If you are an ASTM Compass Subscriber and this document is part of your subscription, you can access it for free at ASTM Compass
    ASTM E328 - 21

    Standard Test Methods for Stress Relaxation for Materials and Structures

    Active Standard ASTM E328 | Developed by Subcommittee: E28.04

    Book of Standards Volume: 03.01

      Format Pages Price  
    PDF 15 $60.00   ADD TO CART
    Hardcopy (shipping and handling) 15 $60.00   ADD TO CART
    Standard + Redline PDF Bundle 30 $72.00   ADD TO CART

    Significance and Use

    5.1 Stress-relaxation test data are necessary when designing most mechanically fastened joints to ensure the permanent tightness of bolted or riveted assemblies, press or shrink-fit components, rolled-in tubes, etc. Other applications include predicting the decrease in the tightness of gaskets, in the hoop stress of solderless wrapped connections, in the constraining force of springs, and in the stability of wire tendons in prestressed concrete.

    5.2 The ability of a material to relax at high-stress concentrations such as are present at notches, inclusions, cracks, holes, and fillets can be predicted from stress-relaxation data. Such test data are also useful to judge the heat-treatment condition necessary for the thermal relief of residual internal stresses in forgings, castings, weldments, machined or cold-worked surfaces, etc. The tests outlined in these methods are limited to conditions of approximately constant constraint and test environment.

    5.3 The general stress-relaxation test is performed by isothermally applying a force to a specimen with fixed value of constraint. The constraint is maintained constant, and the constraining force is determined as a function of time. The major problem in the stress-relaxation test is that constant constraint can be very difficult to maintain. The effects on test results are very significant, and considerable attention shall be given to minimize the constraint variation. Also, experimenters should determine and report the extent of variation in each stress-relaxation test so that this factor can be taken into consideration.

    5.4 There are many methods of performing the stress-relaxation test, each with a different starting procedure. However, the constraint is usually obtained initially by the application of an external force at either a specific force-application rate or a specific strain rate. The two methods will produce the characteristic behavior shown in Fig. 1 when the initial stress, σ0, exceeds the proportional limit. Some testing machines, while reaching the constraint value, do not produce either a constant force-application rate or constant strain rate, but something in between. However, the general characteristics of the data will be similar to those indicated. The stress-application rate in either case should be reasonably rapid, but without impact or vibration, so that any relaxation during the stress-application period will be small.

    5.5 The stress-relaxation test starts at zero time, t0, in Fig. 1.

    Note 2: This zero time is the reference time from which the observed reduction in force to maintain constant constraint is based. Selection of this time does not imply that the force-application procedure and period are not significant test parameters which are important in the application of the data.

    1. Scope

    Note 1: The method of testing for the stress relaxation of plastics has been withdrawn from this standard, and the responsibility has been transferred to Practice D2991.

    1.1 These test methods cover the determination of the time dependence of stress (stress relaxation) in materials and structures under conditions of approximately constant constraint, constant test environment, and negligible vibration. In the procedures, the material or structure is initially constrained by externally applied forces, and the change in the external force necessary to maintain this constraint is determined as a function of time.

    1.2 Specific methods for conducting stress-relaxation tests on materials subjected to tension, compression, bending and torsion stresses are described in Parts A, B, C, and D, respectively. These test methods also include recommendations for the necessary testing equipment and for the analysis of the test data.

    1.3 Bending stress-relaxation tests to determine relaxation properties by using ring-shaped specimens machined from bulk material have been thoroughly developed and widely used to determine stress-relaxation properties (1).2 These tests are outside the scope of these test methods.

    1.4 The long time periods required for these types of tests are often unsuited for routine testing or for specification in the purchase of material. However, these tests are valuable tools in obtaining practical design information on the stress relaxation of materials subjected to constant constraint, constant test environment, and negligible vibration, and in investigations of the fundamental behavior of materials.

    1.5 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

    1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

    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

    D2991 Test Method for Stress-Relaxation of Plastics

    E4 Practices for Force Verification of Testing Machines

    E6 Terminology Relating to Methods of Mechanical Testing

    E8/E8M Test Methods for Tension Testing of Metallic Materials

    E9 Test Methods of Compression Testing of Metallic Materials at Room Temperature

    E139 Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic Materials

    E1012 Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application

    ICS Code

    ICS Number Code 19.020 (Test conditions and procedures in general)

    UNSPSC Code

    UNSPSC Code

    Referencing This Standard
    Link Here
    Link to Active (This link will always route to the current Active version of the standard.)

    DOI: 10.1520/E0328-21

    Citation Format

    ASTM E328-21, Standard Test Methods for Stress Relaxation for Materials and Structures, ASTM International, West Conshohocken, PA, 2021, www.astm.org

    Back to Top