Key Engineering Materials Vols. 353-358

Abstract: A study on corrosion evaluation by using ultrasonic waves and acoustic emission technique is presented. The experimental equipment was established to improve the corrosion process of carbon steel pipe. The carbon steel pipe was under 473K temperatures and 10Mpa pressure conditions, and ultrasonic wave and acoustic emission techniques were used to inspect the degree of corrosion after a certain period of time. Ultrasonic bulk waves are limited by the poor time resolution when used in the measurement of corrosion depth in thin wall structures because the corroded surfaces cause unclear echo signal edges. Therefore, in this study, the ultrasonic guided waves were generated on the pipe because the thickness of pipe was thin. Various wave modes were subsequently generated on the pipe to evaluate the implications of corrosion thinning on group velocity, transmission and reflection amplitudes. The amplitudes of the transmitted and the reflected waves are influenced by couplent material. In order to reduce the effect of coupling acoustic emission sensor was used. Acoustic emission technique has lots of parameters to evaluate the corrosion besides amplitude parameter. Among parameters energy, count, and frequency were useful parameters to measure the degree of corrosion inside the carbon steel pipe under 473K temperatures.

Abstract: In case of large steel water pipe, it have been observed that its fracture mostly occurs due to the complicated outside fatigue load on the pipe in the underground. It is also well known that its damage and leakage happen mainly in a weld zone. In this study we evaluated the fatigue characteristics based on size effect and residual stress by comparing the test results on the standard specimen collected from real pipe with those on full scale pipe.

Abstract: X-ray stress measurement with sin2ψ method is one of useful tools to detect residual stresses in manufactured products. In this study, the residual stresses in the tungsten fiber reinforced polyethylene composite were examined by X-ray stress measurement technique. The transmission diffraction method was employed in residual stress measurement of polyethylene matrix. The X-ray elastic constant of high density polyethylene (HDPE) which formed matrix of the composite was estimated before residual stress measurement. The results of sin2ψ diagram with transmission method show good linearity under the several tensile loading. After that the residual stresses in the composite were investigated for HDPE matrix phase. From the measurement results, the tensile residual stresses existed in fiber longitudinal direction and compressive ones in transverse direction for HDPE matrix.

Abstract: Pieces of large-scale equipment such as a ball mill system are subjected to heavy and alternate loads under the worst working conditions, which result in higher fault rates. However, since such equipment exerts important functions to the economy and industry, it isn’t recommendable to halt production in order to detect the defects under unconfirmed faults. We explore a reliable and practical fault diagnosis scheme for the ball mill system that is widely used in the building material industry. With utilizing the signal acquisition and process system of vibration, the field testing and analysis are performed based on the violent vibration of an edge-transmission Φ3×11m ball mill system. The primary diagnosis that is based on the configuration of the transmission system and foundation stiffness is found, and a feasible resolution scheme is obtained, so that the optimal and economic reform scheme is determined. The detailed scheme has been adopted by the production industry. This study that is based on the fault diagnosis of the edgetransmission ball mill system has a comprehensive significance of theory and reality. This provides a larger basis for vibration inspection and fault diagnosis in building material industries.

Abstract: Beam structures are a common form in many large structures, and therefore the real-time condition monitoring and active control of beams will improve the reliability and safety of many structures. However, the incipient damage, i.e. cracks, is not easy to be detected with using the traditional methods, such as modal analysis, etc. Piezoceramic (PZT) sensors offer special opportunities for the health monitoring of structures constructed by beams. The change of mechanical impedance of structures along with the occurrence of damage is sensitively indicated by the change of electro-impedance of PZT sensors. This paper presents work done on developing and utilizing PZT sensors to detect and quantitatively assess the extent and locations of cracks occurred in simulated structures. The PZT sensors are conducted particularly to generate the longitudinal wave along the beam specimen, and systematic experiments conducted on statistical samples of incrementally damaged specimens were used to fully understand the method, the cracks with different length and location are simulated to indicate the feasibility of the detection and assessment. To estimate the damage conditions numerically, in this paper, we propose the evaluation method of impedance peak frequency shift
F and CC (Correlation Coefficient), Cov (Covariance). The results of experiments verify that the impedance peak frequency shift Δ F uniformly assesses the location of cracks, and as well CC. and Cov assesses the size of cracks efficiently. The study presents the method that is satisfied for much higher frequencies, alternate power, and minute damages.

Abstract: We present a study on the development of a practical and quantitative technique for the assessment of the structural health condition with using piezoceramic (PZT) sensors. The electroimpedance- based technique with the PZT patches is very sensitive for evaluation of the incipient and small damage in a high frequency range, and however the commonly traditional modal analysis method is effective only for considerably larger damages in low frequency range. The paper presents the performance of the performance of the electro-impedance-based technique in detecting and characterizing real-time damage on the specimen that is an aluminum plate fastened with bolts and nuts by different torques. By using the special arrangement of the PZT sensors, the required longitudinal wave is generated through the specimen. A large number of experiments are conducted and the different conditions of the specimen, i.e. the location of loosening bolts and the loosening extent of bolts are simulated, respectively. Since fixing and loosening the loosened bolt is controlled by a torque wrench, we can control exactly the experiment of the different torques. Compared with the simulated healthy condition, we can find whether or not there is a damage in the specimen with using an impedance analyzer with the PZT sensors. Several indices are discussed and used for assessing the different simulated damages. As for the location of bolt loosening, the RMSD is found to be the most appropriate index for numerical assessment and as well the RMSD shows strongly linear relationship for assessing the extent of the bolt loosening. The possibility of repeatability of the pristine condition signatures is also presented and the appropriate frequency range and interval are uniquely selected through large numbers of experiments. The analytical results strongly show the sensibility and reliability of the electro-impedance based technique.

Abstract: This paper will propose an identification algorithm for a small defect in the case of the bending problem of a beam. That is to say, the part where a defect exists is replaced by an equivalent load term. It shows that the defect can be accurately identified even there is observation error if the problem of identifying a defect is converted to that of identifying a load.

Abstract: This paper will report on the investigation results of the influence of observation errors on the identification of external loads in case of the bending problem of a beam. It is found that the resultant force and the resultant moment of the loads will be conserved despite of the divergence of the identified load distribution, when the observation errors are within a certain tolerance. This fact is applicable to the problem of identifying a small defect.

Abstract: In this study, a rectangular interfacial crack in three dimensional bimaterials is analyzed. First, the problem is formulated as a system of singular integral equations on the basis of the body force method. In the numerical analysis, unknown body force densities are approximated by the products of the fundamental density functions and power series, where the fundamental density functions are chosen to express a two-dimensional interface crack exactly. The calculation shows that the present method gives smooth variations of stress intensity factor along the crack front for various aspect ratios. The present method gives rapidly converging numerical results and highly satisfied boundary conditions throughout the crack boundary. It is found that the stress intensity factors K1 and K2 are determined by bimaterials constant e alone, independent of elastic modulus ratio and Poisson's ratio.

Abstract: The thermo-hydrodynamic effect in the spiral groove mechanical seal was investigated. The coupling analysis of the fluid film and the thermal deformation of sealing rings was carried out, the separation angle obtained, and the shape of the gap between the two deformed end faces determined. The results indicate that the increase of the temperature of the fluid film and the thermal deformation of the sealing rings cause the increase of the leakage rate. There exists a critical rotating speed, when the rotating speed is lower than the critical speed, the bearing force increases with the increase of the rotating speed, and once the rotating speed is higher than the critical speed, the bearing force decreases reversely. The thermal deformation weakens the hydrodynamic effect of the spiral groove mechanical seals.