Browsing by Author "Kara Peters, Committee Member"

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Characteristics of Innovative 3-D FRP Sandwich Panels
(2006-02-02) Reis, Engin Murat; Sami H. Rizkalla, Committee Chair; Mervyn J. Kowalsky, Committee Member; Kara Peters, Committee Member; Ajaya K. Gupta, Committee Member
Foam and honeycomb core sandwich composites are widely used in structural applications. Nevertheless, possibilities of core-to-face sheet delamination, crushing and buckling instability are major concerns. This study presents an innovative system for FRP panels designed to overcome delamination problems typically encountered in traditional FRP panels. The panels consist of GFRP laminates and foam core sandwich where top and bottom skin GFRP layers are connected together with through-thickness fibers. Addition of the through-thickness fibers increases the out of plane properties of the panel, delays delamination-type failures, allows low cost manufacturing and ensures full utilization of the panel strength. Fundamental material properties in tension, compression, flexure and shear are evaluated both experimentally and analytically. Failure modes and mechanisms are investigated. The influence of the panel thickness, through thickness fiber configuration and density and other parameters on the tension, compression, flexure and shear behavior of the panels will be discussed. Application of sandwich beam theories, Elementary Sandwich Theory and Advanced Sandwich Theory, are studied in the full behavior of the 3-D FRP sandwich beams. A finite element model is developed to be able to predict the behavior of sandwich panels with different panel thicknesses, through thickness fiber configurations, facing sheet thicknesses and different material properties.
Damage Imaging Algorithms For Structural Health Monitoring Using Electromagnetic Waves
(2007-05-04) Nojavan, Saeed; Fuh-Gwo Yuan, Committee Chair; Mohammad Noori, Committee Member; Kara Peters, Committee Member; Gianluca Lazzi, Committee Member
Reconstructing damage geometry with computationally efficient algorithms is of primary importance in establishing a robust structural health monitoring system (SHMS). To this end, two linearized imaging algorithms, electromagnetic (EM) migration and Born imaging, are proposed for 3-D damage imaging of structures using EM waves. These algorithms are formulated in both differential equation (DE) and integral equation (IE) forms in time-domain for inhomogeneous anisotropic and lossy structures. When sensor data is collected in a common-shot experiment, the proposed imaging algorithms consist of three steps: 1) Back-propagation (migration) of the scattered field measured by the sensors; 2) Zero-lag cross-correlation of the back-propagated scattered field with the incident field in image area; and 3) Summation of partial images obtained from different actuator excitations. The computation of the back-propagated scattered field can be carried out based on either the differential equations or the integral equations associated with this field. In the first approach, the associated differential equations are discretized and solved by a finite difference time domain (FDTD) method. Mathematically, this approach is straightforward. However, its computational time may be very intensive for 3-D cases. In the second approach, the Green's functions of the healthy structure are required. For general 3-D cases, numerical solutions of these Green's functions may be computationally intensive if analytical solutions are not available. But, the numerical solutions of the Green's functions, if needed, are carried out only once before the monitoring stage is started. After calculating the Green's functions, the back-propagated scattered field is computed by performing simple integral (summation) operations during the monitoring stage. It is worth noting that target-oriented capability (i.e., a desired part of the complete image area can be imaged without having to consider the remaining parts) is another distinct advantage of employing the IE approach. To lower the computational cost of the zero-lag cross-correlation imaging condition, step (2), the incident field at each image point is approximated by a single-event model parameterized by a traveltime and an amplitude (modified excitation-time imaging condition). It is shown that by applying similar approximations to the fields associated with the Green's functions of the healthy structure in the IE form of the algorithms, real-time damage imaging algorithms suitable for SHM application can be realized. As another way of reducing the computational cost of the algorithms, the poststack concept, typically used in geophysical exploration, is utilized. This way, the incident field in image area is not involved in the imaging process at all but the sensor data should be collected in a zero-offset experiment. To show the effectiveness of the DE and IE forms of the imaging algorithms, numerical simulations in 2-D Transverse Magnetic case for a reinforced concrete slab and a fiberglass laminated plate with multiple damages are performed. All synthetic sensor data, incident field, back-propagated (migrated) field, and the Green's functions of the healthy structure are computed via a FDTD method with second—order of accuracy in time and space. It is concluded that the proposed imaging algorithms are capable of efficiently identifying the damages geometries, are robust against measurement noise, and in their IE form may be employed in a SHMS.
Dynamic Microstructural Characterization of High Strength Aluminum Alloys
(2008-05-09) Lee, William Morgan; Alina Chertock, Committee Member; Kara Peters, Committee Member; Mohammed A. Zikry, Committee Chair
The use of aluminum alloys for commercial and military applications has increased substantially due to the alloys' low areal density, toughness, and processability. It has recently been shown that an aluminum alloy, Al 2139, with copper, magnesium, and silver can be significantly toughened and strengthened by combinations of θ' and Ω precipitates and dispersed manganese particles. What has not been quantified are how these precipitates and dispersed particles affect behavior and what the material mechanisms and microstructural characteristics are that control the behavior of Al 2139 for strain-rates that span the quasi-static to high rates of strain. Hence, in this investigation, detailed transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), orientation imaging microscopy (OIM), and optical microscopy (OM) were used to delineate the different physical scales that range from the nano for the precipitates and dislocations to the micron for the dispersed particles, grain orientations and texture, grain-sizes, slip-bands, and grain-boundary orientations. The deformed specimens were from an Al 2139 plate that was impacted by 4340 steel fragmentation stimulating projectiles (FSPs) at impact velocities ranging from 813 to 1043 m⁄s. The majority of the projectiles were defeated by the Al 2139 plate, which is another indication of the alloy's potential for damage mitigation and projectile defeat and resistance. Based on this detailed microstructural characterization, mechanisms for projectile defeat and full penetration are proposed. Deformation and damage modes include petalling on the impact face, shear cracking through the middle section of the plate due to projectile penetration, and discing due to bending stresses at a spall plane near the back of the plate. Shear cracking appears to be GB related, and the discing is dependent on the rolling direction. The extent of these modes for cross-sections where the target was penetrated was greater than that in regions where the projectile was defeated. For projectile defeat, large and elongated grains and precipitate deformation due to dislocation interaction can lead to highly ductile performance, which resists discing failure and plate penetration. Large grains significantly reduce the fraction of GBs, which then reduces the amount of GB cracking due to intense shear accumulation and spall. The elongation of the grains due to rolling also increased the dislocation densities, and subsequently the ductility of the grains, which reduced tensile failure due to the bending in the discing regions. High angle GB's can also limit heterogeneous θ' precipitation at the GB's, which would reduce intergranular fracture. Precipitation of Ω also increases the spall strength and decreases localized shear through its multiple cutting interactions with dislocations at the matrix interface. Dispersed particles also increase the strength of the alloy in high strain-rate applications by resisting localized shear. The results of this study are a first step in developing a tailored methodology that can be used to optimize microstructural characteristics and behavior of aluminum alloys for optimal strength and toughness.
Grain Subdivision and Microstructural Interfacial Scale Effects in Polycrystalline Materials
(2006-01-06) Rezvanian, Omid; Murthy Guddati, Committee Member; Mohammed Zikry, Committee Chair; Kara Peters, Committee Member; Larry Silverberg, Committee Member
The major objective of this research is to develop a unified physically-based representation of the microstructure in f.c.c. crystalline materials to investigate finite inelastic deformation and failure modes and scenarios at different physical scales that occur due to a myriad of factors, such as texture, grain size and shape, grain subdivision, heterogeneous microstructures, and grain boundary misorientations and distributions. The microstructurally-based formulation for inelastic deformation is based on coupling a multiple-slip crystal plasticity formulation to three distinct dislocation densities, which pertain to statistically stored dislocations (SSDs), geometrically necessary dislocations (GNDs), and grain boundary dislocations (GBDs). This dislocation density based multiple-slip crystal plasticity formulation is then coupled to specialized finite-element methods to predict the scale-dependent microstructural behavior, the evolving heterogeneous microstructure, and the localized phenomena that may contribute to failure initiation for large inelastic strains. The SSD densities provide a representation of cell-type dislocation microstructures and their related processes. The GND densities provide an understanding of the scale-dependent deformation behavior of crystalline materials as a function of grain and aggregate sizes. The GBD densities are formulated to represent the misfit dislocations that arise due to lattice misorientations across GBs, and to provide a framework to investigate the phenomena associated with the grain boundary orientations and distributions. This provides a local criterion of how GB interfaces, such as triple junctions are potential sites for failure initiation and localized behavior. The evolution of the GNDs is used to predict and understand how crystallographic and non-crystallographic microstructures relate to intragranular and intergranular deformation patterns and behavior. Furthermore, a clear understanding of how GB strength changes due to microstructural evolution is obtained as a function of microstructural heterogeneities that occur at different physical scales.
Intelligent Load Monitoring in Beam Structures
(2003-11-24) Li, Junping; Kara Peters, Committee Member; F. G. Yuan, Committee Chair; Fen Wu, Committee Member
A robust approach for identifying impact load location and impact force history in beam structures is presented in this thesis. Beam strain transients propagating from the impact site can be inverted to yield the impact location and force history. Solving the inverse problem consists of three parts: a transient wave model, an impact location determination, and then an impact history identification. The classical Euler-Bernoulli beam theory (EBT) is used to obtain the dynamic models of a simply-supported beam. The simulated measured strain data are utilized from the transient wave model derived from finite element method and state variable approach. A wavelet analysis using Gabor basis function is employed to determine the impact load location from strain measurements resulting from a pair of sensors which are located on the opposite side of the impact site. The information on traveling dispersive waves is described by the time-frequency representation of the transient strain data analyzed using wavelet transform. A Radial Basis Function network (RBFN) is then employed to efficiently reconstruct the impact load history from a single strain sensor. The back-propagation algorithm in conjunction with Levenberg-Marquardt method is adopted to update the parameters of RBFN by minimizing the difference between model prediction and the sensor measurements, where the transient wave model is embedded in the RBFN to guide and speed up the training process. The effect of noise on the identification of impact site and loading history is also investigated in detail. Several examples demonstrate the effectiveness of the approach.
Mechanical Engineering Capstone Senior Design Course Textbook
(2006-09-08) Barrett, Rolin Farrar; Joseph Hobbs, Committee Member; Larry Silverberg, Committee Member; Eric Klang, Committee Chair; Richard Johnson, Committee Member; Kara Peters, Committee Member
This textbook is intended to bridge the gap between mechanical engineering equations and mechanical engineering design. To that end, real-world examples are used throughout the book. Also, the material is presented in an order that follows the chronological sequence of coursework that must be performed by a student in the typical capstone senior design course in mechanical engineering. In the process of writing this book, the author surveyed the fifty largest engineering schools (as ranked by the American Society of Engineering Education, or ASEE) to determine what engineering instructors are looking for in a textbook. The survey results revealed a clear need for a textbook written expressly for the capstone senior design course as taught throughout the nation. This book is designed to meet that need. This text was written using an organizational method that the author calls the General Topics Format. The format gives the student reader rapid access to the information contained in the text. All manufacturing methods, and some other material presented in this text, have been presented using the General Topics Format. The text uses examples to explain the importance of understanding the environment in which the product will be used and to discuss product abuse. The safety content contained in this text is unique. The Safety chapter teaches engineering ethics and includes a step-by-step guide to resolving ethical conflicts. The chapter includes explanations of rules, recommendations, standards, consensus standards, key safety concepts, and the legal implications of product failure. Key design principles have been listed and explained. The text provides easy-to-follow design steps, helpful for both the student and new engineer. Prototyping is presented as consisting of three phases: organization, building, and refining. A chapter on common manufacturing methods is included for reference.
Mechanics of Ultrasonic Tube Hydroforming
(2008-12-05) Bunget, Cristina Janeta; Gracious Ngaile, Committee Chair; Stefan Seelecke, Committee Member; Kara Peters, Committee Member; Michael Shearer, Committee Member
BUNGET, CRISTINA JANETA. Mechanics of Ultrasonic Tube Hydroforming. (Under the direction of Gracious Ngaile.) Tube hydroforming is a manufacturing process which applies controlled internal pressure and axial feed to expand the tube to desired shapes. The main advantages are: part consolidation, weight reduction, fewer secondary operations, and tighter tolerances. However, it has disadvantages due to many variables, such as loading paths, material formability, and tribological conditions, which limit its applicability and influence parts failure (excessive thinning, wrinkling, buckling or bursting). This research presents ultrasonic technology as a method of improving formability and tribological conditions. The superimposing of ultrasonic oscillations was already proved to have benefits for other metal forming processes, such as reduction in the forming load and frictional stresses. The objectives of this research work are to develop an analytical model to predict the state of stress and strain for the tube expansion under internal pressure and friction conditions, for ultrasonic and non-ultrasonic processes, observe the effects of the vibration on the deformation pattern, design a set of tooling and conduct experiments. An analytical model was derived for both conventional and ultrasonic tube hydroforming processes, using equilibrium of forces, geometric relationships, material flow law and yield criterion. The square dies were chosen for this study, due to the simplicity of plane strain conditions. In conventional process the tube is expanded under internal pressure in the presence of friction. In the ultrasonic process, vibrations are imposed on the die, resulting in alternating gaps at the die/tube interface. The gaps open and close after each oscillation. Two different states of stress alternate during one oscillation in an element of the tube wall. The analytical model was used to predict the internal pressure required, the corner radius, the thickness distribution, and the state of stress and strain. For the conventional process, the influence of some parameters on the deformation pattern and the forming load, such as strain hardening and friction conditions, was studied. Lower friction coefficient is required for more uniform tube wall thickness and lower pressure. In the ultrasonic process, more uniform thickness distribution and state of stress and strain were predicted, as compared to the classical process. When the internal pressure is maintained, the corner radius obtained is smaller. The reduction in the corner radius was between 2.4 and 9%. More uniform thickness and less thinning, as well as smaller corner radius, indicate improvement of the formability of the material. If ultrasonic oscillations are used and the pressure exerted on the tube due to vibration is less than a critical value (equal to the internal pressure), there is a decrease in the maximum internal pressure needed for the same expansion. The most effective ultrasonic pressure is 0.1 MPa. Finite element method was used to approximate the ultrasonic pressure and to design a set of tooling for ultrasonic process at 20 kHz. Four models were proposed and analyzed for three square die sizes. Modal analysis was used to observe the die vibration and the possible useful effects on the forming process. Harmonic response analyses were conducted to evaluate the amplitude of vibration in the deformation zone and the stress in the tooling. Based on the displacement distribution, a method of approximating the ultrasonic pressure was proposed. Most of the average pressure values were found to vary from 5 MPa to 25 MPa. In order to observe the effects of ultrasonic oscillations on tube hydroforming, experiments were conducted with and without vibration. The ultrasonic tests resulted in smaller corner radii as compared to the conventional test, with a reduction of 5.2-7.7%, implying increase in forming capability due to vibration.
Microstructural Modeling of Heterogeneous Failure Modes in Martensitic Steels
(2009-03-18) Hatem, Tarek Moustafa; Larry Silverberg, Committee Member; Kara Peters, Committee Member; Ronald Scattergood, Committee Member; Mohammed Zikry, Committee Chair
A three-dimensional multiple-slip dislocation-density-based crystalline formulation, specialized finite-element formulations, predictive failure models, and infinity-power integrable function based Voronoi tessellations adapted to martensitic orientations, were used to investigate large strain inelastic deformation, dislocation-density evolution in martensitic transformation, and heterogeneous failure modes in martensitic microstructures. The formulation is based on accounting for variant morphologies and orientations, secondary phases, such as retained austenite and inclusions, and initial dislocations-densities that are uniquely inherent to martensitic microstructures. The computational framework and the constitutive formulation were validated with experimental results for 10% Ni high-strength steel alloy. Furthermore, the formulation was used to investigate microstructures mapped directly from SEM/EBSD images of martensitic steel alloys. The interrelated effects of microstructural characteristics, such as parent austenite orientation, variants distribution and arrangement, retained austenite, inclusions, initial dislocation-density, and defects, such as microcracks, and microvoids, were investigated for different failure modes such as rupture, transgranular and intergranular fracture, and shear localization over a broad spectrum of loading conditions that range from quasi-static to high strain-rate conditions. The computational predictions, consistent with experimental observations, indicated that variant morphology and orientations have a direct consequence on how shear-strain accumulation and failure evolves in martensitic microstructures subjected to quasi-static and high strain-rate loading conditions. The analysis shows that shear-strain localization occurs due to slip-system compatibilities corresponding to low-angle blocks boundaries, the loading direction and the long direction of laths, which result in shear-pipes. At specific triple junctions, rotation misalignments due to lattice and slip incompatibilities occur, and this further exacerbated by defects. The results underscore the inherent competition between shear localization, transgranular, and intergranular failure modes. For certain variant arrangements, which correspond to random low angle orientations, cracks can be blunted by dislocation-density activities along transgranular planes. The effects of strain rate and inclusions on the evolution of shear-strain localization were also investigated under both tensile and compressive loadings. Tensile hydrostatic pressure forms under dynamic loads, and combined with plastic shear-slip accumulation between inclusions and the martensitic matrix accelerate shear-strain localization.
Modeling the Dynamic Deformation and Failure Modes in High Strength and Damage Tolerant Aluminum Alloys.
(2010-10-04) Elkhodary, Khalil; Mohammed Zikry, Committee Chair; Lawrence Silverberg, Committee Member; Kara Peters, Committee Member; Donald Brenner, Committee Member
A Point-of-Care Diagnostic Device for Quantifying Estradiol Levels in Human Saliva.
(2005-02-06) Lorek, James D; Stefan Seelecke, Committee Member; Kara Peters, Committee Member; M.K. Ramasubramanian, Committee Chair
This study was carried out focusing upon two primary objectives: the first being to investigate experimentally the merit of a photoelectrochemical process for quantifying estradiol by salivary assay and the second to investigate numerically a novel method of accelerated sedimentation for use in sample processing and purification as an alternative to centrifugation. The presented work began initially in pursuit of an improved means of diagnostic testing for estradiol levels in patients undergoing infertility treatment. The validity of using saliva as an alternative diagnostic medium to serum has been investigated and tested experimentally, demonstrating that saliva may be used as a means to quantify estradiol levels. Initial experimental results of the proposed assay technique hold promise, with an observable photocurrent response relative to the presence of E2-[Ru(bpy)3]2+; however, further experimentation is necessary in full development of an assay. Results of a CFD analysis reveal the proposed actuation method for diagnostic sample purification to perform well in comparison to that of a centrifuge and to offer advantages in a potentially compact design well suited to a fully-integrated point-of-care diagnostic device.
Predictive Microstructural Modeling of Grain-boundary Interactions and Their Effects on Overall Crystalline Behavior
(2009-02-26) Shi, Jibin; Larry Silverberg, Committee Member; Mohammed Zikry, Committee Chair; Ron Scattergood, Committee Member; Kara Peters, Committee Member
A dislocation-density grain boundary interaction scheme (DDGBI) has been developed to account for complex interrelated dislocation-density interactions of emission, absorption and transmission in grain-boundary (GB) regions for bicrystals and polycrystals with different random and coincident site lattice (CSL) GB arrangements. This scheme is coupled to a dislocation-density crystalline plasticity formulation and specialized finite-element scheme at different physical scales. The DDGBI scheme is based on slip-system compatibility, local resolved shear stresses, and immobile and mobile dislocation-density activities at GBs. A conservation law for dislocation-densities is used to balance dislocation-density absorption, transmission and emission in GB regions. It is shown that dislocation-density absorptions and pile-ups will increase immobile dislocation-densities in high angle CSL boundaries, such as Î£17b. Lower angle CSLs, such as Î£1, are characterized by high transmission rates and insignificant GB dislocation-density accumulations. The identification of how different material mechanisms dominate underscores that GB activities, such as dislocation-density absorption, transmission and emission are interrelated interactions. These GB processes can be potentially controlled for desired material behavior. This methodology, together with grain boundary sliding (GBS) scheme and a misorientation dependence on initial GB dislocation-densities, was extended to account for grain size effects on strength. The behavior of polycrystalline aggregates with random low angle and random high angle GBs was also investigated with different crack lengths. For aggregates with random low angle GBs, dislocation-density transmission dominates at the GBs, which indicates that the low angle GB will not significantly change crack growth orientations. For aggregates with random high angle GBs, extensive dislocation-density absorption and pile-ups occur. The high stresses along the GB regions can result in intergranular crack growth due to potential crack nucleation sites in the GB. It is also shown that GB sliding affects crack behavior by attenuating normal stresses and dislocation-density accumulation at critical GB interfaces.
Probabilistic Damage Size Estimation for Structural Health Management.
(2010-10-22) Li, Gang; Fuh-Gwo Yuan, Committee Chair; Kara Peters, Committee Member; Gregory Buckner, Committee Member; Murthy Guddati, Committee Member
Seismic Behavior of Reinforced Concrete Bridge Columns at Sub-Freezing Temperatures
(2008-06-23) Montejo, Luis Alberto; Mervyn J. Kowalsky, Committee Chair; Tasnim Hassan, Committee Co-Chair; Abhinav Gupta, Committee Member; Kara Peters, Committee Member
Semiconductor Crystal Growth by Vertical Bridgman and Gradient Freezing Processes with Applied Fields
(2007-05-08) Wang, Xianghong; Kara Peters, Committee Member; Kevin Lyons, Committee Member; Tarek Echekki, Committee Member; Nancy Ma, Committee Chair
Integrated circuits and optoelectronic devices are produced on surfaces of thin wafers sliced from a semiconductor crystal. The performance of the semiconductor is directly related to the uniformity of its composition. The crystal's composition generally changes due to a changing melt composition with segregation coefficient not equal to unity. Therefore, a major objective during the growth of any semiconductor crystal is to minimize the variations of the crystal's dopant or alloy composition. Externally-applied fields such as magnetic and electric fields can be used to provide electromagnetic damping or stirring of the melt motion in order to minimize the dopant or alloy segregation in the melt and thus in the crystal. This research focuses on investigations of various semiconductor crystal growth processes from the melt in the presence of externally-applied fields. These processes are (1) the Bridgman-Stockbarger process in steady magnetic fields, (2) the vertical gradient freezing process using submerged heater growth in steady magnetic and electric fields, (3) the Bridgman process using submerged heater growth in a rotating magnetic field, and (4) the Bridgman process using submerged heater growth in a combination of steady and rotating magnetic fields. Numerical models are developed using a Chebyshev spectral method with Gauss-Lobatto collocation points. These models provide predictions of the temperature, velocity and concentration fields in the melt as well as the dopant or alloy concentration in the entire crystal.
Transient Waves from Acoustic Emission Sources in Isotropic Plates Using a Higher Order Extensional and Bending Theory.
(2010-03-15) Bogert, Philip B.; Fuh-Gwo Yuan, Committee Chair; Eric Klang, Committee Member; Kara Peters, Committee Member; Yong Zhu, Committee Member
This dissertation presents a derivation for the transient wave response of an infinite isotropic plate to a general acoustic emission (AE) point source discontinuity loading, based on third-order plate theory. The calculation of the wave response is facilitated by employing the concept of a seismic moment tensor (or derived Ã¢â‚¬Å“equivalentÃ¢â‚¬Â body-forces) to describe the loading from highly localized displacement discontinuities on a fracture surface. Further, the body forces from 3-D elasticity are converted to plate loadings for use in the plate theory wave equations of motion. The transient wave response can be detected as AE signals using piezoelectric sensors. In particular, time-dependent surface strains can be readily obtained experimentally. Therefore the results emphasize the calculation of the surface strains for potential comparison with future experiments. The calculated transient response, which represents waves propagating from a general AE point source in the plate, is expressed in an explicit integral form. It is shown that the transient response, which is given by double inverse Fourier transforms, can be simplified into a finite series involving inverse Hankel transforms which only require one-dimensional inversions for an isotropic plate. Thus numerical evaluation of the transient wave is more robust and accurate than that generated using two-dimensional inverse transforms and also, asymptotic solutions can be readily obtained. Nine types of AE sources representing different micro-damage mechanisms and their corresponding plate loads are discussed. Numerical results for four types of AE point sources with a Heaviside time history loading are presented. The long-term goal of the development, having established a relationship between disturbance and response, is to monitor responses in a structure and be able to determine the source, i.e. damage, type and location by solving the inverse problem in real time. What is new and different from previous work upon which this is building is that the extensional formulation is evaluated for general AE loading, and a higher order bending theory is developed and evaluated. Additionally, the polar conversion reduction to a single variable spatial integration is implemented for both theories.
Vibration-based Damage Detection and Health Monitoring of Bridges.
(2010-06-08) Mosavi Khandanhaghighi, Amirardalan; Sami Rizkalla, Committee Chair; Rudolf Seracino, Committee Chair; David Dickey, Committee Member; Kara Peters, Committee Member