Force ductility test

The force ductility test is performed on bituminous binders, in particular those of polymer-modified bitumens, for the determination of the conventional energy of bituminous binders from tensile characteristics. 

The specimens are prepared as in the ductility test and the traction rate is as in the ductility test, 50 2.5 mm/min. 

The test temperature is usually 5.0°C 0.5°C. However, in the case of soft bituminous binders, the test may be performed at a lower temperature (0.0°C 0.5 C), whereas for 

After the bitumen specimen is placed in the apparatus and the testing temperature is obtained, they are stretched to an elongation of 1333% (400 mm). If the specimen breaks prior to the desired elongation, the test is repeated. In case the second specimen also breaks prior to the desired elongation, the test is repeated by increasing the temperature in steps of 5°C, until the test is complete without brittle break. 

For each test specimen, the deformation energy and finally the conventional energy are accomplished from the computerised data of coupled force/elongation. 

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The force ductility test is carried out in accordance to CEN EN 13589 (2008), using the ductilometer apparatus, which is equipped with an additional device capable of measuring the tensile force within the range of 1 to 300 N to an accuracy of 0.1 N (see Figure 4.3). 

The force ductility test is also described in AASFITO T 300 (2011). 

The tensile test is an alternative to the force ductility test for the determination of the tensile properties and cohesion of bituminous binders, particularly polymer-modified binders. 

The test is performed according to CEN EN 13587 (2010) at a temperature of 5 C using the ductilometer apparatus as in the force ductility test but at a constant traction rate of... 

AASHTO T 300.2011. Force ductility test of asphalt materials. Washington, DC American Association of State Highway and Transportation Officials. 

The properties specified for all polymer-modified bitumens ensure (a) consistency at intermediate service temperatures (with reference to penetration at 25°C), (b) consistency at elevated service temperatures (with reference to softening point), (c) cohesion (with respect to force ductility, tensile test or Vialit pendulum), (d) resistance to hardening, (e) brittleness at low service temperature (with respect to Eraass breaking point) and (f) stain recovery (with respect to elastic recovery). 

It should be recognized that tensile properties would most likely vary with a change of speed of the pulling jaws and with variation in the atmospheric conditions. Figure 2-14 shows the variation in a stress-strain curve when the speed of testing is altered also shown are the effects of temperature changes on the stress-strain curves. When the speed of pulling force is increased, the material reacts like brittle material when the temperature is increased, the material reacts like ductile material. 

Theoretical analyses of interfacial debonding and frictional pull-out in the fiber pull-out test were initially modeled for ductile matrices (e.g. tungsten wire-copper matrix (Kelly and Tyson, 1965, Kelly, 1966)) assuming a uniform IFSS. Based on the matrix yielding over the entire embedded fiber length, as a predominant failure mechanism at the interface region, a simple force balance shown in Fig. 4.19 gives the fiber pull-out stress, which varies directly proportionally to the cylindrical surface area of the fiber... 

Instron Three-Point Bending Failure. Three-point bending tests have also been conducted on notched Izod specimens at crosshead rates of 0.02-20 inches/min (Figure 5). Plots of work to break obtained from the areas under the Instron force-displacement traces show abrupt ductile-brittle transitions these are displaced to lower temperatures as the test rate is decreased. However the temperature interval between ductile-brittle transitions of the two materials remains about the same. The force-displacement trace for each specimen shows a yield point with a ductile failure but a sharp termination when the sample breaks in a brittle fashion. 

Figure 7, Temperature dependence of failure stresses in Instron three-point bend tests on Vs inch notched Izod bars cut from (a) extruded polycarbonate sheet and (b) compression molded block polymer B. Crosshead rate = 0,02 inch /min. Span = 2 inches, o = net section stress = force/net cross-section at notch root, O, Craze initiation , ductile failure X, brittle failure ...

The most common type of stress-strain tests is that in which the response (strain) of a sample subjected to a force that increases with time, at constant rate, is measured. The shape of the stress-strain curves is used to define ductile and brittle behavior. Since the mechanical properties of polymers depend on both temperature and observation time, the shape of the stress-strain curves changes with the strain rate and temperature. Figure 14.1 illustrates different types of stress-strain curves. The curves for hard and brittle polymers (Fig. 14.1a) show that the stress increases more or less linearly with the strain. This behavior is characteristic of amorphous poly-... 

The mechanical behavior of polymers is well recognized to be rate dependent. Transitions from ductile to brittle mode can be induced by increasing the test speed. The isotactic PP homopolymer with high molecular weight is ductile at low speed tensile tests. It is brittle at tension under high test speeds at room temperature. Grein et al. (62) determined the variation of Kiq with test speed for the a-PP CT samples (Fig. 11.22). The force-displacement (F-J) curves and the schematic diagrams of the fracture surfaces of CT samples are presented in Fig. 11.23. At a very low test speed of 1 mm s , the F-d curve exhibits a typical ductile behavior as expected. At 10 mm s, the F-d curve stiU displays some nonlinearity before the load reaches its maximum value, but this is substantially suppressed as test speeds increase further. The samples fail in brittle mode at test speeds >500 mm s . From Fig. 11.22, the Kiq values maintain at 3.2 MPam at test velocities from 1 to... 

One term unique to the flexural test is the stress at the conventional deflection. Generally with ductile materials the test piece does not reach a point of fracture but simply keeps bending until eventually it slips from the outer supports. The conventional deflection is defined as 1.5 times the test piece thickness, which for the standard span of 16 times the thickness equates to a strain of 3.5%. The stress at this point forms a useful, if arbitrary, charaeteristic for duetile materials, which occurs before the peak in the force-deflection curve is reached. 

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