Causes of failure

TAFE NSW -Technical and Further Education Commission

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ENMAT101A Engineering Materials and ProcessesAssociate Degree of Applied Engineering (Renewable Energy Technologies)Lecture 26 – Causes of failure

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Causes of failure

EMMAT101A Engineering Materials and Processes

Reference Text Section

Higgins RA & Bolton, 2610. Materials for Engineers and Technicians, 5th ed, Butterworth Heinemann

Ch 26

Reference Text Section


26.2 Causes of failure (Higgins 26.2)


Overstressing (abuse)Fatigue (Alternating loads)Creep (High temp)Sudden loads (earthquake, storm, accident)Expansion (or contraction)Thermal cycling (hot/cold stresses)Degradation (Environmental)


26.2 Causes of failure (Higgins 26.2)


26.2.1 Types of fracture surfacesDuctile failure with metalsBrittle failure with metalsFatigue failure with metalsFailure with polymersFailure with ceramicsFailure with composites


26.3 Non-destructive testing (Higgins 26.3)


26.3.1 The detection of surface cracks and flawsPenetrant methods

http://en.wikipedia.org/wiki/Nondestructive_testing




Magnetic particle methods




Acid pickling methods




26.3.2 The detection of internal defectsX-ray methodsGamma-ray methods




Ultrasonic testing:Principle of ultrasonic testing. LEFT: A probe sends a sound wave into a test material. There are two indications, one from the initial pulse of the probe, and the second due to the back wall echo. RIGHT: A defect creates a third indication and simultaneously reduces the amplitude of the back wall indication. The depth of the defect is determined by the ratio D/Ep

http://en.wikipedia.org/wiki/Ultrasonic_testing


26.4 Degradation of metals by oxidation (Higgins 26.4)


Oxidation26.4.1 Attack by sulphur


26.4 Degradation of metals by electrolytic corrosion (Higgins 26.4)


Electrolytic corrosion is like aBattery.




26.5.1 The Electrochemical (or Galvanic) Series




26.5.2 Cladding of metal sheets




26.5.2 Cladding of metal sheets




26.5.3 Rusting of iron and steel


26.6 The protection of metal surfaces (Higgins 26.6)


26.6.1 Painting26.6.2 Stove-enamelling26.6.3 Coating the surface with another metalHot dippingSprayingSherardisingElectroplatingCladding26.6.4 Protection by oxide coatings


26.6 The protection of metal surfaces (Higgins 26.6)


26.6.5 Metals and alloys which are inherently corrosion-resistant26.6.6 Galvanic protection




26.5.4 Stress corrosion


26.7 Stability of plastics (Higgins 26.7)


26.7.1 Weathering of plastics materials26.7.2 Perishing of rubbers26.7.3 Stress cracking and crazing of polymers26.7.4 Stability to solvents


26.8 Preservation of timber (Higgins 26.8)


26.8.1 Insect pests26.8.2 Fungus attack


26.9 Service life (Higgins 26.9)


• External loading levels, rate of loading (impact loading), frequencyof loading (fatigue), duration of loading (creep).• Material property degradation (corrosion).• Defects in the form of cracks, porosity (in castings), cavities (inwelds) introduced during manufacturing.• Conditions under which used, e.g. temperature, temperature cycling,humidity, chemicals, contact with other materials.• Bad design features such as the presence of notches, sharp corners,small holes, surface roughness.• Lack of, or inappropriate, maintenance.



Videos

Joining MetalsSheppard, Phil. Bendigo, Vic. : Classroom Video, c2006. DVD (29 min.). An introduction to the methods of joining metals, including riveting and fusion and non-fusion methods of welding. Mt Druitt College Library: DVD 671.5/JOINJoining Metals Notes (pdf)Recommended Viewing: All sections.

http://wsilibraries.tafensw.edu.au/mount-druitt/

http://learneasy.info/MDME/MEMmods/MEM30007A/processing/processing_files/Joining-Metals.pdf



Wikipedia: Welding

Resources.

Ashby diagrams

http://en.wikipedia.org/wiki/Welding

http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/spec-spec/basic.html


Glossary


Sacrificial anodeGalvanisingElectro-negativityStress corrosionElectrolysisOxidationDuctile/brittle failureFatigue failure


QUESTIONS: Joining of MaterialsHiggins Ch26, Newell, Timmings, Sheedy, Callister, Ashby

1. Define all glossary terms 2. (a) Explain what is meant by the term corrosion. (b) List three essential conditions

for corrosion to occur. (c) Describe how an anode and cathode can be formed. (d) Describe how corrosion can be controlled or prevented.

3. Briefly describe the different types of corrosion listed below:(a) uniform (general) corrosion(b) galvanic corrosion(c) crevice corrosion(d) stress corrosion(e) corrosion fatigue(f) de-alloying (selective leaching), for example de-zincification(g) high temperature (dry) oxidation corrosion

4. Briefly outline the processes by which plastics suffer degradation5. Explain the differences between corrosion resistance of platinium and titanium.

What other metals would fall into each of these two groups?6. Describe ways to counter galvanic corrosion in PhotoVoltaic systems. http://

www.civicsolar.com/node/10621


http://www.civicsolar.com/node/10621



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Causes of failure