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

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Regarding constant temperature exposure, both types of matrices exhibited similar trends, i.e., non-negligible transverse tensile strength reductions for both extreme temperatures (-15 °C and 60 °C), with the retention values for the lowest temperature being equal to 83% and 74%, respectively, for GFRP_UP and GFRP_VE; however, for these series (T-15 and T60), high data scatter can be observed, particularly in the case of the GFRP_VE_T60 series, with a maximum CoV of 22.3%. Regarding series T20 and T40, negligible or minor improvements were observed, with a maximum transverse tensile strength retention of 105% for series GFRP_UP_T20. Regarding the thermal cycles, marginal increased retention of transverse tensile strength was observed in the GFRP_UP series, whereas a minor transverse tensile strength reduction was observed in the GFRP_VE series. Variations in CTE among composite constituents may contribute to interface degradation between the matrix and fibres, driven by differential expansion and contraction rates. Reductions of the tensile strength retention under thermal cycles have also been reported in previous studies, e.g. ( Sousa et al . 2014).

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120%

120%

(b)

GFRP_VE

(a)

GFRP_UP

110%

110%

105.42% (5.73%)

103.81% (7.13%)

102.85% (2.58%)

100.88% (6.19%)

100.84% (5.44%)

99.47% (5.29%)

100%

100%

94.63% (6.92%)

92.99% (2.95%)

90%

90%

88.56% (13.18%)

83.27% (16.09%)

79.81% (22.26%)

80%

80%

74.11% (19.84%)

70%

70%

60%

60%

50% Tensile strength rentention

50% Tensile strength rentention

40%

40%

T20

T60

T-15

T40

T20

T60

TC100 TC200

T-15

T40

TC100 TC200

Ageing Environment

Ageing Environment

Fig. 3. Tensile strength retention for transverse direction (90°): (a) GFRP_UP; (b) GFRP_VE.

3.2. Effects on compressive strength The results of the compressive strength retention of the GFRP composites are shown in Fig. 4. Apart from the GFRP_UP_TC200 series, both types of GFRP composites (UP and VE) exhibited enhancements in compressive strength. For the GFRP composites studied, the compressive strength is expected to be dominated by the matrix characteristics, although the fibres also make an important contribution to the overall performance.

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100% 110% 120% 130% 140% 150% 160% 170%

100% 110% 120% 130% 140% 150% 160% 170%

(a)

GFRP_UP

(b)

GFRP_VE

130.84% (15.1%)

125.45% (25.3%)

124.94% (10.5%)

122.27% (6.6%)

117.07% (4.1%)

112.01% (17.2%)

105.43% (14%)

105.62% (13.8%)

102.15% (16.2%)

100.00% (12.8%)

100.00% (15.5%)

89.77% (7.6%)

80% 90%

80% 90%

Compressive strength retention

Compressive strength retention

T20

T60

T-15

T40

TC100 TC200

T20

T60

T-15

T40

TC100 TC200

Ageing Environment

Ageing Environment

Fig. 4. Compressive strength retention: (a) GFRP_UP; (b) GFRP_VE.

In general, all constant temperatures used as ageing environment had a positive effect on the compressive strength retention for both UP and VE matrices, probably due to matrix post-curing. Furthermore, the temperature of 40 °C was the one that provided the maximum increase in compressive strength, namely an increase of 22% and 31% for the case of UP and VE, respectively. Despite that, significant results dispersion was observed, with CoV in general higher than 10% and up to 17.2%. Sun et al . (2015) reported significantly higher scatter in their compressive strength