Validation of Selected Optical Methods for Assessing Polyethylene (PE) Liners Used in High Pressure Vessels for Hydrogen Storage
, Karol Wachtarczyk 1, Aleksander Błachut 1, Jerzy Kaleta 1, Neha Yadav 2, Marcin Ozga 3 and Amelie Baron 4
Round 1
Reviewer 1 Report
This paper used the DIC method to detect the damages in PE liner, and used finite element method as numerical analysis of the results. Both experimental and numerical results have a good agreement. I have a couple of quick questions, before the paper is accepted.
- Is it possible to detect the damages inside the structure with DIC method?
- In the finite element method analysis, the strain results show a good agreement with the pressure curve, however, which component of the strain tensor did you use? Can you please specify in the paper?
- Finite element methods and other experimental methods have been used in NDT for a long time, a comprehensive introduction is highly recommended, for example:
[1]Zhang, S., Shen, W., Li, D., Zhang, X. and Chen, B., 2018. Nondestructive ultrasonic testing in rod structure with a novel numerical Laplace based wavelet finite element method. Latin American Journal of Solids and Structures, 15(7).
[2]Li, D., Zhang, S., Yang, W. and Zhang, W., 2014. Corrosion monitoring and evaluation of reinforced concrete structures utilizing the ultrasonic guided wave technique. International Journal of Distributed Sensor Networks, 10(2), p.827130.
Author Response
Dear Reviewer,
Thank you for your kind revision of our paper. Please find below our replies to your comments.
Point 1. Is it possible to detect the damages inside the structure with DIC method?
Response 1. The DIC method enables the measurement of the strain field on the surface of the tested object. Often the defect inside the structure affects this field too. However, it depends on the size of the defect and the depth at which it is located. Solving the inverse problem, i.e., the identification of a defect inside the liner’s structure based on DIC measurements is possible, but more complex and requires a "hybrid" procedure, i.e. the use of additional numerical simulation results. Therefore, it is necessary to prepare a numerical model of the defects’ impact (e.g., pores, bubbles in the liner wall) on the deformation field of the surface. The model must take into account the size of the defect and its location in the liner’s wall. Additionally, possible changes in wall thickness should be taken into account. Then create a "library" of possible defects and their influence on the deformation field on the surface. Such a model shall be identified by the measurement when "programmed" defects are intentionally introduced into the object. By using, e.g., machine learning, we can create an effective tool for identifying defects within a structure, based on DIC measurements. The sensitivity of the above procedure is limited by the sensitivity of the DIC and the accuracy of the numerical modeling.
Point 2. In the finite element method analysis, the strain results show a good agreement with the pressure curve, however, which component of the strain tensor did you use? Can you please specify in the paper?
Response 2. Element coordinate system was defined in this manner: axis 1 defined by the hoop direction, axis 2 the longitudinal direction and tangent to the surface, and axis 3 by normal to the liner surface. Circumferential strain (???) is considered as the logarithmic strain component LE11 and the longitudinal strain (???) is considered as the logarithmic strain component LE22 in Abaqus solver.
Point 3. Finite element methods and other experimental methods have been used in NDT for a long time, a comprehensive introduction is highly recommended, for example:
[1]Zhang, S., Shen, W., Li, D., Zhang, X. and Chen, B., 2018. Nondestructive ultrasonic testing in rod structure with a novel numerical Laplace based wavelet finite element method. Latin American Journal of Solids and Structures, 15(7).
[2]Li, D., Zhang, S., Yang, W. and Zhang, W., 2014. Corrosion monitoring and evaluation of reinforced concrete structures utilizing the ultrasonic guided wave technique. International Journal of Distributed Sensor Networks, 10(2), p.827130.
Response 3. Thank you for these interesting publications. We read them very carefully. The first paper describes the modeling of mechanical wave propagation in a bar using the combination of the Laplace transform and the interval finite element method. And the second one presents a study of the influence of galvanic corrosion on the propagation of a mechanical wave in concrete rebar. NDT methods are the only common denominator for our publication and the ones suggested in the review. Therefore we don't find it necessary to add them to the list in our paper.
We will provide some grammar changes in the final version of our article.
Once again thank you for your interesting questions.
Sincerely yours
Pawel Gasior
Reviewer 2 Report
No changes required.
The reviewed paper falls within the standards of writing an experimental scientific paper, is well written and is of great interest both in terms of the approached subject (structural evaluation of a high-pressure composite vessel) and in terms of the experimental methods used.
Author Response
Dear Reviewer,
Thank you for your kind revision of our paper. We will provide some grammar changes in the final version of our article.
Once again thank you for your support.
Sincerely yours
Pawel Gasior
Reviewer 3 Report
See attached file
Comments for author File: 
Comments.pdf
Author Response
Dear Reviewer,
Thank you for your kind revision of our paper. Please find below our replies to your comments.
Point 1. Major remark
Response 1. The DIC method enables the measurement of the strain field on the surface of the tested object. Often the defect inside the structure affects this field too. However, it depends on the size of the defect and the depth at which it is located. Solving the inverse problem, i.e., the identification of a defect inside the liner’s structure based on DIC measurements is possible, but more complex and requires a "hybrid" procedure, i.e. the use of additional numerical simulation results. Therefore, it is necessary to prepare a numerical model of the defects’ impact (e.g., pores, bubbles in the liner wall) on the deformation field of the surface. The model must take into account the size of the defect and its location in the liner’s wall. Additionally, possible changes in wall thickness should be taken into account. Then create a "library" of possible defects and their influence on the deformation field on the surface. Such a model shall be identified by the measurement when "programmed" defects are intentionally introduced into the object. By using, e.g., machine learning, we can create an effective tool for identifying defects within a structure, based on DIC measurements. The sensitivity of the above procedure is limited by the sensitivity of the DIC and the accuracy of the numerical modeling.
Inside the structure, volume discontinuities in the polymer (local defects) can be observed by strain measurement on the liner surface, and this sensitivity was observed by FBG sensor CD1, with bubble versus CD2 sensor (Table 3). A similar sensitivity trend was observed in FEM analysis, as shown in Figure 15. Investigation of internal defects by surface strain measure needs careful data analysis and used a well-tuned algorithm. In general, on the strain map, we can observe coarse defects, like thickness fluctuation and surface defects. For the observed inside defects, it is necessary to filter the effects from coarse defects and focus on the narrow region of interest. Procedures of filtering data and diagnostic algorithms need to be developed and verified as future work.
Point 2. Minor remarks
Response 2. Thank you for the list of imperfections. We will upgrade the English language as well as address all minor remarks in the final version of our article.
Once again, thank you for your interesting questions.
Sincerely yours
Pawel Gasior
Reviewer 4 Report
In the paper two finite element models were presented:
Figure 6a shows a model investigated in ANSYS V 15 finite element program, in Figure 9 we can see a model built in ABAQUS v 2020 finite element program. The model characteristics are shown for the second model more detailly than in case of the first model. What is the reason of this? Also reader cannot decide if the first model was a 3D or "D model? Only the stress results are shown for the first model, but correct presentation of the finite element running could need the presentation of the stress and deformation results/contours both.
After my congratulations for the high importance and quality of the paper and of the work shown, I would like to ask the authors to answer these questions and complete the commented things before the publication of the paper.
Author Response
Dear Reviewer,
Thank you for your kind revision of our paper. Please find below our reply to your comments.
Point 1. Figure 6a shows a model investigated in ANSYS V 15 finite element program, in Figure 9 we can see a model built in ABAQUS v 2020 finite element program. The model characteristics are shown for the second model more detailly than in the case of the first model. What is the reason of this?
Response 1. The first model is a result of our common work in an EU-funded project: COst & PERformaNces Improvement for Cgh2 composite tanks (COPERNIC). It was performed in cooperation with several Partners, including the vessel producer and its goal was to improve the composite design for the vessel's cost optimization. The goal of figure 6 was to show the influence of the improper design of the composite structure, which can produce too high stress level in the liner, and as its consequence its damage during normal operation (broken liner and leak of the medium).
The second model was made in ABAQUS and was prepared especially for the purpose of this paper, which I devoted to the liner issues.
We will provide some minor changes (grammar and inputs) in the final version of our article.
Once again thank you for your interesting comments.
Sincerely yours
Pawel Gasior
Round 2
Reviewer 3 Report
I appreciate the responses and corrections by the authors. I think that the manuscript is much more suitable for the readers of the Applied Sciences journal after these revisions. I have no further recommendations. Congratulations for the quality of the manuscript.
