Prismatic Samples Research Articles

Improvement of the durability of concrete by substitution of raw ground colemanite

This study investigated the effects of raw ground colemanite (GC) mineral on concrete strength and durability. Concrete mixtures were prepared at six replacement levels of GC (0%, 1%, 2%, 3%, 4% and 5%, by weight of cement). Fresh state properties of concrete samples were measured. Schmidt Hammer, ultrasound pulse velocity, abrasion, flexural, and compressive strength tests were performed on the cube, cylinder and prismatic concrete samples on the 7th, 28th, and 90th days. As concrete durability has a negative impact on many physical and chemical factors, the durability properties of the samples after wet-dry, freeze-thaw, sulphate, and chloride exposure were investigated, resulting in the finding that GC substitution up to 5% yields the desired compressive strength for the C30/37 concrete class. The optimal GC substitution ratio was determined to be 3%, as this ratio increases the strength and durability probabilities. It was decided that raw GC mineral substitution with an average particle size of 12 µm and increasing adhesion force in concrete production is convenient, particularly in the context of improving material properties against environmental circumstances, saving cement, and utilizing boron minerals.

EXPERIMENTAL ANALYSIS OF MESH ELEMENTS GLULAM DOME

To study the stress-strain state of the mesh dome model with the diameter 4 m, the series of glulam rods were prepared for the central compression test. The tests were carried out in the laboratory of the Department of Metal, Wooden and Plastic Structures. The stresses at the distinguished points of the elements were determined through the deformations using the resistance strain sensors. The feature of prismatic samples was the presence of stress concentrators in the support zones in the form of the holes for the location of universal connectors [3]. The significant sizes of the model made it possible to minimize the influence of the scaling factor on the obtained results. The general conclusion of the study should be considered high bearing capacity of the tested samples. The destruction of the samples took place in the support zone due to the crushing of the wood. The next tasks of the research will be the optimization of the elements sizes and testing of the dome model. The cross-section of the elements, in addition to providing the load-bearing capacity, is affected by the need to obtain certain thermotechnical characteristics of the enclosure, i.e. the elements of the dome must have the dimensions that allow placing a layer of effective insulation in their plane. A separate task is the selection of the roof, which can be considered exclusively as a part of the permanent load on the supporting system, or as a continuous shell that unfastens the frame

Вычисление коэффициентов определяющих соотношений нелинейно-упругих материалов с использованием эволюционных алгоритмов

Abstract. The possibility of parameter identification for constitutive relations of materials based on uniaxial stretching of a nonlinear-elastic prismatic sample and on inflating a hollow cylinder has been studied. The experiments are modeled using the semi-inverse method of nonlinear theory of elasticity. To describe the mechanical properties of the studied objects, the potentials of compressible nonlinearly elastic media - Blatz and Ko material, and Murnaghan model are used. In the first stage, a series of direct problems are solved. Analytical expressions for the load-elongation dependence are used for the stretching problem. The three-dimensional problem of a cylinder inflation is reduced to a nonlinear boundary value problem for an ordinary second-order differential equation for the function of the radial displacement of cylinder points. In all cases, load diagrams are constructed based on the specified parameters of the nonlinearly elastic models, which are subsequently considered as initial data for the inverse problem of parameter identification. The problem is reduced to finding the minimum of the objective function which is defined as a least squares function. Two evolutionary algorithms were used for analysis: the Squirrel search algorithm (SSA), based on the model of the foraging behaviour of southern flying squirrel population, and the differential evolution algorithm (DE) from the SciPy library. Reliable identification of material parameters of models was shown using evolutionary algorithms based on load diagrams of samples, including condition of artificial noise of "experimental" data.

Dynamic mechanical properties and failure behaviors of brittle rock materials with a tunnel-shaped opening subjected to impact loads

Since the surrounding rocks of underground tunnels are frequently suffered from the dynamic disturbance of mechanical percussion drilling and explosive blasting, it is significantly meaningful to investigate the mechanical properties and failure behaviors of rock material with a tunnel-shaped opening under dynamic loads. In this work, seven groups of prismatic samples, including the intact samples and the samples with a circular opening of three kinds of diameters, a square opening, a horseshoe-shaped opening and a D-shaped opening, were prepared for dynamic compressive loading. The results show that the prismatic specimens satisfy the stress uniformity condition in impact tests using SHPB testing system with a bar diameter of 50 mm. The weakening effects of the existed openings on the dynamic compressive strength, elastic modulus and peak strain of rocks are closely associated with the size and shape of opening and the loading direction. Based on the energy parameters of the samples, the dissipated energy density of each group of samples can be solved. The failure degree of the samples characterized by dissipated energy density and fractal dimension are in good agreement. Besides, the failure mode of the intact specimen belongs to splitting tensile failure, while that of the pre-holed specimens can be classified as shear-dominated failure due to the coalescence of the openings and the shear cracks occurring along the diagonals of the specimens. The test results provide some insights into the mechanical behavior of rock materials under dynamic loads and lay an important theoretical foundation for support design and rock disaster prevention of underground tunnel.

Multimodal Evolution of Coal Permeability due to Interior Deformations within a Triple Porosity System

Summary Measurements of coal permeability are normally analyzed without considering the interaction among microfracture and pore size distributions within the sample (control volume). Without this inclusion, nearly all permeability predictions are monomodal as reported in the literature. However, experimental observations are multimodal for most cases. In this study, we hypothesize that these discrepancies or mismatches between measurements and analytical predictions are due to the exclusion of the interaction among microfracture and pore size distributions within the sample (control volume). We report a first experimental study of triple-porosity interactions on a prismatic sample containing millimeter-scale fractures (Ⅰ) and micron- (Ⅱ) through nanometer-scale (Ⅲ) pores. Migration speeds of sorbing (e.g., CH4) gases are conditioned by the strain field, which is in turn conditioned by effective stresses and swelling strains. These distinct pore populations exhibit characteristic times for a time-staged equilibration of the strain field as multiple plateaus. This time-staged evolution of strain in turn delimits the evolving fracture permeability into a series of stages. The relatively high permeability of fractures and micropores defines a brief intermediate equilibrium permeability, after which the nanopore system controls the final permeability evolution. Our results indicate that the multimodal evolution of coal fracture permeability can be explained by the time-staged evolution of strain due to multiporosity interactions and could be defined by a time-staged equilibration of the strain fields as multiple plateaus.

Deep cryogenic treatment of AA7050: tensile response and corrosion susceptibility

Cryogenic treatments represent an innovative technology developed with the aim of improving the performance of metallic alloys. The beneficial effects on steels are well documented in the literature, whereas their influence on other materials, such as aluminum alloys, is still not completely clarified. Even if the scientific literature reports conflicting data and conclusions, the industrial applications of such treatments are constantly growing. In the present experimental work, the mechanical and corrosion properties of a high-performance 7050 aluminum alloy plate were studied after cryogenic treatment at − 196 °C in liquid nitrogen. Tensile tests were performed on heat-treated samples, and intergranular corrosion tests were carried out on prismatic samples, according to ASTM G110-92 standard. The specimens were exposed to the corrosive environment and the effect of intergranular corrosion was measured by quantitative analysis using light-optical microscopy (LOM). Whereas trifling variation was observed in the mechanical resistance and plastic behavior, the corrosion tests showed a benefic effect of the cryogenic treatment. The microstructure was investigated by FEG-SEM analysis, revealing a different distribution of precipitates near the grain boundaries, which was able to reduce the electrochemical potential difference among these regions and the center-grain.

Učinak recikliranog stakla kao agregata na svojstva mikrobetona

Micro-concrete (MC) can be defined as a high-performance cement-based material produced using microaggregates and cement in the required proportions. Owing to its high performance, it has the potential to be used in the structural repairs of existing building elements. Within the scope of this study, an evaluation was conducted by creating a usage scenario under which glass, which is a waste product, can be reduced and applied in a way that provides a sufficient MC performance. There are four different binder contents in the mixtures within the scope of the present study, i.e., 570, 580, 599, and 658 kg/m3. From these mixtures, together with the control mixture, 12 %, 27 %, and 50 % microaggregates were replaced with glass sand and 16 different mixtures with a total of 4 different aggregate contents were produced. For the mechanical, physical, and durability tests, 40 × 40 × 160 mm sized prisms and 50 × 50 × 50 mm sized cubes were produced. For the purposes of this research, mechanical tests were carried out on 144 7-, 28- and 56-day old prismatic specimens. In addition, the effects of a freeze-thaw and temperature on the mechanical properties were investigated on 192 prismatic samples. In determination of the durability, physical properties such as the porosity, sorptivity, and specific gravity were tested and determined using cubic samples. The test results show that the replacement of MA with GS has positive effects on all mechanical behaviours of MC.

Natural and recycled aggregate concrete containing rice husk ash as replacement of cement: Mechanical properties, microstructure, strength model and statistical analysis

This study investigated the effects of the replacement ratio of natural aggregates (NAs) by recycled aggregate (RAs), the replacement ratio of cement by rice husk ash (RHA), and their interaction on compressive properties of recycled aggregate concrete (RAC). The RAs used consisted of 37.5 wt% recycled brick aggregates and 62.5 wt% recycled concrete aggregates from construction and demolition waste. To optimise the properties of RAC mixture, a full factorial design of experiment was applied in designing the concrete mixture proportion. The two factors considered were: the replacement ratio (wt.%) of RA with five levels (0%, 30%, 50%, 70% and 100%) and the replacement ratio (wt.%) of RHA with four levels (0%, 10%, 20% and 30%). Axial compression tests based on the full factorial experiment were conducted on cubic and prismatic samples at 28 days to evaluate their compressive properties. In addition, further cubic concrete groups were also tested in axial compression at different concrete ages (i.e., 3, 7, 28, 56 and 91 days) to understand the effect of concrete age on the compressive strength. Statistical analyses including ANOVA, post-hoc pairwise comparisons and effect size (Cohen's d) computation were performed to evaluate the experimental results. The results indicated that the compressive strength of concrete at 28 days was significantly affected by the replacement ratio of RA and RHA (both p-values <0.0001), as well as their interaction (p-value = 0.0001). For the four different replacement ratios (0%, 10%, 20% and 30%) of RHA considered in this study, the optimised ratio was 10%, which resulted in 0.4% and 4.9% increases in compressive strength of NAC and RAC (RA replacement ratio = 100%), respectively. RHA contributed more to the strength improvement of RAC than to that of NAC, both at 28 days and at 91 days. A new compressive strength model was developed for concrete containing RAs and RHA (or for other supplementary cementitious materials such as fly ash, silica fume, metakaolin and ground granulated blast slag). The validation with the experimental results from the literature showed a good accuracy of this model for concrete strength prediction, with 4.45% mean absolute percentage error and 2.3 root mean square error.

Um novo método para a determinação da retração de argamassas nas primeiras 24 horas de hidratação

abstract: The shrinkage of cementitious materials is a complex phenomenon of volume reduction that can result in cracking, affecting the durability of these materials. The Brazilian standard ABNT NBR 15261 addresses long-term shrinkage without emphasis on the initial phase (&lt; 24h) of hydration, which contains the plastic state of the cementitious material. Therefore, a method was proposed to measure the shrinkage in the first 24h of mortar hydration, on a laboratory scale, from prismatic samples, using molds from the Brazilian standard ABNT NBR 15261 (285x25x25mm) and rigid elements that transmit horizontal displacements of the sample to dial gauges. Cement mortar specimens were studied with the water/dry materials ratio fixed at 0.168 and varying the binder/aggregates ratio linearly: 33% (1:3); 25% (1:4); and 17% (1:6). Different exposures to the environment (sealed, open and wind) were applied. The analysis indicated that the proposed method was sensitive enough to indicate statistically significant relationships between the maximum initial shrinkages and the variation in the concentration of the binders, as well as indicating variations in the behavior of the initial shrinkage. The increase in cement concentration caused an increase in the average initial shrinkage of 76% in the samples exposed to air, 54% in those exposed to 5 m/s wind, and 22% in the sealed samples.

Analysis of non-axenic biomasses for self-healing concrete

As an alternative to the usage of axenic bacteria to achieve microbially induced calcium carbonate precipitation (MICP), this study evaluates the usage of two non-axenic biomasses as self-healing agents. A fungi-based consortium (Yeast) and heterotrophic nitrifiers (HTN) were harvested from the incubation of agricultural side streams. The characteristics of the two biomasses were identified through flow cytometry, total suspended solids and volatile suspended solids tests. The incorporation of the biomasses into concrete was evaluated in terms of compressive strength, flow and healing ability. Self-healing ability was analyzed through microscope imaging on prismatic (60x60x220 mm) samples. Cracks were induced with a three-point bending test where the widths were controlled with an LVDT sensor. A curing period of 56 days was applied to the samples and visual inspection was conducted at the start and end of the healing period with an optical microscope. Results compare and discuss the differing effects of active and autoclaved biomasses on the concrete properties and crack closure.

Tensile behavior of a laminated magnesium-aluminum composite with axial elliptical holes

A 3D finite element simulation of the behavior of a prismatic sample of a magnesium-aluminum composite material AMg6-AD1-MA2-1 with an elliptical defect in the AD1 layer under axial tension was carried out, its strength and the change in the stress-strain state were determined when the thickness of the AD1 layer varied from 5 to 1, 25 mm. A change in the stress-strain state and strength during perforation transfer to the MA2-1 layer was revealed.

The influence of novel beam shapes on melt pool shape and mechanical properties of LPBF produced Al-alloy

New generation of multi-core fiber laser sources provide in-source dynamic beam shaping. Such sources can switch between Gaussian and ring beams, providing new irradiance profiles. The new irradiance profiles add up to the process flexibility for controlling the temperature fields generated in the laser powder bed fusion (LPBF) process. On the other hand, they bring further complexity as new process parameters should be defined and their influence on the mechanical properties unveiled. Accordingly, this work studies the use of seven different beam shapes provided by a multi-core industrial fiber laser source with beam diameters varying between 47 μm to 144 μm during the LPBF of AlSi7Mg0.6 alloy. The beam spatial profiles were measured and descriptive irradiance parameters were defined. The Al-alloy constituted a challenging material type due to its high reflectivity and low melting point, hence, more prone to lack-of-fusion and keyhole defects. LPBF experiments were conducted at fixed energy density and peak irradiance levels investigating the influence of the beam shapes on the melt pool geometry in prismatic samples. The results showed that the peak irradiance and the ring intensity had a direct impact on the melt pool aspect ratio (AR) and melt pool depth to layer thickness ratio (h/z). With all the conditions providing adequately dense parts (>99.5 %), the mechanical properties were found to be correlated to the melt pool geometry. The results confirm that the beam shape can be tuned between the central peak and the ring to further manipulate the material properties in LPBF.

Assessment of Shear Bond Strength of Thermal Spray Coatings by Applying Prismatic Samples

The purpose of this study was the research for a non-standardized method of measuring the shear bond strength at constant compression force and compare with the shear testing methods on cylindrical and prismatic samples, like DIN 50161:1977-10, DIN EN15340-2007. The conducted comparative analysis showed a significant shortcoming of the well-known methods for assessing the shear bond strength on samples for industrial application. The main one is an inability to measure the “actual/real” adhesion shear strength of thermal spray coatings for industrial parts. The shear bond strength of plasma-sprayed coating MgAl2O4 with thickness 0.30-has been investigated by applying the prismatic samples (linear dimensions of shear area 1.5-), using Nanovea scratch tester at compression forces ranging from 1 to 70 N. Shear force-displacement curves get essential information about adhesion/cohesion, delamination and cracking properties of thermal spray coating. An increase of shear forces is primarily associated with a rise in friction forces at the coating delamination boundary. Applying for parts of the ITER blanket modules, this research has demonstrated the importance of practical application of the shear testing results at compressive loads for ensuring product life.

Evaluation of the mechanical properties and durability of self-compacting alkali-activated mortar made from boron waste and granulated blast furnace slag

The production of high-strength alkali-activated mortar and concrete by using waste materials instead of cement in order to reduce the amount of carbon dioxide released to nature in cement production is an important study that attracts the attention of researchers. In this study, self-compacting alkali-activated mortar samples were produced using boron waste (BW) and granulated blast furnace slag (GBFS). Prismatic samples of 40 × 40 × 160 mm and cubes of 50 × 50 × 50 mm were produced, in which 0%, 5%, 10%, 15%, 20%, 25% of BW were used. To achieve self-compacting alkali-activated mortar (SCAAM) slump-flow test method was conducted by per The European Federation of Specialist Construction Chemicals and Concrete Systems (EFNARC) guidelines. The samples prepared using Na2SiO3 (NS)/NaOH (NH) = 3.0 were exposed to oven curing at 60 °C and 100 °C for 3 days. The flexural and compressive strength (CS) values of 3, 28 and 90 days were obtained for the samples whose curing period was completed. According to the mechanical strength results, influence of capillary water absorption, porosity, water absorption and density and freeze-thaw from durability tests were carried out. After experimental tests, Scanning Electron Microscope (SEM) and Energy-dispersive X-ray Spectroscopy (EDS) images were utilized to determine microstructures of the samples. As a result of the study, it was determined that the highest strengths were obtained at the curing temperature of 60 °C. Also, it was seen that mechanical strengths and durability decreased with the increase in the BW ratio in the mixtures.

Enhanced 532 nm laser damage threshold and optical performance of KDP crystals by Zn2+ doping

Potassium dihydrogen phosphate (KDP) single crystals doped with a series of trace Zn2+ were prepared by “point seed” technique. The content of Zn of KDP crystal was detected using inductively coupled plasma-optical emission spectrometer (ICP-OES). Small differences were found in Zn content of pyramidal and prismatic samples. The ultraviolet–visible (UV–vis) spectra show that the transmitting percentage of doped KDP crystals increases with trace Zn2+ while the transmittance of crystal samples with excessive Zn2+ reduces in UV region. The structural analysis has been performed using infrared spectroscopy (IR). The results illustrate that the crystal network becomes compact after heat treatment or with low concentration doping. The photoluminescence (PL) spectra analysis indicates that the concentration of micro defects of all doped pyramidal samples is lower than that of un-doped samples as well as doped prismatic samples. After thermal annealing, the intensity of PL spectrum of doped sample decreases not obvious compared to un-doped samples. The laser-induced damage threshold (LIDT) results show that the un-doped prismatic sample has relative the lowest LIDT of 3.59 J/cm2 under the condition of 1-on-1. The LIDT of prismatic sample doped with 1000 ppm Zn2+ reaches 13.88 J/cm2 in the test mode of R-on-1 after heat treatment, which mainly is attributed to the relatively low concentration of micro defects.

Structural use of fiber-reinforced self-compacting concrete with recycled aggregates: Case study of a foundation wall in Spain

This paper is focused on the use of mixed recycled-aggregates (RA), replacing 100% of the natural coarse aggregates, for producing steel fiber reinforced self-compacting concrete (FR-SCC-RA) oriented to the construction of foundation walls. To this end, an extensive experimental program dedicated to the mechanical characterization of FR-SCC-RA foundation walls from the material and structural level was carried out. The former was developed on both molded specimens and cores extracted from the in-situ constructed FR-SCC-RA walls in Barcelona, Spain. The results lead to confirm that the use of RA resulted satisfactorily from both the concrete manufacturing and the mechanical performance, since no affectations on the design mechanical variables (i.e., compressive and flexural tensile strengths) were detected. Likewise, the results derived from the full-scale test evidenced that the residual loads of the slabs tested were significantly higher than those calculated based on the test results of the prismatic core samples. The main outcome derived from the experimental research program is that FR-SCC-RA might be a suitable material for this structural typology and that the tested slabs presented a sufficient post-cracking residual capacity -due to the incorporation of structural fibers- for avoiding fragile failures. These conclusions could be extended to other countries where similar restrictive regulations and standards are present, regarding the use of RA and FRC for structural applications.

COMPARISON OF THE MECHANICAL PROPERTIES, HEAT PERMEABİLİTY CHARACTERISTICS AND RESISTANCE AGAINST HIGH TEMPERATURE OF LIGHT MORTARS MADE WITH EPS AND WASTE POLYURETHANE

Bu çalışmada endüstriyel işlem sonrası açığa çıkan atık poliüretanın hafif harç imalatında kullanımı araştırılmıştır. Hali hazırda hafif harç üretiminde kullanılan EPS (Expanded polystyren foam) ve atık poliüretan kullanılarak hafif harç numuneler üretilmiştir. Üretilen numuneler eşdeğer birim ağırlıklarına göre karşılaştırılarak, atık poliüretanın hafif harç imalatında kullanımı araştırılmıştır. Çalışma kapsamında EPS ve atık poliüretan agrega ile hacimce %20, %40, %60, %80, %100 oranlarında yer değiştirilerek kullanılmış ve 40x40x160 mm’lik prizmatik harç numuneler üretilmiştir. Üretilen harç numunelerin birim ağırlık değerleri, ultrasonik atımlı dalga hızları, ısı iletkenlik katsayıları ile eğilme ve basınç dayanımları ölçülmüştür. Ayrıca hem EPS hem de atık poliüretan ile üretilmiş harç numuneler 300⁰C, 600⁰C, 900⁰C’de yüksek sıcaklığa tabi tutulmuş ve sonrasında numunelerin mekanik dayanımları ile içyapıları incelenmiştir. İçyapı incelemeleri hamur numuneler üzerinde FESEM görüntüleri ile gerçekleştirilmiştir. Elde edilen verilere göre hem orta mukavemetli hafif beton sınıfına giren harçlarda, hem de taşıyıcı hafif beton sınıfına giren harçlarda atık poliüretan ile imal edilen harçların EPS’li harçlara göre daha iyi performans gösterdiği sonucuna varılmıştır. Özellikle yüksek sıcaklık sonrası mekanik dayanımlar incelendiğinde atık poliüretanlı harç numunelerin, EPS’li numunelere oranla daha yüksek eğilme ve basınç dayanımları verdiği tespit edilmiştir.

Estimating the residual resource of basic structures using a model of fatigue durability under complex loading

This paper reports the construction of a durability model of basic structures, which takes into consideration the complex stressed state under the cyclic action of the complex load. The models that take into consideration this factor are categorized on the basis of equivalent for a certain indicator of the stressed-strained state. The equivalence models based on the tangent stresses and strains have been recognized as the most effective ones. However, they hold when the ratio of the limits of fatigue under tangent and normal stresses exceeds 0.5. In addition, determining the latter requires specific testing equipment. The concept of basic bearing structures for industrial equipment has been formulated. The issue related to the multi-axis fatigue of basic structures was considered from the standpoint of combining the reliability indicators of systems. The durability model has been derived from the rule of combining resource safety indices. The load is represented as a combination of individual subprocesses of simple types of deformation with their amplitudes and asymmetries. A model of durability with multi-axis fatigue has been built, which takes into consideration the parameters of the form of the strain cycle, and the type of process (synphase, disproportionate, unchanging static stress). The possibility of obtaining parameters for the multi-axis fatigue model during tests for three-point bending under conditions of varying the multiplicity of the span has been confirmed. According to this scheme, fatigue tests of prismatic samples of the steels 09G2 and 40X were carried out. For them, the parameters of fatigue resistance were found; additionally, the ratio of the fatigue limit for tangent stresses of displacement and fatigue limits for normal bending stresses, which is equal to 0.385, was established. A test procedure has been devised to determine the initial data for the multi-axle fatigue model, which is suitable for conventional test machines and simple-shape samples. The latter advantage is important precisely for basic structures, from fragments of which it is difficult to fabricate a sample of a complex shape

Triaxial compression test study on the influence of single crack on the mechanical properties of reactive powder concrete

AbstractTo investigate the influence of crack‐type defect and confining pressure on the mechanical properties of brittle materials, conventional triaxial compression tests were conducted on five types of prismatic samples with the same size of 41 mm × 70.7 mm × 175 mm at six confining pressures of 0, 5, 10, 20, 40, and 70 MPa, respectively. Among the five types of samples, one is intact, with uniaxial compressive strength of 140 MPa, and the other four are all defective and contain a single prefabricated crack with the length of 10 mm and the inclination angles of 0°, 30°, 60°, and 90°, respectively. All samples are made of reactive powder concrete with the same mix proportion. According to the test results, the following conclusions are obtained. (1) For any kind of defective sample and any confining pressure, relative values of the strength deviation that the defective samples deviating from the intact sample are all less than relative values of the strength range (max–min) of the five samples. (2) There exist two critical values p1 and p2 of the confining pressure p, the inclination angle of the prefabricated crack has significantly different impact on the compressive strength in the interval of 0 ≤ p &lt; p1, p1 ≤ p &lt; p2, and p ≥ p2, respectively.

Scuffing resistance of polyalphaolefin (PAO)-based nanolubricants with oleic acid (OA) and iron oxide nanoparticles

The development and application of nanolubricants has shown great potential to reduce friction and wear, especially in the automotive field for systems operating under boundary and mixed lubrication regimes. The search for additives that do not attack the environment has motivated the use of nanoparticles, especially metallic oxides, because of their characteristics such as low toxicity, high surface area, high wettability, and easy dispersion. The objective of this work was to evaluate the addition of iron oxide nanoparticles as additive to pure PAO 8 base oil. The nanoparticle action mechanisms, lubrication efficiency, friction, and wear rates were evaluated. The concentration of nanoparticles in the oil and the addition of oleic acid as a dispersing agent were varied. The synthesis of the nanoparticles was done by aqueous precipitation; characterization was performed by XRD, FTIR, Raman and SEM analyses. Tribological tests were performed in a reciprocating tribometer (Plint TE 67) using AISI 1020 prismatic samples and AISI 52100 chrome steel balls of 5 mm diameter. Test conditions resulted in boundary lubrication regime, for a starved contact with limited lubricant supply (0.5 µL). Concentrations of 0.4 and 1.6 wt% of nanoparticles were added to the base oil with and without the presence of oleic acid. Friction coefficient was not sensitive to the presence of nanoparticles, with statistically similar values for all the fluids tested. On the other hand, the presence of nanoparticles increased scuffing resistance and reduced wear rates. The lubricants with nanoparticles proved able to withstand relatively high loads, keeping the friction coefficient low for longer test durations due to the formation of protective tribolayers between the worn surfaces. The addition of nanoparticles reduced wear rates by around 27% when compared to tests using pure PAO 8.