An ultrasonic c-scan system for the NDE of advanced composites

A state-of-the-art computer controlled ultrasonic through transmission jet probe c-scan system for the Non- Destructive Evaluation (NDE) of advanced composites has been set up in the Composite Structures Laboratory (NAL), under the advanced composite technology programme funded by the Aeronautical Development Agency (ADA). The system configuration and specification details were arrived at, after considerable studies, with a view to establish a cost effective c-scan system that would meet most of the NDE requirements of advanced composites, notably that of the CFRP rudder - of the Light Combat Aircraft (LCA). The salient features of the NAL c-scan system are presented in this report. In addition, various aspects of the pre-shipment inspection and acceptance tests carried out at the manufacturer's works as well as during the commissioning at NAL are discussed here

Non-Destructive Evaluation—A Pivotal Technology for Qualification of Composite Aircraft Structures

Tremendous advances in composite materials and a deeper understanding of their behavior have been responsible for the increased use of composites in the development of advanced, new generation civil and military aircraft. Composites play an important role in any aircraft development programme and are strong contenders to their metal counterparts due to their significant contributions towards improving strength, stiffness, fatigue properties & weight reduction. As materials, structural design & processing have evolved, strong emphasis is placed on effective & reliable damage detection, durability and damage tolerance. As a consequence, Non-destructive Evaluation (NDE) has also undergone significant advances towards meeting the growing demands of quality assurance. Advanced Composites Division (ACD) of National Aerospace Laboratories (NAL), has been involved in the development of composite structures for both civil and military aircraft for over a decade and a half. Innovative composite processing methods like co-curing/co-bonding have been successfully employed to realize airworthy structures. The role of NDE in the development of these structures has been critical and not limited to damage detection alone. On several occasions, NDE has provided valuable inputs towards improving design and process parameters. In-spite of the complexity of the structures, stringent quality requirements and tight delivery schedules, NDE has been successful in certifying these composite structures for airworthiness. This paper discusses the implementation of key NDE techniques like ultrasonics, radiography, acoustic emission and thermography for reliable flaw detection, characterization and quality assurance of composite aircraft structures

Acoustic Emission Monitoring of Ammonia Transfer Main Weld Joints

Field tests have-been carried out on gas lines under the service conditions when the plant was in operation. The testing procedure involved monitoring of acoustic emissions at six specified locations on the transfer main. The technique involved in the testing and the observations made during the tests are presented in this report

Non Destructive Evaluation of MiG-21 Compsoite Rudder Part II - APT Section Adhesive bond qulality Evaluation

This report contains the results of adhesive bond quality evaluation in the aft section of MiG-21 composite rudder using Fokker Bond Tester. Complete test recordings in respect of four different rudders are included in this report

Acoustic Emission Studies of Bearing Failure in Composites

Superior structural performance of composites has been widely known to the aircraft industry for a long time now. The availability of advanced composite materials and a wide variety of material forms have attracted aircraft designers to adopt composites for the development of large primary and secondary aircraft structures. This growth of composites technology has and their acoustic signatures as they occur in laminated composites. Traditionally, the role of Non-Destructive Testing in quality assurance has been limited to defect detection. With advances in technology, Non-Destructive Testing has evolved into a multi-disciplinary science and has a critical role in ensuring quality and reliability. Of all the available Non-destructive Testing techniques, Acoustic Emission (AE) is probably the only technique that can be applied for monitoring damage initiation and propagation in real-time. Researchers have verified AE as a successful technique for detecting different micro-failures necessitated improvements in quality assurance during both manufacturing and in-service

Application of Acoustic Emission to Study Debond Growth in Co-cured/Co-bonded Composite Structures under Fatigue Loading

Increasing use of fibre-reinforced composite materials for primary and secondary components in aircraft construction has resulted in the development of lightweight and efficient structures. The major emphasis is now towards realization of such structures at reduced cost. In order to achieve this, newer concepts in design and manufacturing of structural composites are being explored. One such concept is to make components with integral construction through co-curing and co-bonding. Through this approach, one can integrate a number of sub-components to realize assemblies in a single cure. Adhesive bonding is one of the most widely used processes for joining two structural members. Adhesive bonding is preferred to mechanical fastening in view of the better structural stiffness that can be achieved. However, the quality of bonding depends on a number of parameters and is very sensitive to the quality of the bonding surfaces. In view of this, it may be extremely difficult and impractical to expect the same degree of bond quality over the bonded region, especially with large aircraft structural components. Hence, we invariably end up with variations in the bond quality. There is a concern from the designers as well as the certifying agencies with regard to these bond quality variations on its long-tem structural performance. With this background, Advanced Composites Division, NAL, has projected a test programme to understand how the structure with inherent good bonds, poor bonds and debonds would behave and to what extent the presence of defects would reflect on the structural integrity. It is essential that the growth of debonds, debond initiation at poorly bonded regions are monitored in real-time to assess the structural integrity. Among the conventional Non-destructive Evaluation (NDE) techniques, Acoustic Emission (AE) is probably the only technique that would provide this information. In this paper, we describe the application of AE technique to monitor defect initiation and growth of debonds during fatigue cycling in co-cured/co-bonded structural components such as flaps for a civilian aircraft. This provides useful information towards establishing damage tolerance of a co-cured/co-bonded composite structure

Non-destructive evaluation of co-cured wing for SARAS

After considerable experience with the development of pre-preg based (mostly Fiberdux T300-914C) autoclave13; moulded carbon epoxy composite airworthy components for both Tejas (LCA) and SARAS programmes, the Advanced Composites Division (ACD) has now come out with an ingenious Vacuum Enhanced Resin Infusion Technology (VERITy) route for the development of Co-cured Carbon Wing for the SARAS aircraft using Carbon Fabric and Epoxy resin. Non-Destructive Evaluation (NDE) has played a crucial role in the formulation of the VERITy process. Also, NDE will be used in the qualification of the wing components and an approach has been evolved

Spectrum analysis of acoustic emission signals from carbon-glass hybrid composites

The use of a simple acoustic emission (AE) technique to study the failure process in carbon-glass hybrid composites is studied. The technique incorporates an unconventional frequency spectrum analysis procedure. The frequency spectrum of AE signals was recorded during the tensile testing of composite specimens. It is found that, in the case of glass-epoxy composites, the high frequency components begin to appear at earlier stages in the load cycle compared to those observed in carbon-epoxy composite

NON- Destructive Evaluation of Mig 21 composite Rudder

This report presents the preliminary studies carried out in connection with the setting up of a procedure, using Fokker Bond Tester, for the Non-Destructive Evaluation of adhesive bonding in MiG-21 Composite Rudder Aft Section

Static testing of bridge deck plate prototypes

This report gives details of the static tests conducted on two types of prototypes : a) Sandwich type with aluminium alloy honeycomb core and Redux bonded GFRP face sheets and b) All GFRP integral web typ