A flow curves, as a tool for the description of rheological properties of materials

Plan of the lecture:

1. Curves for

2. Thixotropic and Repetsky system

Purpose of the lecture: get acquainted with the curves of course, as a tool for the description of rheological properties of materials.

The simplest method for the study of the structural-mechanical properties of food materials consists in the construction of curves kinetics of deformation (of flow curves). These curves can be found seven independent from each other deformation characteristics of the material: modules instant elasticity and elastic aftereffect; viscosity relaxation (flow) and elastic aftereffect; the elastic limits, fluidity and strength. The strength size is not invariant, because it depends on mechanical mode of deformation. These constants allow you to explain deformation behavior of material and adequately described its structural-mechanical properties. The receipt of such characteristics is possible in the process of study of rheological properties of food masses, i.e. the research of the process of their flow under the action of a constant voltage.

Flow curves of (rogramme) Newtonian fluids represent a straight line 1, passing through the origin. All flow curves of (2 - 5)that deviate from the straight line is called non-Newtonian liquids. In this case the curve 2 characterizes diletanty over, typical mainly for concentrated disperse systems, which can increase the speed of deformation occurs «difficulty shift», which is an increase of viscosity; curve 3 describes pseudoplastic-type course, that is characteristic for the «shear softening» due to the destruction of structures with increasing strain rate curve; 4 shows nonlinear plastic flow characteristic of most plastic bodies after the limit shear stress θ0. The linear dependence of 5 characteristic bangnowski tel is the ideal plastic flow, after reaching the ultimate shear stress θ0.

A flow curves (Fig. 1.) graphically depict the laws of behavior of various materials, i.e. the dependence of the form:

Fig. 1. Flow curves of:

Date: 2015-12-24; view: 796