Filters
Selected Mechanical Properties of Glue-Laminated Timber Produced from Locally Repaired Timber
This study aimed to evaluate the mechanical properties determined in a 4-point bending test of beams made of lumber from which knots had been locally removed and the resulting loss replaced with sound wood. Three sets of beams were prepared, which differed in the number of layers/lamellas and the position of the lamellas from which edge knots were removed. All the lamellas used in the tests were subjected to a modulus of elasticity assessment. In addition to the distribution of defects, it determined the position of a given piece in the beam structure. The tests showed that high mechanical properties could characterise the beams produced in this way, i.e., a modulus of elasticity close to 12 kN/mm2 and a strength above 40 N/mm2, if the lamellas without knots were located below the outer tension lamella. Significantly better results were obtained when PUR glue was used in the inserts rather than MUF. In this case, beams with an improved outer lamella in the tension zone using semi-circular inserts glued with PUR glue had an average strength of 34.6 N/mm2.
The Optimization of the Strength of Wood Adhesive Joints Supported by Steel Fasteners in Furniture Components
The strength properties of softwood components with bonded joints reinforced with fasteners were investigated and compared. Initial tests of the strength of the glue joints were carried out, with a change in the type of adhesive used. The application method significantly influenced the shear strength of the joint. With the adhesive and pre-bonding systems used, the shear strength of the adhesive joint of pine wood (Pinus silvestris L.) with PUR and PVAC resin was determined. The industrial results were 31% lower than in the shear test of the wooden joint bonded with PVAC glue. In terms of transverse shear force with staples, the joint has a transverse holding force that is higher than components connected with screws or nails. As the number of glue sticks increased, the shear strength of the pine wood increased. The strengths of the joined components in the glue roller method had an intermediate value. They did not differ significantly between the two-row gluing systems used. An increase in the force required to shear the bonded joint was observed for the different adhesive systems, the fasteners used, and their density.
The Influence of Hemp Fibers (Cannabis sativa L.) on the Mechanical Properties of Fiber–Gypsum Boards Reinforcing the Gypsum Matrix
The modern construction industry is looking for new ecological materials (available, cheap, recyclable) that can successfully replace materials that are not environmentally friendly. Fibers of natural origin are materials that can improve the properties of gypsum composites. This is an important issue because synthetic fibers (hardly biodegradable—glass or polypropylene fibers) are commonly used to reinforce gypsum boards. Increasing the state of knowledge regarding the possibility of replacing synthetic fibers with natural fibers is another step towards creating more environmentally friendly building materials and determining their characteristics. This paper investigates the possibility of manufacturing fiber–gypsum composites based on natural gypsum (building gypsum) and hemp (Cannabis sativa L.) fibers grown in Poland. The effect of introducing hemp fibers of different lengths and with varying proportions of mass (mass of gypsum to mass of fibers) into the gypsum matrix was investigated. The experimental data obtained indicate that adding hemp fibers to the gypsum matrix increases the static bending strength of the composites manufactured. The highest mechanical strength, at 4.19 N/mm2, was observed in fiber–gypsum composites with 4% hemp fiber content at 50 mm in length. A similar trend of increased strength was observed in longitudinal tension. Again, the composite variant with 4% fiber content within the gypsum matrix had the highest mechanical strength. Manufacturing fibers–gypsum composites with more than 4% hemp fiber content negatively affected the composites’ strength. Mixing long (50 mm) hemp fibers with the gypsum matrix is technologically problematic, but tests have shown a positive effect on the mechanical properties of the refined composites. The article indicates the length and quantity limitations of hemp fibers on the basis of which fiber–gypsum composites were produced.
Qualitative and Strength Analysis of Pine (Pinus Sylvestris L.) Wood Materials - Study of Pallet Elements
The manufacture of packaging products requires determining the strength requirements of the components that make up the structural elements of pallets, crates and other packaging. Wood, as a renewable material, is the basic raw material for manufacturing wooden pallets. The premise of the research is that the strength of pallets is derived from the characteristics of the components of the subassemblies. Strength tests of lumber were carried out, which determine the evaluation of the suitability of sawn materials. Verification of raw material properties determines the adaptation of individual assemblies to static and dynamic force loads. Pine (Pinus sylvestris L.) lumber was verified, taking into account the origin of the cross-sectional area and the presence of anatomical structure features. The results of the study confirm the influence of wood origin on the suitability of pine wood for wood packaging. The influence of a certain origin from the log can translate into changes in strength properties. It was found that wood density is not a critical parameter for evaluating the strength of lumber and product. Tests of separated structural lumber for wood packaging indicate significant differences in the condition of the wood and the magnitude of the strength parameter.
Properties of fiber-gypsum composite formed on the basis of hemp (Cannabis sativa L.) fibers grown in Poland and natural gypsum
: Properties of fiber-gypsum composite formed on the basis of hemp (Cannabis sativa L.) fibers grown in Poland and natural gypsum. The popularity of composites reinforced with natural fibers is constantly growing and therefore, they are a subject of many scientific works as well. An example of interesting concept is the use of hemp fibers to reinforce a gypsum matrix and therefore, presented study was aimed to determine the effect of their content on the properties of resultant composites. Moreover, the influence of setting temperature was also investigated. The scope of the research included determination of properties such as: density, setting time, bending strength, modulus of elasticity and thermal conductivity coefficient. Studies have shown that as the amount introduced fibers increases, the density of manufactured composites decreases. Furthermore, increase in the content of hemp causes a significant extension in setting time of the gypsum matrix. Based on the outcomes of mechanical properties, it was found that the optimal content of fibers is 4% and further increase in their share results in a deterioration of flexural strength characteristics. The increase in a setting temperature leads to thereduction in their bending strength and modulus of elasticity. Composites reinforced with hemp fibers demonstrate significantly improved thermal insulation properties
Mechanical Characterization of Glued Laminated Beams Containing Selected Wood Species in the Tension Zone
The aim of this study was to determine the mechanical properties of laminated beams containing selected wood species in the tension zone using a four-point bending test. Three beam types were manufactured with respect to the timber used in the tension zone, i.e., beams containing oak or beech timber of I and II quality class and pine timber with no defects (as defects had been removed). The manufactured beams were assessed with respect to bending strength and the modulus of elasticity. The obtained results were compared with the performance of BSH (Industrial beams GL made in Germany—Brettschichtholz) industrial beams. We concluded that beams made from pine timber are an appropriate alternative to spruce beams. The static bending strength of the beams made with hardwood faces was 70% higher than that of beams made with pine wood. All types of beams manufactured in the laboratory met the requirements of at least the GL24c class.
Possibility to Use Short Sawn Timber in the Production of Glued Laminated Beams
Numerous studies have shown that the geometry of micro-joints significantly affects the strength of the so joined timber element. The bending strength increases by creating a larger bonding area by increasing the length of the wedge joint. Although this type of joint has been successfully used for many years, it can still be troublesome to make. For these reasons, the present study investigated an easy-to-fabricate wedge joint, which we folded during the beams’ formation and glued with the same adhesive as the individual lamellas. Although the research has not fully answered all the questions relevant to both scientific and technological curiosity, it indicates the great potential of this solution. Following the principle adopted in the ongoing wood optimisation work, we concluded that the beams of the target cross-section should be produced, and it should only be possible to cut them to a certain length. In this approach, we only removed defects at critical points for the beam structure and, in this way, up to 30% of the timber processed could be saved or better utilised.
The Strength of Pine (Pinus sylvestris L.) Sawn Timber in Correlation with Selected Wood Defects
Pine timber of Polish origin intended for structural purposes is characterized by significant variability in the quality parameters. Technological suitability determined on the basis of relevant international classifications is based on the assessment of both selected mechanical and physical properties of wood. Moreover, the description of visual properties is also a valuable indicator regarding defect distribution. In the group of quality features playing a crucial role in the classification of sawn timber, there are knots, disruptions of grains, cracks, etc. Thus, the aim of the research was to determine the correlation between the presence of selected defects and the strength properties of individual timber pieces. This type of study is based on a nondestructive test method that allows for high optimization of sawn materials processing. In the case of sawn timber of Polish origin, the modulus of elasticity (MOE) determined using the sonic test is commonly used as a criterion. The research material was harvested from southern Poland. The results of the conducted studies confirmed a correlation between an increasing occurrence of particular types of defects and the results of MOE. Furthermore, as a result of the performed investigations, no significant effect of narrow surface cracks on strength properties was observed.
Physico-Mechanical Characteristics of Gypsum–Fiber Boards Manufactured with Hydrophobically Impregnated Fibers
Although gypsum-based building materials exhibit many positive characteristics, solutions are still being searched for to reduce the use of gypsum or improve the physico-mechanical properties of board materials. In this study, an attempt was made to produce gypsum boards with hemp fibers. Although hemp fibers can be a specific reinforcement for gypsum-based board materials, they negatively affect the gypsum setting process due to their hygroscopic characteristics. Fibers impregnated with derivatives based on polyvinyl acetate, styrene–acrylic copolymer and pMDI (polymeric diphenylmethane diisocyanate) were used in this study. Gypsum–fiber boards produced with impregnated fibers showed approximately 30% higher mechanical properties as determined by the 3-point bending test. The positive effect of the impregnates on the hemp fibers was confirmed by FTIR (Fourier-transform infrared spectroscopy) and TG/DTA (thermogravimetric analysis/thermal gravimetric analysis) analysis.
Influence of pine wood sawing technology on material efficiency indicators
Influence of pine wood sawing technology on material efficiency indicatorsConiferous wood processing is one of the basic methods of using natural wood resources. The aim of the work was to determine the impact of the selection of wood cutting technology, which plays an important role in shaping the material indices, especially the volumetric efficiency index. In the case of pine wood processing, group and individual technologies were assessed.. The use of frame saws guarantees the achievement of repeated sorting’s with a quantitative efficiency rate of 69%. The introduction of individual technology based on band saws results in an increase in quantitative sawing efficiency to 72%. The selection of processing technology and the dimensional structure of processed roundwood have a significant impact on the average sawing rate.