Subfossil wood is a valuable and rare material often used for production of expensive furniture and decorative artistic items of unique beauty. Its mechanical and tribological properties are still ...being studied and are considered specific due to the particular conditions of its long-lasting formation in aqueous sediment sludge. Various elements that have been impregnated into the wood tissue over many years make the machining and grinding of this type of wood rather difficult compared to normal recent wood. The main objective of this study was to determine the influence of the abrasive grain size of sandpaper on the abrasion volume loss of recent and two subfossil oak samples in three characteristic sections (cross, radial, and tangential). The results showed that the average size of abrasive grains and the orientation of the wood structure have an influence on the abrasion volume loss of all three samples. The phenomenon of the critical size of abrasive grains was observed in all samples and on all sections. As the size of abrasive grains increased to the critical size, the abrasive volume loss of the sample increased simultaneously. The lowest abrasion volume loss was observed on recent oak. In all samples, the lowest volume loss was measured on the cross sections, and the tangential and radial sections had mutually equal values. It was also found that the increase in the size of abrasive grains to a critical value resulted in the increasing value of the absolute difference between the abrasion volume loss of the cross, radial, and tangential section samples, while the relative relations between the abrasive volume loss values of three different sections (C/R, C/T, R/T) within the same grit of sandpaper remained quite similar.
The heat treatment of aluminum alloys is very important in industries where low weight in combination with high wear resistance, good strength, and hardness are important. However, depending on their ...chemical composition, aluminum alloys are subjected to different mechanical and thermal treatments to achieve the most favorable properties. In this study, an Al-Zn-Mg alloy was heat-treated including solution annealing at 490 °C for 1 h with subsequent artificial aging at 130, 160, and 190 °C for 1, 5, and 9 h. The hardness (HV1) and abrasive wear resistance with three different abrasive grain sizes were measured for all samples. The highest hardness was measured for the samples artificially aged at 130 °C/5 h, 227 HV1, while the lowest hardness was measured for the samples aged at 190 °C/9 h. The highest and the lowest wear resistance was also observed for the same state, i.e., artificially aged at 130 °C/5 h and 190 °C/9 h, respectively. The critical abrasive grain size was detected for some samples, where a decrease in wear rate was observed with an increase in the abrasive grain size from the medium value to the largest. The Response Surface Methodology (RSM) was applied to demonstrate the influence of the input parameters on the material wear rate.
In this study, metal matrix-based composite (MMC) was subjected to Equal Chanel Angular Pressing (ECAP) in several passes to determine the influence of deformation on the hardness of the samples. ...Composite based on A356 aluminum alloy and reinforced with Fly Ash (FA) particles was obtained by the compo casting method. The microstructural analyses and microhardness measurements were performed on the cast and pressed samples. Vickers hardness measurement of composite samples was performed with different indentation load sizes: HV0.02, HV0.05, HV0.1 and HV0.2. Results showed that hardness increases after each ECAP pass. The lowest hardness value of 42 (HV0.02) as well as the lowest arithmetical mean value of 46 (HV0.2) was measured at the cast composite. The greatest composite hardness of 107 (HV0.1) and the highest arithmetical mean value of 94 (HV0.1) was measured at the three-time pressed sample. The mathematical model named Meyer’s law was used for data analysis. In the cast sample, a decrease in hardness was detected with increasing indentation load, termed Indentation Size Effect (ISE), was confirmed with Meyers index n = 1.9112 < 2. Pressed samples showed opposite behavior—an increase in hardness with increasing indentation load—where Meyers index n > 2 indicated Reverse Indentation Size Effect (RISE). For all samples, a high coefficient of determination R2 > 0.99 confirmed that Meyer’s law described this phenomenon well.
Subfossil oak wood has spent centuries or millennia in the aquatic medium (rivers, lakes, bogs, etc.) and, due to water anoxic conditions, its decomposition is very slow. As a result of its long ...residing in specific conditions, its chemical composition, appearance, as well as mechanical and tribological properties have changed. Because of its aesthetic and mechanical properties, subfossil wood is very attractive and often used to produce valuable objects. The main objective of this study was to test how abrasion wear resistance of subfossil oak is affected by ageing. The effects of ageing on wood density and on the structure of lignin and cellulose were tested, as well as the loss of volume during abrasion in correlation with these changes. A study was conducted on samples of recent (regular) pedunculate oak wood and on six subfossil pedunculate oak samples in the age range of 890 and nearly 6000 years. Abrasion wear resistance was expressed through the loss of volume recorded using the Taber abraser. The smallest abrasion volume loss was measured for the recent oak specimens. Linear regression analyses showed that there was a very strong negative linear relationship between the age of subfossil oak and its abrasion volume loss. There was also a strong, but positive and significant linear correlation between subfossil oak age and density. Ageing also affected the structural composition of wood. Results obtained by Fourier Transform Infrared spectroscopy indicated a reduction of the relative crystalline fraction of subfossil wood in recent oak. The degradation of lignin in subfossil oak samples progressed more slowly over time than cellulose degradation. There was a negative correlation between age and the ratio of cellulose and lignin degradation; however, that relationship was found statistically insignificant. Similar results were obtained for the relationship between abrasion wear resistance and changes in the structural composition of the studied samples of subfossil oak wood.
The effect of annual rings’ orientation on bending strength was examined on subfossil elm wood. Elm is extremely rarely found as subfossil wood, and during the last 50–60 years it has almost ...disappeared from natural forest stands of south-eastern Europe, due to the Elm Dutch disease. The samples were cut from approximately 670 years old subfossil elm trunk retrieved from the bed of the river Sava in the area between the villages Grebnice and Domaljevac in north Bosnia. The wood was identified to the genus level based on optical microscopy analysis of three wood sections—transverse, tangential and radial. Bending strength was determined by the three-point bending test. The load was applied to the longitudinal–tangential surface (LT) and to the longitudinal–radial surface (LR). The bending strength values of subfossil elm do not differ from the values of recent elm, despite the 700-year resting in anoxic river conditions. Bending strength in LT direction was slightly higher than bending strength in LR direction. The coefficient of variation and the standard deviation of the arithmetical mean were higher for LT direction. It was found that the measured bending strength for both directions follows Weibull distribution. Coefficient of determination of Weibull functions was close to 1 for both directions. The Weibull shape parameter was higher for LR direction.
The research is part of a more extensive project in wood science, and its aim was to identify the effects of microstructural orientation on the two-body abrasive wear of sub-fossil wood. Samples to ...be tested were prepared from an approximately 670 year-old sub-fossil elm trunk retrieved from the Sava River bed in the northern part of Bosnia and Herzegovina. The samples were mounted to present three orthogonal planes (transverse, radial, and tangential) to a rotating disk of sandpaper. The effects of three average grit sizes (35, 82, and 201µm) were also investigated. The rate of abrasive wear for each microstructural orientation grew linearly with the number of grinding cycles. The lowest wear rate was observed on the transverse cross-section and the highest on the radial cross-section. As the sandpaper grit size was decreased, the wear rate values decreased for all cross-sections and became similar to one another. The wear resistance appears to be less affected by the heterogeneity of the wood microstructure than it is by a decrease in diameter of the abrasive grains. It was therefore concluded that the abrasion response of subfossil elm wood exhibits the same characteristics as the hitherto researched, more recent wood samples.
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•Rate of abrasive wear for each plane section of ca. 700 year old subfossil elm wood grew linearly with the number of grinding cycles.•The lowest wear rate was observed at the transverse section (cross section) and the highest at the radial section.•With the increasing fineness of sandpaper, the wear rate values decrease for all sections and become mutually very similar.•The old age of the elm bog wood and specific conditions of its origin have produced no significant effect on the wood microstructure and anisotropy of abrasive wear resistance.
U radu je istražen utjecaj mikrostrukturnih promjena, nastalih pri zavarivanju dupleks-čelika, na otpornost eroziji krutim česticama i kavitacijskoj eroziji. Uzorci su izrezani iz valjane ploče ...dupleks čelika 1.4462 i toplinski obrađeni tako da im se mikrostruktura što više podudara s mikrostrukturom realno zavarenog spoja. Na uzorcima je napravljena kvalitativna i kvantitativna analiza mikrostrukture. Istražen je utjecaj porasta volumnog udjela sigma faze (dobiven žarenjem na 800 °C) te utjecaj porasta omjera ferit/austenit (dobiven žarenjem na temperaturi od 1100 do 1300 °C) na otpornost eroziji krutim česticama i kavitacijskoj eroziji. Utvrđeno je da mikrostrukturne promjene koje nastaju u metalu zavara i zoni utjecaja topline dupleks čelika imaju veliki utjecaj na otpornost trošenju ispitanih slučajeva.
This chapter presents a study on the role of thermal oxides on the pitting corrosion of austenitic and duplex (austenitic-ferrite) steels. Specimens of AISI 316L SS with thermal oxide films obtained ...by isothermal heating are examined by using AES, XPS, and optical micrography techniques. The study shows that heating for 20 min in the range between 200 and 1000° C produced visible oxide films adhering to the metal and containing iron and chromium oxides with unimportant quantities of NiO, Mo-oxides, carbon compounds, and sulphides. The oxidation of Cr was much faster than the oxidation of Ni and Mo that causes depletion of Cr and accumulation of Ni under the oxide film with accompanying appearance of crystal lattice defects. Austenitic and duplex specimens with thermal oxides are tested for pitting susceptibility by immersion into FeCl3 solution at 25° C for 3 days according to ASTM G 48-99a. The result shows that thermal oxides on austenitic and duplex steels increase pits density, and maximum increase of pit density is achieved after isothermal heating at 600° C for austenitic specimens and 1300° C for duplex specimens. The thermal oxides ambiguously affected average pits depth and average pits orifice area, and the thermal oxide dissolution decline on pitting propagation.
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