Dynamic stiffness, measurement

Benkelman beam rebound deflection measurements have been obtained during each of these testing phases. The SDHPT Dynaflect Unit has been used to obtain dynamic stiffness measurements. These results also indicate that the sulfur-asphalt mixes and the asphalt mixes are displaying comparable characteristics. 

Where a number of properties are relevant to a product the testing may be carried out with a sequence of tests without superimposing any ageing. Where environmental effects have to be accounted for they are applied separately and the rig tests repeated. An example of this approach is artificial sports surfaces where such characteristics as ball bounce, energy absorption, dynamic stiffness and spike resistance are measured using specifically developed rigs. 

Eoams were extruded from low density polyethylene (LDPE) and blends of LDPE with syndiotactic polypropylene (sPP), using isobutane as the blowing agent. The extruded materials were characterised by measurement of dimensional stability at room temperature, density, tensile properties, dynamic stiffness, and crystallinity determined by differential scanning calorimetry. The sPP, with a slow crystallisation rate, did not interfere with the expansion of the LDPE, and enhanced the temperature resistance by in-situ crystallisation. The blends were flexible, dimensionally... 

The broadened transition response is a general characteristic of power feed polymers as evidenced by the results of stiffness-temperature, stress relaxation and dynamic mechanical measurements. 

The sample s dynamic stiffness is obtained from the measured force and motion amplitudes. The formula for this dynamic stiffness is derived below with reference to the Figure 2 measurement system model. The support impedance element in this model represents the combined effects of the flexibility of the downward force train into the shaker field assembly, the mass of the field assembly, and the oscillating magnetic reaction force exerted on the field assembly from the armature. 

A modulus value increase upon storage under ambient conditions is also reported for other semi-crystalline polymers like, for instance, polypropylene. Struik [11] measured for PP a continuously increasing dynamic stiffness at 20°C in combination with a decrease of the intensity of the glass-rubber (S) transition of PP (the temperature location of the S-transition did not change). Struik called this phenomenon an amorphous phase ageing effect a densification process of the amorphous PP phase due to a free volume relaxation effect. 

Figure 10.9 shows the results of the measurements on an experimental UHMW-PP sample as such and filled with 20 %v. of mica. A standard J-grade PP, filled and non-filled, was measured as reference system. The dynamic stiffness of both reference systems is for temperatures below 160°C higher than that of both UHMW-PP systems due to a difference in crystallinity, x(c) as determined by DSC ... 

Both reference samples fused completely out of the sample clamps at tempertures between 160°C and 170°C. The dimensions of the UHMW-PP samples did change considerably (length not changed, width -23 % and thickness +40 %) but the shape of the samples was still rectangular, which permitted us to continue the measurements up to 250°C. The consideable difference in dynamic stiffness (and hence in strength) between the standard... 

When the applied load is dynamic (short loading rate), the stiffness measured is called elastic or dynamic stiffness modulus or, for simplicity, stiffness. When the applied load is static (long loading time), the stiffness measured is called static stiffness (modulus),... 

The Mettler-Toledo Inc., SDTA 861 DMA analyser [6] is capable of providing DMA measurements over wide frequency ranges (from 1 mHz to 1 kHz) and large dynamic stiffness ranges. A schematic of the instrument is illustrated and examples are presented of test data for various rubbers obtained using this equipment. 

Dynamic rheological measurements show that the cubic phases behave like the viscoelastic vesicle phases, as can be seen from the two examples shown in Figure 10.19. As can be seen, G is independent of the frequency and at least one order of magnitude higher than G", and rj increases to infinity when the frequency approaches zero. However, as can be expected from the stiffness of the samples, both Go and cry are several orders of magnitude higher than for the vesicle phases. As has been found for the latter, the cubic phases have energy elasticity, i.e. the moduli break down at deformations beyond about 10%. 

A variation on the amplitude modulation technique was also used to measure oscillatory surface forces with increased sensitivity in a branched hydrocarbon, squalene. In this technique, the sample was oscillated with low amplitude (c. 1 A), and both the cantilever static and dynamic (induced oscillation from a change in the tip-sample force gradient) deflection was measured. Figure 1.13 shows the static force measurement and Fig. 1.14 the dynamic measurement, shown as an interaction stiffness. The sensitivity of the dynamic force measurement is such that the interdigitation of the branched methyl groups can be detected (indicated by arrows in Fig. 1.14). 

At very low frequencies the movement of the panel will be controlled by the stiffness, as inertia is a dynamic force and cannot come into effect until the panel has measurable velocity. Stiffness controls the performance of the panel at low frequencies until resonance occurs. As the driving frequency increases, the resonance zone is passed and we enter the mass-controlled area. The increase in the sound-reduction index with frequency is approximately linear at this point, and can be represented by Figure 42.8. 

The primary reasons for vibration-profile variations are the dynamics of the machine, which are affected by mass, stiffness, damping, and degrees of freedom. However, care must be taken as the vibration profile and energy levels generated by a machine may vary depending on the location and orientation of the measurement. 

To minimize effects of friction and other lateral forces in the topography measurements in contact-modes AFMs and to measure topography of the soft surface, AFMs can be operated in so-called tapping mode [53,54]. It is also referred to as intermittent-contact or the more general term Dynamic Force Mode" (DFM). A stiff cantilever is oscillated closer to the sample than in the noncontact mode. Part of the oscillation extends into the repulsive regime, so the tip intermittently touches or taps" the surface. Very stiff cantilevers are typically used, as tips can get stuck" in the water contamination layer. The advantage of tapping the surface is improved lateral resolution on soft samples. Lateral forces... 

The studies on adhesion are mostly concerned on predictions and measurements of adhesion forces, but this section is written from a different standpoint. The author intends to present a dynamic analysis of adhesion which has been recently published [7], with the emphasis on the mechanism of energy dissipation. When two solids are brought into contact, or inversely separated apart by applied forces, the process will never go smoothly enough—the surfaces will always jump into and out of contact, no matter how slowly the forces are applied. We will show later that this is originated from the inherent mechanical instability of the system in which two solid bodies of certain stiffness interact through a distance dependent on potential energy. 

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