Impact surfaces

Tilt. The flat impactor must be delivered onto the specimen with a minimum of tilt between the impacting surfaces. Long projectiles help to minimize tilt. 

In most flat-plate impact experiments, the direction of motion of the impacting plate is normal to its surface, such that only a planar compressive shock is introduced into the specimen. Within the last fifteen years, however, techniques have been developed for dynamic pressure-shear loading of specimens (Abou-Sayed et al., 1976 Chhabildas and Swegle, 1980). These involve an oblique impact, as illustrated in Fig. 3.6, in which the impact surface on the... 

These techniques have very important applications to some of the micro-structural effects discussed previously in this chapter. For example, time-resolved measurements of the actual lattice strain at the impact surface will give direct information on rate of departure from ideal elastic impact conditions. Recall that the stress tensor depends on the elastic (lattice) strains (7.4). Measurements of the type described above give stress relaxation directly, without all of the interpretational assumptions required of elastic-precursor-decay studies. 

Mass concentration units for ambient measurements are mass (/xg) per unit volume (m ). Size classification involves the use of specially designed inlet configurations, e.g., PMjq sampling. To determine mass concentration, all the particles are removed from a known volume of air and their total mass is measured. This removal is accomplished by two techniques, filtration and impaction, described in Chapter 13. Mass measurements are made by pre-and postweighing of filters or impaction surfaces. To account for the absorption of water vapor, the filters are generally equilibrated at standard conditions T = 20°C and 50% relative humidity). 

Fig. 3.5. The experimental arrangement used for a typical compressed gas gun is shown. The apparatus is designed to impact a selected impactor upon a target material with precision on the alignment of the impacting surfaces. Velocity at the impact surface can be measured to an accuracy and precision of 0.1%. This loading produces the most precisely known condition of all shock-compression events.

Typical current pulses observed for x-cut quartz, z-cut lithium niobate, and y-cut lithium niobate are shown in Fig. 4.3. Following a sharp rise in current to an initial value (the initial rise time is due to tilt, misalignment of the impacting surfaces), the wave shapes show either modest increases in current during the wave transit time for quartz and z-cut lithium niobate... 

Fig. 5.5. The electrical response of piezoelectric polymers under shock loading is studied experimentally by placing the thin PVDF element on the impact surface of a standard target, either the polymer, Kel F, z-cut quartz, or z-cut sapphire. The im-pactor is typically of the same material. The current pulse is recorded on transient digitizers with frequency responses from 250 to 1000 MHz.

Epoxy acrylate (Ebecryl 3700, 50%) combined with 25% TMPTA, 25% I BOA and with DIBF-OPPI-DIDMA pigment and FC-171 as above was also used to coat panels. These panels showed no removal of coating in the cross hatch adhesion test. With 6.8j there was no loosened coating on the frontal impact surface, and only 30% was loosened on the back surface. Five hundred grams were required to scratch to bare metal with the balanced beam. Performance was... 

If the fluid dynamic conditions of a droplet are within the spreading regime, i.e., below the threshold curve in the We-Oh map, liquid splashing and ejection from the impact surface can be eliminated. The corresponding threshold velocity can be written as ... 

Fitzpatrick Co., Chicago, IL) using the impact surfaces for pulverization through a 0.69 mm (1/37") round hole screen. 

In all three described setups, deposition on the inserts was 50% or less of the amount usually anticipated on an equal sized area without cell culture inserts. This difference may be explained by the changed distance between orifice plate and impaction surface in the cell culture insert. The collection efficacy of an impactor/impinger decreases with an increase in the ratio of the orifice plate to impaction plate distance over jet width. Observations indicate that although the inserts are not at an optimal distance from the orifice plate and are not exactly at the same position compared to the original collection stage, the cell culture inserts do function as an impaction surface for particles in a relevant size range. 

Place an interleaf immediately below the surface layer if the delamination induced by the transverse cracks originating from the impact surface is to be arrested. 

Impactors with various designs as well as different types of impaction surfaces are in use (e.g., see Chow, 1995). Examples include the Lundgren impactor, the Anderson sampler, the Mercer impactor, and the Uni-... 

Turner, J. R., and S. V. Hering, Greased and Oiled Substrates as Bounce-Free Impaction Surfaces, . /. Aerosol Sci., 18, 215-224 (1987). 

Viscous heating of explosive rapidly extruded between the impacting surfaces or grains. 

Friction between the impacting surfaces, explosive crystals, and/or grit particles in the explosive layer. 

Viscous heating of rapidly flowing expl as it escapes from between impacting surfaces... 

In fact, the pattern of motion is such that a certain mass of the gas, located near the impacted surface experiences a pressure which differs from the self-similar value. For a pressure P, acting over a time t, the shock wave travels a distance Ty/P/p0 and compresses the gas mass by m0Ty/Pp0 (per unit surface). 

Most of the very recent studies used gas guns to propel flyer plates. An example of a gas gun is shown schematically in Fig 12 (Ref 59). In this illustration the impacting surface of a flyer plate is in a quartz pressure transducer... 

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