Symmetric impact

Figure 6.7 shows a Lagrangian time-distance diagram of a symmetric impact by a driver plate with the target backed by a spall plate. The symmetry... 

Figure 6.7. Lagrangian time-distance diagram of a symmetric impact shock.

Figure 8.36. Calculation of Taylor impact of a 1100-0 aluminum cylinder including stress wave evolution and damage formation. Symmetric impact at 0.15 km/s.

The precise impact experiment offers both versatility and the highest of precision. In typical experiments, the projectile is faced with an impactor that is either the same material as the sample to be impacted or a standard material whose properties are known and reproducible. In a symmetric impact configuration the impactor and sample are the same upon impact, precisely one-half of the impact velocity is imparted to the sample. As the impact velocity can be readily measured to an accuracy of 0.1%, this condition provides the most accurately known and best characterized condition achieved in shock-compression science. 

The neady symmetrical composition of SBI-PC (T = 230° C) makes birefringence disappear iu homopolymers, but the material becomes very britde due to the blocking of the free rotation of the aromatic rings, which puts its technical appHcation iu question. Only a copolymerization with 80 wt BPA-PC reaches sufficient levels of impact resistance but T is lowered to 170°C and birefringence iucreases to 80% of that of BPA-PC (195,196). In contrast, TMC-PC as a homopolymer already has sufficient impact resistance at a T of 238°C and a birefringence of 83% of that of BPA-PC (195,205) (Table 7). 

More general dynamic loading conditions can lead to more complex domains of tensile stress and spall. For example, in a Taylor impact experiment (Kipp and Davison, 1981), where a short cylinder of material is caused to undergo symmetric normal impact on the flat surface of a large block of material, a roughly spherical region within the cylinder is carried into dynamic tension and can undergo spall. 

Figure 9.20. Experimental setup for symmetric plate impact test.

Figure 9.20 shows the setup for a symmetric plate impact test. The projectile here has a facing plate of ceramic and is backed with a low-density foam, for support of the ceramic during launch. The facing plate of the target is also made of ceramic. The lithium fluoride slab, which backs the target sample, serves as a window for the laser velocity interferometer (VISAR) that measures the time-resolved particle velocity at the sample/window interface. 

The suppliers of nylon 46 have laid particular emphasis on the fact that this polymer, with its highly symmetrical chain structure, leads to both a high level of crystallinity and a high rate of nucleation. In turn the high nucleation rate leads to a fine crystalline structure which in this case is claimed to lead to a higher impact strength (dry as moulded) than with nylons 6 and 66. 

The shuttle shifter moves the plates back one by one towards the fixed header. When each plate parks the cloth is washed at 100 bar with a mechanism that lowers and lifts a pair of symmetrical manifolds with high impact nozzles. 

Recent experiments11 have shown that for symmetric top molecules, such as methyl chloride, electron impact ionization is more probable at the positive end of the dipole. This follows intuitively from simple electrostatics, since it would be expected that an electron should be more strongly attracted to the positive end of the dipole, leading to a greater ionization probability at this end of the molecule. The effect may be quantified in terms of a steric ratio R. 

In the early stages of the metallocene-catalyzed olefin polymerizations the focus of research lay on C2- and CY-symmetric complexes [3, 12, 13], Since the beginning of the 1990s C,-symmetric catalysts have had more and more impact. The reason is... 

The simulation of droplet impact shown in Fig. 16 is conducted under perfectly symmetrical conditions, which is not easy to achieve in the experiments. 

Numerous 2-D models have been developed to simulate droplet deformation processes during impact on a smooth surface. Most of these models assumed axi symmetric deformation of a spherical or cylindrical droplet. The models may be conveniently divided into two groups, i.e., compressible and incompressible. 

The methyl-substitution pattern of the neutral sugar residues can be reliably identified from their mass spectra.41-43 Identification of the substitution pattern from the electron-impact, mass spectra rarely presents any major problems. It should, however, be noted that, in some cases, the occurrence of symmetrical molecules jeopardizes the identification. An example of this is the symmetrical, 3,4-di-O-methyl derivative (6) of mannose, which is commonly found in the analysis of... 

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