Static strength prediction of curved composite joints under internal pressure

Figures & data

Table 1. Mechanical and fracture properties of the adhesives Araldite® AV138,^[32] Araldite® 2015,^[21] and Sikaforce® 7752.^[22].

Property	AV138	2015	7752
Young’s modulus, E (GPa)	4.89 ± 0.81	1.85 ± 0.21	0.493 ± 0.089
Poisson’s ratio, ν	0.35 ^a	0.33 ^a	0.33 ^a
Tensile yield strength, σe (MPa)	36.49 ± 2.47	12.63 ± 0.61	3.24 ± 0.5
Tensile failure strength, σf (MPa)	39.45 ± 3.18	21.63 ± 1.61	11.49 ± 0.3
Tensile failure strain, εf (%)	1.21 ± 0.10	4.77 ± 0.15	19.18 ± 1.4
Shear modulus, G (GPa)	1.56 ± 0.01	0.56 ± 0.21	0.188 ^c
Shear yield strength, τe (MPa)	25.1 ± 0.33	14.6 ± 1.3	5.16 ± 1.1
Shear failure strength, τf (MPa)	30.2 ± 0.40	17.9 ± 1.8	10.17 ± 0.6
Shear failure strain, γf (%)	7.8 ± 0.7	43.9 ± 3.4	54.82 ± 6.4
Toughness in tension, GIC (N/mm)	0.20 ^b	0.43 ± 0.02	2.36 ± 0.2
Toughness in shear, GIIC (N/mm)	0.38 ^b	4.70 ± 0.34	5.41 ± 0.5

^aproducer information

^bdefined in reference,^{[32] c} calculated using Hooke’s law

Figure 1. Geometries of the flat SLJ for the CZM validation process (a) and curved JLJ for the CZM parametric analysis (b).

Figure 2. Boundary conditions and loads applied to the joints, with details at the model supports (a) and overlap (b).

Table 2. CFRP interlaminar and adhesive layer CZM properties.

CZM property	CFRP	AV138	2015	7752
Knn (GPa)	10^3	4.89	1.85	0.493
Kss (GPa)	10^3	1.56	0.56	0.188
tn^0 (MPa)	42.6	39.45	21.63	11.49
ts^0 (MPa)	39.3	30.2	17.9	10.17
GIC (N/mm)	0.54	0.20	0.43	2.36
GIIC (N/mm)	0.93	0.38	4.70	5.41

Figure 3. Experimental cohesive failure in the adhesive layer for the adhesive Araldite® AV138 and L_O = 10 mm (a), experimental interlaminar failure in the CFRP for the adhesive Araldite® AV138 and L_O = 40 mm (b) and respective CZM prediction (c), experimental cohesive failure in the adhesive layer for the adhesive Araldite® 2015 and L_O = 20 mm (d) and respective CZM prediction (e).

Figure 4. Experimental/numerical P-δ curve comparison: example for the joints bonded with the adhesive Araldite® 2015 and L_O = 10 mm.

Figure 5. Experimental/numerical P_m vs. L_O evolution for the joints bonded with the adhesive Araldite® AV138 (a) and 2015 (b), including the standard deviation of the experimental data.

Figure 6. σ_y/τ_avg (a) and τ_xy/τ_avg (b) stresses for the 2015 considering fixed R = 1000 m and varying L_O (10 and 80 mm) and t_P (1.2 and 3.6 mm).

Figure 7. Peak σ_y/τ_avg (a) and τ_xy/τ_avg (b) stresses for the 2015 at x/L_O = 0 and x/L_O = 1 considering fixed L_O = 10 mm, t_P = 1.2 mm and R = 1000 m, and varying R (1000, 2000 and 3000 mm).

Figure 8. Numerical predictions of cohesive failure in the adhesive layer of a joint bonded with the adhesive Araldite® 2015, R = 1000 mm, L_O = 10 mm and t_p = 1.2 mm (a) and interlaminar failure in the CFRP of a joint bonded with the adhesive Araldite® 2015, R = 1000 mm, L_O = 10 mm and t_p = 2.4 mm (b).

Figure 9. Failure plot of the joints bonded with the adhesive Sikaforce® 7752 per t_P and L_O (dimensions in mm).

Figure 10. P_m vs. L_O comparison between the three adhesives for t_P = 1.2 mm (a), 2.4 mm (b), and 3.6 mm (c), considering fixed R = 1000 mm.

Figure 11. P_m vs. L_O comparison for different R, considering fixed adhesive (2015) and t_P = 1.2 mm.

Figure 12. U vs. L_O comparison between the three adhesives for t_P = 1.2 mm (a), 2.4 mm (b), and 3.6 mm (c), considering fixed R = 1000 mm.

Figure 13. U vs. L_O comparison for different R, considering fixed adhesive (2015) and t_P = 1.2 mm.

Neto, J. A. B. P.; Campilho, R. D. S. G.; da Silva, L. F. M. Parametric Study of Adhesive Joints with Composites. Int. J. Adhes. Adhes. 2012, 37, 96–101. DOI: 10.1016/j.ijadhadh.2012.01.019.

 Web of Science ®Google Scholar

Campilho, R. D. S. G.; Banea, M. D.; Neto, J. A. B. P.; da Silva, L. F. M. Modelling Adhesive Joints with Cohesive Zone Models: Effect of the Cohesive Law Shape of the Adhesive Layer. Int. J. Adhes. Adhes. 2013, 44, 48–56. DOI: 10.1016/j.ijadhadh.2013.02.006.

 Web of Science ®Google Scholar

Faneco, T. M. S.; Campilho, R. D. S. G.; Silva, F. J. G.; Lopes, R. M. Strength and Fracture Characterization of a Novel Polyurethane Adhesive for the Automotive Industry. J Testing Eval. 2017, 45(2), 398–407. DOI: 10.1520/JTE20150335.

 Web of Science ®Google Scholar