Flyer plate

Impact resistance is determined usiag flyer plate impact tests, long rod impact tests, Hopkinson bar tests (50), and the Hquid jet technique (51). Impact damage resistance is often quantified by measuring the postimpact strength of the ceramic. 

The peak pressures attainable with explosive facilities can be greatly enhanced, and the initial peak pressure can be better sustained by using a plane-wave generator to accelerate a flyer plate, which then impacts a flat specimen as shown in Fig. 3.2. This technique will generate peak pressures up to a few hundred GPa. (McQueen and Marsh, 1960 McQueen et al., 1970). 

Figure 3.2. Explosive plane-wave generator used to accelerate a flyer plate for planar impact on a specimen.

The most common form of energy deposition used for planar shock wave research has been electrical resistance heating of a metal foil which vaporizes, driving a flyer plate to a high velocity before it impacts a specimen. In a hybrid system incorporation both resistance vaporization and an electromagnetic push, velocities to 18 km/s are reported for kapton flyer plates which are... 

The propagation of a shock wave from a detonating explosive or the shock wave induced upon impact of a flyer plate accelerated, via explosives or with a gun, result in nearly steady waves in materials. For steady waves a shock velocity U with respect to the laboratory frame can be defined. Conservation of mass, momentum, and energy across a shock front can then be expressed as... 

We assume that in (4.38) and (4.39), all velocities are measured with respect to the same coordinate system (at rest in the laboratory) and the particle velocity is normal to the shock front. When a plane shock wave propagates from one material into another the pressure (stress) and particle velocity across the interface are continuous. Therefore, the pressure-particle velocity plane representation proves a convenient framework from which to describe the plane Impact of a gun- or explosive-accelerated flyer plate with a sample target. Also of importance (and discussed below) is the interaction of plane shock waves with a free surface or higher- or lower-impedance media. 

The physical state of the sample before and after impact is sketched in Fig. 4.6(a). Positive velocity, indicating mass motion to the right (in the laboratory), is plotted toward the positive, u, axis. Hence, in the initial state 0, the target B is at Up = 0 and P = 0, whereas the initial state in the flyer plate O is Up = Ufp and P = 0. Upon interaction of flyer plate A with target B, a shock wave propagates forward in the sample and rearward in the flyer plate. Because the pressure and particle velocity are continuous at the flyer-... 

If the Hugoniot of the flyer plate (.4) and the target (B) are known and expressed in the form of (4.7), the particle velocity Ui and pressure Pi of the shock state produced upon impact of a flyer plate at velocity, Ufp, may be calculated from the solution of the equation equating the shock pressures in the flyer and driver plate ... 

Calculate the final shock state pressure and density from the measured shock velocity of 5.77 km/s in a sample of glass (initial density 2.204 g/cm ) which is mounted onto a driver plate of pure Cu. The Cu driver plate is impacted at 4.5 km/s by a Ta flyer plate. Use the impedance match methods. 

In cladding, an explosively driven metal plate (flyer plate) hits another plate (base plate) kept at a specified distance-greater than half the flyer plate thickness in order to allow this plate to achieve its maximum impact velocity. The extreme temperature and pressure produced with high-energy impact, bonds the plates together through a metallurgical bond. This technique is employed to bond... 

Flyer velocity data for 1-D configurations were used to compute the Gurney constants for the six expls shown in Table 2. Most of the data for PBX 9404, Comp B, and Baratol are from SRI flyer plate experiments, and the other data are largely from LRL. The PWG s are either P-80 s or P-120 s (for the six-inch-thick drivers), and we have assumed the same L for both. 

The flyer plates were Al, stainless steel, or brass... 

Benham and Matthews (Ref 20) used the Gumey approach to compute flyer plate velocities of plates propelled by a light-initiated expl. They present a curve that appears to indicate that y/2E is a function of c, the expl real density.. 

Longueville et al (Ref 100) used flyer plates to study the shock sensitivity of RDX (and other expls) as a function of shock amplitude and shock duration. Their results for RDX are shown in Fig 6... 

At one time it was believed (Ref 3) that detonability was detd by the burning rate. It must be understood clearly that high order detonation is a bulk phenomenon and not one governed by the classic proplnt burning theories. The tendency to detonate is a characteristic intrinsic with each formulation which must be studied in shock environments as it is found in a card gap or flyer plate test (see later in this article) or Susan and Wenograd tests (Ref 19) Likewise, density is not a useful measure of the detonability of a proplnt except perhaps to the extent that low density formulations may be porous. A more valid measure of the safe-life of proplnts is the depletion with time of stabilizers such as the nitroamines which are found in double base proplnts or the loss of the plasticizer. Such determinations can now be performed routinely in a quantitative fashion by means of liq chromatography Nuclear Radiation Hazard... 

Much effort is being invested on the development of computer programs for the prediction of initiation thresholds of expls and proplnts but none to date are satisfactory because of the lack of a clear threshold criterion. Shock induced mechanical failure (spall) has been correlated with stress and time by varying the thickness of the flyer plates. Likewise Walker and Wasiey (Ref 15) have attempted to use a P2t criterion (where P is the scalar shock pressure... 

In recent years, flyer plate shock sensitivity tests have begun to be used extensively. Basically these tests consist of propelling a thin plate against the expl sample. The variables in this test are plate velocity, plate material and plate thickness. The shock phenomena involved in the flyer plate expts are sketched in Fig 1. The plate velocity at impact is Ufs, the so-called free surface velocity. The intersection of the reflected characteristics of the shock Hugoniot of the plate material (drawn upwards from Ufs) with the P—u curve of the expl then gives the shock state in the expl at the impacted expl surface (P2, u2 in the example)... 

The advantage of this flyer plate method is that shock duration r can be controlled by varying plate thickness, namely rs = 2h/Us, where h is plate thickness and Us is the shock velocity in the plate... 

The method of propelling flyer plates by donor expls is illustrated in Fig 9 (Ref 55). The system shown uses a two-stage flyer plate arrangement to obtain low impact velocities... 

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... 

A flyer plate technique applicable to gap tests is used at Lawrence Livermore Laboratory. In this technique metal foils exploded by the high energy discharge of a capacitor bank are used to propel plastic flyers. It is illustrated in Fig 15 (Ref 57)... 

Shock initiation data are most amenable to simple interpretation when the initiating shock is plane-wave. Unfortunately, until the recent advent of flyer-plate techniques, plane-wave... 

Further confirmation of the hot-spot nature of shock initiation of granular expls was obtained in some very interesting preliminary expts by Von Holle (Ref 66). He used time-resolved IR radiometry to monitor the brightness temp in 5—8mm thick charges of PBX 9404 impacted by gas-gun driven flyer plates to give "sustained flat pressure pulses in the test samples. His main results are summarized in Fig 21... 

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