DIC-based evaluation of the hydrochloric acid ageing effects on the flexural mechanical behavior of GFRP composite tubes

Glass/vinylester composite tubes are widely used in chemical processing pipelines due to their excellent corrosion resistance and mechanical performance. However, their behavior under long-term exposure to strong acids remains insufficiently characterized. This study investigates the hygrothermal ageing effects of 10% HCl at 25°C, 50°C, and 85°C on the flexural mechanical response of filament wound glass/vinylester composite tubes. Specimens, with and without protective coating, were immersed for 6 months and then tested under four-point bending. Full-field strain analysis was performed using 2D Digital Image Correlation (DIC) complemented by X-ray microtomography for internal damage assessment. Results show that ageing significantly reduces mechanical properties, particularly at higher temperatures. Uncoated specimens are the most affected, highlighting the coating’s role in limiting acid penetration. DIC analysis reveals that ageing alters the damage scenario, shifting from a localized fracture to multiple strain concentration zones. While unaged and 25°C aged specimens fail via a single dominant crack, higher temperatures induce earlier crack initiation and multiple localization zones, indicating increased embrittlement. Tomographic observations confirm a consistent failure mode: tensile rupture of the anticorrosion layer followed by delamination. However, this damage becomes more severe with ageing due to matrix cracking, interfacial debonding, and fiber bending.