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A special issue of Forests (ISSN 1999-4907). This special issue belongs to the section "Wood Science and Forest Products".

Deadline for manuscript submissions: closed (10 June 2023) | Viewed by 7076

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Special Issue Editor

Dr. André Luis Christoforo

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Guest Editor

Department of Civil Engineering, Federal University of São Carlos, São Carlos 13565-905, Brazil
Interests: numerical modeling; experimental campaign; wood; wood composite systems; engineered wood products; statistical modeling
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Wood is a material from a renewable source and with excellent mechanical properties. It is one of the oldest materials used in civil construction. In civil construction, this material stands out because it has an excellent relationship between mechanical strength and density compared to other construction materials, such as concrete and steel. Anatomical issues (which vary from species to species) and soil and climate characteristics directly impact its properties. The crescent interest in building high and robust wooden buildings has stimulated investigations about wood's physical and mechanical properties and their relationships with other relevant material parameters. In this sense, it is important to evaluate the quality of wood through classification methods since defects, and other factors can negatively impact its properties, especially mechanical ones. In this Special Issue of Forests, “Wood Quality and Mechanical Properties”, works are expected to focus on the analysis of wood quality (of great importance in the case of planted forest species), as well as the characterization (determination of physical and mechanical properties) of wood species with little or extensive use and even engineered wood materials, whose quality and characterization is highly important to spread their use.

Potential topics include, but are not limited to:

Characterization of new or few used wood species;
Classification methods;
Non-destructive experimental tests;
Mechanical characterization of engineered wood materials;
Normative procedures for wood testing and characterization.

Dr. André Luis Christoforo
Guest Editor

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Keywords

wood characterization
classification methods
wood testing
non-destructive tests
normative procedures

Published Papers (9 papers)

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Research

Open AccessArticle

Maximizing the Use of Out-of-Grade Hybrid Pine in Engineered Wood Products: Bond Performance, the Effect of Resin Streaking, Knots, and Pith

Rebecca Cherry

Warna Karunasena

and

Allan Manalo

Forests 2023, 14(9), 1916; https://doi.org/10.3390/f14091916 - 20 Sep 2023

Viewed by 280

Abstract

The evolution toward small-diameter and fast-growing plantation timbers such as the Pinus elliotti var. elliottii (Engelm) × Pinus caribaea var. hondurensis (Sénéclauze) (PEE×PCH) hybrids around the world is producing large volumes of core wood that are falling short of structural sawn timber grading requirements. Engineered timber products such as cross-laminated timber (CLT) and glue-laminated (glulam) offer potential solutions to value-adding this resource, but the bond performance of this feedstock and the extent to which current standards and guides address its common characteristics for bond performance need to be understood. This study investigated the bond quality and performance of clear defect-free, low stiffness out-of-grade PEE×PCH and evaluated this performance using the pass/fail criteria of the CLT bond performance requirements of three national CLT standards. 5-layer CLT delamination samples and shear block test samples were glued using one-component polyurethane (PUR). This process was repeated for common occurring characteristics in this resource of resin, knots, and pith to understand their impact and inform an evaluation on the need to restrict their inclusion. Clear samples had an average glue line delamination of 2.9% and an average glue line wood failure of 96.7%. Resin achieved 9.3% and 92.6%, respectively. While knots had the lowest performance at 24.4% and 77.4%, respectively. When pith was at or adjacent to the glue line, wood failure occurred through the pith and its immediate surrounding fiber. Shear strength and wood failure tests were carried out on glulam and CLT-oriented samples. CLT knot samples were tested in two load orientations. Glulam-oriented samples in clear, resin, pith, and knots achieved an average shear strength of 8.5 MPa, 8.2 MPa, 7.9 MPa, and 8.2 MPa, respectively, and wood failure of 86%, 85%, 90%, and 69%, respectively. CLT-oriented samples in clear and resin both achieved average shear strengths of 4.0 MPa; 0°-loaded and 90°-loaded pith samples achieved 3.6 MPa and 2.4 MPa, while 0°-loaded and 90°-loaded knot samples achieved 4.2 MPa and 4.7 MPa respectively. Average wood failures were 90%, 89%, 96%, 96%, 83%, and 51%, respectively. PRG320 was found to be the most restrictive standard. Resin, knots, and pith were not addressed in the evaluation of delamination or shear strength in any standard, and PRG320 was the only standard to restrict these characteristics over and above structural grading rules. The amount and type of characteristics present vary considerably in structurally graded wood, and even more so for this out-of-grade resource. It was determined that the negative impact that resin, knots, and pith have on bond quality and bond performance calls for some restriction of their inclusion in order to achieve the author’s interpretation of the intended bond performance requirements of the CLT standards, which currently do not address these characteristics well or at all. A proposed modification to the PRG320 effective bond area was presented as a proactive solution. Full article

(This article belongs to the Special Issue Wood Quality and Mechanical Properties)

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Open AccessArticle

Microwave Treatments and Their Effects on Selected Properties of Portuguese Pinus pinaster Aiton. and Eucalyptus globulus Labill. Wood

Fernando Júnior Resende Mascarenhas

Alfredo Manuel Pereira Geraldes Dias

André Luis Christoforo

Rogério Manuel dos Santos Simões

and

André Eduardo Palos Cunha

Forests 2023, 14(8), 1671; https://doi.org/10.3390/f14081671 - 18 Aug 2023

Viewed by 472

Abstract

The most widespread wood species in the Portuguese forest and the most widely utilized are maritime pine (Pinus pinaster) and eucalyptus (Eucalyptus globulus Labill). In the case of eucalyptus, except for the pulping sector, it might have limited usage due to drying issues and low permeability. Microwave (MW) treatment is a technology that has been used to improve wood species’ permeability. Therefore, the present paper aimed to evaluate the MW treatment of both Portuguese wood species and to investigate the effects of different MW treatments on wood’s density, water uptake capability, modulus of rupture (MOR), and modulus of elasticity (MOE). Using small clear wood specimens, two MW powers were used, 700 and 1200 W, and the samples were submitted to successive MW cycles of 2 min till they reached the required dryness. The results showed that each wood species had a different behavior during the MW drying in terms of drying rate, supply, and consumption of energy. In general, with the increase in MW power, the densities of both species decreased and the water uptake increased, as a possible indicator that a certain level of microstructural damage might have occurred. Regarding the mechanical properties of MW-treated maritime pine and eucalyptus wood specimens, under the harshest conditions (MW power of 1200 W), MOR and MOE were reduced compared with the wood sample without MW treatment. Full article

(This article belongs to the Special Issue Wood Quality and Mechanical Properties)

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Open AccessArticle

The Mechanical Strength Properties, Treatability Retention and Hazard Classification of Treated Small-Clear Fast-Growing Acacia mangium Superbulk at Different Age Groups

Ahmad Nurfaidhi Rizalman

Hamden Mohammad

and

Khairul Khuzaimah Abdul Rahim

Forests 2023, 14(8), 1529; https://doi.org/10.3390/f14081529 - 26 Jul 2023

Viewed by 437

Abstract

The slow growth rate of primer species has affected the supply available to accommodate the market demand. To overcome these problems, a study was carried out to fully utilise fast-growing timber as the primary resource to ensure the demand for timber logs continues. This paper aimed to determine mechanical strength properties, treatability retention, and hazard classification of 7-, 10- and 13-year-old small-clear samples of Acacia mangium superbulk collected from Daiken Plantation Sdn. Bhd. Bintulu, Sarawak, following treatment with 10% copper chrome arsenic. As a result of this study, the maximum strength was obtained from the 10-year-old age group, with the modulus of rupture (MOR), the modulus of elasticity (MOE), and compression parallel to the grain values of small-clear treated Acacia mangium superbulk reaching 118.76 N/mm², 15,020 N/mm², and 57.82 N/mm², respectively. In addition, the treatability retentions obtained were 149.27 L/m³, 147.25 L/m³, and 141.09 L/m³, which were recorded from the 7-, 10-, and 13-year-old samples, respectively. Meanwhile, the dry-salt retentions obtained from the 7-, 10- and 13-year-old samples were 14.93 kg/m³, 14.73 kg/m³, and 14.11 kg/m³, respectively. Hence, this species is classified as moderately difficult to treat under CCA (treatability retention: 80–160 L/m³) and is categorised under the hazard class of H4 (dry salt retention: 12–16 kg/m³). Full article

(This article belongs to the Special Issue Wood Quality and Mechanical Properties)

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Open AccessArticle

Mechanical Efficiency and Quality Control Preliminary Analysis of Incompletely Bonded Wood-Based Sandwich Panels

and

Forests 2023, 14(6), 1074; https://doi.org/10.3390/f14061074 - 23 May 2023

Viewed by 682

Abstract

Wood-based sandwich panels are building products composed of two skins attached to a lightweight continuous core in which at least one skin is made of wood-based products, contributing to the use of renewable forest goods. Since the connection between the skins and the core is often provided by adhesive bonding, its characteristics affect the mechanical behavior of the sandwich and, therefore, must be thoroughly assessed. Full adhesion is often considered the standard situation, although some batches of the commercial product show incompletely glued surfaces, and scarce data is available with regard to their bonding performance. For this reason, analyses were performed using tensile tests with a load perpendicular to the skins and specific shear tests with a load parallel to the longitudinal direction of the panel. The test samples were obtained from wood-based sandwich panels with extruded polystyrene cores and different skin materials. The tensile tests proved to be suitable only for panels with adequate skin material cohesion, their functionality improving as a control method when the glued surface percentage assessment is used together with the tensile strength. The results of the shear tests provided non-linear models relating the effect of the glued surface to the mechanical properties, revealing that the mechanical efficiency of the incompletely bonded specimens is better than that which might be expected if the core only worked in proportion to the glued surface, due to the help of the adjoining non-glued core material. Full article

(This article belongs to the Special Issue Wood Quality and Mechanical Properties)

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Open AccessArticle

Effect of Alternate Drying Techniques on Cross-Laminated Timber after Exposure to Free-Water Wetting

Maryam Shirmohammadi

and

Adam Faircloth

Forests 2023, 14(5), 1007; https://doi.org/10.3390/f14051007 - 12 May 2023

Viewed by 626

Abstract

Cross-laminated timber (CLT) panels are commonly used in mass-timber multistorey constructions due to their prefabrication, construction flexibility, environmental credentials and weight-to-strength ratio advantages compared to competing building materials. However, the long-term durability and service life of these mass timber panels require further understanding of their performance when exposed to free water. Wetting and drying trials were conducted by exposing Radiata pine (Pinus radiata) CLT sections to either free water (pooling on a single surface) or submerged water (all directions exposed) saturation, followed by either ambient or fan drying. The panels exposed to water pooling only reached MC above the FSP up to 40 mm of the panel depth. For submerged panels, the MC reached values above the fibre saturation point (FSP) at depths of 30 to 40 mm penetration on both panel faces. When comparing the ambient and fan-drying panel sections over the same time period, a less uniform MC profile was observed for the ambient drying, whereas the fan-dried panels fell below the FSP faster and with a more consistent MC profile. A complementary study was conducted on a standalone 3.0 × 3.0 m CLT room, where the room was wetted during a simulated pipe burst event. The moisture monitoring of wall and floor panels during fan drying of the room showed that an MC reduction from an excess of 40% to below 20% could be reached in less than 96 h for the panels’ surface; however, the middle sections of the panels dried slower than the surface sections. The CLT structure fan drying required a longer drying time than the CLT sections tested due to the closed sections (overlaps and connected faces) and a lower rate of airflow. The study of drying CLT sections highlighted the product reaching and maintaining MC higher than FSP points and the need for further drying applied to minimise long-term decay development. Further study is recommended to investigate the effects of closed sections (connected faces) and the duration of drying needed for semi-finished and finished buildings. Full article

(This article belongs to the Special Issue Wood Quality and Mechanical Properties)

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Open AccessArticle

Characterization of Anatomical and Non-Anatomical Properties for the Identification of Six Commercial Wood Species from Vietnamese Plantation Forests

Alvin Muhammad Savero

Jong Ho Kim

Byantara Darsan Purusatama

and

Forests 2023, 14(3), 496; https://doi.org/10.3390/f14030496 - 02 Mar 2023

Cited by 2 | Viewed by 905

Abstract

This study investigated the anatomical and non-anatomical characteristics of six wood species, Acacia mangium, Acacia hybrid, Dillenia pentagyna, Anacardium occidentale, Hevea brasiliensis, and Melaleuca cajuputi, from a plantation in Vietnam. The anatomical characteristics and non-anatomical characteristics were observed following the International Association of Wood Anatomists (IAWA) list. All species showed diffuse porosity and non-septate fibers. Exclusively solitary vessels were only observed in M. cajuputi. Vestured pits were observed in A. mangium, A. hybrid, and M. cajuputi, and tyloses were found in A. occidentale and H. brasiliensis. We observed vasicentric axial parenchyma in A. mangium, A. hybrid, A. occidentale, and H. brasiliensis, whereas diffuse axial parenchyma was observed in D. pentagyna and M. cajuputi. Further, prismatic crystals in the axial parenchyma cells existed in A. mangium, A. hybrid, and H. brasiliensis, and raphides in ray cells were observed in D. pentagyna. Silica bodies in ray cells were found in A. occidentale and M. cajuputi. H. brasiliensis exhibited the greatest vessel diameter and ray height, with D. pentagyna exhibiting the greatest fiber length and wall thickness. All the species showed considerable differences in heartwood fluorescence, water and ethanol extract colors, and froth test reactions. Full article

(This article belongs to the Special Issue Wood Quality and Mechanical Properties)

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Open AccessArticle

Mechanical Properties of Three Bamboo Species: Effect of External Climatic Conditions and Fungal Infestation in Laboratory Conditions

Asier Elejoste

Juan Luis Osa

Alfonso Arevalillo-Roman

Arantxa Eceiza

Jose Miguel Abascal

Jose Miguel Rico-Martinez

Amaia Butron

and

Cristina Peña-Rodriguez

Forests 2022, 13(12), 2084; https://doi.org/10.3390/f13122084 - 07 Dec 2022

Cited by 1 | Viewed by 1009

Abstract

Bamboo is a material with good tensile and flexural resistance. As a construction material with structural capacity, using bamboo implies considerable environmental advantages in relation to other typical materials such as steel or concrete. For its correct implementation, it is necessary to define its mechanical properties and durability. Bamboo is susceptible to degradation due to the lack of natural toxins and thin walls, which means that shallow decomposition processes can imply appreciable reductions in its mechanical capacity. The main degrading agents considered in this study were beetles, termites, and xylophagous fungi. The aim of this study was to analyze the durability of three different species: DS, PA, and AA. Durability and mechanical tests results after 6 months of exposure to biotic and abiotic agents were compared with their original properties and chemical composition. In this study, durability was analyzed in two ways. Firstly, the loss of mass due to fungal infection was investigated. The results obtained were based on the standard EN 113 using the fungus CP. Secondly, bending and compressive strength was evaluated after a durability test according to the standard EN 335:2013 for the CU3.1 use class after a 6 month period in the city of Donostia/San Sebastian, Spain. The DS and AA varieties were rated as very durable CD1, while the PA variety is durable CD2, thus proving to be an attractive material for construction. Full article

(This article belongs to the Special Issue Wood Quality and Mechanical Properties)

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Open AccessArticle

Evaluation of Yield Improvements in Machine vs. Visual Strength Grading for Softwood Species

Gonzalo Moltini

Guillermo Íñiguez-González

Gonzalo Cabrera

and

Vanesa Baño

Forests 2022, 13(12), 2021; https://doi.org/10.3390/f13122021 - 29 Nov 2022

Cited by 1 | Viewed by 1025

Abstract

The current national standard for strength grading in Spain is based on a visual classification, which, for softwood species with small cross-sections (with a thickness equa tol or less than 70 mm), establishes two different visual grades (ME-1 and ME-2). These grades are assigned to the strength classes C24 and C18, respectively, for maritime and radiata pines, and C27 and C18 for Scots pine, according to the European standard EN-1912:2012. The production of engineered wood products, such as glulam or cross-laminated timber is increasing worldwide. The machine grading of wood using non-destructive testing provides the industry with a more reliable, fast, and consistent method for grading. With this background in mind, this study presents the yield comparison of machine grading vs. visual grading for those three pine species from Spain. The machine settings were obtained according to the standard EN 14081-2:2019, providing several possible strength grade combinations. Results allow new possibilities for the industry and improve the structural yield of the studied timber, thus increasing the material optimization. Full article

(This article belongs to the Special Issue Wood Quality and Mechanical Properties)

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Open AccessArticle

Balsam Fir (Abies balsamea (L.) Mill.) Wood Quality after Defoliation by Spruce Budworm (Choristoneura fumiferana Clem.) in the Boreal Forest of Quebec, Canada

Audrey Lemay

Julie Barrette

and

Cornelia Krause

Forests 2022, 13(11), 1926; https://doi.org/10.3390/f13111926 - 16 Nov 2022

Viewed by 818

Abstract

Eastern spruce budworm (Choristoneura fumiferana Clem.) is considered the most important disturbing insect in coniferous stands in eastern North America. During an outbreak, spruce budworm can cause severe defoliation in balsam fir (Abies balsamea (L.) Mill.), which can affect wood properties such as moisture content and mechanical properties. This project aimed to assess the influence of the duration of spruce budworm defoliation on the wood quality of mature balsam fir trees. To do this, we studied sapwood proportion, decay, moisture content, mechanical properties and tracheid dimensions in stands that had suffered three, four or five years of defoliation. We also compared living and dead balsam firs and evaluated the change in wood properties with time. Our results showed that dead balsam firs suffered from a loss of wood quality rapidly after their death, particularly in terms of moisture content and decay in the sapwood. Sapwood proportion was similar between living and dead trees, but the sapwood of dead trees contained more decay and had a lower moisture content than living trees. Mechanical properties and tracheid dimensions were 10% and 4% lower in dead trees than in living trees. We did not observe any major differences in wood properties between the three durations of defoliation, suggesting that wood degradation occurs before that. The study did not make it possible to determine the optimal duration of defoliation to harvest the stands. Full article

(This article belongs to the Special Issue Wood Quality and Mechanical Properties)

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