Papers by Keyword: Failure

Abstract: Condition monitoring is a tool for detection of faults and failure prevention. Fault andfailure are regarded as inevitable during the machine operation as the process of wear and theprocess of degradation. The question is, if one can influence the wear and degradation process,using condition monitoring. The paper will present technology which demonstrates that the use ofthe proper method can influence the wear and machine degradation process, using proper conditionmonitoring techniques and knowing scenarios of wear and degradation process. In the discussionpresented in the paper as a prerequisite has been taken that machinery works in severe dustyenvironment and varying operation conditions. It has been pointed that degradation process is notjust simply development of one fault. Most research for developing technology for conditionmonitoring is concentrated on one fault development. If one considers condition monitoring for acrack and brakeage of a tooth in gearbox, one should take in consideration that tooth crack andbrakeage is the result of several events, like rolling elements bearing frictional wear, which causesecondary misalignment of shaft and gears. The frictional wear is caused by dust particles whichget into oil from the environment in which a gearbox is operating. To avoid an influence ofcontaminated oil, contamination proactive technology should be used for the assessment of thedegree of contamination and the decision on oil purification or change should be taken. The wholeprocess connected with a gearbox condition change (wear and degradation process) shall bedescribed in the paper. The oil purification or its replacement extends the live of gearboxes butlong live of a gearbox, even with very little contamination causes some frictional wear of bearingsand finally secondary misalignment. To avoid further development of degradation process propertechnology should be used. There is a need to measure the degree of misalignment and makedecision on bearings replacement, in order to avoid further gearbox degradation, like teeth scuffingwhich may leads to crack initiation.

Abstract: With the development of electronic technology, the electronic threats faced by microwave semiconductor devices was increasingly serious.In order to study the electrostatic discharge damage mechanism of bipolar silicon transistors, this paper analyzed the basic physical characteristics of bipolar transistor in electrostatic discharge, such as kirk effect and current crowding effect. Through analysis the human body electrostatic discharge model, established the ESD electric injury model of bipolar silicon transistor. If we knew the production process parameter of devices, we can calculate the ESD damage threshold for designing bipolar silicon device and providing a theoretical basis of parameter optimization. Finally the common ESD damage criterion were analyzed from different angles.

Abstract: For MEMS devices actuated by electrostatic force, unexpected failure modes can be hardly predicted when the electrostatic force coupled with the shock. A response model is established when a micro cantilever subjected to electrostatic force and mechanical shock. First, based on the theory of transverse forced vibration in vibration mechanics, the equation of motion under shock and electrostatic fore is presented. Then the reduced order model is gained after simplifying by mode superposition method. The computing results indicate that: the shock amplitude and duration are the key factors to affect the reliability of the device; the shock load and electrostatic forces make the threshold voltage much lower than the anticipated value. The micro cantilever may collapse to the substrate even at a voltage far lower than the pull-in voltage. This early dynamic pull-in instability may cause some failures such as short circuit, adhesion or collision damage.

Abstract: The problem of engineering materials failing in structures like bridges, pipelines, refinery and automobile equipments is becoming a source of concern to the people of the developing nations especially Nigerians. This sometimes might be attributed to the environments in which the materials are being used or stored and the source of the materials. There is a need therefore, to evaluate the effects of these environments on the final property, especially the mechanical properties of the materials. Based on the peculiarity of ductile iron (DI) having its application in most engineering works in different environments, the material was subjected to four different environments namely alkaline (NaOH), brackish (NaCl), air conditioning (A/C), and outside environment, coinciding with the environments of application. The material was later subjected to series of mechanical tests and the behavioural changes (especially the mechanical property) of the materials in these environments were monitored for the period. It was observed that the ductile iron placed outside had the highest elastic properties and hardness of 1341.72Hv while alkaline environment had the highest strength of 3321.75MPa. The alkaline environment gives the highest performance as it had a quality index of 4,038,837, followed by outside environment while salty environment had the least.

Abstract: A refined non-linear air spring model of railway vehicle model is established in this paper and the influences of different air spring failures on ride quality are studied. Results show that the orifice failure makes the air spring loses damping characteristics and deteriorates the vehicle ride quality; The failure of levelling valve has little influence on the ride quality when vehicle running on straight lines; The fracture of air spring diaphragm results in a sudden release of air, and car body secondary support disappears rapidly, excessive wheel unloading will happen and which can easily lead to derailment. In addition, the longer the leakage process, the less the influence on vehicle safety.

Abstract: The effects of loading rate on splitting test, uniaxial compression strength, strength parameters in triaixal compression test, and creep failure of Hangcheng coal rock were investigated through indoor mechanical experiments. Experimental results shown that tensile strength, uniaxial strength and Youngs modulus of coal rock increased with the increase of loading rate and the increment is very small. Triaixal compression strength and loading rate has a linear relation. Brittleness was very marked under high loading rate. Ductility of coal rock in the steady creep stage diminished with the increase of loading rate, and failure mode of coal rock had a change from low ductility failure mode to ductile-to-brittle failure mode. The results of experimental researches can be used to determine the bottom hole flowing pressure of coalbed methane well.

Abstract: A fatigue testing setup based on electromagnetic excitation was built to apply cyclic stresses to the specimens near their resonance frequency. A test near the resonance frequency has the advantage that higher stresses can be applied to test specimens at a reduced input power. Stress amplitude up to 1000 MPa can be applied to the test specimens and up to four specimens can be tested simultaneously. The setup can test specimens at high fatigue cycle regime i.e. 100 million stress cycles can be achieved in 48 hours.The setup has been used to study the effects of internal and external microstructure on the fatigue strength of materials. Specimens especially stainless steel-304 was prepared by different techniques i.e. electric discharge machining EDM, etching and laser cutting. Specimens prepared by these techniques were tested and their fatigue strengths were compared. To probe the material endurance limit, tests were also performed on the above mentioned steel specimens in very high stress cycle regime i.e. > 10⁹ cycles. In order to investigate the effect of internal microstructure on fatigue strength of material, CuZn37 fabricated by etching was tested and the effect of different grain size on fatigue strength was compared. SN curves have been plotted for materials with no prior fatigue strength data. Stainless steel-1.4404 specimens prepared by Rapid Prototyping (RP) has been tested for fatigue analysis. The test results showed higher degree of scattering when compared to the traditionally manufactured steel. Fractography revealed the existence of inherent material flaws which was the main reason of higher degree of test point scattering. In addition to these data, the SN curve was plotted for Innolot which is an important soldering alloy and prompts to fatigue failure in electronic assemblies.

Abstract: This contribution describes the dosing method at die-casting using a mechanical dosimeter, by derivation of back coupling from the motion of the dosimeter arm. The motion of the dosimeter arm is described by motion equations and their analysis by the linear theory of control. Furthermore, there are derived the transfers of actuating quantity, failures and controls. Based on them, the control circuit is stable and periodic after satisfying certain conditions, failing which it is stable, damped and oscillating.

Abstract: Several typical failures of external gear pump are presented. The reasons of the pump failure are analyzed in detail. Solutions of the failure are proposed. In order to improve the efficiency of pumps maintenance and reparation, a new kind of tool is mentioned which could predict the life of gear pump before failure occurred.

Abstract: The present paper analyzes the phenomenon on spallation and failure of driven pile. Based on the nonlinear program LS-DYNA, the dynamical performance of driven pile into the soft soil foundation is studied by numerical simulation. Taking into account the stress-wave theory, some analyses are conducted to discuss the influence factors on spallation and failure of driven pile. The analysis results show that the compression and tension of stress wave plays an important role in the process of pile driven. Some guidance and reference is useful for the design, manufacturing and construction of piles.