A Review of Experimental Research on the Mode I Fracture Behavior of Bamboo

Bamboo is an eco-friendly material with light weight, high strength, short growth cycle and high sustainability, which is widely used in building structures. Engineered bamboo has further promoted the development of modern bamboo structures due to its unrestricted size and shape. However, as a fiber-reinforced material, fracture damage, especially Mode I fracture damage, becomes the most likely damage mode of its structure, so Mode I fracture characteristics are an important subject in the research of mechanical properties of bamboo. This paper summarizes the current status of experimental research on the Mode I fracture properties of bamboo based on the three-point bending (TPB) method, the single-edge notched beam (SENB) method, the compact tension (CT) method and the double cantilever beam (DCB) method, compares the fracture toughness of different species of bamboo, analyzes the toughening mechanisms and fracture damage modes, discusses the applicability of different theoretical calculation methods, and makes suggestions for future research priorities, aiming to provide a reference for future research and engineering applications in related fields

Nanotechnology application on bamboo materials: A review

Bamboo is one of the renewable materials which can be applied in the engineering field widely. Previous research has shown that bamboo's inherent poor durability can limit the application of bamboo materials. And nanotechnology has been receiving more and more attention on improving the properties of natural materials, simultaneously. This article aims to promote the application of nanotechnology on bamboo by presenting some guides. And this article has been organized as follows: first, the characteristics and nanomechanical behavior of bamboo in mesoscopic and nanoscopic scale have been introduced. Then, nanomaterials for modifying bamboo have been presented. Next, some analyses on the improvement of some properties of nano-modified bamboo materials have been made. Finally, future perspectives have been discussed

Impact of thermal modification on color and chemical changes of African padauk, merbau, mahogany, and iroko wood species

Thermal modification is an environment-friendly technology for improving various wood properties, especially the dimensional stability, decay resistance, and color homogeneity. In this work, four tropical wood species (African padauk, merbau, mahogany, and iroko) were thermally modified by the ThermoWood process. The influence of heat treatment on the color and chemical changes of wood was studied by spectrophotometry, Fourier transform infrared (FTIR) spectroscopy, and wet chemistry methods. As the temperature increased, a decrease in lightness (L*) and a simultaneous decrease in chromatic values (a*, b*) were observed, indicating darkening and browning of the wood surface. As a result of the heat treatment, the relative content of hemicelluloses decreased the most in merbau and mahogany, while the thermal stability of iroko and African padauk was higher. All examined wood species showed a strong correlation between the lightness difference value (ΔL*) and the content of hemicelluloses (r = 0.88-0.96). The FTIR spectroscopy showed that the breakdown of C═O and C═C bonds in hemicelluloses and lignin plays an important role in the formation of chromophoric structures responsible for the color changes in the wood.O

Research and Application Progress of Straw

Straw is a general term for the stem and leaf parts of mature crops, and is a multi-purpose renewable biomass energy resource in the agricultural ecosystem. The prospect of comprehensive utilization of straw has become broad with the development of agricultural production, the advancement of science and technology, and the improvement of the level of agricultural mechanization. The comprehensive utilization of straw plays an important role in enhancing the sustainable development ability of agricultural economy and improving the current situation of comprehensive utilization of agricultural resources in my country. This paper briefly combs the development history of straw and the prospect and current situation of comprehensive utilization, and expounds the separation technology of straw components, straw man-made panels, straw concrete, straw returning technology and oyster mushroom cultivation. It focuses on the description of the component separation technology of straw and the manufacturing process of straw-based panels. The different separation methods and separation effects of cellulose, hemicellulose and lignin were introduced in detail, and the static yield strength (MOR), internal bonding strength (IB) and water absorption thickness of several common straw-based panels were compared and studied (TS). Finally, it summarizes the benefit analysis of the comprehensive utilization of straw by scholars from the perspective of economics, and summarizes the corresponding measures based on their own views

Effect of thermal modification on properties and milling behaviour of African padauk (Pterocarpus soyauxii Taub.) wood

The purpose of this study was to analyze the effect of thermal treatment on chemical changes, mechanical properties and machining behavior of African padauk wood. Thermal modification of padauk wood was carried out at 3 different temperatures (160 °C, 180 °C, and 210 °C). Effect of modification temperature on chemical constituents and bending properties of padauk wood were ascertained. Thermally modified and un-modified samples were subjected to milling operation with combination of various processing parameters such as cutting speed (20, 30, 40 m/s), feed speed (4, 8, 11 m/min) and rake angle (15°, 20°, 25°), to obtain the optimum combination in terms superior surface quality (surface roughness and surface waviness) and minimum energy consumption. Cellulose and lignin proportion increased while hemicellulose proportion reduced significantly following thermal modification. Modification temperature, particularly 210 °C, had significant effect on the chemical constituents and bending strength of padauk wood. Modification up to 180 °C did not cause any significant loss in bending strength and bending stiffness, but the strength and stiffness loss was significant when samples were modified at 210 °C. Best surface quality with minimum energy consumption was obtained in African padauk wood thermally modified at 210 °C and milled with a cutting speed of 20 m/s, rake angle of 20° and feed rate of 4 m/min

The Characteristics of Glued Tensile Shear Strength Constituted of Wood Cut by CO2 Laser

The performance of engineered wood products is highly associated with proper bonding and an efficient cutting method. This paper investigates the influence of CO2 laser cutting on the wetting properties, the modified chemical component of the laser-cut surface, and the strength and adhesive penetration near the bondline. Beechwood is cut by the laser with varying processing parameters, cutting speeds, gas pressures, and focal point positions. The laser-cut samples were divided into two groups, sanded and non-sanded samples. Polyvinyl acetate adhesive (PVAc) was used to bond the groups of laser-cut samples. After assembly with cold pressing, the tensile shear test was carried out. Numerical modelling was carried out to determine the partial elongation and shear strain of the glue line. Based on this, the shear modulus and linear elasticity of the glue line were estimated. Scanning electron microscopy was used to assess the adhesive penetration into the porosity structure of the laser-cut samples, and the depth of the heat-affected zone. The laser-cut surface was analysed by Fourier transform infrared spectroscopy. The wetting properties of the laser-cut surface were investigated by using a contact angle goniometer. The numerical model of the strain-stress curve confirmed the experimental model. The highest modulus of the linear elasticity of the glue in the numerical calculation belongs to the joint containing laser-cut samples at a gas pressure of 21 (bar). The penetration depth of PVAc adhesive into the porosity structure of the laser-cut samples was similar to that of sawn samples. The deepest heat-affected zone in the laser-cut samples was 150 µm. A PVAc drop disappeared immediately on the laser-cut surface without sanding, but gradually on the sanded surface. In contrast, the drop on the sawn surface remained with an angle of 32°–48°. The degradation of hemicellulose and lignin was proven by the lower intensity of the C=O and C-O Bonds, compared to the sawn surface

Three-Dimensional Pneumatic Molding of Veneers

The goal of this paper is to introduce a new testing method suitable for the evaluation of the three-dimensional (3-D) moldability of veneers and to use this method to test the impact of specific factors on the 3-D pneumatic molding process. The tested factors included veneer moisture content, wood species, shape of test piece, and fixing method on the maximum wood deflection. Veneers were molded using compressed air on equipment designed by our group for the sole purpose of this experiment. The results indicated that the monitored factors had an effect on deflection during the 3-D molding process. The results of this investigation extend the state-of-the-art knowledge regarding this technology and indicate the possibility of utilizing this innovative testing method for 3-D molded veneers

Flammability Characteristics of Thermally Modified Meranti Wood Treated with Natural and Synthetic Fire Retardants

This paper deals with the effect of synthetic and natural flame retardants on flammability characteristics and chemical changes in thermally treated meranti wood (Shorea spp.). The basic chemical composition (extractives, lignin, holocellulose, cellulose, and hemicelluloses) was evaluated to clarify the relationships of temperature modifications (160 °C, 180 °C, and 210 °C) and incineration for 600 s. Weight loss, burning speed, the maximum burning rate, and the time to reach the maximum burning rate were evaluated. Relationships between flammable properties and chemical changes in thermally modified wood were evaluated with the Spearman correlation. The thermal modification did not confirm a positive contribution to the flammability and combustion properties of meranti wood. The effect of the synthetic retardant on all combustion properties was significantly higher compared to that of the natural retardant

Evaluation of Wood Surface Quality after 3D Molding of Wood by Pressing

The goal of this study was to develop and test an appropriate method for the evaluation of surface quality and to identify and quantify the quality of a surface modified by 3D molding. New software was developed to evaluate the surface quality based on the identification of macroscopic defects such as cracks within a scanned area. The influence of specific factors that affect the development of cracks during the uneven pressing process was assessed. Based on the measured and evaluated results, a process combination of factors was designed which yielded an embossed surface that was formed with the lowest proportion of cracks and with sufficient shape stability. In this work, 432 groups of test pieces were monitored, with each piece exposed to different combination of factors. Based on the measured and evaluated results, we found a combination that provided the lowest crack ratio. This innovative method will contribute to the knowledge of embossed surface quality and to the improvement of the uneven pressing process for wood surfaces

Effect of Cyclic Loading on Modulus of Elasticity of Aspen Wood

This article investigates the modulus of elasticity of solid and laminated aspen wood of various thicknesses after cyclic loading. A three-point static bending test was carried out to determine the modulus of elasticity. Cyclically loaded samples were compared with samples without cyclic loading. For the laminated wood, the results demonstrated a statistically significant impact of cyclic loading on the elasticity modulus. In contrast, no significant impact of cyclic loading was shown for the solid wood. The impact of the number of cycles was significant for both laminated and solid wood. When this number increased, the elasticity modulus values decreased. Generally, higher elasticity modulus values were confirmed for the laminated wood