Conducting Elevated Temperature Normal and Combined Pressure-Shear Plate Impact Experiments Via a Breech-end Sabot Heater System

Summary

Here, we present a detailed protocol of a new approach for conducting elevated temperature reverse normal plate impact, and combined pressure-and-shear plate impact. The approach involves the use of a breech-end resistive coil heater to heat a sample held at the front-end of a heat-resistant sabot to the desired temperature.

Abstract

A novel approach for conducting normal and/or combined pressure-shear plate impact experiments at test temperatures up to 1000 °C is presented. The method enables elevated temperature plate-impact experiments aimed towards probing dynamic behavior of materials under thermomechanical extremes, while mitigating several special experimental challenges faced while performing similar experiments using the conventional plate impact approach. Custom adaptations are made to the breech-end of a single-stage gas-gun at Case Western Reserve University; these adaptations include a precision-machined extension piece made from SAE 4340 steel, which is strategically designed to mate the existing gun-barrel while providing a high tolerance match to the bore and keyway. The extension piece contains a vertical cylindrical heater-well, which houses a heater assembly. A resistive coil heater-head, capable of reaching temperatures of up 1200 °C, is attached to a vertical stem with axial/rotational degrees of freedoms; this enables thin metal specimens held at the front-end of a heat-resistant sabot to be heated uniformly across the diameter to the desired test temperatures. By heating the flyer plate (in this case, the sample) at the breech-end of the gun-barrel instead of at the target-end, several critical experimental challenges can be averted. These include: 1) severe changes in the alignment of the target plate during heating due to the thermal expansion of the several constituents of the target holder assembly; 2) challenges that arise due to the diagnostics elements, (i.e., polymer holographic gratings, and optical probes) being too close to the heated target assembly; 3) challenges that arise for target plates with an optical window, where crucial tolerances between the sample, bond layer, and window become increasingly difficult to maintain at high temperatures; 4) in the case of combined compression-shear plate impact experiments, the need for high-temperature resistant diffraction gratings for the measurement of transverse particle velocity at the free surface of the target; and 5) limitations imposed on the impact velocity necessary for unambiguous interpretation of the measured free surface velocity versus time profile due to thermal softening and possibly yielding of the bounding target plates.By utilizing the adaptations mentioned above, we present results from a series of reverse geometry normal plate impact experiments on commercial purity aluminum at a range of sample temperatures. These experiments show decreasing particle velocities in the impacted state, which are indicative of material softening (decrease in post-yield flow stress) with increasing sample temperatures.

Introduction

In engineering applications, materials are subjected to a wide range of conditions, which can be static or dynamic in nature, coupled with high levels of deformation and temperatures ranging from room to near the melting point. Under these thermomechanical extremes the material behavior can vary drastically; thus, over nearly a century, several experiments have been developed aimed towards probing the dynamic response and/or other characteristics of material behavior while under controlled loading regimes^1,2,3,4,....

Protocol

1. Sample and Target Material Preparation

NOTE: In the following protocol, we will detail the steps necessary for preparing the sample and target materials, which will be later used in a reverse geometry normal plate impact experiment. In this setup, a flyer plate (also the sample), held at the front of a sabot, will be launched via a single stage gas gun and made to impact a stationary target plate housed in the target chamber of the gas gun. A typical flyer and target plate assembly described in the following protocol is shown schematically in Figure 1.

1. Section a 99.999% commercial purity polycrys....

Results

An 82.5 mm bore, 6 m length, single-stage gas gun at CWRU capable of accelerating 0.8 kg projectiles to speeds up to 700 m/s was used in conducting the present experiments. Figure 5 shows a photograph of the modified gas-gun facility at CWRU. Prior to firing, the custom designed sabot is housed within the heater extension piece, shown in Figure 6. The extension piece carries a vertical heater-well enabling a resistive coil heater.......

Discussion

The method and protocol stated above detailed the procedure for properly performing a reverse geometry normal plate impact experiment at elevated temperatures. In this approach, we make custom modifications to the gun barrel at the high pressure (breech) end of the existing gas gun at Case Western Reserve University, to house a resistive heater coil with axial and rotational degrees of freedom. The resistive heater coil system enables thin aluminum specimens, held at the front-end of a heater resistant sabot, to be heate.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
99.999% commercial purity polycrystalline aluminum	Goodfellow	AL007970	Material for flyer plate (sample)
H13 tool steel	Fabrication Center of CWRU	N/A	Material for the sample holder
Solution treat & age Inconel 718 alloy	High Temp Metals	N/A	(1.005/1.015)" Dia x 24", Material for target plate
Photoresist S1805	MicroChem	N/A	Material of the photoresist for holographic grating
Developer CD-26	MicroChem	N/A	Developer to the photoresist for holographic grating
Aluminum 6063 tube	McMaster-Carr	4568T19	Material for the ring in target assembly
Black Delrin (R) Acetal Resin Rod (4-1/2" Dia.)	McMaster-Carr	8576K81	Material for the Delrin holder in target assembly
White Delrin (R) Acetal Resin Rod (1/4" Dia.)	McMaster-Carr	8572K51	Material for the Delrin pins in target assembly
Aluminum 6061 tube	McMaster-Carr	9056K24	Material for the body in projectile assembly
Aluminum 6061 rod	McMaster-Carr	8974K88	Material for the cap in projectile assembly
Teflon sheet	McMaster-Carr	8711K98	Material for the key
LAVA-FF - Alumina Silicate disc	Technical Products	CWR-033116-1
LAVA-FF - Alumina Silicate tube	Technical Products	ALR11515
Alumina Pan Slotted Head Bolt	Ceramco	A83200PANSLT0.500
409 N70 Buna-N O-ring	The O-ring Store	B70409
Loctite Hysol 9412 adhesive	Loctite	83107
High Temperature Cements	OMEGA Engineering	OB-300
Extra fast-set epoxy	Ellsworth	4001
Mylar sheet	McMaster-Carr	8567K94