Does strain rate ever decrease yield stress?

[bryony88]

I've been digging through literature the last few days, and I'm starting to wonder if increasing strain rate EVER decreases yield stress? I found anomalies which increase it with increasing temperature. But I cant' find the reverse, so I was wondering if it was possible?

 

[Mapes]

Fig. 7c is one example. You'll find many more if you do a search for "yield strength"+"negative strain rate sensitivity".