ASTM E328-13
Standard Test Methods for Stress Relaxation Tests for Materials and Structures

Standard No.

ASTM E328-13

Release Date

2013

Published By

American Society for Testing and Materials (ASTM)

Status

Be replaced

Replace By

ASTM E328-20

Latest

ASTM E328-21

Scope

5.1 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.

5.2 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.

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 must 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 is considered to have started at zero time, t₀ in Fig. 1. This 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 or period, or both, are not significant test parameters. These must always be considered in the application of the data.

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 environment, and negligible vibration. In the procedures recommended, the material or structure is ......

ASTM E328-13 Referenced Document

• ASTM D2991 
• ASTM E1012 Standard Practice for Verification of Specimen Alignment Under Tensile Loading
• ASTM E139 Standard Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic Materials
• ASTM E4 Standard Practices for Force Verification of Testing Machines
• ASTM E6 Standard Terminology Relating to Methods of Mechanical Testing
• ASTM E8/E8M Standard Test Methods for Tension Testing of Metallic Materials
• ASTM E83 Standard Practice for Verification and Classification of Extensometer
• ASTM E9 Standard Test Methods of Compression Testing of Metallic Materials at Room Temperature

ASTM E328-13 history

• 2021 ASTM E328-21 Standard Test Methods for Stress Relaxation for Materials and Structures
• 2020 ASTM E328-20 Standard Test Methods for Stress Relaxation for Materials and Structures
• 2013 ASTM E328-13 Standard Test Methods for Stress Relaxation Tests for Materials and Structures
• 2002 ASTM E328-02(2008) Standard Test Methods for Stress Relaxation Tests for Materials and Structures
• 2002 ASTM E328-02 Standard Test Methods for Stress Relaxation Tests for Materials and Structures
• 1996 ASTM E328-86(1996)e1 Standard Test Methods for Stress Relaxation Tests for Materials and Structures