ABSTRACT
In this study, a diagnosis method was successfully implemented to identify different sounds coming from individual mechanical parts within a group of engine moving parts controlled through a variable valve timing system. The novelty of this diagnosis method is in the determination of specific sounds coming from each part within this group when they are in good working condition and without any defects. This will facilitate in early detection of faults occurring on the parts, identified through changes in the sound wave energy. Through this study, this diagnosis method was validated in three ways, namely the consistency of the results with previous studies, the synchronization of sounds from mechanical parts in overlapping cases, and the cross-correlation of engine sound modes that results from analysis using the Hilbert Huang Transform. In this paper, the distribution of sound energy according to its frequencies was utilized to distinguish which of the engine combustion chambers of a Dodge Journey 2.4 was faulty. To conduct that, the noise-based test technique was selected to record the engine sound. The results show that there is a link between the RMS energy of the engine sound and the engine output torque.
ABSTRACT
In this paper, the acoustic impedance property has been employed to predict the ultimate tensile strength (UTS) and yield strength (YS) of pure metals and alloys. Novel algorithms were developed, depending on three experimentally measured parameters, and programmed in a MATLAB code. The measured parameters are longitudinal wave velocity of the metal, density, and crystal structure. 19-samples were considered in the study and divided into 3-groups according to their crystal structure; 7-FCC, 6-BCC, and 6-HCB. X-ray diffraction was used to examine the crystal structure of each sample of each group, while longitudinal wave velocity and metals' density were measured experimentally. A comparison between mechanical properties predicted by the model and the ASTM standards was done to investigate the validity of the model. Furthermore, predicted stress-strain curves were compared with corresponding curves in the pieces literature as an additional validation check. The results revealed the excellence of the model with 85-99% prediction accuracy. The study also proved that if metals are grouped according to their crystal structure, a relation between UTS, YS, and modulus of elasticity (E) properties and wave pressure transmission coefficient (Tr) could be formulated.
ABSTRACT
Refractory metals have attracted increasing interest in recent years because of their use in many high-temperature applications. However, the characteristics of these metals calculated using loaded tests (such as tensile strength tests) differ considerably from those calculated using one of the most famous methods in NDT which is called time of flying of the wave (TOF).The present study presents two solutions based on calculating the pressure transmission coefficient (PTC) of the transmitted wave between the test sample and magnesium metal. The first is based on the development of a highly accurate algorithm that lowers the cost by determining the acoustic impedance of the test specimen to calculating mechanical properties. Up to 26 theoretical tests were done (10 of these tests for refractory materials) according to their known mechanical properties to verify the accuracy of the algorithm. The convergence in results ranged from 92% to 99%. The second solution was designed to solve the same problem for specimens with a thickness of less than 1mm. Eight experimental tests were done (five using refractory materials) to verify the accuracy of the second solution, with the convergence in the results ranging from 94% to 97%. The relationships of the Vrms measured from the oscilloscope with the PTC and with the Fourier transform spectrum were derived. The results of this research were closer to the standard mechanical properties for refractory metals compared with several recent acoustic tests.
