It has been shown that bending stresses that inadvertently occur due to misalignment between the applied force and the specimen axes during the application of tensile and compressive forces can affect the test results. In recognition of this effect, some test methods include a statement limiting the misalignment that is permitted. The purpose of this practice is to provide a reference for test methods and practices that require the application of tensile or compressive forces under conditions where alignment is important. The objective is to implement the use of common terminology and methods for verification of alignment of testing machines, associated components and test specimens.
Alignment verification intervals when required are specified in the methods or practices that require the alignment verification. Certain types of testing can provide an indication of the current alignment condition of a testing frame with each specimen tested. If a test method requires alignment verification, the frequency of the alignment verification should capture all the considerations i.e. time interval, changes to the testing frame and when applicable, current indicators of the alignment condition through test results.
Whether or not to improve axiality should be a matter of negotiation between the material producer and the user.
Included in this practice are methods covering the determination of the amount of bending that occurs during the application of tensile and compressive forces to notched and unnotched test specimens during routine testing in the elastic range. These methods are particularly applicable to the force levels normally used for tension testing, creep testing, and uniaxial fatigue testing. The principal objective of this practice is to assess the amount of bending exerted upon a test specimen by the ordinary components assembled into a materials testing machine, during routine tests.