Cure and strain monitoring of novel unsaturated polyester/phenolic resin blends in the vacuum infusion process using fibre Bragg gratings

Abstract

In recent years, a few research studies have been published on the blending of unsaturated polyester and phenolic resins for the purpose of improving the fire properties of unsaturated polyester resins. However, there has been no published study on the cure and strain monitoring of unsaturated polyester/phenolic blends during composite manufacturing. In this study, non-crimp triaxial glass fabric preforms were infused with the unsaturated polyester/phenolic blends, and the strain developments inside the composites were monitored using fibre Bragg grating sensors, as the long and complex curing stages were progressing at different temperatures. Strain-free fibre Bragg grating sensors and also thermocouples were utilised for temperature monitoring and compensation in order to obtain true strain developments and residual strains. The results were associated with a study presenting the cure analyses of unsaturated polyester/phenolic blends. The unsaturated polyester and the phenolics were found to be incompatible and exhibited different curing mechanisms in the blends, which were also observable in the strain development results. This paper has been the first attempt to (i) process these novel resin systems in the vacuum infusion process and (ii) monitor the long, complex and high-temperature cure cycles and the strain developments in the vacuum infusion process using fibre Bragg gratings.

Structural Health Monitoring by Using Fiber Optic Sensors in Composite Materials

“…Due to its small size, it can be embedded in structures and the behavior of the structure can be monitored [5]. Previous studies have shown that the effect of temperature [6], curing process [7,8], impact [9], stress/strain [10] moisture, delamination and cracking [11,12] can be monitored with fiber optic sensors. According to Yilmaz et al [13] reported using FOS that transverse cracking affects the Poisson ratio.…”

An experimental method for characterizing unsaturated 1D flow in tubular braided preforms during bladder‐assisted resin transfer molding

“…Thus, the compliance of the braided preform has to be taken into account, which leads to locally varying porosity and thus, permeability values along the flow length. As a consequence, process predictions with conventionally determined permeability values is a mathematically complex task, which requires extensive measurement data (permeability and compaction curves) and corresponding material models that often exhibit notable simplifications . A possible influence of fabric curvature on permeability, in particular for tubular preforms with low diameter‐to‐thickness ratio that cannot sufficiently be described through planar measurements, is not considered . Pressure‐induced interaction between the textile preform and the flexible bladder surface and its effect on permeability is not considered. For example, the flexible bladder can conform to the undulating fabric surface, decreasing a significant portion of its porosity. Conventional unidirectional permeability measurements on flat braid‐based specimens (accomplished by either cutting or collapsing the tubular braided material) can be influenced by race tracking effects and distorted fabric edges due to preform preparation. Tubular braidings with rather small diameters cannot meet requirements on a specific test specimen width to enable reasonable permeability characterization.…”