= Rheology
{wiki}
<Rheology> studies how matter deforms and flows under applied <stress>, including the dependence on loading history and observation <time>. Its central task is to connect a measured <stress> to <strain>, <strain rate> and relevant internal state through a <constitutive equation>. A <Newtonian fluid> has an instantaneous proportional response to <strain rate>; an <elastic> solid responds to <strain>; a <viscoelastic> material retains information about previous <deformation>.
These differences can be exposed by changing the experiment rather than only changing the load. Holding <stress> fixed measures <material creep>; holding <strain> fixed measures <stress relaxation>; <small-amplitude oscillatory shear> separates <storage modulus> from <loss modulus>. A <rheometer> supplies controlled motion and measures the resulting <force> or <torque>. Such measurements help predict whether a paste will remain in place, how much <pressure> is needed to drive a <fluid flow>, and whether a material will recover after loading.
Back to article page
