90 research outputs found
Modeling of the matrix porosity influence on the elastic properties of particulate biocomposites
Porozni materijali se koriste za Å”iroki spektar inženjerskih struktura napravljenih na bazi keramike, poroznih legura sa memorijskim efektom, penastih struktura, termiÄki zaÅ”titnih filmova. U skorije vreme primena poroznih biokompozita u inženjerstvu tvrdih tkiva kao i implanata kod koÅ”tanih defekata privlaÄi posebnu pažnju. Uticaj matriÄne poroznosti na karakteristike elastiÄnosti ÄestiÄnih biokompozita analiziran je primenom metode konaÄnih elemenata upotrebom dvofaznog i trofaznog modela napravljenog na bazi reprezentativnog zapreminskog elementa - RZE. Razvijen je trofazni model RZE sa ÄestiÄnim ojaÄanjem rasporeÄenim u povrÅ”inski centrirano kubnom rasporedu sa matriÄnom poroznoÅ”Äu oblika sfere, Äiji su rezultati uporeÄeni sa jednostavnim analitiÄkom modelima. PrimeÄeno je da matriÄna poroznost znaÄajno utiÄe na karakteristike elastiÄnosti ovih vrsta kompozita. Rezultati dobijeni na osnovu dvofaznog modela imaju viÅ”e vrednosti od onih dobijenih na osnovu trofaznog modela u skoro celom analiziranom opsegu usled fiziÄke granice za zapreminski udeo poroziteta kod trofaznog modela koja je oÄigledno odreÄena vrednoÅ”Äu zapreminskog udela Äestice ojaÄanja.For a wide range of engineering structures such as ceramics, porous shape memory alloys, foam-like structures and thermal spray deposits, porous materials have been used. Recently, porous biocomposites for the applications to bone implants and hard tissue engineering have become increasingly important. The effect of matrix porosity on the elastic properties of particulate biocomposite was studied by two-and three-phase unit cell finite element models. A 3D FCC unit cell model of particulate composite with included matrix porosity is developed and compared with the simple theoretical models. It is found that the matrix porosity has noticeable influence on the composite elastic properties. The two-phase predictions overestimate the three-phase ones because of the physical threshold for three-phase model determined by the particle content
Modeling of the matrix porosity influence on the elastic properties of particulate biocomposites
Porozni materijali se koriste za Å”iroki spektar inženjerskih struktura napravljenih na bazi keramike, poroznih legura sa memorijskim efektom, penastih struktura, termiÄki zaÅ”titnih filmova. U skorije vreme primena poroznih biokompozita u inženjerstvu tvrdih tkiva kao i implanata kod koÅ”tanih defekata privlaÄi posebnu pažnju. Uticaj matriÄne poroznosti na karakteristike elastiÄnosti ÄestiÄnih biokompozita analiziran je primenom metode konaÄnih elemenata upotrebom dvofaznog i trofaznog modela napravljenog na bazi reprezentativnog zapreminskog elementa - RZE. Razvijen je trofazni model RZE sa ÄestiÄnim ojaÄanjem rasporeÄenim u povrÅ”inski centrirano kubnom rasporedu sa matriÄnom poroznoÅ”Äu oblika sfere, Äiji su rezultati uporeÄeni sa jednostavnim analitiÄkom modelima. PrimeÄeno je da matriÄna poroznost znaÄajno utiÄe na karakteristike elastiÄnosti ovih vrsta kompozita. Rezultati dobijeni na osnovu dvofaznog modela imaju viÅ”e vrednosti od onih dobijenih na osnovu trofaznog modela u skoro celom analiziranom opsegu usled fiziÄke granice za zapreminski udeo poroziteta kod trofaznog modela koja je oÄigledno odreÄena vrednoÅ”Äu zapreminskog udela Äestice ojaÄanja.For a wide range of engineering structures such as ceramics, porous shape memory alloys, foam-like structures and thermal spray deposits, porous materials have been used. Recently, porous biocomposites for the applications to bone implants and hard tissue engineering have become increasingly important. The effect of matrix porosity on the elastic properties of particulate biocomposite was studied by two-and three-phase unit cell finite element models. A 3D FCC unit cell model of particulate composite with included matrix porosity is developed and compared with the simple theoretical models. It is found that the matrix porosity has noticeable influence on the composite elastic properties. The two-phase predictions overestimate the three-phase ones because of the physical threshold for three-phase model determined by the particle content
Acceptability of Residual Stresses Measurement Methods of Butt Weldments and Repairs
The joints made by fusion of materials are exposed to the influence of
residual stresses induced by welding thermal cycles. Residual stresses
were measured on butt welded plates made of NIOMOL 490K, before and
after reparation. The objective of this paper is to compare three methods
of residual stress measurement (hole-drilling method, x-ray diffraction
and directional effective permeability) induced by two welding processes
(Submerge Arc Welding and Transferred Ionized Molten Energy) of V-butt
welded plates. The residual stresses values are higher after reparation than
before reparation of welded joints
Acceptability of Residual Stresses Measurement Methods of Butt Weldments and Repairs
The joints made by fusion of materials are exposed to the influence of
residual stresses induced by welding thermal cycles. Residual stresses
were measured on butt welded plates made of NIOMOL 490K, before and
after reparation. The objective of this paper is to compare three methods
of residual stress measurement (hole-drilling method, x-ray diffraction
and directional effective permeability) induced by two welding processes
(Submerge Arc Welding and Transferred Ionized Molten Energy) of V-butt
welded plates. The residual stresses values are higher after reparation than
before reparation of welded joints
Influence of initial state on properties of mma welded 14mov 6 3 steel
U radu je ispitan uticaj stanja osnovnog metala na osobine REL zavarenog spoja Äelika 14MoV 6 3. Zavarene su tri kombinacije uzoraka: (i) nekoriÅ”Äen; (ii) koriÅ”Äen-koriÅ”Äen; i (iii) koriÅ”Äen nekoriÅ”Äen. KoriÅ”Äeni uzorci su bili u upotrebi preko 52000 sati. UtvrÄeno je da do loma dolazi uvek u osnovnom metalu koriÅ”Äenog uzorka. Pretpostavljeno je da kritiÄni uslovi nastaju usled puzanjem izazvanog rasta zrna i/ili taloga. NajviÅ”i nivo zatezne ÄvrstoÄe je u kombinaciji dva nekoriÅ”Äena uzorka.The aim of this work was to establish the influence of initial state of base metal on properties of mma welded 14MoV 6 3 steel. Three combinations of specimens were welded: (i) virgin-virgin (N-N); (ii) used-used (S-S); (iii) virgin-used (N-S). Used specimens were 52000 hours in exploitation. It has been established that the fracture is initiated in the zone of used part. It is assumed that the critical conditions were achieved as the consequence of creep induced grain growth and particle coarsening. On the other hand, testing of unused specimens revealed the highest level of strength
Dilemmas in zirconia bonding: A review
This article presents a literature review on the resin bond to zirconia ceramic. Modern esthetic dentistry has highly recognized zirconia, among other ceramic materials. Biocompatibility of zirconia, chemical and dimensional stability, excellent mechanical properties, all together could guarantee optimal therapeutical results in complex prosthodontic reconstruction. On the other hand, low thermal degradation, aging of zirconia as well as problematic bonding of zirconia framework to dental luting cements and tooth structures, opened the room for discussion concerning their clinical durability. The well known methods of mechanical and chemical bonding used on glass-ceramics are not applicable for use with zirconia. Therefore, under critical clinical situations, selection of the bonding mechanism should be focused on two important points: high initial bond strength value and long term bond strength between zirconia-resin interface. Also, this paper emphases the use of phosphate monomer luting cements on freshly air-abraded zirconia as the simplest and most effective way for zirconia cementation procedure today
The analysis of failure of driving reducer for bucket wheel excavator digging subsystem
Bucket wheel excavators for continuous exploitation belong to the modern, complex and expensive
production systems, manufactured in small series or individually for certain operating environment. During
exploitation of bucket wheel excavators, as an effect of variable amplitude loading induced by working conditions and
their own low-frequency oscillations, unpredictable failures (damages and fractures) of main parts and assemblies may
occur. In this paper, the methodological approach to the analysis of failure of the digging subsystem has been presented
with particular attention turned to the driving reducer for bucket wheel. The possibility of application of experimental
methods in an analysis of condition of the main parts and assemblies in exploitation and failure analysis has been
presented, together with the possibility of application of the methods in failure analysis from the point of view of
evaluation of the system reliability (FTA method ā Fault-Tree Analysis, FMEA method ā Failure Mode and Effects
Analysis). The measures for prevention of damages and fractures of the main parts and assemblies of the driving
reducer have also been presented
Determination of Nd-Yag laser parameters for metal threads cleaning in textile artefacts
Textile samples with metallic threads from the collection of the Ethnographic Museum in Belgrade were subjected to Nd: YAG laser irradiation in order to determinate certain parameters for successfully and safely clean corrosion products without degrading the surrounding material. Application of conventional cleaning methods did not give the expected results, and the implementation of laser technology was the next step. The Nd: YAG laser energy 150mJ (1064 nm) and 50 mJ (532 nm) and pulse width 150 ps was used. The commercial, Thunder Art Laser was also used. Effects of the irradiated areas was investigated by optical and SEM microscopy and EDX analysis
Deformation behavior of two continuously cooled vanadium microalloyed steels at liquid nitrogen temperature
The aim of this work was to establish deformation behaviour of two vanadium
microalloyed medium carbon steels with different contents of carbon and
titanium by tensile testing at 77 K. Samples were reheated at 1250Ā°C/30 min
and continuously cooled at still air. Beside acicular ferrite as dominant
morphology in both microstructures, the steel with lower content of carbon
and negligible amount of titanium contains considerable fraction of grain
boundary ferrite and pearlite. It was found that Ti-free steel exhibits
higher strain hardening rate and significantly lower elongation at 77 K than
the fully acicular ferrite steel. The difference in tensile behavior at 77 K
of the two steels has been associated with the influence of the pearlite,
together with higher dislocation density of acicular ferrite. [Projekat
Ministarstva nauke Republike Srbije, br. OI174004
Experimental and Numerical Evaluation of a Steamline Behaviour Using Local Approach
Results of the experimental and numerical comparative analysis of steamline pipes have been presented. New pipes and the pipes used for more than 117,000 hours at 540 Ā°C under pressure of 42 bars have been simultaneously tested. This testing has been carried out because frequent failures of the equipment components exposed to elevated temperatures, such as steam pipelines, make it necessary to pay particular attention to the analysis of the materials used. The most frequent failures were those connected with occurrence of cracks, particularly expressed in case of steel 14MoV6 3. Local approach to fracture has been developed for complete understanding of fracture mechanism. This approach combines theoretical, experimental and numerical solution
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