Stress Wave Method Research Articles

Mechanical characterization of visually graded boards from turkish fir and black pine by nondestructive and destructive tests

For the mechanical characterization of Turkish fir and black pine, 400 board specimens with 22 mm× 50 mm × 420 mm were visually graded according to TS 1265 standard. Nondestructive tests were here upon performed using the stress wave method. After specimens were intentionally tested under flatwise bending to research the applicability as an alternative to tension and edgewise bending tests in European strength grading system. According to analyses of variance, the mean values of MOR and MOE differed in four groups at a p<0,05 significance level for visually graded boards. High correlations were found between MOR-MOE (R2=0,837) for fir and MOR-MOE (R2=0,776) for black pine. In addition, correlations of MOR-Knot rate for fir and black pine were respectively R2=0,669 and R2=0,660 showing the effectiveness of flatwise bending tests with the visual grading standard. For nondestructive tests, the mean values of the dynamic modulus of elasticity were very close in between fir and black pine grades while the usage of defect-free density performed better than the density of the whole specimen. Higher strength classes were found for black pine boards (Class 1= C40, Class 2= C27 and Class 3= C22) compared to fir boards (Class 1= C24, Class 2= C22 and Class 3= C18), respectively. Moreover, a simplified nonlinear material model was proposed for numerical modelling, and the results were found in good agreement in terms of the bending stiffness, strength, and deformation capacity of boards especially for class 1 and class 2 in both softwood species.

Influence of Piston Mass and Working Pressure on the Impact Performance of a Hydraulic Rock Drill Using the Stress Wave Method

To optimize and improve the impact performance of a hydraulic rock drill, it is helpful to test the stress waves of the drill and analyze the impact energy, impact frequency, and energy utilization rate. For this study, a stress wave test bench was designed and built, according to international standards, in order to study the impact process of a hydraulic rock drill under the working pressures of 18 MPa and 23 MPa. The impact energy, impact frequency, and energy utilization rate of two different hydraulic rock drill pistons in low, middle, and high gear were analyzed using a control variable method. The results demonstrate that the impact stress waves of the rock drill periodically occur in the drill rod, and then decay exponentially until they become close to zero. Moreover, the amplitude of the incident stress wave determines the rock-breaking ability of the drill. The impact energy of the short piston is greater than that of the long piston, with a maximum average value of 346.1 J; the impact frequency of the long piston is higher than that of the short piston, with a maximum average value of 62 Hz; and the energy utilization rate of the short piston is higher than that of the long piston, with a maximum average value of 56.92%, which is close to the theoretical ideal efficiency. Therefore, it can be concluded that the impact performance of a hydraulic rock drill can be effectively tested using the proposed horizontal bench, and that piston characteristics and the working pressure are the main factors affecting impact performance. Accordingly, when developing a hydraulic rock drill, it is advisable to select a shorter piston and a higher working pressure, thus allowing the drill to provide good impact performance.

Characterization of Deformation of Bolts and Induced Stress Wave Propagation under Axial Tensile Stress

The nondestructive testing technique used to evaluate the quality of bolt support by detecting the axial force is suitable for the bolt with a short construction time. For the bolt in the support state for a long time period, it may lead to the detection of small axial force only and ignore the fact that the bolt has entered the necking fracture stage, and thus fail to detect safety hazards in time. Three sets of parallel tests were conducted to solve the misjudgment of detection results due to the reduction of axial force when the bolt was in the necking fracture stage. Bolt deformation characteristics and stress wave propagation characteristics in bolts under axial tensile stress were studied by using the bolt tensile and stress wave detection test system which was modified and built independently. The results showed that (1) The diameter of the necking position decreases continuously during the tensioning process of the bolt and the rate of decrease increases abruptly during the necking fracture stage. (2) Due to the bolt stretching, the stress wave propagates in the bolt with different degrees of reflection and transmission, resulting in the attenuation of the stress wave energy; the energy attenuation ratio of the stress wave signal in the necking fracture stage reaches 35%, and the energy attenuation ratio increases exponentially as the necking continues to occur. (3) The frequency distribution of the stress wave signal during the bolt stretching process is from scattered to concentrated, the dominant frequency is gradually prominent and changes from low frequency to high frequency, the high-frequency signal is more sensitive to the cracks and necking of the bolt, and the dominant frequency is between 9500 and 10,000 Hz. (4) The average error of the stress wave method is 1.945% and the maximum and minimum values are 4.12% and 0.51%, respectively. The method is promising and provides a reference for the study of nondestructive testing of bolt stress waves in field support.

Comparative Evaluation of Investigation Testing Methods in Timber Elements considering Moisture Content

ABSTRACT Wood components in existing buildings suffer from deterioration and damage due to environmental conditions and loading effects. Their preservation strongly depends on the knowledge level of their onsite condition supported by the application of low-intrusive methods of investigation. Estimating the mechanical performance of wood in constructions cannot disregard the evaluation of moisture content. In this paper, 31 wood elements (19 recovered from disassembled buildings and 12 new) underwent a series of non-destructive tests (i.e., ultrasonic and sonic stress wave methods) and semi-destructive tests (i.e., resistance drilling and pin penetration). Red/white firs and pine species constituted the recovered elements; red fir and larch the new ones. The effect of moisture content on the results of low-intrusive methods was estimated by either electric or electromagnetic devices. Destructive tests (in bending and compression) were also carried out on 10 recovered and six new elements, and results were correlated with those of semi-destructive tests.

Research on the Vibration and Wave Propagation in Ship-Borne Tethered UAV Using Stress Wave Method

To investigate the vibration behavior of ship-borne tethered UAVs under taut–slack conditions, the Hamilton principle is used to establish the three-dimensional dynamic equations of the ship-borne tethered UAVs while taking into account geometric nonlinearity and simplifying them into the corresponding stress wave equations. By employing the characteristic line technique to solve the stress wave equation of ship-borne tethered UAVs, it is possible to numerically determine the effects of various factors on the vibration behavior of these drones. Dimensional analysis is then used to build the experimental model, ensuring that the numerical outcomes are accurate. The findings show that the impact of equilibrium curvature connects longitudinal and transverse waves and that the geometric dispersion of stress wave propagation in the tethered cable is caused by equilibrium curvature. The standing wave takes the lead and causes subharmonic and frequency doubling components in the top tension response when the end excitation frequency is near the tethered UAVs’ natural frequency. Additionally, the cable’s center as well as its end will display the highest dynamic tension value.

Experimental Study of the Effect of Axial Load on Stress Wave Characteristics of Rock Bolts Using a Non-Destructive Testing Method

Traditional rock bolt inspection methods are destructive and limited. Non-destructive testing (NDT) based on the stress wave method can realize a fast and convenient quality detection of rock bolts. To verify the effectiveness of the stress wave-based anchor NDT method, a multi-functional experimental bench was customized on the basis of a bench-pull tension testing machine. Stress waves can be generated by applying axial loads on rock bolts and then collected using a non-destructive tester. The VMD decomposition method and Hilbert–Huang signal processing method were used to filter and analyze the stress wave signal. The influence of the axial loads of different magnitudes on the stress wave was then investigated. The results showed that the stress wave characteristics of the rock bolt changed with the increase in the axial load. It was found, correspondingly, that the stress wave amplitude decreased gradually and there was a trend of rapid decrease at the beginning and then a slower decline. The change in the time domain amplitude of the stress wave after noise reduction can be used to determine the magnitude of the load on the rock bolt during the elastic deformation stage. Further studies showed that the axial load on rock bolts inversely calculated by the stress-wave time-domain amplitude method is accurate and reliable, which can be validated by comparing the data measured by the rock bolt dynamometer. The research results shed light on the development of the NDT technology on rock bolt inspection, and make this testing method more convenient, efficient, and accurate.

Comparative evaluation of inspection techniques for decay detection in urban trees

A crucial problem associated with urban trees is the need ensure citizens’ safety. It requires the development and application of rapid and precise diagnostic techniques for detecting decay and other types of structural defects in trees to prevent falling due to strength failure or damage caused by internal decay. Significant effort has been devoted to developing robust non-destructive technologies, such as specialized sensors, capable of predicting the intrinsic properties of the wood of individual trees. In this study, the authors used four different devices with its sensors to measure decay: a microsecond timer, an electric resistivity tomograph, an acoustic tomograph and a resistograph. An inspection protocol combined stress wave, electrical resistance, and drilling resistance to detect internal defects on Mindi trees (Melia azedarach L.) located in the city of Reggio Calabria in Southern Italy. The percentages of the decayed wood areas, calculated by the different instruments, were compared to establish at which degree the use of simple and rapid instruments can guarantee reliability in detecting the extent of damaged woody tissues. This study’s experimental results indicate high correlations between the resistance drilling and the stress wave methods. These high correlations may provide the opportunity to replace the resistograph with the microsecond timer or the acoustic tomograph, both of which are less invasive tools for detecting defects in standing trees. Compared to the resistograph, the electrical resistivity tomograph proved to be the least sensitive instrument for detecting wood decay.

Variation in Wood Density and Mechanical Properties of Acacia mangium Provenances Planted in Vietnam

ABSTRACT There is a growing interest in improving wood properties through the appropriate selection of seed provenances within species. In this study, wood density and mechanical properties were investigated for Acacia mangium trees from six different provenances, planted in Quang Tri, Vietnam. Radial and among provenance variation in stress wave velocity (SWV), wood density (WD), dynamic modulus of elasticity (MOEd), modulus of rupture (MOR), and modulus of elasticity (MOE) were determined on a total of 480 small clear specimens (20 × 20 × 300 mm) cut from 30 trees (five per provenance). SWV and selected wood properties near the pith were significantly lower than those near the bark. Differences in all selected mechanical properties among provenances were significant. The highest static properties (MOR and MOE) were found for the Long Thanh provenance indicating its potential suitability for breeding programs in Vietnam focused on improving A. mangium wood quality. A high positive correlation coefficient was found between MOEd and MOE (r = 0.93, P < 0.001) and our results indicate that the stiffness of A. mangium can be predicted using stress wave method provided the density of measured element is known.

Defect detection in concrete plates with impulse-response test and statistical pattern recognition

Statistical and machine learning analysis of structural health monitoring data is a popular approach for efficient structural level defect detection. However, the application of these techniques to stress-wave methods such as impact-echo and impulse-response data for local level detection has been limited. In this research, statistical pattern recognition in conjunction with the impulse-response test is shown to provide an efficient means for the detection of defects in concrete plates. For this purpose, the Frequency Response Function (FRF) derived from the impulse-response test following ASTM C1740 protocols at specific points on the test plate to define the feature space matrix. Analytical results demonstrate that the variability of the FRF increases in the presence of defects, which forms the physical basis for the proposed pattern recognition algorithm. First, Principal Component Analysis (PCA) is performed on the covariance of the feature space matrix to identify the dominant features of the FRFs and to determine the number of statistically significant factors or principal components. Factor scores are next used to identify locations on the plate that are associated most closely to each pattern. The generalized Extreme Value Studentized (ESD) test and box and whisker plots are applied to the factor score vector of all the test points to objectively identify test points with defects and rank these based on their severity. Two experimental specimens are used to demonstrate the applicability of the proposed detection algorithm. The first specimen, a partially reinforced clamped concrete plate, is used to demonstrate the relationship between the shapes and variability of the FRFs and the severity of defects (delaminations), the efficacy of the factor score as damage sensitive feature, and identification and the ranking of the severity of defects by using outlier statistical tests. The second specimen is used to demonstrate the efficiency of the procedure for detecting both void and honeycomb defects in a larger reinforced concrete plate on elastic supports. The proposed procedure is shown to provide similar levels of detectability as the highly refined yet time consuming ultrasonic shear-wave tomography test. While the impulse-response test has been in use for the condition assessment of concrete elements other than drilled shaft piles since 1980′s, defect detection has been based primarily on empirical observations and correlations with limited features of the frequency response function. The use of pattern recognition techniques to the full range of the frequency response function is proposed and shown to greatly improve the detection and characterization of defects.

Application of Ground-Penetrating Radar for Living Trees Detection

In order to evaluate the potential hazards, researchers are working on revealing the inner structural of a living trunk using different diagnostic techniques. Nondestructive techniques (NDTs), such as stress wave method and ultrasonic wave method, have become increasingly convenient and economical in trees detection. To improve forest management and to prevent collapses of trees, it is necessary to investigate the internal part of tree trunks. In order to do it non-invasively, ground-penetrating radar (GPR) appears as a promising inspection device. Each of these NDTs has its pros and cons. Among all, the GPR is capable of multiple measurements with hardly any damage to the body of a tree, perfect for investigations on roots and trunks of living trees. 15 camphor trees are selected and subject to GPR testing for the study. The results of inductive method and GPR wave signals indicate that the GPR image shows “wavy” features when an eccentric void is found inside a tree, meaning that the travel time is the shortest for the return signals when the antenna is closest to the void. However, GPR wave signals appear to be discontinuous and fluctuate when there are irregular cavities. The signal time is defined by using the metal plate to generate strong reflection in the case of on-site monitoring. The internal condition of tree trunk is usually tested based on detecting 2D image of tree trunk by the stress wave method, as to confirm that the application of GPR is feasible to detect the trunk of camphor tree. The method proposed in this paper can realize the accurate localization and imaging distribution of the internal defects of the trees by the radar wave scanning images.

Estimating mechanical properties of clear wood from ten‐year‐old Melia azedarach trees using the stress wave method

The objective of this study was to examine the potential of stress wave velocity (SWV) as a rapid and non-destructive method to estimate the mechanical properties of Melia azedarach wood. The SWV, dynamic modulus of elasticity (MOEd), modulus of elasticity (MOE), modulus of rupture (MOR, bending strength) and density were determined on ninety 20 ⋅ 20 ⋅ 320 mm clear wood specimens, obtained from stems of three ten-year-old M. azedarach trees, and tested at environmental equilibrium in 20°C, 60 % relative humidity (a moisture content of approximately 12 %). There was a statistically significant (0.1 % level) but weak correlation (R2 = 0.23) between the SWV and MOE, but no statistically significant correlation was found between the SWV and MOR. Much better results for prediction of static properties of M. azedarach wood were obtained when SWV and wood density (WD) were used together through calculation of MOEd in the air-dry condition (MOE: R2 = 0.76, MOR: R2 = 0.47), although in the case of MOR a model based on WD alone is slightly better (R2 = 0.58), and WD is also almost as good as MOEd for predicting MOE. It is concluded that SWV coupled with WD can be employed as a predicting parameter to evaluate the mechanical properties of M. azedarach wood during the manufacturing process, although WD alone is also effective. The SWV alone would not be useful due to MOE being almost directly proportional to WD at this moisture content.

Long-term monitoring of the trunk of standing Cryptomeria japonica (sugi) trees by the stress wave method

Long-term monitoring of the trunk of standing <i>Cryptomeria japonica</i> (sugi) trees by the stress wave method

Nondestructive Evaluation of Drilled Shaft Construction Anomalies Using Full Waveform Tomography of Simulated Crosshole Measurements

Construction of drilled shafts for transportation infrastructure presents quality assurance challenges related to structural anomalies, including voids and degraded concrete. Efforts to evaluate anomalies often use stress-wave non-destructive testing (NDT) techniques such as the crosshole sonic logging (CSL) method. CSL relies on the propagation of stress waves between access tubes inserted alongside the reinforcement cage. Differences in travel time and amplitudes can be used to estimate concrete quality within the source-receiver ray paths. Crosshole tomography (CT) advances this approach further and models ray paths to solve an inverse problem based on first arrival times. However, both stress-wave methods cannot typically evaluate anomalies smaller than 10% to 15% of the shaft cross sectional area. Recent advances in wave propagation modeling have led to the development of full waveform inversion (FWI) approaches. FWI attempts to generate a more detailed tomographic model that matches the entire waveform recordings. This paper presents findings from a numerical study where full waveform tomography was performed on a portion of a drilled shaft with a structural anomaly. Crosshole stress-wave propagation was simulated using a spectral element method (SEM) forward modeler. The resulting waveforms were then used as inputs into a CT travel-time inversion algorithm using ray-path modeling and into a FWI algorithm using the entire recorded signals. The results highlighted that FWI estimated concrete velocities and the geometry of the anomaly more accurately than CT in the idealized numerical model. This was the case even though information from more sources and receiver pairs was used for the CT inversion.

Design of an Acoustic-Based Nondestructive Test (NDT) Instrument to Predict the Modulus of Elasticity of Wood

Modulus of elasticity (E) can predict the mechanical characteristics, as well as grade the quality of wood. The Destructive Test (DT) method is the more commonly used, where the wood sample is split up when being tested. This research used the NDT method based on the longitudinal stress wave method (LSWM) whilst utilizing handheld instruments. The calculated E-dynamic (Ed) from the NDT method was compared with the E-static (Es) from the DT method to validate the technique. Six different wood types were tested with ten samples of each kind. An average R-value of 0.898 was obtained, indicating a high correlation between the Ed values and Es values. The LSWM method requires reliable hardware and software to record the impulse response. It starts by hitting the wood with a hammer to create an impulse, finding the resonance frequency (f0), and later calculating the Ed. A more practical and easy-to-use handheld mobile instrument was developed using a Raspberry Pi-2 microcomputer as the signal processor, an LCD touchscreen, a USB soundcard, and a dynamic microphone that covers 0.1-5kHz and -64 ± 3dB. An internal telecommunication system is provided to support measurements conducted at lumber mills. The software includes band-pass filtering of the recorded spectrum where the f0 is depicted. A time-domain envelope fitting is then applied to the filtered spectrum to obtain the R2envelope. A low R2envelope value indicates an inadequate impulse response, and therefore, the test should be redone.

Attenuation characteristics of stress wave in cracked concrete beam using smart aggregate transducers enabled time-reversal technique

Piezoelectric enabled stress wave methods for concrete structural health monitoring have been widely researched. However, the attenuation characteristics of stress wave in cracked concrete structures have barely been studied. As a result, it is hard to quantify the damage levels of the concrete structure. In this paper, the attenuation characteristics of stress wave in cracked concrete beam are studied using stress wave with the time-reversal technique. The attenuation model of stress waves related to the focused signal amplitude and the total crack width of concrete beam is proposed. In this study, a series of 18 concrete beams were tested using a four-point loading. During the test procedure, the signals of stress wave from the piezoelectric smart aggregate transducers in all the test specimens were collected to facilitate the proposed model. The test data of 12 beams are used to determine the attenuation coefficient of stress wave per unit crack width, and the test data of the other six beams are used to validate the accuracy of the proposed attenuation model. The results indicate that the prediction results based on the stress wave attenuation model are in good agreement with the test results of cracked concrete beams.

Lamb wave propagation method for nondestructive characterization of the elastic properties of wood

Nondestructive evaluation (NDE) of the mechanical properties of structural wood is of great importance for quality control purposes in wood industries and construction applications. The currently used ultrasonic and stress wave methods fail to accurately estimate the elastic properties of wood. The present study aimed to propose an NDE method for accurate characterization of the elastic properties of wood using the Lamb wave propagation method. Lamb wave propagation and mechanical three-point-bending tests were performed on the green poplar wood specimens with different moisture content (MC) levels. The fundamental antisymmetric Lamb wave mode was propagated in specimens using an ultrasonic actuator, and an ultrasonic sensor was used to acquire the wave signal at different locations of the specimens along the propagation direction. The Lamb wave velocity was measured for the wood specimens with different MC and found to be in very good agreement with those from semi-analytically obtained dispersion curves. Afterwards, the corresponding inverse Lamb wave propagation problem was solved and the modulus of elasticity (MOE) of the specimens was estimated. The maximum difference between the MOE calculated by the proposed Lamb wave propagation method and that measured from the three-point bending test was less than 2%, proving the validity of the proposed method for nondestructive characterization of wood.

Mogućnosti procene kvaliteta drveta dubećih stabala primenom akustičnih metoda

Based on literature sources, the stress wave and ultrasound methods and tools designed for the evaluation of the effects of decay on wood are discussed in this paper. To make a review of the results obtained in numerous studies, the analytic-synthetic method was used and the evaluation of data was conducted. The results revealed high correlations between the measured properties and the actual wood quality. A number of studies show that the acoustic wave velocities correlate well to wood density and other wood properties. Changes in the acoustic velocity and wood density variations caused by decay have also been detected successfully using the ultrasonic tools. This means that wood quality can be assessed in situ and that the methods and devices in question can help us make the right decisions. Still, it must be pointed out that all the methods and devices used are only measuring and quantifying tools, and practical human experience cannot be replaced by any measuring tools.

Quantitative assessment of compress-type osseointegrated prosthetic implants in human bone using electromechanical impedance spectroscopic methods.

Osseointegrated (OI) prostheses are a promising alternative to traditional socket prostheses. They can enhance the quality of life of amputees by avoiding fit and comfort issues commonly associated with sockets. The main structural element of the OI prosthesis is a biocompatible metallic implant that is surgically implanted into the bone of the residual limb. The implant is designed to provide a conducive surface for the host bone to osseointegrate with. The osseointegration process of the implant is difficult to clinically evaluate, leading to conservative postoperative rehabilitation approaches. Elastic stress waves generated in an OI prosthesis have been previously proposed to interrogate the implant-bone interface for quantitative assessment of the osseointegration process. This paper provides a detailed overview of the various elastic stress wave methods previously explored for in situ characterization of OI implants. Specifically, the paper explores the use of electromechanical impedance spectroscopy (EIS) to assess the OI process in compress-type OI prostheses. The EIS approach measures the electrical impedance spectrum of lead zirconate titanate elements bonded to the free end of the implant. The research utilizes both numerical simulation and experimental verification to establish that the electromechanical impedance spectrum is sensitive (between 400 and 460kHz) to both the degree and location of osseointegration. A baseline-free OI index is proposed to quantify the degree of osseointegration at the implant-bone interface and to assess the stability of the OI implant for clinical decision making.

Classification and characterization of thermally modified timber using visible and near-infrared spectroscopy and artificial neural networks: a comparative study on the performance of different NDE methods and ANNs

Visible and near-infrared (VIS–NIR) spectroscopy was used for classifying and predicting the properties of thermally modified Western hemlock wood. The specimens were treated at 170 °C, 212 °C, and 230 °C. The dimensional reduction was performed using linear discriminant analysis, and the resulted dataset was used for wood classification using the support vector machines and the linear vector quantization neural network. The VIS–NIR dataset was also used to predict the wood moisture content, swelling coefficient, water absorption, density, dynamic modulus of elasticity, and hardness. The “adaptive neuro-fuzzy inference system” (ANFIS), “Group Method of Data Handling” (GMDH), and “multilayer perceptron” (MLP) neural networks were employed for predicting the wood properties. It was shown that regardless of the type of the neural network, NIR dataset provided a robust model with 100% classification accuracy, which can be implemented in industrial scale for in-line timber quality control. The results indicated that the ANFIS and GMDH neural network showed higher performance than the MLP model for predicting the wood properties. While the VIS–NIR data resulted in a promising accuracy for predicting the wood moisture content and dimensional stability parameters, it did not seem suitable for the prediction of wood density and its mechanical properties. The performance of the VIS–NIR spectroscopy method for classification and characterization of heat-treated timber was compared with that obtained using the color measurement and the stress wave method detected by the acoustic emission sensor.

Sub-surface simulated damage detection using Non-Destructive Testing Techniques in reinforced-concrete slabs

Most commonly occurring defects in RC (Reinforced Concrete) bridge decks include voids, spalling, corrosion of reinforcement, leaching, scaling, cracking, honeycombing and delamination/debonding. Research related to the use of different NDTs (Non-Destructive Testing) techniques to locate and identify different defects and its severity have been conducted in the past. Previous research work indicates that no particular technique is complete and each has its own advantages and limitations. This paper discusses the error values in identification of the damage in reinforced concrete using NDTs. This research uses a total of five NDTs and their combination to detect the defects. For this, a total of nine 1800 mm × 460 mm reinforced concrete slabs with varying thicknesses of 100 mm, 150 mm and 200 mm have been prepared. These slabs have been embedded with artificial defects like voids, debonding, honeycombing, and corrosion. The experimental research shows that combining multiple techniques together in evaluating the defects give significantly lower error and higher accuracy compared to that from a standalone test. Combination of multiple techniques such as stress wave, electromagnetic wave, infrared thermography and other electrochemical methods have been used for damage detection in reinforced-concrete slabs.