Recovery fixtures

Figure 6.10. Schematic drawing of the shock-recovery fixture design.

In an experiment in which a sample is subjected to controlled shock loading and preserved for post-shock analysis, the shock-recovery experiment, the quantification, and the credibility of the experiment rest directly upon the apparatus in which the experiments are carried out. Quantification must be established with two-dimensional numerical simulation and this can only be accomplished if the recovery fixtures are standardized. The standardized fixtures must be capable of precise assembly so that the conditions actually achieved in the experiment are those of the simulation. 

The author s work has included the development of the Sandia Bear and Bertha explosive recovery fixtures, that provide a standardized set of fixtures in which recovery experiments can be routinely carried out at peak shock pressures from 4 to 500 GPa. Shock-induced, mean-bulk temperatures from 50 to 1200°C are achieved with variation in the density of the powder compacts under study. 

Fig. 6.5. The shock-compression conditions imposed on powder compacts preserved for post-shock analysis are controlled by details of the shock-recovery fixtures. In all the work of Chap. 6, the Sandia Bear and Bertha fixtures are used. The fixtures represent a standardized system that is highly reproducible and has been subject to extensive numerical simulation.

Shock-synthesis experiments were carried out over a range of peak shock pressures and a range of mean-bulk temperatures. The shock conditions are summarized in Fig. 8.1, in which a marker is indicated at each pressure-temperature pair at which an experiment has been conducted with the Sandia shock-recovery system. In each case the driving explosive is indicated, as the initial incident pressure depends upon explosive. It should be observed that pressures were varied from 7.5 to 27 GPa with the use of different fixtures and different driving explosives. Mean-bulk temperatures were varied from 50 to 700 °C with the use of powder compact densities of from 35% to 65% of solid density. In furnace-synthesis experiments, reaction is incipient at about 550 °C. The melt temperatures of zinc oxide and hematite are >1800 and 1.565 °C, respectively. Under high pressure conditions, it is expected that the melt temperatures will substantially Increase. Thus, the shock conditions are not expected to result in reactant melting phenomena, but overlap the furnace synthesis conditions. 

During the design phase, all of the data derived from the hydraulic characterization are evaluated for use in the selection of recovery pumping equipment and for the determination of the most appropriate subsurface fixtures (whether wells, trenches, or drains, etc.). A variety of generic scenarios may be appropriate to optimize product recovery. If the product thickness is sufficient, the viscosity low, and the formation permeable, a simple pure-product skimming unit may be the best choice. Other combinations of permeability, geology, and product quality will require more active systems, such as one-pump total fluid, or two-pump recovery wells. 

Figure H3.1.4 Structure recovery after loading a sample of a grease or fat on a cone-and-plate fixture on a rotational rheometer. G was measured over a period of 17 hr at constant oscillatory stress, frequency, and temperature.

Jemski, J. (1960). Recoveries and guinea pig LD50s of aerosols of botulinum toxins disseminated by the Hartman Fixture at 75°F and 50 percent relative humidity. Fort Detrick Applied Aerobiology Division - Technical Evaluation Report Test No. 60-TE-1274 DTIC AD0497593. 

Figure 3.9 Setup used for isothermal stress-strain testing and constrained shape recovery testing. The fixture provided a 1-D external confinement and the furnace was used to trigger the shape memory effect by heating the specimen above its Tg. The MTS machine was used to record the resuiting recovery stress...

Fully constrained recovery was performed using the MTS Q-TEST 150 machine and the associated furnace. Once the specimens were programmed under stress-controlled conditions, as described above, they were placed in the fixture shown in Figure 3.9 such that the strain was fixed and the stress was initially zero. Heating was performed at an average rate of 0.3 °C/min from room temperature until 79 °C and then held for approximately 20 minutes (some specimens were held for over 24 hours in order to investigate the stress relaxation behavior). The load cell of the MTS machine was used to record the recovered force as a function of time and temperature. 

Figure 5.12 Thermomechanical behavior of SMPFs by both cold and hot tension programmings, (a) Stress-strain-time diagram for Sample 2. Steps 1 to 5 complete programming and Step 6 completes stress recovery, where step 1 is to stretch the fiber bundle to 100% strain at a rate of200 ram/min at 100 °C step 2 is to hold the strain constant for 1 hour step 3 is to cool the fiber to room temperature slowly while holding the pre-strain constant step 4 is to release the fiber bundle from tbe fixture (unloading) step 5 is to relax the fiber in the stress-free condition until the shape is fixed and step 6 is to recover the fiber at 150 °C in the fully constrained condition (adapted from Reference [20]) (b) Stress-strain-time diagram for Sample 3. Steps 1-4 complete programming and step 5 completes stress recovery, where step 1 is to stretch the fiber bundle to 100% strain at a rate of 200 mm/min at room temperature step 2 is to hold the strain constant for 1 hour step 3 is to release the fiber bundle from fixtures (unloading) step 4 is to relax the fiber in the stress-free condition until the shape is fixed and step 5 is to recover the fiber at 150 °C in the fully constrained condition (adapted from Reference [20]) (c) Stress evolution with time for Sample 2 (d) Stress evolution with time for Sample 3.

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