Stress Wave Velocity Research Articles

Propagation velocity model of stress wave in longitudinal section of tree in different angular directions

In order to detect the size and shape of defects inside wood, a propagation velocity model of stress wave in the longitudinal section of trees in different direction angles was proposed and evaluated. The propagation velocity model was established through theoretical analysis. Four representative tree species in the northeast region of China were taken as test samples. The propagation velocity of stress wave in the longitudinal section of trees in different directions was measured using a nondestructive testing instrument. The corresponding regression model was obtained, which was in good agreement with the theoretical mathematical model. For the larch log samples, a healthy multiple regression model (z = 109.2×2 – 182.1y2 + 36.78x2y2 – 34.76x2y4 + 1627) with correlation coefficient R2 = 0.97 and root mean square error RMSE =17.81 was used to conduct two-dimensional imaging of defective logs. Based on the results of two-dimensional imaging, the highest fitness of the images was 94.24%, and the lowest error rates of defect cavities was 6.11%. The imaging results showed that this method accurately detected the internal defects of trees and was not affected by the size of defects.

Variation in Tree Growth Characteristics, Pilodyn Penetration, and Stress-wave Velocity in 65 Families of Acacia mangium Trees Planted in Indonesia

Growth characteristics [stem diameter (D), tree height (H)] and wood properties [Pilodyn penetration (P) and stress-wave velocity (SWV)] were measured for 65 families of 6-year-old Acacia mangium trees planted in Indonesia, in order to characterize their variation in D, H, P, and SWV. Therefore, the correlations between the measured characteristics were also determined, and their significant differences observed. Furthermore, their low to moderate values of narrow-sense heritability was obtained, and the results indicated the characteristics to be genetically controlled in A. mangium. In addition, highly significant positive correlations were observed among the growth characteristics, suggesting a close relationship, while there was no significant association between the growth characteristics and P, as well as SWV, indicating their independent. Therefore, these results demonstrate a potential for the improvement of both growth and wood properties of A. mangium trees, using the appropriate breeding programs. In addition, 18 families showed good performance in D and SWV, signifying their positive prospect of being considered as plus trees for the next generation breeding cycles.

Environmental factors and wood qualities of African blackwood, Dalbergia melanoxylon, in Tanzanian Miombo natural forest

African blackwood (ABW) (Dalbergia melanoxylon) mainly occurs in the coastal areas of East Africa, including in Tanzania and Mozambique, and its heartwood is commonly known to be one of the most valuable materials used in the production of musical instruments. Although the heartwood is one of the most expensive timbers in the world, very low material yield has recently resulted in the significant reduction of natural individuals. This might have serious impact on local communities, because this tree is apparently the only species that can support their livelihood. Therefore, a solution to the problem is urgently needed in terms of the sustainable development of communities. In this study, we survey environmental factors (stand structure and soil properties) in the Miombo woodlands of southern Tanzania, where ABW was once widely distributed, to clarify the factors affecting growing conditions of ABW. Three community forests located in Kilwa District, Lindi, Tanzania, were selected as the survey sites, and 10–13 small plots (0.16 ha/plot) were randomly established at each site. In addition, the stem qualities of standing trees were evaluated by visual inspection rating and a non-destructive measurement of stress-wave velocity, for understanding the relationship between environmental factors and growth form. It was found that ABW was widely distributed under various environmental conditions with intensive population, and that their growth form depended on environmental factors. Since there was no significant difference of stress-wave velocities among the site, our findings suggest that the dynamic properties of ABW trees does not depend on growth conditions, which is generally influenced by various external factors. These results present important information regarding the sustainable forest management of ABW.

Effects of Radial Growth Rate on Wood and Lumber Properties of 67-Year-Old Japanese Larch (Larix Kaempferi) Trees Planted in Tochigi, Japan

The wood and lumber properties were examined for 67-yr-old Japanese larch (Larix kaempferi) trees with different radial growth rates planted in Tochigi Prefecture, Japan. The trees were categorized into slow-, medium-, and fast-growing groups based on the stem diameter. No significant difference in stresswave velocity of stems, which is closely related with Young’s modulus of wood, was found among three radial growth categories (stem diameter classes). The boundary between juvenile wood (JW) and mature wood (MW) determined by latewood tracheid length (TL) existed about the 20th annual ring from the pith in all sample trees. Significant differences between JW and MW were found in most of examined wood and lumber properties. It was found that trees with fast growth do not always cause lower grade lumberproperties.

4D cardiac magnetic resonance flow in patients with pulmonary hypertension associated with congenital heart disease

Right heart catheterization is an invasive exam that is currently the gold standard to assess pulmonary hemodynamics for diagnosis and follow-up of pulmonary arterial hypertension (PAH) associated with congenital heart diseases (CHD). Cardiac magnetic resonance 4D flow (4D CMR flow) emerges as a promising non-invasive imaging. We assess the accuracy of 4D CMR flow to measure pulmonary cardiac output (Qp). We prospectively included 28 patients with PAH associated with CHD. Qp was measured invasively using Fick principle (direct oxygen consumption measure) during aright heart catheterization (QpF) and compared to Qp measured by 2D (Qp2D) and 4D flow CMR (Qp4D) on the same day. Twenty eight patients was included (median age was 42 years old [35–52]) with PAH and CHD (pre-tricuspid shunt n = 23, 82.1%, median mean pulmonary artery pressure 46 mmHg [40-58]; median pulmonary vascular resistance 15.0 WU.m 2 [7.5–25.6]) 4D CMR flow analysis were feasible in all patients. Qp4D and QpF were strongly correlated (rho = 0.87, P < 0.0001; r 2 = 0.68, P < 0.0001). Using Bland Altman analysis, mean difference was 0.0 ± 1.0 L/min. Mean difference within two observers (interobserver variability) was 0.3 ± 0.4 L/min. Mean difference within one observer (intra-observer variability) was 0.1 ± 0.3 L/min. Qp2D and QpF were moderately correlated (rho = 0.54, P = 0.008; r 2 = 0.41, P = 0.0007). Using Bland Altman analysis, mean difference was 0.6 ± 2.3 L/min ( Fig. 1 ). Qp measured by 4D CMR flow is well correlated to QpF. Further studies are needed to explore other potential interests of using 4D CMR flow to assess PAH, including the derivation of additional hemodynamic parameters such as pulmonary artery compliance, wall shear stress and pulse wave velocities, which could provide further insights into pulmonary artery remodeling and interactions between pulmonary arterial stiffening and right ventricular dysfunction.

Acoustic-Based Prediction of End-Product-Based Fibre Determinates within Standing Jack Pine Trees

The objective of this study was to specify, parameterize, and evaluate an acoustic-based inferential framework for estimating commercially-relevant wood attributes within standing jack pine (Pinus banksiana Lamb) trees. The analytical framework consisted of a suite of models for predicting the dynamic modulus of elasticity (me), microfibril angle (ma), oven-dried wood density (wd), tracheid wall thickness (wt), radial and tangential tracheid diameters (dr and dt, respectively), fibre coarseness (co), and specific surface area (sa), from dilatational stress wave velocity (vd). Data acquisition consisted of (1) in-forest collection of acoustic velocity measurements on 61 sample trees situated within 10 variable-sized plots that were established in four mature jack pine stands situated in boreal Canada followed by the removal of breast-height cross-sectional disk samples, and (2) given (1), in-laboratory extraction of radial-based transverse xylem samples from the 61 disks and subsequent attribute determination via Silviscan-3. Statistically, attribute-specific acoustic prediction models were specified, parameterized, and, subsequently, evaluated on their goodness-of-fit, lack-of-fit, and predictive ability. The results indicated that significant (p ≤ 0.05) and unbiased relationships could be established for all attributes but dt. The models explained 71%, 66%, 61%, 42%, 30%, 19%, and 13% of the variation in me, wt, sa, co, wd, ma, and dr, respectively. Simulated model performance when deploying an acoustic-based wood density estimate indicated that the expected magnitude of the error arising from predicting dt, co, sa, wt, me, and ma prediction would be in the order of ±8%, ±12%, ±12%, ±13%, ±20%, and ±39% of their true values, respectively. Assessment of the utility of predicting the prerequisite wd estimate using micro-drill resistance measures revealed that the amplitude-based wd estimate was inconsequentially more precise than that obtained from vd (≈ &lt;2%). A discourse regarding the potential utility and limitations of the acoustic-based computational suite for forecasting jack pine end-product potential was also articulated.

Establishing patterns of destruction of naturally disturbed rock massifs by an explosion

It is noted that the effectiveness of explosive destruction of naturally broken and fractured rock massifs depends primarily on the strength and structural characteristics of rocks and the characteristics of the formation, interaction and propagation of stress waves in the array. It is proved that one of the main parameters, which characterizes the physical properties of rock, is the propagation velocity of longitudinal stress waves in a mountain massif. Therefore, in the above studies, it has been suggested that this characteristic of the environment retains its significance in naturally disturbed rocks. It has been established that a significant decrease in the intensity of stress waves in inhomogeneous disturbed media with a decrease in the size of natural separations makes it difficult to reasonably describe the process of destruction of an array based on existing patterns of elastic wave propagation. This also includes the development of engineering methods for controlling the energy of an explosion in naturally disturbed arrays, taking into account the parameters of stress waves. However, such difficulties do not exclude the need to take into account stress waves indirectly, in particular, through their propagation velocity. To estimate the volume of destruction of mountain ranges of an impaired structure by an explosion, it was proposed to use the velocity of propagation of stress waves in a real array, as a component in acoustic impedance. It has been established that with an increase in the speed of propagation of longitudinal waves in a naturally disturbed rock massif, the volume of their destruction increases. It is proved that with an increase in the velocity of propagation of stress waves from 1000 m / s to 6000 m / s, the volume of destruction of a naturally disturbed array increases 2.2 ... 2.4 times, depending on the type of rock.

The effects of age at correction of aortic coarctation and recurrent obstruction on adolescent patients: MRI evaluation of wall shear stress and pulse wave velocity

BackgroundCoarctation patients before curative reconstruction are exposed to abnormal flow patterns which potentially could cause wall deterioration. This study evaluated the effect of age at correction on the pulse wave velocity (PWV) and peak wall shear stress (WSS) in adolescent patients with corrected coarctation. Effects of valve morphology and presence of reobstruction were also evaluated.MethodsTwenty-one patients aged 13.7 ± 2.6 years (mean ± standard deviation) were included (bicuspid aortic valve, n = 14; reobstruction, n = 9). Mean age at correction was 1.0 ± 1.8 years. PWV was determined from two high-temporal through-plane phase-contrast magnetic resonance imaging (MRI) acquisitions, for two segments: ascending aorta plus aortic arch and descending aorta. WSS was determined from four-dimensional flow MRI. Peak WSS over five systolic phases was determined for ascending aorta, aortic arch, and descending aorta.ResultsPatients with tricuspid aortic valve showed a significant correlation between the age at correction and descending aorta PWV (rs = 0.80, p = 0.010). Significant differences were found between patients without and with reobstruction for peak WSS in the aortic arch (3.9 ± 1.3 Pa versus 6.5 ± 2.2 Pa, respectively; p = 0.003) and descending aorta (5.0 ± 1.3 Pa versus 6.7 ± 1.1 Pa, respectively; p = 0.005).ConclusionsA prolonged period of abnormal haemodynamic exposure may result in increased aortic wall stiffening. The increased peak WSS as results of a reobstruction possibly promotes different disease progression, which endorse longitudinal follow-up examination of corrected coarctation patients.

Experimental Investigation on Mechanical and Acoustic Parameters of Different Depth Shale Under The Effect of Confining Pressure

Investigations on the effects of confining pressure and burial depth on mechanical and acoustic parameters are significant for studying the deep shale deformation, failure rule, and hydraulic fracturing. Shale specimens at six different depth levels ranging from 1535 to 1635 m have been collected from a shale gas well in southwest China. RTR-1000 rapid rock triaxial testing system has been applied to carry out the mechanical and acoustic experiments with 19 shale specimens. The experimental results revealed that the peak deviatoric stress, peak axial strain, peak volumetric strain, residual stress, and axial wave velocity are directly proportional to confining pressure and burial depth, whereas elastic modulus is not affected much by both confining pressure and burial depth and the Poisson ratio decreases with the increase of confining pressure. In the burial depth range 1535–1635 m, the variation of Poisson’s ratio is not obvious with the depth changes, and their relationship has high randomicity. The Wave velocity Anisotropy of tested shale is greatly affected by the degree of stratification development rather than the corresponding crustal stress. The coefficient of variation and the degree of stratification development are inversely proportional to burial depth. The axial wave velocity of shale is closely related to the loading process. In the compaction stage, wave velocity increases rapidly with the increase of strain. And in the elastic yielding stage, wave velocity increases slowly along with the strain build-up. This study will help to deepen the understanding of the physical and mechanical properties of Wuxi shale and guide the shale gas exploitation in China.

Stress wave evaluation for predicting the properties of thermally modified wood using neuro-fuzzy and neural network modeling

AbstractThis study investigated using the stress wave method to predict the properties of thermally modified wood by means of an adaptive neuro-fuzzy inference system (ANFIS) and neural network (NN) modeling. The stress wave was detected using a pair of accelerometers and an acoustic emission (AE) sensor, and the effect of heat treatment (HT) on the physical and mechanical properties of wood as well as wave velocity and AE signal is discussed. The AE signal was processed in the time and time-frequency domains using wavelet analysis and different features were extracted for network training. The auto-associative NN is used as a dimensional reduction method to decrease the dimension of the extracted AE features and enhance the ANFIS performance. It was shown that while the stress wave velocity using the accelerometer did not result in an accurate model, the network performance significantly increased when trained with the AE features. The AE signal exhibited a significant correlation with wood treatment and porosity. The best ANFIS performance corresponded to predicting the wood swelling coefficient, equilibrium moisture content (EMC) and water absorption (WA), respectively. However, the AE signal did not seem suitable for predicting the wood density and hardness. The performance of ANFIS was compared with the “group method of data handling” (GMDH) NN. Both the ANFIS and GMDH networks showed higher accuracy than the multivariate linear regression (MVLR) model.

Particle-scale insight into transitional behaviour of gap-graded materials – small-strain stiffness and frequency response

This study aims to develop a fundamental understanding of the role of fine particles on the small-strain stiffness of gap-graded granular soils. Stiffness was measured using cyclic triaxial probes, which give a measure of static stiffness, and dynamic wave propagation data, from which the dynamic stiffness can be measured. Assemblies of loosely packed spherical particles were considered. In the laboratory, local deformation transducers were used to measure the static stiffness, while the dynamic stiffness was calculated from stress wave velocities, measured using planar piezoelectric elements. To relate the particle-scale responses to the overall soil stiffness, complementary discrete element method (DEM) simulations were performed in which both static and dynamic stiffnesses were measured. Both the laboratory and the DEM data indicate that at low fines contents (&lt; 30%) the stiffness decreases with increasing fines content. When the fines content increases from 30% to 35% there is a sharp increase in stiffness with increasing fines content; this is understood to mark the transition point at which the fines start to contribute significantly to the overall behaviour. Analyses of the frequency domain response of shear wave signals revealed that the lowpass frequency increases significantly at this transition point. This observation can be used to develop experimental interpretation protocols to assess to what extent fines are contributing to the overall soil stiffness.

Relationship between the dynamic and static modulus of elasticity in standing trees and sawn lumbers of Paulownia fortune planted in Iran

This paper aims to introduce a relationship between the dynamic modulus of elasticity in healthy standing trees of Paulownia fortune (planted in Iran) and the static modulus of elasticity in sawn wood. For this reason, a stress-wave non-destructive testing technique was carried out in longitudinal and transverse directions in 14 trees into two diameter classes (25-31 cm and 32-38 cm) at breast height and in logs at different height of stem to measure the stress wave speed and consequently, dynamic modulus of elasticity. Then, static modulus of elasticity of samples was calculated using 3-point bending tests in the sawn wood. The results revealed that the stress-wave speed and dynamic modulus of elasticity in logs of paulownia are more than those of standing trees in longitudinal direction. Also, the diameter of the tree can significantly affect the stress wave velocity in standing trees and logs of paulownia. Finally, a high correlation coefficient exists between static modulus of elasticity and dynamic modulus of elasticity (r= 0.68) in this tree. Keywords: Modulus of elasticity, non-destructive testing, Paulownia, standing trees, stress-wave

Acoustic Velocity—Wood Fiber Attribute Relationships for Jack Pine Logs and Their Potential Utility

This study presents an acoustic-based predictive modeling framework for estimating a suite of wood fiber attributes within jack pine (Pinus banksiana Lamb.) logs for informing in-forest log-segregation decision-making. Specifically, the relationships between acoustic velocity (longitudinal stress wave velocity; vl) and the dynamic modulus of elasticity (me), wood density (wd), microfibril angle (ma), tracheid wall thickness (wt), tracheid radial and tangential diameters (dr and dt, respectively), fiber coarseness (co), and specific surface area (sa), were parameterized deploying hierarchical mixed-effects model specifications and subsequently evaluated on their resultant goodness-of-fit, lack-of-fit, and predictive precision. Procedurally, the data acquisition phase involved: (1) randomly selecting 61 semi-mature sample trees within ten variable-sized plots established in unthinned and thinned compartments of four natural-origin stands situated in the central portion the Canadian Boreal Forest Region; (2) felling and sectioning each sample tree into four equal-length logs and obtaining twice-replicate vl measurements at the bottom and top cross-sectional faces of each log (n = 4) from which a log-specific mean vl value was calculated; and (3) sectioning each log at its midpoint and obtaining a cross-sectional sample disk from which a 2 × 2 cm bark-to-pith radial xylem sample was extracted and subsequently processed via SilviScan-3 to derive annual-ring-specific attribute values. The analytical phase involved: (1) stratifying the resultant attribute—acoustic velocity observational pairs for the 243 sample logs into approximately equal-sized calibration and validation data subsets; (2) parameterizing the attribute—acoustic relationships employing mixed-effects hierarchical linear regression specifications using the calibration data subset; and (3) evaluating the resultant models using the validation data subset via the deployment of suite of statistical-based metrics pertinent to the evaluation of the underlying assumptions and predictive performance. The results indicated that apart from tracheid diameters (dr and dt), the regression models were significant (p ≤ 0.05) and unbiased predictors which adhered to the underlying parameterization assumptions. However, the relationships varied widely in terms of explanatory power (index-of-fit ranking: wt (0.53) &gt; me &gt; sa &gt; co &gt; wd &gt;&gt; ma (0.08)) and predictive ability (sa &gt; wt &gt; wd &gt; co &gt;&gt; me &gt;&gt;&gt; ma). Likewise, based on simulations where an acoustic-based wd estimate is used as a surrogate measure for a Silviscan-equivalent value for a newly sampled log, predictive ability also varied by attribute: 95% of all future predictions for sa, wt, co, me, and ma would be within ±12%, ±14%, ±15%, ±27%, and ±55% and of the true values, respectively. Both the limitations and potential utility of these predictive relationships for use in log-segregation decision-making, are discussed. Future research initiatives, consisting of identifying and controlling extraneous sources of variation on acoustic velocity and establishing attribute-specific end-product-based design specifications, would be conducive to advancing the acoustic approach in boreal forest management.

Stress wave evaluation by accelerometer and acoustic emission sensor for thermally modified wood classification using three types of neural networks

Classification of thermally modified wood (TMW) allowing the distinction between different processing temperatures and the corresponding changes in wood properties is a crucial task in TMW grading. In this study, stress wave evaluation technique was used to classify the heat treatment level. Accordingly, an acoustic emission (AE) sensor and a pair of accelerometers captured stress waves generated by pendulum impact, and the data was used to classify the heat treatment level of thermally modified Western hemlock wood samples. Sensory features were extracted from time, frequency, and wavelet domain analysis. The extracted features were then used to train multilayer perceptron (MLP), group method of data handling (GMDH), and linear vector quantization (LVQ) neural networks for TMW classification. The results showed that while the features extracted from the accelerometers such as stress wave velocity and wood dynamic modulus of elasticity showed poor classification performance, acoustic emission sensory features were effective for classification of TMW. Wavelet domain features lead to better classification than those extracted from time and frequency domains. Feature fusion approach comprising the features from all the signal domains showed the best classification performance that was further improved by using a dimensionality reduction approach. The linear discriminant analysis was conducted on all acoustic emission features and resulted in 91.1% and 89.1% accuracy obtained from the LVQ and GMDH network, respectively. This performance was further increased to 98% and 97% using the LVQ and GMDH models when the input was combined with wood moisture content. The MLP neural network did not seem as suitable as the other two models. Neural network modeling using the captured stress wave data from an AE sensor could therefore be a promising nondestructive evaluation method for TMW classification.

Image Reconstruction of Internal Defects in Wood Based on Segmented Propagation Rays of Stress Waves

In order to detect the size and shape of defects inside wood, an image reconstruction method based on segmented propagation rays of stress waves is proposed. The method uses sensors to obtain the stress wave velocity data by hanging around the timber equally, visualizes those data, and reconstructs the image of internal defects with the visualized propagation rays. The basis of the algorithm is precisely segmenting the rays to benefit the spatial interpolation. First, a ray segmentation algorithm using the elliptical neighborhood technique is proposed, which can be used to segment the rays and estimate the velocity values of segmented rays by the nearby original rays using elliptical zones. Second, a spatial interpolation algorithm utilizing a segmented ellipse according to the segmented rays is also proposed, which can be used to estimate the velocity value of a grid cell by the segmented ellipses corresponding to the nearby segmented rays. Then, the image of the internal defect inside the wood is reconstructed. Both simulation and experimental data were used to evaluate the proposed method, and the area and shape of the imaging results were analyzed. The comparison results show that the proposed method can produce high quality reconstructions with clear edges and high accuracy.

Predicting structural timber grade-determining properties using acoustic and density measurements on young Sitka spruce trees and logs

Abstract In Ireland, most structural timber from Sitka spruce (Picea sitchensis [Bong.] Carr.) is machine graded into C16 strength class. However, timber from early thinnings is mostly used for non-structural applications. There is an increased demand for structural timber, and timber from young trees could contribute to wood supply. However, this timber has lower mechanical properties than mature timber. In order to pre-sort the resource for structural application of wood from thinning, the possibilities of acoustic and density (D) measurements on young trees and logs have been investigated. The stress wave velocity (SWV) and pin penetration depth (PD) were measured on standing trees, which were then felled and cut into 10-m-long logs and subsequently into 3-m-long logs. Fundamental frequency was measured on logs. Finally, the logs were processed into boards, which were tested in accordance with EN 408 to obtain modulus of elasticity (MOE) in bending, bending strength (BStr) and D. The results showed good relationships between timber properties and acoustic and D measurements. Models for predicting grade properties of timber from thinnings are presented. Pre-sorting of young Sitka spruce trees and logs helped obtain higher C16 yields.

Solid Wood Properties Assessed by Non-Destructive Measurements of Standing European Larch (Larix decidua Mill.): Environmental Effects on Variation within and among Trees and Forest Stands

To avoid unintentional loss of wood quality when selecting for higher productivity in tree breeding programs, non-destructive methods for fast and reliable assessment of wood quality on standing trees are required. In this study, we tested and applied Pilodyn penetration (PP) and measures of stress wave velocity (SWV) in trees within a European larch (Larix decidua Mill.) breeding program. Through testing PP in 4267 trees on 21 afforestation sites across a broad climatic spectrum, we analysed the effects of climate, tree age, and site conditions on PP. Moreover, detailed measures within two selected stands allowed us to estimate measurement variation within and among trees in relation to the measurement angle and individual tree characteristics. We found significant variation of PP and SWV among forests stands, single trees, and even within trees, if measured on opposite sides in mountainous terrain. Both measurements exhibited a high degree of genetic determination, i.e., repeatability was 0.32–0.61 for PP and 0.56 for SWV, respectively. The obtained estimates for wood stiffness were comparable to measures on harvested wood samples of European or hybrid larch. Our results demonstrate that the integration of wood quality parameters into larch breeding programs is highly recommended, and reliable tools are available. Results are discussed in relation to environmental and measurement variation and methods to optimize field measurements are suggested.

Influence of soil plug effect on the vertical dynamic response of large diameter pipe piles

The influence of soil plug effect on the dynamic response of large diameter pipe piles during low-strain integrity testing is investigated based on the additional mass model, considering the soil plug weight and displacement phase difference between soil plug and pipe pile. An analytical solution that can consider the stress wave propagating both in the vertical and circumferential directions is derived in the frequency domain through the transfer function method. The corresponding quasi-analytical solution in the time domain for the pipe pile subjected to a vertical semi-sinusoidal impact force is then obtained by utilizing the Fourier transform technique. The validity and accuracy of the solution presented in this paper is compared against a series of model tests and field experiments of pipe pile. Utilizing the developed solution, a parametric study is performed to illustrate the influence of soil plug properties, pipe pile properties and the impulse width of impact force on the composite velocity of the longitudinal stress wave propagating in pipe pile, and the applicability of the plane-section assumption adopting in pipe pile.

Three-dimensional stress wave imaging of wood internal defects using TKriging method

In order to detect the size, shape and degree of decay inside wood, a three-dimensional stress wave imaging method based on TKriging is proposed. The method uses sensors to obtain the stress wave velocity data sets by hanging around the timber randomly, and reconstructs the image of internal defect with those data sets. TKriging optimizes structural relationship between interpolation point and reference point in space firstly. The searching radius is used to select the reference points accordingly. Top-k query method is introduced to find the k value with relevant points. The values of the estimated points are calculated and three-dimensional image of the internal defect inside wood is reconstructed. The results show the effectiveness of the method and the accuracy rate is higher than that of basic Kriging method.

Velocity Error Correction Based Tomographic Imaging for Stress Wave Nondestructive Evaluation of Wood

Stress wave testing has been applied in the nondestructive evaluation of wood for many years. However, the anisotropy property of wood and the limited number of sensors prevent an accurate stress wave velocity measurement and the high resolution of tomographic inversion. This paper proposes a tomographic imaging algorithm (IABLE) with a velocity error correction mechanism. The proposed algorithm computed the wave velocity distribution of the grid cells of wood cross-sections by the least square QR decomposition (LSQR) iterative inversion, and then optimized the tomography with a velocity error correction mechanism (ECM). To evaluate the performance of the proposed algorithm, several healthy and defective logs and live trees were selected as the experimental samples, and the nondestructive testing procedures were finished. With the stress wave velocity data sets measured via a PiCUS 3 stress wave testing instrument, the IABLE algorithm was implemented, and the tomographic images of the log samples and live trees were generated. The experimental results demonstrated the effectiveness of the proposed imaging algorithm for the nondestructive evaluation of wood.