Effects of Defects on the Performance of Hierarchical Honeycomb Metamaterials Realized Through Additive Manufacturing

Cellular metamaterials are of immense interest for many current engineering applications. Tailoring the structural organization of cellular structures leads to new metamaterials with superior properties providing lightweight and very strong/stiff structures. The incorporation of hierarchy to regular cellular structures enhances the properties and introduces novel tailorable metamaterials. For many complex cellular metamaterials, the only realistic manufacturing process is additive manufacturing (AM). The use of AM to manufacture large structures may lead to several types of defects during the manufacturing process, such as imperfect cell walls, irregular thickness, flawed joints, partially missing layers, and irregular elastic plastic behavior due to toolpath. It is important to understand the effect of defects on the overall performance of the structures to determine if the manufacturing defect(s) are significant enough to abort and restart the manufacturing process or whether the material can still be used in its defective state. Honeycomb structures are often used for the high strength to weight ratio applications. These metamaterials have been studied and several models have been developed based on idealized cell structures to explain their elastic plastic behavior. However, these models do not capture real-world manufacturing defects resulting from AM. The variation of elastic plastic behavior of regular honeycomb structures with defects has been studied, but the performance of hierarchical honeycomb structures with defects is still unknown. In this study, cell wall defects are modeled as the worst case scenario, which is entirely missing cell walls. The effects of missing cell walls are investigated to understand the elastic behavior of hierarchical honeycomb structures using finite element analysis. Hierarchical honeycombs demonstrated more sensitivity to missing cell walls than regular honeycombs. On average, the axial elastic modulus decreased by 45% with 5.5% missing cell walls for regular honeycombs, 60% with 4% missing cell walls for first order hierarchical honeycomb and 95% with 4% missing cell walls for second order hierarchical honeycomb. The transverse elastic modulus decreased by about 45% with more than 5.5% missing cell walls for regular honeycomb, about 75% with 4% missing cell walls for first order and more than 95% with 4% missing cell walls for second order hierarchical honeycomb

Analysis of 2D Spatial Filtering of Simulated Muscle Action Potential Using Grid Arrays

Surface grid electrode is a noninvasive technique, which can be utilized for topographic analysis of EMG signals. In this study, an innovative spatial filtering technique is proposed in the form of grid electrodes to enhance the selectivity of surface EMG signal considering the effect of intermediate tissue layers between source and recording electrode. A simulation algorithm is developed to generate complete profile of single fiber action potential (SFAP) using previously derived mathematical model and published clinical data. A multiple-layer model is investigated in order to determine the potential distribution at the skin, fat and muscle surface based on the solution of the Poisson equation in spatial frequency domain. The arbitrary constants of the solution are determined by imposing the boundary conditions. The characteristics of subcutaneous fat and skin tissues are incorporated in the SFAP model to develop a systematic approach to select an appropriate inter-electrode distance of two dimensional grid arrays in order to eliminate spatial aliasing and distortion. The minimum grid spacing is determined by satisfying the Nyquist criterion for spatial sampling. The subcutaneous tissue layers reduce the frequency contents and attenuate the amplitude of the potential distribution at muscle surface. A two dimensional spatial filter is designed by manipulating the inverse of transfer function of fat and skin in order to compensate their spatial widening effect. The inverse transfer function is approximated to represent it in the form of filter mask for a discrete grid array. This spatial filtering technique is also investigated to eliminate the effect of a particular thick anisotropic medium inside muscle

Experimental and Theoretical Study of the Stress and Strain Fields Around Fatigue Cracks and Plasticity-Induced Crack Closure

This work investigates experimentally and theoretically the local crack tip stress and strain fields, and plasticity-induced crack closure acting on the crack flanks behind the crack tip, in fine-grained aluminium alloy 5091 (Al-Mg-Li-C-O) compact tension fatigued specimens. Compressive residual stresses ahead of the crack tip and plasticity-induced crack closure are often attributed to be the two main mechanisms responsible for crack growth retardation. Specimens investigated were prepared: with constant amplitude fatigue; with constant amplitude fatigue followed by a single overload; and finally with constant amplitude fatigue followed by a single overload followed by further constant amplitude fatigue. Experimental crack tip strain (and hence stress) measurements have been carried out along the midthickness of the specimens using energy dispersive X-ray diffraction (EDXRD) at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. The very small grain size of aluminium alloy 5091 allows minimization of the sampling volume in order to maximize the spatial resolution achievable with EDXRD. High spatial resolution is essential for measuring highly localized crack tip stresses. For theoretical investigations of the crack tip stress and strain fields, existing analytical solution (Westergaard, 1939) and the finite element code ABAQUS (ABAQUS Inc., 2004) have been used. Crack closure has been investigated by finite element analysis and compliance experimental technique. Finite element analyses for both stress fields and crack closure have been carried out in plane stress and plane strain. A possible link between the stresses ahead of the crack tip and the plasticity-induced crack closure on the crack flanks behind the crack tip has been investigated

Econometric Modeling Analysis of Public Transit Ridership: Application for Orlando Region

Policy makers are considering several alternatives to counter the negative externalities of personal vehicle dependence. Towards this end, public transit investments are critical in growing urban regions such as Orlando, Florida. Transit system managers and planners mostly rely on statistical models to identify the factors that affect ridership as well as quantifying the magnitude of the impact on the society. These models provide vital feedback to agencies on the benefits of public transit investments which in turn act as lessons to improve the investment process. We contribute to public transit literature by addressing several methodological challenges for transit ridership modeling. Frist, we examine the impact of new transit investments (such as an addition of commuter rail to an urban region) on existing transit infrastructure (such as the traditional bus service already present in the urban region). The process of evaluating the impact of new investments on existing public transit requires a comprehensive analysis of the before and after measures of public transit usage in the region. Second, we accommodate for the presence of common unobserved factors associated with spatial factors by developing a spatial panel model using stop level public transit boarding and alighting data. Third, we contribute to literature on transit ridership by considering daily boarding and alighting data from a recently launched commuter rail system (SunRail). The model system developed will allow us to predict ridership for existing stations in the future as well as potential ridership for future expansion sites. Fourth, we accommodate for potential endogeneity between bus headway and ridership by proposing a simultaneous model system of headway and ridership. Finally, a cost benefit analysis exercise is conducted for examining the impact of Sunrail on the region

π拡張アリールアルコールの配位したスズ(Ⅳ)ポルフィリンの合成研究

首都大学東京, 2019-09-30, 博士（理学）首都大学東

Crack tip plasticity in mixed mode loading under contained yielding conditions

Mode I, mode II and mixed mode I/II asymptotic crack tip fields have been studied under contained yielding conditions using plane strain and plane stress boundary layer formulations. The effect of the non-singular term in the asymptotic elastic expansion (Williams, 1957) on the plastic zone at the crack tip has been determined. Plane stress mode I, mode II and mixed mode I/II crack tip fields have also been investigated analytically. Analytical solutions were developed by assembling constant stress, fan and elastic sectors. Slip line theory (Hill, 1950) was used to solve constant stress and fan sectors while the stress fields in elastic sectors were solved using the semi-infinite wedge solution of Timoshenko and Goodier (1970). Analytical solutions were validated by numerical results, and represented as slip line fields

Introduction of emergency contraception in Bangladesh: Using operations research for policy decisions

The Directorate of Family Planning, Bangladesh, the Population Council, Pathfinder International, and John Snow Incorporated collaborated to conduct this operations research study to assess the acceptability and feasibility of providing emergency contraception pills (ECP) as a backup support to existing family planning methods. The study demonstrated that all categories of health providers, including NGO outreach workers, could be effectively trained to provide ECP services. The study also demonstrated high acceptability of ECP and revealed that if used correctly, the success rate in avoiding unwanted pregnancy was extremely high. The positive findings of the study have helped the Ministry of Health and Family Welfare, Government of Bangladesh, to approve introduction of ECP in the National Family Planning Program. The present study thus also serves as a good demonstration of how operations research can contribute in policy decisions and how research findings can be translated into action

The Influence of Service Quality and Price on Customer Satisfaction: An Empirical Study on Restaurant Services in Khulna Division

One of the vital needs of increasing population in our country is food. There are a few number of restaurant goers to meet the necessity of food. Most of the people in our country occasionally go to the restaurant to enjoy ethnic and some of western food items. The main purpose of this study is to identify some key drivers of customer satisfaction on restaurant services. The study covers the opinion of restaurant goers in Khulna region. This research is based on empirical study. Primarily, researchers contacted with 450 customers for their valuable opinion regarding restaurant services. But, 246 customers gave their spontaneous response in this regard. Chi-square test has been applied for testing hypothesizes by using SPSS software. This study aims to link some factors of service quality and price fairness of restaurant with the customers' satisfaction. The researchers find out that customers of restaurant have negative impression about product and service quality fairness, price fairness, staff's service, environment of the restaurant, image of the restaurant and loyalty of the restaurant. The researchers suggest emphasizing on those critical issues to attract new customers and retain existing customers. Keywords: Customer Satisfaction, Customer Loyalty, Service Qualit