Typescript (photocopy). / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries / Department: Statistics.

Typescript (photocopy). / Digitized by Kansas Correctional Industries / Department: Computer Science.

Thesis. 1977. M.Arch.--Massachusetts Institute of Technology. Dept. of Architecture. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCH. / Includes bibliographical references. / by Brandt Andersson. / M.Arch.

The safety of engineering structures depends heavily on the presence of cracks, which may propagate and lead eventually to structural failure. This dissertation aims to advance the computational modeling of fracture, within the context of linear elastic fracture mechanics (LEFM) and cohesive zone models (CZMs). The extended finite element method (XFEM) is employed as the discretization method and cracks in both homogeneous and bimaterial solids are considered in this work. First, a novel set of enrichment functions within the framework of XFEM is proposed for the LEFM analysis of interface cracks in bimaterials. The motivation for the new enrichment set stems from the revelation that the accuracy of the widely accepted 12-fold bimaterial enrichment functions significantly deteriorates with the increase in material mismatch. To this end, we propose an 8-fold material-dependent enrichment set, derived from the analytical asymptotic displacement field, that well captures the near-tip oscillating singular fields of interface cracks, including the transition to weak discontinuities of bimaterials. The new enrichment set is tested on various examples and found to outperform the 12-fold set in terms of accuracy, conditioning, and total number of degrees of freedom (DOFs). The formulation is then extended to include high-order enrichment functions and accurate stress and displacement fields are obtained. The complex stress intensity factors (SIFs) of interface cracks are evaluated by employing Irwin's crack closure integral. To this end, a closed-form SIF formulation in terms of the enriched DOFs is derived by matching the leading term in the XFEM with an analytical expression of Irwin's integral. Hence, the SIFs of interface cracks can be directly obtained upon the solution of the XFEM discrete system without cumbersome post-processing requirements. The proposed method is shown to work well on several benchmark examples involving straight and curved interface cracks, giving accurate SIF results. Another contribution of the work is the application of Irwin's integral to the estimation of SIFs for curved homogeneous cracks. At the core, the proposed approach employs high-order enrichment functions to accurately capture the near-tip fields and evaluates the original definition of Irwin's integral through closed-form formulations in terms of enriched DOFs. An improved quadrature scheme using high-order isoparametric mapping together with a generalized Duffy transformation is proposed to integrate singular fields in tip elements with curved cracks. The proposed extraction approach is shown to yield decomposed SIFs with excellent accuracy and avoid the need for auxiliary fields as in J-integral method. Second, with respect to cohesive fracture, a discrete damage zone model (DDZM) is proposed following a rigorous thermodynamic framework similar to that of continuum damage mechanics (CDM). For the modeling of mixed-mode delamination, a novel damage evolution law is proposed to account for the coupled interaction between opening and sliding modes of interface deformations. A comprehensive comparison made with several popular CZMs in the literature demonstrates the thermodynamic consistency of the DDZM. The proposed interface model is integrated with the XFEM and the effectiveness of this framework has been validated on various benchmark problems. Finally, a novel continuous/discontinuous method is proposed to simulate the entire failure process of quasi-brittle materials: from the nucleation of diffuse damage to the development of discrete cracks . An integral-type nonlocal continuum damage model is coupled in this framework with DDZM with a new numerical energetic coupling scheme. The transition from the continuous (CDM) to the discontinuous approach (DDZM) can be triggered at any damage level with a weak energetic equivalence preserved. A few benchmark problems involving straight and curved cracks are investigated to demonstrate the applicability and robustness of the coupled XFEM cohesive-damage approach.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

This project brings the bioinformatics community a new development concept in which users can access all data and applications hosted in the main research centers as if they were installed on their local machines, providing seamless integration between disparate services. The project moves to integrate the sequence similarity searching at EBI and NCBI by using web services. It also intends to allow molecular biologists to save their searches and act as a log book for their sequence similarity searches. The project will also allow the biologists to share their sequences and results with others.

The thesis discusses the development of Multi-Warehouse Inventory Control System (MWICS), a uniquely designed web application that targets membership based food wholesalers. The main goal of MWICS is to provide a real-time inventory control ability to all warehouses and present them as if it were single warehouse. The program consists of three main components: user account management sub-system, product and purchase management sub-system, and a warehouse inventory management sub-system. User interfaces are constructed primarily in HTML, PHP, and Javascript. MySQL is used to add, access, and process data.

In an attempt to achieve more efficient designs, the technological frontier is pushed further and further. Every year science probes for a better understanding of natural phenomena, discovering new and improved methods to perform the same task more efficiently and with better results. One of the new technologies is the nonlinear analysis of structural systems using inelastic post-buckling member performance. Inelastic post-buckling member performance is defined as the constitutive relationship between axial load and displacement after the ultimate member capacity has been exceeded. A nonlinear analysis is able to predict the failure behavior of a structural system under ultimate loads more accurately than the traditionally used linear elastic analysis. Consequently, designs can be improved and become more efficient, which reduces the realization cost of a project. An improved nonlinear analysis solution algorithm has been developed, that allows the analyst to perform a nonlinear analysis using post-buckling member performances faster than previously possible. Furthermore, the original post-buckling member performance database was expanded using results obtained from physical member compression tests. Based on the experimental results, new post-buckling member performance model curves were developed to be used together with the improved nonlinear solution algorithm. In addition, a program was developed that allows the analyst to perform a valid nonlinear analysis using a finite element program (LIMIT). The program combines a numerical pre-processor, and input and output data evaluation modules based on human expertise together with the LIMIT analysis package. Extensive on-line help facilities together with graphical pre- and post-processors were also integrated into the program. The resulting analysis package essentially combines all of the necessary components required to perform a nonlinear analysis using post-buckling member performances into one complete analysis package.