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문제 정의
- The objective of this study is to determine the optimum plastic collapse model that can be used to estimate the failure of a steam generator tube containing two parallel axial through-wall cracks. As a first step for this, plastic collapse tests are performed using plate specimens with two parallel through-wall cracks.
제안 방법
- Plastic collapse tests were carried out for plates containing two parallel through-wall cracks where the crack lengths, 2c, are 5, 8, and 13 mm and the distance between the cracks, d, is are 1, 2, and 4 mm, respectively. Additional tests were also performed for the plates with a single crack of 2c =5, 8, and 13 mm, respectively.
- Three-dimensional elastic and elastic-plastic finite element analyses were performed to investigate the root cause of this. Both elastic analysis, based on the stress intensity factor K, and elastic-plastic analysis, based on the /integral, were carried out. The following two factors were defined to explain the degree of interaction in the elastic analysis and the elastic-plastic analysis, respectively.
- The coalescence load of these multiple cracks was also estimated with each of 9 failure models introduced in our previous study. By comparing the estimated results with the test results, the plastic-zone contact model and the reaction force model were selected as two optimum local failure models for the integrity evaluation of steam generator tubes [13]. Unlike two collinear through-wall cracks that behave as one main crack after coalescing with each other, the thin plate or tube with two parallel through-wall cracks is collapsed plastically, following tearing at a crack tip, without any coalescence of the two adjacent cracks.
- The above local failure models were used to estimate the coalescence loads of two collinear through-wall cracks existing in thin plates or tubes. By comparing the predicted results with the test results, the Reaction Force Model and Plastic Zone Contact Model II & Ⅲ were selected as the optimum local failure models for the coalescence evaluation of multiple collinear cracks existing in thin plates or steam generator tubes.
- 15 mm. Finite element analyses were carried out for the cases where the crack length, 2c, are 5, 8, and 13 mm and the distances between the two adjacent crack, d, are 1, 2, and 4 mm, respectively. The plastic collapse loads of thin plates were estimated by using each of three failure prediction models.
- In this study, 3 failure prediction models were introduced to estimate the plastic collapse loads of thin plates with two parallel through-wall cracks, and their estimation results were compared with the experimental results. The model with the highest accuracy of prediction was found to be the CBM (including the CBM-II) model, followed by the PZC-Ⅲ model, and finally the PZC-II model.
- In this study, plastic collapse tests using Inconel 600 plate specimens w辻h two parallel through- wall cracks were performed. Three failure prediction models were proposed to estimate the plastic collapse loads of thin plates containing two parallel through-wall cracks, and their estimation results were compared with the experimental results.
- Specimens were fabricated in T-L direction and notches were wrought by using the Electro-Dis아】。rge Machining (EDM) method. Plastic collapse tests were carried out for plates containing two parallel through-wall cracks where the crack lengths, 2c, are 5, 8, and 13 mm and the distance between the cracks, d, is are 1, 2, and 4 mm, respectively. Additional tests were also performed for the plates with a single crack of 2c =5, 8, and 13 mm, respectively.
- Thus, the CBM model was selected as the optimum failure prediction model for the plate with two parallel through-wall cracks. The second step of this study will involve applying the obtained optimum failure prediction model to the steam generator tubes with two parallel through-wall cracks for the estimation of failure loads.
- Their plastic collapse loads are also predicted with three local failure models proposed from our previous studies and the optimum failure model is determined by comparing the estimated results with test results. The second step of this study, which will be covered in another paper, is to apply the developed optimum failure model to steam generator tubes with multiple parallel axial through-wall cracks.
- As a first step for this, plastic collapse tests are performed using plate specimens with two parallel through-wall cracks. Their plastic collapse loads are also predicted with three local failure models proposed from our previous studies and the optimum failure model is determined by comparing the estimated results with test results. The second step of this study, which will be covered in another paper, is to apply the developed optimum failure model to steam generator tubes with multiple parallel axial through-wall cracks.
대상 데이터
- Plastic collapse tests were performed by displacement control and a universal testing machine with a 25-ton capacity (Instron model 8802) was used. Both ends of the specimen were fixed using hydraulic grips, as shown in the test facilities of Fig.
- Test specimens were made of Inconel 600 plate material. The thickness of the plate is 6 mm and the chemical composition and tensile properties of the material are given in Tables 1 and 2,
이론/모형
- The results of the CBM model (including the CBM-II model) show a good agreement with the experimental results and explain the negative interaction effects well. From the above results, the CBM model was selected as the optimum failure prediction model for the plate with two parallel through-wall cracks.
성능/효과
- From the experimental results and the finite element analysis results on the interaction effects, it was confirmed that the plates with two parallel through-wall cracks have higher plastic collapse loads than those plates with a single through-wall crack. Stress relaxation takes place around the crack tips; therefore, the failure load of the plate with a pair of parallel cracks becomes higher than that of the plate with a single crack.
- The estimation results derived from the PZC-II model showed a large discrepancy with the experimental results. In the comparison of the estimated results with the experimental results, the estimated failure loads obtained 나sing the PZC-Ⅲ model indicated the maximum difference of 17% and the average difference of 5.3%.
- 11. In the comparison with the experimental results, the maximum and the average difference of the CBM-II model are 11.1% and 5.7%, respectively. The accuracy of the CBM- II model is slightly lower than that of the CBM model.
- The experimental results show that the plate with a pair of parallel through-wall cracks has higher plastic collapse load than the plate with a single through-wall crack. Three-dimensional elastic and elastic-plastic finite element analyses were performed to investigate the root cause of this.
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