Stress Wave Velocity Research Articles

Planar impacts on nanocrystalline SiC: a comparison of different potentials

Silicon carbide ceramics under shock loading is an important aspect in studying their physical and mechanical properties. Molecular dynamics simulations have been carried out using Tersoff-1989, Tersoff-1994, Tersoff-2005 and Vashishta potentials, respectively. The Hugoniot states including compression stress, shear stress, temperature and shock wave velocity are calculated, as well as shock-induced plasticity and the shock wave fronts. A comprehensive comparison among different potentials, as well as comparison to current available experiments, has been made. Tersoff-1989, Tersoff-1994 and Tersoff-2005 potentials are easily to overestimate the shock stress, shear stress and temperature, as well as shock wave velocity, while Vashishta potential shows excellent agreement with experimental data. The Hugoniot elastic limit is ~ 14.5 GPa and the maximum shear stress is ~ 6 GPa using Vashishta potential which are in good agreement with experiments, while Tersoff-like potentials yield much higher values. Due to differences in radial distribution function among these potentials, Vashishta potential is prone to produce plasticity and structural phase transformation basing on the statistics of the coordination numbers of atoms. Besides, the shock wave fronts show little difference among these potentials under elastic shock compression at low particle velocity. However, when it comes to high shock intensity resulting in plasticity or phase transition, the Tersoff-1989 and Tersoff-1994 produce the widest shock wave fronts, followed by Tersoff-2005, while Vashishta potential has the narrowest wave front. By comprehensive comparisons, the Vashishta potential is demonstrated to be the most suitable one to describe the silicon carbides ceramics under shock loadings. Our work provides useful information to select a suitable potential to study the shock response of silicon carbides ceramics using molecular dynamics simulations.

Growth Characteristics and Wood Properties of Two Interspecific Eucalyptus Hybrids Developed in Indonesia

Abstract The aim of this study was to clarify the wood properties of two interspecific Eucalyptus hybrids, Eucalyptus grandis × Eucalyptus pellita (G×P) and E. grandis × Eucalyptus urophylla (G×U), developed in Indonesia. The growth characteristics and stress-wave velocity (SWV) were evaluated for 102 trees from three clones of the G×P hybrid and 105 trees from three clones of the G×U hybrid. Wood properties, such as basic density, shrinkage, compressive strength, modulus of elasticity, and modulus of rupture, were evaluated from nine selected trees of each clone. The G×U hybrid had better tree growth and SWV compared with those of the G×P hybrid. No negative correlation coefficients were observed between growth characteristics and SWV, indicating that the selection of clones for increased wood volume does not reduce their mechanical properties. Hybridizations between E. grandis and E. pellita or E. urophylla showed that E. grandis dominated the growth characteristics with some refinements in the wood properties, especially compressive strength, in the G×P hybrid. Selection based on the superior clones for tree growth would result in higher wood productivity for timber use in these two hybrids.

Geographic variations of wood properties of <i>Larix sibirica</i> naturally grown in Mongolia

Geographic variations in growth, stress-wave velocity of stem, dynamic Young’s modulus of stems and logs, annual ring width, latewood percentage and basic density were investigated for (Münchh.) Ledeb. naturally grown in Mongolia. A total of 250 trees with 20 to 30 cm in stem diameter at a height of 1.3 m above ground level were selected from each natural stand in five different provenances in Mongolia. In addition, five trees in each stand were cut for measuring dynamic Young’s modulus of stems and logs, annual ring width, latewood percentage and basic density. Mean values of stress-wave velocity of stems in each stand ranged from 2.92 to 3.41 km s, and the mean value of five stands was 3.23 km s. Mean values of dynamic Young’s modulus of logs in each stand ranged from 5.17 to 9.72 GPa. A significant correlation ( = 0.798,  < 0.01) was found between stress-wave velocity of stems and dynamic Young’s modulus of logs. Among the five stands, the highest and the lowest values of average annual ring number were 193 and 44, respectively. Mean values of basic density in five trees within each stand were examined and ranged from 0.52 to 0.56 g cm. Significant differences among five stands were found in tree height, stress-wave velocity of stem, dynamic Young’s modulus of stems and logs, annual ring width and latewood percentage, suggesting that trees naturally grown in Mongolia have geographic variations in mechanical properties of wood.Larix sibirica–1–1rp–3L. sibirica

Anatomical characteristics and wood properties of unutilized Artocarpus species found in secondary forests regenerated after shifting cultivation in Central Kalimantan, Indonesia

The anatomical characteristics and wood properties of Artocarpus species naturally regenerated in secondary forests in Central Kalimantan, Indonesia, were investigated to determine their usefulness as alternative wood resources. The following six Artocarpus species were used in the present study: A. dadah, A. nitidus, A. elasticus, A. tamaran, A. anisophyllus, and A. odoratissimus. The mean value of stress-wave velocity was 3.22 km s−1 for 12 trees from the six Artocarpus species. Among the six species, A. dadah, A. nitidus, and A. odoratissimus showed relatively higher stress-wave velocity values compared to those of other tropical commercial plantation species, indicating that the woods in these three Artocarpus species have higher values of Young’s modulus. The mean values for the anatomical and other wood properties of the 12 trees of the six Artocarpus species were as follows: vessel diameter, 150 µm; vessel element length, 0.41 mm; fiber diameter, 19.8 µm; fiber wall thickness, 1.28 µm; fiber length, 1.34 mm; basic density, 0.50 g cm−3; compressive strength parallel to grain at green condition, 31.2 MPa. Basic density was positively correlated with compressive strength, suggesting that the mechanical properties of Artocarpus species can be predicted by measuring the basic density. Based on the results, the six Artocarpus species used in the present study could produce solid lumber for construction, furniture, and other uses, suggesting that these species might be alternative tree species for lumber production in agroforestry in Asian countries.

Accuracy and Reproducibility of Acoustic Tomography Significantly Increase with Precision of Sensor Position

Acoustic tomograms are widely used in tree risk assessment. They should be accurate,repeatable and comparable between consecutive measurements. Previous work has failed to address the effects of different approaches to record sensor positions, operators and models of tomograph on the resulting tomograms.In this study, three operators used the two most common sonic tomographmodels to measure seven cross-sections of Norway spruce trees, whichwere felled after the measurement. We evaluated the effects of model, operator, and different approaches to measure sensor positions on the quality of the tomograms.The largest source of error was the position of sensors, affectingestimated stress wave velocity, the shape of the tomogram, and the sizeof the defect.To produce accurate and repeatable tomograms of trees with complex shapes,it is essential to measure the sensor positions precisely.

Wood properties of 7-year-old balsa (Ochroma pyramidale) planted in East Java

ABSTRACTThe effect of radial growth rate on wood properties was evaluated for 7-year-old balsa trees grown in plantation forest in East Java, Indonesia. The standing trees in the experiment site in the plantation were categorised into three groups (slow-, medium-, and fast-growth) according to their stem diameter. Mean values of stem diameter, tree height, and stress-wave velocity (SWV) were 311 mm, 25.4 m, and 2.96 km/s, respectively. No significant correlations were found between growth characteristics and SWV of stems. The mean values of basic density, compressive strength parallel to grain, modulus of elasticity, and modulus of rupture were 0.14 g/cm3, 10.4 MPa, 4.53 GPa, and 22.9 MPa, respectively. The wood properties were almost constant up to 80-mm from the pith, and then they sharply increased toward the bark. Therefore, separation of the wood at around 80 mm from the pith is likely to be useful for wood industries.

Wood Properties of Three Fruit Tree Species Planted in Central Kalimantan, Indonesia

The objective of this study was to evaluate the properties for wood utilization of fruit trees planted in Central Kalimantan, Indonesia. A total of 9 jambu bol (Syzygium malaccense), rambutan (Nephelium lappaceum), and durian (Durio zibethinus) trees were randomly selected from the plot (20 by 30 m) and measured for stem diameter, tree height, stress-wave velocity (SWV), and Pilodyn penetration of the trees. Mean values of stem diameter were 11.8, 15.9, and 29.3 cm for S. malaccense, N. lappaceum, and D. zibethinus, respectively. Mean values of stress-wave velocity were 3.16, 3.95, and 3.63 km/s for S. malaccense, N. lappaceum, and D. zibethinus, respectively. Core samples (5 mm in diameter) were collected from these trees to investigate the wood properties [basic density (BD) and compressive strength parallel to grain (CS)], anatomical characteristics [vessel diameter (VD), cell wall thickness (CWT) in wood fiber, and cell length (CL) of wood fiber and vessel element], and amounts of chemical components. In VD, CWT in wood fiber, and CL in wood fiber and vessel element, almost the same radial variation patterns were found in the three species. Relatively higher values in SWV, BD, and CS were found in N. lappaceum, suggesting that its wood can be used for construction lumber. On the other hand, S. malaccense and D. zibethinus had relatively thicker CWT in wood fiber, longer CL in wood fiber, and lower Klason lignin content. It is considered that the wood of these two species may be suitable for pulpwood.

Relationship between Growth and Wood properties in Agathis sp. Planted in Indonesia

The present study clarified the relationship between the growth and wood properties of 54-year-old Agathis sp. trees planted in Indonesia. Stem diameter, pilodyn penetration, and stress-wave velocity (SWV) were measured for all trees (35 trees) in a plot (30  30 m) located almost at the center of a stand. Based on the mean stem diameter, 10 standard trees in a plot were selected for measuring the basic density (BD) and compressive strength parallel to grain (CS). Core samples (5 mm in diameter) were collected from the 10 selected trees to determine BD and CS. The mean stem diameter, pilodyn penetration and SWV in the plot were 40.2  11.3 cm, 23.4  2.1 cm, and 3.85  0.43 km/s, respectively. No significant correlation coefficeint (r = -0.327, no significance at 5% level) was obtained between stem diameter and SWV. The mean BD and CS in the 10 trees were 0.42  0.03 g/cm3 and 28.1  2.7 MPa, respectively. A significant positive correlation was observed between BD and CS. Analysis of variance (ANOVA) revealed a significant difference between BD and CS values of the 10 trees, indicating that wood properties may differ among trees with the same standard growth in a stand. From these results, we concluded that wood quality improvement in this species could be achieved by selecting trees with high density and strength in tree breeding programs.

Synchronicity of Stress Wave Propagation in Bolt Body and Anchorage Medium

Accurate assessment of anchoring quality depends on the accuracy of assessing stress wave velocity in the anchor system. Stress wave velocity is closely related to collaborative vibration and depends on the degree of bonding between anchor body and anchorage medium. Bonding differences can be large at different ages. Based on stress wave reflection methods, non-destructive testing of anchors was performed using sensors arranged at the same cross-section of the anchor body and anchorage medium, which showed stress wave synchronization. In the early stage of filling, stress wave synchronicity was poorer between the anchor body and mortar. Therefore, the anchor should not be treated as a composite material when determining its wave velocity. Once the mortar hardens, the stress waves become more synchronous and the anchor can be regarded as a composite material. Stress wave synchronicity between the anchor body and mortar is related to mortar age and anchorage length. The anchor length required to provide stress wave synchronization between the anchor body and mortar decreases with increasing mortar age. Stress wave velocity rules were derived for different ages to provide the basis for accurately determining the stress wave velocity in the anchor.

Stress wave mitigation at suture interfaces

This study investigated the stress wave dissipation in sinusoidal patterned suture interfaces that were inspired by sutures in biological materials. Finite element results showed that a sutured interface decreased the pressure 37% more than that at an unsutured interface, which arose from wave scattering and greater energy dissipation at sinusoidal boundaries. Stress wave scattering resulted in converting compressive waves (S11) into orthogonal flexural (S22) and shear waves (S12), which decreased both the peak pressure (attenuation) and wave speed (dispersion). Higher strain energy occurring at sutured interfaces brought energy loss within viscoelastic gap, too. In addition, we parameterized several variables related to the suture interfaces for their influence in stress wave mitigation. The following seven parameters were examined: (1) waviness of suture (ratio of suture height to suture period), (2) ratio of the suture height over the entire bar thickness, (3) gap thickness, (4) elastic modulus, (5) type of the boundary, (6) impact amplitude, and (7) impact duration. The final result of the parametric study revealed that the high ratio of the suture over the entire bar thickness had the greatest influence, followed by the short impact duration, and then by the low elastic modulus. Additionally, a high ratio of the suture over the entire bar thickness and low elastic modulus decreased the stress wave velocity as well. These findings can be applied for designing various synthetic damping systems so that manmade engineering designs can implement the optimized sutures for impact scenarios.

Coupling effects of inertia and dual-phase-lag heat conduction on thermal shock fracture of a cracked piezoelectric layer

This paper studies the thermal shock fracture mechanics of a piezoelectric material thin layer with an internal crack. The typical model I and model II cracking problems are separately considered. The analyses are based on the dual-phase-lag, non-Fourier heat conduction theory with consideration of material inertia. Laplace transform and dual integral equation technique are applied to solve the problems. Some numerical results of the stress intensity factor and energy release rate are obtained and drawn in figures. It is demonstrated that the effect of the inertia on the fracture behavior depends on the ratio of the thermal wave speed to the stress wave velocity. In addition, the large ratio of the temperature gradient lag to the thermal flux lag will greatly enhance the mode I and mode II stress intensity factors.

Stress wave propagation in Boron-Nitride nanotubes

The propagation of axial stress waves in Boron-Nitride nanotubes of different chirality and length under adiabatic conditions has been studied using molecular dynamics (MD) simulations. The velocities of the axial stress waves are found using three methods - (i) direct MD simulations, (ii) harmonic approximation of the nanotubes, and (iii) one-dimensional (1-D) wave equation. The MD simulation results indicate a small dependence of the wave velocities on the nanotube chirality and the excitation frequency – in armchair and zigzag nanotubes waves travel faster than that in chiral nanotubes, and wave velocities decrease with an increase in the frequency of excitation. The wave speed obtained from the harmonic approximations is ≈20–25% higher than that found from the MD simulations. Likewise, the frequencies of vibrations from the two approaches differ by 15–20% for most of the cases. The computation of the wave speed from 1-D equation requires a prior knowledge of the elastic modulus and the nanotube wall thickness. The values of these parameters are found from MD simulation results – axial tensile tests provide an estimate of the wall thickness scaled elastic modulus and the transverse vibration data relates the standard deviation of the tip displacement with material properties of the nanotube. The wave speed predicted from the 1-D wave equation agrees with that obtained from the MD simulations at low excitation frequencies. The contribution of the anharmonicity to the dynamics during wave propagation is found by matching the response of the anharmonic Fermi-Pasta-Ulam chain with the MD simulation results.

Experimental Study on Working Stress of Concrete Based on Ultrasonic Testing

naturally cured to different ages, to acquire the ultrasonic wave velocity of the test blocks under different ages and working stresses. On this basis, the authors analyze how the ultrasonic wave velocity changes with the age and working stress, and fit the relationship between working stress of concrete and ultrasonic wave velocity. The results show that the ultrasonic wave velocity grows with the age of concrete, but the growth rate slows down over time; the working stress of the concrete has a good correlation with the ultrasonic wave velocity, and the relationship between working stress and ultrasonic wave velocity is well described by the linear function and quadratic polynomial function.

The Effects of Radial Growth Rate on Wood Properties and Anatomical Characteristics and an Evaluation of the Xylem Maturation Process in a Tropical Fast-Growing Tree Species, Gmelina arborea

Abstract The aim of this study was to evaluate the effects of radial growth on wood properties and anatomical characteristics and to clarify the xylem maturation process in Gmelina arborea. Stem diameter, tree height, and stress-wave velocity were investigated for 54 5-year-old G. arborea trees planted in Indonesia. In addition, radial variations of wood properties (basic density and compressive strength parallel to the grain in green condition) and anatomical characteristics (fiber and vessel morphologies) were investigated for nine trees selected from three different radial growth categories (fast, medium, and slow growing). Stem diameter was positively significantly correlated with stress-wave velocity and compressive strength parallel to the grain in green condition. In addition, compressive strength and anatomical characteristics, except for wood fiber diameter, differed significantly among the radial growth categories. Radial variations of the wood properties and anatomical characteristics gradually increased, and then they showed constant values toward the bark. It is thought that the xylem maturation of G. arborea begins at approximately 5 cm from the pith. In addition, in a fast-growing tree species, such as G. arborea, the trees with faster stem diameter do not always form wood with low strength properties.

LONG-TERM IMPACTS OF GROUND SKIDDING ON STANDING TREES: ASSESSMENT OF DECAY USING STRESS WAVES

Timber harvesting and log extraction with conventional ground-based skidding systems in steep, mountainous terrain often results in severe damage to residual stands and forest sites. In this study, the impact of rubber-tired skidders on standing trees along sides of the trails was investigated 5 to 20 years post-harvest in terms of frequency and development of decay at the points of wounding. The study was located in the Hyrcanian mountainous forests of Iran. All standing beech trees (healthy or wounded) were evaluated on both sides of the skid trails; four age classes (determined in relation to time since logging) were selected in chronosequence over 20 years (four 5-year classes) in a managed forests. Stress wave velocity was tested in three directions (on wound, perpendicular to wound and longitudinal directions on trunk) of each standing tree located along sides of trails to characterize the trunk decay. In order to compare the results with a reference wave velocity, 20 healthy beech trees were selected in a non-harvested area. Totally 205 standing beech trees were investigated using stress wave. Results showed that more than 75% of the standing trees located up to 1.5 m from both sides of the skid trails had been injured by skidding operations. Among these, about 24.8% had been decayed as a result of wounding. Most of the decayed trees were observed down slope along the trails and also on both sides of the curves. The percentage of decayed trees and decay intensity were boosted with increasing the age of skid trails from 10 to 20 years. However, traffic intensity had no effect on tree decay. Based on the results of this study, durable injuries were produced on standing beech trees in areas affected by skidder movements; however, many of these injuries were easily prevented.

COMPARISON OF PROPAGATION CHARACTERISTICS OF EXCITED STRESS WAVES IN PILE AND ANCHORAGE WITH BOLT SYSTEMS

Dynamic testing methods for pile systems and anchorage-with-bolt systems are similar andoften confused with each other, possibly resulting in incorrect assessment of the quality of the pileand the anchorage systems. The stress wave velocity is one of the most important parameters forevaluating the quality of dynamic tests. In this paper, the stress wave velocities in standardconcrete specimens of the free rock bolt and the different ages were a reference for comparing thestress wave velocities in a pile-and-anchor system. The tests were conducted using the low strainreflected wave method. Results indicate that the wave velocity in a pile is larger than that in thestandard samples, and that the wave velocity in an anchorage-with-bolt system is smaller than thatin a free steel bar, but larger than that in a pile and in standard samples. Wave velocities in the pileand in the standard samples were found to raise as the ages of samples increased. The wavevelocity in the anchorage-with-bolt system initially decreased as specimen age increased, butincreased with increasing specimen age afterward.

MOE and MOR assessment of in service and dismantled old structural timber

81 timber beams (14 of Spruce and 67 of Silver fir) were salvaged from different historical buildings. All the timber were visually graded, dynamically (vibration and acoustic methods were used) and statically (four point bending test) tested, to calculate the actual MOE/MOR. The results of the visual strength grading and dynamic tests were combined, in order to predict MOE and MOR on-site, or on reclaimed timber after their dismantling.For salvaged timbers, comparable results to those reported in literature for new solid timbers were obtained on MOE/MOR prediction, combining longitudinal vibration tests and wane extension (r2=0.71 and 0.43 for MOE and MOR prediction respectively). Within this research, alternative simplified methods, for the MOE/MOR prediction, which are based on the stress wave velocity and wane extension, applicable on site, were proposed (r2=0.57 and 0.29 for MOE and MOR prediction respectively). Since the results were obtained by testing a sample with large variability, adopting some simplifications, they can be used as a starting point for the assessment of MOE/MOR of timber directly on-site, or to evaluate the mechanical properties of reclaimed timber after their dismantling, to assess their potential reuse in timber structures.

Inspection and Evaluation of Decay Damage in Japanese Cedar Trees Through Nondestructive Techniques

The purpose of this study was to investigate the standard values of living, undamaged Japanese cedar (Cryptomeria japonica) trees through different nondestructive techniques. This study also detects the stress wave velocity (V) and tomogram (VT), and resolves corresponding V maps of Japanese cedar trees with and without decay damage for tree risk assessment. A visual tree inspection form, with seven categories of tree damage, is proposed for tree hazard assessment. Different nondestructive evaluation parameters can serve as an index for diagnosing standard values (with or without decay). The VT and corresponding stress wave velocity maps of decay-damaged and damaged Japanese cedar trees can detect the general location and area of wood deterioration. The transversal acoustic velocity values increased with increasing diameter in undamaged trees, and the difference between the maximum and minimum V value of the trunks in undamaged trees fell within a range of constants. The proposed approach can be combined with other non-destructive techniques to better examine and confirm the situation of trees.

Overview of Structural Life Assessment and Reliability, Part VI: Crack Arresters 1

Overview of Structural Life Assessment and Reliability, Part VI: Crack Arresters 1

Overview of Structural Life Assessment and Reliability, Part VI: Crack Arresters1

Overview of Structural Life Assessment and Reliability, Part VI: Crack Arresters¹