A. James Clark School of Engineering

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Utilization of Dynamic and Static Sensors for Monitoring Infrastructures
(IntechOpen, 2018-12-12) Fu, Chung C.; Zhu, Yifan; Hou, Kuang-Yuan
Infrastructures, including bridges, tunnels, sewers, and telecommunications, may be exposed to environmental-induced or traffic-induced deformation and vibrations. Some infrastructures, such as bridges and roadside upright structures, may be sensitive to vibration and displacement where several different types of dynamic and static sensors may be used for their measurement of sensitivity to environmental-induced loads, like wind and earthquake, and traffic-induced loads, such as passing trucks. Remote sensing involves either in situ, on-site, or airborne sensing where in situ sensors, such as strain gauges, displacement transducers, velometers, and accelerometers, are considered conventional but more durable and reliable. With data collected by accelerometers, time histories may be obtained, transformed, and then analyzed to determine their modal frequencies and shapes, while with displacement and strain transducers, structural deflections and internal stress distribution may be measured, respectively. Field tests can be used to characterize the dynamic and static properties of the infrastructures and may be further used to show their changes due to damage. Additionally, representative field applications on bridge dynamic testing, seismology, and earthborn/construction vibration are explained. Sensor data can be analyzed to establish the trend and ensure optimal structural health. At the end, five case studies on bridges and industry facilities are demonstrated in this chapter.
Quality and Reliability of Elastomer Sockets
(2009) Lopez, Leoncio D.; Pecht, Michael G.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Integrated Circuit (IC) sockets provide hundreds to thousands of electrical interconnects in enterprise servers, where quality and reliability are critical for customer applications. The evaluation of IC sockets, according to current industry practices, relies on the execution of stress loads and stress levels that are defined by standards, having no consideration to the physics of failure (PoF), target operating environment, or contact resistance behavior over time. In a similar manner, monitoring of contact resistance during system operation has no considerations to the PoF or environmental conditions. In this dissertation a physics of failure approach was developed to model the reliability of elastomer sockets that are used in an enterprise server application. The temperature and relative humidity environment, at the IC socket contact interface, were characterized as a function of external environmental conditions and microprocessor activity. The study applied state-of-the-art health monitoring techniques to assess thermal gradients on the IC socket assembly and to establish an operating profile that could be used for the development of a PoF model. A methodology was developed for modeling and monitoring contact resistance of electrical interconnects. The technique combined a PoF model with the Sequential Probability Ratio Test (SPRT). In the methodology the resistance behavior is characterized as a function of temperature. The effective a-spot radius was extracted from the characterization data and modeled with a power-law. A PoF model was developed to estimate the resistance of an elastomer contact, based on the effective a-spot radius and the ambient temperature. The methodology was experimentally demonstrated with a temperature cycle test of the elastomer socket. During the evaluation the difference between estimated and observed resistance values were tested with the SPRT. The technique was shown to be very accurate for modeling contact resistance and to be highly sensitive for the detection of resistance degradation. A qualitative reliability model was developed for the mean contact resistance of an elastomer socket, using fundamental material properties and user defined failure criteria. To derive the model, the resistance behavior of contacts under nominal mechanical load was studied as a function of time and temperature. The elastomer contact was shown to have a very complex resistance behavior, which was modeled by multiple statistical distributions. It was shown that elastomer sockets, in spite of experiencing stress relaxation at the macroscale (elastomer), can exhibit decreases in contact resistance, a result of stress redistribution at the microscale (Ag particles), which increases Ag-Ag particle stress and the effective contact area.
Implementation of Prognostics and Health Management for Electronic Systems
(2007-06-06) Tuchband, Brian Adam; Pecht, Michael G; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
An assessment has been undertaken to identify the state-of-practice for prognostics and health management of electronics. Based on a review of the prognostic approaches, case studies, publications, and the extent of intellectual property of numerous organizations, I identified the companies, universities, and government branches that are currently researching, developing, and/or implementing prognostics for their products and systems. Next, I developed a sensor selection process such that an optimal sensor system can be chosen prior to in-situ life cycle monitoring of electronic products and systems. I developed a questionnaire that can be used to understand the monitoring requirements of a particular PHM application, and identified criteria that one needs to consider in the sensor selection process in order to make the relevant tradeoffs. Finally, I provided guidelines on sensor selection to help a user validate their final selection. The process was demonstrated for two circuit card assemblies inside an avionics unit.

A. James Clark School of Engineering

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