Experimental verification of the detect interlaminar damage of a interface wave method to metal multilayer structure

The interface wave traveling along the bound- ary of two materials has been studied for nearly a century. However, experiments, engineering applications, and interface wave applications to the non-destructive inspec- tion of interlaminar composite have developed slowly. In this research, an experiment that applies Stoneley waves （a type of interfacial wave between two solid half-spaces） is implemented to detect the damage in a multilayer structure. The feasibility of this method is also verified. First, the wave velocity and wave structure of Stoneley waves at a perfectly bonded aluminum-steel interface are obtained by solving the Stoneley wave dispersion equation of two elastic half-spaces. Thereafter, an experiment is conducted to measure the Stoneley wave velocity of an aluminum- steel laminated beam and to locate interlaminar cracks by referring to the Stoneley wave velocity and echo wave time. Results indicate that the location error is less than 2%. Therefore, Stoneley waves show great potential as a non-destructive inspection method of a multilayer structure.

MECHANISM OF WAVE FORMATION AT THE INTERFACE IN EXPLOSIVE WELDING

Some of the main progress on the investigation of the mechanism of the wave formation in explosive welding at the Institute of Mechanics is summarized and otters'previous works are re- viewed.Our systematic experiments and analysis do not substantiate the theory of wave formation based on Karman vortex-street analogy or Helmholtz instability.On the contrary,they show that materi- al strength insensitive to strain rate plays an important role.A simple hydro-plastic model is presented to explain the main features regarding the interracial wave formation and to estimate the magnitude of wave length.The result is in broad agreement with experiment.

Experimental Study on the Identification of Scholte Waves Based on Acoustic Pressure Field Measurement

Scholte waves at the seafloor interface are generally identified by their velocity features and seismic fields,which are measured using ocean bottom seismometers and geophones.These methods are effective in cases where there is a considerable difference between the velocities of Scholte and acoustic waves in water.However,they are ineffective when the velocities of these two types of waves are close to each other.Thus,in this paper,a method based on acoustic pressure field measurement for identifying Scholte waves is proposed according to their excitation and propagation characteristics.The proposed method can overcome the limitations on the velocities of two types of waves.A tank experiment is designed and conducted according to the proposed method,and an ocean environment is scaled down to the laboratory size.Acoustic measurements are obtained along virtual arrays in the water column using a robotic apparatus.Experiments show that changes in Scholte wave amplitudes,depending on different source depths and propagation distances,are consistent with the theoretical results.This means that Scholte waves generated at the seafloor interface are successfully measured and identified in the acoustic pressure field.

Behavior and mechanism of the bonding interface of 0Cr18Nig/16MnR by explosive welding

In order to investigate the bonding behavior and mechanism of the interface prepared by explosive welding, the bonding interfaces of 0 Crl 8Ni9/16MnR were observed and analyzed by means of optical microscope （OM） , scanning electron microscope （SEM） and electron probe microanalysis （ EPMA ）. It is found that the welding interfaces are wavy due to the wavy explosive loading. There are three kinds of bonding interfaces i. e. big wave, small wave and micro wave. There are a few seam defects and all elements contents are less than both of the base and .flyer plate in the transition zone of big wavy interface. Moreover, some ＂holes＂ result in the lowest bonding strength of big wavy interface nearby the interface in the base plate. All elements contents of the small wavy interface are between two metals, and there are few seam and hole defects, so it is the higher for the bonding strength of small wavy interface. There is no transition zone and defects in the micro wavy interface, so the interface is the best. To gain the high quality small and micro wavy bonding interface the explosive charge should be controlled.

FISSION LAWS OF INITIALLY INTERFACE SOLITARY WAVES IN TWO-LAYER OCEAN

A 2-D KdV equation of two-layer stratified o-cean with 2-D topography isrecapitulated in the present paper. Based on a reduced version of this 2-D KdV equation, the fissionlaws of the initially internal solitary waves are studied by means of numerical calculation. Fromthe numerical results , it is shown that the initially interface solitary waves can fission on thecontinental slope like the initially surface solitary waves and the fission process is a significantgenerating mechanism of internal interface soliton packet on the continental shelf.

The quasi-Rayleigh waves in a layered solid medium with a weak interface

The Rayleigh waves in a layered solid medium is dispersive. Using the 'spring' model for a weak interface between two solids, the characteristic equation for the quasi-Rayleigh waves in an isotropic layered solid medium with a weak interface is presented. The numerical results for the typical coating structure with the rigid, slip and weak interface are shown. The influence of the interface stiffness constants on the velocity of the quasi-Rayleigh waves is considered. The numerical results show that the interface characteristics of the coating structure can be nondestructively evaluated by employing the quasi-Rayleigh waves in the low frequency band.

Numerical study on the wave pattern characteristic of air layer in cavity and the effects of multiple influence factors

Air-layer drag reduction (ALDR) technology for ship energy saving is getting more and more attention in recent years because of the outstanding drag reduction effect. In order to promote practical application, it is necessary to fully understand the two phase flow characteristics of the air layer. Recent experimental studies have shown that the surface of the air layer presents wave pattern, which has an important influence on its damage risk. However, it is difficult to measure the wave pattern quantificationally due to the interference of equipment. The main goal of the present paper is to investigate the wave pattern characteristic of air layer in cavity using numerical simulation method. On this basis, the effect of flow and geometric influence factors are discussed to understand the key control conditions. A computational fluid dynamics (CFD) numerical method based on Reynolds averaged Navier-Stokes (RANS) equations and volume of fluid (VOF) interface capturing method is established, and has been successfully applied in the simulation of air layer wave pattern. Both 2-D and 3-D simulations are carried out, aiming at analyzing air-water interface flow and vortex flow directly. Based on the simulation results, several important conclusions about the mechanism of air layer wave pattern can be obtained. Firstly, it is found to be an inherent characteristic that the wave height of the upstream air layer is higher than that of the downstream. The extremely high wave peak is easy to contact with the flat plate, leading to the breakup of air layer and a “central blank area” phenomenon. With the help of flow analysis, it is found that this characteristic is mainly caused by the strong counterclockwise vortex behind the bow wedge block. Secondly, the air layer stability is reduced with the increase of water flow velocity by affecting the wave height. There is a saturation point of air flow rate to reach maximum thickness of air layer. Thirdly, cavity configuration has obvious influence on air layer stability by influencing vortex flow field. The increase of cavity depth and width can aggravate the unsteady and nonlinear characteristics of air layer. Finally, comprehensive design criteria are concluded from the view of geometrical configuration and flow conditions. A cavity with the moderate depth and width can avoid the upstream damage of air layer. Longitudinal position of air nozzles should be set within the low pressure zone behind the wedge block for stable air layer formation.

Interaction of ultrasonic wave with void-containing layer in solid

Using a general mode for sound reflection from multilayered media, we present in this paper the expressions for sound reflection and transmission coefficients on void-containing interface layer in solid and derive the characteristic equation for symmetric and antisymmetric modes of the interface waves along the layer. The method for evaluating the effective elastic moduli of void-containing solid is also introduced. The numerical calculation given in this paper shows the influences of the void volume concentration and layer thickness on the sound reflection coefficients and interface wave velocity, providing a theoretical basis for inverse of the mechanical properties of void-containing layer based on the ultrasonic measurement.