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Experimental Procedures


This section of this paper is highly abbreviated versus the original publication5


describing the database. The original


database project utilized differing procedures for different types of cast iron. This paper only addresses ductile iron, so only the procedures used for ductile iron are contained herein. Furthermore, operative ASTM test methods are only contained in the original publication.


Chemical Analysis and Metallography


An analysis of alloy chemistry was conducted on each of two samples extracted from randomly selected castings from each group of test materials. The concentrations of most ele- ments were determined using optical emission spectrometry (OES) except carbon, nitrogen, and sulfur, which were de- termined using combustometric methods. Copper and mag- nesium were determined by atomic absorption (AA) spec- trophotometry.


Typically, three metallographic specimens were prepared and analyzed for each test material. Transverse cross-sec- tions were extracted from the gage section of tensile bars, mounted and polished using standard metallographic techniques. The samples were final polished using colloi- dal silica media with a 0.05 um particle size. The samples were photographed at two or three appropriate magnifica- tions in the as-polished condition and after etching with 2% Nital. Automated image analysis was performed to measure nodularity, nodule count, and ferrite/pearlite content.


Hardness and Tensile Testing (Su


Brinell hardness measurements were conducted on the shoul- ders of fractured tensile bars using a 3000 kg load. Tensile spec- imens were tested to determine standard tensile properties [i.e., 0.2% offset yield strength (Sy


or YS), ultimate tensile strength or UTS), total elongation (%El), and reduction in area


(%RA)]. Additionally, the monotonic tensile stress-strain re- sponse was characterized for a subset of the specimens in terms of elastic modulus and/or Poisson’s ratio as well as monotonic strength coefficient (K) and monotonic strain hardening expo- nent (n). Figures 1 and 2 show the standard tensile properties and monotonic stress-strain constants, respectively.4


Room temperature tensile tests were conducted on standard round tensile specimens with 0.5 inch (13 mm) gauge diam- eter and 2.0 inch (50 mm) gauge length. In isolated cases, proportional subsize tension specimens were used when ne- cessitated by material size constraints.


Strain gauges were employed for precision modulus and Poisson’s ratio determinations and an extensometer was em- ployed for determining K and n. For standard tension tests, an initial strain-rate of 0.3% per minute was imposed until the yield strength was exceeded; after yield, the strain-rate was increased to 10% per minute. The total elongation was measured by reassembly of the samples and physical mea- surement of the final gauge length. For elastic modulus or Poisson’s ratio determination, a smaller initial strain rate of 0.2% per minute was used.


Fatigue Testing


All fatigue test specimens were machined with low stress procedures and longitudinally polished. The specimens had a 0.314 inch (8 mm) gage diameter, 0.628 inch (16 mm) gage length, 2.51 inch (64 mm) blending radius, and 0.590 inch (15 mm) diameter grip ends.


Figure 1. Engineering and true stress-strain plots and properties from Reference 4.


International Journal of Metalcasting/Spring 2012


Figure 2. Logarithmic true stress-plastic strain plot with monotonic stress-strain constants from Reference 4.


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