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Fatigue Assessment of Cast Components: Influence of Cast Defects
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
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.
Series
Trita-AVE, ISSN 1651-7660 ; 2008:49
Keyword [en]
cast nodular iron, fatigue, design rules, fracture mechanics
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-9133ISBN: 978-91-7415-101-5 (print)OAI: oai:DiVA.org:kth-9133DiVA: diva2:25189
Public defence
2008-09-29, F3, Lindstedtsvägen 26, Stockholm, 10:15 (English)
Opponent
Supervisors
Projects
Gjutdesign
Note
QC 20100712Available from: 2008-09-23 Created: 2008-09-22 Last updated: 2010-07-12Bibliographically approved
List of papers
1. On the prediction of crack propagation in cast steel specimens
Open this publication in new window or tab >>On the prediction of crack propagation in cast steel specimens
2004 (English)In: 9th Portuguese Conference on Fracture, 2004Conference paper, Published paper (Refereed)
Abstract [en]

This investigation deals with the fatigue behaviour of cast steel with respect to defects, crack initiation, crack growth and material parameters. It constitutes the initial part of a larger work in cast materials. The main objectives have been to validate calculations made by FEM and Paris law with data from fatigue tests and to confirm material parameters for Pan's law. Furthermore, the results where put against calculations obtained from the fracture mechanic software AF-GROW. During the accomplishment some difficulties was experienced concerning the initiation of the crack, with result that there where just a few specimens suitable for evaluation by LEFM. However, some conclusions concerning the crack growth behaviour could yet be done. The results in general showed good correspondence, the results from AF-GROW included. Most divergences could be explained by residual stresses and, to some extent, the initiation problems.

National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-14059 (URN)
Conference
February 18th – 20th 2004, Setúbal
Note
QC 20100712Available from: 2010-07-12 Created: 2010-07-12 Last updated: 2010-11-24Bibliographically approved
2. Conventional vs. closure free crack growth in nodular iron
Open this publication in new window or tab >>Conventional vs. closure free crack growth in nodular iron
2005 (English)In: Competent Design by Castings: Improvements in a Nordic Project / [ed] Samuelsson J, Marquis G, Solin J, Valtion Teknillinen Tutkimuskeskus , 2005, 273-286 p.Conference paper, Published paper (Refereed)
Abstract [en]

This investigation deals with the fatigue properties and material parameters for a silicon alloyed nodular cast iron. The material follows the Swedish standard SS 140725. The objectives for this investigation where to evaluate properties of the material in a fracture mechanic sense of view. In this part, the attention was paid to the basic fracture mechanic properties, i.e. da/dN-curves and Pan's law parameters. It also include R-dependence behaviour evaluated for R-values from R= 0 and R= 0.8. The main incitement for using the closure free approach is that it produces the fastest crack propagation rate that can be found at given conditions and load levels. This investigation of nodular iron will be followed by subsequent parts. The investigation in total is a part of the nordic project "Cast Design 2005".

Place, publisher, year, edition, pages
Valtion Teknillinen Tutkimuskeskus, 2005
Series
Valtion Teknillinen Tutkimuskeskus. VTT Symposium, ISSN 0357-9387 ; 237
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-14069 (URN)000231578700016 ()2-s2.0-42149127654 (Scopus ID)951-38-6298-4 (ISBN)
Conference
Seminar on Competent Design by Castings (GJUTDESIGN -2005) Espoo, FINLAND, JUN 13-14, 2005
Note

QC 20100712

Available from: 2010-07-12 Created: 2010-07-12 Last updated: 2012-09-26Bibliographically approved
3. Fracture mechanics evaluation of a nodular cast iron component by 3d modelling
Open this publication in new window or tab >>Fracture mechanics evaluation of a nodular cast iron component by 3d modelling
2005 (English)In: Competent Design by Castings: Improvements in a Nordic Project / [ed] Samuelsson J; Marquis G; Solin J, 2005, Vol. 237, 351-374 p.Conference paper, Published paper (Refereed)
Abstract [en]

The object of this paper was fracture mechanic modelling of solids using finite element (FEM). The main tool that has been utilized was the software Mcrack which is a group of macros intended for use jointly with ANSYS finite element program. One major advantage of the Mcrack software is that it supports solid modelling with a crack located at an arbitrary location. This implies that it is possible to calculate also torsion and mixed mode cases within a most reasonable work effort. However, Mcrack was developed to cover complex weld geometries. Utilizing Mcrack for general solid modelling requires an analysis of the possibility of development for arbitrary crack paths. As test object a cast sleeve made of nodular iron has been used. Previous to this investigation the component was submitted to a test program and a subsequent evaluation according to S/N criteria's at ABB, Sweden. This paper is thus a continuation of the ABB work, and at the same time an extension of the field of application for the Mcrack software. For validation purposes the software AF-Grow as well as elementary cases has been used in parallel. The investigation is a part of the nordic project "Cast Design 2005".

Series
VTT SYMPOSIA, ISSN 0357-9387 ; 237
Keyword
Brittleness; Cast iron; Computer software selection and evaluation; Crack detection; Finite element method; Fracture fixation; Fracture mechanics; Iron; Macros; Mechanics; Modal analysis; Strength of materials; Testing; Three dimensional; 3-D modeling; Arbitrary cracks; Finite element (FE); Finite element programs; General (CO); Mixed modes; Nodular cast iron; Solid modelling; Test object (TO); test programs; Torsion (IGC: D7)
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-14046 (URN)000231578700020 ()2-s2.0-42149099990 (Scopus ID)
Conference
Seminar on Competent Design by Castings (GJUTDESIGN -2005), Espoo, FINLAND, JUN 13-14, 2005
Note
QC 20100709Available from: 2010-07-09 Created: 2010-07-09 Last updated: 2011-10-13Bibliographically approved
4. Fracture-mechanics-founded quality rules for defect classification in nodular cast iron
Open this publication in new window or tab >>Fracture-mechanics-founded quality rules for defect classification in nodular cast iron
(English)Article in journal (Other academic) Submitted
Keyword
nodular iron; quality rules; fracture mechanics; defect classification; fatigue; cast defects
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-14051 (URN)
Note
QC 20100712Available from: 2010-07-12 Created: 2010-07-12 Last updated: 2010-07-12Bibliographically approved
5. A novel tool for crack modelling in finite element analysis
Open this publication in new window or tab >>A novel tool for crack modelling in finite element analysis
(English)Article in journal (Other academic) Submitted
Keyword
FEM; fracture mechanics; crack propagation; crack kinking; embedded crack
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-14052 (URN)
Note
QC 20100712Available from: 2010-07-12 Created: 2010-07-12 Last updated: 2010-07-12Bibliographically approved
6. Fatigue crack growth in ductile iron
Open this publication in new window or tab >>Fatigue crack growth in ductile iron
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.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-14053 (URN)000231578700017 ()2-s2.0-42149131532 (Scopus ID)
Note

Updated from manuscript to article in journal.

QC 20100712

Available from: 2010-07-12 Created: 2010-07-12 Last updated: 2014-12-05Bibliographically approved

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