**5.1 Metallic foil electrically exploding driving highvelocity flyers 5.1.1 Short-pulse shock initiation of explosive**

The apparatus of metallic foil electrically exploding driving high velocity flyer offers an attractive means of performing shock initiation experiments. And the impact of an electrically exploding driven flyer produces a well-defined stimulus whose intensity and duration can be independently varied. Experiments are low-cost and there is fast turnaround between experiments.

Short-pulse shock initiation experiments will be very useful in developing more realistic theoretical shock initiation models. For the present, the models predicting shock initiation thresholds is short of, where very short pulses are employed . The technique can provide data to test the capability of improved models.

Based on our experimental apparatus, the shock initiation characteristics of TATB and TATB-based explosives are studied[35,36]. Fig.23 and Fig.24 show the experimental results of shock initiation thresholds and run distance to detonation of a TATB-based explosive.

Magnetohydrodynamics of Metallic Foil Electrical

driving high velocity flyer.

exploding driving high velocity flyer

researched. Fig.26 is the experimental results[38].

Explosion and Magnetically Driven Quasi-Isentropic Compression 371

dynamic behaviors of materials. The loading strain rates and stress duration vary easily. In order to study damage properties of materials using the apparatus of metallic foil electrically exploding driving high velocity flyer, a concept of two-stage flyer is put forward[37]. The Mylar flyer flies some distance to impact a buffer plate such as PMMA or nylon with different thickness, and the pressure produced in the buffer is attenuated to the expected value, and then the attenuated pressure propels the impactor on the buffer to some velocity to impact the target. The impactor is the same material as the target. Fig.25 is the diagram of the two-stage flyer based on the apparatus of metallic foil electrically exploding

Fig. 25. Sketch of two-stage flyer based on the apparatus of metallic foil electrically

By means of the two-stage flyer, the spallations of steel and copper samples were

(a) (b)

It is also convenient to study other dynamic behaviors of materials using the electric gun. Further experimental researches about materials are being done by our research group.

Fig. 26. Experimental results of spallation , steel target (a) and copper target (b).

Fig. 23. Shock initiation threshold of 50% probability of initiation

Fig. 24. Run distance to detonation in a TATB-based explosive

These experiments have the additional advantage of being applicable to relatively small explosive samples, an important consideration for evaluating and ranking new explosives.

#### **5.1.2 Spallation experiments of materials**

Compared with gas gun and explosively driven loading, The apparatus of metallic foil electrically exploding driving high velocity flyer is also a good tool used to research

Fig. 23. Shock initiation threshold of 50% probability of initiation

Fig. 24. Run distance to detonation in a TATB-based explosive

**5.1.2 Spallation experiments of materials** 

These experiments have the additional advantage of being applicable to relatively small explosive samples, an important consideration for evaluating and ranking new explosives.

Compared with gas gun and explosively driven loading, The apparatus of metallic foil electrically exploding driving high velocity flyer is also a good tool used to research dynamic behaviors of materials. The loading strain rates and stress duration vary easily. In order to study damage properties of materials using the apparatus of metallic foil electrically exploding driving high velocity flyer, a concept of two-stage flyer is put forward[37]. The Mylar flyer flies some distance to impact a buffer plate such as PMMA or nylon with different thickness, and the pressure produced in the buffer is attenuated to the expected value, and then the attenuated pressure propels the impactor on the buffer to some velocity to impact the target. The impactor is the same material as the target. Fig.25 is the diagram of the two-stage flyer based on the apparatus of metallic foil electrically exploding driving high velocity flyer.

Fig. 25. Sketch of two-stage flyer based on the apparatus of metallic foil electrically exploding driving high velocity flyer

By means of the two-stage flyer, the spallations of steel and copper samples were researched. Fig.26 is the experimental results[38].

Fig. 26. Experimental results of spallation , steel target (a) and copper target (b).

It is also convenient to study other dynamic behaviors of materials using the electric gun. Further experimental researches about materials are being done by our research group.

Magnetohydrodynamics of Metallic Foil Electrical

Fig.28 (c).

Explosion and Magnetically Driven Quasi-Isentropic Compression 373

Fig.28(a) are the typical free-surface velocity histories measured by DISAR, which show that the slope become steeper for thicker sample. The experimental compression isentropes, theoretical compression isentropes and shock Hugoniots data are presented in Fig.28(b) and

(c)

The results show that the experimental compression isentropes are consistent with the theoretical ones within a deviation of 3%, and are close to the shock Hugoniot data under the pressure of 40GPa and lies under them. Different from the shock method, the whole isentrope can be obtained in one shot, and tens of shots are needed to gain one shock Hugoniot curve. The calculation results[40] show that the compression isentropes gradually deviate from the shock Hugoniots with the increasement of loading pressure over 50 GPa. Therefore, the compression isentropes mainly reflect the off- Hugoniot properties of materials. Under 50 GPa, the compression isentropes are close to the shock Hugoniots, so

Fig. 28. Results of ICEs.(a) typical histories of free-surface velocity. (b) experimental, theoretical isentropes and Hugoniots data of T1 copper. (c) experimental isentrope of L1 pure aluminum, isentrope ang Hugoniot data of 6061-T6 aluminum from reference [39].

we can use the isentrope data to check the validity or precision of shock Hugoniots.

(a) (b)
