Vol.6 No.5 October 1998
NON-METALLIC MATERIALS FOR STRATEGIC APPLICATIONS
The speciality non-metallic materials find use in diverse applications ranging from protection of structures to structural materials, tailored materials, electronic materials, and camouflage materials. Many of these materials are of strategic importance. DRDO has therefore set up necessary infrastructure and expertise to design, develop and productionise such speciality non-metallic materials and systems based on basic and applied research.
Non-Metallic Structural Materials
Non-Metallic Speciality Materials
Special Materials for Strategic Applications
Research on New Speciality Materials
During the development stage of any Defence structure/system, it is always stressed that structural design concept must take advantage of the material properties required to achieve weight and cost benefits.
DRDO, through its well-directed and concerted efforts, has made it possible to develop a wide range of non-metallic materials for diverse applicationsmany of which are strategic.
The range of materials covered under this category includes structural, electronic, tailor-made, protective, and camouflage/smart materials. These developments owe inspiration from the DRDOs mission objective of self-reliance in defence preparedness by meeting the tactical requirements of the Armed Forces in areas as diverse as one can imagine. Some of the technologies of non-metallic materials development have been highlighted here.
A large number of technologies have been developed related to non-metallic composites based on glass-fibre, carbon-fibre and hybrid reinforcement epoxy composites for applications as airframe components, such as nose, wing, fuselage, tail boom, and engine-air intake for unmanned aerial vehicle Lakshya developed by DRDO.
Several semi-structural composites have also been developed using rigid foams mainly of polyurethane and polyacrylamide. They have been practically used in specific programmes successfully and are suited to multifarious non-military applications, such as light-weight rehabilitation aids and riot control equipment. Floor reaction orthosis (FRO), a noteworthy spin-off benefit in respect of a light-weight rehabilitation walking aid for polio-affected children, is made of glass/polypropylene composite materials by processes, such as injection and compression moulding to predetermined standard sizes to replace metallic calipers.
Strategic components using glass/epoxy skins and syntactic foam cores have also been developed for strategic applications requiring specific responses to microwave and electric fields. Microwave transparent polymer/composite products, finding applications either as airframe components like airborne radomes for fighter aircraft or as radar cross-section (RCS) augmenting dielectric device like Luneberg lens have been developed. Both thermoplastic and thermoset materials have been used for these developments.
Also, kevlar/carbon hybrid reinforced composites have been developed with carbon fibre on the facings and kevlar fabric in the core. Shielding EMI effectiveness of deve- loped composite has been evaluated to be 100 dB in the 100-200 MHz frequency range and about 70 dB up to 2 GHz frequency range.
Luneberg lens reflector is a device used to enhance the RCS of small dummy aerial targets towed to a pilotless target aircraft during testing of aerial weapons. It is a spherical dielectric lens having two foci, one located on the surface of the lens and the other at infinity. This two-segment device has been constructed from low density polystyrene foam shells filled with polystyrene granules, a matching section, metal reflector and radome cover. The device gives large back-scattered reflection of micowave energy over a wide viewing angle.
In fact, a large number of composite technologies are available at DRDO, encompassing design, processing, testing and performance monitoring. Some important key technologies established to develop advanced composites for aerospace systems are:
Design & Analysis
Material Characterisation & Testing
These technologies find wide range of applications, such as structural, thermostructural, ablative, electromagnetic, and ballistic as in armoured vehicles and personnel protection. FRP composites, having thermoset resin as binder and high tensile strength fibres as reinforcement have been developed as substitutes for metals in protective systems. The FRP composites of lower density and excellent energy absorption capacity developed for Kanchan armour are suitable for use in AFVs. Various aramid reinforced ballistic composites of various thicknesses ranging from 5 to 40 mm have been designed and developed to meet the requirement of protection level of 1.1 g FSP, 9 mm SMC, and 5.56 mm and 7.62 mm rifle bullets. These composites have been found to be stable under extreme tropical and marine conditions. In addition, DRDO has become self-reliant in advanced composites, e.g., multidirectionally reinforced carbon-carbon composites for re-entry and brake disc applications, using advanced weaving and braiding technologies. DRDOs capability in developing any advanced composite has been a successful deterrent to the technology denial concept imposed on the country.
Non-Metallic Speciality Materials
Ceramic materials occupy a unique place in the realm of non-metallic materials for strategic applications. Technologies have been developed for the production of PZT-based piezoceramics and high temperature resistant and durable ceramics, such as toughened alumina and zirconia for coating applications for use as high temperature and abrasion-resistant coating. The piezoceramics developed are dedicated towards transducer applications, such as sonar and fuse systems for armament and for the development of composites of various connectivities for high sensitivity hydrophone applications. These materials also have promise for application for various missions of the country, including ocean-wave energy conversion. The suitability of both PZT material and zirconia powder for the above applications has been realised by employing fine particle technologies. This process technology involves purification of raw material, preparation of powders of mixed solutions and characterisation and processing of powders. Chemical homogeneity and other properties are strictly controlled to obtain the combination of desired microstructure and properties in the production.
Other speciality ceramics and high temperature inorganic materials, such as silicon carbide, yttria-stabilised zirconia (YSZ), boron carbide, titanium boride and nitride have been developed in various forms, such as powder, compacts and whiskers. These are, in most applications, critical in nature and also hold promise for diverse applications of future technologies where extreme conditions are anticipated. Some of these materials in large size compacts are not available due to import restrictions. These chlenging technologies involving complex processing steps and stringent quality requirements have been successfully developed for application as thrust bearing, bearings bushes, and components in inertial guidance system of missiles and other critical areas.
Ceramics spacers based on YSZ powder compacts have replaced the conventional steel spacers by improving thermal gradient, temperature stability and electronic chamber temperature in the inertial guidance systems. These improve- ments, realised due to low thermal conductivity and high fracture toughness of YSZ material, has resulted in reduction of error probability of hitting the target. Silicon carbide (SiC) whiskers and particulate find application in the reinforcement of plastics, metals and ceramics. The technology for the production of SiC whiskers from the rice husk has been developed. Also, the technology has been developed for reaction-bonded SiC bearingscritical components for main feed water pumps used by the Indian Navy. The technology development included powder preparation from polymeric mixtures, cold compaction of tubular components, controlled carbonisation, etc. As a spin-off of this technology, several small seal rings and wear parts have been developed for automative and textile industry.
Polymer technologies involve use of speciality polymers as such for various components or in conjunction with other materials also. The technology has been set up for fast setting and high strength resin system based on unsaturated polyester resin for different service applications, such as rapid repair of runways, class A roads and helipads, launching pads and anchorage in the sandy soil, and anchorage of mooring rings for ground test run of aircraft.
Technologies have been developed for a variety of high temperature polymers including PEEK (polyetheretherketone) and polyimides, and are being explored for use in strategic areas. A number of speciality polymers/resins have been developed as components of superadhesives (to bond diverse materials, such as metals, ceramics, rubbers and plastics), putty and structural resins. These include bismaleate resins and styrene-less polyester resins, isocyanate-capped polyols and toughened epoxies. Bismaleimides, having excellent thermal stability under hot, humid conditions, have been synthesised up to the pilot plant scale using a cheaper acetone solvent method. Also, technologies for synthesis of nadimides having temperature stability up to 350 oC have been established. Technology for productionisation of fibre-reinforced polymer composite using these speciality polymers/resins is very well established and various components of strategic items can be developed using the newly made polymer and resins with enhanced properties. Technology has also been established for the synthesis of another class of speciality polymers called conducting polymers. Conducting polymers are one of the speciality polymers derived from monomers like pyrrole furan, thiophene and aniline and doped with a variety of organic and inorganic electron acceptors by using both chemical and electrochemical techniques.
Conducting polymers find extensive use in diverse applications as light-weight rechargeable batteries, light-emitting diodes, corrosion protection, sensors for toxic gases, etc. Protection of defence structures and establishments under diverse and harsh conditionsas severe as marine conditionscalls for sound protective systems. DRDO is self-sufficient in this area in having established technologies, such as anticorrosive and antifouling paints, solvent-free paints for corrosive but confined compartments, non-skid paint with anti-slip properties and fire retardant intumescent paint. The technologies are fully exploited and the compositions are available from selected paint manufacturers. These paints have wider applicability and can find application extensively in non-defence sectors as well.
Special Materials for Strategic Applications
A large number of materials have been developed which can be termed as speciality materials and technologies for which have been established and are being constantly improved. These have a wide spectrum usage range, covering structural to camouflage materials. Technologies have been established for specific finished products based on non-metallic materials such as polymers and ceramics.
Development of materials for better hiding and seeking is an important technological area where good amount of effort has gone. Some of the materials developed include camouflage paints and synthetic camouflage nets against visible, near IR and radar detection. The colour combination, diffusivity and microwave properties have been so adjusted as to ensure hiding against green belt, desert and semidesert terrains. They are tested to prevent detection of warfare equipment, vehicles and manpower against enemy surveillance.
Solvent-based paints suitable for visible and near IR regions have been developed in five shades, namely, olive green, deep Burnswick green, dark beacon, light green, and Beige, each having IR value of 20, 35, and 50 per cent. These paints have been found compatible with mild steel, PVC sheet, wood, rubbersheets, etc. The Radar Scattering Camouflage Net has been very effective to prevent detection by devices working on different ranges of electromagnetic spectrum, including X-band region. This net has been developed in reversible design having disruptive pattern garnishing on one side for green belt and on the other side for desert terrain. It is pregarnished and can be used instantaneously within a few minutes. There is a great possibility of application of these devices in sensitive installations in non-defence sector. Also developed and extensively tested are other energy dissipative devices, such as mounts against shock and vibration and containment of underwater sound.
A number of technologies, such as those involving polymer blends, interpenetrating polymer networks, etc. are well established and are awaiting production for high technology applications.
|.||Research on New
Fundamental studies encom- passing basic and applied research are an integral part of technology development in speciality materials. Such studies are pursued in earnest by DRDO. Notable among them are studies on high efficiency ion-exchange resins, smart polymeric systems, special polymeric binders for explosives, photocurable thermosets, adhesives for transparent armour, encapsulant for microelectronics and conducting polymers. These materials are destined to play important roles in the development of strategic systems and components of defence in future. Besides studies on the development of new basic raw materials, it is also important to study their specificity in properties and processing technologies for component development. A staunch basic database is essential for effective performance evaluation. All these aspects are also being studied seriously by DRDO.