Mode - I low cycle fatigue delamination of woven glass fibre reinforced polymer matrix composite

• Main Author: Mohd Aidy Faizal Johari
• Format: Thesis
• Language: English
• Published: 2008
• Subjects: TA Engineering (General). Civil engineering (General)
• Online Access: https://eprints.ums.edu.my/id/eprint/10158/1/mt0000000517.pdf

Most parts of the failures in structural elements in use were consequences of mechanical fatigue. Therefore, fatigue had been a critical factor in designing durable mechanical elements. In laminated woven GFRP composite material, the fatigue process involves different damage mechanism that results in the degradation of the materials. One of the most important damage mechanisms was the delamination between plies of the laminates. Outstanding performance woven E-glass/Polyester composites, which were increasingly used for various applications were susceptible to delamination. In response to this problem, the mode-I interlaminar fracture and fatigue delamination toughness of woven E-glass/ Polyester laminates had been studied under tensile loading by using a double cantilever beam (DCB) specimen. Results were presented from an experimental study to determine the mode-I quasi-static and fatigue delamination toughness of a reinforced laminated composite. Mode-I double cantilever beam (DCB) tests had been performed on woven GFRP unsaturated polyester composite, E-Glass EWR 600 NISER, specimens. Static delamination had been first obtained. The specimen design and test procedure were performed with reference to the BS ISO 15024 and ASTM D5528. Specimens were then cycled at low cycle fatigue with 2Hz, 5Hz and 9Hz frequencies at constant amplitude of 1.5mm. These data used to determine the fatigue delamination growth onset characteristic. The results from this investigation were used to generate a surface plot relating fracture toughness to mode-land the number of cycles achieved before the onset of fracture. This plot characterizes the behaviour of the material under all static and fatigue conditions, thus providing a valuable tool for the design of composite structures in those applications where delamination growth had been of concern. Fatigue delamination growth onset test was carried out according to the ASTM D6115. The experimental results of mode-I fracture toughness, as a function of crack length had been obtained. Experimental data obtained were analyzed using the modified beam theory, MBT method. The delamination-resistance curve or the R-curve effect had been found as the general characteristics of the laminate system. Constant amplitude cyclic opening displacement fatigue test was also conducted to establish the delamination growth rate (da/dN) as a function of maximum cyclic energy release rate (G1max). The test then continues to identify the fatigue life characteristic. Fracture mechanic based total life model for delaminated woven GFRP composite was then established. The model includes the delamination growth predominant in the linear domain. Fibre bridging phenomenon with slow and stable crack propagation and extensive half-arm fiber bridged were also observed and identified from the fractographic analysis, with lower curing pressure was found to produce higher GIC and GImax propagation toughness values.