Ultra-high-molecular-weight polyethylene fibers like Dyneema or Spectra are employed in a vast variety of cable-driven parallel robots. The stress-strain dynamics of such cables are highly non-linear with time-varying mechanical parameters, resulting in involved modeling and control of robot dynamics. To improve controllability of cable robots, the cable stress-strain dynamics need to be known and explicitly considered feedforward or closed-loop control. A model can only be deemed suitable, if its inherent dynamics is confirmed through experiments and if it allows for reasonable parameter estimation. We present results of experimental identification of stress-strain dynamics of UHMWPE cables made of Dyneema in different stages of operation. Due to the internal material mechanics, four stages can be identified: the tensing and relaxing transition as well as plateaus coming from either. The implications of verified and parametrized stress-strain models for cable robot tension control strategies is expedited.