Research Progress and Applications of Fe-Mn-Si-Based Shape Memory Alloys on Reinforcing Steel and Concrete Bridges

Round 1

Reviewer 1 Report

In this manuscript, the authors summarized the material science basis, function performance and engineering applications. At the end, unsolved questions and prospects also were proposed. In general, this manuscript has abundant content, clear logic sufficient figures and tables. Therefore, I think it can be published in our journal.

 

Comments:

1.      In this manuscript, the material system was only focused on Fe-Mn-Si-based SMAs. Therefore, I suggest that the Fe-based change to Fe-Mn-Si-based in the title.

2.      Using rulers as scale in Fig.4 is not recommended, which should be replaced with scale bars.

3.      The caption of Table 3 is inaccurate.

4.      In Fig.5, the composition of the Fe-based SMA corresponding to each curve should be provided besides references.

5.      I think Fig.10 could be deleted due to it is completely meaningless to the topic of this manuscript.

Author Response

Comment1: In this manuscript, the material system was only focused on Fe-Mn-Si-based SMAs. Therefore, I suggest that the Fe-based change to Fe-Mn-Si-based in the title.

Response: Thanks to the reviewer's suggestion. The authors have modified the title accordingly.

Comment2: Using rulers as scale in Fig.4 is not recommended, which should be replaced with scale bars.

Response: The authors fully agree with the reviewer's comment on that the scale bars are commonly used in scientific publications. However, Fig.4 is a photograph of other scholars cited by the authors. To provide accurate and truthful scale instructions, the authors have not modify it in this manuscript.

Comment3: The caption of Table 3 is inaccurate.

Response: The authors have modified the caption of Table 3 to make it more proper.

Comment4: In Fig.5, the composition of the Fe-based SMA corresponding to each curve should be provided besides references.

Response: The authors agree with the comment provided by the reviewer. However, only the Reference [12] provides the element composition of Fe-SMA in Fig.5, other papers only describe that it is a Fe-Mn-Si alloy. Therefore, the authors can not made modifications to the figure at the current time.

Comment5: think Fig.10 could be deleted due to it is completely meaningless to the topic of this manuscript

Response: Thanks to the reviewer. The authors agree with this suggestion and have deleted Fig.10 from the manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper investigates the properties and application in structural engineering of Fe-based shape alloys.  The concept and application seem very interesting and authors are commended for taking on such research. There is a great potential for this material for strengthening of structural elements. One exception may be that concrete may be affected negatively from the high activation temperatures and pose issues to practicality of the method for RC elements.

The following are comments for the authors to consider in revising their manuscript;

-        An overall English technical editing is required. 

-        Table 3- please define what standard is used for steel grades

-        Section 4.1 and 6.1- Activation of Fe-SMA requires raising temperature considerably to Af. This will definitely and negatively affect the concrete substrate for the case of reinforced concrete strengthening. Please explain. Also discuss the effect of raising temperature on the steel substrate as well.

-        Section 4.2 and 5.2 talks about the application of Fe-SMA for steel substrate. It implies that this material can be used to repair cracked steel. If the substrate steel is cracked it loses its tensile strength and it cannot be repaired unless an equivalent area is also added to the section. Please explain.

-        Section 5.1- Different methods of anchoring. Please note that drilling holes in the substrate steel (the element for which the strengthening is performed) will reduce the strength of substrate steel therefore somehow defeats the main purpose. Please explain.

-        Section 5.2- Implies that post-tensioning with Fe-SMA can improve fatigue behavior of steel. The post-tensioning may reduce the level of permanent tension in the steel but in no way can change the stress range (variation of tensile stress) due to live load. The authors should be reminded that fatigue in steel is mainly due to the level of stress range not he minimum tension stress. Please explain.

-        Does/can Fe-SMA practically go through martensite cycles in the ambient temperature variations? Is there a fatigue concern under martensite transform cycles?

-        Could you please provide an order of magnitude comparison for cost of Fe-SMA and regular steel?

-        Is Fe-SMA weldable?

Author Response

Please see the attached point-to-point replies for Reviewer 1.

Comment1: An overall English technical editing is required.

Response: Thanks for the kind suggestion of the reviewer. The authors have double checked the English writing of the whole article and revised it with marking yellow.

Comment2: Table 3- please define what standard is used for steel grades.

Response: The steel grades is defined by the Chinese standards of Carbon structural steels (GB/T 700-2006) and High strength low alloy structural steels (GB/T 1591-2018) [73-74]. This supplement has been added under Table 3 of the revised manuscript.

Comment3: Section 4.1 and 6.1- Activation of Fe-SMA requires raising temperature considerably to Af. This will definitely and negatively affect the concrete substrate for the case of reinforced concrete strengthening. Please explain. Also discuss the effect of raising temperature on the steel substrate as well.

Response: Many thanks for the questions raised by the reviewer. In practical applications, the activation temperature is not high, usually ranging from 150 to 200℃, and the activation time is relatively short, resulting in a lower temperature transmitted to the structure. Although there are individual cases where the activation temperature exceeds 200℃, no damage has been caused to concrete according to the available references, see the attached Table 1.

For steel structures, the activation temperature in current applications is below 300℃, and the activation time is also short. According to the author's previous research, when the temperature exceeds 400℃, it will cause secondary damage to the steel structure, while when the temperature is controlled below 300℃, the mechanical properties of the steel structure remain unchanged after returning to room temperature. ([1] Xuhong Qiang, Frans S.K. Bijlaard, Henk Kolstein. Post-fire performance of very high strength steel S960. Journal of Constructional Steel Research, 2013, 80: 235-242. [2] Xuhong Qiang, Frans S.K. Bijlaard, Henk Kolstein. Post-fire mechanical properties of high strength structural steels S460 and S690. Engineering Structures, 2012, 35: 1-10.)

Table 1. Available references related to effects on concrete during activation

Structure	Temperature	Activation description	Ref
Concrete	300℃	—	[1]
	160℃	—	[2]
	200℃	The time above 100℃ is 2 minutes during activation.	[3]
	160℃	During the activation process, the highest temperature on the concrete material around the Fe-SMA bars is 80.8℃.	[4]
	155℃	—	[5]
	160℃	The time above 100℃ is 1 minutes during activation.	[6]
Steel	275℃	The time above 100℃ within 4 minutes during activation.	[7]
	275℃	The time above 100℃ within 5 minutes during activation.	[8]
	180℃	—	[9]

References:

[1] Soroushian, P.; Ostowari, K.; Nossoni, A.; Chowdhury, H. Repair and Strengthening of Concrete Structures Through Application of Corrective Posttensioning Forces with Shape Memory Alloys. Transportation Research Board 2001, 1770, 20-26.

[2] Montoya-Coronado, L.A.; Ruiz-Pinilla, J.G.; Ribas, C.; Cladera, A. Experimental Study on Shear Strengthening of Shear Critical Rc Beams Using Iron-based Shape Memory Alloy Strips. Engineering Structures 2019, 200(Dec.1), 109680.

[3] Czaderski, C.; Shahverdi, M.; Michels, J. Iron Based Shape Memory Alloys as Shear Reinforcement for Bridge Girders. Construction & Building Materials 2021, 274, 121793.

[4] Hong, K.; Lee, S.; Yeon, Y .; Jung, K. Flexural Response of Reinforced Concrete Beams Strengthened with Near-Surface-Mounted Fe-Based Shape-Memory Alloy Strips. International Journal of Concrete Structures and Materials 2018, 12(1), 45.

[5] El-Hacha, R.; Rojob, H. Flexural strengthening of large-scale reinforced concrete beams using near-surface-mounted self-prestressed iron-based shape-memory alloy strips. Pci Journal, 2018, 63(6), 55-65.

[6] Shahverdi, M.; Czaderski, C.; Motavalli, M. Iron-based shape memory alloys for prestressed near-surface mounted strengthening of reinforced concrete beams. Construction & Building Materials 2016, 112, 28-38.

[7] Izadi, M.; Ghafoori, E.; Motavalli, M.; Maalek, S. Iron-based shape memory alloy for the fatigue strengthening of cracked steel plates: Effects of re-activations and loading frequencies. Engineering Structures 2018, 176, 953-967.

[8] Izadi, M.; Hosseini, A.; 1,4+(AUTHOR))" >Michels, J.; Motavalli, M.; Ghafoori, E. Thermally activated iron-based shape memory alloy for strengthening metallic girders. Thin-Walled Structures 2019, 141, 389-401.

[9] Izadi, M.; Hosseini, A.; 1,4+(AUTHOR))" >Michels, J.; Motavalli, M.; Ghafoori, E. Thermally activated iron-based shape memory alloy for strengthening metallic girders. Thin-Walled Structures 2019, 141, 389-401.

Comment4: Section 4.2 and 5.2 talks about the application of Fe-SMA for steel substrate. It implies that this material can be used to repair cracked steel. If the substrate steel is cracked it loses its tensile strength and it cannot be repaired unless an equivalent area is also added to the section. Please explain.

Response: Thanks for the kind reminder from the reviewer. The cracks will reduce the load-bearing capacity of the structure and compromise its safety. To repair the cracked steel, it is important to restore its tensile strength.

When Fe-SMA members are used to repair local cracks, the stress response can be reduced by increasing the stiffness of the cracked region, and the average stress can be further reduced by introducing precompression through activating Fe-SMA.

As the reviewer mentioned, however, the cracked steel loses its tensile strength and simply adding Fe-SMA to the cracked area may not be enough to restore the original load-bearing capacity of the structure sometimes. In such cases, in addition to increasing the cross-section of Fe-SMA components, additional reinforcement or material could be added to the section to ensure that the load-bearing capacity is restored to the required level. However, in most cases, the loss strength can be supplemented by the Fe-SMA members, since the tensile strength of Fe-SMA is 2-3 times of the regular steels.

Comment5: -Section 5.1- Different methods of anchoring. Please note that drilling holes in the substrate steel (the element for which the strengthening is performed) will reduce the strength of substrate steel therefore somehow defeats the main purpose. Please explain.

Response: As the reviewer pointed out, methods such as bolt anchorage or nail-anchor that involve drilling holes in the substrate steel will damage the integrity of the steel. Drilling holes will weaken the cross-section of the steel, create stress concentration, and reduce its load-bearing capacity. Therefore, it is necessary to study the load-bearing performance of the connection, evaluate its weakening effect on the substrate steel, and choose the optimal solution after comprehensive consideration.

On the other hand, it is essential to use connection methods that do not weaken the substrate steel, such as frictional clamp and adhesive bonding. The selection of an appropriate anchoring method should consider many factors such as the type of substrate steel, the strengthening material, the required load-bearing capacity, etc.

Comment6: -Section 5.2- Implies that post-tensioning with Fe-SMA can improve fatigue behavior of steel. The post-tensioning may reduce the level of permanent tension in the steel but in no way can change the stress range (variation of tensile stress) due to live load. The authors should be reminded that fatigue in steel is mainly due to the level of stress range not the minimum tension stress. Please explain.

Response: Many thanks for the reminder raised by the reviewer. Indeed, as the reviewer pointed out, the fatigue in steel is mainly due to the level of stress range rather than the minimum tension stress. The reinforcement of Fe-SMA can increase the stiffness of the structure, reduce its stress response, and decrease the stress amplitude under the same cyclic load. Moreover, the activated Fe-SMA can introduce pre-compression stress in the structure, in order to reduce the average stress and stress peak under cyclic load, and to effectively decrease the positive stress amplitude of the structure when the stress valley is less than zero. Through the above two mechanisms, the propagation rate of fatigue cracks can be reduced, and the service life of the steel structure can be extended.

Comment7: Does/can Fe-SMA practically go through martensite cycles in the ambient temperature variations? Is there a fatigue concern under martensite transform cycles?

Response: Many thanks for the questions from the reviewer. According to the current investigation on the characteristic temperatures during transformation process of Fe-SMA (which are summarized in Table 2 of the manuscript), the austenite start temperature is above 70℃, higher than the ambient temperature, while the martensite start temperature is room temperature (20°C) or even lower. Therefore, Fe-SMA will not undergo martensite cycles in the normal range of ambient temperature variations. In addition, the martensite transformation induced only by temperature will not cause macroscopic deformation and stress change in the absence of external force.

Comment8: Could you please provide an order of magnitude comparison for cost of Fe-SMA and regular steel?

Response: At present, Fe-SMA is still in the laboratory customization stage with small-scale production, and Fe-SMA is priced in conjunction with its strengthening system in existing research. With the promotion of market application, Fe-SMA can be produced on a large scale through traditional metallurgical equipment such as electric arc furnace to reduce the cost. In that case, the price of Fe-SMA can be similar to regular steels. We will continue to follow and report any relevant information in future articles.

Comment9: Is Fe-SMA weldable?

Response: Fe-SMA is weldable and has been studied using various welding technologies such as tungsten-inert gas, laser beam, and electron beam welding [1-4]. However, further research is needed to investigate welding between Fe-SMA and conventional structural steel and to study the mechanical properties of the weld itself and the heat-affected zone in addition to the effect on the SME of Fe-SMA.

References:

[1] Lin, H.C.; Lin, K.M.; Chuang, Y.C.; Chou, T.S. The welding characteristics of Fe-30Mn-6Si and Fe-30Mn-6Si-5Cr shape memory alloys. Journal of Alloys & Compounds. 2000, 306, 189-192.

[2] Dong, Z.Z.; Sawaguchi, T.; Kajiwara, S.; Kikuchi, T.; Kim, S.H.; Lee, G.C. Microstructure change and shape memory characteristics in welded Fe-28Mn-6Si-5Cr-0.53Nb-0.06C alloy. Materials Science and Engineering A 2006, 438-440, 800-803.

[3] Druker, A.V.; Perotti, A.; Esquivel, I.; Malarría, J. A manufacturing process for shaft and pipe couplings of Fe-Mn-Si-Ni-Cr shape memory alloys. Materials & Design 2014, 56, 878-888.

[4] Krooß, P.; Gunther, J.; Halbauer, L. Electron beam welding of Fe-Mn-A-Ni shape memory alloy: Microstructure evolution and shape memory response. Functional Materials Letters 2017, 10(4), 1750043.

Author Response File: Author Response.docx

Reviewer 3 Report

This study provides a comprehensive overview of the current research status and applications of Fe-SMA in civil engineering, as well as future research directions. It is excellent for a scholar who is beginning to learn this intelligent material. Please find the detailed comments as follows:

1. How do the authors define the color of Figure 1's atoms? Why are certain atoms yellow while others are red? Does the color indicate something?

2. Table 4 summarizes the mechanical characteristics of Fe-SMA. Significant difference exists between them. Could you provide a brief explanation as to why the difference exists?

3. Figure 8 is difficult to understand. Could you please reorganize it and the sentences that describe it?

4. Which activation method did you employ during the Sutong bridge repair process? It seems like flame-spraying gun. Please clarify when Figure 17 is presented.

 

5. Figure 15 can have a unit in its caption since it contains dimensions.

Author Response

Comment1: How do the authors define the color of Figure 1's atoms? Why are certain atoms yellow while others are red? Does the color indicate something?

Response: The color of the atoms in Figure 1 does not have a specific meaning. The color of the atoms in Figure 1 does not have a specific meaning. It is only used to represent the microscopic atomic positions of Fe-SMA with different crystal structures. The atoms visible in the three-dimensional solid space are integrated into red, and those that cannot be directly seen in the stereogram or inside the solid are marked in yellow.

Comment2: Table 4 summarizes the mechanical characteristics of Fe-SMA. Significant difference exists between them. Could you provide a brief explanation as to why the difference exists?

Response: Thanks for the kind reminder from the reviewer. Due to the various factors such as elemental composition, processing technology, precipitated crystals, etc., the mechanical characteristics of Fe-SMA studied by scholars are different. This brief explanation has been added to Section 3.1 and marked yellow.

Comment3: Figure 8 is difficult to understand. Could you please reorganize it and the sentences that describe it?

Response: Many thanks for the kind suggestion of the reviewer. When Fe-SMA is used to repair local cracks, the stress response can be reduced by increasing stiffness of the cracked region. Moreover, the activated Fe-SMA can introduce precompression, reduce the average stress and stress peak in the structure under cyclic load, and effectively decrease the positive stress amplitude of the structure when the stress valley is less than zero. Figure 8 and the sentences that describe it have been reorganized and marked yellow.

Comment4: Which activation method did you employ during the Sutong bridge repair process? It seems like flame-spraying gun. Please clarify when Figure 17 is presented.

Response: The Fe-SMA plates were activated by a hot-air gun during the reinforcement of the Sutong bridge. The corresponding statement was added and marked yellow in the illustrated section of Figure 17 (Notably, Figure 17 is adjusted to Figure 16 in the revised manuscript).

Comment5: Figure 15 can have a unit in its caption since it contains dimensions.

Response: Many thanks for the kind suggestion of the reviewer. The authors have supplemented the unit in Figure 15 (Notably, Figure 15 is adjusted to Figure 14 in the revised manuscript).

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Thank you for responding to the comments.