Gergely Czél

A Study of Water Absorption and Mechanical Properties of Glass Fiber/Polyester Composite Pipes – Effects of Specimen Geometry and Preparation

Ring-shaped glass fiber/polyester composite specimens cut from composite pipes with various lengths and cut edge quality were immersed into deionized water, and their water absorption was noted regularly by registering their mass gain. Monotonic ring compression tests were performed to monitor the stiffness properties during the water absorption process. Effect of specimen length and cut edge sealing with the matrix material of the pipe on the water absorption process was analyzed. Water absorption curves were fitted to the experimental data with very high correlation coefficients. Specimen types with cut edge sealing were found to absorb significantly less water than the other types, and the absorbed water showed a nonlinear monotonic decreasing tendency with specimen length. Mechanical properties were found to be only slightly affected by moisture probably because of the small amount of absorbed water.

Image processing assisted stress estimation method for ring compression tests of polymer composite pipes at large displacements

A novel method for estimating the fracture stress of ring specimens cut from polymer composite pipes is presented. The method applies image processing for determining the large displacements of the specimen. For image processing, photographs of the deformed specimen were taken before fracture, and a Fourier polynomial was fitted to the points of the digitalized cross section of the ring specimen. The presented mechanical model is based on the captured deformed shape, and it considers the geometrical nonlinearities of the problem. For stress calculation from bending moments, the Navier formula was selected. It was found that the developed method is capable of estimating the stress at break of polymer composite specimens under ring compression.

Analysing fluctuation of material properties of non-circular profile filament wound composite pipes along perimeter of cross-section

Abstract Periodic changes in the material properties of egg shaped profile filament wound fibreglass reinforced unsaturated polyester composite sewer liner pipes were investigated around the perimeter of the cross-section that has constant radii of curvatures in certain sections. On the basis of numerous test results and geometrical and mechanical models of the problem, linear relationships were set up between the origin of the specimens around the section and the density or fibre volume fraction of the material. The inverse proportion between the packing forces (perpendicular to the pipe wall) and the local radii of curvatures means that besides constant fibre tension, higher packing forces appear at the lower radii areas of the section, more matrix material is compressed out of the fibre bundles and the density or the fibre volume fraction becomes higher than in the higher radius areas.

New method for determining the bending modulus of solid and hollow fibers from deflection tests

The bending moduli of solid and hollow glass fibers were determined by means of fiber deflection tests. The test method was modified by measuring both the vertical and horizontal displacements of the end of the deflected fiber, without increasing the number of tested fibers, in order to reduce the high scatter of conventional test results obtained by measuring only the vertical displacement. Upper and lower boundary curves of the fiber end displacements were determined to filter out inaccurate measurements, for example, when the neutral line of the fiber is not a plane but a spatial curve. The mean and coefficient of variation of the fiber bending modulus were estimated from the recorded coordinates of the fiber ends, applying two newly-developed statistical evaluation methods based on the individual coordinates or on their average. After comparing several evaluation methods, it was demonstrated that the individual coordinate-based method provided the least relative error of the average.