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Background Late-night salivary cortisol (LNSC) is used as a screening test for Cushing syndrome (CS), but there is no community-derived normative data for the normal upper limit in the South Asian population. This study aimed to determine the upper limit of normal (97.5th percentile) for LNSC in an Asian Indian population using a commercially available second-generation electrochemiluminiscence immunoassay (ECLIA). Methods LNSC in apparently healthy community-dwelling individuals was assessed by multistage cluster sampling. Healthy individuals age 18 to 60 years from 8 urban and 8 rural clusters of Thiruvananthapuram district were studied. Thirty people from an approximate population of 1000 individuals from each cluster participated in the study. A saliva sample was collected between 11 PM and 12 midnight and analyzed using Roche COBAS-e-411 and ultrasensitive Cortisol II kits the next day. Results Cortisol values from 474 salivary samples were available for final analysis after exclusion of improperly collected samples. The 97.5th percentile of the LNSC concentrations was 0.25 μg/dL (6.89 nmol/L) (90% CI, 0.23-0.27 μg/dL; ie, 6.34-7.45 nmol/L). In postmenopausal women, median LNSC was significantly higher but the 90% CI for the upper limit of their LNSC (0.28μg/dL or 7.72 nmol/L) overlapped with that of premenopausal women. Conclusions This study establishes the normal value of LNSC estimated by second-generation ECLIA in healthy community-dwelling Asian Indian individuals for the first time. Salivary cortisol at 11 pm to 12 am is less than 0.25μg/dL (6.89 nmol/L) in the general Asian Indian population. Menopause causes a significant increase in LNSC and may lead to overdiagnosis of CS if not interpreted carefully.

Objectives Injectable tetracosactide hexa-acetate, ACTH 1-24 (Synacthen), is not marketed in many countries including India, whereas Injectable long acting porcine sequence, ACTH 1-39 (Acton Prolongatum®) is easily available and much cheaper. This study aimed to find the diagnostic accuracy of ACTH stimulation test using i.m. Acton Prolongatum® (acton prolongatum stimulation test, APST) in comparison with Synacthen (short synacthen test, SST) for the diagnosis of glucocorticoid insufficiency. Methods Subjects with a suspicion of adrenal insufficiency based on clinical features underwent a SST with 250 µg Synacthen followed by APST using 30 units of Acton Prolongatum®. Serum cortisol levels were measured at 60 and 120 min following injection of Acton Prolongatum®. Stimulated peak cortisol of less than 18 µg/dL on SST was considered as adrenal insufficiency. Results Forty seven patients with mean age of 36.7 ± 14.4 years were enrolled for the study. Based on SST, twenty (n = 20) persons were classified as having adrenal insufficiency, whereas twenty-seven (n = 27) were found to be normal. Area under the curve of APST (at 120 min) was 0.986 when compared to SST, thus proving its high accuracy. A serum cortisol cut off value of 19.5 µg/dL at 120-min following stimulation with Acton Prolongatum® showed a sensitivity of 100% and specificity of 88%. Conclusion ACTH stimulation test using Acton Prolongatum® is an economical and accurate alternative to the short Synacthen test.

Primary hyperparathyroidism is not common in children and adolescents. Association of slipped capital femoral epiphysis and hyperparathyroidism is rare. We report the case of a 15-year-old boy who presented with pain in both hips and limping. He was diagnosed to have bilateral slipped capital femoral epiphysis (SCFE) and underwent cancellous screw fixation of both hips. He had proximal myopathy and pain at multiple points over the chest. Examination revealed an emaciated patient with genu valgum, rachitic rosary, Harrison's sulcus, and bony tenderness over the ribs. Investigations showed PTH-dependent hypercalcemia with serum calcium levels reaching >17 mg/dL and electrocardiography showing QTc shortening. Imaging revealed parathyroid adenoma. The work up for multiple endocrine neoplasia syndromes (MEN) was negative. Serum calcium was controlled by medical management and patient underwent expedited surgery. Postoperatively serum calcium levels normalized and patient became better biochemically and clinically including resolution of skeletal changes on follow-up. Only 12 cases of SCFE associated with primary hyperparathyroidism have been reported worldwide till date including the current case. The literature has been reviewed and it indicates that SCFE is associated with late adolescent age and severe hyperparathyroidism (severe bone disease, higher parathormone, serum calcium, and alkaline phosphatase levels).

A 2-year-old child reared as a girl child was brought by parents with ambiguous genitalia noticed since birth. There was no history of failure to thrive or salt-losing crisis. On examination, the child had normal height and weight with normal blood pressure and no dysmorphism or Turners stigmata with external genitalia Prader Score 2. Ultrasound of the pelvis revealed hypoplastic uterus with no gonads visualized. There was no evidence of hypocortisolemia (8 am cortisol 14.08 mcg/dl) or elevated level of 17-OH-progesterone (1.1 ng/mL). Pooled follicle-stimulating hormone and luteinizing hormone levels were 2.66 mIU/ml and 0.1 mIU/ml, respectively, thyroid-stimulating hormone: 2.36 mIU/L, T4: 134.5 nmol/L, total testosterone: 2.5 ng/dl. Posthuman chorionic gonadotropin stimulation showed total testosterone levels 267 ng/dL, dihydrotestosterone: 155 pg/mL, androstenedione: 0.3 ng/mL indicating functioning testicular tissue without any evidence of 17-beta hydroxylase or 5-alpha reductase deficiency. Karyotyping revealed 45, XO genotype on two separate occasions. In view of the discrepancy between karyotype finding and ultrasound reports with the clinical and hormonal picture, fluorescence in situ hybridization cytogenetic study was carried out and showed MONOSOMY X (90% cells)/SEX ANEUPLOIDY XYY (10% cells). Laparoscopic examination showed gonad in the right ovarian fossa and left streak gonad with bilateral fallopian tubes and hypoplastic uterus. Genitoscopy showed normal vagina and cervix. Cystoscopy showed normal urethra and urinary bladder. Biopsy was taken from both gonads. A thorough histopathological examination of this specimen showed the structure of seminiferous tubules with Leydig cells in the right gonad with streak ovary on the left side. The child underwent bilateral gonadectomy and rehabilitated her to lead a life as a girl.

OBJECTIVE Reduction of atherosclerotic cardiovascular disease (ASCVD) risk in patients with diabetes requires proper management of lipid parameters. This study aimed to find the pattern of dyslipidemia and scope of ASCVD risk reduction in patients with diabetes by lipid management. METHODS Clinical, biochemical, and medication profiles of all patients with diabetes attending a tertiary diabetes care hospital over a 2-year period were collected. The prevalence of various lipid abnormalities was determined after excluding patients with thyroid dysfunction and those on lipid-lowering medications. Patients were stratified according to LDL cholesterol, HDL cholesterol, and triglyceride levels, and other clinical parameters were compared among the groups. The adequacy of statin treatment was assessed based on American Diabetes Association guidelines. RESULTS Nine hundred and seventy-one patients were included. The prevalence of hyperlipidemia was 40.0%, of whom 14.6% were newly diagnosed. The most common lipid abnormality was elevated LDL cholesterol. Higher A1C and fasting blood glucose values were found to be associated with higher LDL cholesterol levels. Twenty-seven percent of patients with indications for treatment with statins were receiving them. Of those being treated with statins, 42.6% had an LDL cholesterol level ≥100 mg/dL. CONCLUSION In South Indian patients with type 2 diabetes and fair glycemic control, high LDL cholesterol is the predominant lipid abnormality. There remains a huge potential for ASCVD risk reduction in this population if the knowledge practice gap is addressed.

Introduction: Fasting is observed as a religious custom in various forms across the globe. Among them, the Ramadan fasting is very common and widely practiced. People with diabetes observe fasting with or without obtaining medical advice. Uncontrolled diabetes appears to be a risk factor for COVID-19 infection and its poorer outcomes. Fasting during Ramadan is challenging in people with diabetes. This year, the background of COVID-19 made it difficult for both the patients and health care workers to effectively manage diabetes and its complications during Ramadan. Because of a lack of sufficient evidence, clinicians were perplexed in handling this difficult situation. Materials and Methods: We accessed PubMed, Google Scholar, various guidelines and other evidence-based articles to review the available current literature which deals with diabetes, Ramadan, and COVID-19. Results: The importance of pre-Ramadan assessment, adequate nutrition, and hydration, choosing the right therapy has been emphasized. This review tries to address the common practical challenges and relevant possible solutions for the same. Due consideration has been given to various socio-cultural practices that can influence the management of diabetes patients in the setting of Ramadan and COVID-19 pandemic. Conclusions: Diabetes is associated with increased severity and susceptibility to COVID-19. People with diabetes should go through systemic and structure-based management during fasting. Family physicians who deliver personalized care play a vital role in managing diabetes during this crisis period. Telemedicine is emerging as an effective mode of managing various needs of individuals.

In recent years, magnetic particle spectroscopy (MPS) has emerged as a new technology for immunoassay applications. In MPS, alternating magnetic fields are applied to magnetic nanoparticles (MNPs). The magnetic responses of these nanoparticles are collected and recorded by a pair of specially designed pick-up coils. These magnetic responses contain higher harmonics that are specific to the physical changes of the nanoparticles such as the binding events of target analytes to nanoparticles. This volumetric-based bioassay method analyses the response signal from the whole nanoparticle suspension, thus, allows one step and wash-free immunoassay with minimum technical requirements. In this work, we developed a handheld MPS system as a future highly sensitive, cheap, in vitro, and easy-to-use point-of-care (POC) detection kit.

Background Synacthen stimulated salivary cortisol has been previously evaluated and found beneficial in the diagnosis of adrenal insufficiency (AI), especially in situations with altered cortisol-binding protein (CBG) levels. Unfortunately, Synacthen is not marketed in many parts of the world whereas porcine sequence corticotrophin (Acton Prolongatum) is readily available. This study aimed to find the diagnostic accuracy of Acton prolongatum stimulated salivary cortisol test (APSST) compared to the short synacthen test (SST). Methods Consecutive outpatients with suspected AI underwent SST initially, followed by APSST after 3 days. For APSST, saliva was collected at 0, 60 and 120 minutes after administering 30 units Acton Prolongatum intramuscularly. Serum and salivary cortisol were estimated using electrochemiluminescence assay. (Cobas e 411, Elecsys Cortisol II kits) RESULTS: Sixty-seven patients with clinically suspected AI were enrolled for the study. Based on SST, 35 patients were classified as having AI [primary AI (n=19) and secondary AI (n=16)] whereas 32 had normal glucocorticoid reserve. The area under receiver operator curve of 0.99 and 0.98 was observed for salivary cortisol values at 60 and 120 minutes, respectively, for APSST. A cut-off value of 18.5 nmol/L (0.67 µg/dL) and 29.3 nmol/L (1.06 µg/dL) at 60 and 120 minutes, respectively, had a sensitivity as well as specificity of 93%-100% in diagnosing AI. Conclusion Salivary cortisol estimation following stimulation using intramuscular porcine ACTH (Adrenocorticotrophic hormone) (30 units) is an economical and accurate alternative to SST in the diagnosis of AI, m and its level of 30 nmol/L or more at 2 hours confirms adrenal sufficiency.

Key Messages: Octreotide can be used as an adjunctive therapy to increase phosphorus levels in patients with tumor-induced osteomalacia. Malignant phosphaturic mesenchymal tumor (PMT) may benefit from treatment with peptide receptor radionucleotide therapy. Context: The success of treatment modalities for malignant PMT is limited. Octreotide has been used to treat hypophosphatemia in patients with tumor-induced osteomalacia with equivocal results. To our knowledge, there are no reports of octreotide or peptide receptor radionuclide therapy use for malignant PMT. Case Description: We report a 40-year-old man having hypophosphatemia, phosphaturia (tubular maximum of phosphorus corrected for glomerular filtration rate of, Octreotide was used in osteomalacia caused by a malignant phosphaturic tumor, with moderate results; peptide receptor radionuclide therapy with 177Lutetium then produced a moderate response lasting 6 months.

Context Noncompliance with thyroxine therapy is the most common cause of poor control of hypothyroidism. An open-label prospective study to compare once-weekly thyroxine (OWT) with standard daily thyroxine (SDT) was undertaken. Design Patients taking thyroxine doses of >3 μg/kg/d, with or without normalization of TSH, were included and administered directly observed OWT or nonobserved SDT according to patient preference based on their weight for 6 weeks. Furthermore, patients on OWT were advised to continue the same at home without supervision. Results Twenty six of 34 patients on OWT and 7 of 18 patients on SDT achieved a TSH Conclusion OWT benefits a majority of patients in the long-term treatment of thyroxine-resistant hypothyroidism, in the real-world setting.

It is generally assumed that the internal stress distribution in foods under high pressure processing (HPP) is uniform, which may not be true for solid foods with hard inclusions, like meats with bones or for particulate foods. Our objective was to simulate the internal stress distribution during HPP of a model heterogeneous solid food made with a gel and a wood inclusion and determine how mechanical properties affect the internal stress distribution. It was determined that hydrostatic pressure decreased and shear stress was generated at the interface between the soft solid and the hard inclusion. The differences in pressure and shear stresses increased as the shear modulus of the soft solid increased. Our studies suggest that a better understanding of the mechanical properties that affect the development of the internal stress field is needed, since they could affect the achieved microbial inactivation levels at different locations in HPP solid foods.

Both type 2 diabetes and hypothyroidism are highly prevalent disorders in the community. The existing data regarding prevalence of hypothyroidism in patients with diabetes comes mostly from small studies. There are only two studies with a sample size of more than 1000 diabetic patients, none of which have been done in South Asians. The present study evaluated patients with type 2 diabetes for presence of hypothyroidism and the clinical factors associated with it. The demographic, anthropometric, clinical, and biochemical parameters of consecutively enrolled patients with diabetes were systematically collected and analyzed. A total of 1152 middle aged patients with type 2 diabetes with a mean duration of diabetes of around 10 years were enrolled. Nearly 40 percent of the patients were obese and overweight, respectively, for South Asian standards and abdominal obesity was seen in around 90% patients. Clinical hypothyroidism (TSH>10 mIU/ml) was present in 113 of patients (9.83%) and another 68 patients (5.9%) had subclinical hypothyroidism (TSH 5-10 mIU/ml). Anemia (odds ratio : 2.19), overweight/obese status (odds ratio 2.07), and known dyslipidemia (odds ratio : 1.99) were found to have independent association with clinical hypothyroidism. HbA1c, abdominal obesity, poor control of hypertension, lipid parameters, microalbuminuria, and renal dysfunction showed no difference among patients with hypothyroidism when compared with euthyroid patients. Subclinical hypothyroid patients had no difference in any of the above analyzed parameters when compared to the euthyroid patients. This study shows that a significant proportion of type 2 diabetes patients suffer from clinical or subclinical hypothyroidism and screening for the same may be appropriate.

In this article we propose macroscopic (continuum) simulation schemes to predict response of porous heterogeneous material systems subjected to weak and moderate impact velocities. The proposed simulation model includes (1) an equation of state for porous solids that describes the evolution of porosity in the material as a function of shock pressure and, (2) a macroscopic rate dependent plasticity model for the porous composite that accounts for the deviatoric strength of the material at weak to moderate shock strengths. In addition, the numerical scheme employs cold-mixture theory to predict shock response of porous intermetallics. The material model is validated using gas-gun impact experiments on Ni/Al Intermolecular Reactive Composite (IRC) at 70% TMD. The proposed model is also used to understand the effect of microstructure on the material response predictions.

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.

In this article, a novel implicit time-integration scheme for the generalized interpolation material point method (GIMP) is discussed. The implicit algorithm discussed in this article is an extension of the algorithm introduced for the material point method (MPM) by Sulsky and Kaul [1]. In this article, the numerical solution employs the Newton-Krylov technique coupled with the conjugate gradient (CG) method to solve the governing equations in a robust, matrix-free fashion. In implicit MPM, the solution procedure needs to be re-ordered in terms of momentum if the algorithm has to solve large deformation problems [1]. This is a direct consequence of the cell-crossing issues in MPM. The solution procedure in this case uses the generalized minimum residual method to solve the resulting non-symmetric equations. However, GIMP is specifically formulated to overcome these particle cell-crossing issues in MPM; hence, a specialized procedure for large deformation is not required. The proposed implicit algorithm fo...

A theoretical framework is developed for solvent diffusion in solids with large dilatation due to solvent induced swelling. The resulting non-linear governing differential equations are not amenable to a closed form solution, and hence, a solution technique based on the finite element method is presented and implemented. Several demonstration problems are solved using an in-house finite element code (NOVA-3D) to highlight the importance of including the effect of finite dilatation in a diffusion model for hygroscopic materials. The effect of finite dilatation on the calculation of diffusivity is discussed, as well as the presence of large shearing stresses induced by the concentration gradient.

Accelerated ageing experiments have been conducted to address durability issues of carbon/epoxy composites to be used for emerging facilities and infrastructure, such as, bridges and buildings, in different climatic zones. The degradation of carbon/epoxy composites under UV, hygrothermal exposure, and applied tensile stress has been investigated. The tests were designed to capture the synergistic effects of field exposure and extreme temperatures, viz., hot/dry, hot/wet, cold/dry, and cold/wet conditions. Short beam shear tests (SBST) were performed for the determination of interlaminar shear strength (ILSS) of conditioned composite specimens. The hot/dry samples showed increased strength, while the hot/wet ones showed a decrease in strength. It is conjectured that conditioning at 90 °C possibly contributed to an increase in the ILSS from post curing. For the hot/wet samples (90 °C, immersed in water) the results indicate that strength degradation due to moisture-induced hydrolysis overshadowed the post-curing effect. The samples subjected to shear stress under hot conditions (90 °C) showed a higher ILSS, possibly due to improved crosslink density arising from post-cure. There is insignificant variation in the ILSS of UV treated and the UV untreated control samples. All the SBST test data reported in this work are from tests performed at room temperature and ambient humidity after environmental ageing. A two-dimensional cohesive layer constitutive model with a prescribed traction-separation law constructed from the basic principles of continuum mechanics, taking into account hygrothermal mechanisms that are likely to occur within a cohesive bi-material interface, such as between adjacent plies in a laminate, was applied to simulate interlaminar failure in the SBST specimens, using Finite Element Analysis (FEA). A phenomenological predictive model was developed using the finite element results.

Composites are extensively used for various aerospace applications and one of its important potential uses is as cryogenic fuel tank material for crew launch vehicles. Composites offer high specific strength and stiffness, and therefore are preferred over many other materials. However under structural mechanical loads and/or thermal loads, transverse micro-cracks develop in the polymer matrix. These cracks along with interlaminar delaminations produced at the crack tips, lead to permeation of cryogenic fuel permeation through the laminates. In this study, mathematical models have been proposed to determine the delaminated crack opening displacement (DCOD) for each ply of a damaged laminate and the permeability associated with it. In addition, a stitch crack model has been proposed to address experimental observations. The through-thickness DCOD distribution for a damaged composite under the action of thermal and/or mechanical load is predicted using a five-layer model which is developed based on first order shear deformation theory. The DCOD predicted by this mathematical model, with and without stitch cracks, shows good agreement with two dimensional finite element analysis. The DCOD values predicted for IM7/5250-4 laminate of lay-up [0/45/−45/90]S were used to predict permeability using Darcy’s law for fluid flow through porous media. The analysis results were benchmarked using test data from Air Force Research Laboratory. A parametric study for permeability conducted with varying stitch crack lengths shows that the permeability of the composite is sensitive to this form of damage in individual plies.

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.

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.

The effect of environmental and loading conditions on the degradation of Interlaminar Shear Strength (ILSS) of the carbon-epoxy composite specimens was studied. The hygrothermal conditions capture the synergistic effects of field exposure and extreme temperatures. A short beam shear test (SBST) was performed to determine the Interlaminar Shear Strength (ILSS) of environmentally aged composite specimens in accordance with ASTM D2344-84. Initially, a standard two-dimensional cohesive layer constitutive model was employed in order to simulate the experiment using an in-house FEA code (NOVA-3D). Numerical instabilities, encountered using the standard cohesive layer model, were overcome by incorporating viscoelastic regularization in the constitutive equations of the cohesive layer. This modification also enabled the analysis to continue beyond the point of peak failure load. The model was able to accurately simulate the load vs. displacement behavior of most of the SBST samples aged under various hygrothermal and synergistically applied stress conditions. Further, the effect of displacement rate on the ILSS of specimens was studied using NOVA-3D. The model indicated a strong dependence of viscoelastic cohesive strength on the displacement rate. Regrettably, the predicted rate dependence could not be verified experimentally.

Mechanical characterization data for nanoclay reinforced pultruded EGlass/polypropylene (PP) and compression molded E-Glass/Nylon-6 composite samples with 3-4 weight % nanoclay and baseline polymer (polymer without nanoclay), has shown significant improvements in compressive strength (~122%) and shear strength (~60%) in the nanoclay modified nanocomposites, in comparison with baseline properties. While the synergistic reinforcing influence of nanoparticle reinforcement is obvious, a simple rule-of-mixtures approach fails to quantify the dramatic increase in mechanical properties. Consequently, there is an immediate need to investigate and understand the mechanisms at the nanoscale that are responsible for such unprecedented strength enhancements. The proposed method involves a concurrent simulations approach in which the information from molecular dynamics (MD) is seamlessly exchanged with continuum mechanics based method called the embedded statistical coupling method (ESCM). In this research, a novel particle-in-cell method called Generalized Interpolation Material Point Method (GIMP) is used to simulate the macroscopic response of the larger (and continuous) system which is under displacement boundary conditions from the molecular dynamics region. To our knowledge, large scale concurrent coupling of nanoparticle reinforced polymer systems has not been attempted before. The current research will contribute towards the understanding of advanced nanostructured composite materials. An example problem involving concurrently coupled crack propagation in a crystalline solid material is presented. Work is underway to extend the coupled analysis to dynamic crack propagation in amorphous polymeric systems. Nomenclature

Recent mechanical characterization experiments with pultruded EGlass/polypropylene (PP) composite samples with 3 weight % nanoclay and baseline PP (polymer without nanoclay) indicated significant improvements in compressive strength (~100%) and interlaminar shear strength (~60%) in modified pultruded PP nanocomposites, in comparison with baseline properties. While the synergistic reinforcing influence of nanoparticle reinforcement is obvious, a simple rule-of-mixtures approach fails to quantify the dramatic increase in mechanical properties. Consequently, there is an immediate need to investigate and understand the mechanisms at the nanoscale that are responsible for such unprecedented strength enhancements. It is envisioned that a better understanding of the mechanisms at the nanoscale will lead to optimization of materials processing variables at the macroscale, which in turn will lead to the manufacture of nanocomposites more efficiently and at lower cost. In this paper, an innovative and efficient method to model nano-structured components in a thermoplastic composite is proposed by employing a large-deformation hyperelastic constitutive model. Effort is directed toward finding fundamental answers to the reasons for significant changes in mechanical properties of nanoparticle-reinforced thermoplastic composites, and then using this knowledge to optimize processing variables to further enhance the targeted properties of the nanocomposite. The proposed method involves a concurrent simulations approach in which the information from molecular dynamics (MD) is seamlessly exchanged with continuum mechanics based method called the Embedded Statistical Coupling Method (ESCM), as introduced in Saether et al.

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-toweight 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 paper, 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. Using this model, the permeability is calculated for a quasi-isotropic laminate of lay-up [0/45/-45/90]s for a given delamination length, crack density and loading conditions. Also, a simple methodology to model stitch cracks has been proposed to address experimental observations. Further, the proposed model was used to determine strain energy release rates under mode I (matrix cracking) and mode II (delamination) conditions. 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 (AFRL).

This study examines the theory and performance of Jacobian-Free Newton Krylov (JFNK) methods for the efficient, iterative solution of steady state dynamics of linear vibrating systems in the frequency domain. Currently, most commercial FEM algorithms employ use direct factorization of large system matrices to achieve steady state solution. Such approaches are usually quite demanding on memory and CPU requirements. Some implementations exploit iterative solutions, but still use large, assembled system matrices, requiring significant memory. The methods investigated in this work avoid the formation of a matrix completely, minimizing memory requirements and enabling much larger problems to be performed on desktop computers. Here, the Conjugate-Gradient (CG) and Transpose Free Quasi Minimal Residual (TFQMR) algorithms are studied as possibilities. These methods are of particular interest for adaptation to finite element software which uses explicit transient dynamics, because such software's optimal architecture prevents the formation and solution of a stiffness (or a tangent stiffness) matrix. In order to demonstrate the advantages of these algorithms, we choose examples that use the JFNK-CG and JFNK-TFQMR technique to show computational advantages over regular matrix based solutions, with significant decrease in memory requirements.

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-toweight 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 paper, 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. Using this model, the permeability is calculated for a quasi-isotropic laminate of lay-up [0/45/-45/90]s for a given delamination length, crack density and loading conditions. Also, a simple methodology to model stitch cracks has been proposed to address experimental observations. 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.

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-toweight 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 paper, an expression for predicting delaminated crack opening displacement (DCOD) is derived based on first-order shear laminate theory applied to five-layer and three-layer models. The DCOD obtained using both five-layer and three-layer model is verified using a twodimensional finite element analysis. A mathematical model to predict permeability in graphite-epoxy laminate system (IM-7/PETI-5) is developed using Darcy’s law for isothermal, viscous flow of gases through porous media. The results obtained from both fivelayer and three-layer model are used as input to the permeability model. Using this model, the permeability is calculated for an orthotropic laminate lay-up for a given delamination length, crack density and loading conditions. In addition to the [0/90]s cross-ply configuration, the model is enhanced to include laminates with arbitrary ply orientations. Model predictions of DCOD are compared with 3-D FEA results for a [45/0/-45/90]s laminate for verification.