George T. Flowers

Vibration thresholds for fretting corrosion in electrical connectors

Single frequency vibration tests were used to induce fretting corrosion in tin alloy plated contacts. The samples used in this study were connectors consisting of 25 pairs of mated pin and socket contacts. Experimental results for a variety of vibration levels, frequencies, and wiring tie-off lengths are presented. The experiments consisted of running a series of vibration tests at each frequency where the excitation level was stepped through a range of g-levels. During each test run contact resistance was monitored as a performance characteristic. The results exhibit threshold behavior at each frequency for the onset of fretting degradation. Typically a plateau region was observed where similar g-levels produced similar fretting rates. It was also found that outside the plateau region the g-levels varied according to the dynamic behavior of the mechanical system. In addition, a transfer matrix model was used to analyze these results. An empirical fit of the data correlated well with the model when damping was used. This analysis revealed the importance of the bending moment induced at the contact interface as a result of excitation levels and tie-off configurations. Consequently, it is concluded that dynamic response of the mechanical system under various g-levels and tie off configurations can greatly impact the performance of a connector system subjected to vibration stresses.

A Characterization of the Performance of a MEMS Gyroscope in Acoustically Harsh Environments

Microelectromechanical systems (MEMS) gyroscopes are typically smaller and less expensive than their macroscale counterparts. For this reason, they are being used in many new applications, including in harsh environments. It has been well documented that the performance of unprotected MEMS gyroscopes can be deleteriously affected by exposure to mechanical shock or high-frequency vibrations. The results of this investigation experimentally demonstrate that MEMS gyroscopes are also susceptible to high-power high-frequency acoustic noise when acoustic energy frequency components are close to the resonating frequency of the gyroscopes proof mass. Additionally, due to microfabrication tolerances and the resulting differences between otherwise identical devices, there can be significant differences in the acoustically sensitive bandwidth between otherwise identical MEMS gyroscopes. This phenomenon is characterized for the ADXRS300 MEMS gyroscope.

Steady-State Dynamic Behavior of a Flexible Rotor With Auxiliary Support from a Clearance Bearing

This paper investigates the steady-state responses of a rotor system supported by auxiliary bearings in which there is a clearance between the rotor and the inner race of the bearing. A simulation model based upon the rotor of a production jet engine is developed and its steady-state behavior is explored over a wide range of operating conditions for various parametric configurations. Specifically, the influence of rotor imbalance, clearance, support stiffness and damping is studied. Bifurcation diagrams are used as a tool to examine the dynamic behavior of this system as a function of the aforementioned parameters. The harmonic balance method is also employed for synchronous response cases. The observed dynamical responses is discussed and some insights into the behavior of such systems are presented.

Interaction Dynamics Between a Flexible Rotor and an Auxiliary Clearance Bearing

This study investigates the application of synchronous interaction dynamics methodology to the design of auxiliary bearing systems. The technique is applied to a flexible rotor system and comparisons are made between the behavior predicted by this analysis method and the observed simulation response characteristics. Of particular interest is the influence of coupled shaft/bearing vibration modes on rotordynamical behavior. Experimental studies are also perFormed to validate the simulation results and provide insight into the expected behavior of such a system.

Modeling early stage fretting of electrical connectors subjected to random vibration

Fretting corrosion induced by vibration is a topic of major concern for automotive applications, often leading to increased contact resistance and connector failure. Presently, modeling of the behavior of connectors during fretting corrosion is a difficult matter, requiring many parameters, and is generally highly nonlinear in nature. Experimental testing of sample connectors is currently the only practical method of evaluating connector performance; however, testing can be a time-consuming and inexact task. Prior work by the authors studied the fretting behavior of connectors subjected to single frequency vibration. Correlation of experimental results with simulated behavior showed that, for the primary mode of connector interface motion observed (rocking-type motion), the relative moment at the interface was a good indicator of the observed fretting rate. It was also shown that the moment applied as the result of a given excitation level and frequency could reasonably be predicted via simulation. The current work extends this approach to random vibration profiles, which are a more realistic representation of the connector application environment. A simple model is developed which relates the early stage fretting corrosion rate to the threshold vibration levels for the connector, the dynamic characteristics of the connector/wiring configuration, and the vibration profile. A high degree of consistency between this model and the experimental data was demonstrated. Interestingly, regardless of the excitation profile applied to the overall system, the existence of a characteristic vibration threshold at the connector interface was observed.

A Study of the Effect of Various Vehicle Properties on Rollover Propensity

This paper investigates the effect of various vehicle parameters on rollover propensity using computer simulation. The computer simulation’s accuracy is verified by comparing it to experimental data from NHTSA’s Phase IV testing on rollover of passenger vehicles. The vehicle model used in the simulation study considers the non-linear, transient dynamics of both yaw and roll motion. The vehicle model is subjected to a specific steering input defined by NHTSA, the Fishhook 1a. A correlation between the vehicle parameter of center of gravity location and rollover propensity is found using the validated vehicle simulation.

A Multi-Physics Finite Element Model of an Electrical Connector Considering Rough Surface Contact

Any engineering component possesses roughness on its surface when it is observed microscopically, including electrical connectors. Electrical connectors usually consist of a spring and a pin. In this study, the spring part is in the shape of a compliant curved beam whereas the pin one is of a flat form and these two parts are in contact during operation. This work presents a multi-physics (structural, electrical and thermal) finite element model of the bulk region of an electrical connector. The rough surfaces of the spring and pin parts are considered using a multi-scale sinusoidal rough surface (MSRS) contact model. The resulting coupled multi-physics connector model is used to analyze the performance of the connector while the applied current is incremented from 5 to 20 A. As expected, this produced a proportional rise in voltage drop and temperature across the bulk regions of the connector parts. The coupled multi-physics model together with the MSRS model should provide greater accuracy in the prediction of contact forces, electrical contact resistance (ECR) and thermal contact resistance (TCR). The present work also provides valuable information on stresses and strains distributions, current flow and temperature variations in the bulk regions of the electrical connector.

The influence of contact interface characteristics on vibration-induced fretting degradation

Vibration induced fretting degradation is a widely recognized failure phenomenon; however, the basic mechanisms that control the onset and progression of such fretting behavior are not well understood and are a topic of considerable interest in the electrical connector community. One specific issue is the need for a more detailed understanding of the mechanisms controlling the fretting degradation. The present study addresses these questions and develops answers using the results from a series of experimental tests of sample connectors which are subjected to single-frequency vibration profiles at room temperature. These test specimens are a series of dual-row 16-circuit automotive connectors in which the plating finish and contact normal force are varied. The results are presented and discussed in light of earlier investigations.

Synchronous dynamics of a coupled shaft/bearing/housing system with auxiliary support from a clearance bearing: Analysis and experiment

This study examines the response of a flexible rotor supported by load sharing between linear bearings and an auxiliary clearance bearing. The objective of the work is to develop a better understanding of the dynamic behavior of a magnetic bearing supported rotor system interacting with auxiliary bearings during a critical operating condition. Of particular interest is the effect of coupling between the bearing/housing and shaft vibration on the rotor-dynamic responses. A simulation model is developed and a number of studies are performed for various parametric configurations. An experimental investigation is also conducted to compare and verify the rotor-dynamic behavior predicted by the simulation studies. A strategy for reducing sychronous shaft vibration through appropriate design of coupled shaft/bearing/housing vibration modes is identified. The results are presented and discussed.

Micromachined Vibration Isolation Filters to Enhance Packaging for Mechanically Harsh Environments

Some harsh environments, such as those encountered by missiles, rockets and various types of industrial machinery, contain high frequency mechanical vibrations. Unfortunately, some very useful components are sensitive to these high frequency vibrations. Examples include MEMS gyroscopes, oscillators and some micro-optics. Exposure to high frequency mechanical vibrations present in the operating environment can result in problems ranging from an increased noise floor to component failure. Passive micromachined silicon lowpass filter structures (spring-mass-damper) have been demonstrated in recent years. Since they usually possess a low vertical profile, they can be utilized as the packaging substrate for the sensitive component requiring vibration isolation. The performance of these filter structures is typically limited by low damping and a lack of tunability after fabrication. However, filter performance can be enhanced by integrating fluidic damping techniques with the passive filter or by integrating a ...