For some viscoelastic polymers that are subjected to stress relaxation tests, th
ID: 1849665 • Letter: F
Question
For some viscoelastic polymers that are subjected to stress relaxation tests, the stress decays with time according to?(t)=?(0)exp(-t/?)
where ?(t) and ?(0) represents the time-dependent and initial (i.e., time =0) stresses, respectively, and t and ? denote elapsed time and the relaxation time; ? is a time-independent constant characteristic of the material. A specimen of some viscoelastic polymer with the stress relaxation that obeys equation above was suddenly pulled in a tension to a measured strain of 0.34; the stress necessary to maintain this constant strain was measured as a function of time. Determine Er(10) for this material if the initial stress level was 3.7 MPa (530 psi), which dropped to 0.58 MPa (83 psi) after 43 s.
Explanation / Answer
what does ? mean here i see it???