PSI - Issue 54

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Jaroslav Václavík et al. / Procedia Structural Integrity 54 (2024) 294–299 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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=− ( +1) − = , ∙ − , where = , and =√ 2 1 =√ ( 1 + 1 )

(1)

(2)

Where P = σ·A s is the loading force, σ corresponding nominal stress, b a is steel and CFRP width and x is the distance of reinforced end, E s , A s , E f , A f are steel plate end CFRP plate Young’s modulus and section area, G a is adhesive sheer modulus. The sheer stress level is the indicator of unbonding the CFRP layer. The debonding failure load can be estimated as follows =(1− − ) −2 2, ∙( +1) ∙ (3) An estimation of the required length l of the adhesive joint in order to achieve a 99% of the maximum strength was derived to be l min ≥ 5/ λ . The calculation of stress distribution and limit nominal stress was made for specimen used for experimental tests. The width of the steel specimen was 50 mm, thickness 3 mm and the length 450 mm. The adhesive layer thickness was 0.3 mm. The CFRP plate has the length 140 mm, the thickness 1.2 mm and 25 mm width. The required minimum length of CFRP plate was calculated for our sample of investigation l min = 39 mm. The specimens were manufactured from the ferritic stainless steel 1.4003 with a nominal Young’s modulus E s = 210,000 MPa, a tensile strength equal to 480 MPa and a yield stress equal to 350 MPa. The reinforcement plate was realized using pultruded CFRP plate Sika ® CarboDur ® S512 with Young’ modulus E f = 170,000 MPa, tensile strength equal to 2800 MPa. For all tests a polyurethane structural adhesive SikaPower® 1277 was used, which has reasonable mechanical strength as well as high ductility. The mechanical and fracture properties in tension and shear of this adhesive were investigated by M.G.Cardoso at al. (2020). Some characteristics, not given in the adhesive datasheet, were obtained, like tensile (G IC ) and shear fracture energies (G IIC ) and some other were not in agreement with data sheets (sheer strength τ f = 20.35 MPa). Based on above mentioned theory the distribution of sheer stress τ a and peeling stresses σ a (relations are not presented here) at the CFRP end for one side reinforced (OSR) sample were calculated for maximum allowable adhesive sheer strength and are given in Fig. 1.

Fig. 1. Shear and peeling stress distribution in the OSR adhesive sample ( P = 32 kN), corresponding to tensile stress σ = 213 MPa

Fig. 2. Relation between sheer stress in the adhesive and the tensile stress with allowable steel and adhesive stress limits

According the linear relation between the structure tensile stress and sheer stress in adhesive at the reinforced ends (presented in Fig. 2) it is obvious, that the maximum allowable tensile stress at the CFRP end without interface delamination can reach 213 MPa; this value is lower than the yield point of the steel material. Using double side