Dynamic stiffness

The apex (often referred to as bead filler) compound must be formulated for excellent dynamic stiffness to facilitate stress distribution and provide good car handling properties. The bead insulation compound must possess good adhesion to this most important component for enclosing the pHes of the tire and holding the tine to the rim. The chafer/rim strip compound protects the pHes from rim abrasion and seals the tire to the rim. 

FIG. 8-75 Frequency response curves for a pneumatic positioner/actuator (a) input signal to stem travel for a 69-inch spring and diaphragm actuator with a 1.5-inch total travel and. 3-15 psig input pressure (h ) dynamic stiffness for the same positioner/actuator. 

Fig. 15. Dynamic stiffness images of alternating layers of polyethylene (PE) of two molecular weights at (a) 105 Hz and (b) 200 Hz. The contrast is due to changes in contact compliance (1/stiffness) of the nanoindenter probe in contact with each of the two polymers. The probe-sample respon.se (1/stiffness) as a function of frequency shown in (c) is consistent with the dynamic stiffness images.

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 dynamic stiffness is the ratio of force amplitude to deformation amplitude ... 

The viscoelastic behaviour of rubbers is not linear stress is not proportional to strain, particularly at high strains. The non-linearity is more pronounced in tension or compression than in shear. The result in practice is that dynamic stiffness and moduli are strain dependent and the hysteresis loop will not be a perfect ellipse. If the strain in the test piece is not uniform, it is necessary to apply a shape factor in the same manner as for static tests. This is usually the case in compression and even in shear there may be bending in addition to pure shear. Relationships for shear, compression and tension taking these factors into account have been given by Payne3 and Davey and Payne4 but, because the relationships between dynamic stiffness and the basic moduli may be complex and only approximate, it may be preferable for many engineering applications to work in stiffness, particularly if products are tested. 

Marshall properties and dynamic stiffness. Temperature sensitivity studies also were performed on these materials. 

Direct Substitution Method. Sulfur and asphalt were poured together at 300°F and were added to the heated aggregate at 300°-320°F. The three materials were mixed in the Hobart mixer for 2 min. Standard Marshall test samples for Marshall and dynamic stiffness tests were prepared as in the emulsification method. Bar samples for fatigue testing were prepared by kneading the mix into 3 X 3 X 12-in. bars to obtain compaction equal to the Marshall compacts. 

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. 

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. 

Figure 9.18 Dynamic stiffness as a function of compressibility of impact sound insulation slabs depends on its dimensions...

He DZ, Jia S, Dallos P. 2003. Prestin and the dynamic stiffness of cochlear outer hair cells. J Neurosci 23 9089-9096. 

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. 

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