Browsing by Author "Mulugeta Habtemariam"

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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.
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    Investigation on the Intralaminar Fracture Toughness of Acacia Tortilis/Glass Fiber Reinforced Hybrid Polyester Composite.
    (Addis Ababa University, 2024-10) Yohannes Molla; Mulugeta Habtemariam
    Natural fiber-reinforced polymer composites as well as their hybridization with synthetic fibers become a choice for their advantages such as being cheap in cost and light in weight. However, the use of these composites for different applications needs an investigation of the fracture behavior of the composite to know the damage tolerance and capability of crack resistance. To study the intralaminar fracture toughness of chopped acacia tortilis/glass fiber reinforced composite, Mode-I intralaminar fracture toughness experimental test on five 2TCT (doubly tapered compact tension) specimens from the four fabricated composite laminates (pure AT (acacia tortilis), pure Glass, and two hybrids H1(G-AT-G-AT-G-AT-G), H2(G-G-AT-AT-AT-G-G)) as per ASTM E399-09 testing standard were carried out. The total fiber volume fraction of the composite laminates was 30% the volume fraction for both hybrid composites was composed of 13% AT fiber and 17% of glass fiber. A recommended data reduction technique based on finite element analysis was employed. From the experimental result, a load-displacement curve for all composite laminates was obtained. The fracture toughness values based on critical energy release rate (GIC ) value were evaluated for all composite laminates. The resistance curve (R-curve) was plotted and discussed for all composite laminates. The fractography of fractured surfaces for all composite laminates was qualitatively discussed and from the results, a brittle fracture behavior was observed. The critical energy release (GIC) value for pure AT, Hybrid 1 (H1), Hybrid 2 (H2), and pure Glass composite laminates were evaluated as , , , and respectively. From the result of critical energy release (GIC) values of the four composite laminates, pure AT composite laminate have very small value and hybridization of it with glass fiber resulted a significant change in the GIC value. The two hybrids composite laminates have a GIC value in between the two monolithic laminate composites also have a comparable value with other natural fiber hybrid composites. Finally, a recommendation of the hybrid composite for semi structural or non-structural application was made.