ASTM E 328-13 Standard test method for Stress Relaxation for Materials and Structures

ASTM E 328-13 Standard test method for Stress Relaxation for Materials and Structures

ASTM E 328-12 covers a broad range of testing activities. These test methods cover a broad range of testing activities. To help decide the subject matter for particular testing, the standard is divided into a general four-section, which applies to all materials and structures for stress relaxation test.

    Scope:

    This test method is used to determine stress relaxation of materials and structures under conditions of Constant environment, Constraint, and negligible vibration. In this test, the testing material or structure is initially constrained by extremely applied forces and changes in external forces to keep constraint are determined as a function of time. Specific methods for conducting stress relaxation tests on materials subjected to tension, compression, bending and torsion stresses are described in sections A, B, C, and D, respectively.

    TestSection
    Method for conducting stressRelaxation tension tests A13-21
    Method for conducting stressRelaxation compression tests B22-29
    Method for conducting stressRelaxation bending tests C30-38
    Method for conducting stressRelaxation torsion test  D39-47

    Figure 1: Tension Stress-Relaxation Test Using Periodic Force Measurement

    Figure 2: Compression Stress-Relaxation Test

    Result:

    For the method for conducting stress relaxation torsion test 

    Strain will be taken as equal to the angle of twist per unit length, multiplied by the radius of the specimen.

    1. The initial maximum torsional stress may be calculated as follows, Obtain a torque versus angle-of-twist-per-unit-length curve up to the desired angle of twist, If the curve is linear, use the following equations.

    1.1 For a cylindrical specimen

    Where,

    τ0 = initial maximum torsional stress,

    T0 = initial torque,

    d = specimen diameter.

    1.2. for a tubular specimen,

    Where,

    d0 = specimen outside diameter,

    di = specimen inside diameter.

    2. If the torque-twist curve is nonlinear, the initial maximum torsional stress can be estimated for a cylindrical specimen or for a thin-walled tubular specimen.

    2.1 For a cylindrical specimen,

    Where

    θ = angle of twist per unit length at torque T0, and

    α = slope of the torque-twist curve at torque τ0.

    3. The accuracy with which the remaining torsional stress may be determined, at any instant, depends upon the nature of the specimen.

    3.1For a thin-walled tubular specimen, the remaining torsional stress may be approximated by,

    Where

    τ = remaining maximum torsional stress, and

    T = remaining torque.

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