3D Preforming technologies for composite applications

With the high end applications like aerospace, the orientation of the fibrous reinforcement is becoming more and more important from load bearing point of view as well as need of placing the reinforcement oriented in the third dimension. In textile process, there is direct control over fiber placements and ease of handling of fibers. Textile technology is of particular importance in the context of improving certain properties of composites like inter-laminar shear and damage tolerance apart from reducing the cost of manufacturing. Depending upon textile preforming method the range of fiber orientation and fiber volume fraction of preform will vary, subsequently affecting matrix infiltration and consolidation. As a route to mass production of textile composites, the production speed, material handling and material design flexibility are major factors responsible for selection of textile reinforcement production. This article reviews the developments occurred in this field of textile preforming along with their advantages and disadvantages and also presents the studies on 3D multilayer interlocked woven reinforced composite materials performance

Development of 3D Angle-Interlock Woven Preforms for Composites

The advent of three dimensional (3D) reinforcements has been mainly to overcome the issue of delamination and improve upon the damage tolerance properties by introducing fibres in the thickness direction for advanced composite applications. 3D preforms can be developed using various techniques. Angle-interlock weaving is one of them. This paper details about the efforts being put at CSIR-NAL for developing angle-interlock woven preforms. Four types of angle-interlock structures viz., layer-to-layer and through thickness (both with and without stuffer yarns) were developed using 6K, 400 Tex TC-33 grade Carbon tows on a custom designed handloom. The preforms without stuffer yarns had 4 layers of warp and were of 1.5± 0.2 mm thick. Preforms with stuffer yarns had 6 layers of warp (including 2 stuffer yarn layers) and were of 2.3±0.1 mm thick. Thermoset composites were prepared from these preforms using EPOLAM 2063 (an epoxy based resin system) by RTM process. The fibre weight fraction for these composites ranged from 0.53 to 0.58 and they were subjected to mechanical tests such as tensile, flexural and interlaminar shear strength. Test results showed improved response (in the warp direction) with respect to shear properties while the tensile and flexural properties were equivalent to that of the plain woven composites

Experimental Characterisation of GLass Aluminum REinforced (GLARE™) laminates

Fibre metal laminates such as GLARE™ have found promising application in the aerospace industry. These laminates were developed at the structures and materials laboratory of Delft University of Technology, Netherlands. GLARE™ is a material belonging to the family of Fibre Metal Laminates consisting of thin aluminum layers bonded with unidirectional S2-Glass fibres with an adhesive. Aluminum and S2-Glass when combined as a hybrid material can provide best features of the both metals and composites. These materials have excellent fatigue, impact and damage tolerance characteristics and a lower density compared to aluminum. GLARE™ has found major application in front and aft upper fuselage, leading edges of empennages of advanced civil aircrafts like A380. This document looks into the evaluation of two configuration of GLARE™ for its mechanical and impact characteristics. The mechanical characterisation was carried out for tensile, compression, Flexure, ILSS, Open Hole Tension, Open Hole Compression and Shear (Iosipescu). The impact behaviour were characterised based on a low velocity drop weight impact carried on these laminates. The study shows that the basic properties evaluated were more dictated by the property of the S2-Glass used. The studies show that GLARE™ laminates posses’ high impact damage resistance compared to other composite material. All the test datas generated for this study will be brought out in this document

3D WEAVING POSSIBILITIES ON AN 8 SHAFT LOOM

This work’s focus is towards exploring the possibilities of weaving select type of 3D reinforcements on the commercially available 2D weaving looms of the textile industry. In this context, two classes of 3D reinforcements were developed using 6K Carbon rovings of 400 Texon an 8 shaft handloom. The first class comprised of weaving single layer profiles wherein, ‘T’and ‘p’ profiles were woven. The second class comprised of weaving planar multilayer (angle interlock structure) samples of two types viz., layer to layer and through-thickness. In this class, a ‘T’ profile was also woven. Weave Design Plan for these structures were developed using the warp(for single layer profiles) and weft ( for angle interlock structures) yarn cross-sections. It has finally been inferred that, woven cloth construction design and 2D weaving technology can be successfully utilized to develop select class of 3D reinforcements for composite applications

Of Weaves, Knits and Their Composites

Utilisation of aerospace related Research & Development activities to meet the societal missions applications the societal missions/applications

Knitted Preforms for Composite Application

Knitted structures occupy a special position in composite preforming due to their inimitable characteristics. An insight into the knitted structures with respect to their composite preforming characteristics is presented in this article. Directionality of knitted structures and requirements of high performance fibers for knitting have been discussed. Contourability, net-shape preforming, high dynamic mechanical properties along with easy and rapid manufacturability are the important features of knitted structures to match the composite preform requirements. In this article, the work done in the above areas of research have been critically reviewed

Impactor Mass effects in polymer Matrix Composites under Low Velocity Conditions: A Repeated Drops Test Approach

This paper utilizes the concept of repeated drop tests to understand impactor mass effects under low velocity test conditions on Polymer Matrix Composites. Twill woven glass fabric reinforcements and epoxy matrices(three variants) with differing cure schedules were used to prepare composite specimens. These specimens were then subjected to Repeated Drop Tests using an instrumented Impact test facility. Judicious combinations of Mass and Height were used to simulate equivalent incident energies (E in) ranging from 3 J to 15J. Number of Drops to failure data (N,) was obtained for the varied impactor mass in each case. Ein - Nf plots and the Threshold Incident Energy (E*J values obtained from the overlay of these plots. showed. clear demarcable failures at lower incident energies, i.e., the specimen impacted with heavier impactor failed in less number of drops as compared to the specimen impacted with lighter mass for the same E,n. Also, E*!" obtained, clearly identified the point below which impactor mass effected earlier damage in composites. The hallmark conclusion that has been inferred from this research work is that "It is preferable to use lighter tools during routine service and overhauling of aircraft/ similar structures, so that they inflict minimum impact damage during work execution1 accidental drops"

Impact Damage Tolerance Assessment in Polymer Composites : A New Approach

The impact behaviour of polymer composites is a complex phenomena affected by material parameters, instrument parameters, testing conditions and process variations. As it has not been possible to quantify the impact behaviour based solely on impact studies, post-impact tests such as compression-after-impact or tension-after-impact have been used to study the degradation in strength properties and quantities impact damage. Since these post impact tests are very expensive and rigorous, this work, gives a simpler approach route for evaluation of impact damage tolerance of advanced composites by the use of repeated drop tests. Low velocity (1.2-2.4 m/s, incident energy range being 3.55 - 159 impact tests have been carried out on three variants of glass and one variant of carbon epoxy composites using an instrumented impact test machine ( DYNATUP 8250). The composites were subjected to repeated impacts until failure for a fixed energy level. Number of drops to failure (Nf) data were obtained for each of the pre-determined incident energies (E in) in the above range. E in, Vs Nf plot for each) composite was obtained and a relationship between them was evolved and verified. Further, &om the I&, Vs Nf plots, a critical incident energy parameter termed Ec was obtained. This critical energy value turns out to be the threshold value, below which the composite takes infinite drops to fail, and above which, it fails after very few drops. Ec, therefore, can be used as an important input in the design of impact damage tolerant composites by composite designers. This E, forms yet another criteria for damage tolerance assessment in advanced composites, apart from the very expensive/ sophisticated compression-After-Impact tests, hitherto being considered

3D Composites: Opportunities and Challenges

3D composites are creating a furore among the composites community, especially the aeronautics, space and defense sectors. Literature reports on 3D composites discuss a wide spectrum of 3D technologies encompassing weaving, stitching, braiding, tufting etc., that are at various stages of development and implementation. Choice of technology for a particular end use is based on various factors such as need, problem to be addressed, expected performance requirement, practicality of development and the like. Two broad areas of application for 3D composites are in the structural and thermal segments. Opportunities for 3D composites exist in the form of performance improvements for components having multidirectional stress states, simplified & radically different designs, reduced part count and reduced labor cost. Challenges that need to be addressed include achieving a balance between in-plane & out-of-plane properties, processing issues for thick & compact 3D structures, out-of-plane testing approaches and integration challenges with metal/2D composites. This paper reviews the current status and looks at what the future has to offer for this upcoming technology

Low Velocity Impact Studies on Carbon Fiber Metal Laminates

Fibre Metal Laminates(FML) are a new family of materials built up using a combination of thin metal foils(0.2 to 0.5mm thick) and intermediate fibre-reinforced polymer layers. An FML based on carbon fibres/glass/ aluminum (CFML) is being thought of with the objective of an energy absorbing material which is also lower in weight. Carbon Fibre Metal Laminate (CFML) is an FML developed at NAL consisting of thin aluminum foil combined with carbon-epoxy and glass-epoxy prepreg materials. CFML is proposed as the candidate material for the leading edges of wing and empennage of an aircraft. However, these carbons based laminated composites shows localized sub surface damage under relatively low energy impact events like tool fall etc. Such localized damages known as ‘Barely Visible Impact Damages (BVIDs)’ are a potential source of strength reduction particularly under compressive loads. It is very important to know the impact damage resistance, shape retention and the energy absorption capability during such impact events. A test program to understand the impact behavior of carbon fibre metal laminates was conducted. The results based on the low velocity impact tests for low energy levels like 3J, 6J, 9J, 17J and 30J for CFML and aluminum 2024-T3 alloy are presented in this document. A separate study carried out to understand the impact behavior of two different configurations is also analysed in this document