This page contains a Flash digital edition of a book.
Another key difference between high and low cycle fa- tigue is that high cycle fatigue is strength and crack-ini- tiation controlled where stronger materials exhibit greater fatigue lives in the high cycle range. High cycle fatigue testing commonly produces an endurance or fatigue limit (strength) at long lives (10 million cycles). The fatigue lim- it for p %survival is defined as the limiting value of fatigue strength for p %survival as N becomes very large (like 10 million cycles), where p may be any number, such as 95, 90, and so forth.1


tests, and a database containing the strain-life fatigue prop- erties of multiple grades of cast iron was developed and published5


U.S. Department of Energy/Cast Metals Coalition (DOE/ CMC)6


in 2003. The work was originally funded by the with guidance by the American Foundry Society


Low cycle fatigue on the other hand


considers the regime where ductility and crack propaga- tion dominate life such that more ductile materials exhibit greater fatigue lives in the low cycle range.


For several reasons, bending fatigue strength has been a property that was measured historically. Now, modern de- signers require low cycle or strain-life fatigue properties of cast iron to populate their computer-aided design data- bases so that cast iron can be compared to compendia4


of


strain-life properties of steels and other competing materials. Strain-life fatigue properties can not be determined in bend- ing and must be determined axially so that the cyclic stress and strain can be related.


Another important distinction is that mod- ern fatigue databases do not contain fatigue limits, which are essentially the stresses be- low which materials are expected to survive fatigue. Rather, finite element modeling programs must be able to predict lives and locations of fatigue fractures in the vicinity of holes, thickness changes, and other stress concentrators. The cast iron strain-life fa- tigue database discussed in this paper offers designers the opportunity to perform such calculations with cast iron.


Motivation for the Database


Strain-life fatigue testing was conducted on a variety of cast irons for a variety of rea- sons. Such fatigue data is intended for use in current endurance modeling methods. Thus, designers can select optimal materials and design geometries to foster


(a) lighter products, (b) energy efficient operations, (c) longer and more predictable product service life, and


(d) more energy efficient product man- ufacture.


Database Description


Multiple grades of a variety of cast irons were subjected to a considerable variety of


8 International Journal of Metalcasting/Spring 2012


(AFS). Since the publication of the original DOE report,7 additional grades have been tested and the database con- tents have been augmented on an ongoing basis with ad- ditional AFS research funds. AFS has also developed an on-line materials database searching tool called CADS, which will eventually include this strain-life fatigue data- base product. For information see: http://www.metalcast- ingvirtuallibrary.com/cads/cads.aspx


Table 1 shows the current contents of the database based on testing by the author.5


The database also contains con-


tributed datasets from other sources, but these results are not included in the analysis conducted for this paper. Test samples for most of the grades were obtained from Y-blocks in the as-cast condition, but a few grades were tested with heat treated Y-blocks or with specimens ma- chined from cast parts.


Table 1. Materials Tested at Element (as of March 2012) The conditions marked in yellow were selected for analysis in this paper.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91