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Javad Heidarian and Aziz Hassan

Abstract

Carbon nanotube (CNT)-, carbon black (CB)-filled fluoroelastomer (FE) and unfilled-FE compounds were prepared (CNT/FE, CB/FE and FE). The compounds were subjected to heat air aging and characterized by tensile test and X-Ray Diffraction (XRD) analysis. Results show that CNT improved tensile properties of FE before and after aging. All samples show stress induced crystallization (SIC) during tension. XRD results show that under all conditions, the crystals were in the form of γ-phase. For both aged and un-aged specimens, the degree of crystallinity (Xc) is low. After tensile stretching, Xc of un-aged specimens increases tremendously, with larger crystal size. Under the same conditions, the order of elongation at break (EL) was FE > CB/FE > CNT/FE. Normal modulus (NM) and tangent modulus (TM) at the same conditions was in the order of CNT/FE > CB/FE > FE. Tensile strength had the order of CNT/FE > CB/FE > FE.

Open access

Piotr Grzejszczak and Roman Barlik

References [1] RĄBKOWSKI J., PEFTITSIS D., NEE H.-P., Parallel-Operation of Discrete SiC BJTs in a 6-kW/250-kHz DC/DC Boost Converter, IEEE Trans. on Power Electron., 2014, Vol. 29, No. 5, 2482-2491. [2] LI X., ZHANG L., GUO S., LEI Y., HUANG A.Q., ZHANG B., Understanding switching losses in SiC MOSFET: Toward lossless switching, Wide Bandgap Power Devices and Applications (WiPDA), IEEE 3rd Workshop, Blacksburg, 2015, 257-262. [3] HUGHES B. et al., Normally-off GaN switching 400V in 1.4ns using an ultra

Open access

Martyna Wiciak, Paweł Twardowski and Szymon Wojciechowski

References [1] Bhattacharya D., Lane C., Lin J.T.,Machninability of silicon carbide reinforced aluminium metal matrix composite, Wear 181-183 (1995) 883-888 [2] Davim J.,Diamond tool performance in machining metal-matrix composites, Journal of Materials Processing Technology 128 (2002) 100-105 [3] El-Gallab M., Sklad M.,Machning of Al./SiC particulate metal matrix composites Part I: Tool performance, Journal of Materials Processing Technology 83 (1998) 151-158 [4] El-Gallab M., Sklad M

Open access

M. Bonek

W pracy przedstawiono wyniki badań laserowego stopowania na strukturę i własności warstwy wierzchniej stali szybkotnącej HS6-5-2-5, przetapianej za pomocą lasera diodowego dużej mocy (HPDL). Jako materiał stopujący użyto proszków WC, VC, TiC, SiC, Si3N4 i AI2O3. Stwierdzono, że do przetopienia i stopowanie laserowe twardymi cząstkami powoduje poprawę własności warstwy wierzchniej w całym zakresie mocy lasera. Odpowiedni dobór warunków pracy lasera jak również jakość wiązki ma wpływ na wyniki przetopienia co potwierdzono badaniami twardości, mikrotwardości, mikroanalizy rentgenowskiej i rentgenowskie analizy fazowej. W strefie przetopionej i stopowanej stwierdzono występowanie drobnoziarnistej oraz dendrytycznej struktury z kierunkiem krystalizacji związanym z dynamicznym przepływem ciepła ze strefy oddziaływania wiązki laserowej. Drobnoziarnista struktura martenzytu jest odpowiedzialna za wzrost twardości warstwy stopowanej. Zmiany mikrotwardości ściśle zależą od efektów oddziaływania wiązki laserowej na obrabianą powierzchnię. Wyniki badań pozwalają na lepsze zrozumienie mechanizmów strukturalnych towarzyszących przetapianiu i stopowaniu laserowemu. Laserowa obróbka powierzchniowa stanowi szczególnie obiecujące narzędzie do rozwiązywania problemów inżynierii powierzchni dzięki wykorzystaniu własności fizycznych wiązki lasera umożliwiających precyzyjną obróbkę cieplną w warstwie wierzchniej.

Open access

P. Kurtyka and N. Rylko

The paper presents applications of a new theory of the representative volume element (RVE) based on the Mityushev- Eisenstein-Rayleigh sums (M-sums) to describe particle-reinforced composites. This theory is applied to study F3K.10S metal matrix composites reinforced SiC particles. The most important M-sum e2 is calculated for the initial state as e2 = -0.00206281. This shows considerable heterogeneity of distribution of reinforcing particles and its anisotropic properties. Further, the results are compared with the results obtained by the FSP. It is established that the use of a single FSP process causes a significant change in the distribution of particles reinforcing phase when the value e2 becomes 3.19488. It follows from Mityushev’s theory that e2=π corresponds to isotropic distributions. The article confirms that the new RVE theory resolves the problem of the constructive pure geometrical description of the properties of composites. Further work requires the optimization and extension of the theory to three-dimensional models.

Open access

A. Kurzawa and J.W. Kaczmar

References [1] Shalaby, E.A.M., Churyumov, A.Y., Solonin, A.N. & Lotfy, A. (2016). Preparation and characterization of hybrid A359/(SiC+Si 3 N 4 ) composites synthesized by stir/squeeze casting techniques. Materials Science & Engineering . A 674, 18-24. [2] Jiang, J. & Wang, Y. (2015). Microstructure and mechanical properties of the rheoformed cylindrical part of 7075 aluminum matrix composite reinforced with nano-sized SiC particles. Materials and Design. 79, 32-41. [3] Chou, S-N., Huang, J-L., Lii, D-F. & Lu, H-H. (2007). The mechanical

Open access

I. Uygur

Notch Behavior and Fatigue Life Predictions of Discontinuously Reinforced MMCs

In this study, three notch geometries were assessed with different stress concentration factors. The severity of a notch increased with the stress concentration, hence the fatigue lives dramatically reduced due to increasing stress concentration factor. Fatigue life predictions for the notch geometries have been performed by using a critical strain life approach. It is shown that the model provides a reasonable fatigue life estimation for various notch geometries, volume fraction, and reinforcement particle size of the Al metal matrix composites. Typical crack initiation sites related with the particle clusters, large particles, and intermetallic particles. Although, crack propagation in the reinforced alloy occurred predominantly in the matrix material, SiC particles (SiCp) played a significant role in influencing the crack path.

Open access

Jasna Rupnik

Obvladovanje Tobaka in Alkohola V Zdravstvenem Domu Logatec

Za preventivo na področju tobaka in alkohola so odločilnega pomena ukrepi na ravni družine in lokalne skupnosti. V članku so prikazane dejavnosti v Zdravstvenem domu Logatec ob takšnem razumevanju dejavnikov tveganja. Raziskava zajema pregled izsledkov nekaterih dejavnosti na področju tobaka in alkohola, posebej načrtovanih za preventivo v zadnjih treh letih. Potrjuje, da si za to vsaj nekoliko prizadevajo vse službe zdravstvenega doma: otroški in šolski dispanzerji ter ambulante družinske medicine, in sicer v okviru specifičnih preventivnih dejavnostih iz programa CINDI, v okviru posebnih dejavnosti za splošno populacijo in v okviru tistih, ki so oblikovane posebej za bolnike Centra za preventivo in zdravljenje odvisnosti od prepovedanih drog.

Open access

Sackl Tina Petras, Kaligarič Mitja, Ivajnšič Danijel and Škornik Sonja

Abstract

In the present study, we investigated plant communities with Yellow Oat Grass (Trisetum flavescens (L.) Pb.) in the submontane and montane regions of Slovenia. In 2005-2007 ninety-one relevés were collected by using the standard procedure of the Braun-Blanquet approach. Relevés were analysed with multivariate analysis and classified within two associations: Astrantio-Trisetetum (Polygono-Trisetion) and the Pastinaco-Arrhenatheretum (Arrhenatherion). Management practices, soil conditions and altitude were found to be significant factors for a further subdivision of both associations. Within the Astrantio-Trisetetum association three subassociations could be distinguished: -typicum, -buphthalmetosum and -trollietosum, and subassociations -typicum, -medicagetosum lupulinae, as well as -lolietosum subass. nova in the Pastinaco-Arrhenatheretum. The floristic composition and ecological characteristics of these plant communities are described and their implications for grassland conservation in Slovenia are discussed.

Open access

Zdzisław Skupień

Abstract

Significant values of a combinatorial count need not fit the recurrence for the count. Consequently, initial values of the count can much outnumber those for the recurrence. So is the case of the count, Gl(n), of distance-l independent sets on the cycle Cn, studied by Comtet for l ≥ 0 and n ≥ 1 [sic]. We prove that values of Gl(n) are nth power sums of the characteristic roots of the corresponding recurrence unless 2 ≤ n ≤ l. Lucas numbers L(n) are thus generalized since L(n) is the count in question if l = 1. Asymptotics of the count for 1 ≤ l ≤ 4 involves the golden ratio (if l = 1) and three of the four smallest Pisot numbers inclusive of the smallest of them, plastic number, if l = 4. It is shown that the transition from a recurrence to an OGF, or back, is best presented in terms of mutually reciprocal (shortly: coreciprocal) polynomials. Also the power sums of roots (i.e., moments) of a polynomial have the OGF expressed in terms of the co-reciprocal polynomial.