PSI - Issue 45

Yuanpeng Zheng et al. / Procedia Structural Integrity 45 (2023) 96–103 Author name / Structural Integrity Procedia 00 (2019) 000–000

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static performance. But Liu et al. (2010) indicate that fatigue loading undermines the deformation properties of the adhesive. In order to characterize the fatigue damage of the adhesive, the softening behavior is then minimized via a fracture energy definition plainly containing the elastic part of the bond-slip curve, illustrated in Fig. 5. The slashed fracture energy value potentially downplays the efficacy of CFRP patches, especially in the early stage of fatigue crack propagation, which consumes the most of the fatigue life, providing more conservative SIF as well as fatigue life prediction results.

Table 2. Material properties Material

Modulus (GPa)

Strength (MPa)

Steel

199.66 (Elastic modulus)

356.28 (Yield strength) 496.5 (Ultimate tensile strength) 1967 (Longitudinal tensile strength) 205 (Transverse tensile strength)

Carbon fiber sheet (FTS-C8-30, thickness t =0.143 mm) Adhesive (Araldite 2014, thickness t =1.09 mm)

681.3 (Longitudinal direction) 26.2 (Transverse direction)

4 (Tensile modulus)

26 (Tensile strength) (0.7% elongation at break)

1.2 (Shear modulus)

20.8 (Shear strength) (Estimated via Xia and Teng, (2005))

τ

P

Previously ,

P max

Adhesive with elas�c assump�on

(1- R )· P max

K

Δ K =K max -K min

=

CFRP

(1- R ) ·K max

P min

Steel

O

O

Δ

Slip

P

In this paper ,

≠

Adhesive using a bond - slip model

P max

τ max τ

(1- R )· P max

CFRP

Δ K=K max -K min

K

(1- R )· K max

G f

P min

Steel

Δ

O

δ 0

O

Slip

Fig. 3. SIF range calculation considering the nonlinearity of the bonding behavior

τ /MPa

τ /MPa

Consider the effects of fa�gue loading

Monotonic sta�c behavior

τ max

τ max

K

G f ↓ K

G f

Slip/mm

δ 0

δ 0

O

Slip/mm

O

Fig. 4. A typical bond-slip model for linear adhesive

Fig. 5. The revised bond-slip model in the simulation

3.3. Other FEM implementation details Carbon fiber sheet-repaired specimens share the same mesh and boundary conditions as the bare CT specimen, with different patch configurations identical to the previous experimental program. The mechanical properties of steel