INTRODUCTION

The Material Laboratory at the University of Florida Research and Engineering Education Facility (UF-REEF) provides an environment for the impact testing of materials and structures for aerospace applications. It includes of the following major pieces of equipment: Split Hopkinson bar apparatus, drop weight instrumented impact test facility and data acquisition system Dynatap 930-I .

SPLIT HOPKINSON BAR APPARATUS

In general, the rate of deformation has a dramatic effect on the the performance of materials. The Split Hopkinson bar apparatus located at the UF-REEF (Fig. 1) generates a stress-strain response of materials at high strain rates in the range 10²-10⁴ s^-1 what is necessary for accurate modeling of impact events and verifying of numerical test results. Method allows obtaining the high strain rate stress-strain curves based on stress wave propagation analysis and measurements of strain and in elastic bars.

DROP WEIGHT INSTRUMENTED IMPACT TEST FACILITY

Instrumented impact testing enables to simulate a wide variety of real-world impact conditions and collect detailed performance data. The UF-REEF drop weight impact facility includes Dynatup® Model 8120 (GRC 8120) High Capacity Impact Test Machines and in-house-designed Mini-Tower which is fully compatible with the Instron data acquisition system.

Dynatup® Model 8120 (GRC 8120) High Capacity Impact Test Machine

The Model GRC 8120 is designed to perform high-energy impact testing of large metal and composite specimens and structures (Fig.2).

Key Features:

• Impact energies: up to 2,105 Joules (1,554 ft lb)
• Impact velocities: up to 7 m/s (22 ft/s)
• Minimal mass of the falling weight: 102.1 kg (225 lb)
• Operation: Automatic return to drop height for next test
• Load cell: 289.1 kN (65,000 lbs) tup
• Specifications:

§         ASTM E-436 Drop Weight Tear

§         ASTM E-604 Dynamic Tear

§         ASTM E-208 Nil Ductility

§         ASTM E-23 Charpy/Izod

Mini-Tower

In-house-designed drop weight impact test device “Mini-tower” allows conducting instrumented impact testing of plastics, composites and metals (Fig.2). Device is fully compatible with the Instron data acquisition system and delivers a wide range of impact energies. In comparison with the GRC impact machine, the minimal mass of the falling weight is reduced from 225 lb (102.1 kg) to 5 lb (2.3 kg), with the possibility to add additional mass.

Key Features:

• Impact velocities: up to 5.7 m/s (18.7 ft/s)
• Minimal mass of the falling weight: 2.3 kg (5 lb)
• Operation: manual
• Load cell: 44.5 kN (5,000 lbs) tup
• Specifications:

§         ASTM D-3763 Puncture (Plastics)

§         ISO 6603-2 Puncture (Plastics)

§         Boeing BMS-256 Composites Penetration/Damage

§         Boeing BMS-7260 Compression/Impact

§         NASA ST-1 Compression/Impact

§         Other configurations are also available

DATA ACQUISITION SYSTEM DYNATUP 930-I

The experimental research facility located in the Material Laboratory (UF-REEF) incorporates a load cell (tup) and data system Dynatap 930-I for the instrumented impact testing. The outputs of the impact test machines include a trigger signal used for starting data acquisition and determining impact velocity as well as the load signal generated by the impact force transducer (tup). The instantaneous velocity of striker slightly before the moment of impact is measured with a photo-diode and double pronged flag system. An analog-to-digital board is installed in the computer to acquire and digitize the tup impact data under software control. The elements of signal processing and conditioning system are shown in Fig. 3. A powerful integrated software package processes the data reporting load, energy, velocity, time or deflection throughout the impact event (Fig. 4).