Blast and Impact Dynamics Lab

Shock Tube and Split-Hopkinson Pressure Bar (tension and compression) test facilities have been commissioned at the University of Mississippi, for the high pressure and high-strain rate evaluation of nano-reinforced panels and sandwich composites.

I. Shock Tube

The Shock tube enables high pressure and temperature shock testing of materials. Two configurations: (a) without piston and (b) with piston attachment (very high pressure), allow generation of blast pressure wave forms up to 15 Kpsi (100 MPa) and 50 milli sec duration at 1000 ft/sec (300 m/sec) velocity. Shock tests can be performed on sandwich beam specimens held under simply supported conditions as well as thinner specimens under clamped (fixed all around) boundary conditions. An innovative 20-pin finger sensor is used for measuring the deformations when fingers contact the backside of specimen.

Shock Tube Sandwich Beam Specimen

Sandwich Beam Specimen

Tube Diagram

Figure 1: Shock Tube facility at UM

Shock Tube Specifications:
  Parameter Range
1 Output Shock Wave  
  Pressure 0-15000 psi (0-103.42 MPa)
  Time Duration 5-50 millisec
  Shock wave velocity in tube Mach 4 (approx.)
2 Piston  
  Mass ~2 kg (4.4 lb)
  Max. Velocity in shock tube <300 m/sec (984 ft/sec)
3 Operating Pressure Range in high pressure chamber 0-5000 psi (0-34.47 MPa)
4 Shock Tube  
  Internal Diameter 80 mm (3.15 in.)
  Outer Diameter 140 mm (5.51 in.)
  Overall Length 6273 mm (247 in.)
  Individual Section Length 2000 mm(78.74 in.)
5 Dump Tank  
  Outer Diameter 1640.63 mm (64.6 in.)
  Inner Diameter 1620 mm (63.78 in.)
  Length 4560 mm (179.53 in.)
  Weight 4500 kg (9921 lb.)
6 Specimen Boundary Conditions Flexure, Fixed (clamped all around)
  Typical Specimen Dimensions Beam Specimen: 304x101x10 mm (12x4x0.4 in.)
    Clamped All-Around Specimen: 152.4x152.4 mm (6x6 in.)
7 Diaphragm  
  Material Low carbon steel
  Machining Tool 3/8 ball head milling tool
  Groove Length: 101.6 mm (4 in.), Depth: 0.381 mm (0.015 in.)
  Repeatability ~50 psi variation in rupture pressure within a single batch
8 Nozzle Diameter ID: 12.7 mm & 76.2 mm (0.5 & 3.0 in.)
II. Split Hopkinson Bars: Compression and Tension

Split-Hopkinson Pressure Bars (SHPB) enable the high-strain rate evaluation of metals, nano-reinforced specimens, foams and sandwich composites, in both tension and compression. The facility is equipped with various sets of bars consisting of maraging steel as well as aluminum 6061-T6, all of which are 0.75 inches in diameter. The striker bars in both compressive and tensile Hopkinson bars are propelled by means of pneumatic pressure. Strain rates in the range of 500-3000/sec have been achieved during tests.

Split Bars Compression Bar

(a)Schematic of Compression Bar

Tension Bar

(b)Schematic of Tension Bar

A solid I-Beam with a height of 24" (609.6 mm) serves as the base of SHPB. A stainless steel liner is mounted on the top surface of the beam for proper leveling and smoothness. The bars are mounted on aluminum support brackets which are designed with oval holes on the base for horizontal alignment of the bar and ball bearings support the bars with minimal friction effects. A reservoir with a pressure rating of 175 psi provides compressed air for propelling the striker bar. For most of the tests the operating pressure range is 10 psi to 50 psi. Honed steel barrels 48" (1220 mm) long with inside diameter of 1.5" (38.1 mm) house each striker bar and a manual safety valve is used to transfer the compressed air from air chamber to barrel. In case of tensile SHPB, a hollow striker bar with inside diameter of 0.75" (19.05 mm) and outside diameter of 1.25" (31.75 mm) and length of 18" (457.2 mm) slides over the incident bar. A pair of diametrically opposing strain gauges are installed on each bar and connected in series to one arm of the wheatstone bridge to form a quarter bridge circuit. Signal conditioner Model 2310B from Vishay Micromeasurements is used for data acquisition. Digital oscilloscope model TDS 3014C from Tektronix is used for recording signals.

Split Hopkinson Bar Specifications:
Parameter Range
Bar Dimensions  
Length of Striker Bar, Ls (in) 18
Length of Incident Bar, Li(in) 144
Length of Transmission Bar, Lt(in) 96
Bar Diameter, D(in) 0.75