ABSTRACT:The main drawback of fiber reinforced composites is inter-laminar fracture, especially delamination. Due to the nature of composite fabrication delamination is being a common failure. Composites are made in a variety of manufacturing techniques that are available. Commonly, a layered stacking of fibers in a primary plane is observed in each of these techniques. The interfacing part between the layers of the composites is not obviously reinforced with fibers which in turn lead to the inter-laminar fracture or delamination. The strain energy release rate (G C ) is the best material property that can represent the resistance to delamination which can be both experimentally and numerically obtained. The principal attention of the present study is to obtain the inter-laminar fracture toughness in composites caused because of the pure sliding mode. An inter-laminar fracture for mode II (G IIC ) crack propagation is studied for GFRP materials having unidirectional 00 orientation of fiber. Compliance calibration method is used to study on the experimental investigation of toughness G IIC for fiber volume of 40%, 50% and 60%. Investigation was directed according to ASTM D7905 using End Notched Flexure specimen which is fabricated using E-glass fiber and epoxy matrix in hand layup method. Results obtained are again correlated with numerical analysis using virtual crack closure technique (VCCT) method. Keywords: Energy Release rate, Fracture Toughness, Virtual Crack Closure technique, Edge Notch Flexure specimen. I. INTRODUCTIONThe composite materials undergo failure due to many aspects like impact or static overloading, fatigue, overheating, hygrothermal effect, creep etc. One of the most regularly used manufacturing technique used of set up a composite structure is laminating of composite materials. Delamination is being the major limiting factor for the composite structures that are laminated. Delamination being a mainly significant mode of failure observed particularly in reinforced fiber laminate composites structures. Delamination is the separation of the laminated fiber reinforced layers that are bonded together to form laminated composite. These de-laminations are the results of the impact by any foreign object or manufacturing defects and this can cause a significant reduction in strength and stiffness of the component or the structure. Linear fracture mechanics depending on energy have been extensively used in de-lamination model of composite and their study. The strain energy release rate 'G' to be verified for resolving loads that cause delamination expansion by using this fracture mechanics approach. In some of the conditions that involve the inter-laminar fracture-toughness or critical strain-energy-release rate, 'G C ' in composites. The energy that is released for the crack to grow for unit area in the test specimen undergoing constant displacement is called as the strain-energy-release rate. The capacity of a material having a crack to resist the growth of fracture on that material is called as cr...
ABSTRACT-To develop the usefulness of Caesalpinia pulcherrima and Catharanthus roseus plants as bioindicators, which entail an utmost importance for a particular situation. This study focuses on the assessment of air pollution tolerance index (APTI) of two selected plant species commonly found along roadsides in Bengaluru, India. The plant species selected for the study were Caesalpinia pulcherrima and Catharanthus roseus. The plants were evaluated in terms of APTI by analyzing four different biochemical parameters: Leaf relative water content (RWC), Ascorbic acid content (AA), Total leaf chlorophyll (TCh), and pH of leaf extract. Based on APTI Caesalpinia pulcherrima was found to be more tolerant compared to Catharanthus roseus. Species with lower APTI value are considered sensitive species, which can be used as a biological indicator for further monitoring of air quality. Species with higher APTI value are tolerant species and thus, can be planted for pollution abatement in order to control and reduce environmental pollution.
-Unstable propagation of a crack results in fracture due to applied stress. Fracture mechanics provides a methodology for prediction, prevention, and control of fracture in materials, components and structures subjected to static, dynamic, and sustained loads. De-lamination is considered to be the most occurring failure mode in composites, a partition of the layers that are stacked together to form laminates. Delaminations appear at stress free edges due to the difference in properties of the individual layers, at ply drops where thickness should be reduced, and at regions subjected to out-of-plane loading like bending of curved beams. An experimental analysis was performed for analyzing the energy release rate for mode I crack propagation of the DCB specimen for different volume fractions. Double Cantilever Beam Specimen was analyzed for mode I crack propagation subjected tensile load and Energy Release Rate was evaluated for different crack lengths using ANSYS 15. Virtual Crack Closure method was used to find the Energy Release Rate by considering the displacements (V) at the flagged nodes near the crack tip and then was compared with the analytical results. Virtual Crack Closure method showed very good agreement with the experimental results. Convergence was achieved through refinement and results were extracted for variation of SIF along the crack front. It was observed from the results that the ERR increased at a very slow rate in the beginning of the crack growth (a/w = 0.2 to a/w = 0.4). As a/w reached 0.5 there was a steep increase in the Energy Release Rate. This was purely because of the plastic zone at the crack tip getting increased. This in turn increases the resistance offered by the crack to the propagation. Keywords -Virtual Crack Closure Technique, Energy Release Rate, Crack propagation.I. INTRODUCTION De-lamination is considered to be the most occurring failure mode in composites, a partition of the layers that are stacked together to form laminates. Delaminations appear at stress free edges due to the difference in properties of the individual layers, at ply drops where thickness should be reduced, and at regions subjected to out-of-plane loading like bending of curved beams. Opening mode (mode I), the sliding shear mode (mode II), and the scissoring shear mode (mode III) are the three different modes of crack propagation. The fracture toughness linked with each fracture modes must be characterized and the equivalent strain energy release rates for each mode connected with the design and loading of interest must be evaluated to predict de-lamination onset and growth. M. Kenane et, al [1] carried out a de-lamination fatigue-crack growth experiments on unidirectional glass/epoxy laminates. Three specimen types were tested: double cantilever beam (DCB), mixed-mode bending (MMB), and end-loaded split (ELS), for mode I, mixed-mode I + II, and mode II loading, respectively. Fracture mechanics technology was applied through the principles of strain-energy release rate. The measured de-lamin...
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