Closure Effect on Interaction of Two Surface Cracks Under Cyclic Bending

2010 ◽  
Author(s):  
Masanori Kikuchi ◽  
Yoshitaka Wada ◽  
Maigefeireti Maitireyimu ◽  
Hirotaka Sano
Keyword(s):  
Crack Growth ◽  
Crack Closure ◽  
Crack Front ◽  
Surface Crack ◽  
Specimen Surface ◽  
Surface Cracks ◽  
Paris Law ◽  
C Value ◽  
Closure Effect ◽  
Surface Crack Growth

Crack closure effect on interaction of two surface crack growth processes by fatigue is studied. At first, change of C value in Paris’ law along crack front of single surface crack is measured experimentally. It is shown that C value decreases near specimen surface. Crack closure effect is studied numerically for a surface crack by elastic-plastic cyclic analyses. It is found that closure effect appears more strongly near specimen surface than the maximum-depth point. By determining effective stress intensity factor including closure effect, it is shown that change of C value is equal to the change of closure effect along crack front. Using new C value considering closure effect, fatigue crack growth is predicted using S-FEM. It is shown that fatigue life and crack configuration agree well with experimental ones. Finally, interaction of two surface cracks is evaluated numerically, and it is shown that crack closure plays important role on the interaction of two cracks.

Numerical Investigation on Surface Crack Growth in Steel Plates Repaired With Carbon Fiber-Reinforced Polymer

2019 ◽  
Author(s):  
Zongchen Li ◽  
Xiaoli Jiang ◽  
Hans Hopman
Keyword(s):  
Crack Growth ◽  
Surface Crack ◽  
Steel Structures ◽  
Steel Plates ◽  
Fiber Reinforced Polymer ◽  
Carbon Fiber Reinforced Polymer ◽  
Surface Cracks ◽  
Fiber Reinforced ◽  
Reinforced Polymer ◽  
Surface Crack Growth

Abstract Fatigue crack growth is a major challenge to the structural integrity of steel structures. In technical practice, surface cracks are of great importance since cracks in components and structures often exhibit this geometry. Fiber-reinforced polymer (FRP) strengthening technology is a reliable technique to repair cracks in steel structures. Yet the investigation on FRP repairing surface cracks in steel structures is lacking. What’s more, the crack growth might cause crack-induced debonding at the interface of FRP reinforcement, generating negative effects to the reinforcement effectiveness. Unfortunately, there are limited studies in the open literature for this issue. In this paper, we conduct the investigation on surface crack growth in steel plates reinforced with Carbon Fiber-reinforced polymer (CFRP) under tensile load. Three-dimensional finite element models are built to predict the stress intensity factors of the surface cracks. The crack-induced debonding is considered in the finite element analysis by introducing the cohesive zone model and a bond failure criterion. In accordance with Paris law, surface crack growth rate of different models are predicted. The influential parameters of crack-induced debonding are analyzed by means of parametric studies. The results indicate that CFRP reinforcement could significantly decrease the surface crack growth rate, while the crack-induced debonding might generate negative effect on CFRP reinforcement. In addition, the crack-induced debonding is affected by not only the interfacial properties, but also the reinforcement scheme, such as thickness of the adhesive layer, CFRP layer number and its elastic modulus, and the depth of surface cracks.

Internal Surface Crack Growth in Offshore Rigid Pipes Reinforced With CFRP

2018 ◽  
Author(s):  
Zongchen Li ◽  
Xiaoli Jiang ◽  
Zhiping Liu ◽  
Hans Hopman
Keyword(s):  
Crack Growth ◽  
Surface Crack ◽  
Bending Moment ◽  
Internal Surface ◽  
Surface Cracks ◽  
Reliable Technique ◽  
Reinforced Polymer ◽  
Offshore Industry ◽  
Offshore Oil ◽  
Surface Crack Growth

Rigid pipelines have been widely applied in offshore oil & gas operation and transmission industries on account of their structural simplicity, cost-effectiveness, ease of installation and maintenance. However, surface cracks frequently appear in the internal surface of rigid pipes due to dynamic loads or hydrogen embrittlement, etc. Under dynamic fatigue loads, surface cracks may continue to propagate and finally develop into penetrated cracks, which may cause leakage and serious accidents. Fiber-reinforced polymer (FRP) strengthening technology is already a reliable technique for structure maintenance in onshore pipelines and penetrated cracks in load-bearing circular hollow sections (CHS). Nevertheless, there are very limited systematic investigations of surface crack in rigid pipes reinforced with FRP, which has a remarkable significance for offshore rigid pipes. This paper aims to understand the mechanism of semi-elliptical surface crack growth in the internal surface of rigid pipes under fatigue bending moment reinforced with FRP. Stress intensity factors along the crack front are computed through finite-element (FE) models, which are validated by experimental data from references. The influence of wrapping orientation of CFRP are discussed as well. The numerical results show that under CFRP reinforcement, surface crack growth rate decreases significantly which ensures the safety use of rigid pipes in offshore industry.

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