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Processing of Data Obtained by the Testing of Steel under Low Cyclic Fatigue (Part I)
Get PDFThe design of mechanical components exposed to fatigue load, at a low number of cycles, requires knowledge of the behaviour of the material under the impact of variable load in conditions of controlled strain when cyclic plasticity is present. The aim of testing the quality of the material of the components exposed to low cycle fatigue (LCF) in many industries: Nuclear, aerospace, mechanical, civil engineering and shipbuilding. In order to ensure the reliability and consistency of the results from different laboratories, it is necessary to collect all test data using test and data processing methodologies that are in accordance with a number of key points of ISO 12106: 2017 and/or ASTM E 606-04 standards. This paper defines a new data processing methodology after the LCF testing of steel
Analysis of contact fatigue coupled with geometry and material nonlinearities by Theory of critical distances
Get PDFThe contact fatigue is a localized phenomenon that occurs in highly
stressed local zone of the material under the loaded contact region and as such is
highly nonlinear problem. This phenomenon exists in almost all real mechanical
systems with contact strains coupled with other sources of nonlinear behaviour.
The improvements of existing procedures and methods for standard calculation
of contact fatigue have a potential to give significant contribution to increase
accuracy of calculation of life assessment, reliability and efficiency of complex
mechanical systems. This paper gives the basic explanation of the Theory of
critical distances and its application on direct estimation of fatigue crack
initiation in contact zones. Analysis of contact fatigue when the contact zones
are subjected to additional nonlinearities such as geometry manufacturing
deviations, geometry microscale-damages or nonlinear material characteristics
are presented in detail. Few different real multi-nonlinear problems are used for
analysis performing. The benefits of presented approach are discussed by detail
analysis of the obtained results, and could be based on the increasing accuracy
of contact fatigue prediction considering all existing nonlinearities in loaded
contact zones of complex mechanical systems
Combinatorial Vacuum-Deposition of Wide Bandgap Perovskite Films and Solar Cells
No full textThe development of vacuum-deposited perovskite materials and devices is
partially slowed down by the minor research effort in this direction, due to
the high cost of the required research tools. But there is also another factor,
thermal co-deposition in high vacuum involves the simultaneous sublimation
of several precursors with an overall deposition rate in the range of few Å s−1.
This leads to a deposition time of hours with only a single set of process
parameters per batch, hence to a long timeframe to optimize even a single
perovskite composition. Here we report the combinatorial vacuum deposition
of wide bandgap perovskites using 4 sources and a non-rotating sample
holder. By using small pixel substrates, more than 100 solar cells can be
produced with different perovskite absorbers in a single deposition run. The
materials are characterized by spatially resolved methods, including optical,
morphological, and structural techniques. By fine-tuning of the deposition
rates, the gradient can be altered and the best-performing formulations in
standard depositions with rotation can be reproduced. This is viewed as an
approach that can serve as a basis to prototype other compositions, overcoming
the current limitations of vacuum deposition as a research tool for
perovskite films
Analiza uticaja predtretmana vrelom vodom (LHW) na hemijski sastav drvnog iverja
Get PDFThe goal of this paper is to analyze the chemical composition of untreated and
treated wooden chips from the native narrow-leaved ash (Fraxinus angustifolia
Vahl. ssp. Pannonica Soó & Simon). In order to determine the effect of pretreatment
with liquid hot water (LHW) on changes in chemical composition, the content
of moisture, cellulose, lignin, minerals (ash), extractives soluble in hot water, extractives
soluble in organic solvents, for treated and for untreated wooden chips
was determined. This was done in accordance with TAPPI and ASTM standard
methods. The properties of wooden chips, treated for 30 min and 60 min at a
temperature of 100 °C, are compared to untreated wooden chips and changes
in the chemical composition that occurred are defined as a result of the applied
treatments. The research was performed under controlled conditions in a laboratory,
and the results of treatments were the subject of comparative analysis. Applied
treatments had a statistically significant effect on decreasing the content of
extractives. The content of cellulose and hemicellulose increased in the treated
wooden chips compared to untreated wooden chips, while the lignin content did
not significantly change.The results were obtained within the master's paperwork of Aleksandar Drpić, "THE INFLUENCE OF
WATER PRETREATMENT ON THE PROPERTIES OF CHIPBOARDS" defended at the University of Belgrade, Faculty of Forestry, Serbi
Fired pressed pellet as a sample preparation technique of choice for an energy dispersive X-ray fluorescence analysis of raw clays
Get PDFIn this paper, the main subject concerns comparing different techniques to prepare raw clay samples for energy dispersive X-ray fluorescence spectrometry (EDXRF). Three kinds of sample preparation procedures are examined,such as loose powder, pressed pellet, and fired pressed pellet. The fired pressed pellet approach was observed as a part of universal sample preparation for physic, mechanical, and instrumental analysis, which has not been previously tested as a solution in chemical analysis by the EDXRF method. The observed sample preparation techniques were compared by calculating the parameters of validation (recoveries, limit of detection-LOD, limit of quantification - LOQ, precision, and expanded uncertainties of measurements) of 11 elements (Si, Al, Fe, Ca, Mg, K, Na, Ti, P, Mn, and S) using 15 certified reference materials (CRMs). Calibration curves were created and evaluated using 30 reference materials (RM) for all three approaches. Results proved that the fired pressed pellet is the most practical and precise approach for sample preparation of raw clays
Experimental and numerical analysis of a walls made from aerated concrete blocks exposed to fire
Get PDFThe unsteady heat conduction in composite planar structure, with arbitrary number of layers, using analytical approach based on Greeds Functions (GF) is analyzed. The analytical solution for spatial and temporal temperature distribution is evaluated in the general form and expressed in the terms of the convolution integrals. The GF are employed in the novel approach for calculation of Thermal Response Factors (TRF) with arbitrary shape functions for unsteady heat conduction in composite planar structure. The two pairs of TRF for spatial and temporal distribution of the temperature and the thermal flux are obtained. The whole analysis is performed in the time domain. A numerical scheme for efficient evaluation of convolution integral suitable for practical application in the case of the long term measurements with lower sampling rates is developed. The in-situ measurements of inside and outside surface temperatures and outside heat flux for a building wall under real dynamical environmental conditions during the period of then days are used for validation of the presented results and to demonstrate the possible practical application. Using developed approach and recorded surface temperatures as inputs the temporal and spatial distributions of the temperature and the thermal flux are obtained. These results are compared with experimental data and numerical simulations obtained by the Finite Volume Method (FVM)
Evaluation of Inverted-Pendulum-with-Rigid-Legs Walking Locomotion Models for Civil Engineering Applications
Get PDFBipedal models for walkers, originally developed in the research field of biomechanics,
have been identified as potential candidates for modelling pedestrians in structural engineering
applications. These models provide insight into both the kinetics and kinematics of walking locomotion and are considered to have a significant potential to improve the vibration serviceability
assessment of civil engineering structures. Despite this notion, the ability of the bipedal models to
represent the key features of the walking gait and natural variability within the pedestrian population are still under-researched. This paper critically evaluates the performance of two bipedal models with rigid legs to realistically both reproduce key features of an individual pedestrian’s walking gait and represent a wide range of individuals. The evaluation is performed for walking on a rigid, rather than vibrating, structure due to the availability of experimental data and expectation that successful modelling on rigid surfaces is a necessary condition for progressing towards modelling on the vibrating structures. Ready-to-use equations are provided and the ability of the models to represent the kinematics and kinetics of individual pedestrians as well as the inter-subject variability typical of the human population is critically evaluated. It was found that the two models could generate realistic combinations of the gait parameters and their correlations, but are less successful in reproducing genuine kinetic and kinematics profiles
Determining of the Fatigue Crack Growth Rate of HSLA Steel at Room Temperature
Get PDFWelded joint is a critical region of a welded structure and fracture mechanics analysis is inevitable
in the structural integrity assessment of all welded structures. This paper shows the determining of
parameters of the fatigue crack for constituents of welded joints produced of high strength low
alloyed steel. The applied methodology refers to the Paris relation where the link was established
between the variable load quantity or the corresponding stress intensity factor range and crack
growth per cycle. Results have shown that the position of the notch and crack initiation affect the
values of the stress intensity range of fatigue threshold ΔKth and parameters in the Paris’ equation.
This is mostly expressed when determining growth parameters of the fatigue crack in heat affected
zone of HSLA steel, where different changes of growth speed of the fatigue crack clearly express
differences in structure of the crack pas
Application of pyrophyllite in building and refractory ceramic materials
No full textPhyllosilicate mineral pyrophyllite possesses talc’s characteristic softness and crystalline structure, but it also exhibits high refractoriness. Pyrophyllite is predominantly being used in the ceramic materials (tiles, porcelain) as a replacement of quartz, clay or feldspar. Due to its thermal transformation into mullite, pyrophyllite is stable at elevated temperatures. Its ion-exchanging properties are crucial for stabilization of the toxic elements in building materials. In this study pyrophyllite is used as a mineral additive for two types of construction products: traditional ceramic materials and refractory mortars. The experimental samples were prepared using 50 % of pyrophyllite and 50 % of refractory clay, ceramic clay, and carbonate brick clay, respectively. The samples were formed into discs or tiles using the compression method. The following characteristics have been investigated: resistance to firing (900 – 1300°C), carbonate content, plasticity coefficient, dimensional changes after drying at 105°C and upon firing, water absorption, and mechanical strength. Refractory samples were prepared using andalusite as aggregate, ordinary Portland cement and/or high aluminate cement as binder, and pyrophyllite as an additive (10 %, 20 %, and 30 %). Compressive and flexural strength both at normal and at elevated temperature were tested on the samples, along with the refractoriness. The changes that pyrophyllite addition brings to the material’s mineral composition, microstructure, as well as to bonding/sintering mechanisms were monitored using instrumental techniques (DTA, TGA, XRD). The aim of the investigation was to prove potential suitability of pyrophyllite as efficient and sustainable resource for the production of ceramic and refractory materials
Hemometrijski pristup ispitivanju uticaja hemijskih svojstava elektrofilterskog pepela, zeolita i bentonita na svojstva ekološko prihvatljivih građevinskih materijala
No full textIntenzivna industrijalizacija i urbanizacija dovela je do sve veće potrebe za rešenjima koja će doprineti očuvanju životne sredine. Isto se dešava i u oblasti građevinske industrije, gde se čvrst neorganski otpad sve više koristi kao mineralna sirovina u cementoj industriji. U tom smislu nameću se novi izazovi za prilagođavanje hemijskih metoda za analizu sastava višekomponentnih materijala...Intensive industrialization and urbanization impose increasing needsfor solutions that will contribute to the preservation of the environment. This is also the case in the construction industry, where deposited solid inorganic waste is increasingly used as a mineral raw material in the cement industry. In this sense, new global tendencies are imposed to improve the performance of chemical analysis methods for the analysis of multi-component materials..