Modeling and Verification of Cryogenic Permeability of Graphite-epoxy Laminates with Delaminations and Stitch Cracks

Polymer matrix composite (PMC) materials are ideal for aerospace structural applications, such as cryogenic fuel tanks of Reusable Launch Vehicles (RLVs) and Expendable Launch Vehicles (ELVs), due to their high strength-to-weight and stiffness-to-weight ratio. For the confident application of these materials, it is necessary to evaluate the permeation of cryogenic fuel caused due to transverse matrix cracks in conjunction with inter-ply delaminations resulting in an intersecting network of passages. In this thesis, an expression for predicting delaminated crack opening displacement (DCOD) is derived based on first-order shear laminate theory applied to a five-layer model. The DCOD obtained using the five-layer model is verified using a two-dimensional finite element analysis. A mathematical model to predict permeability in graphite-epoxy laminate system (IM7/5250-4) is developed using Darcy's law for isothermal, viscous flow of gases through porous media. The result obtained from the five-layer model is used as input to the permeability model. Also, a simple methodology to model stitch cracks has been proposed to address experimental observations. Further, a model has been proposed to study damage evolution within the plies of the composite. Model verifications are carried out by comparison with finite element analyses, and by comparison with permeability test data provided by the Air Force Research Laboratory.Mechanical & Aerospace Engineerin

Process and structural health monitoring of advanced fibre reinforced composites using optical fibre sensors

The focus of this research was to design, optimise and deploy a practical multi-measurand sensor (MMS) for process monitoring of glass and carbon fibre preforms in an autoclave. The MMS design was based on the optical fibre-based extrinsic Fabry-Perot interferometric (EFPI) strain sensor. The EFPI sensor consisted of a pair of cleaved optical fibres, with a defined gap that were housed in a precision bore capillary. Interferometric interrogation was used to measure the cavity length hence, permitting the strain to be determined. The basic EFPI sensor design was modified in the following manner to enable multi-measurand monitoring. Firstly, a fibre Bragg grating (FBG) was inscribed on one of the optical fibres that were destined to be housed in the capillary; the end-face of this cleaved optical fibre was sputter coated with Au/Pd to produce a reflective surface. This FBG is in a relatively strain-free condition and only responds to temperature. Secondly, a technique was developed to manufacture optical-quality end-faces of the capillary and this too was sputter coated with Au/Pd. Thirdly, secondary cleaved optical fibres were packed around the lead-in optical fibre of the EFPI sensor with a defined (secondary) cavity thus, permitting transmission/reflection FTNIR spectroscopy. Finally, cleaved secondary optical fibres were also secured to the lead-in fibre and these served as Fresnel reflection sensors. The interrogation of the MMS was carried out using a conventional fibre-coupled multi-channel FTNIR spectrometer. The feasibility of monitoring strain, temperature, cross-linking kinetics and refractive index simultaneously during the processing of glass and carbon fibre preforms was demonstrated

Prevalence of pulmonary tuberculosis in young adult patients with type 1 diabetes mellitus in India

Background: There is limited information on Prevalence of Pulmonary Tuberculosis (PTB) in patients with type-1-diabetes. We assessed the prevalence of PTB in patients with type-1-diabetes attending the outpatient-clinic in a tertiary-care hospital. Methods: 151 patients with type-1-diabetes were screened for PTB by clinical examination and chest-radiography. Sputum Acid-Fast Bacilli Test (AFB) and Mycobacterium tuberculosis (M. tb) culture were performed in patients with clinical and radiological features suggestive of a possibility of PTB and also in those with history of PTB in the past. Their average glycated haemoglobin (HbA1c) during preceding 2 years was assessed. Sputum culture positive patients were managed by a pulmonologist. Results: 5/151 patients had respiratory symptoms and radiographic findings suggestive of PTB. 20/151 patients were asymptomatic but had history of PTB. Four of the five symptomatic patients and 12 with past PTB were positive for sputum M. tb by culture, giving a prevalence of 10.6% sputum culture positive in type-1-diabetes. Average HbA1c was comparable in patients with and without positive sputum culture. ESR and Mantoux test were not discriminatory in these groups. Four clinically symptomatic M. tb culture positive and four asymptomatic patients with sputum culture positive for M. tb on two occasions (6 weeks apart) were put on Antitubercular Treatment (ATT). Patients who were culture positive for M. tb only on one occasion were kept on a close follow up. Conclusions: Patients with type-1-diabetes mellitus in India have high prevalence of PTB. They need to be actively screened for PTB by sputum M. tb culture in order to initiate early treatment and to prevent transmission in the community

Process monitoring of fibre reinforced composites using a multi-measurand fibre-optic sensor

AbstractThis paper reports on the design, fabrication, characterisation and deployment of a multi-measurand optical fibre sensor (MMS) that is capable of simultaneously monitoring strain, temperature, refractive index and cross-linking chemistry. The sensor design is based on the extrinsic fibre Fabry–Perot interferometer. A feature of this sensor system is that a conventional multi-channel fibre-coupled near-infrared spectrometer is used to monitor the four independent parameters. The issues relating to the measurement resolution of the individual sensors and the associated interrogation equipment are discussed. The MMS was embedded in between the fourth and fifth plies of an eight-ply E-glass plain-weave fabric. A commercially available thermosetting epoxy/amine resin system was used to impregnate the fabric layers manually. The laminated preform was vacuum-bagged and cured in an autoclave. The following parameters were monitored: the depletion rates of the epoxy and amine functional groups in the resin system; the temperature in close proximity to the “chemical sensor”; the evolution of strain; and the refractive index of the resin system. The effect of post-processing on the output from the embedded optical fibre sensors is also considered

Nonsuppressible Oral Dexamethasone Suppression Tests but Not Cushing Syndrome

In spite of the presence of definitive diagnostic criteria to diagnose Cushing syndrome diagnosis may become challenging. We report a young female with mild clinical features of Cushing syndrome, who had nonsuppressible oral dexamethasone suppression tests; also she had a suspicious pituitary lesion. She underwent pituitary surgery and a pituitary microadenoma (non-ACTH staining) was removed. Now she had come to us with similar complaints to those before. Again she had nonsuppressible oral dexamethasone suppression tests. As the diurnal variation of serum and salivary cortisol was maintained and urinary free cortisol was normal, further evaluation with IV dexamethasone suppression test was performed which clearly ruled out Cushing syndrome. The patient was not on any medicines known to alter dexamethasone metabolism. Fat malabsorption was also ruled out using appropriate tests. The reason for this discrepancy is thought to be altered (increased) metabolism of dexamethasone in this patient as it is widely variable in the general population

An obese young man with uncontrolled diabetes and insatiable hunger: Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a rare cause of obesity. With the rising incidence of obesity, clinicians need to be aware of genetic causes of obesity and when to suspect them. A case of PWS, which was diagnosed in adulthood, has been discussed. This case is special because of lack of history of floppiness in infancy and predominance behavioral problems

A multi-measurand fibre-optic sensor system for process and health monitoring of fibre reinforced composites

Advanced fibre reinforced composites (AFRCs) are being used extensively in areas where weight is at a premium, for example, aerospace, automotive, marine and civil engineering. Autoclave-based processing of this class of material can be influenced by a number of factors including the temperature, chemical integrity of the resin system and the thermal properties of the constituent materials. Therefore, simultaneous monitoring of multiple measurands is essential to enable cross-correlation of evolving chemo-physical properties of the material as a function of the processing parameters. Majority of the fibre optic-based sensors reported to-date are suitable for single or at the most, dual-measurand systems. This paper presents an overview of the design, fabrication and deployment of a novel multi-measurand optical fibre sensor (MMS). The MMS is capable of simultaneously monitoring strain, temperature, refractive index and cross-linking chemistry. The sensor design is based on the extrinsic fibre Fabry-Perot interferometer. A unique feature of this sensor system is that a conventional multi-channel fibre-coupled near-infrared spectrometer is used to monitor the four independent parameters. The MMS was embedded in between the fourth and fifth plies of an eight-ply E-glass fabric laminate. A commercially-available thermosetting epoxy/amine resin system was used to impregnate the fabric layers which were laminated manually. The laminated preform was cured in an autoclave and the results on the simultaneous monitoring of the specified functional groups in the resin system, evolution of fabrication strain, temperature and the refractive index are reported in this paper. Attention is drawn to the effect of processing and post-processing on the output from the embedded optical fibre sensors.</p

A multi-measurand fibre-optic sensor system for process and health monitoring of fibre reinforced composites

Advanced fibre reinforced composites (AFRCs) are being used extensively in areas where weight is at a premium, for example, aerospace, automotive, marine and civil engineering. Autoclave-based processing of this class of material can be influenced by a number of factors including the temperature, chemical integrity of the resin system and the thermal properties of the constituent materials. Therefore, simultaneous monitoring of multiple measurands is essential to enable cross-correlation of evolving chemo-physical properties of the material as a function of the processing parameters. Majority of the fibre optic-based sensors reported to-date are suitable for single or at the most, dual-measurand systems. This paper presents an overview of the design, fabrication and deployment of a novel multi-measurand optical fibre sensor (MMS). The MMS is capable of simultaneously monitoring strain, temperature, refractive index and cross-linking chemistry. The sensor design is based on the extrinsic fibre Fabry-Perot interferometer. A unique feature of this sensor system is that a conventional multi-channel fibre-coupled near-infrared spectrometer is used to monitor the four independent parameters. The MMS was embedded in between the fourth and fifth plies of an eight-ply E-glass fabric laminate. A commercially-available thermosetting epoxy/amine resin system was used to impregnate the fabric layers which were laminated manually. The laminated preform was cured in an autoclave and the results on the simultaneous monitoring of the specified functional groups in the resin system, evolution of fabrication strain, temperature and the refractive index are reported in this paper. Attention is drawn to the effect of processing and post-processing on the output from the embedded optical fibre sensors.</p