Issue 74

V. J. Kalyani et alii, Frattura ed Integrità Strutturale, 74 (2025) 89-114; DOI: 10.3221/IGF-ESIS.74.07

Ultimate Tensile Strength

Modulus of Elasticity

Ultimate Load SD CoV (%)

Stiffness

Rupture Strain

Specimen Configuration

Epoxy

SD CoV (%) SD CoV (%)

SD

CoV (%)

SD

CoV (%)

GG GS

1.44 0.54 0.05 1.05 0.75 0.26 0.06 1.02 0.29 0.26 1.50 1.35 0.86 0.82

2.86 1.71 0.47 1.69 1.35 0.73 0.35 2.27 0.98 2.67 2.45 2.81 2.52 5.95

6.01 2.45 0.25 3.60 2.68 1.09 0.20 4.81 2.28 1.36 5.45 5.25 3.71 3.27

2.85 1.70 0.47 1.67 1.33 0.73 0.36 2.27 1.62 2.59 2.45 2.73 2.54 5.87

0.33 0.11 0.01 0.57 0.31 0.12 0.01 0.38 0.19 0.02 1.34 0.51 0.12 0.06

2.60 1.93 0.25 3.19 2.65 1.84 0.53 3.45 3.32 1.42 8.14 4.71 1.77 4.65

0.0005 0.0003 0.0001 0.0004 0.0004 0.0004 0.0002 0.0006 0.0006 0.0005 0.0009 0.0007 0.0003 0.0017

2.62 1.11 0.25 3.22 2.66 1.83 0.52 3.46 3.32 1.41 8.15 4.73 1.79 4.65

173.26 43.48 70.07 478.66 159.24 99.40 60.62 242.75 153.76 53.56 106.14 169.01 123.19 173.58

1.10 0.50 4.02 2.60 1.28 1.23 2.69 1.49 1.88 2.58 0.69 1.26 1.46 7.72

SS

Sikadur 30LP

GGG GSG SGS

SSS GG GS

SS

Sikadur 330

GGG GSG SGS

SSS

SD = Standard Deviation, CoV = Coefficient of Variance

Table 5: Statistical indicators for mechanical parameters evaluated during tensile test. The average ultimate load results for all configurations indicates that the number and type of reinforcing layers significantly influence the tensile performance of the coupon specimens. For specimens bonded with Sikadur 30 LP, the highest ultimate load of 62.23 kN is observed for the GGG configuration, followed closely by 55.67 kN for GSG and 50.25 kN for GG specimen. These results suggest that multiple layers of GFRP, substantially enhance load carrying capacity of coupon specimens. Among all, SS and SSS configurations, consisting entirely of SSWM, show the lowest load carrying capacity with 10.45 kN and 15.56 kN, respectively, reflecting the relatively lower tensile strength contribution of SSWM compared to GFRP. However, hybrid configurations such as GS, SGS, and GSG exhibit a balanced performance, bridging the gap between the high strength of GFRP and the ductility of SSWM. For instance, the GSG configuration bonded with Sikadur 30 LP achieves an average ultimate load of 55.67 kN, which is approximately 89.46% of the GGG configuration, while incorporating only two GFRP layers and one SSWM layer instead of three GFRP layers. Similarly, the GS configuration records an average load of 31.74 kN, which is 63.16% of GG, despite replacing one GFRP layer with a single SSWM layer. This highlights the efficiency of the hybrid layup in achieving high tensile strength with reduced GFRP usage. A similar trend is observed for specimens bonded using Sikadur 330, where the GGG configuration again exhibits the highest average ultimate load of 61.43 kN, followed by 48.28 kN for GSG and 44.29 kN for GG specimen. The hybrid GS configuration registers an ultimate load of 29.20 kN, which is approximately 64.10% of the GG specimen. However, when compared to the SS specimen (9.90 kN), the GS hybrid achieves nearly three times the load capacity, indicating the significant enhancement that a single layer of GFRP provides even in a hybrid assembly. Similarly, the SGS configuration reaches 34.27 kN, which is 149.24% higher as compared to SSS, and closely approaching GG at 76.17% of its strength despite using only one GFRP layer. A comparison of ultimate load capacity observed for different specimen configuration when prepared using Sikadur 30 LP and Sikadur 330, is also presented in Fig. 8(a). Fig. 8(b) presents the comparison of ultimate tensile strength for coupon specimens of different configurations. Tensile strength is measured as the ratio of ultimate tensile load to the cross-sectional area of the respective wrap configuration. Among all the specimens, the highest tensile strength is observed for GGG specimens for both the epoxy adhesives, followed by specimen GG. For instance, the GGG configuration shows the highest tensile strength of 213.12 MPa for Sikadur 30 LP and 222.57 MPa for Sikadur 330, indicating excellent load-carrying capacity of the GFRP under uniaxial tension. The GG specimens also show comparably high tensile strength for both adhesives, with 210.25 MPa for Sikadur 30 LP and 212.22 MPa for Sikadur 330, further confirming the superior strength contribution of GFRP. In contrast, specimens strengthened only with SSWM layers i.e. SS and SSS, display the lowest tensile strengths. The tensile strength of SS specimen is observed as 52.51 MPa and 51.03 MPa, respectively, when prepared with Sikadur 30 LP and Sikadur 330. This trend remains similar for the three-layer SSS specimens, showing tensile strength of 57.42 MPa and 55.00 MPa respectively, for Sikadur 30 LP and Sikadur 330, reflecting the lower tensile strength of SSWM compared to GFRP. The relatively lower tensile strengths across all coupon specimens, compared to individual material capacities, are influenced by the presence of multiple (3-4) thin layers of epoxy adhesive. The low tensile strength of the adhesive layer, combined with parameters such as specimen dimensions, loading rate, and number of wrap layers etc., contributes to this reduction.

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