Abstract
Composite materials usage in several industrial fields is now widespread, and this leads to the necessity of overcoming issues that are still currently open. In the aeronautic industry, this is especially true for Barely Visible Impact Damage (BVID) and humidity uptake issues. BVID is the most insidious kind of impact damage, being rather common and not easily detectable. These, along with the ageing that a composite structure could face during its operative life, could be a cause of fatal failures. In this paper, the influence of water absorption on impacted specimens compressive residual strength was studied. Specimens were impacted using a modified Charpy pendulum. Two different locations were chosen for comparison: Near-Edge (NE) and Central (CI). Accelerated hygrothermal ageing was conducted on impacted and reference nonimpacted coupons, placing them in a water-filled jar at 70 °C. Compressive tests were performed in accordance with the Combined Loading Compression (CLC) test method. A Dynamic Mechanical Analysis (DMA) was performed as well. The results showed the influence of hygrothermal ageing, as expected. Nevertheless, the influence of impact location on compressive residual strength is not clearly noticeable in aged specimens, leading to the conclusion that hygrothermal ageing may have a greater effect on composite compressive strength than the analysed BVI damage.
Highlights
Water absorption is a significant issue for advanced composite materials due to its significant effect on physical, mechanical, and chemical properties
This is especially true for Barely Visible Impact Damage (BVID) and humidity uptake issues
The results showed the influence of hygrothermal ageing, as expected
Summary
Water absorption is a significant issue for advanced composite materials due to its significant effect on physical, mechanical, and chemical properties. Matrix-conditioned properties, such as compressive and interlaminar shear strength, are affected by hygrothermal ageing [1]. This is due to the plasticisation of the polymer chains [2,3,4,5,6,7], detected by measuring the material glass transition temperature (Tg) by means, for example, of the Dynamic Mechanical Analysis (DMA). Many parameters affect water uptake: the environmental temperature and percentage of humidity, matrix system, matrix/fibre interface, fibre material, fibre surface roughness, defects, etc. Water absorption could be caused by means of diffusion and capillary flow mechanisms [11,12,13]. Epoxy resins, which have a high concentration of hydrogen bonds, are subjected to a higher moisture uptake compared to other thermoset resins, like vinyl ester and urethane acrylate [14]
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