620 Matching Results

Search Results

Advanced search parameters have been applied.

Workshop on Concepts for Self-Healing Critical Infrastructures

Description: This report describes a workshop on self-healing infrastructures conducted jointly by Sandia National Laboratories, Infrastructure & Information Division, and the Massachusetts Institute of Technology, Engineering Systems Division. The workshop was held in summer, 2002 and funded under Laboratory-Directed Research and Development (LDRD) No.5 1540. The purpose of the workshop was to obtain a working definition of a self-healing infrastructure, explore concepts for self-healing infrastructures systems, and to propose engineering studies that would lay the foundation for the realization of such systems. The workshop produced a number of useful working documents that clarified the concept of self-healing applied to large-scale system-of-systems exemplified by the US National Critical Infrastructure. The workshop eventually resulted in a joint proposal to the National Science Foundation and a continuing collaboration on intelligent agent based approaches to coordination of infrastructure systems in a self-healing regime.
Date: June 1, 2003
Partner: UNT Libraries Government Documents Department

An Initial Overview of Iwan Modeling for Mechanical Joints

Description: The structural dynamics modeling of engineering structures must accommodate the energy dissipation due to microslip in mechanical joints. Given the nature of current hardware and software environments, this will require the development of constitutive models for joints that both adequately reproduce the important physics and lend themselves to efficient computational processes. The exploration of the properties of mechanical joints--either through fine resolution finite element modeling or through experiment--is itself an area of research, but some qualitative behavior appears to be established. The work presented here is the presentation of a formulation of idealized elements due to Iwan, that appears capable of reproducing the important joint properties as they are now understood. Further, methods for selecting parameters for that model by joining the results from experiments in regimes of small and large load are developed. The significance of this work is that a reduced order model is presented that is capable of reproducing the important qualitative properties of mechanical joints using only a small number of parameters.
Date: March 1, 2001
Partner: UNT Libraries Government Documents Department

Some approaches for modeling and analysis of a parallel mechanism with stewart platform architecture

Description: Parallel mechanisms represent a family of devices based on a closed kinematic architecture. This is in contrast to serial mechanisms, which are comprised of a chain-like series of joints and links in an open kinematic architecture. The closed architecture of parallel mechanisms offers certain benefits and disadvantages.
Date: May 1, 1998
Creator: Sapio, V. De
Partner: UNT Libraries Government Documents Department

MEMS Packaging - Current Issues and Approaches

Description: The assembly and packaging of MEMS (Microelectromechanical Systems) devices raise a number of issues over and above those normally associated with the assembly of standard microelectronic circuits. MEMS components include a variety of sensors, microengines, optical components, and other devices. They often have exposed mechanical structures which during assembly require particulate control, space in the package, non-contact handling procedures, low-stress die attach, precision die placement, unique process schedules, hermetic sealing in controlled environments (including vacuum), and other special constraints. These constraints force changes in the techniques used to separate die on a wafer, in the types of packages which can be used in the assembly processes and materials, and in the sealing environment and process. This paper discusses a number of these issues and provides information on approaches being taken or proposed to address them.
Date: January 19, 2000
Partner: UNT Libraries Government Documents Department

First passage failure: Analysis alternatives

Description: Most mechanical and structural failures can be formulated as first passage problems. The traditional approach to first passage analysis models barrier crossings as Poisson events. The crossing rate is established and used in the Poisson framework to approximate the no-crossing probability. While this approach is accurate in a number of situations, it is desirable to develop analysis alternatives for those situations where traditional analysis is less accurate and situations where it is difficult to estimate parameters of the traditional approach. This paper develops an efficient simulation approach to first passage failure analysis. It is based on simulation of segments of complex random processes with the Karhunen-Loeve expansion, use of these simulations to estimate the parameters of a Markov chain, and use of the Markov chain to estimate the probability of first passage failure. Some numerical examples are presented.
Date: April 17, 2000
Partner: UNT Libraries Government Documents Department

A Review of Structural Health Review of Structural Health Monitoring Literature 1996-2001.

Description: Staff members at Los Alamos National Laboratory (LANL) produced a summary of the structural health monitoring literature in 1995. This presentation will summarize the outcome of an updated review covering the years 1996 - 2001. The updated review follows the LANL statistical pattern recognition paradigm for SHM, which addresses four topics: (1) Operational Evaluation; (2) Data Acquisition and Cleansing; (3) Feature Extraction; and (4) Statistical Modeling for Feature Discrimination. The literature has been reviewed based on how a particular study addresses these four topics. A significant observation from this review is that although there are many more SHM studies being reported, the investigators, in general, have not yet fully embraced the well-developed tools from statistical pattern recognition. As such, the discrimination procedures employed are often lacking the appropriate rigor necessary for this technology to evolve beyond demonstration problems carried out in laboratory setting.
Date: January 1, 2002
Creator: Sohn, H. (Hoon); Farrar, C. R. (Charles R.); Hemez, F. M. (Fran├žois M.) & Czarnecki, J. J. (Jerry J.)
Partner: UNT Libraries Government Documents Department

Damping dependence on bolt torque for a simple frame structure.

Description: Damping quantifies the energy dissipation properties of a material or system under cyclic stress. Damping is also one of the most difficult properties of a mechanical structure to model using first principles (Ewins, 2002) . Damping in uniform metal structures is often low. In built up structures dissipation occurs at mechanical joints or through introduction of viscoelastic materials ( Ungar, 1973, Goodman, 1996) . Energy dissipation at joints, associated with microslip, macroslip and hystersis increases the total damping of a structure so built up structures virtually always have greater damping than structures composed of a single part . Since damping is sensitive to interface properties, damping is a good feature for quantifying interface condition.
Date: January 1, 2003
Creator: Hunter, N. F. (Norman F.) & Paez, Thomas L.,
Partner: UNT Libraries Government Documents Department


Description: The problem of designing a reactor to withstand the shocks and vibration incident to shipboard service in Naval craft consists of three principal parts. First the loads must be defined in some rational manner, then the responses of the various reactor structures to these loads must be predicted, and finally the responses must be compared to some damage criteria to determine whether the design is adequate or not. A brief discussion of each of these major parts is given, and then a specific example is worked through to illustrate what is involved in the whole process. (auth)
Date: October 31, 1957
Creator: Mains, R.M.
Partner: UNT Libraries Government Documents Department

Module strap tests and how they effect the 25 cm stack construction

Description: We were asked at the previous Atlas collaboration meeting to confirm our proposal that the Argonne design option could maintain the tie straps in a prestressed condition after welding. This was deemed necessary to maintain compression loading of the steel plate stack. The compression load requirement was set at a load equivalent to that necessary to maintain continuity of the stack using friction. We will attempt to prove that through the strap testing and the ultimate construction of the 25 cm prototype stack that we have in fact met these requirements.
Date: September 6, 1994
Creator: Hill, N.F.
Partner: UNT Libraries Government Documents Department