Variational Reduced-Order Modeling of Thermomechanical Shape Memory Alloy Based Cooperative Bistable Microactuators
Round 1
Reviewer 1 Report
Dear Authors
please find enclosed my review.
with best regards
Comments for author File: 
Comments.pdf
Author Response
Dear reviewer,
Please find the attached response letter.
Regards
Muhammad Babar Shamim
Author Response File: Author Response.pdf
Reviewer 2 Report
The paper deals with an interesting topical issue concerning the modeling of shape memory alloys (SMAs). As can be seen from the exposition and the numerical application, the proposed reduction of order method (ROM) contributes to the reduction of the calculation time with appropriate accuracy compared to the finite element method (FEM). In this regard, the paper is useful and has its undoubted merits.
Despite these undeniable benefits of the ROM idea, I would like some purely applied aspects of method development and its application, verification and validation to be clarified.
In the discussion of the results, the authors say that they investigated an actuator containing an SMA NiTiHf layer, a molybdenum layer, and a polymethyl methacrylate (PMMA) layer. Some actuator data as shown in Table 1 concerning the molybdenum layer, but it is not clear what the data is used for the SMA layer. More precisely, what are the thermal and the mechanical properties of the NiTiHf material? What is the relationship between these properties and the tensor quantities described in section 2 entitled "Modeling of the thermomechanical SMA based actuator"?
For modeling of the shape memory alloys the biggest challenge is the hysteresis in terms of displacement and temperature, force and temperature, and force and displacement (respectively stress and strain). It is not clear from the paper presentation how this problem was solved?
The comparison of MOR with FEM is in my opinion still not enough to validate the results. It would be more convincing for the developed method if the authors apply some experimental data.
Regarding bistability, could the authors clarify how the two stable states are defined? From the description, the reader is left with the doubt that bistability is more of a two-way shape memory effect than a mechanical transition that usually concerns triggering between two stable equilibrium states through an unstable equilibrium state of the beam. A little more information regarding the two bistable states and what they are due to will help to clarify the idea of bistability that is mentioned in the paper.
Author Response
Dear reviewer,
Please find the attached response letter.
Regards
Muhammad Babar Shamim
Author Response File: Author Response.pdf
Reviewer 3 Report
It is an interesting work on modelling of SMA based micro-actuators. I have some comments before I can recommend it to be published.
One of the drawbacks of SMA actuators is a low actuation speed caused by problems with thermal cooling (see for instance DOI: 10.1038/srep21118). One of the approaches was proposed using elastic substrate and SMA as tunable active layer (https://doi.org/10.1063/1.4998006 or https://doi.org/10.3390/nano8020116)
The proposed model may be of interest just I wonder whether authors can also provide some experimental comparisons or at least suggest some experiments similar to recently published by Samal et al. on PMMA combined with NiTi (https://doi.org/10.3390/polym14142932).
Author Response
Dear reviewer,
Please find the attached response letter.
Regards
Muhammad Babar Shamim
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
I agree with the changes and additions made and recommend that the paper be published.
