Dynamic stresses

Stress Corrosion Up to maximum of Branched cracks, Stainless steels in Almost any grade of Stresses—dynamic Use material which... 

There are several other comparable rheological experimental methods involving linear viscoelastic behavior. Among them are creep tests (constant stress), dynamic mechanical fatigue tests (forced periodic oscillation), and torsion pendulum tests (free oscillation). Viscoelastic data obtained from any of these techniques must be consistent data from the others. 

The four variables in dynamic oscillatory tests are strain amplitude (or stress amplitude in the case of controlled stress dynamic rheometers), frequency, temperature and time (Gunasekaran and Ak, 2002). Dynamic oscillatory tests can thus take the form of a strain (or stress) amplitude sweep (frequency and temperature held constant), a frequency sweep (strain or stress amplitude and temperature held constant), a temperature sweep (strain or stress amplitude and frequency held constant), or a time sweep (strain or stress amplitude, temperature and frequency held constant). A strain or stress amplitude sweep is normally carried out first to determine the limit of linear viscoelastic behavior. In processing data from both static and dynamic tests it is always necessary to check that measurements were made in the linear region. This is done by calculating viscoelastic properties from the experimental data and determining whether or not they are independent of the magnitude of applied stresses and strains. 

Stresses—dynamic or static— concentrate at bases of small corrosion pits, and cracks form with vicious circle of additional corrosion and further crack propagation until failure occurs. Stresses may be dynamic, static, or residual. 

Dynamic Experiments. We will now consider the response of a Maxwell element subjected to a sinusoidal stress, as in a controlled-stress dynamic mechanical analyzer. In such a case the strain will also be sinusoidal but out of phase with the stress by the angle 8, as discussed in Chapter 2. Thus... 

Kee and Durning (1990) reviewed two principal methods of measuring yield stresses dynamic and static methods. One example of the dynamic method is the extrapolation from the flow curve. Equation (4) is often used to determine the yield stress of gum solutions. Table VIII lists the examples of yield stress of several selected food commodities measured from different methods. It is noted that for the same food product, different methods have different yield stress value. In addition to the measuring method, the embedded factor—the composition of food products—also needs to be emphasized. For instance, in mayonnaise, the concentration of oil and xanthan gum significantly affected the yield stress since it increased from... 

A very good way to characterize and differentiate between elastomers and rigid plastics is by the measurement of dynamic mechanical properties. A most convenient method to study dynamic mechanical properties is to impose a small, sinusoidal shear or tensile strain and measure the resulting stress. Dynamic mechanical properties are most simply determined for a small sinusoidally varying strain, for which the response is a sinusoidally varying stress. An increase in frequency of the sinusoidal deformation is equivalent to an increase in strain rate. 

A part can encounter two types of stresses—dynamic and residual. Dynamic stresses are simply those that result from the functioning of the part. Because this stress occurs only when the unit is used, its stress level is zero when it is not in use. The designer must as a result understand the part s function to calculate its dynamic stresses. 

Metal soaps are found as lubricant in numerous applications. It prevents excessive friction during processing so that high output together with protection from overheating of plastic materials is possible. Metal soaps provide excellent flow characteristics. They help plastics to be stressed dynamically in an extrusion or injection molding machine. The metal soaps have very little or no effect on the end products. 

The amount of a vitamin required by a human being varies from moment to moment, according to diet, activity, health, response to stress, dynamic equilibria in the body, etc. The amount also varies from one individual to another according to body size, activity, sex, age, drugs, diet, etc. 

Physieal models and equivalent circuit representations for conducting polymer actuators and sensors are presented, including mechanical, electrical, and electromechanical descriptions. The underlying concept of most models is that strain is proportional to charge density, and sense voltage is proportional to stress. Dynamics are determined by the rate of charge transfer, as well as the mechanical properties of... 

F. (2013) A low-cost, multiplexable, automated flow cytometry procedure for the characterization of microbial stress dynamics in bioreactors. Microb. Cell Fact., 13, 100. 

Next, if we impose a sinusoidal stress (dynamic creep test) or(0 = or e then the response will be... 

Equations (1.11.30) are supplemented by stress dynamical equations and strain-displacement equations which take the same form as in classical elasticity. Likewise, boundary conditions may take any of the forms appropriate to the classical (dynamic) theory of elasticity in particular the type of boundary condition specified at a point on the boundary of a body may change with time and further, the boundary of the body may change with time, through the process of ablation, for example. 

This chapter covers some of the methods and instruments used to determine the mechanical properties of polymers. Examples of instrument designs and typical data generated in these measurements will be introduced. In particular, automated axial tensiometers (to find elastic modulus, yield stress, and ultimate stress), dynamic mechanical analyzers (to determine storage and loss moduli), and rheometers (to measure flow viscosity) will be introduced. This chapter considers the principles behind the devices used to establish and measure the properties of viscometric flows. One of the common techniques used to determine viscous flow properties, PoisueiUe (laminar) flow in cylindrical tubes, is also important in technical applications, as polymer melts and solutions are often transported and processed in this manner. The time-temperature superposition principle is also covered as a way to predict polymer behavior over long timescales by testing materials across a range of temperatures. 

In a general perspective, not solely related to testing of adhesives, the problem of the dispersion has been considered by Tyas and Watson (2001). They have proposed to correct the measurement by means of two factors, termed Mj and M2, one relating measured surface strain to average strain over the cross-section, the other relating average axial strain to average axial stress (dynamic elastic modulus). 

---