I've got results of torsion and double shear test on titanium alloy. The values of strength are higher on torsion stress than on double shear (ex. 1080 MPa torsion and 700 Mpa in double shear). Why the values are different? From my understanding the stress state in both tests are the same (pure shear).
It's the high strength Ti 55531 (tensile strength about 1400 Мpa). I've got results on different alloys and regardless of actual values the torsional strength always higher than in double shear. In torsion it's about 0.85*UTS and in double shear 0.7-0.5 * UTS (dependent on strength, on low tensile strength it's 0.7*UTS, in high strength condition it's 0.5*UTS)
I think you should be careful when setting torsion test, since any twist angle will affect the results.
Judging by very high values of shear strength your measurements are incorrect. Especially as there are no references
It's the results from high strength alloy with ultimate tensile strength up to 1600 Mpa (rolled bars), what do you think would be the correct results of shear strength for such alloy?
Irrespective what the value is if you have large differences then there must be something wrong with your set up
Gabi, but are you sure that the results from double shear and torsion test should be the same? Could it be because of the stress concentration on the edges of the cutting tool in double shear experiment that lead to earlier yield whereas in torsion test there is no such concentration?
i did not say that it should be the same. I meant that there should not be a lot of differences
I personally would not expect the tests to give similar results, as both setups are very sensitive to the actual stress triaxiality during the test. Double shear specimens will undoubtedly rapidly deviate from pure shear depending on the sample geometry and material properties. FEM studies on sample geometries for different test setups have, among many others, frequently been done by P. Verleysen et al. from Ghent University, showing the rapidly developing stress triaxialities for seemingly trivial test setups. Regarding the torsion test, you must either work with a preload (and already induce a stress triaxiality) or have a balanced compensation for any contraction along the sample axis. If you have fixed clamps, you will always have stress triaxialities and deviate from pure shear, even if you would not expect them to occur. Some authors have reported on this, but I currently can't recall any names. If I find any, I will be back in touch!
Tests will not give similar results due to shear compensation and not due to the stree concentration
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science