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Per Newton's Third Law of Physics (action-reaction of forces) and Engineering Mechanics (Statics-Principle of' Transmissibility), the loading of multiple tensile samples in series produces valid test conditions as long as the following constraints are observed:

A) Tensile test samples are of the same or similar Notched Ultimate Tensile Strength. All known hydrogen embrittlement notch tensile test loading is governed by ASTM E-8, which requires a loading accuracy of +/- 1%. Therefore, valid series loading of test samples can occur with different sample lots of varying notch tensile strengths of 2% maximum spread.

B) Axial alignment is maintained. ASTM E-1012 requirements for axial alignment are utilized for verification.

C) Compression, shear, and torsional loads are zero.



Check and Balance: Traditionally, when test failures occur, testing validity is reviewed.

I) Are the samples embrittled?
2) Are the test samples defective?
3) Is the test machine accurate?

Series loading of multiple test samples can actually enhance the accuracy of the test data. This is because if failures occur in one process and not another this demonstrates that:

* Actual sample bar lot anomalies are moot. i.e.
- sample bar anomalies would show up in all plating processes
* A testing machine problem would cause failures in different plating process samples.

The above data applies only to traditional sustained load hydrogen embrittlement tests. Tests based on constant displacement do not produce a constant load, and do not follow the Principle of Transmissibilitv as referenced above. Examples of non-valid constant displacement embrittlement tests are 1) bend tests using linear torque application (full ring, C-ring, or square bar) 2) tensile tests using displacement monitoring - hold features.


3.2. Principle of Transmissibility. Equivalent Forces. The principle of transmissibility states that the conditions of equilibrium or of motion of a rigid body will remain unchanged if a force F acting at a given point of the rigid body is replaced by a force F' of the same magnitude and same direction, but acting at a different point, provided that the two forces have the same line of action (Fig. 3.3). The two forces F and F' have the same effect on the rigid body and are said to be equivalent.


From "Vector Mechanics for Engineers - STATICS & DYNAMICS By Beer & Johnson Jr. copyright McGraw Hill 1972 used by permission"

 
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