There are many inspection methods for the mechanical properties of rivet nuts, but they are not very detailed. Now R-Best rivet nuts summarize the methods for testing the mechanical properties of rivet nuts. We welcome supplements or comments.
1. Experimental load
The experimental load is an axial external load. Under this load, the nut must not show signs of thread peeling or breakage. For testing, the experimental load is a numerical value; for applications in design, the experimental load is a limit.
In the test, the test load is applied to the nut to be tested through the test bolt or the machine spindle that has been axially loaded. When the load is removed, the rivet nut must be free to remove from the bolt or mandrel. The latter requirement is very interesting, because it proves that the threads are not twisted to a degree enough to bond the occluding threads together. Tests have shown that when the applied load reaches 95% of the load that causes the thread to peel off, the phenomenon of thread bonding will occur.
2. Rivet nuts
The experimental load of rivet nuts is expressed by the term "stress" in most rivet nut strength grade standards-pounds per square inch. When calculating the actual experimental load in pounds, the experimental stress (psi) is multiplied by the force-bearing area.
A very important point: the experimental load has nothing to do with the specified externally threaded fasteners except in the normal stress area.
3. Taper test load
The taper test load is an axial external load that the nut must bear, and the rivet nut must not have the thread peeling off or the inner wall cracked during the load. In the test, the rivet nut was installed on a hardened tapered washer with an angle of 120°. The purpose of placing the conical washer is to produce a strong effect of expanding the inner wall of the nut when the nut is axially stressed. If the nut fails the test, it is usually due to a cracked inner wall rather than peeling off the nut.
Nuts used in high-temperature environments—covered in ASTM A194—are subject to cone test load testing. In addition, the standard for the bearing limit of the discontinuous surface of the rivet nut defines that the nut with a joint should be subjected to a cone test load test. Passing the test means that the seam on the rivet nut has not yet reached the level that affects the working function of the nut.
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