Keywords: fibre, composite, filament winding, joint, optimization, experiment.

Composite products are being increasingly used and are becoming an important class of engineering materials for a wide range of applications. One of these of our interests is the composite of long fibers and polymer matrix. We will consider on production of so called performance product, made by filament winding technology. The axial winding technology was developed in company Compo Tech PLUS Ltd. with the close collaboration at CTU Prague. The original feature of this technology is possibility of axial fiber orientation (0 degree winding angle) allowing the significant increase of stiffness and strength. Complete technology CNC machines systems up to length of 8 meters were developed. A special computer program for design of filament wound composite beams and some methods of optimization have been made at CTU Prague [1,2].

The widely known problem for the successful application of composite parts in a real structure is the joint between the composite part and usually the part of isotropic material. Three types of joints are generally used in composite engineering: adhesive joints, bolted joints and integrated joints. We have focused on the third type of joint, the high performance integrated joint (IHPJ). The main principle in the case of filament winding is that fiber tow is wrapped directly around the shape of the alloy pin or tapered rod part. It is important to apply the methods of deformation measuring and failure detection for the deformation analysis and damage process of the composite joint. Strain gauges and acoustic emission were used. Strain measurement methods based on fibre optic sensors (FOS), fibre Bragg grating is now a focus of attention. New proposals for multilayer lugs with layers of different stiffness of layers were calculated and tested [3]. The analytical formulas appropriate for the optimum design of the IHPJ were derived for the main damage mode, parameters of the used material and geometric characteristics of each type of IHPJ. New proposals for multilayer lugs with layers of different stiffness were calculated and tested [5].

Mechanical tests of composite loop made of carbon fiber Tenax HTS800, epoxy resin LG120/EM100 and GRM Systems hardener were performed. More than thirty samples were tested so far. All samples were loaded by a tensile force up to failure and hence the results of the test were stifness, maximal breaking force and maximal strength in a loop cross-section during failure. The breaking stress for samples of a typical batch (20 fibers in a loop) was 556,329,2 MPa which corresponds with previous results of hydraulic cylinder tests [4]. The loop fastening effect was studied and several tests were done to confirm and quantify this. Although there is more than 25% higher maximum force for a loop hard fastened than a free loop on a pin, the FEM analysis gives only about 15% increase of the maximum force. FEM simulations were made using the ABAQUS v6.5 solver. The real pin-joint of the composite-steel differs from tension test samples in boundary conditions of loop fastening. These differences produce different stress distributions, which result in lower strengths of the experimental tension test samples. The FEM computations of the tension-loaded composite loop showed that the stress distribution in the loop head is similar to the stress distribution in the thick-walled pressure vessels, however these lugs are loaded with higher tangential stresses than the thick-walled pressure vessels. The boundary conditions of the loop fastening causes the uniform pressure load leading to tension and bending loading, which produce more complicated stress distribution, especially in the orthotropic material models that were used. The results of the isotropic material model are approximately the same as the results of the analytic solution. Creating multilayer composite loops from diferent material layers leads to lower stresses, however the influence of multilayers on lug load capacity is smaller than the influence of multilayers on vessels.

The results obtained for all parts of the solution lead to optimization of the parameters and the design of a new generation of IHPJ. These joints are of better strength properties (static and dynamic) than existing ones thanks to the newly designed and optimized technology.

1

M. Ruzicka, J. Sun, O. Uher, "Development and application of computer program for design of filament wound composite beams with circular and noncircular cross-section", Proceedings of the First Asian-Pacific Congress on Computational Mechanics, Sydney, 1761-1766, 2001.

2

T. Mares, "Laminate tube stiffness maximization by winding angle control", Bulletin of Applied Mechanics, 1, 29-54, 2005.

3

J. Sun, M.Ruzicka, "A Computational Method of Filament Wound Composite Cylindrical Beam Under General Load", In: World Congress of Computational Mechanic (WCCM VI) . Sept. 5-10, 2004, Beijing, China, Tsinghua University Press & Springer-Verlag 2004, CD ROM, ISBN 7-89494-512-9, pp. 1-10.

4

K. Blahous, J. Chromy, R. Poul, O. Uher, M. Ruzicka, "The strength tests of pin joints of composite cylinders (in Czech)", In.: Reinforced Plastic, May 24.-26, 2005, Karlovy Vary, Czech Republic, 25-29, 2005.

5

M.Sirovy, "Experimental and computational analysis of composite poin joints", Thesis CTU Prague, Fac. of Mech. Eng., 2006.

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