STP608: Comparison of Manual to Automatic Unloading During Relaxation Tests

    Schmieder, AK
    Manager, Materials Testing Unit, and Supervisor, Creep Testing, General Electric Co., Schenectady, N. Y.

    Robinson, RS
    Manager, Materials Testing Unit, and Supervisor, Creep Testing, General Electric Co., Schenectady, N. Y.

    Pages: 16    Published: Jan 1976


    Abstract

    Relaxation tests are commonly made using the two following procedures: first by using a special machine, load is removed automatically in many small steps as the strain tends to increase. In the second procedure, a creep machine is used, and the load is reduced manually whenever the strain reaches a certain limit. In this case, the number of stress steps down is relatively small. One of a pair of specimens was tested by each method for several materials and the relaxation curves compared. They were found to be in good agreement when the magnitude of the stress step down is chosen in a particular manner. The factors involved in this choice are discussed in detail. The incremental creep curves obtained at each stress level of the manual test are compared with the normal creep curves at constant load. The previously reported disagreement between the results of these two methods of relaxation testing are discussed, and an explanation is offered.

    Keywords:

    mechanical tests, stress relaxation tests, unloading, strains, creep tests, extensometers, stresses


    Paper ID: STP27860S

    Committee/Subcommittee: E28.11

    DOI: 10.1520/STP27860S


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