Rapid modulus test

The classical means for following vulcanization by physical methods is to vulcanize a series of sheets for increasing time intervals and then measure the stress strain properties of each and plot the results as a function of vulcanization time. A modification of this test generally called a rapid modulus test is widely used in the industry as a production control test. A single sample taken from a production batch of compounded rubber is vulcanized at a high temperature and its tensile modulus is measured. Temperatures as high as 380°F are used to reduce the vulcanization test time to only a few minutes. Any modulus value deviating from a predetermined acceptance limit indicates that the batch is defective and is to be rejected. 

Mechanical Properties and Stability at Elevated Temperature. One increasingly important characteristic of carbon fibers is their excellent performance at elevated temperatures. Strength tested in an inert environment remains constant or slightly increases to temperatures exceeding 2500°C. Amoco s high modulus pitch carbon fiber P-50 maintains approximately 80% of room temperature modulus at temperatures up to 1500°C, then decreases more rapidly to 30% at 2800°C (64). The rapid decrease in modulus is a result of increased atomic mobiHty, increa sing fiber plasticity. 

Modtilus Measurements Another SCC test technique is the use of changes of modulus as a measure of the damping capacity of a metal. It is known that a sample of a given test material containing cracks will have a lower effec tive modulus than does a sample of identical material free of cracks. The technique provides a rapid and reliable evaluation of the susceptibility of a sample material to SCC in a specific environment. The so-called internal friction test concept can also be used to detect and probe nucleation and progress of cracking and the mechanisms controlling it. 

Increasing temperature decreases the modulus of elasticity of elastomers at the same time that accelerated chemical effects occur. In our constant strain fatigue tests it has been found that the effect on the modulus (lower stress at the same strain) is significantly more important than chemical degradation effects, as shown in Figure 2. Thus, failure occurred much more rapidly at 4°C than at 37°C or 60°C. This may be one manner in which fatigue... 

The modulus changes rapidly with temperature and, at 100°C, retention can be in the 32-38% range for two tested grades. 

Profusion of branching should be proportional to number of rubber particles greater in size than the minimum discussed above. At a given rubber content, the number of rubber particles varies as the reciprocal of the third power of particle diameter. Thus, number of particles drops rapidly as particle size climbs above the effective minimum. Laboratory tests show that stiffness properties depend on total rubber content irrespective of particle size (provided the specimen dimensions are large compared with particle dimensions) hence, narrow particle size distribution is essential if maximum toughness is to be combined with minimum loss in stiffness properties (modulus, creep). 

The extensional melt behavior was assessed with the new SER Universal Testing Platform from X-pansion Instruments, described by Sentmanat (53,54) and shown in Fig. 12. 25. The obtained tensile stress of the two resins at 170°C and extensional rate of 20 s-1 are shown on Fig. 12.26. It is evident that Resin E has a higher modulus and higher tensile stress values, at a given strain below yield, than Resin C. From this, and the experimental data discussed previously, we see that the values of the critical shear rate and shear stress for the onset of sharkskin fracture are inversely proportional to the magnitude of the tensile stress of the resins. This suggests that the rapid increase... 

Another important point is the question whether static offsets have an influence on strain amplitude sweeps. Shearing data show that this seems not to be the case as detailed studied in [26] where shear rates do not exceed 100 %.However, different tests with low dynamic amplitudes and for different carbon black filled rubbers show pronounced effects of tensile or compressive pre-strain [ 14,28,29]. Unfortunately, no analysis of the presence of harmonics has been performed. The tests indicate that the storage (low dynamic amplitude) modulus E of all filled vulcanizates decreases with increasing static deformation up to a certain value of stretch ratio A, say A, above which E increases rapidly with further increase of A. The amount of filler in the sample has a marked effect on the rate of initial decrease and on the steady increase in E at higher strain. The initial decrease in E with progressive increase in static strain can be attributed to the disruption of the filler network, whereas the steady increase in E at higher extensions (A 1.2. .. 2.0 depending on temperature, frequency, dynamic strain amplitude) has been explained from the limited extensibility of the elastomer chain [30]. 

In continuous systems consisting of solid phases, the parameter G is the modulus of elasticity of rigid body. Its values may fall in the range between 109 and 10" N m 2. The elasticity modulus of common liquids under the conditions of uniform (hydrostatic) compression is also of the same order of magnitude. However, due to low viscosity, the shear elasticity of liquids may only be observed by rapid tests in which the time of stress action is close to the relaxation period. For this reason at typical times of mechanical action liquids with low r values behave as viscous media. 

The elastic modulus by this dynamic method is slightly higher than by load extension, a quasistatic method. Tests involving elastic deformations, where either stress or strain is held constant, are called static tests. In quasistatic tests, stress or strain is changed slowly with time, and in dynamic tests, stress and/or strain are varied rapidly with time. 

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