83 KB331 KB48 KB199920252007Campos, A. R.Cunha, A.M.Gantar, GašperHančič, AlešKosel, Francštevilka:1215 straniletnik:53str. 819-833ISSN:0039-2480COBISSID:10394651URN:URN:NBN:SI:doc-1XSX84W8enslAssociation of Mechanical Engineers and Technicians of Slovenia et al.Zveza strojnih inženirjev in tehnikov Slovenije et al.Strojniški vestnikbiopolimerikompozitimehanske lastnostinaravna vlaknaAnalitični model določevanja mehanskih lastnosti biopolimernih kompozitov - mikromehanski postopek| A model for predicting the mechanical properties of wood-plastic composites - a micro-mechanical approach|The development of a new composite that is made up of natural fibres and low-price polymers, such as HDPE or PP, began in the 1990s. Because this material is relatively new to the market and due to the random characteristics of the fibres, no attempts have been made to analytically define the mechanical properties of this material. In this paper a micro-mechanical approach, called the generalised method of cells (GMCs), is introduced to describe the properties of injection-moulded wood-plastic composites made up of polypropylene (PP) or polystyrene (PS) and wood or cellulose short fibres. The main problem with an analytical approach is that the natural fibres are not uniform in shape and size, which makes them hard tofit into standard mathematical models. In this paper the average values of the fibre sizes were used. The materials were first scanned with optical and electron microscopes to determine the fibre properties and their scatter. These values were then used to determine the elastic and plastic response of the composite together with the maximum strength and elongation of the composite, where the Tsai-Hill failure-criterion was used. The results were then compared to the experimental data in order to evaluate the practical usefulness of this method. The time-dependent mechanical behaviour of the composite was not considered due to the complex and random properties of the fibreV zadnjem desetletju prejšnjega stoletja se je pričel razvoj novih kompozitov,sestavljenih iz naravnih vlaken in cenejših polimerov, kakor sta npr. HDPE in PP. Zaradi relativno kratkega časa prisotnosti na trgu in naključnih lastnosti vlaken do sedaj se ni bilo poskusov analitičnega določevanja mehanskih lastnosti omenjenih kompozitov. V tem prispevku je uporabljen mikromehanieni postopek, imenovan posplošena metoda celic (PMC - GMC) za popis lastnosti injekcijsko brizganih biopolimernih kompozitov, sestavljenih iz polipropilena (PP) ali polistirena (PS) ter lesnih ali celuloznih vlaken. Glavni problem pri analitičnim postopku je, da naravna vlakna nimajo enotne dolžine, prereza ali oblike, zato jih je težko popisati z običajnimi matematičnimi modeli, tako da so v prispevku uporabljene povprečne vrednosti geometrijskih lastnosti vlaken. Kompoziti so bili najprej pregledani z optičnim in elektronskim mikroskopom z namenom določiti lastnostiin razporeditev vlaken. Ti podatki so bili nato uporabljeni pri ugotavljanju elastičnega in plastičnega odziva kompozita ter njegovih porušnih vrednosti, ki so bile izračunane po Tsai-Hillovi porušni hipotezi. Rezultati so bili nato primerjani z eksperimentalnimi podatki, tako da je bilo mogoče oceniti praktično uporabnost te metode. Časovno odvisne mehanske lastnosti materiala tu niso bile upoštevane zaradi zapletenosti in naključnih lastnosti vlakenTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaUniverza v Ljubljani, Fakulteta za strojništvo