Significance and Use

Relaxation test data are necessary when designing most mechanically fastened joints to assure 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 the stability of wire tendons in prestressed concrete.

The ability of a material to relax at high-stress concentrations such as are present at notches, inclusions, cracks, holes, fillets, etc., may 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 environment.

The test results are highly sensitive to small changes in environmental conditions and thus require precise control of test conditions and methods.

The reproducibility of data will depend on the manner with which all test conditions are controlled. The effects of aging or residual stress may significantly affect results, as may variations in material composition.

1. Scope

Note 1The method of testing for the stress relaxation of plastics has been withdrawn from this standard, and the responsibility has been transferred to Practice D 2991 .

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 environment, and negligible vibration. In the procedures recommended, 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 It is recognized that 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 the conditions enumerated, and in investigations of the fundamental behavior of materials.

1.4 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.

1.5 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.

13.1 This test method covers the determination of the time-dependent decrease in stress in a specimen subjected to an uniaxial constant tension strain under conditions of uniform environment and negligible vibration. It also includes recommendations for the necessary testing equipment.

22.1 This test method covers the determination of the time-dependent decrease in stress in a specimen subjected to a long duration, uniaxial, constant compression strain in a uniform environment and negligible vibration. It also includes recommendations for the necessary testing equipment.

30.1 This test method covers the determination of the time-dependent decrease in stress in a specimen subject to long duration, constant bending strain, in a uniform environment, and negligible vibration. Recommendations for some typical test equipment are included. Methods included are only those in which the outer fiber strain is essentially uniform in the test section.

39.1 This test method covers the determination of the time-dependent decrease in torsional stress in a specimen subjected to long duration, constant torsional strain in a uniform environment and negligible vibration. Recommendations for some typical test equipment are included. The test method applies when the outer fiber strain is essentially uniform in the test section.

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

E8/E8M Test Methods for Tension Testing of Metallic Materials

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

E83 Practice for Verification and Classification of Extensometer Systems

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

Keywords

bending relaxation; bolting; compression relaxation; hoop stresses; riveting; springs; stress relaxation; tension relaxation; torsion relaxation; Bending relaxation; Castings; Compression testing--metallic materials; Elongation--metallic materials; Extensometers; Forgings; Gaskets; Hoop stress test; Humidity; Inclusions--metals/alloys; Joints; Loading tests--metals/alloys; Stress relaxation tests; Metals and metallic materials; Metals and metallic materials--inclusion rating; Notches; Springs; Strain testing; Stress cracking tests; Structural metals/alloys; Tensile properties/testing--metallic materials; Welding/welds;

ICS Code

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

DOI: 10.1520/E0328-02R08

ASTM International is a member of CrossRef.

ASTM E328