 9

10 Two body abrasive wear Three body abrasive wear 19 Adhesive wear (Galling) 20 10

11 21 Wear mechanisms Stainless steel bushing in contact with a polymer bearing has completely worn through in short time! Corrosion wear 22 11

12 23 Wear mechanisms Hertzian contact Surface fatigue Maximum shear stress 24 12

13 25 Wear mechanisms Adhesive scuffing, galling, cold welding, seizure, smearing Abrasive ploughing, polishing wear, grinding, scratching Corrosion thermo chemical wear, oxidative wear Surface fatigue pitting, spalling, flaking Motion related: fretting, false Brinelling 26 13

14 How rolling bearings fail? Adhesive scuffing, galling, cold welding, seizure, smearing Abrasive ploughing, polishing wear, grinding, scratching Corrosion thermo chemical wear, oxidative wear Surface fatigue pitting, spalling, flaking Flaking Motion related: fretting, false Brinelling 27 Failure mode classification for bearing damage 28 14

15 How gears fail Adhesive wear Surface fatigue Fatigue fracture Forced tooth breakage Fatigue fracture Forced tooth breakage Pitting Scuffing

16 Angivna prestandabegränsande fenomen är: Wear = nötning Scoring = repbildning Spalling = gropbildning eller ytutmattning Breakage = kuggbrott. 31 How cams fail Yielding Yielding Adhesive wear Surface fatigue Abrasive wear Galling Pitting Spalling Spalling Mild abrasive wear 32 16

17 How journal bearings fail Scuffing Adhesive scuffing, galling, cold welding, seizure, smearing Abrasive ploughing, polishing wear, grinding, scratching Corrosion thermo chemical wear, oxidative wear Surface fatigue pitting, spalling, flaking Scuffing Motion related: fretting, false Brinelling 33 How journal bearings fail Fatigue fractured Crankshaft Fatigue fractured surface with band shaped progression marks 34 17

18 How shaft-hub connections fail Fatigue fracture 35 How transmission chains fail Fatigue fracture Abrasive wear Corrosive wear Yielding Fatigue fracture Fatigue fracture formed without deformation Yielding Abrasive wear Corrosion 36 18

19 How rail-wheel systems fail Abrasive wear Adhesive wear Fatigue fracture Yielding Yielding Fracture initiated by surface fatigue 37 Friction determines the life of clutches 38 19

20 Friction change with running time 39 Failure modes of machine elements 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 40 20