Dent Damage on Pipe Surface: (a) Dent on Specimen of S2N2; (b) Dent on Specimen of S2N3; (c) Dent on Specimen of S2N4; 

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... dent damage are from S2N8 to S2N11. Due to the lacking of specimens with metal loss (single V-notch), the specimens with single crack is set to the fourth group. And the fifth group contains specimens with combined damage. Each damage is denoted by its length (l (i) ), width (w (i) ), depth (d (i) ) and rotation angle (θ (i) ), as illustrated in Fig. 1, where i denotes the damage type, varying with different types. The rotation angle of damage is defined as the angle be- tween damage length and the longitudinal direction of specimen. Furthermore, the structural damage is intentionally introduced in the center of each specimen, either on the compression side (C) or on the tensile side ...

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... on the sample mean and variance, a mean and 95% confidence interval for pipe diameter and wall thickness with an assumption of normal distribution are presented in Fig. 10. It shows that the spread of wall thickness and outer diameter are small. Meanwhile, the real variations of pipe thickness and outer diameter along specimen longitudinal direction are shown in Fig. 11, which reflects the fact that uneven thickness with a minus manufactured tolerance in these seamless specimens ex- ists. Line 1 and 2 in ...

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... and variance, a mean and 95% confidence interval for pipe diameter and wall thickness with an assumption of normal distribution are presented in Fig. 10. It shows that the spread of wall thickness and outer diameter are small. Meanwhile, the real variations of pipe thickness and outer diameter along specimen longitudinal direction are shown in Fig. 11, which reflects the fact that uneven thickness with a minus manufactured tolerance in these seamless specimens ex- ists. Line 1 and 2 in Fig. 11 (a) are two respective parallel lines that measurements of thickness are conducted. ...

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... in Fig. 10. It shows that the spread of wall thickness and outer diameter are small. Meanwhile, the real variations of pipe thickness and outer diameter along specimen longitudinal direction are shown in Fig. 11, which reflects the fact that uneven thickness with a minus manufactured tolerance in these seamless specimens ex- ists. Line 1 and 2 in Fig. 11 (a) are two respective parallel lines that measurements of thickness are conducted. ...

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... should be noted that the specimen S.N. has been renum- bered so that some marks on specimens such as the mark on Fig. 12 (d), do not coincide with those in the former tables. And due to exceptions and failure of data measurements, some of the results are not correctly obtained, for instance, the reinforcement of half sleeve is going to lose strength which introduce a large boundary effect. Hence, these data are intentionally removed in this ...

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... failure modes of different types of specimens are shown in Figs.12 and 13. For intact specimens, the failure pattern con- sists of an inward buckle with an adjacent secondary outward buckle at the places close to the loading heads, as seen in Fig. 12 (a). For a pipe with dent on compression side, a major inward buckle occurs in the dented region but without a secondary out- ward buckle, as seen in Fig. 12 (b). A similar failure pattern happens for the specimen with metal loss and combined dam- age on the compression side of specimen, as seen from S3N1 in Fig. 12 (c) and S5N1 in Fig. 13 ...

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... in Figs.12 and 13. For intact specimens, the failure pattern con- sists of an inward buckle with an adjacent secondary outward buckle at the places close to the loading heads, as seen in Fig. 12 (a). For a pipe with dent on compression side, a major inward buckle occurs in the dented region but without a secondary out- ward buckle, as seen in Fig. 12 (b). A similar failure pattern happens for the specimen with metal loss and combined dam- age on the compression side of specimen, as seen from S3N1 in Fig. 12 (c) and S5N1 in Fig. 13 (a). Furthermore, a single crack damage on the compression side of specimen has not changed the failure pattern compared with the intact specimen, as seen in ...

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... the loading heads, as seen in Fig. 12 (a). For a pipe with dent on compression side, a major inward buckle occurs in the dented region but without a secondary out- ward buckle, as seen in Fig. 12 (b). A similar failure pattern happens for the specimen with metal loss and combined dam- age on the compression side of specimen, as seen from S3N1 in Fig. 12 (c) and S5N1 in Fig. 13 (a). Furthermore, a single crack damage on the compression side of specimen has not changed the failure pattern compared with the intact specimen, as seen in Fig. 12 (d). Nevertheless, the combined damage on tensile side introduces the fracture failure of specimen at low strength, as seen from S5N5 in Fig. 13 ...

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... in Fig. 12 (a). For a pipe with dent on compression side, a major inward buckle occurs in the dented region but without a secondary out- ward buckle, as seen in Fig. 12 (b). A similar failure pattern happens for the specimen with metal loss and combined dam- age on the compression side of specimen, as seen from S3N1 in Fig. 12 (c) and S5N1 in Fig. 13 (a). Furthermore, a single crack damage on the compression side of specimen has not changed the failure pattern compared with the intact specimen, as seen in Fig. 12 (d). Nevertheless, the combined damage on tensile side introduces the fracture failure of specimen at low strength, as seen from S5N5 in Fig. 13 ...

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... 12 (b). A similar failure pattern happens for the specimen with metal loss and combined dam- age on the compression side of specimen, as seen from S3N1 in Fig. 12 (c) and S5N1 in Fig. 13 (a). Furthermore, a single crack damage on the compression side of specimen has not changed the failure pattern compared with the intact specimen, as seen in Fig. 12 (d). Nevertheless, the combined damage on tensile side introduces the fracture failure of specimen at low strength, as seen from S5N5 in Fig. 13 ...

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... from S3N1 in Fig. 12 (c) and S5N1 in Fig. 13 (a). Furthermore, a single crack damage on the compression side of specimen has not changed the failure pattern compared with the intact specimen, as seen in Fig. 12 (d). Nevertheless, the combined damage on tensile side introduces the fracture failure of specimen at low strength, as seen from S5N5 in Fig. 13 ...

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... Therefore, there is no sudden instability phenomenon hap- pening, as in the tests from Sjors et al. [16]. Since the strategy of load-controlled is deployed in this test, a slight instability un- avoidably occurs during loading due to the plastic effect, espe- cially during the intervals that for specimen checking, as shown from the vibration in Figs. 14 (a). It could cause a little overesti- mate of the specimen strength and structural behaviors. In prac- tice, the occurrence of the ultimate bending moment is mostly associated with local buckling and accumulating of curvatures, resulting in eventually ...

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... intact specimens with low diameter-to-thickness ratios, The typical moment-curvature diagram is shown in Fig. 14. Two types of curvatures including global curvature (κ) and lo- cal curvature (κ 1 ) are presented. It is obviously that the bend- ing strength keeps stable within a large curvature range until a slight drop due to the sliding between supports and specimen has occurred. The bending moments in all four specimens present nearly the same ...

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... damage obviously has effect on the structural be- haviors, as from the comparisons between Fig. 15 and Fig. 14. Due to the limitation of space in this paper, only qualitative re- sults are provided and discussed. For quantitative analysis of the effect of damage and corresponding numerical results, please re- fer to the papers that are going to be published soon. Figure 15 denotes the moment-curvature diagrams of dented specimens ...

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... damage obviously has effect on the structural be- haviors, as from the comparisons between Fig. 15 and Fig. 14. Due to the limitation of space in this paper, only qualitative re- sults are provided and discussed. For quantitative analysis of the effect of damage and corresponding numerical results, please re- fer to the papers that are going to be published soon. Figure 15 denotes the moment-curvature diagrams of dented specimens with differ- ...

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... quantitative analysis of the effect of damage and corresponding numerical results, please re- fer to the papers that are going to be published soon. Figure 15 denotes the moment-curvature diagrams of dented specimens with differ- ent dent rotation angles and shapes. Clearly, the occurrence of dent has considerably reduced the strength of specimen com- pared with the intact specimens from Fig. 14. ...

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... and corresponding numerical results, please re- fer to the papers that are going to be published soon. Figure 15 denotes the moment-curvature diagrams of dented specimens with differ- ent dent rotation angles and shapes. Clearly, the occurrence of dent has considerably reduced the strength of specimen com- pared with the intact specimens from Fig. 14. And it speeds up the failure of almost every specimen since the stable inter- val of specimen has been significantly reduced as shown from these curves. Furthermore, the difference between the local and global curvature is getting larger during the post-buckling stage, which demonstrates that the plastic distribution as well as the ...

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... seems like the effect of dent angle is insignificant on the pipe strength and structural behaviors, as seen in Fig. 15 (a), (b) and (c). And it is the similar situation accounting for the effect of dent shape, as shown in Fig. 15 (d) for a specimen with rectan- gular shape dent and Fig. 15 (e) for a specimen with cylindrical shape. It is also found that a dent on tensile side of specimen has less negative effect on pipe strength and curvature compared with ...

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... seems like the effect of dent angle is insignificant on the pipe strength and structural behaviors, as seen in Fig. 15 (a), (b) and (c). And it is the similar situation accounting for the effect of dent shape, as shown in Fig. 15 (d) for a specimen with rectan- gular shape dent and Fig. 15 (e) for a specimen with cylindrical shape. It is also found that a dent on tensile side of specimen has less negative effect on pipe strength and curvature compared with the one on compression side, as seen in Fig. 15 ...

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... seems like the effect of dent angle is insignificant on the pipe strength and structural behaviors, as seen in Fig. 15 (a), (b) and (c). And it is the similar situation accounting for the effect of dent shape, as shown in Fig. 15 (d) for a specimen with rectan- gular shape dent and Fig. 15 (e) for a specimen with cylindrical shape. It is also found that a dent on tensile side of specimen has less negative effect on pipe strength and curvature compared with the one on compression side, as seen in Fig. 15 ...

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... situation accounting for the effect of dent shape, as shown in Fig. 15 (d) for a specimen with rectan- gular shape dent and Fig. 15 (e) for a specimen with cylindrical shape. It is also found that a dent on tensile side of specimen has less negative effect on pipe strength and curvature compared with the one on compression side, as seen in Fig. 15 ...

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... impact-induced damage has a smaller reduction effect on the specimen strength due to the smaller size of dent damage, as shown in Fig. 16. The results imply that the dynamic effect of impact is insignificant. However, further research are needed to be done in order to account for the specific effect. Figures 17 and 18 denote the moment-curvature diagrams of specimens with shallow crack and deep crack, respectively. It should be noted that an extra local curvature (κ 2 ) ...

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... further research are needed to be done in order to account for the specific effect. Figures 17 and 18 denote the moment-curvature diagrams of specimens with shallow crack and deep crack, respectively. It should be noted that an extra local curvature (κ 2 ) in some cases has been calculated for com- parison, and the measurement points for vertical displacement in pipe with crack on tensile side have been changed to 05D, 1D and End-50 due to the occupation of location by damage. ...

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... longitudinal direction. However, from the strength point of view, the occurrence of sur- face crack has not affected the cracked specimens as long as no In order to further investigate the effect of crack, more spec- imens with deeper (d c from 1.5 to 3.0 mm on wall thickness of around 8 mm) and longer crack (20 mm) have been tested, as shown in Fig. 18. Similarly, fracture has not been observed for the specimens with crack under tension. No obvious differ- ences happen on the bending strength and curvatures, as seen in Fig. 18 (a) and (b). An exception of displacement meter drop- ping has happened on the measurements of 1D location of spec- imens S4N11 and S4N13. Hence, the local ...

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... the effect of crack, more spec- imens with deeper (d c from 1.5 to 3.0 mm on wall thickness of around 8 mm) and longer crack (20 mm) have been tested, as shown in Fig. 18. Similarly, fracture has not been observed for the specimens with crack under tension. No obvious differ- ences happen on the bending strength and curvatures, as seen in Fig. 18 (a) and (b). An exception of displacement meter drop- ping has happened on the measurements of 1D location of spec- imens S4N11 and S4N13. Hence, the local curvatures in these two cases have not been recorded, as seen in Fig. 18 (c) and ...

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... specimens with crack under tension. No obvious differ- ences happen on the bending strength and curvatures, as seen in Fig. 18 (a) and (b). An exception of displacement meter drop- ping has happened on the measurements of 1D location of spec- imens S4N11 and S4N13. Hence, the local curvatures in these two cases have not been recorded, as seen in Fig. 18 (c) and ...

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... com- bined damage on pipe surface has significant influence on the pipe strength and curvature, as seen in Fig. 19. Specimens of S5N1, S5N2 and S5N5 include combined damage of dent, notch and crack, while specimens of S5N3 and S5N4 include combined damage of notch and crack. Fracture failure happens on S5N3, S5N4 and S5N5 with damage on tensile side, as shown in Fig. 13 (b). ...

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... on pipe surface has significant influence on the pipe strength and curvature, as seen in Fig. 19. Specimens of S5N1, S5N2 and S5N5 include combined damage of dent, notch and crack, while specimens of S5N3 and S5N4 include combined damage of notch and crack. Fracture failure happens on S5N3, S5N4 and S5N5 with damage on tensile side, as shown in Fig. 13 (b). ...

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... overview of the critical strain and its variation range of specimens that can resist further strength is depicted in Fig. 21. The bar line denotes the range that critical strain varies dur- ing the stable stage of specimens. To avoid the effect of local bending, the strain is calculated from measured curvatures and nominal outer diameter instead of the strain gauges, expressing as ε = κD/2, where the global curvature is deployed and the localization effect ...