Static mechanical testing

Finally, there is the extremely important group of relaxation methods for determining T. These can be based on either mechanical (sometimes thermomechanical) or electrical relaxations occurring within the material, and, although they do not always give results that are completely consistent with those obtained by the static mechanical tests already mentioned, they are considered very reliable and are widely used. 

Table 47.2 lists the Qj (in GPa) for human (haversian) bone and bovine (both haversian and plexiform) bone. With the exception of Knefs [1978] measurements, which were made using quasi-static mechanical testing, aH the other measurements were made using bulk ultrasonic wave propagation. 

Static mechanical testing involves applying a constant stress or strain to a gel sample in tension or compression. 

The main dilferences between conventional quasi-static mechanical testing and a dynamic impact event on large samples have been well demonstrated in the open literature. Generally, the strain rate for quasi-static mechanical testing is on the order of lO -lO s while dynamic testing is in the range of 10 -10" s Therefore, the stressed volume in an impact event is much larger than that in the... 

DMS techniques yield the loss modulus E" in addition to the storage modulus (See Section 1.5.5.) As is the case with the static mechanical tests discussed above, DMS and electron microscopy techniques provide complementary information on two-phase materials The former is a sensitive... 

Quasi-static mechanical tests of extruded and drawn blends, as well as MFCs based on PET, PBT, PAG, PA66 and of the neat polymers are shown in Figure 11.7 [41,42,45,90]. 

At this point, it should be mentioned that for these two MFC systems, PP/PET and PE/PET, static mechanical test data were obtained only for the compositions 1 1 (by wt), but were compared to those of commercial PP and PE composites containing 30% (by wt) glass fibers. An independent study [50] on the effect of blend composition (30/70, 50/50, 70/30 by wt) of PP/PET and PE/PET blends showed that the respective values of the mechanical parameters (cr, E, and s) differ only slightly (around 20%) between blends containing 50 or 30% (by wt) reinforcing component (PET). In other words, the observed differences in the mechanical behavior of the short GF-reinforced composites (30% by wt) and the MFC systems (with 50 wt% reinforcing component) cannot be explained by the various contents of reinforcement, but are due to the specific characteristics of the MFCs. 

Characterization of the viscoelastic properties of polymers are classified into two categories static and dynamic measurements. The static mechanical tests involve creep, stress relaxation, and stress-strain measurements. In a creep test, a constant stress is applied to the specimen, and its deformation is measured as a function of time. In a stress relaxation test, the specimen is deformed a fixed amount, and the change in the stress is measured as a function of time. The stress-strain measurement is carried out by stretching the sample at constant tensile speed and then recording the load and deformation simultaneously. 

FIGURE 5.13 Schematic illustration of static mechanical testing. 

The static mechanical tests of most interest for FRC composites are flexural (bending) tests. To characterize the flexural behaviour of FRC, it is necessary... 

The stability of a static mechanical system can, as we know, be tested very easily by looking at how the potential energy is affected by any changes in the orientation or position of the system (Eig. 5.3). The stability of more complex systems can be tested in exactly the same sort of way using WJr (Eig. 5.4). 

Fracture Mechanics tests on a grade of ABS indicate Aat its K value is 2 MN and Aat under static loading its growA rate is described by the equation. 

The mechanical properties of plastics enable them to perform in a wide variety of end uses and environments, often at lower cost than other design materials such as metal or wood. This section reviews the static property tests. Chapter 5 provides more information on the meaning of these type data. 

Environmental Cracking The problem of environmental cracking of metals and their alloys is very important. Of all the failure mechanism tests, the test for stress corrosion cracking (SCC) is the most illusive. Stress corrosion is the acceleration of the rate of corrosion damage by static stress. SCC, the limiting case, is the spontaneous cracking that may result from combined effects of stress and corrosion. It is important to differentiate clearly between stress corrosion cracking and stress accelerated corrosion. Stress corro-... 

DSC studies have shown that multifunctional monomers react quickly to form densely crosslinked networks from liquid monomer solutions. However, even a small amount of unreacted monomer can effectively plasticize a crosslinked network, rendering it more pliable. Eor this reason, mechanical analysis was combined with DSC studies to characterize the physical changes occurring in the proposed dimethacrylate system as polymerization proceeds. Static compression tests (Perkin-Elmer, DMA7e) were completed on disks (d = 11.5 mm, t = 1.7) immediately after they were irradiated for varied times. 

The term dynamic test is used here to describe the type of mechanical test in which the rubber is subjected to a cyclic deformation pattern from which the stress strain behaviour is calculated. It does not include cyclic tests in which the main objective is to fatigue the rubber, as these are considered in Chapter 12. Dynamic properties are important in a large number of engineering applications of rubber including springs and dampers and are generally much more useful from a design point of view than the results of many of the simpler static tests considered in Chapter 8. Nevertheless, they are even today very much less used than the "static" tests, principally because of the increased complexity and apparatus cost. 

In l02) the authors describe the design of an experimental plant for studies of acoustic cavitation in flowable high polymers with the help of optic methods the plant employs a flat-slit transprent-wall capillary acoustic treatment of a polymer was carried out at a frequency of 17.8 kHz, and amplitude of vibration between 0 and 15 mcm. The study was conducted on 1,2 polybutadienes of narrow molecular-mass distribution tests were arranged at room temperature. It has been demonstrated that static mechanical stresses occur in a stationary (non-flowing) polymer under the action of acoustic treatment isochrome lines in the viscosimetric tank form a cellular structure with cell size of about 1-3 mm, and in the capillary the isochromes are observed in form of longitudinal strips (Fig. 19). The authors have also found that acoustic... 

Two leach test procedures were used a modified IAEA dynamic leach test and a static leach test. In the former test the leachant was gently agitated on a mechanical shaker and was changed at selected intervals. A typical sampling schedule was three times daily for the first week, twice per day for week 2, once per day for weeks 3 through 5, and once per week through week 9. 

Mechanical testing was conducted on samples 25 mm in length, 10 mm in width and 0.1 mm in thickness, Because of the high compliance of the films, it was difficult to mount an extensometer on the samples to measure E. A DMA was therefore used to assess the elastic properties of the composite samples in the tensile mode of loading. A 5 N static tensile load and displacement amplitude of 16 /tm at a frequency of 1 Hz were applied. Nine measurements for each sample were made and the average values are reported here. 

The processes at the crack tip of a notched specimen in a stress cracking liquid under mechanical stresses and possibly elevated temperatures can be regarded as local aging phenomena. Fracture mechanics, on the one hand, is a very sensitive method of detecting a polymer s behavior with regard to these influences. On the other hand, as demonstrated in the previous examples, FCP measurements can distinguish between small material differences. As depicted in Fig. 21, PE-HD shows the different behavior in static fracture mechanics tests with respect to water at a temperature of 80 °C for two different stabilizers. Stabilizer 2 leads to higher K values at comparable da/dt values and is therefore more appropriate for hot-water applications when oxidation processes also have to be taken into account [88]. 

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. 

The DGEBA/DDS network (Table 3) were calculated using Eq. (2) (with Q, A and equal to unity) and near equilibrium rubbery moduli determined from both static tensile tests and low frequency (0.16 hz) dynamic mechanical... 

Most of the mechanical properties of propylene oxide-modified wood are reduced (116). The modulus of elasticity is reduced 14%, modulus of rupture is reduced 17%, fiber stress at proportional limit is reduced 9%, and maximum crushing strength is reduced 10% (116). Ethylene oxide-modified wood showed no reduction in static bending tests (107). 

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