= Solution
Use a <rheometer>, for example a <cone-and-plate rheometer> or a <parallel-plate rheometer>, to impose a small deformation and measure the required torque, or impose a torque and measure the deformation. The apparatus geometry converts these into <shear stress> and <strain>. First check that reducing the imposed amplitude does not change the normalized response; this identifies the linear regime and avoids yielding or structural rearrangement.
Three complementary protocols characterize the material's memory. In a <stress relaxation> experiment impose a small step $\epsilon_0H(t)$ and hold the deformation fixed. The output is the <relaxation modulus> $G(t)=\sigma(t)/\epsilon_0$, revealing how stored <stress> decays and whether an elastic plateau remains. In a <creep compliance> measurement impose a small <stress> step $\sigma_0H(t)$ and record $J(t)=\epsilon(t)/\sigma_0$. Removing the load also distinguishes recoverable deformation from permanent flow.
In <small-amplitude oscillatory shear>, impose sinusoidal <strain> over a range of frequencies and measure both <stress> amplitude and phase. With $\epsilon=\epsilon_0\cos\omega t$, fit
$$
\sigma(t)=\epsilon_0[G'(\omega)\cos\omega t-G''(\omega)\sin\omega t].
$$
The outputs are the <storage modulus> $G'$ and <loss modulus> $G''$, or equivalently amplitude ratio and <loss tangent> $\tan\delta=G''/G'$. These measure elastic storage and dissipative response, respectively. The step experiments give time-domain information and the oscillatory experiment gives the corresponding frequency-domain response. All comparisons must use the same deformation convention and controlled <temperature>.
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