Project on Analytical and experimental investigation of Mode-1 fracture toughness of GFRP

ContentIntroductionEffect of DelimitationNeedsAvailable TechnologyGoalsTimelineReferences

IntroductionComposite MaterialRecently, the application of fibre reinforced composite materials in various branches of the technology (mechanical engineering, ship building, aeronautics, civil engineering, car industry) has undergone a huge development.The basic advantage of the composites is their high strength-to-weight ratio in comparison with the conventional structural materials. Therefore, they are very suitable for application in load-bearing structures, where the low weight is of primary concern. Fibre reinforced composite materials are replacing standard isotropic materials in many applications. Aerospace vehicles, aircraft, marine equipment, and common items such as civil structures, prosthetic devices, and sports equipment are currently being constructed of such composite materials.

DrawbackA major drawback to laminated composite materials stems from the manufacturing process used to construct them. Placing fabric or fibres in strata to obtain a desired architecture allows resin rich layers to form between fabric layers. These regions are without reinforcement and are prone to develop discontinuities such as pores and voids. The performance of the composite material at these locations is dominated by the properties of the resin. Often the failure of a composite structure begins with the separation of these layers or delamination.Effects of Delamination failures in Composite MaterialsThe primary limitation of fibre reinforced composites is fracture toughness, specifically delamination.Delamination is a mode of failure for composite materials.In laminated materials, repeated cyclic stresses, impact, and so on can cause layers to separate, forming a mica-like structure of separate layers, with significant loss of mechanical toughness. The interface between these layers is typically not reinforced with fibers and is the source of delamination or interlaminar fracture. Porosity and other manufacturing related defects also introduce nucleation sites for delamination.

The cause of fiber pull-out (another form of failure mechanism) and delamination is weak bonding. Thus, delamination is an insidious kind of failure as it develops inside of the material, without being obvious on the surface, much like metal fatigue.Delamination failure may be detected in the material by its sound; solid composite has bright sound, while delaminated part sounds dull, reinforced concrete sounds solid, whereas delaminated concrete will have a light drum-like sound when exposed to a dragged chain pulled across its surface.

Some manufacturers of carbon composite bike frames suggest to dispose of the expensive frame after a particularly bad crash, because the impact could develop defects inside the material.Due to increasing use of composite materials in aviation, delamination is increasingly an air safety concern, especially in the tail sections of the airplanesTherefore, the analysis of delamination in composites is an important problem of the fracture mechanics. The focus of this study is on the delamination and interlaminar fracture performance of composite materials.

Delamination of Composite Materials under compression load

NeedsComposite designers and engineers recognize delamination as a primary failure mode. Unfortunately, modelling and predicting this behaviour is not easy. In general, designers and engineers have the ability to implement a stress analysis and utilize this in parallel with empirically obtained strength data. In the case of engineering composites, fracture toughness and delamination resistance are not as easily accounted for a general need exists for an organized approach that designers can use to evaluate and improve interlaminar fracture properties and capabilities. Both analytical and experimental approaches are viable and will be discussed.

Literature Survey (Available Technology)Classical lamination theory can be applied to determine an appropriate composite architecture. However, techniques for designing a delamination resistant material with necessary interlaminar fracture toughness properties for service, are not as well established. Testing procedures, failure criteria, and finite element analysis techniques are at the engineers disposal to evaluate and predict interlaminar fracture toughness of composite materials. Standard test procedures have been applied to unidirectional laminated composites to evaluate and quantify fracture toughness. These procedures have been focused at the evaluation of resin performance in composite architectures. Goals Ultimately the procedures and techniques used to quantify the fracture toughness performance of composite specimens can be used to predict failure of more complex composite structures. The objective of this project is that to develop improved analytical solution for delamination modelling of composite beams. The following methods are include:Calculation of the compliance and strain energy release rate of delaminated composite beams under a general loading condition by using higher order beam theory based on beam-on-elastic-foundation concept.Application of the developed model to the few delamination specimens and verification of the developed model by experiments.

Construction of the R-Curve for glass/polyester composite.To solve the above-mentioned problems, the concepts of linear elastic fracture mechanics and the concepts of differential equations are applied. The derivation of the formulae will be performed by using the code MATHEMATICA.

Project TimelinePhase-I ------- Last week of NovemberIntroduction of Project synopsisPhase-II ------- Last week of FebruaryAnalytical model of Specimen Phase-III ------ Last week of April Experiments and result and validation ReferencesK.Kaw, Mechanics of composite materialsAnderson, Fracture MechanicsStandard Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites.CHATTERJE S.N. (1991) Analysis of test specimens for interlaminar mode II fracture toughness, Part 1. Elastic laminates, Journal of Composite Materials.

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