I personally would think that work-hardening could also play a part in this. By the look of the anchors they are likely made of stainless steel, most grades of

I personally would think that work-hardening could also play a part in this. By the look of the anchors they are likely made of stainless steel, most grades of which will work-harden under the correct circumstances. I am only familiar with the effects of work-hardening in a workshop situation though, so I'd hesitate to say for sure what the effect of that kind of friction/strain load would be...