Crack propagation prediction of CFRP retrofitted steel plates with different degrees of damage using BEM
- Authors: Yu, Qian Qian , Zhao, Xiao , Chen, Tao , Gu, Xianglin , Xiao, Zhigang
- Date: 2014
- Type: Text , Journal article
- Relation: Thin-Walled Structures Vol. 82, no. (2014), p. 145-158
- Full Text: false
- Reviewed:
- Description: Although carbon fibre reinforced polymer (CFRP) materials have proven effective in strengthening steel structures especially when used to improve fatigue behaviour, further study is required to investigate their effectiveness when applied at different stages of crack propagation in steel elements. This paper presents a numerical study on CFRP retrofitted steel plates with different degrees of damage using the boundary element method (BEM). The numerical results compared well with the experimental data, which demonstrated that the BEM is reliable for crack propagation analysis of CFRP laminate retrofitted steel plates. Finally, a parametric analysis was conducted to investigate the influence of bond length, bond width, CFRP stiffness and adhesive shear modulus on stress intensity factor (SIF) values. © 2014 Elsevier Ltd.
Evaluation of stress intensity factor for CFRP bonded steel plates
- Authors: Yu, Qian Qian , Zhao, Xiao , Xiao, Zhigang , Chen, Tao , Gu, Xianglin
- Date: 2014
- Type: Text , Journal article
- Relation: Advances in Structural Engineering Vol. 17, no. 12 (2014), p. 1729-1746
- Full Text: false
- Reviewed:
- Description: Recent studies on the application of carbon fibre reinforced polymer (CFRP) materials to defected steel structures have demonstrated the potential for significant reduction of stress intensity factor (SIF) values at crack tips leading to extended fatigue lives. However, most of the previous research relied on experimental and numerical methods, which were either expensive or time-consuming. In this paper, the SIF values at crack tips of steel plates strengthened with bonded composite materials were evaluated using linear elastic fracture mechanics. The analysis was based on the classical solution of SIF values of plain steel plates, considering load share effect and geometry correction factor change resulted from the overlay patch. The effect of different parameters were demonstrated and compared with experimental results, including initial damage degrees of specimens, geometric and mechanical properties of retrofitting materials and bond locations. Good agreement with the experimental data indicated that this approach could conservatively predict the SIF values with reasonable accuracy. A parametric study on variables including the CFRP modulus, the bond width and bond length was conducted based on this method to further investigate their effect on the SIF values.
CFRP repaired welded thin-walled cross-beam connections subject to in-plane fatigue loading
- Authors: Xiao, Zhigang , Zhao, Xiao
- Date: 2012
- Type: Text , Journal article
- Relation: International Journal of Structural Stability and Dynamics Vol. 12, no. 1 (2012 2012), p. 195-211
- Full Text: false
- Reviewed:
- Description: Cracked cross-beam connections made of thin-walled rectangular hollow sections (RHS) are repaired with carbon fiber-reinforced polymer (CFRP) sheets. Constant amplitude fatigue experiments are conducted on the repaired specimens. A pilot test is conducted on a T-connection of square hollow sections (SHS) to explore the effective method of applying CFRP. Due to the peeling effect at the corner region of the SHS-to-SHS connection, early debonding happens in the pilot test that only results in a slight extension in fatigue life. In the following experiments of repairing RHS-to-RHS cross-beam connections, circumferential or transverse restraining CFRP patches are applied in the corner region that prevents early debonding successfully and leads to significant increase in fatigue life. Finally, an improvement is made with the addition of steel strengthening plates that increase both the flexural stiffness and fatigue life of the cracked specimens significantly. The proposed retrofitting method may be useful for repairing other similar fatigue-cracked welded tubular connections.
Modified stress intensity factor equations for semi-elliptical surface cracks in finite thickness and width plates
- Authors: Peng, Yang , Tong, Lewei , Zhao, Xiao , Xiao, Zhigang
- Date: 2011
- Type: Text , Conference paper
- Relation: The Twelfth East Asia-Pacific Conference on Structural Engineering and Construction p. 2601-2608
- Full Text: false
- Reviewed:
- Description: Weld defects and severe variation of shape near the welds cause high stress concentration at weld toes or weld roots. This high stress concentration reduces fatigue lives of welded structures. A stress intensity factor (SIF) which includes this effect increases the accuracy of fatigue lives prediction. A magnification factor is commonly used to multiply the SIF of semi-elliptical surface cracks to account for the stress concentration effect in welded connections. Yamada and Hirt model is one of these methods. Comparison between Yamada & Hirt SIF equations and Newman & Raju SIF equations are applied to SIF of semi-elliptical surface cracks. The results suggest that Yamada & Hirt SIF equations are valid when the crack aspect ratio is less than 0.6. New empirical SIF equations are developed based on Yamada & Hirt SIF equations. The newly derived SIF equations are verified by comparing with experimental data.
Prediction of natural frequency of free spanning subsea pipelines
- Authors: Xiao, Zhigang , Zhao, Xiao
- Date: 2010
- Type: Text , Journal article
- Relation: International Journal of Steel Structures Vol. 10, no. 1 (2010), p. 81-89
- Full Text: false
- Reviewed:
- Description: Free spans or suspended spans normally occur in subsea pipelines due to the irregularity of seabed and/or the scouring action of sea water. A problem of significance to the free spans of subsea pipeline is that currents or waves flowing across pipelines can shed vortices and induce vibration which may cause fatigue damage to the pipelines. Natural frequencies of free spans are required when solving vibration amplitude and cyclic stresses in the free span. The natural frequency is usually calculated with simplified equations, where factors such as boundary conditions and axial forces are not accurately taken into account. In this study, the influence of boundary conditions, mass of hydrocarbon products, axial force, and multiple spans on the natural frequencies of pipeline are investigated and corresponding suggestions are provided for frequency calculation.
Fatigue experiments on CFRP repaired welded thin-walled RHSTO-RHS cross-beam connection
- Authors: Xiao, Zhigang , Zhao, Xiao , Mashiri, Fidelis
- Date: 2008
- Type: Text , Conference paper
- Relation: Proceedings of the Tenth International Symposium on Structural Engineering for Young Experts (ISSEYE-10) p. 971-978
- Full Text: false
- Reviewed:
- Description: Cracked thin-walled rectangular hollow section (RHS)-to-RHS cross-beam connections are repaired with carbon fibre reinforced polymer (CFRP) composites and constant amplitude fatigue experiments are conducted on them. A pilot test is first conducted on a square hollow section (SHS)-to-SHS T-connection to explore an effective method of applying CFRP. Due to the “peel off” effect at the corner region of the SHS-to-SHS specimen, early debonding appears in the pilot test which only results in a small increase in fatigue life. Circumferential or transverse restraining CFRP patches are added in the RHS-to-RHS cross-beam specimens which prevent early debonding successfully and lead to significant increase in fatigue life.