Accessing the Residual Strain Development in Thick FRP Composite Laminates Using Embedded Temperature and FBG Strain Sensors

Abstract:

This work investigates the development of residual stress in thick laminates based on measured internal strain and temperature information. Here, FBG and conventional strain gauges are used to investigate the effect of curing on residual stresses in a thick Epoxy-glass composite laminate incorporated. A 14 mm thick EP-FRP laminate is manufactured by embedding strain and temperature sensors to acquire the signals during curing. Later, the EP-FRP composite is cured and the temperature and strain variation at different layers are monitored using embedded strain and temperature sensors. The experimental temperature development is used to predict the degree of cure at different layers. The knowledge of degree of cure in turn helps to estimate the resin shrinkage percentage at different layers. Strain is mainly developed due to the chemical shrinkage of resin during curing and due to the mismatch in CTE of resin and reinforcement material. Both the components of strain are measured by using the embedded strain sensors. It is observed that the middle layers gelled first (Layer 6 and 13), followed by bottom layer (Layer 1), and top layers gelled last (Layer 16,18): the gel times were 28-30 min for middle plies, 34 min for lower plies and 36 min for top layers. The temperature gradient along the thickness is resulted from the heat evolved during exothermic curing reaction. Maximum temperature peak of 99 °C is observed in the middle layer of the laminate. The measured temperature variation can be further related to the variation in cure shrinkage strain and thermal residual strain levels. This work shows embedded strain and temperature sensors are useful to monitor the cure progression as well as residual strain development in a thick composite laminate

• Periodical: Key Engineering Materials (Volume 1058)
• Pages: 55-60
• DOI: https://doi.org/10.4028/p-aUlW7F
• Online since: June 2026
• Authors: Santoshi Mohanta*, Swati Neogi
• Keywords: Cure Shrinkage, FBG Sensor, Residual Stress, Thick FRP Composite

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