STRAIN RATE CONSTANT FOR DIFFERENT LOADING VALUES

I am working on plasticity in a tensile specimen now. I am getting the stress pulse in the transmitted bar very similar to the oscilloscope trace. I gave the yield stress and the plastic strain according to the experiment in the material properties for the aluminum specimen. But I was not able to give a failure strain and hence I gave a yield stress of 1Pa at a strain of 11% where it fails in the real experiment. I am encountering 2 problems.
Problem1: I am not able to achieve the required strain rate of 1000/s by adjusting the load. For a load of 130MPa(experimental) as well as for a load of 300MPa, the strain rate seems to be the same. What I have observed is that the strain values(goes to 15% for 300MPa and 30% for 130MPa) adjust accordingly to achieve the same strain rate(1800/s)
Problem2: In these cases, I would like to see the specimen separated near the gage section. But I don't see that happening although there is severe distortion in the elements. Is there any failure criterion to use so as to get them separated. Is there any option to input a failure strain?  I found a ductile damage model which doesn't work well.

Thanks IN ADVANCE.