Significance and Use

The determination of the superplastic properties of a metallic sheet material is important for the observation, development and comparison of superplastic materials. It is also necessary to predict the correct forming parameters during an SPF process. SPF tensile testing has peculiar characteristics compared to conventional mechanical testing, which distort the true values of stress, strain, strain hardening, and strain rate at the very large elongations encountered in an SPF pull test, consequently conventional mechanical test methods cannot be used. This test method addresses those characteristics by optimizing the shape of the test coupon and specifying a new test procedure.

The evaluation of a superplastic material can be divided into two parts. Firstly, the basic superplastic-forming (SPF) properties of the material are measured using the four parameters of stress, temperature, strain, and strain rate. These are obtained using conversions from the raw data of a tensile test. Secondly, derived properties useful to define an SPF material are obtained from the basic properties using specific equations.

1. Scope

1.1 This test method describes the procedure for determining the superplastic forming properties (SPF) of a metallic sheet material. It includes tests both for the basic SPF properties and also for derived SPF properties. The test for basic properties encompasses effects due to strain hardening or softening.

1.2 This test method covers sheet materials with thicknesses of at least 0.5 mm but not greater than 6 mm. It characterizes the material under a uni-axial tensile stress condition.

Note 1Most industrial applications of superplastic forming involve a multi-axial stress condition in a sheet; however it is more convenient to characterize a material under a uni-axial tensile stress condition. Tests should be performed in different orientations to the rolling direction of the sheet to ascertain initial anisotropy.

1.3 This method has been used successfully between strain rates of 10 ^-5 to 10 ^-1 per second.

1.4 This method has been used successfully on Aluminum and Titanium alloys. The use of the method with other metals should be verified.

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

ASTM Standards

E4 Practices for Force Verification of Testing Machines

E6 Terminology Relating to Methods of Mechanical Testing

E21 Test Methods for Elevated Temperature Tension Tests of Metallic Materials

E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods

E646 Test Method for Tensile Strain-Hardening Exponents (n -Values) of Metallic Sheet Materials

E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

Keywords

constant strain rate; metallic materials; m value; SPF; superplastic forming; superplastic properties; temperature; true strain; true stress; Metallic sheet materials; Superplastic forming properties (SPF);

ICS Code

ICS Number Code 77.140.50 (Flat steel products and semi-products)

DOI: 10.1520/E2448-11

ASTM International is a member of CrossRef.

ASTM E2448