Microsecond Timer Research Articles

Nondestructive Techniques for Determination of Wood Mechanical Properties of Urban Trees in Madrid

The aim of this paper is to analyze the mechanical properties of Robinia pseudoacacia L. (black locust), Platanus × hybrida Brot. (London plane), Ulmus pumila L. (Siberian elm), and Populus alba L. (white poplar), estimated using ultrasound wave equipment (USLab y Sylvatest Duo) and impact wave equipment (Microsecond Timer) on standing trees, felled logs and on specimens obtained from different parts of the trees. Bending strength, axial compression strength and tension parallel to grain were determined for each specimen, in order to subsequently correlate the strength and stiffness with the acoustic properties determined in the standing tree. For the relationship between the static modulus of elasticity of the specimens and the dynamic modulus of elasticity determined in standing trees using the USLab, coefficients of determination were found to be between 0.30–0.92, between 0.52 and 0.80 using the Sylvatest Duo and between 0.60 and 0.94 with the Microsecond Timer. It would be necessary to determine whether the removal of bark for the correct coupling of the ultrasonic sensors would provide an entry route for pests or diseases that could affect the health of the tree.

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.

Influence of length on acoustic time-of-flight (ToF) measurement in built-in structures of Norway spruce timber

Abstract Time-of-flight (ToF) measurements were conducted on twelve 76×226-mm2 in cross-section, 4.52-m long specimens of Norway spruce timber pieces from a dismantled 19th-century building in Barcelona (Catalonia, Spain). Two commercially available acoustic devices were used: the USLab ultrasound device with conical 22 and 45 kHz sensors and the MicroSecond Timer (MST) stress wave device with spike sensors. ToF were obtained for the full-length (4.52 m) specimens in an end-to-end arrangement and for lengths of 0.5, 1, 1.5, 2, 3 and 4 m on the same surface and on opposite surfaces. The differences between the velocities obtained from end-to-end and semi-direct measurements were less than 4.5%. Apparent velocity dependence on length was observed in short-distance measurements. This could be corrected by determining a time lag (tL) from a linear regression between the ToF and the distance. Estimation of the modulus of elasticity (MOE) from the dynamic MOE (MOEdyn) is acceptable (r2=0.45–0.69) depending on the measurement procedure, and the best results for in situ timber are obtained in edge surface velocity. Although modulus of rupture (MOR) estimation from MOEdyn improves slightly when knottiness is included, it has low predictive capacity.

Determining the predictive accuracy of whole tree modulus of elasticity (MOE) of 14-year-old loblolly pine using density and dynamic MOEs estimated by three different acoustic tools

Resonance based acoustic tools for evaluating wood properties have been reported to be more accurate in estimating the expected log MOE than time-of-flight (ToF) ones. However, there is no published study on the variations within different brands on these two major classes of acoustic tools. In this study, models were developed to predict the whole tree static MOE (WMOET) and rupture (WMORT) using log dynamic MOEs estimated by two resonance tools [Director HM200 (EHM200) and FAKOPP resonance log grader (ERLG)], ToF [FAKOPP Microsecond Timer (EFMT)], and density (green density, air-dry density) for a 14-year-old loblolly pine stand from two sites in the southern USA. The log velocity estimated by ToF was 33 and 30% more as compared to the resonance-based tools (Director HM200 and FAKOPP RLG respectively); translating into whole log static MOE (WMOEL) been 11 and 20% lower than those estimated by the resonance (HM200 and RLG respectively), and 90% lower than that estimated by the ToF tools (EFMT). Although the dynamic MOE estimated by ToF tool (EFMT) was higher, its WMOET predictive performance (R2 = 51%) lies between the 39 and 74% for the resonance based tools (HM200 and RGL respectively). This result supports the theory that ToF tools generate dilatational wave, and hence their velocity will be generally higher than resonance tools. The presence of predictive variation within the resonance suggests the need for within tools calibration. The linear relationship between the WMOET vs Etree was stronger than that of WMOET vs EHM200 suggesting that the ToF acoustic tool measurements are not restricted to the outer wood zone for small diameter logs.

Sensitivity of acoustic tools to variation in equilibrium moisture content of small clear samples of loblolly pine (Pinus taeda)

There are several types of acoustic tools commercially available for wood characterization, but they are generally classified into resonance and time-of-flight (ToF) tools. This classification is based upon the mode of velocity estimation for wood. In this study, we explored how the equilibrium moisture content of small clear wood samples (2.5 cm × 2.5 cm × 41 cm) affect the predictive capabilities of two types of acoustic tools namely a microsecond timer (ToF) and a resonance log grader (resonance). The results indicated the acoustic velocity is sensitive to equilibrium moisture content of loblolly pine, and sensitivity to EMC is similar for both type of tools. The acoustic velocity decreased by 32.9 and 28.8 m/s for ToF and the resonance acoustic tools respectively for a unit increase in EMC below fiber saturation point (FSP); 5.4 and 6.1 m/s respectively for a unit increase in EMC above FSP although the slope was statistically equivalent to zero. Also, the static MOE of the green samples was overestimated by 16% by both resonance and ToF tools with oven-dried density, while it was 72% when estimated with density at test. The insignificant slope coupled with better accuracy in MOE supports the hypothesis that the cell wall controls the acoustic velocity while the water in the lumen of the cell wall is insignificant. These results bring into question the standard use of green density to estimate acoustic MOE of live trees and oven dry density is instead recommended.

Influence of length and sensor positioning on acoustic time-of-flight (ToF) measurement in structural timber

Abstract The mechanical properties of timber can be estimated from wave propagation velocity by measuring wave time-of-flight (ToF). However, a time-lag complicates the measurements, which produces an apparent velocity dependency on length and this species and instrument dependent property is also influenced by knottiness. This research is dealing with time-lag determination by different sensor positioning in situ ToF measurements. ToF longitudinal measurements were conducted on 120 90 mm×140 mm specimens of the coniferous species radiata pine, Scots pine, laricio pine and maritime pine. The following commercially available acoustic devices were used: Sylvatest Duo, USLab, and Microsecond Timer. The sensors were arranged for the measurement types “end-to-end”, “on the same surface” and “on opposite surfaces”. ToF data were obtained from the full-length (4 m) specimens and then from the same specimens shortened to 3 m, 2 m and 1 m in length. The in situ procedures of ToF are applicable for a reliable length determination independently from the time-lag (tL) and velocity. The differences observed by end-to-end measurements, with respect to velocity, are below 4.4%. A velocity correction factor can be deduced for each instrument, which is independent of species.

Time-of-Flight Adjustment Procedure for Acoustic Measurements in Structural Timber

The effect of timber length on time-of-flight acoustic longitudinal measurements was investigated on the structural timber of four Spanish species: radiata pine (Pinus radiata D. Don), Scots pine (Pinus sylvestris L.), laricio pine (Pinus nigra Arn.), and maritime pine (Pinus pinaster Ait.). Time-of-flight longitudinal measurements were conducted on 120 specimens of dimensions 90 × 140 mm using three commercially available acoustic instruments (Sylvatest Duo, USLab, and Microsecond Timer). Time-of-flight data were initially obtained from the full-length (4 m) specimens, and then from the specimens cut to 3, 2, and 1 meter in length by successively cutting off 0.5 m from each end. The acoustic longitudinal velocity of the timber specimens of different lengths was also measured using a resonance-based acoustic method. The apparent acoustic longitudinal velocity for all species increased linearly as the timber length decreased from 4 to 1 meter. Acoustic velocity determined from time-of-flight data was significantly higher than the acoustic velocity determined using the resonance method, indicating systematic measurement errors associated with the time-of-flight instruments. Empirical models were developed for the relationships between time-of-flight measurements on timber specimens and timber lengths in the range of 1 to 4 m. Finally, a procedure was proposed to correct the time-of-flight data.

Early genetic selection for wood stiffness in juvenile Douglas-fir and western hemlock

Wood stiffness, or modulus of elasticity (MOE), is an important property of structural wood products. The ability to genetically improve wood stiffness has increased because of the availability of tools that can measure acoustic velocity (AV, an indirect measure of MOE) on standing trees. Our goals were to optimize methods for measuring AV on young (6- to 12-year-old) Douglas-fir and western hemlock, and then use these methods to understand the genetics of wood stiffness. In Phase I, we evaluated four standing-tree tools (TreeSonic-TS, TreeSonic-SD02, Microsecond Timer, and Ultrasonic Timer) by comparing AV2 measured on standing trees to AV2 measured on logs cut from these trees (i.e., using the HM200). We found that measuring across a whorl of branches had little adverse effect on AV measurements, and that placing the acoustic sensors on the same-face of the tree was slightly better than placing them on opposite faces. In Phase II, we used full-sib heritabilities (hfs2) to compare the TreeSonic-SD02 and Microsecond Timer, sensor orientations (same-face versus opposite-face), and flight path adjustments. Because the effect of standing-tree tool and sensor orientation was non-significant, we recommend that breeders use the TreeSonic-SD02 and same-face orientation for practical reasons. Using this approach, hfs2 for AV2 was 0.90 to 0.56 in Douglas-fir and 0.51 in western hemlock, and we concluded that genetic gains of 7.0–17.2% can be obtained by measuring 10 or more trees per full-sib family, depending on species and seed production strategy. Because we found no strong statistical support for substantial non-additive genetic variation, the current approach of breeding for additive genetic value, and then collecting open-pollinated seed from orchards seems appropriate for improving wood stiffness. AV2 had weak genetic correlations with growth traits (height, diameter at breast height, and volume) in Douglas-fir (−0.21 to 0.33), but moderately positive correlations in western hemlock (0.36–0.54). Therefore, there is ample opportunity to improve the stiffness of young trees without adversely affecting growth. Although mean stiffness was higher for Douglas-fir, about 10% of the western hemlock families (7 out of 80) had higher AV2, and about 28% of the families (22 out of 80) had higher dynamic MOE than the mean for Douglas-fir. This suggests that intensive selection and breeding in western hemlock could be used to create varieties of trees that compare favorably with unselected Douglas-fir. This may improve the ability of western hemlock to compete with Douglas-fir where stiffness is important.

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.