Applied Mechanics

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Browsing Applied Mechanics by Author "Daniel Tilahun (Assoc. Prof.)"

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    Influence of Nanoclay on Interlaminar Fracture Characterization of GFRP, and Intralaminar Fracture Characterization of SIMS & Glass Mat Reinforced Thermoplastics Materials
    (Addis Ababa University, 2020-06) Mulugeta Habtemariam; Belingardi, Supervisor: Giovanni (Prof.); Daniel Tilahun (Assoc. Prof.); Ermias G. Koricho (Asst. Prof.)
    The needs of lightweight and customizable structural materials instigate researchers to conduct rigorous materials characterization, with particular attention toward failure mechanisms and safety standards, and to study the materials’ development. Furthermore, the currently available structural and semi-structural composite materials made up of fiber-reinforced plastic, that are presently considered to keep the environmental regulations, require multidimensional examination and analysis because of its heterogeneous nature a non-isotropic behavior. Consequently, this research aims to improve the knowledge on specific lightweight material and to contribute the confidence that toward their use in spite of its poor nature and suspicious to fail, focusing on some fundamental material properties, such as interlaminar and intralaminar behaviors. The research started from failure characteristics and mechanisms, followed by the analysis of the modifications adopted to enhance its structural properties in advanced level, and finally report the adopted experimental characterization procedures and discuss the main findings. The first part of the study has been focused on composite materials with special targets of enhancement and the structural behavior of these materials was experimentally characterized. The material was manufactured with a plain-woven S-glass fiber-reinforce plastic. The material modification was obtained by adding nanoparticles to the matrix; therefore a nano-modified composite was developed by the appropriate combination of epoxy and nanoclay family particles, Cloisite 20B. Thus, the fundamental experimental work included the effect of nanoclay, Cloisite 20B inclusion on the mechanical behavior of a woven type glass fiber reinforced plastic (GFRP) composite. Specifically, the study examined the effect of nanoclay, added with various weight percentages, on the tensile, compressive strengths, and modulus of elasticity of GFRP in both weft and warp directions. Results showed that depending on the warp and weft directions, the inclusion of nanoclay, Cloisite 20B, altered the mechanical behavior of GFRP. The advanced investigations focus on the interlaminar characteristics of the material. In this work, the effect of meticulous nanoclay, Cloisite 20B, inclusion on the interlaminar fracture toughness glass fiber reinforced plastic composite was investigated using careful experimental procedure. Afterwards the study moved to the fracture mechanics behavior, with particular reference to the mode-I interlaminar behavior. Tests were conducted based on a double cantilever beam (DCB) specimen using the specific American Society of Testing Materials standard (ASTM D5528). Results showed that the inclusion of nanoclays improved the interlaminar fracture toughness of the GFRP composite in the range of 12.65% and 54.07% relative to pristine, with progressive percentage increment of the nanoclays weight percentage content (from 0.5 to 2%). Therefore, the dissemination of this experimental research results contributes to overlook a better understanding of nanoclay fillers and their contribution to mechanical behaviors; this can lead to a better design of novel structural composites. Moreover, it guides how Cloisite fillers contribute to improve the delamination resistance with this special composite material having a better retardant flame propagation property that can be relevant for some structures. The second part dealt with lightweight materials that are intended for the vehicle /automotive industry. The intralaminar behavior of the two types of materials, which were supplied by two international companies, was investigated. The fundamental behavior, impact, and special structural application studies of these two types of innovative materials were examined, once again with particular attention toward the impact response and the fracture nature of these materials. The first material type is semi impregnated micro sandwich structure (SIMS) and it is manufactured with two specific reinforcing fibers (carbon and glass). The other material belongs to the glass mat thermoplastic (GMT) family that has also two types: the conventional GMT and the GMT modified by adding unidirectional fibers (GMT-UD) to stiff the structure. For those materials, the intralaminar fracture and the nature of the crack behavior were experimentally investigated using compact tension specimen test. The intralaminar fracture toughness of each material was determined along with crack propagation behavior. As a result, the output of this research fills the gaps and it can contribute to having a full picture of the GMT and SIMS materials.