PSI - Issue 64

Omid Hassanshahi et al. / Procedia Structural Integrity 64 (2024) 81–88 Hassanshahi et al. / Durability of GFRP Composites Produced by Pultrusion under Thermal Environments

87

7

Despite minor differences between the two composite materials, they responded similarly to constant temperatures. While in the UP series, a temperature of 40 °C yielded the highest property increase (of ~17%), in the case of the VE series, similar improvements were observed for the T-15, T40, and T60 series. Concerning thermal cycling, as observed in compressive and flexural strengths, for the UP series, IP shear strength retention was reduced from 100 to 200 cycles. For the VE series, this trend was not observed for 100 and 200 cycles, where almost similar IP shear strength retention was observed, with 7-9% of strength increase. For both series, reduction in IP shear strength was never observed. In the previous study by Grammatikos et al . (2016) negligible reductions in IP shear strength after 300 thermal cycles were reported. 3.5. Effects on interlaminar shear strength The interlaminar shear strength (ILSS) retentions of GFRP_UP and GFRP_VE are illustrated in Fig. 7a and Fig. 7b, respectively. Overall, both GFRP_UP and GFRP_VE composites exhibited a variation trend of ILSS similar to that of flexural strength, with relatively minor retention variations. Typically, ILSS is notably reliant on the adhesion at laminae interfaces and is influenced by fibre bridging mechanisms. Fibre-matrix adhesion, interfacial adhesion and fibre bridging underscore the dominant role of the fibre-matrix interface in controlling ILSS retention. Regarding the constant temperatures ageing environments, for both types of matrices, an almost linear reduction of ILSS retention with the temperature increase from -15 °C to 40 °C occurred. This reduction trend does not include the highest temperature of 60 °C. For GFRP_UP, exposure to the extreme temperatures of -15 °C and 60 °C led to ILSS retentions slightly higher than 100%. For the remaining series of GFRP_UP and for all series of GFRP_VE, ILSS retentions were lower than 100%, but in general above 90%. With respect to the thermal cycles, a ~10% reduction in ILSS retention was observed for both matrices after 200 cycles. Despite relatively low variations, this decrease was more pronounced in the case of the VE matrix.

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

120%

120%

(b)

GFRP_VE

(a)

GFRP_UP

110%

110%

103.56% (8.6%)

101.92% (5.2%)

101.74% (5.5%)

99.95% (1.7%)

99.9% (5.8%)

100%

100%

94.77% (5%)

92.19% (2.9%)

91.64% (4.4%)

91.87% (5.8%)

90.35% (2.9%)

88.81% (9.6%)

88.71% (1.6%)

90%

90%

80%

80%

T20

T60

T-15

T40

TC100 TC200

T20

T60

T-15

T40

TC100 TC200

Interlaminar shear strength (ILSS) retention

Interlaminar shear strength (ILSS) retention

Ageing Environment

Ageing Environment

Fig. 7. Interlaminar shear strength (ILSS) retention: (a) GFRP_UP; (b) GFRP_VE.

4. Conclusion This study provides results about the durability of glass fibre-reinforced polymer (GFRP) composites produced by pultrusion under thermal ageing environments. Through an experimental program involving accelerated laboratory ageing tests, the changes in the mechanical properties of thick GFRP laminates using unsaturated polyester (UP) and vinyl ester (VE) matrices were assessed. The findings reveal reductions in transverse tensile strength, particularly after exposure to extreme temperatures: minimum property retentions of 74.1% (GFRP_VE) and 83.3% (GFRP_UP) at -15 °C and 79.8% (GFRP_VE) and 88.6% (GFRP_UP) at 60 °C were obtained, highlighting possible vulnerability of these composites to sub-zero and elevated temperatures, namely for such matrix-dominated property. However, other properties showed minimal reductions or even increases. Notably, the compressive strength of GFRP_VE exhibited significant increases under certain conditions (for instance, a 41% increase after exposure to