ASTM A438 - Transverse Testing of Gray Cast Iron

Test Method for Transverse Bending Tests on Gray Cast Iron Cylindrical Test Bars

1. Introduction

This test method outlines the procedure for conducting transverse bending tests on separately cast cylindrical test bars made of gray cast iron. The purpose of this test is to provide a quick and cost-effective estimation of the test bar's approximate strength. It also offers valuable data for comparing the relative ductilities of different gray cast iron test bars. Additionally, the test can be used to calculate the modulus of rupture or the apparent modulus of elasticity.

2. Significance and Use

Transverse bending tests on unmachined test bars of gray cast iron serve as a rapid and economical means of estimating the test bar's strength. However, it is essential to note that this test cannot entirely replace the accuracy of a tension test on a machined specimen. The test results provide easily measurable deflection values that aid in comparing the relative ductilities of various gray cast iron test bars. Furthermore, this test can be utilized to calculate the modulus of rupture or apparent modulus of elasticity.

3. Dimensions and Form of Test Bars

The test bars used in this method shall be separately castings with an essentially cylindrical shape. They are available in three standard sizes (0.88mm, 1.20mm, 2.00mm). The test bars may contain a reasonable amount of pattern draft, but the diameter at the middle of the test bar must conform to the tolerances specified.

The molds for the test bars should be at approximately room temperature during pouring. After casting, the test bars shall be cooled in the mold to a temperature below 900°F (490°C) and then cooled to room temperature in still air.

4. Test Procedure

Perform the transverse bending test on an as-cast (unmachined) test bar, loading it as a simple beam with the load applied midway between the supports. The supports and the loading fixture must be designed to make essentially point contact with the test bar. Satisfactory contact is achieved when the supports and loading fixture have a cylindrical surface with a diameter of about 1/4 to 1 inch (6.4 to 25.4 mm) and are positioned perpendicular to the length of the test bar.

For round bars, which are defined as those with a difference of less than 0.025 inches (0.64 mm) between their minimum and maximum diameters at the middle of the length, determine the reported breaking load in pounds. Divide the actual breaking load by a correction factor (Table 1), using the arithmetic average of the minimum diameters of the bar. The load should be applied in line with the minimum diameter.

For elliptical bars, defined as those with a difference of more than 0.025 inches (0.64 mm) between their minimum and maximum diameters at the middle of the length, apply the load in line with the minimum diameter. Determine the reported breaking load in pounds by dividing the actual breaking load by a correction factor.

(Note: The complete Table 1 with correction factors should be provided in the official test method documentation.)

This comprehensive test method allows for a reliable evaluation of the strength and ductility of gray cast iron test bars using transverse bending tests. It is essential to strictly adhere to the specified procedures to ensure accurate and consistent results.