|Vol.7 No.5 October1999 ISSN:0971-4413|
DRDO has developed various grades of high quality modified Lead Zirconate Titanate (PZT)-based ceramic for strategic defence applications. Development of PZT-based piezoceramics was started by DRDO in the sixties. As a result of intensive and systematic experimental work spread over three decades, five distinct grades of hard and soft ferroelectric materials with extremely good electromechanical properties have been developed, standardised and produced.
Basic characteristics of various types of PZT materials are :
PZT Type4:It has low dielectric heating loss, high mechanical quality factor (Qm), reasonably good coupling coefficient and high mechanical and electrical strain properties. This material is suitable for high power ultrasonic applications, acoustic projectors etc.
PZT Type8:It has higher mechanical quality factor, greater resistance to depolarisation, low dielectric heating loss and possesses maximum power handling capacity. Material is suitable for applications requiring high electric drive.
PZT Type5A:It is characterised by high sensitivity, permittivity and time stability. Applications of this material include hydrophones, accelerometers, pressure gauges etc.
PZT Type5J:It has higher dielectric constant combined with relatively high piezoeletric voltage and charge constants. Useful for hydrophones and low power acoustic projectors.
PZT Type5H:It has still higher dielectric constant, coupling factor and piezoelectric d constant but suitable for only low temperature operations.
Piezoceramic elements produce high voltage pulses on impact and are used in the fuzing system of hollow charge warheads for initiating the detonation train. Piezoelements are in use in the manufacture of several antitank ammunition. Some of the applications are described below:
Piezoceramics are extensively used in underwater transducers for SONAR, SONOBUOY, Sesimic Systems, Homing Torpedoes, Imaging Arrays, etc. The transducer converts electrical energy to acoustic energy and vice versa. Suitable materials for various transducer applications are PZT Type4, Type8, Type5A, Type5J, PT, etc. according to the relevant specifications.
Axially Polarised Hard Ferroelectric Rings for Active SONAR Arrays
This product is developed from a superior quality hard ferroelectric material capable of withstanding high mechanical stress. This material is best suited for high power acoustic raDIATing transducers used in the active SONAR arrays. The work involved preparation of this material and fabrication of large diameter rings, using special fabrication techniques and controlling several interdependent process parameters to achieve optimum electromechanical properties. Large size piezoelements of this type with tight physical tolerance have been successfully produced for the first time in the country.
Electrostrictive Relaxor Ceramic Material
These ceramics display the phenomenon of expanding when an electric field is applied. The material characteristics include large mechanical strain, low hysteresis, immune to environmental conditions and low aging rate. Developed indigenously for the first time, this material is best suited for deformable mirrors and similar actuator applications.
PZT Hemispherical Shell for Piezoelectric Resonator Gyros
This can be used in the modern solid state gyro system for inertial reference and rotation sensing of navigational system of launch vehicles, satellites and guided missiles, replacing conventional Quartz elements. Hemispherical piezoceramic element with 32 slots forming equal number of electroded actuators for different functions forms the heart of Piezoelectric Resonator Gyro (PRG). High sophisticated and precision work of this type has been carried out for the first time in DRDO.
Piezoceramic materials are also suitable for commercial applications such as high voltage generators, gas igniters, flaw detectors, accelero- meters, pressure and excitation gauges, ultrasonic cleaning, welding and drilling equipments, buzzers, pick-ups, relays, delay lines and several medical diagnostic equipments. Materials currently in use for these applications are selected from PZT Type4, Type8, Type5A and Type5H.
Some other applications of piezoceramics are:
¨Axially polarized hard ferroelectric Rings of various sizes for active SONAR Arrays
¨Electrostrictive relaxor ceramic material with large strain property, low hysteresis and aging rate and suitable for applications like deformable mirrors and other actuators
¨PZT hemispherical shell for use in Piezoelectric Resonator Gyros
In view of the pioneering work and achievements and wide ranging applications, DRDO in association with CSIR is setting up a national centre for development and production of PZT elements.
TEST & EVALUATION
The importance of experimental work assumes greater importance in case of design of armament stores, wherein some of the phenomena last only for nano- or microseconds and the behaviour of materials at high strain rate is not known to the extent desired. This inadequacy also needs to be covered by experimental validation.
DRDO has established dedicated Range facilities in different parts of the country for the test and evaluation of armament systems during design and development. Pashan Range at Pune, Ramgarh Range at Chandigarh, Interim Test Range and Proof & Experimental Range at Chandipore are all well equipped with sophisticated instruments and techniques for providing necessary testing/validation of indigenously developed armament stores. Continuous updating of the facilities and instrumentation has been the key technological objectives in developing these Ranges.
The Pashan Range, spread over 150 hectares of land surrounded by hills on three sides, is being utilised for testing the Armament stores.
Following facilities exist at the range:
þ Small arms firing up to 1000 m range
þVelocity measuring tunnel up to 100 m
þSand Butt tunnel for Artillery, AD Artillery and Missiles warheads
þLeaning Tower for seat ejection studies
þEnvironmental testing for life assessment of Armament stores
þHigh speed photography & video recording
þPhotometric tunnel for measuring luminosity of illuminating stores
þ30 m paradrop tower.
The Range also has an ammunition storage house for breakdown and assembly of explosive filled stores.
This range covers an area of 5000 acres with separate technical zones and a Rail Track Rocket Sled (RTRS) facility. Each technical zone has been equipped to undertake various facets of test and evaluation independent of the other technical zone. The facilities mainly provide high speed photography, flash radiography, blast and pressure parameters, lethality and fragmentation studies and impact phenomenon studies. Some of the exclusive facilities established at Ramgarh range are briefly described herein.
Rail Track Rocket Sled (RTRS)
The RTRS is a ground facility for subjecting the components or sub-systems to any specific or comprehensive captive flight test conditions. The RTRS bridges the gap between traditional wind tunnel testing and free flight testing.
The facility allows for obtaining acceleration and velocity profiles, accurate performance evaluation under controlled test conditions and recovery of test items for post-test examination and analysis. This helps in achieving considerable reduction in flight test cost besides compressing the time frames in developmental programmes of sub-system of missiles , aircraft and weapon systems.
During the last few years, several successful trials have been conducted on the 1200 m long track and very useful data have been generated for a number of projects of national importance, including light combat aircraft, missiles warheads and pilotless target aircraft. The time and cost thus saved is invaluable. Extension of the track to 2000 m for increasing its capabilities to test higher calibre system has been initiated.
Underwater Shock Pressure Tank
An underwater shock pressure tank (6 m dia & 6 m depth) has been set up for undertaking dynamic shock pressure measurements by recording pressure-time profile of shock wave and bubble pulses, on detonation of scaled down high explosive charges. The facility has been extensively used to investigate and compare the performance characteristics of different explosives and also to determine the heat of detonation of unknown explosives.
Baffle Range for Small Arms
The conventional firing range for small arms firing practice requires more than 100 hectares of land. Due to population pressure and sky rocketing land cost, the Services find it extremely difficult to establish such ranges in their cantonments. This problem has been overcome by developing a new design of range called Baffle Range, which requires an area of just two hectares. Some salient features of this range are :
At Chandipore, DRDO has established the Proof Range, specifically devoted to live fire testing and proving of various types of projectiles and their projecting systems/sub-systems.
The Proof Range extends up to 50 km along with coast, 50 km into sea and 500 m inland from the high water line. Sophisticated and modern facilities established at the range accomplish all types of proof and range work.
Some of the special features of Chandipore making it a unique range area in the country and as one of the best proof ranges in the world are :
Armaments,Indian Small Arms System, MultiBarrel Rocket System- Pinaka ,Fin Stabilized Armour Piercing Discarding Sabot, Illuminating Ammunition ,Bund Blasting Device,30mm HE Grenade for AGL,Charge Line Mine Clearing Equipment ,Propellant Technology, 84mm Light Weight RL Weapon ,Warheads ,Lead Zirconate Titanate Based Piezoceramics ,Armament Research Board