In-situ high resolution dynamic X-ray microtomographic imaging of olive oil removal in kitchen sponges by squeezing and rinsing

Recent advances in high resolution X-ray tomography (mu CT) technology have enabled in-situ dynamic mu CT imaging (4D-mu CT) of time-dependent processes inside 3D structures, non-destructively and non-invasively. This paper illustrates the application of 4D-mu CT for visualizing the removal of fatty liquids from kitchen sponges made of polyurethane after rinsing (absorption), squeezing (desorption) and cleaning (adding detergents). For the first time, time-dependent imaging of this type of system was established with sufficiently large contrast gradient between water (with/without detergent) and olive oil (model fat) by the application of suitable fat-sensitive X-ray contrast agents. Thus, contrasted olive oil filled sponges were rinsed and squeezed in a unique laboratory loading device with a fluid flow channel designed to fit inside a rotating gantry-based X-ray mu CT system. Results suggest the use of brominated vegetable oil as a preferred contrast agent over magnetite powder for enhancing the attenuation coefficient of olive oil in a multi fluid filled kitchen sponge. The contrast agent (brominated vegetable oil) and olive oil were mixed and subsequently added on to the sponge. There was no disintegration seen in the mixture of contrast agent and olive oil during the cleaning process by detergents. The application of contrast agents also helped in accurately tracking the movement and volume changes of soils in compressed open cell structures. With the in house-built cleaning device, it was quantified that almost 99% of cleaning was possible for contrasted olive oil (brominated vegetable oil with olive oil) dispersed in the sponge. This novel approach allowed for realistic mimicking of the cleaning process and provided closer evaluation of the effectiveness of cleaning by detergents to minimize bacterial growth

CT-Based Micro-Mechanical Approach to Predict Response of Closed-Cell Porous Biomaterials to Low-Velocity Impact

In this study, a new numerical approach based on CT-scan images and finite element (FE) method has been used to predict the mechanical behavior of closed-cell foams under impact loading. Micro-structural FE models based on CT-scan images of foam specimens (elastic-plastic material model with material constants of bulk aluminum) and macro-mechanical FE models (with crushable foam material model with material constants of foams) were constructed. Several experimental tests were also conducted to see which of the two noted (micro- or macro-) mechanical FE models can better predict the deformation and force-displacement curves of foams. Compared to the macro-structural models, the results of the micro-structural models were much closer to the corresponding experimental results. This can be explained by the fact that the micro-structural models are able to take into account the interaction of stress waves with cell walls and the complex pathways the stress waves have to go through, while the macro-structural models do not have such capabilities. Despite their high demand for computational resources, using micro-scale FE models is very beneficial when one needs to understand the failure mechanisms acting in the micro-structure of a foam in order to modify or diminish them

Development and characterization of aluminum porous structures

Metalne pene su dobar izbor za multidisciplinarnu primenu, jer ih njihove fizičke i mehaničke karakteristike čine posebno atraktivnim za automobilsku industriju. Ova studija ima za cilj da utvrdi pogodnost metalnih pena ispitivanjem njihovih mehaničkih i fizičkih svojstava. U ovom radu su projektovane i razvijene porozne aluminijumske strukture, a nakon toga je realizovana njihova karakterizacija. Jedan od glavnih ciljeva je odreĎivanje metodologije proizvodnje poroznih struktura sa poboljšanim elastičnim i plastičnim karakteristikama. Eksperimentalna istraţivanja i numeričke simulacije su realizovane da bi se utvrdio mehanizam deformacije, kao i izbora materijala za primenu pena na bazi aluminijuma. Prvi korak u razvoju metalne pene bio je korišćenje različitih proizvodnih tehnologija. Opisano je nekoliko glavnih proizvodnih tehnologija, uključujući livenje plastike korišćenjem prekursora polimera ili voska, ekspanziju zarobljenog gasa, LC N proces i ubrizgavanje rastopljenog gasa (mehurići vazduha). UtvrĎeno je da je metoda ubrizgavanja rastopljenog gasa efikasnija u proizvodnji homogenih veličina pora jer se parametri procesa mogu lako menjati. Iz tog razloga su uzorci pripremljeni ovom metodom. Ovom metodom su dobijeni uzorci metalne pene sa porama duţine oko 1 mm i gustine 0,6 g/cm3 . Ovi uzorci su ispitivani jednoosnim pritiskivanjem pri brzini pomeranja od 0,001 mm/s. Eksperimentalni rezultati daju vrednosti napona i deformacije u funkciji zatezanja i opterećenja, respektivno. Eksperimentalni rezultati pokazuju da do potpunog loma uzoraka dolazi pri opterećenju od 90 kN. Uzorci pripremljeni metodom uduvavanja gasa pokazali su: elastičnu zonu, zonu uniformnog ponašanja (pri oko 23 MPa) i zonu sabijanja pri oko 35 MPa. Tokom ispitivanja pritiskivanjem odredjen je napon tečenja koji iznosi 20 MPa. Zanimljivo je da su zona sabijanja i brzo povećanje napona počeli od oko 52% deformacije uzorka metalne pene. Razvijen je novi model za numeričku simulaciju zasnovan na Voronoi modelu i kodu (Voronoi Tessellated Model, VTM) za generisanje porozne strukture otvorenih pora. Razvijeni model je korišćen za proučavanje mehanizma deformacije. Ispitivanje jednoosnim pritiskivanjem je izvedeno sa opterećenjem od 20 N. Ispitivanja su izvedena na tri različita uzorka različite poroznosti (30%, 60% i 80%) radi proučavanja uticaja poroznosti. Model elastično-plastičnog materijala zasnovan na von Mises-ovom kriterijumu tečenja materijala sa idealnom plastičnošću (bez deformacionog ojačavanja) primenjen je za deformacije manje od 10%. Numeričkim simulacijama su dobijene vrednosti napona i deformacija koje pokazuju da uzorci sa većom poroznošću imaju značajno veću normalnu komponentu napona i širi opseg ravni maksimalnog napona. Naponi pri ispitivanju pritiskivanjem i zatezanjem rastu sa povećanjem poroznosti. Slično, strukturni ligamenti porozne strukture (zidovi pora) su pokazali komplikovanu raspodelu polja napona. Rezultati dobijeni numeričkim metodama su u skladu sa eksperimentalnim ispitivanjima. Da bi se steklo bolje razumevanje, potrebna su dodatna istraţivanja rezultata dobijenih numeričkim simulacijama stvarnog dinamičkog ponašanja u zoni elastičnosti, plastičnosti i u uslovima jednoosnog pritiskivanja za strukturu otvorenih pora kreiranu Voronoi modelom. Za modeliranje zatvorenih pora, korišćene su 3D slike aluminijumskih pena dobijene kompjuterskom tomografijom (CT skeniranje). 3D model je razvijen nakon obrade slika dobijenih sa CT skenera i dalje je primenjen za numeričku simulaciju. Mreţa konačnih elemenata je kreirana korišćenjem tetraedarskih elemenata. Jednačine elasto-plastičnog modela sa svojstvima izotropnih materijala su korišćene za nelinearnu statičku analizu. Numerička simulacija je realizovana u uslovima jednoosnog pritiskivanja. Tokom testa pritiskivanja, opterećenje je zadato na gornjoj strani uzorka u pravcu y-ose. Rezultati pokazuju da kompleksna raspodela polja napona utiče i na napone pri ispitivanju zatezanjem i pritiskivanjem. Na deformaciju takoĎe utiče napon smicanja. Zona sa većim prečnikom pora je podloţnija naponima koji nastaju usled pritiskivanja, dok je zona sa maksimalnim brojem pora i tankim zidovima podloţnija naponima koji nastaju prilikom zatezanja...Metal foams are excellent candidates for multidisciplinary applications, as their physical and mechanical properties make them particularly attractive for the automotive industry. This study aims to determine the suitability of metal foams by investigating their mechanical and physical properties. In this project, porous aluminium structures will be designed, developed and characterized. One of the main objectives is to find out how to fabricate porous structures with improved elastic, plastic and densification regime. Experimental and numerical simulations have been carried out to determine the deformation mechanism as well as the material selection method for structural applications of aluminium-based foams. The first step in the development of metal foam was to use different processing techniques. Several main production technologies have been described, including plastic casting using a polymer or wax precursor, trapped gas expansion, the ALCAN process, and melt gas injection (air bubbling). The melt gas injection method was found to be more effective in producing homogeneous pore sizes because the process parameters can be easily adjusted. Therefore, the samples were prepared using the gas blowing method. The results of this method show a foam with cells of about 1 mm length and a density of 0.6 g/cm3 . These specimens were subjected to a uniaxial compression test at a displacement rate of 0.001 mm/s. The experimental results provide stress and strain values as a function of extension and load, respectively. The experimental results show that complete failure of the specimens occurs at a load of 90 KN. The specimens prepared by the gas blowing method showed: an elastic region, a uniform plateau region at about 23 MPa and densification region at about 35 MPa. During compression, a yield or collapse stress was measured at about 20 MPa. Interestingly, the densification region and the rapid increase in stress started at about 52%. A new model was developed for numerical simulation based on a Voronoi tessellation code to generate an open-cell porous structure. The developed model was used to study the deformation mechanism. A uniaxial compression test was performed with a uniformly applied load of 20 N. The tests were performed on three different specimens with different porosity (30%, 60% and 80%) to study the effect of porosity. The elastic-plastic material model based on Von Mises yield criterion with perfect plasticity (without strain hardening) was applied below 10% strain. Numerical simulations yielded stress and strain values and interestingly, the results show that specimens with higher porosity exhibited significantly higher normal stresses and larger stress plateaus. Both compressive and tensile stresses increase with increasing porosity. Similarly, ligaments and struts showed complicated stress fields. The results also show that the developed Voronoi-based numerical model are consistent with the experimental results in the case of quasi-static conditions up to the linear elastic region. In order to gain a better understanding, the simulation of the real dynamic behavior under elastic, plastic and compaction conditions for the open cell structure created with the Voronoi code needs to be investigated. For closed cell modelling, computer tomography is used to create 3D images of closed cell foam made of aluminum. The 3D model was developed and used for numerical simulation after thresholding and identifying the correct images. The mesh was very finely tuned using size 10 tetra-node elements. Moreover, elastic and plastic equations with isotropic material properties were applied to a nonlinear static test. Numerical simulation was performed under uniaxial compression conditions. During the compression test, a uniform compressive load was applied to the top surface of the specimen in the y-direction. The results show that the complicated stress fields affect the compressive and tensile stresses. The deformation is also strongly influenced by the shear stress. The zone with larger cells diameter exhibits compressive stresses, while the zone with a maximum number of cells and thin walls exhibits tensile stresses