2. Thesis and Dissertations
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Item Performance Evaluation of Flexible Jute-Natural Rubber Composites for Impact Behaviour(National Institute of Technology Karnataka, Surathkal, 2020) M, Vishwas.; Joladarashi, Sharnappa.; Kulkarni, S M.A composite material is made from two or more constituent materials with significantly different physical or chemical properties which are combined to produce a material with characteristics different from the individual components. ‗Flexible composites‘ is a term coined to identify the composites making use of elastomeric polymers as matrix. These flexible composites exhibit usable range of deformations which are much larger than conventional stiff composites. The ability of flexible composites to undergo larger deformation and still provide high load carrying ability makes them suitable for many engineering applications. Flexible composites are better energy absorbers compared to conventional stiff composites subjected to impact loading. The objectives and scope of the present study includes proposing, developing and characterizing the flexible ‗green‘ composite for impact applications. An extensive literature review was carried out to explore the potential constituent materials for impact applications and accordingly the present study is carried out to explore the possible use of jute and rubber for impact applications. Initially, the feasibility of using natural rubber (NR) as a constituent material in composite is studied using commercially available finite element (FE) package. Further different stacking sequences of the flexible green sandwich composite are optimized and the three stacking sequences are selected for experimental study. These three optimized stacking sequences of the proposed flexible green sandwich composite are prepared using compression moulding technique and are characterized for their physical and mechanical properties. Further, the proposed flexible green composites are studied for their abrasive behaviour under two body environments and erosive behaviour under slurry environment. Finally, the impact behaviour of the proposed flexible composites is studied under low velocity impact (LVI) and lower ballistic impact. The mechanical characterization of the proposed flexible composites revealed that the composite with jute/rubber/jute (JRJ) exhibits better tensile and tear strength compared to jute/rubber/rubber/jute (JRRJ) and jute/rubber/jute/rubber/jute (JRJRJ) with JRJ exhibiting 57.7% and 64.47% higher tensile strength compared to JRRJ and JRJRJ respectively. Also, the tear strength of JRJ is found to be 0.4% and 2.38%higher than JRRJ and JRJRJ respectively. The interlaminar shear strength (ILSS) studies shows that short beam strength of JRJRJ is better compared to JRRJ and JRJ with JRJRJ exhibiting nearly 2.1 times and 2.75 times better ILSS compared to JRRJ and JRJ respectively. The proposed flexible green composites are further studied for their abrasive behaviour under two body environments and erosive behaviour under slurry environment, the outcome of which reveals that JRJ provides better results compared to its counterpart JRRJ and JRJRJ. Various factors affecting the wear behaviour of the flexible composites are also studied from which it is clear that abrading distance and sand concentration affects the weight loss of the proposed flexible green composite in case of two body wear and slurry erosion respectively. Flexible ‗green‘ composites of different stacking sequences are further subjected to impact tests at low velocity and lower ballistic velocity at different impact energies. The results of low velocity impact reveals that flexible green composite with JRJ stacking sequence exhibit better energy absorption and the stacking sequences JRJRJ exhibit better resistance to damage with no appreciable variation in specific energy absorption of the composites. The lower ballistic impact study reveals that the flexible composites are better energy absorbers with JRJRJ exhibiting better lower ballistic response compared to JRJ and JRRJ. The ballistic limit of JRJRJ is enhanced by 39.7% and 6% compared to JRJ and JRRJ respectively. The energy absorption at ballistic limit of JRJRJ is more compared to JRJ and JRRJ by 97.7% and 12.7% respectively. The energy absorption of JRRJ is enhanced by 75.5% compared to JRJ. The specific energy absorption (SEA) of JRJRJ is enhanced by 52% and 2.7% compared to JRJ and JRRJ respectively. The proposed flexible green composite can be a potential material for sacrificial structures in order to protect the primary structural components.Item Development of Sandwich Composites from Natural Materials for Bullet Proofing(National Institute of Technology Karnataka, Surathkal, 2019) Sangamesh; RaviShankar, K. S.; Kulakarni, S. M.Ballistic protective materials have been used in the past are replaced with synthetic polymer composites due to their strength to weight ratio. Nowadays, these synthetic materials are being replaced by natural fiber reinforced composites due to the cost and environmental issues. The present investigation relates to the development of natural sandwich/laminated composite material interlock blocks for bullet arresting. Bullet arresting capacity depends on energy absorption. The energy absorption of the material could be increased by different ways. Among which sandwich form of the composite is one of the effective ways of improving the energy absorption capability of PMCs. This study was undertaken to explore the use of natural materials such as Jute epoxy fly ash composite (JEFC), Jute-epoxy fly ash rubber (JEFRC) sandwich composite for ballistic energy absorption. Prior to FE analysis, mechanical characterization of three varieties of jute composites were carried out namely Tossa jute single woven composite (TSWC), White jute single woven composite (WSWC), White jute double woven composite (WDWC) among all Tossa jute single woven composite (TSWC) revealed better mechanical properties. Hence for further analysis, Tossa jute single woven epoxy fly ash composite nothing but Jute epoxy fly ash composite (JEFC) is only used for ballistic FE simulation and as well as for ballistic impact testing of composite plates, blocks and interlock blocks. Finite Element analysis of these plates was carried out for thicknesses (5, 10, 15 mm). JEFC plates and JEFRC sandwiches with the same thickness (15 mm) were fabricated and tested to measure residual velocity and energy absorbed. Among JEFC and JEFRC, JEFRC showed better ballistic performance hence further analysis is carried out on jute-epoxy-fly ash natural rubber sandwich block composite (JEFRC), at different thicknesses of the target plate (50, 75, 100, 150 mm) and three velocities of the projectile (150, 250, 350 m/s). Ballistic parameters were evaluated using commercial FE software. Further same thickness and same configuration sandwich blocks were produced using compression molding machine; these prepared samples were subjected to ballistic impact test by impacting the projectile. From FE analysis and ballistic test, it is confirmed that at about 75 mm thickness the sandwich blockswere capable of arresting the bullet. Further interlock sandwich blocks were produced and tested for ballistic impact, which arrested the bullet half of its thickness. Hence such sandwich interlock blocks are produced to prototype for arresting bullet up to velocity 350 m/s. Fracture behavior is analyzed using SEM.