Sample thickness

Relationships between the intensity of incident light, sample thickness, concentration and intensity of transmitted light are embodied in Beer s law and Lambert s law. ... 

Fig.2. Tomographic (a) and graphic (b, for depth 13 mm) images of relative change of Young s modulus 5E% (average on volume Eo=218,310 Pa) of material in section perpendicular to surface of thick-sheet sample (thickness 26 mm).

Examination of oven-aged samples has demonstrated that substantial degradation is limited to the outer surface (34), ie, the oxidation process is diffusion limited. Consistent with this conclusion is the observation that oxidation rates are dependent on sample thickness (32). Impact property measurements by high speed puncture tests have shown that the critical thickness of the degraded layer at which surface fracture changes from ductile to brittle is about 0.2 mm. Removal of the degraded layer restores ductiHty (34). Effects of embrittled surface thickness on impact have been studied using ABS coated with styrene—acrylonitrile copolymer (35). 

Test pieces for Brinell testing must have two parallel sides and be reasonably smooth for proper support on the anvil of the test machine. Minimum sample thickness must be 10 times indentation depth. Successive indentations must not be closer than three indentation diameters to one another or to the edge of the test piece. 

Operator skih and experience are necessary to obtain consistent results usiag a Durometer. Speed of load appHcation, dweh time, and sample thickness can affect reproducibhity of results. Durometer cahbration prior to each test series is done usiag a test block provided with the iastmment. When large numbers of tests are required, improved consistency of results are obtained if the Durometer is used with the accessory vertical stand rather than hand held. 

From a modehng standpoint statisticians would define this problem as a two-population test oihypothesis. They would define the respective sample sheets as two populations from which 10 sample thickness determinations were measured for each. 

None, except there are techniques that measure sample thickness... 

With polarizers fidly crossed and the specimen rotated to maximum brightness, the sample thickness is determined with the aid of a calibrated eyepiece micrometer, and the polarization (retardation) color is noted. From these the birefringence may be determined mathematically or graphically with the aid of a Michel-L vy chart. 

In TEM, a focused electron beam is incident on a thin (less than 200 nm) sample. The signal in TEM is obtained from both undeflected and deflected electrons that penetrate the sample thickness. A series of magnetic lenses at and below the sample position are responsible for delivering the signal to a detector, usually a fluorescent screen, a film plate, or a video camera. Accompanying this signal transmission is a... 

The im< e mode produces an image of the illuminated sample area, as in Figure 2. The imj e can contain contrast brought about by several mechanisms mass contrast, due to spatial separations between distinct atomic constituents thickness contrast, due to nonuniformity in sample thickness diffraction contrast, which in the case of crystalline materials results from scattering of the incident electron wave by structural defects and phase contrast (see discussion later in this article). Alternating between imj e and diffraction mode on a TEM involves nothing more than the flick of a switch. The reasons for this simplicity are buried in the intricate electron optics technology that makes the practice of TEM possible. 

The resulting PL intensity depends on the absorption of the incident light and the mechanism of coupling between the initial excited states and the relaxed excited states that take part in emission. The spectrum is similar to an absorption spectrum and is useful because it includes higher excited levels that normally do not appear in the thermalized PL emission spectra. Some transitions are apparent in PLE spectra from thin layers that would only be seen in absorption data if the sample thickness were orders of magnitude greater. 

Trade literature can provide a wealth of information. Users should, however, bear in mind that suppliers will naturally wish to emphasise data in the best possible light. For example, if the Izod impact strength increases sharply with decrease in sample thickness, then results may be quoted for thinner section test pieces. Whilst the facts may be stated, the underlying significance may not be fully appreciated by the casual reader. 

Fig. 2.15. Release wavespeeds at very high pressure can be determined by experiments in which the sample thickness is varied for fixed thickness of a high velocity impactor. Data on aluminum alloy 2024 are shown. As indicated in the figure, shear velocity (C ) and Poisson s ratio (cr) at pressure can be calculated from the elastic and bulk speeds if thermodynamic equilibrium is assumed (after McQueen et al. [84M02]).

Observations of smooth spalls in iron provided an early, dramatic demonstration of the importance of release wave behaviors. In 1956, Dally [61E01] reported the existence of remarkably smooth fracture surfaces in explosively compressed steel. The existence of these smooth spalls was a sensitive function of the sample thickness. Analysis and experiments by Erkman [61E01] confirmed that the smooth spalls were associated with interaction of release-wave shocks and shocks from reduction of pressure at free surfaces. These release shocks are a consequence of differences in compressibility at pressures just below and just above the 13 GPa transformation. 

Given limits to the time resolution with which wave profiles can be detected and the existence of rate-dependent phenomena, finite sample thicknesses are required. To maintain a state of uniaxial strain, measurements must be completed before unloading waves arrive from lateral surfaces. Accordingly, larger loading diameters permit the use of thicker samples, and smaller loading diameters require the use of measurement devices with short time resolution. 

Fig. 5.4. The electrical signals from shock-compressed piezoelectric solids depend explicitly on the electrical circuit and mechanical arrangement (the sample thicknesses). In the current mode (low electrical impedance), the current pulse either follows the loading as a close analog, or, in the thin mode of PVDF, follows the derivative of the stress pulse in time.

When a toroidal ferromagnetic sample is subjected to shock loading, a pressure wave of pressure P moves through the sample with a velocity U and produces a change in magnetization AM. An N-turn detection coil with inductance L is wound around the sample and connected to a resistive circuit in which the L/R time constant is longer than the time required for the shock wave to traverse the sample thickness. The current i in the coil is then... 

Figure 4 Light permeability of polypropylene as a function of the sample thickness 1-3-quenched polypropylene 4-6-normal polypropylene 1 and 4-100 /ac thick 2 and 5-150 jLtc thick 3 and 6-500 /jlc thick.

Figure 6 Light transmission of quenched cured polyethylene as a function of the sample thickness (vulcanization temperature 160°C, time 15 min.). 1-sample of normal polyethylene 2 mm thick 2, 3, and 4-quenched cured samples of different thickness 2-1 mm, 3-2 mm, 4-4 mm.

Figure 12 shows the dependence of the average aspect ratio and the TLCP volume fraction on the relative sample thickness for the four processing conditions in the core layer, transition layer and skin layer, respectively, by a morphological examination [13]. Generally, the aspect ratio increases from core to skin layer, whereas the situation is reversed for the volume fraction. An average volume fraction about 20% can be clearly seen. 

Figure 12 Average aspect ratio and volume fraction of TLCP fibers as functions of halved relative sample thickness for four processing conditions.

Figure 14 Calculated shear rate as function of the halved sample thickness for two injection volume fluxes Q.

Figure 15 Calculated viscosity as function of the halved sample thickness for two melt temperatures and for (a) injection volume flux of 8 cmVs and (b) injection volume flux of 80 cm /s.

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