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Thermo-mechanical fatigue of castiron for engine applications
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
2014 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Termomekanisk utmattning av gjutjärn för motortillämpningar (Swedish)
Abstract [en]

In an engine component the repeated start-stop cycles cause temporal and local inhomogeneous

temperatures, which in turn lead to a type of low-frequency loading, plastic deformation and

eventually failure due to thermo-mechanical fatigue. Simultaneously, high-frequency mechanical

loading arises from the cyclic combustion pressure and from road induced vibrations. These

types of loadings that mainly are in the elastic region are usually denoted high cycle fatigue

(HCF). In order to improve efficiency, power density and to reduce emissions, future truck

engines will be subjected to higher temperatures and higher combustion pressures which will

affect the service life of the different engine components. As a consequence, there is a need to

determine the limitations of the used alloys under these service conditions as exactly as possible.

In this master thesis work the fatigue properties of one grey iron (EN-GJL 250) and one

compacted graphite iron (EN-GJV 400) has been investigated under realistic loading conditions.

The results show that a change from the grey iron to the compacted graphite iron will result in a

significant increase of the fatigue life. The investigation also reveal that the life will increase

significantly if the maximum temperature can be decreased tens of degrees. Further, the results

indicate that addition of a relatively small HCF load may give a large decrease of the fatigue life.

Abstract [sv]

Motorkomponenter utsätts för upprepade start och stopp, vilka skapar tillfälliga och lokala

temperaturvariationer. Dessa resulterar i lågfrekventa lastväxlingar, plastiska deformationer och

eventuella brott i form av termodynamisk utmattning (TMF). Det sker dessutom en högfrekvent

mekanisk last, genererad av förbränningen och från vägvibrationer. Dessa laster är mestadels

elastiska och benämns högcykelutmattning (HCF). För att kunna förbättra verkningsgrad och

minska emissioner kommer framtida lastbilsmotorer att utsättas för högre förbränningstryck och

högre temperaturer, vilket kommer påverka motorernas livslängd. För detta krävs det att

materialens begränsningar utreds under ett verklighetstroget förhållande.

I detta exjobb kommer utmattningsegenskaperna för ett gråjärn (EN-GJL 250) och ett

kompaktgrafikjärn (EN-GJV 400) utredas under realistiska lastförhållanden.

Resultatet påvisar att ett byte från gråjärn till kompaktgrafitjärn ger en signifikant ökad

livslängd. Det framkommer också att livslängden kan ökas genom att sänka den maximala

temperaturen ett tiotal grader. Analysen påvisar även att en relativt liten HCF last kan ge kraftigt förkortad livslängd.

Place, publisher, year, edition, pages
2014. , 70 p.
Series
MMK 2014:14 MKN104
Keyword [en]
Thermo-mechanical fatigue, TMF, CGI, LGI, fatigue, thermal strain.
Keyword [sv]
Termomekanisk utmattning, TMF, CGI, LGI, termisk töjning.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-156880OAI: oai:DiVA.org:kth-156880DiVA: diva2:768318
Supervisors
Examiners
Available from: 2014-12-03 Created: 2014-12-03

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