Propagation Velocity Of Stress Wave Research Articles

Research on stress wave wood nondestructive testing technology

As a kind of nondestructive testing technology, stress wave technology has the advantages of long propagation distance, strong anti-interference ability and convenient use, and has become one of the important means to detect wood properties and defects at home and abroad. This paper introduces several stress wave wood testing equipment commonly used in the field of wood non-destructive testing at this stage, and analyzes its characteristics. The research status of stress wave wood nondestructive testing technology is analyzed from three aspects: mechanical property testing, internal defect testing and factors affecting stress wave propagation velocity. Finally, the existing problems and development trends of stress wave technology in wood nondestructive testing are discussed to provide reference for further research in this field.

Predictive model of the modulus of elasticity in static bending (MOE) of larch wood based on gray relation analysis (GRA) and gene expression programming (GEP)

To accurately evaluate the modulus of elasticity in static bending (MOE) of wooden components in ancient timberwork buildings under the “minimum intervention principle,” the nondestructive testing of physical and mechanical properties were conducted on larch. Using moisture content (MC), density (ρ), the stress wave propagation velocity ( ), the modulus of elasticity in dynamic bending (Ed), the rotational resistance value of the drilling needle (fdrill), and the resistance value of the feeding needle (ffeed) as the main parameters, the correlation between several parameters and MOE was firstly calculated using the Gray Relation Analysis (GRA) and ranked according to the strength of the correlation. Six combinations were selected according to the ranking, and the Gene Expression Programming algorithm (GEP) was used to build models for predicting MOE. The results showed that the correlation between several parameters and MOE was good (between 0.5 and 0.8), and the prediction model established with combination 6 was the best, which indicated that the prediction model established based on GRA-GEP algorithm had a certain feasibility and effectiveness, and the combined effect of the six parameters to evaluate the MOE of wooden components of ancient buildings was better in the field inspection.

Propagation velocity model and two-dimensional defect imaging of stress wave in larch (Larix gmelinii) wood

The propagation law of stress wave in larch (Larix gmelinii) wood was studied in this work. External factors affecting the propagation velocity of stress wave in wood cross-section were studied using the orthogonal experiment method. The most influential factors were shown by the experimental results, and the parameters of the propagation velocity model of stress wave in larch wood were optimized. Based on the optimized propagation velocity model, combined with the traditional defect determination method, a twelve-directional stack imaging (TDSI) steps system was developed for larch wood internal defect detection. The analysis results showed that of the three external factors of temperature, moisture content, and illumination duration, temperature had the greatest influence on the propagation velocity model of stress wave in larch wood cross-section. Using TDSI to image the defective larch wood not only can locate the defective area, but also it can achieve a high imaging precision of 95.52%, and the imaging precision is unrelated to the location of the defect, which has a good quantitative defect detection effect.

Study on dynamic fracture behaviour and fracture toughness in rock-mortar interface under impact load

The stability of grouting reinforced rock structures under impact loading mainly depends on the interface strength between rock and mortar. In this paper, a Bi-material Single Cleavage Triangle (BSCT) specimen was employed in a split Hopkinson pressure bar experiment to investigate the dynamic fracture of the rock-mortar interface under impact loading. The interfacial roughness of the specimen was considered in the experiment as well as the loading rates effect. The crack extension velocity in the interface was obtained by the Crack Propagation Gauge (CPG). The stress wave propagation behavior and failure mechanism in the interface were analyzed by the AUTODYN software. Notably, the Complex Stress Intensity Factors (CSIF) were calculated by using the experimental–numerical method. The results show that interfacial roughness and loading rate have a great effect on interfacial fracture behaviour. Compared with the granite-mortar specimen, the stress wave propagation velocity in the sandstone part and mortar part are very close, making it hard to find shear failure in the sandstone-mortar interface. The interfacial crack propagation velocity of the sandstone-mortar specimen may outpace the Rayleigh wave in the intact sandstone. The complicated relationship amongst the loading rates, interfacial roughness, and parameter K1 of the CSIF has been unveiled elaborately in the present paper.

Propagation velocity model of stress waves in larch wood (Larix gmelinii) three-dimensional space with different moisture contents

Based on the effects of stress wave propagation in larch (Larix gmelinii) wood, the propagation mechanism of stress wave was explored, and a theoretical model of the propagation velocity of stress waves in the three-dimensional space of wood was developed. The cross and longitudinal propagation velocities of stress wave were measured in larch wood under different moisture contents (46% to 87%, 56% to 96%, 20% to 62%, and 11% to 30%) in a laboratory setting. The relationships between the propagation velocity of stress waves and the direction angle or chord angle with different moisture contents were analyzed, and the three-dimensional regression models among four parameters were established. The analysis results indicated that under the same moisture content, stress wave velocity increased as the direction angle increased and decreased as chord angle increased, and the radial velocity was the largest. Under different moisture contents, stress wave velocity gradually decreased as moisture content increased, and the stress wave velocity was more noticeably affected by moisture content when moisture content was below the fiber saturation point (FSP, 30%). The nonlinear regression models of the direction angle, chord angle, moisture content, and the propagation velocity of stress wave fit the experiment data well (R2 ≥ 0.97).

Condition assessment tool for timber utility poles using stress wave propagation technique

ABSTRACT Timber utility poles are significantly used in power and telecommunication infrastructures all over the world. The deterioration of timber with time is common due to various factors including termite attacks and climatic conditions. Failure of poles can have serious safety concerns and economic implications. Hence, the condition assessment of timber poles is important for safe and economical operation of the power network. This paper presents the development and application of a non-destructive testing tool using stress wave propagation technique for the condition assessment. Shear waves are generated in timber poles by the application of transverse impacts and both the generated and reflected waves are recorded for further analysis. Short Kernel Method is used as a signal processing technique to address the dispersive nature of the generated shear waves and developed technique is validated with numerically simulated signals using ANSYS finite element programme. The pole condition estimation software is developed and implemented within the tool for on-site assessment. The developed tool is tested using laboratory and field-collected signals from in-service poles. Further, the effects of pole length, age and diameter for stress wave propagation velocity are investigated with the use of a database of collected stress waves using the developed equipment.

Theoretical and experimental research on moisture content and wood property indexes based on nondestructive testing

A set of reformulated theoretical formulas was developed to measure the relationships between moisture content (MC) and stress wave propagation velocity, dynamic modulus of elasticity ( “E” _”d” ), and modulus of stress-resistograph of the wood. The theory of wood science, elastic mechanics, wave science, and stress wave propagation were used as the theoretical basis. Using larch as the material, both stress wave and micro-drilling resistance technologies were used to study the timber property changes under different moisture contents. The results showed that when the MC of wood did not reach the fiber saturation point (FSP), the wood property decreased sharply with increased MC. However, the study also found that when the MC of wood was higher than the FSP, the wood property decreased with increased MC. In addition, the experimental results showed that the variation trend calculated by the new set of theoretical formulas was consistent with the numerical variation trend measured by the experiment, and the coupling effect of stress wave and micro-drilling resistance was high. This set of theoretical formulas can provide a reference for the research on nondestructive testing and performance evaluation of ancient building timber.

A coupling model based on grey relational analysis and stepwise discriminant analysis for wood defect area identification by stress wave

Based on the experimental idea of reverse simulation, a quantitative area of hole was excavated at the sectional center of a wood specimen. The excavation area was 1/32S, 1/16S, 1/8S, 1/4S, and 1/2S (where S represents cross-sectional area of the complete specimen) and stress wave nondestructive testing of six sensors was performed. The stress wave propagation paths were statistically summarized to obtain the stress wave propagation velocity (Va) for two adjacent sensors, the stress wave propagation velocity (Vb) for two separated sensors, and the stress wave propagation velocity (Vc) for two opposite sensors. Furthermore, by analyzing the advantages and disadvantages of grey relation and stepwise discriminant model when both of them were used alone, a coupling model generated from them was established to dispose the test data. The attenuation ratios Ψa, Ψb, and Ψc of stress wave under three propagation paths and their relation ratios Va/Vb, Vb/Vc, and Va/Vc, a total of six groups of measured data, were selected as discriminant factors for the hole area grade of the wood specimen. The verification results showed that the discriminant accuracy of the coupling model was 100%, and it was concluded that the attenuation ratio (Ψb) of the stress wave propagation velocity for two separated sensors had the strongest discriminant ability against cross-sectional area of the specimen.

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.

Influence of moisture content on estimating Young’s modulus of full-scale timber using stress wave velocity

The effect of moisture content on the stress wave propagation velocity was investigated in order to estimate the Young’s modulus of full-scale timbers in an air-drying state using the measurement of stress wave propagation velocity above the fiber saturation point. Using Japanese cedar lumber, the velocity and the density under high-moisture condition and air-drying states were measured respectively; after measuring the modulus of elasticity in an air-drying state, the moisture content of each condition was measured. By performing numerical analysis on these data, the relationship between the moisture content and the rate of change of velocity of full-scale timbers was derived. This relationship was used to estimate the Young’s modulus of the timber in the air-drying state from the velocity in high-moisture condition. First, the velocity and the Young’s modulus in an air-drying state were estimated accurately from its density, moisture content and velocity under high-moisture condition. In cases where the density could not be measured, using the database of mechanical properties with the Monte Carlo simulation method, the Young’s modulus of the full-scale timber in an air-drying state might be estimated within 20% accuracy from its moisture content and velocity under high-moisture condition.

An improved multidirectional velocity model for micro-seismic monitoring in rock engineering

An improved multidirectional velocity model was proposed for more accurately locating micro-seismic events in rock engineering. It was assumed that the stress wave propagation velocities from a micro-seismic source to three nearest monitoring sensors in a sensor’s array arrangement were the same. Since the defined objective function does not require pre-measurement of the stress wave propagation velocity in the field, errors from the velocity measurement can be avoided in comparison to three traditional velocity models. By analyzing 24 different cases, the proposed multidirectional velocity model iterated by the Simplex method is found to be the best option no matter the source is within the region of the sensor’s array or not. The proposed model and the adopted iterative algorithm are verified by field data and it is concluded that it can significantly reduce the error of the estimated source location.

Simulation Research of Blasting Vibration Prediction with Cylindrical Dynamite

Blasting vibration not only damages architectural structures but also harms people heath. Numerical simulation provides an effective method to study explosion and shock problems. Herein, the paper performed numerical simulation to predict blasting vibration. At first, analyzed the propagation velocity of stress wave, which validated the feasibility of the model. The simulation and test agreed well both at vibration waveform and at the order of magnitude of both nodes 1 and 2. The simulation could provide reasonable accuracy. The achievement provided reference for other researches.

Determining Young’s modulus of timber on the basis of a strength database and stress wave propagation velocity II: effect of the reference distribution database on the determination

A method of determining the Young’s modulus of timber using the stress wave propagation velocity without knowing the timber density was developed in our previous study. This method enables the estimation of Young’s modulus by Monte Carlo simulation using an existing database of the Young’s modulus versus density relationship as reference. Here, in Part II, we consider the effect of the reference distribution database on the accuracy of the estimated Young’s modulus by the developed method. Twelve different reference distribution databases were used in this study, containing Young’s modulus versus density data for more than 13 000 real-size timber specimens of ten different species. We obtained the following results: (1) the distribution of Young’s modulus estimated using an arbitrary stress wave propagation velocity depends on the reference distribution database employed, (2) the most important factor is not that the reference database has data on the same species as the timber in the test, but rather that the reference distribution database covers the foreseeable range of timber densities within the test, and (3) the estimation accuracy is higher than about 80% when the database covers many species and has wide ranges of densities and Young’s moduli. This estimation method was developed in order to measure the Young’s modulus of timber whose density cannot be measured. Considering that the quality of lumber has a large variation, such estimation accuracy will be useful for practical applications.

Determining Young’s modulus of timber on the basis of a strength database and stress wave propagation velocity I: an estimation method for Young’s modulus employing Monte Carlo simulation

In this article, we report on an estimation method for Young’s modulus that entails measuring only the stress wave propagation velocity of timber built into structures such as wooden buildings. Methods of estimating Young’s modulus that use the stress wave propagation velocity and characteristic frequency of timber in conjunction with timber density have long been used. In this article, we propose a method of easily and accurately estimating Young’s modulus from the stress wave propagation velocity without knowing the timber density. This method is based on a database of wood strength performance and density accumulated from a variety of research data and the method estimates Young’s modulus by a simulation method. We compared the Young’s moduli estimated by this method with those obtained by the bending test and by the measurement of the stress wave propagation velocity and density, and found similar results. This coincidence suggests that the method of estimating Young’s modulus presented in this article is valid. For example, the method is effective for convenient evaluation on site when determining whether a wooden building’s structural components should be reused or replaced when repairing or remodeling a building.

A comparative study on the velocities of stress wave propagation in standing Fraxinus mandshurica trees in frozen and non-frozen states

In order to improve the accuracy and reliability of identifying wood defects and to realize the maximum wood utilization of trees, we employed an experimental method to test the stress wave propagation velocity in standing Fraxinus mandshurica trees selected from the Harbin Forest Experimental Station in winter. Thirty standing trees in good conditions were taken as test specimens and stress wave propagation velocities were measured using a FAKOPP Microsecond Timer in trees in both fall and winter. The test data were processed with the aid of Excel and SPSS software. The results show that 1) the velocities in longitudinal and radial stress wave propagation in frozen F. mandshurica trees were much higher than those in the non-frozen trees; 2) there was a highly positive correlation between longitudinal stress wave propagation velocity in frozen and non-frozen states, with a correlation coefficient of 0.82, as well as a positive correlation between radial stress wave propagation velocity in frozen and non-frozen states with a correlation coefficient of 0.87; 3) in the frozen state, the longitudinal stress wave propagation velocity was significantly affected by the moisture content (MC) of standing tree, while it was not obvious in the non-frozen state and 4) the radial stress wave propagation velocity was not significantly affected by MC in either frozen or non-frozen state.

Analysis and numerical simulation of dynamic effect on rock under high pressure water jet

Based on continuum mechanics and rock dynamics, analyzed the micro-structure damage of rock and the impulsive effect under high pressure water jet and developed the dynamic model. Further, on the assumption of that rock was homogeneous and isotropic, a computational model was established based on nonlinear finite element and Arbitrary Lagrangian-Eulerian(ALE) method. The dynamic effect impacted on rock under high pressure water jet was simulated by the dynamic contact method. The propagation of stress wave in rock was numerically simulated at different impacting velocity. The results show that the propagation velocity of stress wave is proportional to the impacting velocity of high pressure water jet. The faster the impacting velocity is, the quicker the comedown of stress wave.

Polymer Effects on the Vibration Damping Behavior of Cement

In this paper, the vibration damping properties of polymer-modified-cement (PMC) have been studied. The storage modulus (E′) and loss tangent (tan δ ) of PMC were studied by using a free vibration method. The propagation velocity of stress wave V and the scattered damping of stress wave in PMC were studied by using an ultrasonic testing method. When a suitable polymer is added in the cement, the storage modulus, the velocity of stress waves are decreased with an increase of the polymer/cement ratio (P/C), and the loss tangent is increased with an increase of P/C, thus the ability to vibration damping of PMC is improved. As the P/C is between 15 and 20%, the PMC demonstrates the best vibration damping within the adopted range of testing.

Dynamic properties impact toughness and abrasiveness of polymer-modified pastes by using nondestructive tests

This paper reports on the results of a study of the dynamic properties impact toughness and abrasiveness of polymer-modified pastes (PMPs) using a styrene–acrylic ester copolymer emulation. The dynamic elastic modulus E d and the specific damping capacity Y of PMP were studied using a free vibration method. The propagation velocity of stress wave V and the scattered damping of stress wave in PMP were studied using an ultrasonic testing method. The impact toughness and abrasiveness were also studied. The dynamic modulus and the velocity of stress wave decreased with an increase in polymer–cement ratio (P/C) by mass. The specific damping capacity, impact toughness, and abrasiveness increased with an increase in P/C, thereby improving the ability of PMP to resist dynamic loads. When P/C is 15–20%, PMP demonstrates the best dynamic behaviour within the adopted range of testing.

On the evaluation of crack propagation velocity by the observation of stress waves created during tensile fracture

The purpose of the work described in this paper is to study the relation of crack propagation velocity to stress variation arising due to the arrival of a longitudinal unloading wave created during a tensile fracture. The time dependent stress due to the compression wave emanated from the rupture section of the notched round bar specimen of annealed JIS-SS41 steel is observed using the strain gage method. The same problem is theoretically analyzed by postulating three different crack growth models. A crack front of circular shape possessing a radius which increases at a constant rate ( c o k ) with time is assumed, where c o is the propagation velocity of the elastic stress wave and k is the crack velocity factor determined by comparing the experimental results with the theory.

Stress wave propagation in a medium with internal friction

1. On the basis of a dilatancy model of the plasticity of a rock mass [1] elastic-plastic relationships between the stress and strain are deduced for complete and incomplete plasticity. 2. Dilatancy laws are obtained for cylindrical and spherical symmetry. 3. Cylindrical and spherical wave propagation is considered by solving the dynamics equations within the framework of the model mentioned. 4. The laws obtained for the stress wave propagation velocity and the damping of the maximal amplitudes in the wave are in agreement with those in [3] and correspond to test results. 5. A piecewise-continuous approximation of the variable A is indicated that agrees with experiments. 6. The applicability of the model to the description of rock mass properties under dynamic loading is shown.