Load frequency, effect

The SPATE technique is based on measurement of the thermoelastic effect. Within the elastic range, a body subjected to tensile or compressive stresses experiences a reversible conversion between mechanical and thermal energy. Provided adiabatic conditions are maintained, the relationship between the reversible temperature change and the corresponding change in the sum of the principal stresses is linear and indipendent of the load frequency. 

A material that is subjected to cyclic application of stresses may fail after a large number of load cycles without nearly reaching the maximum failure stress of direct loading. The effect of such cyclic stresses is to initiate microscopic cracks at centres of stress concentration within the material or on the surface, and subsequently to enable these cracks to propagate, leading to eventual failure. For high stress amplitudes less cycles are needed for failure than for low stress amplitudes. For high frequencies less cycles are needed for... 

Fig. 4. Crack jump into the craze in PVC under cyclic loading. The same effect may be obtained in other polymers under other loading frequency and temperature conditions...

Fig. 15. The craze stress versus loading frequency in the case of a cyclic loading, in experimental conditions where hysteretic heating occurs in PMMA at the crack-tip. Note the increase of the craze stress due to strain rate effects at low frequencies, and the decrease of craze stress due to hysteretic heating above 100 Hz. From Refs. and courtesy of Society of Plastics Engineers Edn.

Besides frequency effects due to strain-rate hardening and/or specific cyclic damage of the fibrils, there is another typical effect in the case of cyclic loading at high frequencies, namely hysteretic heating. The increase of temperature T near the crack tip, in that case, scales as in Eq. (5)" ... 

Effect of Time, Loading Frequency, and Dispersion on Solute Distribution... 

Three figures of solute transport in a soil column will be discussed to contrast unsteady-state and quasi steady-state behavior, to illustrate the effect of loading frequency on solute distribution in a soil column, and to show the effect of the magnitude of the dispersion coefficient on decreasing the magnitude of the ampli-... 

Where k = two Pq/Mq. P is the bulk density of the medium in contact with the vibrating surface of the solid, a film or a liquid, and heff is the thickness of the layer that responds to the quartz oscillations. In the case of the film, heff coincides with the thickness. For a semi-infinite hquid, hgff presents a thickness of liquid involved in the motion and it should be taken as equal to S/2. The difference in the frequency dependence of the QCM response in the two cases is a result of the frequency dependency of 8. However, in contrast to the case of pure mass loading, the effect of a hquid results not only in a frequency shift but also in a broadening of the resonance. 

Loading frequency and moderate variation of temperature have little effect upon the number of cycles to fracture in dry fatigue. These factors are more important in CF. The effect of frequency is significant because flie corrosion effect is time dependent, and the temperature is known to be an important factor in connection with corrosion. These two factors are mentioned at the same time because they both represent possible ways of accelerating CF tests. Reliable test results can, however, be obtained only if the fatigue acceleration factors are quantitatively known. 

In conjunction with the environmental effect, the loading frequency is an important factor. Since the environmental effect is due to the reaction between the environment and the freshly exposed material t the crack tip, the period of time for reaction is important. The degree of crack extension due to environmental crack tip damage during each cycle has been studied and reported by Wei [ ] and Bradshaw and Wheeler [" j. Also, test frequency can have a marked effect on results, if creep is a contributor to the fatigue processes [" ]. 

In Fig. 7, the growth rate vs. AAT plots for 1-Hz loading frequency in air, water, and argon show relatively the same effects described above. 

Originally, the most wildly used predictive equation was Witczak s equation (Andrei et al. 1999 Witczak 2005), also known as the original Witczak equation. The dynamic modulus was determined with respect to percentage passing through certain sieves, binder viscosity, air voids, effective binder content and loading frequency. 

For vessels and tanks that contain liquids, the effects of sloshing and impulsive loads, including frequency effects, should be considered. The effects of liquid motion or pressure changes on submerged structures should also be considered. These effects may involve hydrodynamic loads from the fluid and a reduction of functional capability (e.g. loss of shielding efficiency of fuel pools or disturbance of instrument signals). 

Secondary spot network Simple inexpensive when available in a given area protects against local power interruptions no maintenance required by user Not available in all locations provides no protection from area-wide utihty failures provides no protection against transient disturbances or surge/sag conditions Virtually no loss, 100% efficient presents low impedance to the load no effect on frequency or harmonic ntent... 

RQ. 4— The effect of solution pH and loading frequency on CF crack propagation in an o/p titanium alloy expo to aqueous chloride [49]. 

FIG. 8—The varied effects of loading frequency on CF crack propagation rate in peak aged AA7075, 7017, 7475, and 7079 exposed to aqueous chloride eoiution (free corrosion) at constant AK and R. The fatigue crack is parallel to the plate rolling plane in the SCC sensitive S-L orientation [50]. 

FIG. 9—The effect of loading frequency on CF propagation In API-2H and A710 steels, at the 625 to 750 MPa yield strength level, exposed to aqueous NaCI solution with CP to -1000 mVgce at constant A/C and R [5f ]. 

Figure 10 illustrates the minimal effect of loading frequency on CF crack formation and early growth for blunt notched steel specimens in aqueous chloride solution at free corrosion 46]. These data are notable for the rare combination of low f and high cyclic lives (175 days were required to obtain 3 x 10 cycles at 12 cpm), and for the lack of a frequency effect on the cycles required to produce 1 mm of CF cracking. This result indicates that one or more of the early... 

Near-threshold CF crack formation and propagation, and environment-dependent crack closure, must be characterized including the important effect of low loading frequency [118]. 

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