Development of CGLARE: Design, Fabrication and Characterisation

Fibre Metal Laminates (FMLs) are hybrid materials consisting of metal layers bonded to fibre-reinforced polymer layers. CGLARE is an FML developed at NAL consisting of thin aluminum foil combined with carbon-epoxy and glass-epoxy prepreg materials. CGLARE is proposed as the candidate material for the leading edges of wing and empennage of an aircraft as it has superior characteristics in terms of shape retention (due to highly linearly elastic material like carbon/epoxy), energy absorption capability (due to layered structure and plastic deformation), lightning protection (due to the presence of aluminum layers), and also due to its cost effectiveness (lightweight construction and simple production techniques). This paper describes the issues regarding the development of CGLARE such as surface preparation of aluminum foils and bonding of aluminum with glass. Tensile, Compression, ILSS and Flexure testing of ASTM standard CGLARE specimens for different layups have been done. An important design issue is the internal residual stresses built into the laminate during curing due to differential coefficients of thermal expansion of the different material systems. The paper presents these results that indicate some properties of these material systems that could be exploited for energy absorption in the leading edges of the aircraft

Population-level risks of alcohol consumption by amount, geography, age, sex, and year: a systematic analysis for the Global Burden of Disease Study 2020

Background The health risks associated with moderate alcohol consumption continue to be debated. Small amounts of alcohol might lower the risk of some health outcomes but increase the risk of others, suggesting that the overall risk depends, in part, on background disease rates, which vary by region, age, sex, and year. Methods For this analysis, we constructed burden-weighted dose–response relative risk curves across 22 health outcomes to estimate the theoretical minimum risk exposure level (TMREL) and non-drinker equivalence (NDE), the consumption level at which the health risk is equivalent to that of a non-drinker, using disease rates from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2020 for 21 regions, including 204 countries and territories, by 5-year age group, sex, and year for individuals aged 15–95 years and older from 1990 to 2020. Based on the NDE, we quantified the population consuming harmful amounts of alcohol. Findings The burden-weighted relative risk curves for alcohol use varied by region and age. Among individuals aged 15–39 years in 2020, the TMREL varied between 0 (95% uncertainty interval 0–0) and 0·603 (0·400–1·00) standard drinks per day, and the NDE varied between 0·002 (0–0) and 1·75 (0·698–4·30) standard drinks per day. Among individuals aged 40 years and older, the burden-weighted relative risk curve was J-shaped for all regions, with a 2020 TMREL that ranged from 0·114 (0–0·403) to 1·87 (0·500–3·30) standard drinks per day and an NDE that ranged between 0·193 (0–0·900) and 6·94 (3·40–8·30) standard drinks per day. Among individuals consuming harmful amounts of alcohol in 2020, 59·1% (54·3–65·4) were aged 15–39 years and 76·9% (73·0–81·3) were male. Interpretation There is strong evidence to support recommendations on alcohol consumption varying by age and location. Stronger interventions, particularly those tailored towards younger individuals, are needed to reduce the substantial global health loss attributable to alcohol. Funding Bill & Melinda Gates Foundation

Development of a computer based process control system for an autoclave to cure polymer matrix composites

Autoclave is a process control system used in a number of industries such as aerospace, pharmaceutical, chemical, food processing and health care. NAL has pioneered the design and development of autoclaves in India to cure polymer matrix composites. This paper explains the development of a computer based multi-mode process control system for an autoclave, which is used to fabricate composites structures for aircrafts, satellites and other aerospace applications. This system comprises of a desktop computer, Programmable Logic Controller (PLC), analog data scanner, PID based Front-End Controllers (FEC) etc. It provides Auto, Semi-auto and Manual modes of operation. This paper also presents the strategies for control of autoclave temperature, part temperature and autoclave pressure along with the computer integration aspects. These techniques have been realized and successfully implemented in a couple of autoclaves

Advanced hot bonding system for repair of Aerospace Structures

Repair techniques play an important role in increasing the useful life of the aerospace structures. They increase the confidence level of the user and promote the application of composites. Among the various repair techniques, hot bonding is widely acclaimed for its ability to restore the strength close to the original values. It is used for the repair of metal or composites structures. Hot bonding performed using flexible heater blanket and vacuum bag is the most suitable method for in-situ repair. Hot bonding is performed through elevated temperature cured adhesive system, which increases the glass transition temperature and hence the service temperature of the final product. These adhesive systems are sensitive to temperature gradient. If the gradient exceeds ±5oC, the cross-linking process and the quality of repair is adversely affected. In the hot bonding process, only the repair area is heated and the rest of the part is left in atmospheric condition. Due to partial heating, the region below the centre of the heater gets hotter than the surrounding. This problem worsens if the job has skin and spar construction or has non-uniform cross-section as in the case of aircraft control surfaces or windmill blades. The hot bonding equipment currently being imported (none manufactured within India) does not ensure temperature uniformity. This paper discusses the design and development aspects of multi-zone, portable hot bonding equipment, which overcome the above problems. Multiple numbers of appropriately placed heater blankets, sensors and a data acquisition device coupled with a novel control algorithm and multi-threaded software has resulted in the portable and reliable hot bonder. The equipment was tested on typical aircraft parts, such as an aluminium rudder and a composites fin tip. The conventional single heater blanket method has resulted in a temperature gradient of over 12oC, while this product has limited the temperature gradient to within ±1.5oC

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