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Article

Modulus of Elasticity in Plywood Boards: Comparison between a Destructive and a Nondestructive Method

by
Ricardo de la Cruz-Carrera
1,
Artemio Carrillo-Parra
2,
José Ángel Prieto-Ruíz
3,
Francisco Javier Fuentes-Talavera
4,
Faustino Ruiz-Aquino
5 and
José Rodolfo Goche-Télles
3,*
1
Programa Institucional de Doctorado en Ciencias Agropecuarias y Forestales, Universidad Juárez del Estado de Durango (UJED), Durango 34113, Durango, Mexico
2
Instituto de Silvicultura e Industria de la Madera, Universidad Juárez del Estado de Durango (UJED), Durango 34113, Durango, Mexico
3
Facultad de Ciencias Forestales y Ambientales, Universidad Juárez del Estado de Durango (UJED), Durango 34113, Durango, Mexico
4
Departamento de Madera Celulosa y Papel, Centro Universitario de Ciencias Exactas e Ingenierías (CUCEI), Universidad de Guadalajara (UdG), Guadalajara 44100, Jalisco, Mexico
5
Instituto de Estudios Ambientales, Universidad de la Sierra Juárez (UNSIJ), Ixtlán de Juárez 68725, Oaxaca, Mexico
*
Author to whom correspondence should be addressed.
Forests 2024, 15(9), 1596; https://doi.org/10.3390/f15091596
Submission received: 1 August 2024 / Revised: 7 September 2024 / Accepted: 9 September 2024 / Published: 11 September 2024
(This article belongs to the Special Issue Recent Advances in Wood Identification, Evaluation and Modification)
Browse Figures
Versions Notes

Abstract

:
Nondestructive methods are a fast and accurate way to obtain information about the mechanical properties of plywood panels. The objective was to determine the modulus of rupture and compare the modulus of elasticity (MOE) in plywood boards made with Pinus spp. and Eucalyptus urograndis using the destructive method of three-point static bending and the nondestructive method of ultrasound in parallel and perpendicular directions, as well as in complete board and test specimens, both with the ultrasound method and the correlation between the variables studied. The plywood boards evaluated were 18, 25 and 30 mm nominal thickness. Five structures were evaluated using pine and pine–eucalyptus veneers. Three boards were collected per structure, and 28 specimens were made from each board (14 in a parallel direction and 14 in a perpendicular direction). The elastic modulus was determined by the ultrasound method in complete plywood boards and in specimens obtained from them using the IML Micro Hammer® equipment and through the conventional bending test, carried out in an Instron® universal mechanical testing machine. The Tukey test of means (p < 0.05) shows that in the nominal thickness of 18 mm, the modulus of elasticity by ultrasound was lower compared to the result obtained by static bending in four of the five structures in the perpendicular direction and lower in all the structures evaluated in the parallel direction; while in the nominal thickness of 25 and 30 mm, it was greater in all structures and in both directions. The results of static bending by ultrasound, in complete boards and specimens, show that the only significant difference (p < 0.05) occurs in the nominal thickness of 30 mm in the treatment made with pine–eucalyptus with urea formaldehyde resin being lower in the parallel direction and in complete boards The correlation between the modulus of elasticity determined on specimens using the nondestructive method and the destructive method was r = 0.75 and Pr < 0.05; while comparing the nondestructive method on test specimens and complete plywood panels, r = 0.73 and Pr < 0.05 were obtained. It is concluded that the mechanical bending property of plywood boards can be characterized by the ultrasound method.

1. Introduction

Plywood boards are products made with wooden veneers that are bonded together using resin, seeking to ensure that the fiber’s direction of two consecutive veneers is perpendicular to each other, to minimize the anisotropy in the board [1], and it is one of the composites most important wood derivatives in the economy of many countries [2]. This product has a wide application in the fields of construction, furniture and packaging, among other uses [3]. It has the advantage of having great resistance and lightness, depending on the wood species used, compared to solid wood [4]. However, its performance depends on the knowledge of its properties, which is why it is vitally important to determine the physical–mechanical behavior that allows the design of products and structures that distribute loads efficiently to minimize deformations [5,6]. This behavior can be evaluated using destructive, semi-destructive and nondestructive methods [7]. Nondestructive methods allow the identification of the physical and mechanical properties of a given material, without altering its final use capacity [8,9]; the advantages of these methods are safety, low-cost equipment, time savings, portable equipment and the fact that they do not require laboratory stand equipment [8]. In this sense, the nondestructive evaluation is based on finding a physical phenomenon that, when interacting with the test sample, is affected by it but does not modify the properties of the sample [10]. Various nondestructive testing techniques have been studied, such as methods based on ultrasound, radiographic, dynamic, acoustic emission techniques and acoustic–ultrasonic; although each of these techniques has advantages and disadvantages, they have proven to be useful in determining the modulus of elasticity of wood [11].
Through ultrasonic acoustic emission, it can be possible to examine the mechanical properties of wood-based composites by analyzing their response to the ultrasonic waves [12]. Nondestructive wood techniques and evaluations are currently used that are based on the measurement of the wave speed that propagates within the material under investigation; transverse wave can be used to detect, locate and measure defects, as well as to determine some properties, such as the modulus of elasticity (MOE) of wood, which is one of the most important mechanical properties for the design of structures [6,13]. In one study, the wave speed was analyzed in relation to the basic density and the elastic modulus, and they found a correlation between this speed and the basic density of r = 0.52 and the elastic modulus of r = 0.96 [14]. In another study, they evaluated the elastic modulus of glued laminated wood made with Tectona grandis L.f., Pinus oocarpa Schiede and Lyptus® obtained through the transverse vibration test [15]. For their part, other researchers [16] studied the determination of the modulus of elasticity (MOE) in the three directions (radial, tangential and longitudinal) in saw timber using the wave propagation method in Pequi wood (Caryocar villosum (Aubl.)), agreeing that it is possible to determine the values of the elastic constants through nondestructive testing, with good precision, quickly and at a reduced cost.
Therefore, the fundamental objective of this research is to determine the bending test property of plywood boards made with different species of wood and compare the traditional evaluation method with the ultrasound method, as an alternative for the characterization of these materials, even for commercial dimensions.

2. Materials and Methods

2.1. Materials

The plywood panels used in this work were obtained from a forestry company in the State of Durango. The company uses veneers from the following species: Pinus durangensis Martínez, Pinus engelmannii Carr, Pinus arizonica Engelm, from the natural forest in the Northeast of the state of Durango, Mexico, and Eucalyptus urograndis, from commercial plantations established in Huimanguillo, Tabasco, Mexico.

2.2. Preparation of Plywood Boards

The veneers were obtained by unrolling the logs, with a width of 1.3 m and a length of 2.6 m; their thickness was 1 mm for the face and backside and 3.2 mm for the centers and interiors. The recovered veneer was obtained from the veneers that presented some defect in their production, which had a length of 1.3 m and a width of 32.5 cm and was used only as an interior in the production of the plywood boards. The plywood boards had nominal thicknesses of 18, 25 and 30 mm, following the structures shown in Table 1. To make the boards, urea formaldehyde adhesive and another product produced by the company based on flour, resin, melamine and low-molar ratio urea formaldehyde were used, with a dosage of 530 g/m2. The press used was an Ormamachine/NPC DIGIT 26/14 AF-NPO, and a pressure of 1 MPa was applied at 118 °C for 11 min for the nominal thickness of 18 mm and 130 °C for 25 min for the nominal thickness of 25 and 30 mm.

2.3. Mechanical Properties

2.3.1. Bending Test Nondestructive Method

The nondestructive test was carried out using the ultrasound method following the protocol used by the Michoacana University of San Nicolás de Hidalgo, which indicates that two screws are inserted into the sample on opposite sides, and it is placed on two supports at a distance equal to its length and then, an impulse is applied through the impact screw by hitting the hammer (impulse generator), which is absorbed by the microsensor (impulse receiver); in such a way that the speed of propagation of wave is displayed on the screen of the IML Micro Hammer® device [17].
This procedure was applied to both complete plywood boards and specimens. The idea of applying it to complete boards is to verify whether there is a need to also make specimens or if only the measurements on complete boards are sufficient. For each treatment, three plywood boards were evaluated for each nominal thickness, and 28 specimens were obtained from each board (Figure 1a), 14 in a parallel direction and 14 in a perpendicular direction, prepared in accordance with the ASTM D 3043 standard [18], which indicates that the dimensions of the specimens must be equal to the nominal thickness × 50.8 mm wide; the length will depend on the direction in which they are made with respect to the face of the plywood board, this is 48 times the nominal thickness in the parallel direction (Figure 1b) and 24 times in the perpendicular direction (Figure 1c).
For the plywood boards, three measurements were made, one in the center and the other two 20 cm from each of the ends, both in a parallel and perpendicular direction (Figure 2a). For the specimens, only one measurement was made in the center of each of them (Figure 2b). The elastic modulus was determined with Equation (1):
M O E U = V 2 × D h % 1000000 ,
where MOEu is the ultrasound modulus of elasticity (MPa), v2 is the wave propagation speed (m/s) and Dh% is the density at the time of the test (k gm−3).

2.3.2. Static Bending Destructive Method

The conventional static bending test was carried out in accordance with ASTM D 3043 [18]. For this purpose, the Instron® brand universal mechanical testing machine was used, which has a 600 kN load cell.
From this test, the load–deformation graph was obtained and the point up to which the deformation was no longer proportional to the load was determined, considering this as the load in the proportional limit. From these values, the calculation of the MOE and MOR [18] was carried out with Equations (2) and (3).
M O E e s t = P 1 × L 3 4 × d 1 × b × h 3
where MOEest is the static modulus of elasticity (MPa), P1 is the load at the limit of proportionality (N), L is the separation between supports (mm), d1 is the deformation suffered by the specimen at the limit of proportionality (mm), b is the width of the specimen (mm) and h is the thickness of the specimen (mm).
M O R = 3 × P m × L 2 × b × h 2
where MOR is the modulus of rupture (MPa), Pm is the maximum load supported by the specimen (N), L is the separation between supports (mm), b is the width of the specimen (mm) and h is the thickness of the specimen (mm).

Test Speed

In the parallel direction, the tests were carried out at a speed of 10.368, 14.4 and 17.28 mm/min in the thickness of 18, 25 and 30 mm, respectively, and in the perpendicular direction, the test speed was 2.592, 3.6 and 4.32 mm/min corresponding to the thickness of 18, 25 and 30 mm. The velocity was determined with Equation (4), suggested in the ASTM D-3043 standard, resulting in higher values in the parallel direction, because the distance between supports is greater in this direction.
N = z L 2 / 6 d
where N = rate of motion of moving head, (mm/min), L = span, (mm), d = depth of beam, (mm) and z = unit rate of fiber strain (mm/mm × min) of outer fiber length = 0.0015.

2.4. Physical Properties

The moisture content and density of the plywood boards were determined at the time of the test; the moisture content in accordance with the ASTM D 4442 standard [19] and the density at the time of the test in accordance with the ASTM D 2395 standard [20].

2.5. Statistical Analysis

To identify statistical differences between evaluation methods, an analysis of variance was performed, and when significant statistical differences were found in the modulus of rupture or modulus of elasticity, Tukey tests were performed at a significance level of ∝ = 0.05. Correlations were determined according to the Pearson method. The information analysis was carried out with the InfoStat free version 2020 program [21].

3. Results and Discussion

3.1. Modulus of Rupture

The plywood board made with Pinus spp. and Eucalyptus urograndis, with urea–formaldehyde (PEU) resin, in the nominal thickness of 18 mm, presented the highest resistance value with 46.5 MPa and was statistically different from the other structures with respect to the modulus of rupture. Meanwhile, in plywood boards with a nominal thickness of 25 mm, the values varied from 34.6 to 38.2 MPa, but there were no statistical differences between structures. For the nominal thickness of 30 mm, the plywood boards that achieved the highest resistance were made with Pinus spp. and Eucalyptus urograndis (PEU), and Pinus spp. with resin made by the company (PI), which showed a modulus of rupture of 42 and 38.5 MPa, respectively, coinciding with the values of modulus of rupture of 32 to 54 MPa, reported in plywood panels made with Acrocarpus fraxinifolius Wight et Arn. and Pinus oocarpa wood and mixtures of these [22]. The rest of the structures remained at the lower statistical level (Table 2).
The high values observed in the modulus of rupture for the 18 and 30 mm plywood boards coincide with the high-density values of the boards, since there is a direct relationship between the density and the resistance of the plywood board, given that increasing the density increases its resistance [23,24,25]. However, this relationship is more complex, so other factors must be analyzed such as the thickness of the sheets, the amount of adhesive used and the thickness of the samples used [26].

3.2. Modulus of Elasticity

3.2.1. Comparison between Methods

In the thickness of 18 mm in a parallel direction, it was observed that only in the PRU manufacturing structure, there was no evidence of statistical differences in terms of the evaluation method; in three of the four structures where there were statistical differences, the value of the elastic modulus obtained by ultrasound was lower than that determined by static bending, only in the PEU structure was the value determined by ultrasound higher. This behavior of the elastic modulus in the structures can be attributed to the thickness of the board; since for the 25 and 30 mm boards, the behavior was inverse. In this sense, in a study where they used different dimensions of test pieces for the same species to evaluate the influence of the dimensions in the calculation of the dynamic characteristics of the wood, they found that the parameters determined with the same device were different, assigning this behavior to the variation in the dimensions of the wood samples and mentioning that in wood sciences each procedure must be referred to a particular case [27,28].
Regarding the thickness of 25 and 30 mm, the modulus of elasticity by ultrasound was shown to be statistically different from that obtained in static bending, and in all the manufacturing structures, the value of this parameter was higher than that obtained in static bending (Figure 3). Regarding this, some authors also found that the elastic modulus obtained by ultrasound was greater than that obtained in static bending [29,30,31,32], and this difference can be attributed to the viscoelastic behavior and the damping properties of wood, since it presents an elastic behavior when a force is administered in a short period and behaves like a viscous material when the force applied is for a longer period [32,33,34]. The correlation between both methods presented a value of r = 0.75 with a reliability of p < 0.0001, coinciding with other studies [35].
In the perpendicular direction, the modulus of elasticity in the 18 mm thickness showed evidence of statistical differences between the evaluation methods in the PU and PEU structures, and in both cases, the modulus of elasticity obtained by static bending turned out to be higher than that evaluated in ultrasound. In the thickness of 25 mm, the structures that presented statistical differences regarding how the elastic modulus was determined were PEU and PEI, and in the thickness of 30 mm, the structures that showed statistical differences were PEU, PEI and PRU and both at a thickness of 25 to 30 mm, the modulus of elasticity by ultrasound was found to be greater than that obtained in static bending (Figure 4). In this case, the greatest fluctuations between the elastic modulus obtained by ultrasound and static bending were observed in the plywood boards where their manufacturing structure included eucalyptus, with values from 1 to 23%, and for the manufacturing structures where only pine was included, these values ranged from 1 to 11%. These results agree with what was found by other authors, who detected a pattern similar to that of this study, where the greatest variation between the static elastic modulus and the elastic modulus obtained by ultrasound was found in broadleaf trees with up to 47% and a lower measured in conifers with up to 28%; this difference may be due to the fact that hardwoods, in comparison with conifers, present a greater heterogeneity in terms of type, proportion and distribution of xylem tissues, as shown by the variation models generated for hardwoods, which show the complexity of their anatomical structure [36,37,38]. Another factor that may explain these differences is the method used to determine the dynamic modulus of elasticity, since variations from 2 to 60% are reported according to the method used, where the ultrasound method is the one that presents the greatest variation with respect to other nondestructive methods [39].

3.2.2. Comparison between Specimens and Complete Boards for Nondestructive Testing

In the comparison of the modulus of elasticity by ultrasound between specimens and complete boards in parallel direction, it was found that in the thickness of 18 mm, there were statistical differences in the PU, PEU and PEI structures, where the modulus of elasticity found in the complete boards was greater than that found in the specimens. At the thickness of 25 and 30 mm, only statistical differences were perceived in the PEU structure in both thicknesses; in the same way, it was found that the elastic modulus evaluated in the complete boards was greater than that evaluated in the test pieces (Figure 5). The variations between the elastic modulus by ultrasound in complete boards and specimens varied from 1 to 23%, with the greatest fluctuation observed in the PEU structure both in the thickness of 25 and 30 mm, with 23 and 20%, respectively.
In the perpendicular direction, all structures in the nominal thickness of 18 mm turned out to be statistically different in relation to the elastic modulus evaluated in specimens and complete boards; in the thickness of 25 mm, only in the PEU structure, there were no statistical differences, and similarly in the PRU structure for the thickness of 30 mm. The behavior of the modulus of elasticity in all cases where there was evidence of statistical differences was that the modulus of elasticity in complete boards was greater than in specimens (Figure 6). The elastic modulus determined by the ultrasonic method in complete boards and specimens showed the greatest difference in boards with a thickness of 18 mm, ranging between 15 and 37%. In cases where there was evidence of statistical differences between the elastic modulus in specimens and complete boards, it can be attributed to the fact that when testing specimens, they are free of defects, since their small sizes allow the exclusion of relevant defects [40].

3.3. Correlation between Variables

Table 3 shows that there is a statistically significant correlation (p < 0.05) between all the variables evaluated. Regarding the moisture content with the evaluated variables, the correlation is negative, which agrees with other studies, where they found that by increasing the moisture content the modulus of rupture, static and dynamic elasticity modulus decreased [41,42]. Regarding density, this presented a positive correlation with the mechanical properties studied, indicating that higher density increases the MOE and MOR values [43]. The correlation between the modulus of elasticity determined on specimens using the nondestructive method and the destructive method was r = 0.75 and Pr < 0.05 and the elastic modulus obtained by ultrasound in specimens and in complete boards (r = 0.80). It was also found that the modulus of elasticity by ultrasound evaluated in both specimens and complete boards has a significant statistical correlation (p < 0.0001) with the modulus of rupture and static modulus of elasticity. These correlation values are consistent with those found in another study, where the elasticity modulus was evaluated by dynamic methods and the correlation values ranged from 0.68 to 0.96 [44]. These results coincide with what was reported in other studies, where they found that this parameter measured by ultrasound, in addition to having the advantage of being easy to apply and its potential for use in performing in situ measurements, is ideal for predicting its mechanical behavior [45,46,47]. The equipment used must be calibrated at the time of the test and checked frequently to obtain acceptable results.

4. Conclusions

  • The plywood panels that included eucalyptus veneers in their processing structure had a higher modulus of rupture.
  • The modulus of elasticity in a parallel direction can be obtained by the ultrasonic method on 18 mm thick boards with a PRU structure. While in the perpendicular direction, it is feasible to use in a PI structure in the three studied board thicknesses 18, 25 and 30 mm.
  • The modulus of elasticity in the parallel direction can be obtained in full boards using the ultrasonic method in PU and PRU structures with a thickness of 18 mm; while for boards with thicknesses of 25 and 30 mm, the modulus can be obtained in PU, PI, PEI, PRU structures.
  • The modulus of elasticity in the perpendicular direction can be obtained in complete boards by means of the ultrasonic method, in boards with a PEU structure of 25 mm thickness, and in the PRU structure of 30 mm thickness.
  • There is a significant correlation (r = 0.75) between the modulus of elasticity determined on specimens using the nondestructive method and the destructive method, as well as between the ultrasonic modulus of elasticity in specimens and the ultrasonic modulus of elasticity obtained from complete boards (r = 0.80); therefore, there is the possibility of predicting static values from the ultrasonic test.

Author Contributions

Conceptualization, R.d.l.C.-C., A.C.-P. and J.R.G.-T.; methodology, R.d.l.C.-C., A.C.-P., F.J.F.-T. and J.R.G.-T.; software, R.d.l.C.-C.; validation, R.d.l.C.-C. and A.C.-P.; formal analysis, R.d.l.C.-C., A.C.-P. and J.R.G.-T.; investigation, R.d.l.C.-C.; resources, R.d.l.C.-C., A.C.-P., J.Á.P.-R., F.J.F.-T., F.R.-A. and J.R.G.-T.; data curation, R.d.l.C.-C.; writing—original draft preparation, R.d.l.C.-C., A.C.-P. and J.R.G.-T.; writing—review and editing, R.d.l.C.-C., J.Á.P.-R., F.J.F.-T. and F.R.-A.; visualization, R.d.l.C.-C.; supervision, A.C.-P. and J.R.G.-T.; project administration, R.d.l.C.-C.; funding acquisition, R.d.l.C.-C. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors thank the SEZARIC group for donating the boards for the experiment.

Conflicts of Interest

The authors declare no conflicts of interest.

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Forests 15 01596 g001
Figure 1. Location of specimens in relation to board size (a). Dimensions of the specimens according to the test direction: (b) in parallel direction and (c) in perpendicular direction.
Figure 1. Location of specimens in relation to board size (a). Dimensions of the specimens according to the test direction: (b) in parallel direction and (c) in perpendicular direction.
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Forests 15 01596 g002
Figure 2. Ultrasound test: (a) in complete plywood boards and (b) in specimens.
Figure 2. Ultrasound test: (a) in complete plywood boards and (b) in specimens.
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Forests 15 01596 g003
Figure 3. Modulus of elasticity in parallel direction. PU = pine-adhesive veneer urea formaldehyde, PI = pine-adhesive veneer with the company’s own formulation, PEU = pine–eucalyptus veneer adhesive urea formaldehyde, PEI = pine–eucalyptus veneer adhesive with the company’s own formulation, PRU = recovered sheet metal–urea formaldehyde adhesive. Equal letters between methods for each structure by nominal thickness are not significantly different, Tukey α = 0.05.
Figure 3. Modulus of elasticity in parallel direction. PU = pine-adhesive veneer urea formaldehyde, PI = pine-adhesive veneer with the company’s own formulation, PEU = pine–eucalyptus veneer adhesive urea formaldehyde, PEI = pine–eucalyptus veneer adhesive with the company’s own formulation, PRU = recovered sheet metal–urea formaldehyde adhesive. Equal letters between methods for each structure by nominal thickness are not significantly different, Tukey α = 0.05.
Forests 15 01596 g003
Forests 15 01596 g004
Figure 4. Modulus of elasticity in perpendicular direction. PU = pine-adhesive veneer urea formaldehyde, PI = pine-adhesive veneer with the company’s own formulation, PEU = pine–eucalyptus veneer adhesive urea formaldehyde, PEI = pine–eucalyptus veneer adhesive with the company’s own formulation, PRU = recovered sheet metal–urea formaldehyde adhesive. Equal letters between methods for each structure by nominal thickness are not significantly different, Tukey α = 0.05.
Figure 4. Modulus of elasticity in perpendicular direction. PU = pine-adhesive veneer urea formaldehyde, PI = pine-adhesive veneer with the company’s own formulation, PEU = pine–eucalyptus veneer adhesive urea formaldehyde, PEI = pine–eucalyptus veneer adhesive with the company’s own formulation, PRU = recovered sheet metal–urea formaldehyde adhesive. Equal letters between methods for each structure by nominal thickness are not significantly different, Tukey α = 0.05.
Forests 15 01596 g004
Forests 15 01596 g005
Figure 5. Ultrasound in parallel direction. PU = pine-adhesive veneer urea formaldehyde, PI = pine-adhesive veneer with the company’s own formulation, PEU = pine–eucalyptus veneer adhesive urea formaldehyde, PEI = pine–eucalyptus veneer adhesive with the company’s own formulation, PRU = recovered sheet metal–urea formaldehyde adhesive. Equal letters between elastic modulus in specimens and complete boards for each structure by thickness are not significantly different, Tukey α = 0.05.
Figure 5. Ultrasound in parallel direction. PU = pine-adhesive veneer urea formaldehyde, PI = pine-adhesive veneer with the company’s own formulation, PEU = pine–eucalyptus veneer adhesive urea formaldehyde, PEI = pine–eucalyptus veneer adhesive with the company’s own formulation, PRU = recovered sheet metal–urea formaldehyde adhesive. Equal letters between elastic modulus in specimens and complete boards for each structure by thickness are not significantly different, Tukey α = 0.05.
Forests 15 01596 g005
Forests 15 01596 g006
Figure 6. Ultrasound in a perpendicular direction. PU = pine-adhesive veneer urea formaldehyde, PI = pine-adhesive veneer with the company’s own formulation, PEU = pine–eucalyptus veneer adhesive urea formaldehyde, PEI = pine–eucalyptus veneer adhesive with the company’s own formulation, PRU = recovered sheet metal–urea formaldehyde adhesive. Equal letters between elastic modulus in specimens and complete boards for each structure by thickness are not significantly different, Tukey α = 0.05.
Figure 6. Ultrasound in a perpendicular direction. PU = pine-adhesive veneer urea formaldehyde, PI = pine-adhesive veneer with the company’s own formulation, PEU = pine–eucalyptus veneer adhesive urea formaldehyde, PEI = pine–eucalyptus veneer adhesive with the company’s own formulation, PRU = recovered sheet metal–urea formaldehyde adhesive. Equal letters between elastic modulus in specimens and complete boards for each structure by thickness are not significantly different, Tukey α = 0.05.
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Table 1. Schemes for making plywood panels.
Table 1. Schemes for making plywood panels.
Thickness
Nominal (mm)		Species and ResinBoard Structure *
18PUPForests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001P
PIPForests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001P
PEUPForests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002P
PEIPForests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002P
PRUPForests 15 01596 i001PForests 15 01596 i001RForests 15 01596 i001P
25PUPForests 15 01596 i001Forests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001P
PIPForests 15 01596 i001Forests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001P
PEUPForests 15 01596 i002Forests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002P
PEIPForests 15 01596 i002Forests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002P
PRUPForests 15 01596 i001Forests 15 01596 i001PForests 15 01596 i001RForests 15 01596 i001RForests 15 01596 i001P
30PUPForests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001P
PIPForests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001PForests 15 01596 i001P
PEUPForests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002P
PEIPForests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002PForests 15 01596 i002P
PRUPForests 15 01596 i001PForests 15 01596 i001RForests 15 01596 i001PForests 15 01596 i001RForests 15 01596 i001P
P = pine veneer, E = eucalyptus veneer, R = recovered pine veneer, PU = pine-adhesive urea formaldehyde veneer, PI = pine-adhesive veneer with the company’s own formulation, PEU = pine–eucalyptus veneer–urea formaldehyde adhesive, PEI = pine–eucalyptus veneer adhesive with the company’s own formulation, PRU = recovered sheet metal–urea formaldehyde adhesive. * The direction of the letter indicates in which direction the sheet was placed within the assembly of the board.
Table 2. Modulus of rupture by manufacturing structure of plywood panels.
Table 2. Modulus of rupture by manufacturing structure of plywood panels.
Species and Resin18 mm25 mm30 mm
MOR
(MPa)		MC
(%)		Density
(kg/m3)		MOR
(MPa)		MC
(%)		Density
(kg/m3)		MOR
(MPa)		MC
(%)		Density
(kg/m3)
PU39.8 (11.96) b8.3 (0.42) a618 (29.9) b34.6 (14.53) a8.3 (3.12) a589 (28.0) b32.4 (10.46) b16.4 (9.88) a619 (59.2) c
PI35.6 (14.02) b7.6 (1.57) b575 (20.8) c35.8 (12.90) a7.4 (0.29) ab567 (26.4) c38.5 (10.85) a6.9 (1.00) b572 (19.8) e
PEU46.5 (19.43) a5.7 (0.92) c654 (36.4) a35.4 (15.21) a6.4 (1.85) c674 (31.7) a42.0 (8.33) a5.9 (0.36) b670 (37.7) a
PEI38.5 (9.42) b7.2 (0.46) b663 (23.1) a35.8 (10.63) a7.1 (3.54) bc684 (33.7) a32.6 (9.19) b5.7 (2.67) b650 (27.6) b
PRU39.4 (9.59) b5.6 (1.00) c557 (24.9) d38.2 (16.94) a6.5 (0.74) bc598 (29.0) b34.1 (8.43) b5.7 (0.58) b599 (26.9) d
MOR = modulus of rupture, MC = moisture content, PU = pine-adhesive veneer urea formaldehyde, PI = pine-adhesive veneer with the company’s own formulation, PEU = pine–eucalyptus veneer adhesive urea formaldehyde, PEI = pine–eucalyptus adhesive with the company’s own formulation, PRU = recovered sheet metal–urea formaldehyde adhesive. Columns with averages with the same letter in common are not significantly different, Tukey α = 0.05. The standard deviation is shown in parentheses.
Table 3. Pearson correlation coefficient between the evaluated variables.
Table 3. Pearson correlation coefficient between the evaluated variables.
MCDTTMORMOEMOEUPMOEUT
MC1−0.18
(0.0031)		−0.15
(0.0141)		−0.19
(0.0020)		−0.20
(0.0007)		−0.21
(0.0005)
DTT 10.13
(0.0299)		0.34
(<0.0001)		0.50
(<0.0001)		0.45
(<0.0001)
MOR 10.80
(<0.0001)		0.48
(<0.0001)		0.56
(<0.0001)
MOE 10.75
(<0.0001)		0.73
(<0.0001)
MOEUP 10.80
(<0.0001)
MOEUT 1
MC = moisture content, DTT = density at the time of test, MOR = static modulus of rupture, MOE = static modulus of elasticity, MOEUP = elasticity modulus by ultrasound in specimens, MOEUT = elasticity modulus by ultrasound in complete boards. The significance value is shown in parentheses.
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de la Cruz-Carrera, R.; Carrillo-Parra, A.; Prieto-Ruíz, J.Á.; Fuentes-Talavera, F.J.; Ruiz-Aquino, F.; Goche-Télles, J.R. Modulus of Elasticity in Plywood Boards: Comparison between a Destructive and a Nondestructive Method. Forests 2024, 15, 1596. https://doi.org/10.3390/f15091596

AMA Style

de la Cruz-Carrera R, Carrillo-Parra A, Prieto-Ruíz JÁ, Fuentes-Talavera FJ, Ruiz-Aquino F, Goche-Télles JR. Modulus of Elasticity in Plywood Boards: Comparison between a Destructive and a Nondestructive Method. Forests. 2024; 15(9):1596. https://doi.org/10.3390/f15091596

Chicago/Turabian Style

de la Cruz-Carrera, Ricardo, Artemio Carrillo-Parra, José Ángel Prieto-Ruíz, Francisco Javier Fuentes-Talavera, Faustino Ruiz-Aquino, and José Rodolfo Goche-Télles. 2024. "Modulus of Elasticity in Plywood Boards: Comparison between a Destructive and a Nondestructive Method" Forests 15, no. 9: 1596. https://doi.org/10.3390/f15091596

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