Fook Fah Yap

MR damper and its application for semi-active control of vehicle suspension system

In this paper, a semi-active control of vehicle suspension system with magnetorheological (MR) damper is presented. At first a MR damper working in flow mode is designed. Performance testing is done for this damper with INSTRON machine. Then a mathematical model, Bouc–Wen model, is adopted to characterize the performance of the MR damper. With optimization method in MATLAB® and experimental results of MR damper, the coefficients of the model are determined. Finally, a scaled quarter car model is set up including the model of the MR damper and a semi-active control strategy is adopted to control the vibration of suspension system. Simulation results show that with the semi-active control the vibration of suspension system is well controlled.

Testing and steady state modeling of a linear MR damper under sinusoidal loading

A linear magnetorheological (MR) damper, supplied by Lord Corporation, was tested and modeled. Under dynamic conditions, the effects of displacement amplitude, frequency, and magnetic fields on the mechanical properties of MR damper, such as damping force, equivalent-damping capability, were experimentally studied with an INSTRON test machine. A viscoelastic-plastic model is proposed to model the MR behavior. It is shown that the damper response can be satisfactorily predicted with this model.

Vibration reliability characterization of PBGA assemblies

Abstract Generally, the low-cycle fatigue induced by thermal cycling is the major concern in the reliability of surface mount technology for electronic packaging, but the high-cycle fatigue induced by vibration can also contribute significant effect, especially for applications in automobile, military, and avionic industries. To assess vibration induced fatigue failures, the dynamic properties of printed circuit board (PCB) assemblies play a very important role. In this paper, the dynamic properties of a plastic ball grid array (PBGA) assembly were characterized by using experimental modal testing and finite element analysis. The bare PCB and PCB assembly with PBGA modules mounted were tested and analyzed separately, so that the influence of PBGA modules on the PCB’s dynamic properties could be identified. It was found that mounting PBGA modules to PCB increased the stiffness of the PCB. Results of constant-amplitude vibration reliability testing of the PBGA assembly are also reported. It was found that the PBGA assembly was vulnerable to vibration, and fatigue failure always occurred at the corner solder balls of the PBGA module.

Reliability of PBGA assemblies under out-of-plane vibration excitations

Vibration testing of plastic ball grid array (PBGA) assemblies to assess the reliability of the solder joints under external vibration excitations was reported in this paper. The test vehicle was an assembly with four 256 I/Os PBGA modules assembled on a printed circuit board (PCB). During the test, the assembly was clamped at two opposite sides to a vibration shaker. It was found that the dynamic displacement of the assembly under external out-of-plane sinusoidal vibration excitations was highly nonlinear. In order to determine the reliability of the solder joints, the resistance of each module was continuously monitored during the test. Under an out-of-plane sweep sinusoidal excitation with a constant acceleration amplitude of 2.5 G within a narrow frequency band around the fundamental resonant frequency of the assembly, the first-time-to-failure and mean-time-to-failure of the solder joints were found to be 0.46 and 6.19 million vibration cycles respectively. The failed solder joints were at the corners of the PBGA module. Most failures were due to cracks near the copper pad on the PCB side.

A Model for a Hard Disk Drive for Vibration and Shock Analysis

We propose a model for a hard disk drive (HDD) based on a flexible multibody dynamics formulation. All the main components in the HDD, i.e., the spindle head actuator, spindle disk, and base are considered flexible components connected by bearing joints. The model takes into account nonlinearity and discontinuity caused by the contact between the dimple and flexure. The air bearing force is obtained by solving the Reynolds equation using the finite volume method and considering Intermolecular force. We found that the intermolecular force will lower the flying height. We investigated the effect of the base stiffness on the shock tolerance of the HDD and found that a stiffer base will benefit the increase of the shock tolerance.

Design and analysis of shock and random vibration isolation system for a discrete model of submerged jet impingement cooling system

High-powered embedded computing equipment using air transport rack (ATR) form-factors are playing an ever-increasing role in critical military applications in air, land and sea environments. High power and wattage of the electronics and processors require large heat dissipation, and thus more sophisticated and efficient thermal cooling systems such as loop heat pipes or jet impingement systems are demanded. However, these thermal solutions are more susceptible to harsh military environments and thus, for proper performance of thermal and electronic equipment, they need to be protected against shock and vibration inherent in harsh environments like those in military applications. In this paper, an isolated ATR chassis including two jet impingement chambers is modeled as a three-degrees-of-freedom system and its response to random vibration and shock has been studied. Both finite element and experimental modal analysis is utilized to characterize dynamics of the components of the jet impingement system. The response of the model is compared to that of the traditional single-degree-of-freedom model, and the isolation system is optimized in terms of its damping.

ANALYTICAL RANDOM VIBRATION ANALYSIS OF BOUNDARY-EXCITED THIN RECTANGULAR PLATES

Fatigue life, stability and performance of majority of the structures and systems depend significantly on dynamic loadings applied on them. In many engineering cases, the dynamic loading is random vibration and the structure is a plate-like system. Examples could be printed circuit boards or jet impingement cooling systems subjected to random vibrations in harsh military environments. In this study, the response of thin rectangular plates to random boundary excitation is analytically formulated and analyzed. In the presented method, closed-form mode shapes are used and some of the assumptions in previous studies are eliminated; hence it is simpler and reduces the computational load. In addition, the effects of different boundary conditions, modal damping and excitation frequency range on dynamic random response of the system are studied. The results show that increasing both the modal damping ratio and the excitation frequency range will decrease the root mean square acceleration and the maximum deflection of the plate.

Experimental modal analysis of PBGA printed circuit board assemblies

In order to understand the dynamic properties and develop a valid finite element model of a plastic ball grid array (PBGA) PCB assembly, a series of experimental modal tests have been conducted and reported in this paper. Firstly, the purpose and importance of conducting these experimental modal tests are discussed. Secondly, detailed test results of our PBGA PCB assembly are presented, which can serve as a valuable reference for those who are interested in the vibration fatigue reliability of PBGA PCB assemblies. Lastly, some factors which have an important influence on the modal test results of the PCB assembly are discussed.

Design and Analysis of Shock and Random Vibration Isolation of Operating Hard Disk Drive in Harsh Environment

An effective vibration isolation system is important for hard disk drives (HDD) used in a harsh mechanical environment. This paper describes how to design, simulate, test and evaluate vibration isolation systems for operating HDD subjected to severe shock and random vibrations based on military specifications MIL-STD-810E. The well-defined evaluation criteria proposed in this paper can be used to effectively assess the performance of HDD vibration isolation system. Design concepts on how to achieve satisfactory shock and vibration isolation for HDD are described. The concepts are tested and further enhanced by the two design case studies presented here. It is shown that an effective vibration isolation system, that will allow a HDD to operate well when subjected to severe shock and random vibration, is feasible.

Feasibility of Modeling Air Bearing as Linear Springs in Hard Disk Drive Dynamics Simulation

A model to predict the shock response of a 1.8-inch hard disk drive (HDD) is developed and validated by experiment. The head-actuator assembly (HAA), spindle disk and flexible base are included in the proposed model. The feasibility of modeling the air bearing as linear springs is investigated for HDD operating shock simulation. Result shows that as far as the vibration of the arm-suspension assembly is concerned, the air bearing between the disk and slider can be modeled by linear springs to speed up the simulation. However, if head/disk interface is concerned, the air bearing should not be modeled as linear springs in the studies of head-disk interface.