IOSR Journal Of Applied Physics (IOSR-JAP) e-ISSN: 2278-4861.Volume 12, Issue 3 Ser. II (May – June 2020), PP 01-15 www.Iosrjournals.Org DOI: 10.9790/4861-1203020115 www.iosrjournals.org 1 | Page Application of strength criteria in describing modified wood Lesław Kyzioł 1 , Daria Żuk 2 1 Department of Mechanical Engineering, Gdynia Maritime University, Poland 2 Department of Mechanical Engineering, Gdynia Maritime University, Poland Abstract: The study was carried out on a series of 360 samples of Scots pine wood (Pinus sylvestris). A part of them were in their natural state, but the majority of them were superficially polymerized with poly(methyl acrylate). The test specimen comprised natural and modified wood with varying poly(methyl acrylate) (PMM) contents. The samples were tested for tensile strength on a universal testing machine. The purpose of the experiment was to examine the ways, in which polymerization improves on the strength properties and how the properties of materials change if the angle α between the load direction and the fiber orientation changes. An additional purpose of the study was to select an adequate strength criterion to describe the tested composite materials. Samples made of modified wood were uniaxially stretched at an angle of α = 0, 15, 30, 45, 60 and 90 ⁰ , measured between the direction of the load and the longitudinal direction of the fibers. It was claimed that the higher the polymer contents, the better the strength properties of modified wood. The study proposed its own model, which describes the bending stiffness of modified wood. Key Word: natural wood, modified wood, static tensile test, strength criteria. --------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 13-05-2020 Date of Acceptance: 25-05-2020 --------------------------------------------------------------------------------------------------------------------------------------- I. Introduction A number of methods has been developed with the purpose of increasing durability of wood as structural material. One of them is impregnation with a monomer and subsequent polymerization in situ. The resulting material is termed wood polymer composite (WPC). There are two types of composites obtained in this way: cell lumen type and cell wall type [1]. Cell lumen impregnation of wood creates a material in which the polymer fills the wood cell cavities, which increases the stability of the internal structure of the wood. Such modification results in a material with higher resistance to crushing and higher overall stiffness and hardness [1–5]. In the case of extension the polymer filling the cell cavity decreases freedom of deformation of the entire cell, whereas in the case of compression it retards buckling of the cell walls oriented parallel to the external compressing forces. The fuller the polymer fills the cavities, the more pronounced this reinforcing effect is. Tensile strength, although it provides merely rough characteristics of a given material’s mechanical properties, is commonly used in industry due to the ease of conducting and relatively low cost of the tensile test comparing to other, more precise, tests. Out of voluminous literature on mechanical properties of wood and WPC only a few articles treat tensile strength, and among those that do most cover tensile of natural, untreated wood. Research on this property of wood can be traced back to the prewar times [6] for tensile strength of birch and for earlier references and already then effort was directed towards establishing relation between tensile and density. In recent times some revival of interest in this topic is noticeable. The subject-matter of this work is strength of sapwood obtained from Scots pine (Pinus sylvestris) and the WPCs manufactured by its polymerization with the use of methyl methacrylate (MMA). Scots pine is ubiquitous throughout Northern Europe and is commonly used as a relatively cheap and easily available construction material. Its application ranges from civil engineering through port and harbor engineering to broadly understood shipping. It is commonly used as a material for dock fenders and for the upper layer of the keelblocks where ship’s bottom comes into contact with the support. Combined action of seasonal, cyclic variation of temperature and moisture, especially when these members work within the water-air interface, leads to their accelerated deterioration and eventually damage. The wintertime is particularly critical in this respect, since below-zero temperatures can cause bursting of internal wood structure. Besides, fenders fastened to the wharfs are subject to impact loads while mooring and cargo handling, which often results in their mechanical damage. This work was motivated by possible application of WPC in a broadly understood marine industry, where materials are exposed to the action of unfavorable environmental factors. Assuming that strength provides valuable macroscopic index of usefulness of the material, an experiment was designed to assess the necessary level of impregnation with polymer form the point of view of specific needs and to investigate how content the polymer and load direction