Istraživanje i procjena zaostalih naprezanja u plinski naštrcanim NiCrBSi slojevima

For thermally sprayed coatings, beside good wear and corrosion resistance there is also a need for a good coating/substrate adhesion, reduced porosity and reduced level of residual stresses. Residual stresses that occur in the substrate/coating system are very significant because their relaxation can cause different coating failures. In this paper, different approaches to investigation of residual stresses in thermally sprayed coatings, have been presented. An analytical model (authors Tsui and Clyne) was used to estimate the distribution of residual stresses in flame sprayed and fused NiCrBSi coatings. These data can be used as input data for the numerical model.Za toplinski naštrcane slojeve, uz dobru otpornost slojeva na trošenje i koroziju, postoje i zahtjevi za dobrom prionjivosti sloja na podlogu,smanjenom poroznosti i smanjenom razinom zaostalih naprezanja. Zaostala naprezanja koja se pojavljuju u sustavu podloga/naštrcani sloj, osobito su važna, jer se njihovom relaksacijom mogu pojaviti razna oštećenja sloja. U ovome radu prikazani su pristupi istraživanju zaostalih naprezanja u toplinski naštrcanim slojevima, te je na osnovi analitičkog modela (autori Tsui i Clyne) procijenjena raspodjela zaostalih naprezanja za NiCrBSi slojeve nanesene postupkom plinskog naštrcavanja praha s utaljivanjem. Ovi podaci mogu se koristiti kao ulazni podaci za numerički model

Crack roughness and avalanche precursors in the random fuse model

We analyze the scaling of the crack roughness and of avalanche precursors in the two dimensional random fuse model by numerical simulations, employing large system sizes and extensive sample averaging. We find that the crack roughness exhibits anomalous scaling, as recently observed in experiments. The roughness exponents ($\zeta$, $\zeta_{loc}$) and the global width distributions are found to be universal with respect to the lattice geometry. Failure is preceded by avalanche precursors whose distribution follows a power law up to a cutoff size. While the characteristic avalanche size scales as $s_0 \sim L^D$, with a universal fractal dimension $D$, the distribution exponent $\tau$ differs slightly for triangular and diamond lattices and, in both cases, it is larger than the mean-field (fiber bundle) value $\tau=5/2$

Statistical properties of fracture in a random spring model

Using large scale numerical simulations we analyze the statistical properties of fracture in the two dimensional random spring model and compare it with its scalar counterpart: the random fuse model. We first consider the process of crack localization measuring the evolution of damage as the external load is raised. We find that, as in the fuse model, damage is initially uniform and localizes at peak load. Scaling laws for the damage density, fracture strength and avalanche distributions follow with slight variations the behavior observed in the random fuse model. We thus conclude that scalar models provide a faithful representation of the fracture properties of disordered systems.Comment: 12 pages, 17 figures, 1 gif figur

Effect of Disorder and Notches on Crack Roughness

We analyze the effect of disorder and notches on crack roughness in two dimensions. Our simulation results based on large system sizes and extensive statistical sampling indicate that the crack surface exhibits a universal local roughness of $\zeta_{loc} = 0.71$ and is independent of the initial notch size and disorder in breaking thresholds. The global roughness exponent scales as $\zeta = 0.87$ and is also independent of material disorder. Furthermore, we note that the statistical distribution of crack profile height fluctuations is also independent of material disorder and is described by a Gaussian distribution, albeit deviations are observed in the tails.Comment: 6 pages, 6 figure

From traditional use to scientific data: Helichrysum italicum

U novije vrijeme kozmetička i farmaceutska industrija posebnu pažnju posvećuju pronalaženju dragocijenih biljaka koje svoju primjenu pronalaze u formulacijama kozmetičkih i farmaceutskih proizvoda. Jedna tako dragocijena biljka je zbog bogatstva biološki aktivnih komponenti i smilje. Dugo je vremena bila potisnuta u zaborav, no u novije vrijeme postaje velika atrakcija u svijetu. U flori Europe se nalazi 25 vrsta roda Helichrysum, dok je na editeranskom podneblju od posebnog značaja vrsta Helichrysumitalicum. U radu je dan taksonomski pregled europskih vrsta smilja. Opisane su morfološke i fiziološke karakteristike smilja, način uzgoja, način berbe te količina prinosa. Najvažniju grupu biljnih pripravaka čine ekstrakti koji se dobivaju primjenom različitih metoda ekstrakcije, počevši od jednostavnih do naprednih tehnika poput ekstrakcije pomoću superkritičnih fluida. Koji će se postupak primijeniti ovisi o vrsti i svojstvu sirovine, primarnoj obrada smilja, kvalitativnom i kvantitativnom sastavu eteričnog ulja, a posebno o njegovoj primjeni što je detaljno opisano u radu.In recent years, cosmetic and pharmaceutical industry special attention give to the valuable plants that can find their application in the formulation of cosmetic and pharmaceutical products. One such precious herb is Immortelle due to its rich biologically active compounds. For a long time this plant has been unfairly neglected, but today we are witnessing the increasing popularity of Immortelle in the world. In the Europe flora there is about of 25 species Helichrysum, while for the Mediterranean area particularly important is type Helichrysum italicum. This paper presents an overview of European taxonomic species of Immortelle. The morphological and physiological characteristics of Immortelle were described, plantation cultivation, harvesting method and extraction yield. The most important group of herbal products make extracts that can be obtained using different extraction methods, ranging from simple to advanced techniques such as supercritical fluid extraction. What procedure will be applied depends on the type of raw materials, processing conditions, qualitative and quantitative composition of the essential oil, and its application as described in detail in this review

Crack Roughness in the 2D Random Threshold Beam Model

We study the scaling of two-dimensional crack roughness using large scale beam lattice systems. Our results indicate that the crack roughness obtained using beam lattice systems does not exhibit anomalous scaling in sharp contrast to the simulation results obtained using scalar fuse lattices. The local and global roughness exponents ($\zeta_{loc}$ and $\zeta$, respectively) are equal to each other, and the two-dimensional crack roughness exponent is estimated to be $\zeta_{loc} = \zeta = 0.64 \pm 0.02$. Removal of overhangs (jumps) in the crack profiles eliminates even the minute differences between the local and global roughness exponents. Furthermore, removing these jumps in the crack profile completely eliminates the multiscaling observed in other studies. We find that the probability density distribution $p(\Delta h(\ell))$ of the height differences $\Delta h(\ell) = [h(x+\ell) - h(x)]$ of the crack profile obtained after removing the jumps in the profiles follows a Gaussian distribution even for small window sizes ($\ell$).Comment: 8 pages, 6 figure

Investigation and estimation of residual stress in flame sprayed and fused NiCrBSi coatings

For thermally sprayed coatings, beside good wear and corrosion resistance there is also a need for a good coating/substrate adhesion, reduced porosity and reduced level of residual stresses. Residual stresses that occur in the substrate/coating system are very significant because their relaxation can cause different coating failures. In this paper, different approaches to investigation of residual stresses in thermally sprayed coatings, have been presented. An analytical model (authors Tsui and Clyne) was used to estimate the distribution of residual stresses in flame sprayed and fused NiCrBSi coatings. These data can be used as input data for the numerical model

Entrepreneurial education for students of non-economics educational programs

Poduzetničke vještine su nužne svim diplomantima koji planiraju pokrenuti vlastito poduzeće. Dodatno, te vještine sve više traže i poslodavci, čak i od diplomanata tehničke izobrazbe. Ovaj rad uspoređuje dva ekstrakurikularna programa u koje su bili uključeni student četiri različita ne-ekonomska obrazovna profila iz Hrvatske i SAD. Tijekom istraživanja je identificirano nekoliko izazova. Priprema i izvršavanje poduzetničkog obrazovnog programa za studente s vrlo različitom razinom relevantnih predznanja je jedan od njih. Integracija nastavnih metoda iz učionice s \u27distance learning\u27 metodama i postizanje učinkovite ravnoteže pristupa \u27biti edukativan\u27 i \u27biti zanimljiv i atraktivan\u27 predstavljaju dodatne izazove. Spol sudionika edukativnih programa, prethodna izobrazba, poduzetničko iskustvo njihovih obitelji i neposredni planovi nakon diplomiranja su identificirani kao utjecajne varijable na njihovo zadovoljstvo programom.Entrepreneurial skills are necessary for all graduates who are planning their own start-up business. Those skills are asked more and more by employers, even from fresh graduates of technical backgrounds. This paper compares two extracurricular programs involving students of four different, all non-economics programs from Croatia and the USA. Several challenges were identified during the research. Preparing and executing entrepreneurial educational programs for students with very uneven level of relevant foreknowledge was one of them. Integration of classroom and e-learning methods and achievement of an effective combination of being educational, interesting and attractive in the same time were additional challenges. Gender of the participants, previous education, entrepreneurial background of their families and immediate plans upon the graduation were determined as influencing variables on their satisfaction with the program