Quasi-Static Flexural Properties of a Pultruded Glass Fiber/Unsaturated Polyester Square Pipe

Abstract

This paper explores quasi-static flexural properties and fracture behavior of a pultruded glass fiber/unsaturated polyester square pipe for automotive structural applications. Three-point flexural testing is performed in an Instron Universal Testing Machine with steel jigs supporting the top and bottom surfaces of the pipe. Acoustic emission (AE) measurements are recorded during flexural testing to evaluate initial fracture in the pipe structure. After final fracture, five cross-sections of the pipe are cut at 50-mm intervals along the longitudinal axis, with the first cut located at the mid-span of the pipe. Cross-sections of a pipe from an interrupted test where initial fracture is detected from the AE method are also prepared. Damage locations and behavior on each cross-section are observed. The flexural testing results show that the cumulative AE counts increase rapidly from 2.5 kN, that final failure occurs at a maximum load of approximately 13 kN, and that corresponding initial and final failure occurs in the two corner regions on the compressive side of flexural loading. Failure initiates by stress concentrations due to the upper jig on the top surface during bending. The cross-sectional observations also reveal clear deformation behavior of the pipe where failure is present, marked by inward bending of the top surface and upper corners located on the compressive side, near the jig. The locations of maximum stresses and deformations obtained from finite element analysis of this pipe structure are in very good agreement with the experimental observations.

Relationship between the Initial Fracture Stress and Fatigue Limit—Simple Prediction Method of Tensile Fatigue Limit of Composite

“…They reported the relationship between AE measurements and bending test. AE measurements were able to find out the initial fracture stress [15].…”

Mechanical failure analysis of pultrusion glass fiber pipe based on acoustic emission technology

“…Jing Rong studied the change law of parameters related to resin flow during the pultrusion process of glass fiber/polypropylene composite yarn. [ 23 ] They found that parameters such as pre tension and forming temperature have a significant impact on the performance of pultrusion tubes. Hui alleviates the defect of wrinkle and fracture of pipe fittings by reducing the axial compressive stress at the upper end and the tensile stress at the lower end during the forming process of thin‐walled pipes.…”