EXPERIMENTAL METHOD TO INCREASE THE LOADING CAPABILITY OF GLASS-FIBRE REINFORCED COMPOSITE TUBES H. Teodorescu-Draghicescu1, I. Goia2, D. Rosu3, C. Birtu4, F. Teodorescu-Draghicescu5 1 Research Institute for Production Systems SN ROMARM SA–ICPSP Bucharest, 107-111 Sos. Oltenitei, sector 4, 75651 Bucharest, ROMANIA 2 “Transilvania” University of Brasov, 1 Colinei street, 2200 Brasov, ROMANIA 3 SC COMPOZITE SRL Brasov, 14A Plevnei street, 2200 Brasov, ROMANIA 4, 5 Mechanical Engineering and Research Institute SC ICTCM SA Bucharest, 103 Sos. Oltenitei, sector 4, 75651 Bucharest, ROMANIA ABSTRACT The paper presents an original method to increase the loading capability of glass-fibre/polyester composite tubes by applying internal stresses in thin-walled cylinders with only a few wound layers. A very simple device has been developed to attain this end. Various tube specimens with following features were carried out at SC COMPOZITE SRL Brasov: - inner diameter: 80 mm; - fibre content: 15% and 35%; - total wall thickness: 2…5 mm; - number of layers: 8; - length: 100 mm and different fabric disposal of reinforced material. The method consists in the accomplishment of following steps: Stage one. A tube specimen is manufactured in the fabric winding process. Stage two. The device is positioned and fixed vertically. Stage three. The specimen is heated above the glass transition temperature. Stage four. While keeping the temperature, a silicone rubber is pressed at the inner of the tube specimen. Stage five. While keeping the inner pressure, the tube specimen is cooled at environmental temperature. Stage six. After cooling, the tube is discharged from the inner pre-tension pressure and in wall structure will remain internal stresses. In the High Pressure Laboratory of Mechanical Engineering and Research Institute SC ICTCM SA Bucharest, the pre-tensioned tube specimens were subjected to internal hydraulic pressure until weeping occur. Micro cracking and delamination were the most observed damage mechanisms and combination of the two constituted most failures. Using this original method of pre-tension, the loading capability of glassfibre/polyester composite tubes is increased up to 43%. INTRODUCTION Purpose of pre-tensioning glass-fibre reinforced composite tubes is to introduce internal stresses in tube wall structure, that can work against the operational stresses. These internal stresses increase the tube loading capability and its cracking limits. To attain this aim, a very simple device has been designed and developed. A silicone rubber that can be pressed at the inner of the composite tube represents the central part of the device. This rubber has the property to transmit the pressure in any direction.
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