Car Soundproof Improvement through an SMA Adaptive System^†

Round  1

Reviewer 1 Report

The authors have described a novel solution based on SMA to reduce the inside car noise. They have widely described the concept, the finite element analysis and performed experiments validation.

The manuscript deserve publication after addressing the following points:

1. Part of this work was presented in a conference, Actuator 2018, not mentioned in any reference. Please, include it and describe how this study has improved the previous reported work.

2. SMAs are light and they have high power vs. weight ratio. Major problems are high consumption and fatigue reliability. Fatigue is related to the overall SMA strain, which is not described in detail in the manuscript. Please include the SMA strain. Also, include a detailed consideration of the fatigue issue in the conclusion including references.

3. System power consumption is reported 6.1 W (figure 18) although, page 4, line 131, is reported that in a car, a device power consumption should not exceed 5W per door. Can you describe this inconsistence?

4. If you assume that this system is used in 4 doors, the total power consumption will be at least 24.4W. The system, to work, needs to keep the SMA active, which means providing continuous power. This will create 2 problems. The first one will be the overheat of the car door, even if in a small section. The second one, is the high power consumption. Do you think this will be a problem in the design of an electrical car?

5. A strain gage is used to measure the deformation. It is well known issue related to the temperature drift in the measurement. In picture 12, it looks that only 1 strain gage is used, not in Winston bridge configuration. Can the authors describe how they managed this un-reliable measurement?

6. No details of the used strain gauge, i.e. brand and type, were reported. Please include it.

7. Figures have poor text resolution. Please update all of them and use the same fonts of the manuscript.

8. Section conflict of interest is the one in the “MDPI Actuator” template. It should be updated including any conflict of interest.

Author Response

Please find enclosed the file with point response to the arisen questions. We used a single file for all the reviewers. Reviewers ID and related comments are indicated in the first two columns of the table enclosed within the attached file. Moreover, in the attached manuscript those same responses are indicated by specific review notes. 

Would you accept our sincere thanks for making possible a significant upgrade of the work.

Kindest regards,

The authors.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper presents the design and implementation of a SMA-driven structure for soundproofing on gaps in car doors. The content related to SMA actuation is not new, but the implementation as a soundproofing is interesting. The paper's presentation needs improvement.

The most flagrant issues are related to Figure 6. The effect of the initial curvature on what? Show where h and L are on a diagram. What does each curve in Figure 6 correspond to (no legend)? What are the arrows pointing at? Both P_0 and P_cr are used, aren't they the same? Where can we see the values as a function of the distance from the origin since it is used in the explanation below Figure 6? What are the values of P_0 and P_cr?

Figure 3 a to f: Might be useful to show the state of SMA to better explain the concept.

Section 3.1: First sentence makes little sense, and titanium is not mentioned anywhere else in the text.

Page 3 line 200: It would be better to use the real name of the equation rather than calling it "the well-known equation"

Page 4 line 229: Four basic requirements refers to the system design requirements? Better to refer to it by name and section for clarity.

Page 6: Is it right that the Martensite start temperature higher than the Austenite start temperature? What is the manufacturer of the SMA wire?

Figure 10: Please add a legend for the temperature values of each curve.

Page 7 line 300: "A fused deposition modeling 3D printer was used to […]." Better to specify the technology and not to refer to it as a "3D ABS printer".

Page 7 line 305: "campaign" seems like the wrong word. Also found at other place in the text.

Figure 15: This appears as a black block in print.

Figure 16: Typo in bottom left picture

Page 10 line 345: Please spell out "FBG"

Page 10 line 350: "interrogated" seems like the wrong word.

Page 12 line 378: There is no such zone on Figure 21

Figure 21-22-24: It is not clear exactly where and how the system is installed

Figure 22: This figure is not referenced in the text.

Figure 25-26: Please add error bars. Results look more random than anything and there is no explanation related to why in some cases the sound is amplified. Again, these results appear random.

Author Response

Please find enclosed the file with point response to the arisen questions. We used a single file for all the reviewers. Reviewers ID and related comments are indicated in the first two columns of the table enclosed within the attached file. Moreover, in the attached manuscript those same responses are indicated by specific review notes. 

Would you accept our sincere thanks for making possible a significant upgrade of the work.

Kindest regards,

The authors.

Author Response File: Author Response.pdf

Reviewer 3 Report

In the work entitled “Car soundproof improvement through an SMA adaptive system”, the authors study the feasibility of system composed of expanding cells controlled by a SMA actuator activated by Joule effect for improving car soundproof by integrating that system in the doors seal cavity. The authors have developed a model for describing the SMA wire features, as well as designed and checked in lab a prototype, finding a significant noise level attenuation for the habitual gaps of the doors for the analyzed octave bands. 

The manuscript is well organized and clear, the results are novel and promising. In my opinion, the work deserves to be published. Nevertheless, with the aim to help the authors to improve the manuscript quality, I would like to mention some issues that should be addressed:    

 I really believe that the introduction could be shortened without loss of quality; for instance, I do not see the need of specifying all the research programs or all the aspects in which the industry focusses.

I would like the authors to explain the last system automotive requisite; basically, I would like to understand why the maximum power consumption should be 5 W.

Probably I have missed the composition of the SMA wire and its dimensions. But, in case that they have been omitted, I would suggest the authors to include such information. Besides, I would recommend adding any information about the thermal/mechanic fatigue of the SMA material, since it is one of the main drawbacks of the system.

Do the authors have any clue why the performance of the system decreases at larger gaps? Can it be related with the fact that, as the actuator is activated by Joule effect, the response is not fast enough? Could be improved by using a magnetic Shape Memory Alloy?

Minor concerns:

Please, use \Delta x and \Delta y instead Dx and Dy respectively, when possible.

In the conclusions, the sentence “providing detailed … on possible improvements” should be revised, since it has not been well established

Author Response

Please find enclosed the file with point response to the arisen questions. We used a single file for all the reviewers. Reviewers ID and related comments are indicated in the first two columns of the table enclosed within the attached file. Moreover, in the attached manuscript those same responses are indicated by specific review notes. 

Would you accept our sincere thanks for making possible a significant upgrade of the work.

Kindest regards,

The authors.

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper presents an actuator for active sealing adjustment based on SMA wires. The solution proposed adresses a well-known problem with state-of-the art sealing systems. The authors describe an interesting approach, but the paper is missing depth on the topic of SMA actuators.

I have several suggestions and comments that should be adressed:

-The introduction does not include a sufficient literature review on SMA actuators. Numerous possible actuators based on shape memory alloys have been presented before, the authors should review the literature on similar SMA actuators (and possibly other technologies besides SMA...)

-Also, this specific actuator has been presented at the Actuator Conference in Bremen, but this conference publication is not mentioned. It should be clearly stated in the introduction, which parts of this paper have been published before and what is the novelty described in this paper. Also, figures that have been used before have to be cited.

-Fig. 2 right: values on both axes could be useful

-Fig. 3 (g) is misleading:to reach point (f) the material had to be heated higher before, as point (f) is now on the "cooling" path again. The upper hysteresis should be drawn in higher, showing how the austenitic branch is reached through heating.

-In line 262, a specific SMA model [24] is chosen. Why is this specific model suited better than other published, well proven SMA models. A short review of the most popular SMA models and a comparison could help the reader understand, why the chosen model is best suited for this design problem.

-A general question: What is the reason for using superelastic wire instead of regular actuator wire (e.g. SAES smartflex 90°C)? The proposed solution means, that the material stress reaches over 600 MPa at about 30 N. Might be a concern looking at life cycle times? Also very high temperatures necessary for full transformation lead to a high energy consumption during the proposed activation. What is the reason not to use actuator wire, as their transformation temperature can be slightly increased by pre-stress to guarantee functionality at 80°C.

-During assembly of the actuator, how is the actual pre-stress determined or how do you guarantee a sufficient pre-stress for reaching 100% martensite (+)?

-What is the actual voltage used in this activation? Is it the automotive standard 12-14 V or what is the strategy on for controlling this actuator in the application?

-Have you considered a bi-stable SMA actuator as this application only requires two defined switching states? Bi-stable SMA actuators have been presented and could also solve the problem of high energy consumption during longer high-speed driving phases. Might be worth mentioning in the outlook, as the next steps described are not very specific

-Also how if not through design, is the energy management problem going to be adressed. at -50°C the energy consumption (also the electrical power necessary) will be much higher then the required 5 W.

-When usina a thermocouple to measure to wire temperature, how is the temperature of the wire affected, especially locally at the attachment point...

-Some minor grammar and spelling issues:

switching between past tense and present tense

typos: line 14 "field", 58 "Germany's", 60 "measure the noise", 65 "[18]18", 137 "an SMA", 218 "to the fact", 221 "values"?,

whole paper should be spell checked again.

Author Response

Please find enclosed the file with point response to the arisen questions. We used a single file for all the reviewers. Reviewers ID and related comments are indicated in the first two columns of the table enclosed within the attached file. Moreover, in the attached manuscript those same responses are indicated by specific review notes. 

Would you accept our sincere thanks for making possible a significant upgrade of the work.

Kindest regards,

The authors.

Reviewer 5 Report

In this work the authors describe the design and testing of an SMA-based actuator system which may be used for soundproofing purposes in cars. The analysis was conducted using Finite Element Analysis and analytical modelling on the separate plastic and SMA components respectively followed by experimental testing on a prototype. The concept is interesting and has been experimentally shown to be valid. However, certain aspects of the methodology used are unclear and the authors do not describe how their works fits with the current state of the art on SMA actuators and therefore the following changes should be made to improve the manuscript before it can be considered to be suitable for publication:

1)     The introduction is too focused on funding sources and their research aims. This part should be much briefer and to the point. It is more important from a scientific perspective to focus on introducing the state-of-the-art on SMA actuator systems and current soundproofing technologies employed in vehicles. An extensive re-write of this section of the manuscript is therefore necessary. A few suggestions for possible reference works for SMA actuators are proposed here, although additional relevant works should also be included:

 i)                 Bettini P, Riva M, Sala G, Di Landro L, Airoldi A, Cucco J. Carbon Fiber Reinforced Smart Laminates with Embedded SMA Actuators—Part I: Embedding Techniques and Interface Analysis. J Mater Eng Perform 2009; 18:664–71.

ii)                Spaggiari A, Dragoni E. Analytical and numerical modeling of shape memory alloy Negator springs for constant-force, long-stroke actuators. J Intell Mater Syst Struct 2013;25:1139–48.

iii)              Reynaerts D, Brussel H Van. Design aspects of shape memory actuators. Science

iv)              Nespoli A, Besseghini S, Pittaccio S, Villa E, Viscuso S. The high potential of shape memory alloys in developing miniature mechanical devices: A review on shape memory alloy mini-actuators. Sensors Actuators, A Phys 2010;158:149–60.

v)                Ishii H, Ting KL. SMA actuated compliant bistable mechanisms. Mechatronics 2004;14:421–37

vi)              Renata C, Huagn WM, He LW, Yang JJ. Shape change/memory actuators based on shape memory materials, J. Mech. Sci. Tech 2017; 31;10; 4863-4873

2)     In section 2, the authors describe a number of system automotive requirements – it would be useful if they were to provide a reference to the guidelines or laws which specify these requirements.

3)     In section 3, there is some confusion on the description of the SMA effect. The authors state that upon stretching the austenitic SMA wire it undergoes a full martensitic transformation. This is not technically correct – upon stretching an austenitic phase SMA one may only reach a detwinned martensitic phase, which is part of the superelastic regime used to describe austenitic material behaviour. The term ‘martensitic SMA’ is used to describe the ‘cold’ state behaviour of an SMA material where upon stretching and releasing the SMA it does not return to its original shape, i.e. it undergoes a twinned to detwinned martensitic transformation which is only reversable by heating the material to undergo an austenitic transformation and then recooling it to reachieve a twinned martensitic state. The behaviour described in this paper on the other hand involves induced actuation as a result of the difference between a lower and a higher temperature austenitic phase and the occurring transformation as a result of heating is from detwinned martensite to austenite. This part (line 149-167) should be corrected using the proper nomenclature.

4)     The same applies to Figure 3.

5)     The geometric parameters used to describe the cell shape should be indicated in Figure 4 or 7.

6)     There is a typo in Table 2, “Poisson’s modulus” should be Poisson’s ratio. And how is the wire cross-sectional geometry incorporated in the SMA model? 

7)    The authors should also provide information on the SMA material used, i.e. type, brand … A curve fitting of the analytical model onto the experimental stress-strain behaviour of the SMA at various temperatures should also be included in order to allow for a comparison of the goodness of the fit.

8)     The article lacks a general discussion on the acoustic results (section 5). The authors show in Figures 25 and 26 that generally the decibel level decreases upon activation of the SMA system, however at certain octave orders it actually increases. The authors should discuss and provide possible explanations for this behaviour. In addition, while the overall SMA system expands upon activation, the effective porosity of the unit cell increases. Does this affect the soundproofing properties of the device?

9)     There are a number of anacronyms within the text which are not defined such as TRL, LVDT and FBG and make it difficult to follow.

Author Response

Please find enclosed the file with point response to the arisen questions. We used a single file for all the reviewers. Reviewers ID and related comments are indicated in the first two columns of the table enclosed within the attached file. Moreover, in the attached manuscript those same responses are indicated by specific review notes. 

Would you accept our sincere thanks for making possible a significant upgrade of the work.

Kindest regards,

The authors.

Author Response File: Author Response.pdf

Round  2

Reviewer 2 Report

All comments have been taken into account. Two minor revision:

Poisson's ratio, not modulus

The text in Figure 16 should be in English.

Author Response

Please, would you consider the file attached, the same both the reviewers.

Thank you again fro your fruitful suggestions.

Author Response File: Author Response.pdf

Reviewer 4 Report

Thank you for the extensive review of the paper and answering most of my questions.

- I still think Fig. 3 should be corrected: when the SMA wire is heated, the equilibrium point of SMA hysteresis and bias force will always be on the dashed line. Thus, to reach the austenite slope, the red dashed line has to intersect the bias force curve. If the SMA then cools down, the equilibrium point will be "pulled down" by the solid (upper) part of the hysteresis curve.

- The biggest issue of the system stays the energy consumption problem. The authors mentioned solutions like bistability, and solutions suited for this actuator have been published before. These patented solutions should be listed (maybe also on the conclusion/outlook):

US020130081933A1

WO002017194591A1

US000005977858A

- Also the control strategy itself is likely to lead to better energy efficiency. The authors mentioned that the necessary voltage is lower than automotive standard. It has been shown, that activation with higher voltages generally leads to better energy-efficiency (maybe in combination with a PWM) and should thus be mentioned:

A fast and powerful release mechanism based on pulse heating of shape memory wires

Y Malka, D Shilo - Smart Materials and Structures, 2017

High-Speed and High-Efficiency Shape Memory Alloy Actuation

P Motzki, T Gorges, M Kappel, M Schmidt, G Rizzello… - Smart Materials and Structures, 2018

Thank you again for adressing all my comments

Author Response

Please would you consider the file attached, the same for both the reviewers.

Thanks again once more for your fruitful indications.

Author Response File: Author Response.pdf