Papers by Keyword: Stress Wave

Abstract: To study the injury mechanism of stress wave from temporary cavity in gelatin, a stress wave propagation model is established. Based on experimental phenomena, gelatin around the trajectory is divided into fail region and elastic region. In the fail region, gelatin is considered to be incompressible and loop stress is zero. Gelatin in the elastic region is assumed to be plane-strain. Moving equations in the two regions are built. A 4.8 mm steel sphere is fired into gelatin at 720 m/s. Displacements of the temporary cavity are obtained from the experiment. By solving the moving equations with boundary conditions, amplitude of cavity pressure, radial stress distribution in gelatin are obtained. The theoretical results can be used to explain stress waves produced by temporary cavity.

Abstract: There are two conventional techniques i.e. the approach based on structural testing and non-damaged detecting method, of which the former is partial to structural integrity analysis while the latter focuses on partial detection. The damage identification approach is discussed from the perspective of detection medium in the paper. And non-destructive testing in civil engineering (NDT-CE), of which the research status and existing issues are presented, can be attributed into three categories as following: one is based on the stress wave theory, such as impact-echo method, acoustic emission technique and ultrasonic pulse method; one employs the mechanism of electromagnetic wave propagation on behalf of GPR; one uses radiography as the medium, for instance, infrared imaging and computerized tomography. It is emphasized that ground penetrating radar (GPR) has been applied in practice and studied more and more, and moreover, the prospects in the field are provided.

Abstract: The elm wood samples were tested by the technique of stress wave, and the testing results were analyzed by using the statistic software of SPSS. The results showed that the moister content of wood, wood crack, the sizes of holes and numbers of holes have significant influence on propagation parameters and dynamic modulus of elasticity. Under the same specifications, the propagation time of the stress wave was longer in the wood with holes or cracks than the perfect wood samples, and the time become longer with the increasing the sizes and numbers of holes or cracks. The studying results of the thesis will provide a sound background for the application of stress-wave technique in detecting the inner defects of wood products and other wooden structures.

Abstract: This paper presents an experimental method to investigate the attenuation performance of stress waves in concrete structures embedded in piezoelectric ceramics. To get the research objective, a series of test were hold. The relationship curve between the frequency and the attenuation coefficient was fit. The calculation method for propagation distances of stress waves with constant amplitudes and frequencies in the concrete medium was proposed. The research results show that the relationship curve of attenuation coefficient and frequency conform to the cubic polynomial function approximately. The attenuation performance for the concrete structure embedded into piezoelectric ceramics is relevant to the frequency, the amplitude and the medium character, and the frequency is the main factor. The research results of this paper can provide an effective evidence for correctly placing transducers.

Abstract: Blasting vibration not only damages architectural structures but also harms people heath. Numerical simulation provides an effective method to study explosion and shock problems. Herein, the paper performed numerical simulation to predict blasting vibration. At first, analyzed the propagation velocity of stress wave, which validated the feasibility of the model. The simulation and test agreed well both at vibration waveform and at the order of magnitude of both nodes 1 and 2. The simulation could provide reasonable accuracy. The achievement provided reference for other researches.

Abstract: By establishing numerical simulation model of SPBH and comparing dynamic response of four kinds of coal-rock combination media subjected to three different stress waves, changes law of the reflected wave, incident wave, strain and strain rate were obtained. The results show that rock-rock combination has almost the same rules of reflected waves as rock-coal combination, coal-coal combination and coal-rock combination, while the coal-coal combination has the largest peak of reflected wave, followed by the coal-rock combination and the rock-coal combination, and the rock-rock combination ranks last. With increasing incident wave peak, the coal-rock combination weakens the peak more apparently. Strain softening occurs in coal samples under stress wave of peak value with the law that strain rate firstly increases, and then maintains a constant value, continues to increase and then decreases, increases reversely and then decreases. Constant strain rate of the phenomenon over time occurs. The results provide guidelines for both the study on propagation mode of stress wave in coal and rock combination media and the prevention of mining-induced dynamic disasters.

Abstract: The propagation of the stress wave in axial direction during the impact between the front-end-coated projectile and the substrate coated by ceramic films is described by the stress wave theorem. The impact process is numerically simulated by ANSYS/LS-DYNA, where the shell unit is used for precision. The effects of thickness of the front-end coating on the interfacial stress are discussed in detail. Dependence of different ceramic films are also considered. Simulation results show that interfacial normal stress is much greater than tangential stress. The interfacial normal stress is greatest when the thickness of the projectile coating is 0.2 mm. The interfacial tangential stress increases slightly as the thickness of coating increases. Similar stress history in the interface occurs when the acoustic impedance of the films are close. Greater acoustic impedance results in smaller stress.

Abstract: Foreign object damage of engine blades often occurs when they are working with high rotating speed. Nonlinear finite element models for foreign object damage of blades with different centrifugal prestress were established. And the initializations of stress and displacement field for blade due to centrifugal preload were obtained by the dynamic relaxation method in the beginning of the dynamic analysis of impact. The effect mechanism of centrifugal stress on the foreign object damage of the blade was also investigated based on the impact theory of prestressed Timoshenko beam and the principle of stress wave propagation. The results indicate that the local plastic deformation on the impact location of the blade with centrifugal preload, which is produced at the moment of impact, is decreasing with the increase of preload. Attenuation speed of compressive stress wave, which is produced by the moment of impact on the blade face, is reducing with the augment of preload.

Abstract: The testing experiments to healthy larch logs samplings whose diameter scopes are in 5-12cm and the length respectively are 10cm and 30cm were conducted by using Arbotom stress wave testing instrument and universal mechanics testing machine. The relationships between dynamic modulus of elasticity of stress wave and MOE, between MOR and MOE were all studied in the larch logs samplings. The results indicated that, in the two larch logs samplings, the dynamic modulus of elasticity of stress wave had positive linear correlation with MOE. Moreover, MOR also had a good linear correlation with MOE.

Abstract: Air conditioning refrigerant leakage is often in the course of one fault occurs, the event of leakage, in a very short period of time cooling system will be unable to function properly. In order to realize the reign of air pipelines leak detection, this article is brought forth new ideas that pipe leak detection of air conditioning is achieved by the stress wave technology and by programming in the development environment of LabVIEW. Experimental results show that this new method is quick, accurate and reliable to detect and to locate the leak source occurred, the system measures the absolute positioning error is less than 0.3% and the relative error is better than 1.5%.