Stress Wave Energy Research Articles

Experimental and Modeling Studies of Stress Wave Propagation and Energy Dissipation Mechanism in Layered Composite Structures

Four composite structures (SiC/UHMWPE/TC4, SiC/TC4/UHMWPE, SiC/UHMWPE/MR/TC4, and SiC/TC4/MR/UHMWPE) were prepared using silicon carbide (SiC) ceramics, ultrahigh molecular weight polyethylene (UHMWPE), titanium alloy (TC4), and metal rubber (MR). The transmitted waves, failure forms, stress wave propagations, and energy dissipations of the composite structures were studied through Split Hopkinson Pressure Bar (SHPB) tests and numerical simulations. The results show that MR in composite structures can delay, attenuate, and smooth the stress wave, thereby reducing SiC damage. UHMWPE on the back of SiC provides cushioning for SiC, while TC4 on the back of SiC aggravates the damage of SiC. The composite structures with MR mainly dissipate the impact energy by reflecting energy, and the energy dissipation performance is better than that of composite structures without MR. A comprehensive comparison of transmitted waves, damage forms, stress wave propagations, and energy dissipations of the four composite structures shows that SiC/UHMWPE/MR/TC4 structure has the best impact resistance. Increasing the thickness of MR in the composite structures can improve the impact resistance, but there are also stress concentration and interface tensile stress.

Stress Wave Propagation and Energy Absorption Properties of Heterogeneous Lattice Materials under Impact Load

A heterogeneous lattice material composed of different cells is proposed to improve the energy absorption capacity. The heterogeneous structure is formed by setting layers of body‐centered XY rods (BCCxy) cells as the reinforcement in the body‐centered cubic (GBCC) uniform lattice material. The heterogeneous lattice samples are designed and processed by additive manufacturing technology. The stress wave propagation and energy absorption properties of heterogeneous lattice materials under impact load are analyzed by finite element simulation (FES) and Hopkinson pressure bar (SHPB) experiments. The results show that, compared with the GBCC uniform lattice material, the spreading velocity of the stress of the (GBCC)3(BCCxy)2 heterogeneous lattice material is reduced by 18.1%, the impact time is prolonged 27.9%, the stress peak of the transmitted bar is reduced by 34.8%, and the strain energy peak is reduced by 29.7%. It indicates that the heterogeneous lattice materials are able to reduce the spreading velocity of stress and improve the energy absorption capacity. In addition, the number of layers of reinforcement is an important factor affecting the stress wave propagation and energy absorption properties.

Waveform characterization and energy dissipation of stress wave in sandstone based on modified SHPB tests

The changeable stress environment directly affect the propagation law of a stress wave. Stress wave propagation tests in sandstone with different axial stresses were carried using a modified split Hopkinson Pressure bar (SHPB) assuming the sandstone has a uniform pore distribution. Then the waveform and stress wave energy dissipation were analyzed. The results show that the stress wave exhibits the double peak phenomenon. With increasing axial stress, the intensity difference decreases exponentially and experiences first a dramatic decrease and then gentle development. The demarcation stress is σ/σc=30%, indicating that the closer to the incident end, the faster the intensity difference attenuates. Under the same axial stress, the intensity difference decreases linearly with propagation distance and its attenuation intensity factor displays a quadratic function with axial stress. With increasing propagation distance, the time difference decays linearly and its delay coefficient reflects the damage degree. The stress wave energy attenuates exponentially with propagation distance, and the relations between attenuation rate, attenuation coefficient and axial stress can be represented by the quadratic function.

A power waveform design based on OVSF-PPM for stress wave based wireless power transfer

The lifetime of wireless sensors and devices is restricted by their limited battery capacities, since it is quite time-consuming and costly to replace batteries. Wireless power transfer is recognized as a feasible solution to charge wireless sensors and portable devices, since it can provide energy continuously for wireless electronic devices. This paper explores a waveform design for stress wave power transfer. In the proposed method, pulse position modulation (PPM) signals are firstly designed based on orthogonal variable spreading factor (OVSF) code. Then, power transfer waveforms for multiple receivers are created via analyzing the correlation among the PPM signals. When applied in stress wave power transfer, the proposed waveform is demonstrated to effectively improve power transfer performance at the intended receiver. We investigate three different transmission schemes, namely the pulse waveform, the time reversal waveform, and the proposed power transfer waveform, by comparing and analyzing their performances in experiments when one energy transmitter and one energy transfer array are respectively used. Due to multiple stress wave modes, rich dispersion and mutual interference among energy transfer signals, energy transfer efficiencies (ETE) and peak to average power ratios (PAPR) tend to be low by using pulse waveforms or traditional time reversal waveforms to transfer stress wave energy. On the contrary, by implementing the proposed waveform in stress wave power transfer, the ETE and the PAPR are effectively improved. In the experiment, three piezoceramic transducers mounted on a pipeline are used for stress wave power transfer. The experimental results demonstrate that the proposed waveform significantly improves the ETE and the PAPR, as compared with the other two waveforms.

Experimental study of stress wave propagation and energy characteristics across rock specimens containing cemented mortar joint with various thicknesses

Stability and safety of rock structures are easily influenced by the dynamic disturbance, especially when weak joint planes exist. In order to investigate the filling joint effect on the dynamic response of rock specimens, a series of impact dynamic tests were conducted by a modified split Hopkinson pressure bar (SHPB) system. A sandwich type of sandstone specimens filling with different thicknesses layer of cemented mortar (filling joint) were tested in the study. The results show that the transmission coefficient, dynamic strength and energy absorption all decrease with increasing joint thickness. However, the reflection coefficient, peak strain and joint closure show an opposite variation trend. In addition, the deformation of the cemented mortar joint is the main reason to cause the deformation and final failure of jointed rock specimens. Tensile cracks dominate the fracturing behavior during the dynamic loading, but they have a slight influence on the final failure mode which transforms from localized slabbing to axial splitting failure with the filling joint becoming thicker.

Real time monitoring of screw insertion using acoustic emission can predict screw stripping in human cancellous bone

BackgroundTo develop experience, orthopaedic surgeons train their own proprioception to detect torque during screw insertion. This experience is acquired over time and when implanting conventional/non-locked screws in osteopenic cancellous bone the experienced surgeon still strips between 38 and 45%. Technology needs to be investigated to reduce stripping rates. Acoustic-Emission technology has the ability to detect stress wave energy transmitted through a screw during insertion into synthetic bone. Our hypothesis is Acoustic-Emission waves can be detected through standard orthopaedic screwdrivers while advancing screws through purchase and overtightening in cancellous human bone with different bone mineral densities replicating the clinical state. Methods77 non-locking 4 mm and 6.5 mm diameter cancellous bone screws were inserted through to stripping into the lateral condylar area of 6 pairs of embalmed distal femurs. Specimens had varying degrees of bone mineral density determined by quantitative CT. Acoustic-Emission energy and axial force were detected for each test. ResultsThe tests showed a significant high correlation between bone mineral density and Acoustic-Emission energy with R = 0.74. A linear regression model with the mean stripping load as the dependent variable and mean Acoustic-Emission energy, bone mineral densities and screw size as the independent variables resulted in r2 = 0.94. InterpretationThis experiment succeeded in testing real time Acoustic-Emission monitoring of screw purchase and overtightening in human bone. Acoustic-Emission energy and axial compressive force have positive high correlation to bone mineral density. The purpose is to develop a known technology and apply it to improve the bone-metal construct strength by reducing human error of screw overtightening.

Effects of a set of parallel joints with unequal close-open behavior on stress wave energy attenuation

Rock joints with unequal close-open behavior have significant influences on stress wave propagation across them. A stress wave of sufficiently large amplitude does not only mobilize the nonlinear deformation of joints, but also force the joints to close and open. In the present study, the Bandis-Barton model and the Coulomb-slip model are adopted to describe the normal and tangential behavior, respectively, of the closed joints. However, when the joints are open, both sides of the joints behave as two free surfaces. The improved time-domain recursive method is employed to derive wave propagation equations for three cases, i.e. the joint is closed but does not slide, the joint is closed and slides, and the joint is open. Then, the normal and tangential relative displacements of joints, as well as the energy attenuation coefficient, are calculated. A comparison of transmitted waves based on different methods is conducted to verify the validity of the present approach. Eventually, parametrical studies show that the higher in-situ stress causes the smaller energy attenuation coefficient, and the wave energy attenuation is also dependent on the frequency and amplitude of the incident wave, the incident angle, the joint spacing and the joint number.

Numerical study of monitoring of early-age concrete strength development using PZT induced stress wave

The purpose of this paper is to verify the validity of concrete strength monitoring method based on piezoelectric wave dynamic technology by the numerical simulation ways. Since the elastic modulus of concrete increases linearly with its strength, the elastic modulus of concrete at different ages is set to simulate its strength growth. The stress wave is transmitted and received by the piezoelectric sensor embedded in concrete, and the stress wave energy value is taken as the strength identification parameter, and its variation trend with the strength is analyzed. The results show that with the increase of concrete strength, the energy value of monitoring signal has a monotonically decreasing trend. In the early stage of concrete, the monitoring signal energy decreases at a large rate and then tends to be flat. In the early stage, the strength growth rate of concrete is faster, and tends to be flat in the later stage. Furthermore, the curve of capability ratio and strength ratio was established, and the two presented good linear lines. The results of this paper show that the concrete strength monitoring method based on pressure wave dynamic technology can be used to monitor the concrete strength.

Experimental study on stress wave attenuation and energy dissipation of sandstone under full deformation condition

Excavation behaviours not only destroy the balance of original stress in rock mass but lead to the redistribution of initial stress, resulting in rock mass in a new stress environment. The static stress in rock mass has the characteristics of dynamic change. For the purpose of investigating the effect of increasing static stress on attenuation mechanism and energy dissipation of stress wave in sandstone under the overall deformation condition, small disturbance experiments on sandstone bar are carried out with a modified split-Hopkinson pressure bar test system. The stress waveform, p wave velocity, temporal and spatial attenuation of amplitude, and energy dissipation are studied under various static stresses. Results show that stress waveforms at different locations are approximately the same, those at the same locations vary greatly, and the tensile waves that appeared at the tails of stress waves are larger with increasing static stress. With increasing static stress, p wave velocity experiences a dramatic increase, then develops gently, and finally a sharp decrease; the stress demarcation points are σs/σc = 30% and σs/σc = 55%, respectively. P wave velocity can be predicted by a quadratic equation when σs/σc > 63.69%. The relation between longitudinal wave velocity and static stress can be described by a quadratic function. Stress wave amplitudes decrease exponentially with increasing distance and time. Values of temporal spatial response intensity (RI) and spatial RI are approximately equal and present the same development tendency of nonlinear and linear stages due to the same dimensions. Values of temporal attenuation characteristic (AC) and spatial AC are differed by 2 or 3 orders of magnitude although they present the same development tendencies. Ratios of RI and AC can indicate the sensitivity of temporal and spatial attenuation to different static stresses. Full-wave energy declines in an exponential function with increasing static stress and decays as a logarithmic function with increasing distance. Widespread attenuation characteristics like these should provide a theoretical basis for rock mass stability analysis.

Shear-wave generation from cavitation in soft solids

The formation and dynamics of cavities in liquids lead to focusing of kinetic energy and emission of longitudinal stress waves during the cavity collapse. Here, we report that cavitation in elastic solids may additionally emit shear waves that could affect soft tissues in human bodies/brains. During the collapse of the cavity close to an air-solid boundary, the cavity moves away from the boundary and forms a directed jet flow, which confines shear stresses in a volume between the bubble and the free boundary. Elastographic imaging and high-speed imaging resolve this process and reveal the origin of a shear wave in this region. Additionally, the gelatin surface deforms and a conical crack evolves. We speculate that tissue fracture observed in medical therapy may be linked to the non-spherical cavitation bubble collapse.

Effects of Porosity of Dry and Saturated Sandstone on the Energy Dissipation of Stress Wave

A SHPB experiment of porous sandstone was conducted to discuss the influencing principle of porosity on the energy dissipation of stress wave across dry and saturated porous sandstones. Changes in porosity before and after the SHPB experiment were analyzed by nuclear magnetic resonance. Results show that the number of wave peaks in the T2 spectrum before and after the impact test of sandstone is unchanged, but the wave peak value corresponding to small pores increases. This result indicates that the sandstone structure remains in the microcrack formation stage because the stress wave energy is adequate only for forming new microcracks but not for tearing pores and increasing pore diameter. Results further show that, at the same porosity, saturated sandstone consumes less energy than dry sandstone. With increased porosity, the energy dissipation of saturated sandstone decreases, whereas that of dry sandstone increases. This phenomenon can be explained based on three aspects. First, according to the fracture mechanics theory, the surface tension of water and Stefan effect significantly hinder crack expansion. Therefore, generating a new surface to dissipate stress wave energy of saturated sandstone is more difficult than that of dry sandstone under the same porosity. Second, during impact loading, saturated sandstone is in a nondrainage state, and its deformation can be viewed approximately as the sum of compressive deformation of sandstone and water. Water has smaller comprehensive deformation than sandstone. The deformation of saturated sandstone decreases with increased porosity, i.e., water content. Plastic deformation and the probability of new cracks decrease, so energy dissipation of saturated sandstone decreases. Third, with increased porosity, the dynamic strength of dry sandstone declines accordingly. Developing new cracks during loading to dissipate stress wave energy as surface energy is easy. Therefore, high porosity causes great energy dissipation.

A Feasibility Study on GFRP Tubular Concrete Column Damage Detection Using Piezoceramic-transducer-enabled Active Sensing

Aiming at the crack damage of concrete in GFRP tubular concrete column, a method based on piezoelectric wave method was developed to monitor the crack damage. By transmitting and receiving stress waves from a pair of piezoelectric ceramic sensors embedded in GFRP tubular concrete, the damage degree of GFRP tubular concrete columns was evaluated by using wavelet packets to obtain the stress wave energy and damage index under different load levels. By analyzing the change of stress wave energy and damage index of concrete with different strength under different loads, the time-domain signal response, load-energy curve and load-damage index curve were obtained. In this test, four test pieces were designed according to different concrete strength grades. Two piezoelectric ceramic sensors were placed in the test piece and used to monitor the test piece under static loading. After the static loading was completed, the GFRP tube was severely broken and peeled off from the concrete. A large number of cracks appeared on the concrete surface. The results show that: The test results were consistent with the actual damage of the specimen. The development trend of concrete damage in GFRP tubular concrete columns was well revealed by the wave method.

Numerical study on interface debonding detection mechanisms with 2D spectral element method for concrete-filled steel tube using embedded PZT sensor

Interface debonding detection approaches based on stress wave measurement for concrete-filled steel tube (CFST) members have received a great deal of attention in civil and infrastructural engineering societies. The development of efficient computing approaches to investigate the mechanisms of the interface debonding detection approaches and the effect of interface debonding on wave propagation within CFST members is critical. In this study, the wave propagation within the cross section of CFST members with and without interface debonding under a single point excitation force is simulated with a two-dimensional (2D) spectral element method (SEM) at first and that of CFST models coupled with a surface-mounted piezoelectric lead zirconate titanate (PZT) actuator and an embedded PZT sensor in the concrete core under continuous and sweep sinusoidal signals is simulated with the 2D SEM and a piezoelectric spectral element. The debonding defect is modeled by removing concrete elements between the steel tube and the concrete core. Results show that interface debonding affects the wave propagation process, the output potentials of the embedded PZT sensors as well as the displacement responses at different locations of CFST specimens obviously. Rayleigh damping identified from experiments is introduced to the SEM models to reflect wave attenuation in the coupled models. The effect of interface debonding on the amplitude, the Fourier spectra and the wavelet packet energy of stress waves are analyzed. For comparison, another numerical model in which the PZT actuator is not located near the interface debonding defect is studied numerically and the effect of the debonding defect on the response of the embedded PZT sensor is illustrated. SEM provides an efficient way to simulate stress wave propagation and to understand the mechanisms of interfacial debonding defect detection for CFSTs with PZT technique.

Effects of Geometrical Parameters on Stress Wave Propagation across the Rough Joint

The contact surface of the rough joint has geometrical parameters as the joint matching coefficient (JMC) and the distribution pattern of the contact segments. The specimen used in the modified SHPB test got the artificial joint by sawing some notches on the surface contacted to the output bar. Different assemblies of the notches formed various contact areas and distribution patterns. Using the modified SHPB tests data, the altered thin-layer interface model was used to analyze the effects of geometrical parameters on one-dimensional stress wave transmission and energy dissipation across a single rough joint. It revealed that the transmission coefficient decreased with the diminution of JMC, and it increased with the scattered distribution pattern as the similar trend for each JMC set. As for the energy coefficients, with the decrease of JMC, the transmission energy coefficient reduced sharply, but it increased very slowly with the reflection energy coefficient and irreversible energy coefficient. It revealed that the JMC of 0.5 was the critical point of the energy dissipation. More energy transmitted across the joint rather than reflecting back and dissipating, when JMC > 0.5. Nevertheless, the irreversible energy coefficient was much larger than the transmission and reflection coefficients, when JMC < 0.5.

Numerical simulation methodology of multi-layer Kevlar 49 woven fabrics in aircraft engine containment application

ABSTRACTA numerical simulation method was developed to provide effective tools to estimate the ballistic resistance of Kevlar 49 fabric for gas turbine engine containment system in LS-DYNA. Material model based on representative unit cell and three-element viscoelastic constitutive equation was employed to describe the dynamic response of single-layer and multi-layer fabrics. The influences of mesh size, hourglass control method in the material model were discussed. The numerical simulation method is used to predict the ballistic performance of Kevlar fabrics in testing condition. The failure mechanism, the stress wave propagation and energy absorption mechanism were investigated and compared with testing results and achieved good agreements. It is indicated that the developed numerical method provides promising results in modelling the high-speed ballistic impact events and engine fan blade off events.

Energy dissipation from two-glass-bead chains under impact

The mechanisms of energy dissipation during the dynamic fracture and fragmentation of granular materials play a significant role in controlling the evolution of geological structures, enhancing the efficiency of industrial comminution and blasting, and reducing the geoenvironmental hazards. In this research, impact tests on two-glass-bead chains accompanied by micro-CT of crushed fragments are performed. The results reveal that only a small portion of the input stress wave energy is dissipated through the fragmentation of the two-bead-chain system and that the energy dissipation efficiency increases with increasing input energy. It is found that generally the glass bead at the back of the chain always experiences more damage regardless of the input stress wave energy level. The micro-CT results show that the fracture energy only accounts for a small portion (0.3%–1.4%) of the chain system absorbed energy. Such a low conversion rate is attributed to the underestimated surface area of the micro-cracks, caused by the finite resolution of the micro-CT. By pursuing a fractal dimension analysis, designed to account for the undetected micro-crack surface area, it is estimated that the energy conversion rate could be increased to 0.7%–5.1%. It appears that friction dissipation appears to always be predominant, in particular during severe fragmentation.

Effect of the Preexisting Fissure with Different Fillings in PMMA on Blast‐Induced Crack Propagation

In order to study the dynamic crack propagation law in fissured rock under the different fillings, a borehole with 7 mm diameter was processed in the center of a polymethyl methacrylate (PMMA) specimen. The preexisting fissure with different angles (θ = 0°, 45°, and 90°) and different distances (L = 20, 30, 40, 50, and 60 mm) was prefabricated around the borehole. Air, soil, and water were employed as fillings in the fissure, respectively. The experiment of explosive loading was carried out by a single detonator, and the dynamic crack propagation process of the experimental specimens was simulated by nonlinear dynamics software AUTODYN. The results show that the blast‐induced cracks are the most favorable and unfavorable to propagate when θ = 0° and θ = 45°, respectively. The length of the far‐end wing crack decreases with the increase of the distance L, and the length of the far‐end wing crack in the air‐filled specimens is larger than those in soil‐filled and water‐filled specimens. The damage‐pressure curve of the far‐end wing crack initiation point shows “S”‐type change, and the damage‐pressure curve shows two obvious damage evolution processes of initial nonlinear and later linear stages. With the increase of the angle, the distance from the borehole to the crack initiation point decreases and the compressive stress wave peak value should increase, but the tensile force peak value decreases. Meanwhile, the relationships between pressure and average velocity of the initiation point and L, θ, and fillings are established, respectively. The numerical simulation agrees with the experimental results well. It can be seen that the fillings types, angle, and distance have a mutual restraint relationship with the reflected and absorbed stress wave energy. The phenomenon of crack propagation under different fillings can be explained well from the viewpoint of discontinuity degree and stress wave energy, which reveals the general law of blast‐induced crack propagation.

Monitoring of Grouting Compactness in a Post-Tensioning Tendon Duct Using Piezoceramic Transducers.

A post-tensioning tendon duct filled with grout can effectively prevent corrosion of the reinforcement, maintain bonding behavior between the reinforcement and concrete, and enhance the load bearing capacity of concrete structures. In practice, grouting of the post-tensioning tendon ducts always causes quality problems, which may reduce structural integrity and service life, and even cause accidents. However, monitoring of the grouting compactness is still a challenge due to the invisibility of the grout in the duct during the grouting process. This paper presents a stress wave-based active sensing approach using piezoceramic transducers to monitor the grouting compactness in real time. A segment of a commercial tendon duct was used as research object in this study. One lead zirconate titanate (PZT) piezoceramic transducer with marble protection, called a smart aggregate (SA), was bonded on the tendon and installed in the tendon duct. Two PZT patch sensors were mounted on the top outside surface of the duct, and one PZT patch sensor was bonded on the bottom outside surface of the tendon duct. In the active sensing approach, the SA was used as an actuator to generate a stress wave and the PZT sensors were utilized to detect the wave response. Cement or grout in the duct functions as a wave conduit, which can propagate the stress wave. If the cement or grout is not fully filled in the tendon duct, the top PZT sensors cannot receive much stress wave energy. The experimental procedures simulated four stages during the grout pouring process, which includes empty status, half grouting, 90% grouting, and full grouting of the duct. Experimental results show that the bottom PZT sensor can detect the signal when the grout level increases towards 50%, when a conduit between the SA and PZT sensor is formed. The top PZT sensors cannot receive any signal until the grout process is completely finished. The wavelet packet-based energy analysis was adopted in this research to compute the total signal energy received by PZT sensors. Experimental results show that the energy levels of the PZT sensors can reflect the degree of grouting compactness in the duct. The proposed method has the potential to be implemented to monitor the tendon duct grouting compactness of the reinforced concrete structures with post tensioning.

Numerical Investigation on the Failure Behavior of Brittle Granular Chain under Impact

In brittle granular materials, the fragmentation waves have received far less attention due to their complexity despite of their significant role in mineral processes, earthquake hazards control, etc. In this research, the Material Point Method (MPM) is used to analyze how fragmentation waves propagate in a 3-dimensional 10 brittle beads chain with a rate-dependent elasto-damage model. The simulations show that generally, the second bead will become the most severely damaged one, followed by the third bead. Most failure points will appear near the contact surface between the brittle spheres and extend to interior conically. An interesting phenomenon is that with a lower damage threshold or fracture energy, despite of the increase of total damage in the whole chain, less damage is developed in some beads after a period of time. This is mainly because more damage in the beginning dissipates excessive stress wave energy to the extent such that the reflected wave will not be able to cause more damage in the local system.

Analysis and Numerical Simulation on the Reduction Effect of Stress Waves Caused by Water Jet Slotting Near Blasting Source

As one of the most serious “side effects” of blast excavation, blast-induced vibration must be controlled for existing buildings and human beings. This paper proposes a method for blast-induced vibration reduction with water jet assistance according to the cutting characters of low-noised, environment-friendly water jet. The mechanism of vibration-isolation with water jet assistance was analyzed, and the stress wave energy attenuation models were established based on blasting theory and stress wave theory. Influence law on shock wave attenuation by vibration-isolation slot was studied by numerical simulation. Simulation results agree with the theoretical analysis roughly. The results of this study put forward a method for blast-induced vibration near blasting source and provide a certain theoretical basis.