Hi,
While 4-bending tests on a sandwich we got Identation to avoid that we use a small rectangular plate under loading pins.
can this affect the outcome of the Test?
Thank you
You should used larger diameter pins rather than flats. Flats will have sharp edges that will act as stress risers. That tests for bearing strength rather than pure shear in the core. However, a test with flats could be more realistic for your application, and is better than using pins that are too small.
Ideally the pin diameter is slightly smaller than the curvature of the test specimen at max load. Too small a pin causes crushing or dimpling (deformation) of the skin, as you have observed. I believe 1/4" or 1/2" diameter is fairly standard. This kind of information is usually in the ASTM test methods.