Monitoring of mechanical properties of prestressed glass fiber epoxy composites over 12 months after fabrication

Abstract

Fiber prestressing during matrix curing can significantly improve the mechanical properties of fiber-reinforced polymer composites. One primary reason behind this improvement is the generated compressive residual stress within the cured matrix, which impedes cracks initiation and propagation. However, the prestressing force might diminish progressively with time due to the creep of the compressed matrix and the relaxation of the tensioned fiber. As a result, the initial compressive residual stress and the acquired improvement in mechanical properties are prone to decline over time. Therefore, it is necessary to evaluate the mechanical properties of the prestressed composites as time proceeds. This study monitors the change in the tensile and flexural properties of unidirectional prestressed glass fiber reinforced epoxy composites over a period of 12 months after manufacturing. The composites were prepared using three different fiber volume fractions 25%, 30%, and 40%. The results of mechanical testing showed that the prestressed composites acquired an initial increase up to 29% in the tensile properties and up to 32% in the flexural properties compared to the non-prestressed counterparts. Throughout the 12 months of study, the initial increase in both tensile and flexural strength showed a progressive reduction. The loss ratio of the initial increase was observed to be inversely proportional to the fiber volume fraction. For the prestressed composites fabricated with 25%, 30%, and 40% fiber volume fraction, the initial increase in tensile and flexural strength dropped by 29%, 25%, and 17%, respectively and by 34%, 26%, and 21%, respectively at the end of the study. Approximately 50% of the total loss took place over the first month after the manufacture, while after the sixth month, the reduction in mechanical properties became insignificant. Tensile modulus started to show a very slight reduction after the fourth/sixth month, while the flexural modulus reduction was observed from the beginning. Although the prestressed composites displayed time-dependent losses, their long-term mechanical properties still outperformed the non-prestressed counterparts.

Manufacturing of prestressed glass fiber reinforced polymer rebars and effect of fiber pretension on durability of rebars after conditioning in alkaline solution

“…Fancey 18 pointed that exposing elastically prestressed FRP composites to elevated temperatures may exacerbate matrix creep, thereby reducing the residual tensile force within the fiber and hence decreases the compressive residual stress and its beneficial effect. Mohamed et al 39 showed that when prestressed FRP composites stored in room temperature for 60 days after manufacturing, the tensile strength lost about 3% of its initial strength. However, the absolute guaranteed tensile strength of the prestressed rebars after conditioning (923 MPa) is higher than that of the unprestressed rebars (873 MPa).…”

Durability of Viscoelastic Fibre Prestressing in a Polymeric Composite

“…Although the fibre prestressing technique is promising, its applications depend on the mechanical properties of the prestressed fibres [ 12 , 13 ]. Commonly, EFP is applicable to brittle (elastic) fibres such as carbon fibres and glass fibres [ 14 , 15 , 16 , 17 ], whilst VFP is more suitable for tough fibres such as semi-crystalline thermoplastic fibres [ 18 ]. As for structural applications, it is demonstrated that VPPMCs are superior to EPPMCs in terms of product geometry and longevity [ 19 , 20 ].…”