nan Kishore

On the use of an instrumented set-up to characterize the impact behaviour of an epoxy system containing varying fly ash content

The impact response of a varying fly ash bearing epoxy system was studied. It is observed that with the increase in filler volume fraction there is a net reduction in the impact strength, fracture area and time to maximum load. The Ductility Index of the system, on the other hand, shows an increase with filler level. From visual observations on the failed samples, analyses of the crack length, shift of crack and point at which the slope of the crack reaches 45° are made. The work clearly shows that a curvilinear path for the crack gives place to straighter ones as the ash content in the matrix increases. Consequently, the crack shift also gets reduced when filler particles are introduced in larger quantities into the resinous system. The SEM pictures unambiguously demonstrate how the initiation, propagation and termination regions have distinct appearances whose features vary with ash content, thereby demonstrating that ash particles do influence the crack at all stages, viz., from its development to final rupture of the test coupon due to impact. The work also throws light on the larger-sized particles playing a role in the furtherance of the crack progression.

On evaluating erosion by sand particles in polythene system without and with ceramic particles

The effect of the inclusion of ceramic particles in polythene material on the response to erosion due to impingement by sand particles at three angles is investigated. It is seen that erosion resistance varies with ceramic inclusions. The work also considers the limitations posed by the system in adopting weight change measurements as a measure to follow erosive wear owing to the softer nature of the matrix material. Consequently, the investigation looks at two other experimental parameters that can readily be measured to quantify erosion. Of the two approaches, the advantages of following wear through measuring linear dimension of the resulting crater is stressed in this work. The study also highlights the problems associated in assessing the depth of the crater as a parameter to express the extent of erosion owing to the phenomenon of material flow suggested and schematically illustrated in the work. Corroborative evidence for this flow behaviour through scanning electron microscopic studies is presented.

On the utility of an instrumented impact set-up to characterise the response of discontinuous buffer strips in carbon–epoxy systems in dry and wet conditions

The use of an instrumented impact test set-up to evaluate the influence of water ingress on the impact response of a carbon–epoxy (C–E) laminated composite system containing discontinuous buffer strips (BS) has been examined. The data on the BS-free C–E sample in dry conditions are used as reference to compare with the data derived from those immersed in water. The work demonstrated the utility of an instrumented impact test set-up in characterising the response, first owing to the architectural difference due to introduction of buffer strips and then due to the presence of an additional phase in the form of water ingressed into the sample. The presence of water was found to enhance the energy absorption characteristics of the C–E system with BS insertions. It was also noticed that with an increasing number of BS layer insertions, the load–time plots displayed characteristic changes. The ductility indices (DI) were found to display a lower value for the water immersed samples compared to the dry ones.

Studies on the impact response of carbon-epoxy laminates with and without buffer-strip layers

The work looks at the dynamic behaviour of laminated carbon-epoxy (C-E) composites with inserted interleaf material. Instrumented impact tests were performed to study the impact response of C-E system containing the interleaved PTFE-coated fabric material. Significant differences were noticed in the trend of the load-time plots. It was inferred that the introduction of small amounts of less adherent layers of material at specific locations causes a decrement in the load carrying capability of this material. An attempt to correlate these trends with the post impact observed failure features has been made in this work.

The role of the interface in foam-bearing glass-epoxy composites subjected to impact loading

The responses to impact and the attendant fractographic features for the case of flexible foam, either stacked together as three layers (MC) or inserted at three different positions (3L) while arranging the stacking sequence during the fabrication of glass fiber-epoxy composites, form the subject of investigation. This stacking variation resulted in a different interfacial area between these foam materials and the glass-epoxy regions in the laminates. This area in designed to be maximum for the 3L variety. The energy of impact being high enough to cause development of the crack in the samples, how the change in interfacial area affects the traverse of the crack front and the failure feature of the laminated composite are reported in the form of photomacrographs in this work. The results point to significant changes for the impact data, like for instance the peak load attained by the different samples, through thickness crack propagation and tensile fracture features on the non-impacted end for the plain v...

Influence of foam/glass-epoxy interface on the macroscopic compressive failure features

The effect on the macroscopic compressive failure features of introduction of two flexible foam layers, either together at mid-region or separately at two locations that are away from the midregion, into a glass-epoxy (G-E) system is studied in this work. In this experimental approach an attempt to look at the possible influence the foam/G-E interface region has on the way the materials respond to compressive loading is made by involving an analyses of macrofractographic features. While foam-free samples fail by extensive ear formation and separation nearer to the mid-region, the foam bearing ones display pronounced interface separation. The positioning of the foam sheet(s) has a bearing on the failure features.