Fast Electrical Activation of Shape Memory Alloy Spring Actuators: Sub-Second Response Characterization and Performance Optimization
, Matteo Chiodo 2, Antonio Corigliano 2, Giuseppe Rota 2 and Carmine Maletta 1,2Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper studied the rapid appearance of shape memory effect in tensioned springs by Joule heating under large current. The term "Optimization" in the title means there is the upper limit of applied current not to raise temperature too high. Although these conclusions may be self-evident, but it may have a significance in the field of robotics. I would like to recommend this paper be published in the journal if the following points are reconsidered.
1. Readers may wonder why the authors mentioned “current density” in Line 11 of Abstract, but it did not consider later. It is easily seen that the rate of adiabatic temperature rise by Joule heating is proportional to the square of current density, but not that of current. For springs with different spring-constants, the difference in cross-section area should be the principal factor determining the heating rate.
2. All equations in the section of 2.2.2. Systematic Stress Level Selection are exactly same as those in [42]. You mentioned “To achieve this, classical spring theory [43] is combined with a simplified approach proposed by An et al. [42]” , but it is not enough to show courtesy to the original authors, An, et al [42].
3. Similarly, the analysis of An, et al.[42] considers the change in the pitch angle from the initial magnitude. The initial pitch angles of the springs used at this study should be listed in Table.
4. The “activation time, tA” in Fig.9 and 10 are the principal results of this study leading Conclusions. I cannot find the method to draw the contour lines in these figures.
5. It looks like in Fig.9 and 10 that the experiments were performed to control the “holding time, tM” not to exceed the temperature over 160C. Readers would like to know how to determine the duration of square waves.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper investigates the fast electrical activation characteristics of NiTi shape memory alloy spring actuators, and the results have certain engineering significance. The overall research idea is clear and the experimental data are relatively sufficient, but the innovation and theoretical depth need to be further improved. The authors are advised to highlight the originality of the work and streamline the writing in the revised version. Specific comments are as follows:
1. The authors should further clarify the differences and improvements of this study compared with previous works to better emphasize its innovation.
2. Several symbols are not clearly defined, such as K_B in Eq. (1) and G and E in Eq. (2); please provide definitions in the manuscript.
3. The authors determine the final inclination angle by inverting Eq. (4), which contains two angle variables. Please specify which angle is being solved and its physical meaning.
4. The discussion of experimental results is mainly descriptive; it is recommended to further analyze the underlying mechanisms and physical reasons to enhance the persuasiveness of the conclusions.
5. It is recommended to supplement relevant references in the Introduction to enhance the literature review.
R1: Finite-Iteration Learning Tracking Control of Magnetic Shape Memory Alloy Actuator Based on Neural Network, DOI: 10.1109/TCSII.2025.3619257.
R2: 3-D Meso-Scale Finite Element Calculations of Free Energy on Twin Boundaries in Magnetic Shape Memory Alloys, DOI:10.1109/TMAG.2024.3404333.
R3: Magnetic Field Sensing With Magnetic Shape Memory Alloy and Fiber Bragg Grating on Silica and Polymer Optical Fibers, DOI: 10.1109/TIM.2025.3554890.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsContributions of this paper is at several levels: characterization of SMA-based high speed spring actuators (thermal, mechanical and material parameter), dynamic response analysis with high-current electrical activation, and guidelines with performance mapping for engineering design applications. Authors investigated fast actuation for different SMA springs. The results are very interesting for people that use SMA actuators.
The state of the art is up-to-date and relevant for the article. Experimental Results are numerous and impressive. You can find some comments below.
Fig1a and b are interesting, notably with comparisons of wire diameters, but the different graphs cannot be seen properly. You may change colors or change markers to show the differences between them.
l.64 MRI is not defined.
In equation (5), you introduced a variable C that seems to be a mistake.
Texts in Figure 4 are too small to read.
Even if the numbers are too small, the idea of putting the spring on the graphs is great. Fig.5 is nice.
In FIg.6, you have recovery displacement that goes from 20% to more than 700, but you did not discuss this point. You may add more information about this point that is quite important for different applications.
l.353 there is a typo with MPa/C.
In 3.2, you said that you have been carried out tests at two different load states for each spring, but it is not the case for the first one.
In Fig8, from my point of view, this graph is not the most important, tm could be added on (b) It may be interesting to have a detailed view of individual activation with current and temperature.
You may give more information about how to use properly the graph 9 and 10 to get, for example, the results written from 396 to 398. Those are very interesting, but i did not see how those graphs could tell you this information.
In table 4, you but a OK mark for 11.5 and not for 7, is it really the case or a typo. If it is really the case, I think more information should be given on why it is not working for 7 and 8.5 for spring 8.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsAll of my inquiries are answered, and corresponding writing are added. I have still some questions, but it will be done by readers after the draft is open to public. One minor suggestion is that all figure captions should be ended with a period.
Author Response
Thank you, fixed figure captions and tables also.
Reviewer 2 Report
Comments and Suggestions for AuthorsHowever, the author still has some issues that need to be addressed. I have noticed that many of the information in the references is incomplete or incorrect, and needs to be corrected one by one. For example, the author information of references 7, 20, 26, especially reference 24, is incorrect.
Author Response
We thank the reviewer for noting some inconsistencies within the references. However, we are confident that all information in the references is correct, as they are managed through Zotero, which automatically extracts bibliographic information. We have now modified the citation style to IEEE format to better align with other MDPI Actuators papers. We respectfully note that manually correcting each individual reference would not be an efficient use of our time, as we rely on Zotero a widely recognized and commonly used reference management software in the scientific community.
