scispace - formally typeset
Search or ask a question
Author

John Berger

Bio: John Berger is an academic researcher from Colorado School of Mines. The author has contributed to research in topics: Stress intensity factor & Boundary element method. The author has an hindex of 18, co-authored 76 publications receiving 1000 citations. Previous affiliations of John Berger include University of Maryland, College Park & University of Alaska Anchorage.


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the authors considered the problem of a point force acting in an unbounded, three-dimensional, isotropic elastic solid, where the material is inhomogeneous; it is "functionally graded" and the Lame moduli vary exponentially in a given fixed direction.
Abstract: The problem of a point force acting in an unbounded, three–dimensional, isotropic elastic solid is considered. Kelvin solved this problem for homogeneous materials. Here, the material is inhomogeneous; it is ‘functionally graded’. Specifically, the solid is ‘exponentially graded’, which means that the Lame moduli vary exponentially in a given fixed direction. The solution for the Green9s function is obtained by Fourier transforms, and consists of a singular part, given by the Kelvin solution, plus a non–singular remainder. This grading term is not obtained in simple closed form, but as the sum of single integrals over finite intervals of modified Bessel functions, and double integrals over finite regions of elementary functions. Knowledge of this new fundamental solution for graded materials permits the development of boundary–integral methods for these technologically important inhomogeneous solids.

88 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the application of the Method of Fundamental Solutions (MFS) to two-dimensional problems of steady-state heat conduction in isotropic and anisotropic bimaterials.
Abstract: In this paper, we investigate the application of the Method of Fundamental Solutions (MFS) to two-dimensional problems of steady-state heat conduction in isotropic and anisotropic bimaterials. Two approaches are used: a domain decomposition technique and a single-domain approach in which modified fundamental solutions are employed. The modified fundamental solutions satisfy the interface continuity conditions automatically for planar interfaces. The two approaches are tested and compared on several test problems and their relative merits and disadvantages discussed. Finally, we use the domain decomposition approach to investigate bimaterial problems where the interface is non-planar and the modified fundamental solutions cannot be used. Copyright © 1999 John Wiley & Sons, Ltd.

81 citations

Journal ArticleDOI
TL;DR: In this paper, a coupled electrochemical-mechanical model is developed and applied to predict transient three-dimensional stress fields within reconstructed Li x CoO 2 cathode particles from commercial Li-ion batteries.

75 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the application of the fundamental solutions to two-dimensional elasticity problems in isotropic and anisotropic single materials and bimaterials, where the interface continuity conditions were approximated in the same manner as the boundary conditions.
Abstract: In this paper, we investigate the application of the method of fundamental solutions to two-dimensional elasticity problems in isotropic and anisotropic single materials and bimaterials. A domain decomposition technique is employed in the bimaterial case where the interface continuity conditions are approximated in the same manner as the boundary conditions. The method is tested on several test problems and its relative merits and disadvantages are discussed.

74 citations

Journal ArticleDOI
TL;DR: An overdeterministic method for determining the opening mode stress intensity factor from many measurements of the radial strain was described in this paper, which was verified with an experimental study of a compact-tension specimen where strains along the 0, 45 and 90 degree lines were measured using strip gages with ten strain sensors per strip gage.
Abstract: An overdeterministic method for determining the opening-mode stress-intensity factor,K I , from many measurements of the radial strain,∈ rr , is described The method was verified with an experimental study of a compact-tension specimen where strains along the 0, 45 and 90-degree lines were measured using strip gages with ten strain sensors per strip gage The results indicated errors in the range of one to three percent with three or four parameter models of the strain field in the region near the crack tip

47 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: Techniques by which MFS-type methods are extended to certain classes of non-trivial problems and adapted for the solution of inhomogeneous problems are outlined.
Abstract: The aim of this paper is to describe the development of the method of fundamental solutions (MFS) and related methods over the last three decades. Several applications of MFS-type methods are presented. Techniques by which such methods are extended to certain classes of non-trivial problems and adapted for the solution of inhomogeneous problems are also outlined.

958 citations

Journal ArticleDOI
17 Sep 2010-Sensors
TL;DR: The performance of ZnO-based photodetectors is analyzed, discussing recent achievements, and comparing the characteristics of the variousPhotodetector structures developed to date.
Abstract: Ultraviolet (UV) photodetection has drawn a great deal of attention in recent years due to a wide range of civil and military applications. Because of its wide band gap, low cost, strong radiation hardness and high chemical stability, ZnO are regarded as one of the most promising candidates for UV photodetectors. Additionally, doping in ZnO with Mg elements can adjust the bandgap largely and make it feasible to prepare UV photodetectors with different cut-off wavelengths. ZnO-based photoconductors, Schottky photodiodes, metal–semiconductor–metal photodiodes and p–n junction photodetectors have been developed. In this work, it mainly focuses on the ZnO and ZnMgO films photodetectors. We analyze the performance of ZnO-based photodetectors, discussing recent achievements, and comparing the characteristics of the various photodetector structures developed to date.

558 citations

Journal ArticleDOI
TL;DR: A review of discrete element and hybrid finite-discrete element modeling techniques that have emerged in the field of rock mechanics as simulation tools for fracturing processes in rocks and rock masses is provided in this paper.
Abstract: The goal of this review paper is to provide a summary of selected discrete element and hybrid finite–discrete element modeling techniques that have emerged in the field of rock mechanics as simulation tools for fracturing processes in rocks and rock masses. The fundamental principles of each computer code are illustrated with particular emphasis on the approach specifically adopted to simulate fracture nucleation and propagation and to account for the presence of rock mass discontinuities. This description is accompanied by a brief review of application studies focusing on laboratory-scale models of rock failure processes and on the simulation of damage development around underground excavations.

388 citations

Journal ArticleDOI
TL;DR: A review of the progress made over the last 20 years in the development and applications of liquid xenon detectors in particle physics, astrophysics, and medical imaging experiments is given in this paper.
Abstract: This article reviews the progress made over the last 20 years in the development and applications of liquid xenon detectors in particle physics, astrophysics, and medical imaging experiments. A summary of the fundamental properties of liquid xenon as radiation detection medium, in light of the most current theoretical and experimental information is first provided. After an introduction of the different type of liquid xenon detectors, a review of past, current, and future experiments using liquid xenon to search for rare processes and to image radiation in space and in medicine is given. Each application is introduced with a survey of the underlying scientific motivation and experimental requirements before reviewing the basic characteristics and expected performance of each experiment. Within this decade it appears likely that large volume liquid xenon detectors operated in different modes will contribute to answering some of the most fundamental questions in particle physics, astrophysics, and cosmology, fulfilling the most demanding detection challenges. From detectors based solely on liquid xenon (LXe) scintillation, such as in the MEG experiment for the search of the rare ''{mu}{yields}e{gamma}'' decay, currently the largest liquid xenon detector in operation, and in the XMASS experiment for dark matter detection, to the class ofmore » time projection chambers which exploit both scintillation and ionization of LXe, such as in the XENON dark matter search experiment and in the Enriched Xenon Observatory for neutrinoless double beta decay, unrivaled performance and important contributions to physics in the next few years are anticipated.« less

332 citations

08 Jul 2010
TL;DR: In this paper, first-principles calculations for both amorphous and crystalline phases observed during lithiation of Si anodes were performed and the anisotropic elastic tensors as well as the homogenized Young's, shear, and bulk moduli and the Poisson's ratios were analyzed.
Abstract: Knowledge of the elastic properties of Li–Si alloys as a function of Li concentration is crucial in the development of reliable deformation and fracture mechanics models for Si anodes in Li-ion batteries. Here, we have studied these properties using first-principles calculations for both amorphous and crystalline phases observed during lithiation of Si anodes. In the case of crystalline alloys, we present the anisotropic elastic tensors as well as the homogenized Young's, shear, and bulk moduli and the Poisson's ratios. We find that while these moduli decrease in an approximately linear manner with increasing Li concentration leading to significant elastic softening (by about one order of magnitude) in both crystalline and amorphous systems, the Poisson's ratios remain in the range of 0.05–0.20 and 0.20–0.30 in the case of crystalline and amorphous systems, respectively. Further, for a given Li concentration, we find that the amorphous structures are elastically somewhat softer than their crystalline counterparts, the difference being more significant (about 30–40%) in Li-poor phases. Our results underscore the importance of including the concentration dependence of elastic constants in the analysis of stress and deformation fields during lithiation and de-lithiation of Si anodes.

324 citations