Stress Wave Energy Research Articles

Crack detection and leakage monitoring on reinforced concrete pipe

Reinforced concrete underground pipelines are some of the most widely used types of structures in water transportation systems. Cracks and leakage are the leading causes of pipeline structural failures which directly results in economic losses and environmental hazards. In this paper, the authors propose a piezoceramic based active sensing approach to detect the cracks and the further leakage of concrete pipelines. Due to the piezoelectric properties, piezoceramic material can be utilized as both the actuator and the sensor in the active sensing approach. The piezoceramic patch, which is sandwiched between protective materials called ‘smart aggregates,’ can be safely embedded into concrete structures. Circumferential and axial cracks were investigated. A wavelet packet-based energy analysis was developed to distinguish the type of crack and determine the further leakage based on different stress wave energy attenuation propagated through the cracks.

Influence of wave action on the partitioning and transport of unattached and floc-associated bacteria in fresh water.

The dynamic interaction of bacteria within bed sediment and suspended sediment (i.e., floc) in a wave-dominated beach environment was assessed using a laboratory wave flume. The influence of shear stress (wave energy) on bacterial concentrations and on the partitioning and transport of unattached and floc-associated bacteria was investigated. The study showed that increasing wave energy (0.60 and 5.35 N/s) resulted in a 0.5 to 1.5 log increase in unattached cells of the test bacterium Pseudomonas sp. strain CTO7::gfp-2 in the water column. There was a positive correlation between the bacterial concentrations in water and the total suspended solids, with the latter increasing from values of near 0 to up to 200 mg/L over the same wave energy increase. The median equivalent spherical diameter of flocs in suspension also increased by an order of magnitude in all experimental trials. Under both low (0.60 N/s) and high (5.35 N/s) energy regime, bacteria were shown to preferentially associate with flocs upon cessation of wave activity. The results suggest that collecting water samples during periods of low wave action for the purpose of monitoring the microbiological quality of water may underestimate bacterial concentrations partly because of an inability to account for the effect of shear stress on the erosion and mobilization of bacteria from bed sediment to the water column. This highlights the need to develop a more comprehensive beach analysis strategy that not only addresses presently uncharacterized shores and sediments but also recognizes the importance of eroded flocs as a vector for the transport of bacteria in aquatic environments.

Analytical and experimental studies on ballistic impact behavior of carbon nanotube dispersed resin

An analytical formulation is presented for the prediction of ballistic impact behavior of multi-walled carbon nanotube (MWCNT) dispersed epoxy resin. The formulation is based on stress wave propagation and energy balance between the projectile and the target. During the ballistic impact event, the energy lost by the projectile is absorbed by the target through various damage and energy absorbing mechanisms such as compression of the target directly below the projectile, compression in the region surrounding the impacted zone, shear plugging, formation of ring and radial cracks in the resin leading to tensile failure and energy absorbed due to the presence of carbon nanotubes. Complete failure of the target was due to catastrophic brittle fracture and shattering. Experimental studies are carried out on ballistic impact behavior of neat epoxy and MWCNT dispersed epoxy. Typical results on ballistic limit velocity and energy absorbed by various mechanisms are presented. Ballistic impact behavior of neat epoxy resin and MWCNT dispersed epoxy resin are compared. A good match is observed between the analytical and experimental results.

Analytical and experimental studies on ballistic impact behavior of 2D woven fabric composites

A generalized analytical formulation is presented for the prediction of ballistic impact behavior of 2D woven fabric composite laminates impacted with a rigid cylindrical projectile. The formulation is valid for a wide range of laminate thicknesses. The formulation is based on stress wave propagation and energy balance between the projectile and the composite target. During the ballistic impact event, the energy lost by the projectile is absorbed by the target through various damage and energy absorbing mechanisms such as compression of the target directly below the projectile, compression in the region surrounding the impacted zone, shear plugging, stretching and tensile failure of yarns/layers in the region consisting of primary yarns, tensile deformation of yarns/layers in the region consisting of secondary yarns, conical deformation on the back face of the target, delamination, matrix cracking, and friction between the projectile and the target. The formulation presented considers both shear plugging and tensile failure during conical deformation. Solution procedure for the evaluation of ballistic impact performance is presented. Experimental validation is performed on the ballistic impact behavior of two types of composite specimens: 2D plain weave E-glass/epoxy and 2D 8H satin weave T300 carbon/epoxy. Typical results on ballistic limit velocity and energy absorbed by various mechanisms are presented.

Investigation of blast-induced traumatic brain injury

Objective: Many troops deployed in Iraq and Afghanistan have sustained blast-related, closed-head injuries from being within non-lethal distance of detonated explosive devices. Little is known, however, about the mechanisms associated with blast exposure that give rise to traumatic brain injury (TBI). This study attempts to identify the precise conditions of focused stress wave energy within the brain, resulting from blast exposure, which will correlate with a threshold for persistent brain injury.Methods: This study developed and validated a set of modelling tools to simulate blast loading to the human head. Using these tools, the blast-induced, early-time intracranial wave motions that lead to focal brain damage were simulated.Results: The simulations predict the deposition of three distinct wave energy components, two of which can be related to injury-inducing mechanisms, namely cavitation and shear. Furthermore, the results suggest that the spatial distributions of these damaging energy components are independent of blast direction.Conclusions: The predictions reported herein will simplify efforts to correlate simulation predictions with clinical measures of TBI and aid in the development of protective headwear.

Experimental and Modeling Studies of the Interlayer Effect on Stress Wave Propagation of Ceramic/Ti6Al4V Armors

The effect of steel, copper and aluminum interlayer on the stress wave propagation of ceramic/ Ti6Al4V armors were studied by traditional Split Hopkinson Pressure Bar system in this paper. Based on the SHPB experimental results, the stress wave propagation mechanism and energy absorption in tri-layered structure were discussed. Compared to ceramic/Ti6Al4V structure without interlayer, the steel, copper and aluminum interlayer could attenuate the transmission stress level and greatly increase the energy absorption of the structure. Due to the high acoustic reluctance of steel and copper interlayer, the reflected shock wave was in compressed situation and extended a tri-axial compressive stress within the ceramic which could improve the anti-penetration properties of ceramic plate. The numerical modeling studies of ballistic testing were carried on, and then the energy densities were compared. The results showed the steel and copper interlayer could increase the energy absorption of ceramic and improve the anti-penetration of ceramic plate. The three kinds of interlayer structures all could attenuate transmitted energy and decrease the residual penetration.

Stress Wave attenuation in SiC3D/Al Composite

SiC3D/Al composite is a kind of special composite with interpenetrating network microstructure. The attenuation properties of stress wave propagation along the SiC3D/Al composite are studied by a Split Hopkinson Pressure Bar system & FEM simulations, and the attenuation mechanism is discussed in this paper. Results show that the attenuation rate of the stress wave in the composite is up to 1.73MPa·mm−1. The reduction of the amplitude of waves is caused by that plenty of interfaces between SiC and Al within the composite acting with stress waves. When the incident plane wave reaches the SiC3D/Al interface, reflection wave and transmission wave propagates in different directions along the irregular interface between SiC phase and aluminium phase due to the impedance mismatch of them, which leads to the divergence of stress wave. At the same time, some stress micro-focuses occurs in the aluminium phase for the complex wave superimposition, and some plastic deformation may take place within such micro-regions, which results in the consumption of stress wave energy. In conclusion, the stress wave attenuation is derived from divergence and consumption of stress wave.

Directional Wave Propagation in a Highly Nonlinear Square Packing of Spheres

We studied the dynamic response of a two-dimensional square packing of uncompressed stainless steel spheres excited by impulsive loadings. We developed a new experimental measurement technique, employing miniature tri-axial accelerometers, to determine the stress wave properties in the array resulting from both an in-plane and out-of-plane impact. Results from our numerical simulations, based on a discrete particle model, were in good agreement with the experimental results. We observed that the impulsive excitations were resolved into solitary waves traveling only through initially excited chains. The observed solitary waves were determined to have similar (Hertzian) properties to the extensively studied solitary waves supported by an uncompressed, uniform, one-dimensional chain of spheres. The highly directional response of this system could be used as a basis to design granular crystals with predetermined wave propagation paths capable of mitigating stress wave energy.

Experimental investigation of stress wave propagation in standing trees

Abstract The objective of this study was to investigate how a stress wave travels in a standing tree as it is introduced into the tree trunk through a mechanical impact. A series of stress wave time-of-flight (TOF) data were obtained from three freshly-cut red pine (Pinus resinosa Ait.) logs by means of a two-probe stress wave timer. Two-dimensional (2D) and three-dimensional (3D) stress wave contour maps were constructed based on the experimental data using a commercial software. These stress wave contour maps represent the wave fronts in a time sequence, illustrating the flow of stress wave energy within a log. The analysis of TOF data and wave fronts indicates that stress wave propagation in standing trees is affected by tree diameter, travel distance, and internal wood conditions (wood properties and structural defects). When a stress wave is introduced into a tree trunk from a point source, it initially propagates in the impact direction as a 3D wave. Then the flow of the stress wave energy gradually changes towards the longitudinal directions. As the diameter-to-distance ratio reaches 0.1 or below, the wave begins to travel as a quasi 1D wave.

A new concept of shock mitigation by impedance-graded materials

Over the last several decades, homogenous single-layer armor has been replaced by multi-layer integral armor to improve ballistic penetration resistance. This has led to better attenuation of shock wave energy by multiple interface reflections and transmissions. Efforts have been reported to improve the penetration resistance by providing higher energy dissipation at higher levels of impedance mismatch. However, high stress concentrations and stress reversals have made these interfaces the primary sources of failure. This paper discusses a concept for a new class of blast and penetration resistant (BPRM) materials which are layer-less but designed to have a continuous gradient of impedance that can dissipate the shock energy without material failure. In a simplistic approach by applying the classical theory of uniaxial stress propagation, it has been shown that attenuation of the stress wave energy would be possible by controlling the impedance distribution within the body of such a material. The development of such material to resist blast or impact will overcome the current common difficulty of interfacial delamination failure in any protective barrier system or armors.

Stress-wave energy management through material anisotropy

Stress-wave propagation in solids can be controlled through imposing a gradual change of anisotropy in the material elasticity tensor. In this study, a transversely isotropic material is incorporated with a smoothly varying axis of anisotropy. It is shown that if this axis initially coincides with the stress-wave vector, then the energy of the plane waves would closely follow this gradually changing material direction. A fiber-reinforced composite is used to induce the required anisotropy, and to experimentally demonstrate the management of stress-wave energy in a desired trajectory. The material has isotropic mass-density and is considered homogeneous at the scale of the considered wavelengths, even though microscopically it is highly heterogeneous.

Study on stress wave propagation in fractured rocks with fractal joint surfaces

This paper presents the experimental and theoretical investigation of property of stress wave propagation in jointed rocks by means of SHPB technique and fractal geometry method. Our aim focuses on the influence of the rough joint surface configuration on stress wave propagation. The comparison of behavior of reflection and transmission waves, deformation and energy dissipation of a rough joint surface characterized by its fractal feature with that of a smooth plane joint has been carried out. It has shown that the rough joint surface distinctly affects the stress wave propagation and energy dissipation in the jointed rocks. The rougher the joint surface was, the more permanent deformation occurred and the more attenuation stress wave took place as well. A nonlinear relationship between the normalized energy dissipation ratio W J/ W I of the jointed rock and the joint roughness in terms of the fractal dimension has been formulated. It seems that the ratio W J/ W I, presenting how much energy has been dissipated in the joint, nonlinearly increased with the increment of the fractal dimension D of the jointed surface. The ratio W J/ W I of a roughly jointed rock, however, tends to be the same as that of a smoothly jointed rock if the fractal dimension is less than a critical value D c = 2.20. The energy dissipation ratio at the critical point D c seem to be a constant, not dependent of rock type but fractal joint configuration.

On Solving the Coronal Heating Problem

The question of what heats the solar corona remains one of the most important problems in astrophysics. Finding a definitive solution involves a number of challenging steps, beginning with an identification of the energy source and ending with a prediction of observable quantities that can be compared directly with actual observations. Critical intermediate steps include realistic modeling of both the energy release process (the conversion of magnetic stress energy or wave energy into heat) and the response of the plasma to the heating. A variety of difficult issues must be addressed: highly disparate spatial scales, physical connections between the corona and lower atmosphere, complex microphysics, and variability and dynamics. Nearly all of the coronal heating mechanisms that have been proposed produce heating that is impulsive from the perspective of elemental magnetic flux strands. It is this perspective that must be adopted to understand how the plasma responds and radiates. In our opinion, the most promising explanation offered so far is Parker's idea of nanoflares occurring in magnetic fields that become tangled by turbulent convection. Exciting new developments include the identification of the “secondary instability” as the likely mechanism of energy release and the demonstration that impulsive heating in sub-resolution strands can explain certain observed properties of coronal loops that are otherwise very difficult to understand. Whatever the detailed mechanism of energy release, it is clear that some form of magnetic reconnection must be occurring at significant altitudes in the corona (above the magnetic carpet), so that the tangling does not increase indefinitely. This article outlines the key elements of a comprehensive strategy for solving the coronal heating problem and warns of obstacles that must be overcome along the way.

Development of a Spreadsheet for Modeling SPT Stress Wave Data

Abstract The advantages of measuring and correcting for variations of Standard Penetration Test (SPT) stress wave energy are well documented. Despite this fact, geotechnical engineers are often hesitant to measure SPT energy, due to high cost and uncertainty about data quality or the reliability of energy calculation methods. Two spreadsheets that model the propagation of stress waves through simple and safety hammers (and attached rod strings) were developed to address the issue of data quality. This paper describes the development of the spreadsheets, including critical aspects of hammer-anvil interaction that are not well documented in the geotechnical literature. Spreadsheet output is verified by comparison to stress wave data collected under controlled laboratory conditions. The safety hammer spreadsheet is then used to assess the quality of stress wave data collected during an actual field investigation. In all cases, the modeled and measured data are in good-to-excellent agreement.

Energy partitioning in elasto-plastic impact by sharp abrasive particles in the abrasive water jet machining of brittle materials

In the abrasive water jet machining (AWJM) of brittle materials, the stress wave energy, associated with the impact of abrasive particles, plays an important factor in material removal by fracture. The models currently available are idealised and simplified and cannot take into account the particle shape or size. The present paper addresses the problem of taking into consideration the size and shape of the particles. The results indicate that use of spherical blunt particles in the AWJM of brittle materials will lead to more fracture.

Reflection and refraction of plane stress waves at interfaces modelling various rock joints

Abstract Upon stress wave interaction with joints, incident energy is reflected and refracted. To gain insight into the mechanisms associated with dynamic processes such as blasting, percussion drilling and seismicity, knowledge of the amplitudes of the reflected and refracted waves is of importance. This paper compiles stress, energy, displacement and velocity amplitudes of stress waves, which are reflected and refracted by a variety of interface types. In addition to covering the well-known wave interactions with standard discontinuities, such as a free boundary and welded interface, some new interface conditions are analysed, e.g. interfaces with friction and shear strength, and interfaces with normal and shear stiffness related to measurable rock properties. The aim of this tutorial paper is to act as an educational guide and reference for the blasting engineer, seismologist, geophysicist and rock engineer, and to assist in further understanding stress wave interactions with rock mass discontinuities.

An erosion model for abrasive waterjet milling of polycrystalline ceramics

A modeling study was conducted on the abrasive waterjet milling (AWJM) of polycrystalline ceramics. The optimum jet incidence angle was determined from experiments. A conclusion from previous studies, which indicated intergranular cracking to be the dominant erosion mechanism, was applied. A hypothesis that links the intergranular cracking to impact-induced stress waves was used. An existing expression for the input stress wave energy was adopted in a crack network model to evaluate material removal. A new material constant “AWJM Erosion Resistance” was defined. The derived erosion model is verified with single-pass AWJM experiments.

Identification of a percussive drill rod joint from its response to stress wave loading

In percussive drilling of rock, elastic stress waves are generated in a drill string through repeated axial impacts by the hammer of a rock drill. For holes deeper than a few meters, several drill rods are commonly joined by means of cylindrical coupling sleeves with internal threads which connect drill rods with external threads at their ends. Each coupling sleeve (CS) joint serves to transfer stress wave energy from one drill rod to the next with minimum loss of energy due to reflection and dissipation. This paper deals with the development of an identification procedure for the nonlinear dissipative spring mass (NDSM) model of a CS joint developed by Lundberg et al. Stiffness, friction and mass parameters were determined by minimizing the diffence between simulated and measured responses of the joint, in reflection or transmission, to the same incident stress wave loading. Similar results were obtained as with an existing mixed static and dynamic identification procedure, but with considerably less expenditure of equipment and time. The most reliable results and the smallest deviation between simulated and measured responses were achieved in transmission.

Axisymmetric Analysis of Spall Damage Based on Damage Mechanics.

Elaboration of the preceding one-dimensional analysis of ductile spall damage based on damage mechanics was discussed by performing axisymmetric two-dimensional analyses. The effects of surface energy due to cavity nucleation and elastic-viscoplastic-damage coupling were incorporated into the energy conservation law. Then, the application of the commercial finite-difference program MANJUSRI-3D for nonlinear dynamic analysis to the axisymmetric two-dimensional problem was discussed. Finally, a plate impact of OFHC copper discs was analyzed by the present method, and the effects of the radial stress wave and surface nucleation energy on the spall damage process were elucidated. The results of analysis were compared with those of one-dimensional analysis and experiments.

Transmission and dissipation of stress wave energy at a percussive drill rod joint

Transmission and dissipation of stress wave energy at a percussive drill rod joint is determined for three joint types, three joint preload levels, three hammer lengths (∼ incident wave lengths) and a range of impact velocities (∼ incident wave amplitudes). The energies of the incident, reflected and transmitted waves are evaluated from measured strains, and then the dissipated energy is determined as the deficit of energy in the two latter waves compared with the first. The accuracy needed is obtained by introducing a compensation factor and determining its value from the requirement of momentum conservation. The experimental results for threaded standard joints are compared with experimental results for threadless dummy joints, made in one piece, and also with theoretical results. The latter are based on one model which represents the joint as a well on a one- dimensional elastic rod (characteristics impedance or CI model) and on another model which represents the joint as a rigid mass between one-dimensional elastic rods (rigid mass or RM model). For the joints 70–100% of the incident wave energy is transmitted and 0–20% is dissipated. The corresponding figures for the dummies are 90–100% and (±)1%, repectively. The latter figure indicates the inaccuracy in the measurement and evaluation procedures. The two models agree fairly well with the dummies. Under certain conditions they also give reasonably accurate predictions for the energy transmitted through a joint. As they sometimes give quite inaccurate results for energy transmission and furthermore fail to predict energy dissipation they need be refined.