Impact action of a projectiles on special protective structures and ways to increase their protective capacity

A method for studying the reaction of elastic elements of protective structures to a series of impact actions of shells has been developed. In the work, the elastic elements of the protective structure are modeled by homogeneous beams, and the dynamic action of the shells is simulated by instantaneous point-applied forces. A mathematical model of this dynamic process is constructed, which is a boundary value problem for a hyperbolic equation with an irregular right-hand side. The latter is described using Dirac delta functions. Cases of both fixed and free ends of protective elements are considered. The main ideas of perturbation methods are used for the researches carried out in the work. Analytical dependences for the description of elastic deformations of a protective element which are basic for definition of its strength characteristics are received. They and the graphical dependences built on their basis for specific cases show that the dynamic deformations of the protective element for the fixed ends are greater in the case of the projectile closer to its middle, at the same time for the free ends – closer to the end. With regard to the modernization of protective structures, the dynamic effect on their elements can be reduced by using elastic reinforcement or changing the method of fixing the ends of the protective element: elastic or with a certain angle of inclination of the bearing surfaces. It is proposed to use special plastics, soil layer, flexible wood flooring, etc. as elastic reinforcement. The technique used in the work is the basis for determining the strength characteristics of protective elements, and from so – to check the reliability of the protective structure; study of the dynamics of protective and similar types of structures, taking into account the nonlinear characteristics of the elastic elements of protective structures; study of more complex oscillations of elements of protective structures. In the case of a series of impacts, it is obvious that the amplitude of deflection of the protective element after each impact will increase over time, because the model does not take into account the force of viscoelastic friction. These tasks will be the subject of further research.

The duration of export trade relations and its influential factors in China's wooden floor

PurposeThis article will select 25 years of subdivided data to perform Kaplan–Meier survival analysis on the export trade relations of Chinese wooden flooring, use discrete-time cloglog models to analyze influencing factors, use logit and probit models to test the robustness, and try to systematically reveal the duration of China's wood flooring export trade and its influencing factors.Design/methodology/approachThis study used Kaplan–Meier survival function estimation method. In the survival analysis, survival function and hazard rate function are often used to characterize the distribution of survival time.FindingsThe continuous average export time of China's wooden flooring is relatively long, about 14 years. China's wooden flooring has a negative time dependency. After the export trade exceeds the threshold value of 15 years, the failure rate of trade greatly decreases, which has a “threshold effect.” Gravity model variables have a significant impact on the duration of China's wooden floor export.Originality/valueStudying the duration of forest products trade is of great significance for clearing deep-level trade relations and promoting sustainable development of forest products trade.

Wood flooring in combination with underfloor heating systems

The main objective of the article is to inform about the wood flooring in combination with underfloor water heating systems. Wood is a very sensitive material that responds to its surroundings. For this reason, it is necessary to select a suitable wood, meeting the criteria of suitability for laying as flooring in combination with underfloor heating systems. It is also important to comply with the conditions of storage of wooden flooring and its installation under acceptable climatic conditions at the construction site, together with the technical regulations for the installation of wooden flooring in combination with underfloor heating systems, during the whole life cycle of the wood flooring. This article defines the basic input premise for the implementation of wooden floors in combination with underfloor heating systems, regarding the relevant technical standards and technological procedures valid in the Czech Republic. At the same time, the article describes possible failures of wooden floors in case of non-compliance with the above conditions. In the conclusion, we propose measures based on the described installation process failures of the wooden flooring in combination with underfloor heating systems, and after its use.

Dimensional Stabilization of Engineered Wood Floor Using Linseed Oil and Paraffin Wax Impregnation

Engineered wood flooring comprises three or more layers of wood veneer adhered together to create a plank. The surfaces were coated to scale back water absorption. However, as wood is a hygroscopic substance, it loses and gains moisture from the atmosphere. This affects the dimensional stability of the floor badly, which emanates wide gaps between boards, cupped edges, crowning edges, and bulking of boards. Hence, the main intention of this study was to stabilize the engineered wood flooring by filling the wood cavity with linseed oil, paraffin wax, and a mixture of both, and evaluate the physical, mechanical property of treated and non-treated engineered wood flooring boards. The treatments were conducted at different temperature and durations. Keywords: Dimensional stabilization, Wood modification, Wood floor, Linseed oil, Paraffin wax, Impregnation

Self-Healing UV-Curable Acrylate Coatings for Wood Finishing System, Part 2: Impact of Monomer Structure and Self-Healing Parameters on Self-Healing Efficiency

Wood is increasingly used in construction for the benefits it brings to occupants and for its ecological aspect. Indoor wood products are frequently subject to mechanical aggressions, their abrasion and scratch resistance thus need to be improved. The coating system ensures the wood surface protection, which is, for wood flooring, a multilayer acrylate UV-curable 100% solid system. To increase the service life of wood flooring, a new property is studied: self-healing. The objective of this study is to observe the impact of monomer structure on self-healing efficiency and the effect of self-healing parameters. A previous formulation was developed using hydrogen bond technology to generate the self-healing property. In this paper, the assessment of the formulation and the self-healing parameters’ impact on self-healing efficiency as well as the physicochemical properties are presented. The composition of the monomer part in the formulations was varied, and the effect on the conversion yield (measured by FT-IR), on the Tg and crosslinking density (measured by DMA) and on mechanical resistance (evaluated via hardness pendulum, indentation, and reverse impact) was analyzed. The self-healing efficiency of the coatings was determined by gloss and scratch depth measurements (under constant and progressive load). It was proven that monomers with three acrylate functions bring too much crosslinking, which inhibits the chain mobility necessary to observe self-healing. The presence of the AHPMA monomer in the formulation permits considerably increasing the crosslinking density (CLD) while keeping good self-healing efficiency. It was also observed that the self-healing behavior of the coatings is different according to the damage caused. Indeed, the self-healing results after abrasion and after scratch (under constant or progressive load) are different. In conclusion, it is possible to increase CLD while keeping self-healing behavior until a certain limit and with a linear monomer structure to avoid steric hindrance. Moreover, the selection of the best coatings (the one with the highest self-healing) depends on the damage.

Innovative Polyelectrolyte Treatment to Flame-Retard Wood

Fire protection has been a major challenge in wood construction for many years, mainly due to the high flame spread risk associated with wood flooring. Wood fire-retardancy is framed by two main axes: coating and bulk impregnation. There is a growing need for economically and environmentally friendly alternatives. The study of polyelectrolyte complexes (PECs) for wood substrates is in its infancy, but PECs’ versatility and eco-friendly character are already recognized for fabric fire-retardancy fabrics. In this study, a new approach to PEC characterization is proposed. First, PECs, which consist of polyethyleneimine and sodium phytate, were chemically and thermally characterized to select the most promising systems. Then, yellow birch (Betula alleghaniensis Britt.) was surface-impregnated under reduced pressure with the two PECs identified as the best options. Overall, wood fire-retardancy was improved with a low weight gain of 2 wt.% without increasing water uptake.

Color Classification and Texture Recognition System of Solid Wood Panels

Solid wood panels are widely used in the wood flooring and furniture industries, and paneling is an excellent material for indoor decoration. The classification of colors helps to improve the appearance of wood products assembled from multiple panels due to the differences in surface colors of solid wood panels. Traditional wood surface color classification mainly depends on workers’ visual observations, and manual color classification is prone to visual fatigue and quality instability. In order to reduce labor costs of sorting and to improve production efficiency, in this study, we introduced machine vision technology and an unsupervised learning technique. First-order color moments, second-order color moments, and color histogram peaks were selected to extract feature vectors and to realize data dimension reduction. The feature vector set was divided into different clusters by the K-means algorithm to achieve color classification and, thus, the solid wood panels with similar surface color were classified into one category. Furthermore, during twice clustering based on second-order color moment, texture recognition was realized on the basis of color classification. A sample of beech wood was selected as the research object, not only was color classification completed, but texture recognition was also realized. The experimental results verified the effectiveness of the technical proposal.

Homogenization of Maritime Pine Wood Color by Alkaline Hydrogen Peroxide Treatment

The color of maritime pine wood is a critical parameter for manufacturing high added value materials (wood flooring or wood paneling for indoor applications). Actually, the color inhomogeneity between heartwood (Hw) and sapwood (Sw) can lead to a depreciation of the wood value and, therefore, to financial losses for wood products companies. In this article, the development of a color homogenization process based on alkaline hydrogen peroxide chemistry was studied. Maritime pine heartwood and sapwood powders were used to facilitate the chemical characterizations and colorimetric analyses by the CIEL*a*b* system. Brighter materials were obtained after the treatment by reducing significantly the color difference. The chemical modifications of wood surface were characterized by infrared spectroscopy analyses. The color evolution of the material overtime was also studied thanks to an accelerated ageing under UV irradiation. It was demonstrated that even if a color reversion occurred by oxidation, the color remained homogeneous between heartwood and sapwood.