THE EFFECT OF HOOP WINDING ON MECHANICAL PROPERTIES OF GFRP-FW PIPES

Abstract

The effect of hoop winding on tensile and compressive properties of glass fiber reinforced plastic (GFRP)-filament winding (FW) pipes has been investigated experimentally. Winding angles of the helical filaments in FW pipes were ±20°, ±30°, ±45°, and ±60°.
Both in tensile and compressive tests, specimens with the same shape and size were used. As for the specimen with hoop winding, Young's moduli on tension and compression are nearly equal. But the breaking strengths of the specimens with winding angle of ±20° and ±30° are considerably larger on tension than on compression, because of the difference of the failure modes: On tension, tensile breakage of fibers (+θ) and shear slippage between fibers (-θ) are observed simultaneously. While on compression, the fibers (±θ) are buckled and broken by bending.
The effects of adding the hoop winding (winding angle_??_90°) to the GFRP-FW pipe are as follows: (1) On tension, Young's modulus and Poisson's ratio decrease and breaking strength increases. (2) On compression, Young's modulus and breaking strength increase remarkably. (3) The pantographic deformation observed on tensile test of the ±45° specimen without hoop winding is restricted. (4) The helical propagation of cracks observed on compression of the specimen without hoop winding is arrested by adding the hoop winding.