Shear behavior

The dynamic shear behavior of the polymer melt can be used to determine the ratio of weight average, to number average, molecular weight (33). 

A rotational viscometer connected to a recorder is used. After the sample is loaded and allowed to come to mechanical and thermal equiUbtium, the viscometer is turned on and the rotational speed is increased in steps, starting from the lowest speed. The resultant shear stress is recorded with time. On each speed change the shear stress reaches a maximum value and then decreases exponentially toward an equiUbrium level. The peak shear stress, which is obtained by extrapolating the curve to zero time, and the equiUbrium shear stress are indicative of the viscosity—shear behavior of unsheared and sheared material, respectively. The stress-decay curves are indicative of the time-dependent behavior. A rate constant for the relaxation process can be deterrnined at each shear rate. In addition, zero-time and equiUbrium shear stress values can be used to constmct a hysteresis loop that is similar to that shown in Figure 5, but unlike that plot, is independent of acceleration and time of shear. 

Figure 2-13 Unidirectional Lamina Shear Behavior (2) Relation of E45. to E. ...

Several experiments will now be described from which the foregoing basic stiffness and strength information can be obtained. For many, but not all, composite materials, the stress-strain behavior is linear from zero load to the ultimate or fracture load. Such linear behavior is typical for glass-epoxy composite materials and is quite reasonable for boron-epoxy and graphite-epoxy composite materials except for the shear behavior that is very nonlinear to fracture. 

Fig. 47—Load-carrying and shearing behavior of confined ILs thin film. Liquid volume is decreased from volume 1 to volume 6 corresponding to a decreasing thickness of ILs films. The confined thin film of ILs exists at the contact area under a normal load of hundreds of MPa and undertakes shearing stress like a solid-solid contact.

F. J. Medellin-Rodriguez, C. Burguer, B. S. Flsiao, B. Chu, R. Vaia, S. Phillips, Time-resolved shear behavior of end tethered nylon 6-clay nanocomposites followed by non-isothermal crystallization, Polymer, vol. 42, pp. 9015-2023, 2001. 

Madhukar, M.S. and Drzal, L.T. (1991a). Fiber-matrix adhesion and its effect on composite mechanical properties I. In plane and interlaminar shear behavior of graphite/epoxy composites. J. Composite Mater. 25, 932-957. 

The same test method, although not standardized, can be used to characterize the laminate in-plane shear behavior. This is accomplished by winding a multiorientation (hoop/helical and/or helical only) tube. Other test methods that can be used to measure in-plane shear stiffhess/strength of filament wound composites are discussed by Tamopol skii and Kinds [45]. These methods include schemes for torsion of intact rings and split rings. Both of these ring test methods are used to evaluate the in-plane shear modulii G0r and G0z for a filament-wound laminate. 

In this illustration, the spatially nonuniform body forces cause an internal source of vortic-ity. Vorticity is also generated due to shearing behavior at the walls. 

Saba,R.G., Sauer,J. A., Woodward,A.E. Dynamic shear behavior of poly (y-benzyl L-glutamate), poly(D, L-propylene oxide), and polyfethyl vinyl ether). J. Polymer Sd. A1, 1483 (1963). 

The complete flow curve allows for the response of the test sample to be predicted at rest (zero-shear behavior), when being poured out of a container (early Power Law region), when being pumped (middle Power Law region), or when being processed or consumed. Each part of the curve is important in assessing a sample s suitability. 

Holden et al. (47) first noted the peculiar characteristics in the steady shear behavior of the SBS block copolymer melts. For a certain composition of styrene and butadiene, no limiting Newtonian viscosity was found at low shear rates. For some of the others, there exist two distinct viscosity vs. shear rate relationships (Figure 10). Arnold and Meier (73) carried out the experiments in oscillatory shear and found the same... 

Monodisperse melts appear to exhibit a plateau region in the stress vs shear rate flow curve [51,62,65]. The capillary flow behavior actually closely resembles the oscillatory shear behavior in the sense that the flow curve essentially overlaps on the absolute value of complex modulus G vs the oscillation frequency (0 [62]. Thus.it appears that the transition-like capillary flow behavior of highly entangled monodisperse melts reflects constitutive bulk properties of the melts and is not interfacial in origin. It remains to be explored whether this plateau indeed manifests a real constitutive instability, i.e., whether it is double-valued. 

The shear behavior also involves matrix cracking and fiber failure.26 However, the ranking of the shear stress-strain curves between materials (Fig. 1.6) differs appreciably from that found for tension (Fig. 1.5). Preliminary... 

Water-in-oil emulsions, generally appear to be black, do not dilute with water, and have electrical conductivity lower than that of the brine. The viscosities may be very high, and the shear behavior is thixotropic. 

PC shows either craze or shear behavior, with no mixed behavior, i.e., successively regenerated localized DCG zones. There is a sharp transition between the craze and the shear branches, as seen in Fig. 35. The competition between crazing and shear is temperature and stress sensitive. The mode, once determined, persists as the barrier is high between these two modes. At 75 °C and above, no craze-crack growth is observed, although shear fracture does persist down to —25 °C, albeit only at high stresses. 

S. A. Gupta, H. D. Cochran, and P. T. Cummings,/. Chem. Phys., 107,10316 (1997). Shear Behavior of Squalane and Tetracosane Under Extreme Confinement. 1. Model, Simulation Method, and Interfacial Slip. 

In the study of Hannon and Wissbrun (10), which forms another point of departure for this work, a range of properties was investigated for the phenoxy-calcium thiocyanate system. The glass transition was observed to increase at a rate of 1.8°/mol % salt this, and the absence of negative deviations from additivity of specific volume, suggests that the interactions here are weaker than those in the systems studied by Moacanin and Cuddihy. The viscosity behavior reflected exclusively the increase in Tg. A strong shear-rate dependence of the viscosity was observed over the entire 40° range (170°-210°C) studied, and even at the lowest shear rates (3 X lO sec"1) the curves did not approach zero shear behavior. The samples could not be studied above 210 °C because of incipient decomposition. 

The dynamic mechanical shear behavior of several blends, viz. PS with PMMA, PDMS with PEG, PS with PEMA, were studied by Graebling... 

PMMA/PEG dynamic shear behavior Colby, 1989 Booij Palmen, 1992... 

Table I compares typical test results for low-, mid-, and high-effective molecular weight thickeners in a vinyl-acrylic latex paint. Many of the same trends are present with cellulosic and HE UR thickeners when the effective molecular weight designation for HEUR thickeners is used. As the effective molecular weight of an HEUR increases, Stormer thickening efficiency, roller spatter, and water resistance increase, whereas ICI viscosity decreases. The major difference between these two thickener types is in their low-shear behavior. As effective molecular weight increases, cellulosic paints improve in leveling and decrease in sag resistance. HEUR paints decrease in leveling and improve in sag resistance. Other property differences between these two thickener types are highlighted in Table II.

Jawad [54] has u.sed the determination of shear moduli to examine molecular processes in liquid crystalline copolymers, while Hedner et al. [55] describe a test for general use with thermoplastics. Boyce ct al. [40] compare the large strain compre.ssion. tension, and shear behavior of polycarbonate. 

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