Pressure tests of composite braided tube specimens
Wojciech Błażejewski, Andrzej Czulak, Paweł Gąsior, Tomasz Pawlak, Werner Hufenbach
Quarterly No. 3, 2009 pages 291-296
DOI:
keywords: braided composites, braided methods, optical fiber sensors, FBG, NDT, mechanical properties, pressure tests, GFRC (Glass Fiber Reinforced Composite), tube specimen
abstract In the present paper tests of composite tube specimens made from glass-epoxy composite by braiding method are presented. That technique is an alternative one to the classical winding method and allows realization of reinforcement layer at an any angle in a range from 5° to 86°. However, because there are not precise strength analysis of finished structures, that new method is not a widespread. A main target of presented research was to carry out an experiment and prepare FEM analysis to compare obtained results. Three different tube types were tested: 30, 45 and 60°. They were differ from each other only by an angle of reinforcement. As a working medium a heap of rubber disks inside a specimen was applied. Application of rubber disks allowed to short an experiment duration. During the test a compressive force (pressure), displacement of pistons as well as deformation (strain) in circumferential direction were measured. Because of large deformation on the outer surface of specimens (even few percents) Fiber Bragg Gratings for strain measurements were used. It let to perform strain measurement very precisely in a range which was not possible to obtain by classical method (electric resistance wire strain gauge). Obtained test results will be very useful to realize FEM analysis in a nearest future. Fiber optic sensor technology offers the possibility of implementing ”nervous systems” for infrastructure elements that allow health and damage assessment. Fiber Bragg Gratings used in measurements give information on local strain values of the composite specimens caused by internal pressure. It also makes possible to detect and monitor damages in a composite structure. The sensor system should ensure the assessment of the safety condition of the monitored object during production, long-term operation and periodic checks. Optical fiber sensor systems with Bragg gratings belong to the class of sensors where the measurement of the physical pheno-menon causes the modulation of the light wavelength. The advantages of those solutions arise from properties of the optical fiber. The Bragg gratings sensors systems are easy to integrate with the composite material structures, and because of their spark-safety and first of all high sensitivity in wide measurement range as well as insensitiveness on the external electromagnetic field are particularly suitable for different types of applications, also in so called ”smart materials”. The basic principles of FBG sensors applications is a linear relation between wavelength B on external variables like temperature and strain. The key question in the case of using FBG for monitoring the level of strain of composite layers is such an arrangement of sensors that it would be possible to monitor deformation of the object under examination in critical points of the structure. In the present paper sensors were installed on the outer surface of the composite tube specimens to measure its local deformations.