Modeling of the matrix porosity influence on the elastic properties of particulate biocomposites

Porozni materijali se koriste za široki spektar inženjerskih struktura napravljenih na bazi keramike, poroznih legura sa memorijskim efektom, penastih struktura, termički zaštitnih filmova. U skorije vreme primena poroznih biokompozita u inženjerstvu tvrdih tkiva kao i implanata kod koštanih defekata privlači posebnu pažnju. Uticaj matrične poroznosti na karakteristike elastičnosti čestičnih biokompozita analiziran je primenom metode konačnih elemenata upotrebom dvofaznog i trofaznog modela napravljenog na bazi reprezentativnog zapreminskog elementa - RZE. Razvijen je trofazni model RZE sa čestičnim ojačanjem raspoređenim u površinski centrirano kubnom rasporedu sa matričnom poroznošću oblika sfere, čiji su rezultati upoređeni sa jednostavnim analitičkom modelima. Primećeno je da matrična poroznost značajno utiče na karakteristike elastičnosti ovih vrsta kompozita. Rezultati dobijeni na osnovu dvofaznog modela imaju više vrednosti od onih dobijenih na osnovu trofaznog modela u skoro celom analiziranom opsegu usled fizičke granice za zapreminski udeo poroziteta kod trofaznog modela koja je očigledno određena vrednošću zapreminskog udela čestice ojačanja.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 čelika 14MoV 6 3. Zavarene su tri kombinacije uzoraka: (i) nekorišćen; (ii) korišćen-korišćen; i (iii) korišćen nekorišćen. Korišćeni uzorci su bili u upotrebi preko 52000 sati. Utvrđeno je da do loma dolazi uvek u osnovnom metalu korišćenog uzorka. Pretpostavljeno je da kritični uslovi nastaju usled puzanjem izazvanog rasta zrna i/ili taloga. Najviši nivo zatezne čvrstoće je u kombinaciji dva nekorišćena 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

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 1250°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 °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

Inženjerske metode procene integriteta zavarenih konstrukcija i njihova primena

U radu se analiziraiu tri inženjerske metode: KING, REI i JWES2805 i mogućnost njihove primene na zavarene spojeve, imajući u vidu osobine zavarenih spoieva, a sve sa ciljem dobijanja dovoljno tačne i jednostavne inženjerske procedure za određivanie sile rasta prsline u zavarenim spoievima u koiima su prisutni zaostali naponi i geometrijske nepravilnosti