Sharif Digital Repository

Finding leakage in valves is important to troubleshoot performance of internal combustion engines. Leakage can lead to a reduction in engine power and an increase in emissions. The main objective of the present study is to investigate relationship between valve leakage and the acoustic emission generated from the steady flow in the cylinder head of the internal combustion engine. The test rig is the cylinder head for a spark-ignited engine. The test rig simulates the valve leakage due to valve clearance. The valve clearance fault was artificially simulated by a very small lift in valve. The acoustic emission method was used to measure acoustic emission signals generated by valve flow.... 

A new method to detect leakage in a water-filled plastic pipe is proposed. In this method, a leakage signal-signature in time domain is first captured by monitoring the Short Time Fourier Transforms (STFT) of AE (Acoustic Emission) signals over a relatively long time-interval. The captured signal is then used to find a mother wavelet (tuned wavelet) for the best signal localization in time and frequency domains. The technique for AE signal detection using tuned wavelet is then described. Practical application of the method proposed herein is then presented using a water-filled plastic pipe as a case study. Signals generated from this experimental setup are collected to identify leakage... 

Failure of basic structures material is usually accompanied by expansion of interior cracks due to stress concentration at the cracks tip. This phenomenon shows the importance of examination of the failure behavior of concrete structures. To this end, 4 types of mortar samples with different amounts of nano-silica (0%, 0.5%, 1%, and 1.5%) were made to prepare twelve 50×50×50 mm cubic samples. The goal of this study was to describe the failure and micro-crack growth behavior of the cement mortars in presence of nano-silica particles and control mortars during different curing days. Failure of mortar samples under compressive strength were sensed with acoustic emission technique (AET) at... 

Failure of concrete structures is usually accompanied by expansion of interior cracks due to stress concentration at the cracks tip. This phenomenon shows the importance of examination of the failure behavior of concrete structures. For this purpose, 4 types of concrete samples with different amounts of nano-SiO2 (0%, 0.2%, 0.5%, and 0.8%) were made to prepare some Central Straight-through Crack Brazilian Disk (CSCBD) specimens. The key focus of the investigation conducted was to investigate two assumptions. First, to check the pure mode I (tension) and pure mode II (shear) by compressing the standard discs with central cracks by an angle of 0° and 27° with respect to the loading axis;... 

The use of acoustic emission (AE) technique for damage diagnostic is typically challenging due to difficulties associated with discrimination of events that occur during different stages of damage that take place in a material or a structure. In this study, an unsupervised kernel fuzzy c-means pattern recognition analysis and the principal component method were utilized to categorize various damage stages in plain and steel fiber reinforced concrete specimens monitored by AE technique. Enhancement of the discrimination and characterization of damage mechanisms were achieved by processing time and frequency domain data. Both domains (time and frequency) were taken into account to propose new... 

The aim of this study was to investigate the applicability of acoustic emission (AE) technique to evaluate delamination crack in glass/epoxy composite laminates under quasi-static and fatigue loading. To this aim, double cantilever beam specimens were subjected to mode I quasi-static and fatigue loading conditions and the generated AE signals were recorded during the tests. By analyzing the mechanical and AE results, an analytical correlation between the AE energy with the released strain energy and the crack growth was established. It was found that there is a 3rd degree polynomial correlation between the crack growth and the cumulative AE energy. Using this correlation the delamination... 

The use of acoustic emission (AE) technique for damage diagnostic is typically challenging due to difficulties associated with discrimination of events that occur during different stages of damage that take place in a material or a structure. In this study, an unsupervised kernel fuzzy c-means pattern recognition analysis and the principal component method were utilized to categorize various damage stages in plain and steel fiber reinforced concrete specimens monitored by AE technique. Enhancement of the discrimination and characterization of damage mechanisms were achieved by processing time and frequency domain data. Both domains (time and frequency) were taken into account to propose new... 

This paper presents the potential of acoustic emission (AE) technique to detect valve damage in internal combustion engines. The cylinder head of a spark-ignited engine was used as the experimental setup. The effect of three types of valve damage (clearance, semicrack, and notch) on valve leakage was investigated. The experimental results showed that AE is an effective method to detect damage and the type of damagein valves in both of the time and frequency domains. An artificial neural network was trained based on time domain analysis using AE parametric features (AErms, count, absolute AE energy, maximum signal amplitude, and average signal level). The network consisted of five, six, and... 

The noise emission level associated with two types of speed reducers has been investigated numerically and experimentally for different dimensions and different speeds of vehicle (20, 40 and 60 km/h) and zero acceleration. Numerical analysis has been performed using an FEM method in the ANSYS environment. The experiments show that for a bump of height 0.04 m, the peak noise level is increased by between 1 and 14 dB (A) whereas, for bump of height 0.055 m, the peak noise level increases by between 1 and 19 dB (A). There is an excellent agreement between the numerical and experimental results. © 2006 Elsevier Ltd. All rights reserved  

Dual phase steels (DPS)s have a microstructure consisting of a hard second phase called Martensite in the soft Ferrite matrix. In recent years, there has been interest in dual-phase steels, because the application of these materials has made significant usage; particularly in the automotive sector Composite microstructure of (DPS)s exhibit interesting characteristic mechanical properties such as continuous yielding, low yield stress to tensile strength ratios(YS/UTS), and relatively high formability; which offer advantages compared with conventional high strength low alloy steels(HSLAS). The research dealt with the characterization of damage in (DPS)s. In this study by review the mechanisms... 

A body insonified by a constant (time-varying) intensity sound field is known to experience a steady (oscillatory) force that is called the steady-state (dynamic) acoustic radiation force. Using the classical resonance scattering theorem (RST) which suggests the scattered field as a superposition of a resonance field and a background (non-resonance) component, we show that the radiation force acting on a cylindrical shell may be synthesized as a composition of three components: background part, resonance part and their interaction. The background component reveals the pure geometrical reflection effects and illustrates a regular behavior with respect to frequency, while the others... 

Leak detection based on acoustic emission needs robust time delay estimation in the presence of various types of noise. Considering several aspects of leakage signal and noise, the present work introduces wavelet based optimized residual complexity (WORC), in order to minimize the probability of false alarms in the presence of correlated, uncorrelated, and impulsive noise. The proposed method utilizes two approaches simultaneously. First, it optimizes residual complexity “for robustness against both correlated and uncorrelated noise”, then it employs wavelet basis in order to reduce the complexity of mixture of correlated and impulsive noise. In order to compare the resolution and percentage...