Tangential Hardness Research Articles

Prediction of Mechanical Properties of Thermally Modified Wood Based on TSSA-BP Model

In order to demonstrate whether the sparrow search algorithm can show good performance in optimization, this paper improves the prediction model by this algorithm and predicts the change data of wood mechanical properties under different conditions, which better reflects the connection between the process parameters of wood heat treatment and the change of wood mechanical properties. The article takes the five main mechanical property parameters of thermally modified wood: compressive strength along the grain, flexural strength, flexural elastic modulus, radial hardness, and tangential hardness, respectively, as the objects of study and improves the sparrow search algorithm by Tenting chaotic mapping and then optimizes the Back Propagation (BP) network model by this algorithm. The results show that the number of iterations of the optimized Tent-Sparrow search algorithm-Back Propagation network model (TSSA-BP) is only one-eighth that of the original BP network model, and the convergence speed is greatly improved, the root mean square error of the TSSA-BP model is at least one-half times that of the original BP model, and the optimized model fits the original data better in terms of predicted values; thus, this article provided a feasible prediction algorithm for the field related to the mechanical property changes of wood after heat treatment.

Variation in Wood Properties of Hybrid Poplar Lumber by Radial and Vertical Position in Stem: A Case Study from Boardman, Oregon

Understanding of wood quality of hybrid poplar is critically important for manufacturers who want to know the suitability of the wood for specific products. To this end, lumber was milled from the merchantable stem of four hybrid poplar clones ages 10-11 yr., grown at single site near Boardman, OR. The vertical and radial position in the stem were recorded for each board and the boards were kiln dried, surfaced, and samples from each board tested to determine specific gravity (SG), dimensional stability, hardness, screw withdrawal, and bending strength and stiffness (modulus of rupture [MOR] and modulus of elasticity [MOE], respectively) from small clear specimens. Results show differences in wood properties relative to vertical and radial position in the stem. SG, hardness, screw withdrawal, and bending properties of lumber samples generally increased with height in tree. Tangential hardness, SG, and MOR varied significantly between different sides of the trees corresponding to predominant wind in the area. Boards milled from the center of the stem had lower MOE and MOR than boards milled from nearer the bark. The results of this study may be used to target specific stem locations for different end uses.

Properties of thermally modified teakwood

Thermal modification is a treatment that seeks to improve the properties of wood and reduce the heterogeneity in its color. The objective of this work was to evaluate the effect of thermal treatment on the anatomical, chemical, physical, mechanical, colorimetric, and thermal stability properties of teakwood. For this, teakwood samples were treated by an industrial autoclave at final cycle temperature of 160 oC. The reduction of cell wall thickness, the formation of cross-fissures and the crystallization of the wax inside the pores were observed in the anatomical structure. Chemically, the extractives evaporated and the polysaccharides ruptured, of which hemicellulose was the most affected. The heat treatment promoted lower equilibrium moisture, reducing the hygroscopicity and improving the dimensional stability of the wood. Considering the mechanical properties, the rupture modulus and the longitudinal and tangential hardness decreased after the heat treatment. The color of the wood changed significantly, from pink to dark brown. The treated wood had higher thermal stability, with greater weight loss at higher temperatures than the untreated wood

Representative Stress Correlation of Global Scratch Quantities at Scratch Testing: Experimental Verification

Evaluation and correlation of global quantities, i.e., normal and tangential hardness, at scratch testing in the context of a representative stress description was investigated. In particular, verification based on experimental results is at issue. It has been shown previously that within the framework of classical von Mises elasto-plasticity and quasi-static conditions, correlation can be achieved by using a combination of stresses at different levels of plastic strains to define representative quantities at scratching, accounting for the difference in mechanical behavior at elasto-plastic and rigid plastic scratching. However, verification from experimental results is required, which has been attempted in this study. Predictions based on previous theoretical results were compared with experimental findings for polymeric materials, as well as for different metals. Good agreement was found between the two sets of results, particularly so for the case of polymers modelled by von Mises elasto-plasticity. Accordingly, these results are of direct practical, accurate, and novel relevance for semi-crystalline polymers where viscoelastic effects are negligible.

Scratching of hcp metals: A molecular-dynamics study

Using molecular-dynamics simulation, we study the scratching of Ti and Mg crystals by a hard tip. Both the basal and a prismatic surface orientations are considered. We focus on the characterization of defects and plasticity in the crystal. Among the various types of dislocations generated the partials b=13〈1¯100〉 are most prominent. During scratch dislocation reactions constantly reorganize the dislocation network adherent to the scratch groove. Plastic activity is more pronounced for the prismatic surface, where dislocation loops – mainly consisting of b=13〈2¯110〉 and 13〈1¯100〉 dislocations – are emitted into the substrate. Under the basal surface I2 intrinsic stacking faults, corresponding to b=13〈1¯100〉 partials are formed parallel to the scratch groove bottom, while they are oriented perpendicular to the surface under the prismatic surface. We find that mainly the {011¯0}〈2¯110〉 slip system is activated, and relate the form of the pile-up generated to this slip. The tangential hardness is systematically smaller than the normal hardness under scratching. The basal surface has smaller hardness than the prismatic surface.

Effects of Thermomechanical Densification and Heat Treatment on Density and Brinell Hardness of Scots Pine (Pinus sylvestris L.) and Eastern Beech (Fagus orientalis L.)

The effects of thermomechanical densification (TMD) and heat treatment on density and Brinell hardness of Scots pine (Pinus sylvestris L.) and Eastern beech (Fagus orientalis L.) woods were investigated. Samples were densified using a specially designed hydraulic press with target compression ratios of 20 and 40%, and at 110 °C and 150 °C. Then, the heat treatment was applied to the samples at three different temperatures. To determine whether the changes occurred because of technological properties, tests of Brinell hardness and air-dry density were conducted. Increases of 42 and 35% were obtained for the density of Scots pine and beech samples, respectively. After the densification process, increases in radial and tangential hardness values were obtained. Decreases were observed in the density and hardness values of the samples because of the increase in temperature during heat treatment. After heat treatment, there were 4 and 5% decreases in the respective densities of Scots pine and beech, and decreases in their radial and tangential hardness values.

Nanoscratching of iron: A molecular dynamics study of the influence of surface orientation and scratching direction

Using molecular dynamics simulation we study scratching of Fe crystals by a hard repulsive tip. Three surface orientations – (100), (110), and (111) – are studied with two scratch directions in each case. We take care to analyze the projected normal and transverse contact areas properly to take the loss of contact of the tip to the substrate beneath it and its increased contact to the pile-up into account. We find that the form of the pile-up generated depends strongly on the surface orientation and scratch direction; this dependence is analyzed with the help of the dominant slip system in bcc Fe. The normal force to keep the tip at fixed depth and the transverse scratching force vary by only 15% between the different scratch systems investigated. The normal contact area decreases considerably during the initial stage of scratching as the trailing part of the tip loses contact with the substrate. The normal hardness shows similarly small variations between the different systems studied and is smaller than the hardness during the indentation process. The transverse contact area increases continuously during the scratch as the pile-up is generated. As a consequence the tangential hardness varies more strongly (by 26%) between the systems studied. For the (100)[011] scratch system we analyze the depth dependence of scratching. We find the friction coefficient to increase with scratch depth. The dependence of the normal and tangential hardness on depth are discussed with the help of the variation of the respective projected areas with depth.

THE EFFECT OF DENSIFICATION TEMPERATURE ON SOME PHYSICAL AND MECHANICAL PROPERTIES OF SCOTS PINE (PINUS SYLVESTRIS L.)

As wood’s density increases, strength properties tend to increase due to a decrease in cavity volume. This study aimed to determine the effect of temperature levels in the densification process with an open-system thermomechanical method on the density, bending, modulus of elasticity in bending, compression, shear strength, and Brinell hardness in radial/tangential directions of Scots pine. The densification process significantly increased the strength properties of Scots pine. This increase stemmed from the decrease in the rate of cavities with the densification process, which also resulted in an increase in cell wall elements that have load-bearing properties per unit volume. An increase in densification temperature decreased strength properties. The decrease in the strength values can be explained by increasing chemical degradation with a rise in the temperature level. The most suitable temperature level was 120oC for a higher bending, shear, and compression strength, and it was 140oC for a higher radial and tangential hardness in the densification of Scots pine. Increases of 42% in the bending strength, 20% in the shear strength, 47% in the compression strength, 242% in the radial hardness, and 268% in the tangential hardness were obtained after densification.

Influence of wood properties and technological parameters of processing on cutting power in milling of thermally modified beechwood

The paper presents results of influence of thermal modification on cutting power required for milling wood processing. The experiment was conducted for the different treatment temperatures (170?C, 190?C and 210?C) and different technological parameters of processing (feed and cutting depth). Cutting powers during milling were measured on four groups of beech wood samples, dimensions 35?16?400 mm, separately for heartwood and sapwood. The following mechanical and physical properties of the processed samples were tested: bending properties (modulus of rupture and modulus of elasticity), cross-sectional and tangential hardness, and air-dry density. The measuring device used for measuring, monitoring and displaying cutting power was developed at the Wood Machining Centre at the Faculty of Forestry in Belgrade. The results point out the differences in the powers required for processing heat-treated wood compared to untreated wood. The analysis shows that with the increase in treatment temperature, the required cutting powers decrease.

Prediction ofPinus sylvestrisclear-wood properties using NIR spectroscopy and biorthogonal partial least squares regression

Thirteen wood parameters were predicted using near infrared (NIR) spectra in the range 780–2380 nm modelled by biorthogonal partial least squares regression. The analysis of parameters and NIR measurements was done on clear-wood samples from the base and midstem of Scots pine ( Pinus sylvestris L.) from trees at two sites. Calibrations based on the measured parameters at seven growth rings (cambial age ranging between 6 and 42 years) could be divided into three groups: (i) the best accuracy was found for longitudinal modulus of elasticity (r > 0.9) followed by bending, compression, and cell length (0.8 < r < 0.9); (ii) microfibril angle, longitudinal hardness, proportion of latewood, and creep with correlations in the range of 0.7–0.8; and (iii) tangential hardness, cell diameter, and cell wall thickness with 0.4 < r < 0.7. It was also shown that juvenile (cambial age ≤20 years) and mature wood can be classified using NIR techniques.

Effective non-destructive segregation of Eucalyptus grandis logs according to radial and tangential hardness

SummaryBasic density and hardness strongly influence the quality of high—value end products, such as floor boards. Significant variations in wood properties have been identified both within and amongst logs of plantation-grown Eucalyptus grandis (flooded gum or rose gum), which typically feature an inner cylinder of corewood characterised by low wood density, hardness and strength. These and other defects near the core are not easily detected until the log is sawn open and thus committed to a particular end-use. Despite this, it is important that only logs with suitably dense and hard wood in the core are processed into high-quality flooring.This study assessed the utility of a non-destructive tool, the Pilodyn, for gauging the radial variation in density and hardness amongst plantation-grown E. grandis logs prior to sawing. Pilodyn readings were taken at intervals across the ends of 40 typical fresh flooded gum logs about 5 m long. A sub-sample of 15 logs, representative of the Pilodyn penetration (P-pen) spectrum, was selected for more intensive testing. Janka hardness tests on air-dried specimens indicated characteristically low hardness (<3 kN) in the inner zone of every log. However, Janka hardness in the outerwood was found to be highly variable amongst logs. The segregation of logs into classes of P-pen readings (low, medium and high) provided a useful basis for predicting Janka hardness values: the correlation between the weighted average P-pen reading and weighted average Janka hardness was 0.80 and 0.81 for hardness on the radial and tangential faces respectively. Within each of the Pilodyn classes, the bending stiffness and strength, and compression strength parallel to grain of the timber, increased in the radial direction.Pilodyn tests on the end face of logs may assist processors to identify those logs with particularly problematic proportions of corewood and/or quality.