Modelling of Fiber/Matrix Debonding of Composites Under Cyclic Loading

The micromechanics theory, generalized method of cells (GMC), was employed to simulate the debonding of fiber/matrix interfaces, within a repeating unit cell subjected to global, cyclic loading, utilizing a cyclic crack growth law. Cycle dependent, interfacial debonding was implemented as a new module to the available GMC formulation. The degradation of interfacial stresses, with applied load cycles, was achieved via progressive evolution of the interfacial compliance. A periodic repeating unit cell, representing the fiber/matrix architecture of a composite, was subjected to combined normal and shear loadings, and degradation of the global transverse stress in successive cycles was monitored. The obtained results were compared to values from a corresponding finite element model. Reasonable agreement was achieved for combined normal and shear loading conditions, with minimal variation for pure loading cases. The local effects of interfacial debonding, and fatigue damage will later be combined as sub-models to predict the experimentally obtained fatigue life of Ti-15-3/Sic composites at the laminate level

Fatigue Analysis of Notched Laminates: A Time-Efficient Macro-Mechanical Approach

A coupled transversely isotropic deformation and damage fatigue model is implemented within the finite element method and was utilized along with a static progressive damage model to predict the fatigue life, stiffness degradation as a function of number of cycles, and post-fatigue tension and compression response of notched, multidirectional laminates. Initially, the material parameters for the fatigue model were obtained utilizing micromechanics simulations and the provided [0], [90] and [plus or minus 45] experimental composite laminate S-N (stress-cycle) data. Within the fatigue damage model, the transverse and shear properties of the plies were degraded with an isotropic scalar damage variable. The damage in the longitudinal (fiber) ply direction was suppressed, and only the strength of the fiber was degraded as a function of fatigue cycles. A maximum strain criterion was used to capture the failure in each element, and once this criterion was satisfied, the longitudinal stiffness of the element was decreased by a factor of 10 (sup 4). The resulting, degraded properties were then used to calculate the new stress state. This procedure was repeated until final failure of the composite laminate was achieved or a specified number of cycles reached. For post-fatigue tension and compression behavior, four internal state variables were used to control the damage and failure. The predictive capability of the above-mentioned approach was assessed by performing blind predictions of the notched multidirectional IM7/977-3 composite laminates response under fatigue and post-fatigue tensile and compressive loading, followed by a recalibration phase. Although three different multidirectional laminates were analyzed in the course of this study, only detailed results (i.e., stiffness degradation and post-fatigue stress-train curves as well as damage evolution states for a single laminate ([30/60/90/minus 30/minus 60] (sub 2s)) are discussed in detail here

The relationship between information literacy, internet addiction and general health of an Iranian medical students

Introduction: Given the prevalence of Internet use worldwide and its existing risks to societies especially the youngsters, information literacy can affect the use of Internet. Hence, the objective of present study is to assess the relationship between information literacy and Internet addiction and then to investigate the relationship between Internet addiction and general health of students in Iran University of Medical Sciences. Materials and Methods: It is an analytical cross-sectional study which was conducted during 2016 on students in Iran University of Medical Sciences (Tehran, Iran). The sample size for the surveyed community of 6,500 university students was 362 from the Cochran sample size formula. Then, using a simple random sampling method, from each of the colleges, the sample size was selected according to the student population. Three questionnaires of information literacy, Yang's Internet addiction, and general health scale (GHQ-28) were distributed among students. Finally, 365 questionnaires were collected and analyzed. Results: 29.9 of students were about to be addicted to the Internet, 1.3 had symptoms of Internet addiction and 68.8 had no addiction. In terms of information literacy, most of the students were in moderate level (60.5 moderate, 3.3 low, and 36.2 high information literacy level). There was a significant inverse relationship between increasing of information literacy and the Internet addiction (r = -0.45 and p<0.001). The score of general health demonstrated an inverse and significant relationship in different levels of Internet addiction (P <0.001). Conclusion: According to the findings of this study, it was perceived that the higher the information literacy, the lower the level of Internet addiction; besides, reduction of internet addiction increased the general health of students. Therefore, considering the importance of students as the leading group in societies, and favorable consequences of increased information literacy, universities' authorities have to develop and run specific programs within the educational and research schedule in order to increase the students' information literacy. Accordingly, undesirable outcomes of Internet use would be diminished and general health of society would be improved. © 2018, Semnan University of Medical Sciences. All rights reserved

The relationship between information literacy, internet addiction and general health of an Iranian medical students

Introduction: Given the prevalence of Internet use worldwide and its existing risks to societies especially the youngsters, information literacy can affect the use of Internet. Hence, the objective of present study is to assess the relationship between information literacy and Internet addiction and then to investigate the relationship between Internet addiction and general health of students in Iran University of Medical Sciences. Materials and Methods: It is an analytical cross-sectional study which was conducted during 2016 on students in Iran University of Medical Sciences (Tehran, Iran). The sample size for the surveyed community of 6,500 university students was 362 from the Cochran sample size formula. Then, using a simple random sampling method, from each of the colleges, the sample size was selected according to the student population. Three questionnaires of information literacy, Yang's Internet addiction, and general health scale (GHQ-28) were distributed among students. Finally, 365 questionnaires were collected and analyzed. Results: 29.9 of students were about to be addicted to the Internet, 1.3 had symptoms of Internet addiction and 68.8 had no addiction. In terms of information literacy, most of the students were in moderate level (60.5 moderate, 3.3 low, and 36.2 high information literacy level). There was a significant inverse relationship between increasing of information literacy and the Internet addiction (r = -0.45 and p<0.001). The score of general health demonstrated an inverse and significant relationship in different levels of Internet addiction (P <0.001). Conclusion: According to the findings of this study, it was perceived that the higher the information literacy, the lower the level of Internet addiction; besides, reduction of internet addiction increased the general health of students. Therefore, considering the importance of students as the leading group in societies, and favorable consequences of increased information literacy, universities' authorities have to develop and run specific programs within the educational and research schedule in order to increase the students' information literacy. Accordingly, undesirable outcomes of Internet use would be diminished and general health of society would be improved. © 2018, Semnan University of Medical Sciences. All rights reserved

Thermal Analysis of Potted Litz Wire for High-Power-Density Aerospace Electric Machines

Increasing the power density and efficiency of electric machines (motors and generators) is integral to bringing Electrified Aircraft (EA) to commercial realization. To that end an effort to create a High Efficiency Megawatt Motor (HEMM) with a goal of exceeding 98% efficiency and 1.46 MW of power has been undertaken at the NASA Glenn Research Center. Of the motor components the resistive losses in the stator windings are by far the largest contributor (34%) to total motor loss. The challenge is the linear relationship between resistivity and temperature, making machine operation sensitive to temperature increases. In order to accurately predict the thermal behavior of the stator the thermal conductivity of the Litz wire-potting-electrical insulation system must be known. Unfortunately, this multi material system has a wide range of thermal conductivities (0.1 W/m-K 400 W/m-K) and a high anisotropy (axial vs transverse) making the prediction of the transverse thermal conductivity an in turn the hot spot temperatures in the windings is difficult. In order to do this a device that simulates the thermal environment found in the HEMM stator was designed. This device is not unlike the motorettes (little motors) that are described in IEEE standards for testing electrical insulation lifetimes or other electric motor testing. However, because the HEMM motor design includes significant rotor electrical and thermal considerations the term motorette was not deemed appropriate. Instead statorette (or little stator) was adopted as the term for this test device. This paper discussed the design, thermal heat conjugate analysis (thermal model), manufacturing and testing of HEMM's statorette. Analysis of the results is done by thermal resistance network model and micro thermal model and is compared to analytical predictions of thermal conductivity of the insulated and potted Litz wire system

PCR Improves Diagnostic Yield from Lung Aspiration in Malawian Children with Radiologically Confirmed Pneumonia

Accurate data on childhood pneumonia aetiology are essential especially from regions where mortality is high, in order to inform case-management guidelines and the potential of prevention strategies such as bacterial conjugate vaccines. Yield from blood culture is low, but lung aspirate culture provides a higher diagnostic yield. We aimed to determine if diagnostic yield could be increased further by polymerase chain reaction (PCR) detection of bacteria (Streptococcus pneumoniae and Haemophilus influenzae b) and viruses in lung aspirate fluid.A total of 95 children with radiological focal, lobar or segmental consolidation had lung aspirate performed and sent for bacterial culture and for PCR for detection of bacteria, viruses and Pneumocystis jirovecii. In children with a pneumococcal aetiology, pneumococcal bacterial loads were calculated in blood and lung aspirate fluid.Blood culture identified a bacterial pathogen in only 8 patients (8%). With the addition of PCR on lung aspirate samples, causative pathogens (bacterial, viral, pneumocystis) were identified singly or as co-infections in 59 children (62%). The commonest bacterial organism was S.pneumoniae (41%), followed by H. influenzae b (6%), and the commonest virus identified was adenovirus (16%), followed by human bocavirus (HBoV) (4%), either as single or co-infection.In a select group of African children, lung aspirate PCR significantly improves diagnostic yield. Our study confirms a major role of S.pneumoniae and viruses in the aetiology of childhood pneumonia in Africa