Dynamic modulus test

The dynamic modulus test is conducted in accordance to the AASHTO T 342 (2011) or AASHTO TP 79 (2013) procedures. Both determine the dynamic modulus and phase angle over a range of temperatures and loading frequencies. 

According to AASHTO T 342 (2011), the dynamic modulus, l l, is the absolute (normal) value of the complex modulus, E, calculated by dividing the maximum (peak-to-peak) 

The dynamic modulus values measured over a range of temperatures and loading frequencies can be shifted into a master curve for characterising bituminous mixture for pavement thickness design and performance analysis. 

The specimens are cored from gyratory-compacted specimens with an average diameter 

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Fig 4. Typical arrangement for Fig 5. Quasi-static and dynamic modulus results for the dynamic modulus test. each of the three materials. 

The beams, fabricated in the material testing laboratory, having dimensions of 7.5 cm x 7.5 cm X 30 cm were tested for relative dynamic modulus in accordance with ASTM C 666-97. Three-inch cubes were sawn from each of the beams after the relative dynamic modulus test. The cubes were tested using procedures presented in ASTM C 116-90, Test Method for Compressive Strength of Concrete Using Portions of Beams Broken in Flexure. When the specimens were 28 days old, the freeze-thaw durability specimens were cured in lime-saturated water until testing was begun. 

Figure 7.10 Schematic representation of the dynamic modulus test, (a) Sample In testing device, (b) Details on the position of the LVDT (GL, gauge length d, specimen diameter). (From AASHTO T 342, Determining Dynamic Modulus of Hot Mix Asphalt [HMA], Washington, DC American Association of State Highway and Transportation Officials, 2011. With permission.)...

More details for the dynamic modulus test can be found in AASHTO T 342 (2011). 

Dynamic mechanical tests measure the response or deformation of a material to periodic or varying forces. Generally an applied force and its resulting deformation both vary sinusoidally with time. From such tests it is possible to obtain simultaneously an elastic modulus and mechanical damping, the latter of which gives the amount of energy dissipated as heat during the deformation of the material. 

Dynamic properties are more relevant than the more usual quasi-static stress-strain tests for any application where the dynamic response is important. For example, the dynamic modulus at low strain may not undergo the same proportionate change as the quasi-static tensile modulus. Dynamic properties are not measured as frequently as they should be simply because of high apparatus costs. However, the introduction of dynamic thermomechanical analysis (DMTA) has greatly widened the availability of dynamic property measurement. 

Dynamic Mechanical Tests. Plasticizer efficiency, can be measured, not only be the lowering of T , but also by temperature dependence of typical dynamic mechanical properties, such as modulus and damping. 

Dynamic mechanical tests measure the response of a material to a periodic force or its deformation by such a force. One obtains simultaneously an elastic modulus (shear, Young s, or bulk) and a mechanical damping. Polymeric materials are viscoelastic-i.e., they have some of the characteristics of both perfectly elastic solids and viscous liquids. When a polymer is deformed, some of the energy is stored as potential energy, and some is dissipated as heat. It is the latter which corresponds to mechanical damping. 

The variation of the damping factor (tan 5) with temperature was measured using a Polymer Laboratories Dynamic Mechanical Thermal Analyzer (DMTA). The measurements were performed on the siloxanfe-modified epoxies over a temperature range of — 150° to 200 °C at a heating rate of 5 °C per minute and a frequency of 1 Hz. The sample dimensions were the same as those used for flexural modulus test specimens. 

E = storage modulus determined in a dynamic mechanical test, GPa... 

The bulk rheological properties of the PFPEs, including the melt viscosity (p), storage modulus (G ), and loss modulus (G"), were measured at several different temperatures via steady shear and dynamic oscillation tests. Note that we denoted p as melt viscosity and r as solution viscosity. An excellent description of the rheology is available in Ferry [99]. 

Fig. 1 a,b. Strain amplitude dependence of the complex dynamic modulus E E l i E" in the uniaxial compression mode for natural rubber samples filled with 50 phr carbon black of different grades a storage modulus E b loss modulus E". The N numbers denote various commercial blacks, EB denotes non-commercial experimental blacks. The different blacks vary in specific surface and structure. The strain sweeps were performed with a dynamical testing device EPLEXOR at temperature T = 25 °C, frequency f = 1 Hz, and static pre-deformation of -10 %. The x-axis is the double strain amplitude 2eo... 

The modulus measured by making an acoustic pulse travel down a fiber axis is called the dynamic modulus to distinguish it from the static modulus measured in a mechanical testing machine. 

An obvious and very important consideration in dynamic modulus comparisons is the uniformity of test samples. Candidate materials should be checked to be stable in time. Sample fabrication should be meticulous. Special care should be given to different sample geometries, especially when the chemical reaction during fabrication is exothermic. Finally, comparisons should be made with materials that possess a relatively narrow glass transition region and high loss factors. These materials more readily display differences among the test apparatus. 

For low strains and damping the dynamic modulus G will have the same magnitude as that obtained from other methods like stress relaxation or tensile tests, provided the time scales are similar in these experiments. 

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