Stress Relaxation Test
. Stress relaxation test
of the uncrosslinked and radiation crosslinked samples were carried out at 60[degrees]C at a fixed strain of 70.03% in a rubber process analyzer (RPA 2000).
The loading system for the FRP bar relaxation test
consisted of a hollow jack, steel casing with threaded support rods connecting outer screw nuts and connection to two bearing plates and bed plates, as shown in Figure 3.
The constant level of input strain is a key parameter in the relaxation test
. It should be noted that, in the uniaxial relaxation test
, there was no standard evaluation method for defining the constant level of input strain until Walubita et al.
Another dough was prepared for each treatment, and when the desired consistency was reached, it was extruded, sheeted, and divided into five pieces that were used for a stress relaxation test
with a texture analyzer.
Figure 3 shows the plot of log Mooney unit from the stress relaxation test
of NR for different forms.
However, a different pattern was observed in the stress relaxation test
of accelerated weathered coatings, which indicates the combined effect of photodegradation and structure relaxation, as exhibited in Fig.
The Temperature Scanning Stress Relaxation (TSSR) meter performs the anisothermal stress relaxation test
(AISR), a new test method that subjects a specimen to a constant tensile stress at a constantly rising temperature.
When a short-term relaxation test
is performed under these conditions, stress in the amorphous phase [absolute value of [[sigma].sub.a]] decreases strongly with time, but this reduction in the absolute value of negative stress is observed as an increase in [[sigma].sub.a], whereas stress in the crystalline phase [[sigma].sub.c] changes with time rather slowly, which implies that stress [sigma] increases monotonically with time (inverse relaxation).
The experiments investigated here consist of four kinds of loading conditions, i.e., (i) monotonic tension tests at various strain rates, which was used to investigate the rate-dependent nonlinear stress-strain responses of the PC; (ii) stress-controlled cyclic tension-tension, tension-unloading, and tension-compression tests to consider the effects of stress level and stress rate on the ratchetting (whose loading cases are listed in Table 2); (iii) a creep test following a monotonic tension with an initial stress of 50 MPa and at a stress rate of 1.2 MPa/s, and (iv) a stress relaxation test
following a monotonic tension with an initial strain of 2% and at a strain rate of 0.0005/s.
The load relaxation test
provided the flow data in a much wider range of strain rate with minimal microstructural change or constant microstructure during the test [7, 8], making it possible to analyze the flow curves within the framework of the internal variable theory of SSP.
The obtained if values for HDPE from the dynamic and the stress relaxation test
are very similar, which is consistent with the data from Larson [6).