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Fatigue crack growth in ductile iron
Chalmers University of Technology, Department of Material and Production Technologies.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2005 (English)In: Valtion Teknillinen Tutkimuskeskus. VTT Symposium, ISSN 0357-9387, Vol. 237, 287-310 p.Article in journal (Refereed) Published
Abstract [en]

Crack initiation and propagation of two ductile irons are studied. The main reason for the study is to propose a common set of reliable fatigue data based on fracture mechanics. Material in this investigation is one standard feritic/pearlitic ductile iron (SGJ 500-7) and one silicon alloyed ductile iron with a solution hardened ferritic matrix (SS 140725). Basically the threshold value and the scaling constants in Pan's equation are evaluated. The data used at Volvo Truck has been gathered and re-evaluated. Complementary experiments have been conducted. All experiments have been in accordance with ASTM-647. Scaling constants in Paris equation is set to m= 4,5 and C= 9,4 10(-14) (m/cycle)/MNm(-3/2) for the standard grade material and m= 5,0 and C= 1,9 10-14 (m/cycle)/MNM-3/2 for the silicon alloyed material. These results are valid for -I < R < 0,5. The difference in the slope between the materials is due to different fracture behaviour. Threshold values for the materials can be found in Tables 2 and 3. Crack closure and the influence on crack propagation is expressed in a in a new algorithm. The new algorithm is valid for -I < R < 0,5 but should be used with caution due to meagre statistical foundation.

Place, publisher, year, edition, pages
2005. Vol. 237, 287-310 p.
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-14053ISI: 000231578700017ScopusID: 2-s2.0-42149131532OAI: diva2:329431

Updated from manuscript to article in journal.

QC 20100712

Available from: 2010-07-12 Created: 2010-07-12 Last updated: 2014-12-05Bibliographically approved
In thesis
1. Fatigue Assessment of Cast Components: Influence of Cast Defects
Open this publication in new window or tab >>Fatigue Assessment of Cast Components: Influence of Cast Defects
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

 This thesis is on the fatigue assessment of cast components with special attention to defects. The primary material in view is nodular cast iron, but also cast steel is considered. However, the fatigue behaviour is in principle valid for general use on other cast metals.The first two papers is about general cast material behaviour in fatigue loading. The materials considered are a high strength alloyed cast steel and a medium strength nodular cast iron. It is concluded that cast defects is the main fatigue initiation cause and it is only in exception that the fatigue life is not ruled by fracture mechanics. The third paper is a fracture mechanics evaluation of a nodular iron cast sleeve. The analysis of the component is based on crack initiation from cast defects and low-cycle fatigue. Fracture mechanics material parameters for Paris law, c and m, are extracted for the materials considered. In paper D design quality rules for nodular cast iron based on the Swedish standard SS 11 40 60 is presented. The quality rules regard cast defects in fatigue assessments and facilitate defect-based component design. In paper E, a finite element tool that is capable to predict and calculate 3D crack propagation for embedded cracks and defects is presented. The tool is an add-on for ANSYS finite element program. In paper F, closure equations for nodular cast iron are proposed in parallel to refined fracture mechanics material data. The paper includes crack propagation at different load ratios and in different microstructures.Summarized, the thesis composes a further development of the fatigue assessment of cast components. The central role of defects in fatigue is clarified and tools are provided for fracture mechanics evaluations of defects as well as for defect based design. The quality rules are also fit for application in manufacturing and for acceptance tests, hence covering the span from design to complete product.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. vi, 55 p.
Trita-AVE, ISSN 1651-7660 ; 2008:49
cast nodular iron, fatigue, design rules, fracture mechanics
National Category
Vehicle Engineering
urn:nbn:se:kth:diva-9133 (URN)978-91-7415-101-5 (ISBN)
Public defence
2008-09-29, F3, Lindstedtsvägen 26, Stockholm, 10:15 (English)
QC 20100712Available from: 2008-09-23 Created: 2008-09-22 Last updated: 2010-07-12Bibliographically approved

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