Key Engineering Materials Vol. 588

Abstract: Minehunters are subjected to specific sea loads due to waving and dynamical impacts associated with underwater explosion. Sea waving can be sufficiently exactly modeled by means of statistical methods. Much more problems arise from modeling impacts due to underwater explosion. Knowledge of a character of impulse loading which affects ship shaft line can make it possible to identify potential failures by means of on-line vibration measuring systems. The problem of influence of sea mine explosion on hull structure is complex and belongs to more difficult issues of ship dynamics. Underwater explosion is meant as a violent upset of balance of a given system due to detonation of explosives in water environment. A paper presents a proposal of identification of a degree of hazard the ships hull forced from underwater explosion. A theoretical analysis was made of influence of changes of hull structure in vicinity of hull. The main problem of naval vessels is a lack of dynamical requirements of stiffness of the hull. Modeled signals and hull structure were recognized within sensitive symptoms of three sub models: model of hull structure, model of impact and model of propulsion system. All sub models allow testing forces and their responses in vibration spectrum using SIMULINK software and FEM models.

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: A growing interest in non-destructive testing methods based on nonlinear acoustics have been observed for the last ten fifteen years. The majority of methods in this area take their origin from the observation that fatigue damaged materials often behave like mesoscopic nonlinear materials (e.g. rocks) in which nonlinear phenomena have been observed for years. The most important phenomena include: higher harmonics generation, vibro-acoustic wave modulations, amplitude dependent resonance frequency shift and slow dynamic effects. All these phenomena result mainly from elastic wave interactions with contact-type defects. There is enough experimental evidence in the literature showing that these nonlinear effects are much more distinct in damaged materials than in intact ones. Despite the fact that many experimental techniques - based on nonlinear acoustic phenomena - have been developed for the last ten years, the physical mechanism of elastic wave interaction with damage materials still not clear. The main reason is the variety of possible nonlinear mechanisms involved. This includes: nonlinear elasticity and dissipation, contact acoustic nonlinearity based on herztian and rough surfaces contact theories and other effects such us adhesion, friction and thermoelasticity. This paper provides a short summary of various theoretical developments and examples of applications to damage detection in different materials.

Abstract: The article presents the scope of works which were performed while constructing a testbed for examining a multi-fuel Diesel engine with a Common-Rail injection system. The testbed has been designed in a way which allows to carry out tests in a climatic chamber. The paper also proposes a method of using a relational database to store the information on the completed experiments and the conclusions drawn from them.

Abstract: The paper discusses real-time parameters identification methods of the mechatronics subsystems in the automobile for the on-board diagnostics and adaptive control. In particular, the significant increase in electric power consumption requires predictive management strategy that detects critical loads situations. To accomplish these goals we investigated diverse vehicular powernet circuits and devices. This paper presents the results of the extended Kalman filtering algorithm for the parameters estimation of the wiring harness of a cooling fan system.

Abstract: The detection of local damage in rotating machinery (gears, bearings) via vibration signal analysis is one of the most powerful techniques in condition monitoring. However, in some cases, especially in heavy industrial machinery, it is difficult to detect damage because of the poor signal-to-noise ratio of the measured vibration. Therefore it is necessary to use unconventional advanced techniques to enhance the signal. In this paper, a novel approach based on parametric time-frequency analysis and further processing for: i) time-varying spectral content modelling, ii) the identification of informative frequency bands by statistical analysis, iii) local damage detection and iv) cycle identification via cepstral analysis, is presented. The proposed procedure is validated using real vibration data from bearings and gearboxes. It is worth noting that this methodology can be also successfully used in time-varying speed conditions (with limited fluctuation).

Abstract: The article provides a discussion on the studies comprising active experiments conducted on passenger car and analytical experiment on application of neural networks in the identification of pressure level in tires of a vehicle based on vibration signals. The purpose of research was to analyze the possibilities of monitoring of pressure in tires during the diagnostics tests of shock absorbers. The paper presented on last International Congress on Technical Diagnostics in 2008 examined the influence of changes of pressure in tires on the results of diagnostics test of shock absorbers. Those influences were observed in typical test methods used in vehicles service stations and even in new vibration methods. The article presents some results of research on neural network classification method of pressure in tires level. Tested solutions can be used as the preliminary module of diagnostics system during the shock absorber test. The signal processing methods were based on application of time, frequency and time-frequency transformations which enables obtaining the signals information carried in one or two domains simultaneously, namely those of time and frequency.

Abstract: The present paper describes the development of a monitoring, analysis and diagnosis system of power plant equipments based on strain measurements. The objective is to help companies increase availability and reduce maintenance costs. The aim is the integrity evaluation of a main steam and a hot reheat steam piping through inspection, strain monitoring and computational diagnosis. The benefits are, among others, reduction in the uncertainty of the remaining life prediction and reduction of work, through process automation and integration and real time monitoring (through the Internet) of the operational condition of the equipment. Thus, greater confidence and availability of the monitored generating unit is sought as well as cost reduction as a consequence of reduced frequency of unnecessary unit stops and greater speed in decision making due to more precise follow up of the operational condition of the target-equipment and of its remaining life.

Abstract: Thermal fatigue occurred in many engineering constructions made of polymeric composites subjected to the intensive loading and vibrations. During this process the mechanical energy is dissipated in the form of heat due to the hysteretic behaviour of the material, which introduces the self-heating effect. In some cases the self-heating effect dominates the fatigue process and intensifies much structural degradation of composite elements. The paper presented a survey of engineering applications in which the self-heating effect and thermal fatigue occurred and recent advances in theoretical and experimental research in this area. Selected results of experimental studies were presented and discussed.

Abstract: One of the major issues from a structural integrity point of view of the aircraft structure is an appropriate health monitoring technology delivery for the damage tolerant philosophy. This paper presents a development of a system for fatigue crack growth monitoring and early damage detection in the PZL 130 ORLIK TC II turbo-prop military trainer aft structure. The maintenance system of the aircraft shifts from the safe-life to the hard-time. The aircraft started Full Scale Fatigue Test (FSFT) which will continue up to 2013. In the article a built block approach for the system design, signal modeling, sensing and signal processing as well as damage detection is presented. Taking into the consideration a previous experience of AGH as well as AFIT, a network of PZT transducers was deployed in the aircraft structure hot-spots. The system components are: remote monitoring unit, signal analysis, graphical user interface, sensor self-diagnostic tools, and data classification model. Description of damage detection capabilities are delivered in the paper. In particular some issues concerning the proposed damage indices and its application to crack growth estimation models are discussed. Fishers Linear Discriminant is used as a method to obtain effective crack growth predictors and one of the self-diagnostic tools used in the system. The results of the data collected from specimen fatigue tests are delivered and cross-validation technique is used to evaluate a classification model based on the damage indices derived.