Experimental Study on the Effect of Humidity on the Mechanical Properties of 3D-Printed Mechanical Metamaterials

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

I appreciate the effort made by the authors. However, the research question is still weak - the degradation of the mechanical properties of the lattices with moisture will scale with the degradation of the mechanical properties of the polymer with moisture

Author Response

A1: I appreciate the effort made by the authors. However, the research question is still weak - the degradation of the mechanical properties of the lattices with moisture will scale with the degradation of the mechanical properties of the polymer with moisture

Q1: Thank you for your comment. We fully agree that the degradation of the mechanical properties of the lattices with moisture will scale with the degradation of the mechanical properties of the polymer with moisture. We would like to emphasize that the objective of this work was not to verify this general conclusion. Our focus is instead on comparing the mechanical performance of different metamaterials under the same RH and RD conditions. Since previous studies were conducted under inconsistent conditions, a systematic comparison was not feasible. In addition, we are particularly interested in investigating the negative Poisson’s ratio behavior of the metamaterials under various RH and RD conditions. We have modified the manuscript as follows:

 

From line #135 to #147:

“In this work, the performance of polymer-based metamaterials will be systematically evaluated as a function of RH and RD—two key factors governing moisture uptake, inter-layer bonding, and the overall mechanical response, which have not been comprehensively investigated before. This study aims to systematically quantify humidity-driven changes in mechanical response of architected lattices by measuring water-uptake kinetics under immersion to determine equilibrium moisture content and diffusivity for each polymer, characterizing tensile properties as a function of controlled RH to isolate hygroscopic effects on modulus, strength and ductility, and evaluating compressive performance of lattices across a combination of RD and RH while recording full-field strain and Poisson’s ratio via digital image correlation (DIC). Based on the above research, it is speculated that the negative Poisson’s ratio of each material varies with changes in RD and RH. However, whether this relationship is positive or negative still requires systematic investigation.”

 

We sincerely hope that the reviewer will recognize the value of our work in these other aspects.

Author Response File: Author Response.docx

Reviewer 2 Report (Previous Reviewer 4)

Comments and Suggestions for Authors

I thank the authors for their effort in improving the manuscript. I suggest accepting the manuscript for publication.

Author Response

Q1: I thank the authors for their effort in improving the manuscript. I suggest accepting the manuscript for publication.

A1: We sincerely thank the reviewer for all the comments and suggestions provided regarding this work, which have led to the improvement of this article. Thank you for your big support.

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

Comments to the authors

• Some general discussion must be excluded from the abstract like Lines 22-26 in abstract are not required.
• The references must be cited properly at the end of the statement eg. Ref [1].
• The author must try to explore the advantages of 3D printing by using the reverence doi.org/10.1016/j.jma pro.2025.08.002
• Quality of Fig. 2 can be improved
• Novelty of the work must be explored more clearly.

Author Response

Q1: Some general discussion must be excluded from the abstract like Lines 22-26 in abstract are not required.

A1: Thank you for your suggestion. We have removed these general discussions from line 22-26.

 

Q2: The references must be cited properly at the end of the statement eg. Ref [1].

A2: Thank you for your comment. We have revised the citation format:

 

From line #40 to #42:

“Mechanical metamaterials leverage precisely engineered geometries and internal porosity to achieve exceptional mechanical performance—combining low density, high strength and tunable deformation [1,2].”

 

Q3: The author must try to explore the advantages of 3D printing by using the reverence doi.org/10.1016/j.jma pro.2025.08.002

A3: Thank you for your suggestion and providing valuable reference. We have added this reference to our manuscript as follows:

 

From line #42 to #44:

“With the maturation of fused filament fabrication (FFF) and other additive manufacturing techniques [3,4], a variety of polymer filaments are now widely employed to fabricate functional metamaterial components.”

 

Ref. [3]:

[3]   A. Soni, P.C. Yadav, D. Veeman, J.K. Katiyar, Fruit waste-derived hybrid biofillers as a potential reinforcement in 3D printed biocomposites for building construction applications, Journal of Manufacturing Processes 152 (2025) 205–221. https://doi.org/10.1016/j.jmapro.2025.08.002.

 

Q4: Quality of Fig. 2 can be improved

A4: Thank you for your suggestion. We have improved the quality of Fig. 2.

Figure 2: please see the attachment

Figure 2. Sample structures used for compression testing of 3D‑printed mechanical metamaterials. The upper side shows the 3D‑printing models, from left to right at 25 %, 35 %, and 45 % RD. The lower side are the actual 3D‑printed samples at 25 %, 35 %, and 45 % RD, respectively, from left to right. The right side shows the unit-cell dimensions for lattices at 25 %, 35 %, and 45 % RD.

 

Q5: Novelty of the work must be explored more clearly.

A5: Thank you for your comment. In this work, the performance of polymer-based metamaterials was systematically evaluated as a function of environmental humidity and infill density—two key factors governing moisture uptake, interlayer bonding, and the overall mechanical response, which have not been comprehensively investigated before. The humidity-induced variations in the mechanical behavior of architected lattices were quantified by measuring water uptake kinetics under immersion to determine the equilibrium moisture content and diffusivity of each polymer. Furthermore, tensile tests were conducted under controlled RH conditions to isolate the hygroscopic effects on modulus, strength, and ductility. The compressive behavior of the lattices was also examined across different combinations of RD and RH, with full-field strain and Poisson’s ratio recorded using DIC. We have modified the manuscript as follows:

 

From line #135 to #147:

“In this work, the performance of polymer-based metamaterials will be systematically evaluated as a function of RH and RD—two key factors governing moisture uptake, inter-layer bonding, and the overall mechanical response, which have not been comprehensively investigated before. This study aims to systematically quantify humidity-driven changes in mechanical response of architected lattices by measuring water-uptake kinetics under immersion to determine equilibrium moisture content and diffusivity for each polymer, characterizing tensile properties as a function of controlled RH to isolate hygroscopic effects on modulus, strength and ductility, and evaluating compressive performance of lattices across a combination of RD and RH while recording full-field strain and Poisson’s ratio via digital image correlation (DIC). Based on the above research, it is speculated that the negative Poisson’s ratio of each material varies with changes in RD and RH. However, whether this relationship is positive or negative still requires systematic investigation.”

 

 

Author Response File: Author Response.docx

Reviewer 4 Report (New Reviewer)

Comments and Suggestions for Authors

1. Add a succinct study objective paragraph enumerating (A) water-uptake kinetics (immersion), (B) tensile under RH, (C) compressive RD×RH with Poisson’s ratio via DIC plus your hypotheses (e.g., hygroscopic polymers show mid-RH strengthening in tension due to improved interlayer slip; lattices shift Poisson’s ratio nearer zero with RD).
2. Provide thickness-normalized diffusion analysis: plot M_t/M_∞ vs √t and estimate D (Fickian fit) per material; the current “three-phase” narrative needs quantification.
3. Replace with in-chamber testing or a shroud and log RH at grips; alternatively, report weight just before/after testing to demonstrate negligible drift. Report time to equilibrium for each polymer at each RH (mass-change criterion and curve).
4. Include subset size, step, lens, calibration, gauge region definition, and strain window used to compute Poisson’s ratio; state whether ν is instantaneous (dε_trans/dε_ax) at small strain or averaged to a specified ε.
5. You claim “metamaterials are highly sensitive to structural changes” → support with references on humidity effects in printed lattices.
6. State infill pattern, raster angle, nozzle size, perimeter count for tensile samples. Provide unit-cell dimensions for lattices (length, thickness, angle).
7. Clarify why tension at 0.05 mm/s and compression at 0.5 mm/s (rate sensitivity?).
8. Relate humidity effects to DMA data only if humidity-conditioned DMA is performed; otherwise restrict to dry baseline.

Author Response

Q1: Add a succinct study objective paragraph enumerating (A) water-uptake kinetics (immersion), (B) tensile under RH, (C) compressive RD×RH with Poisson’s ratio via DIC plus your hypotheses (e.g., hygroscopic polymers show mid-RH strengthening in tension due to improved interlayer slip; lattices shift Poisson’s ratio nearer zero with RD).

A1: Thank you for your suggestion. We have added a paragraph to the manuscript as follows:

 

From line #135 to #147:

“In this work, the performance of polymer-based metamaterials will be systematically evaluated as a function of RH and RD—two key factors governing moisture uptake, inter-layer bonding, and the overall mechanical response, which have not been comprehensively investigated before. This study aims to systematically quantify humidity-driven changes in mechanical response of architected lattices by measuring water-uptake kinetics under immersion to determine equilibrium moisture content and diffusivity for each polymer, characterizing tensile properties as a function of controlled RH to isolate hygroscopic effects on modulus, strength and ductility, and evaluating compressive performance of lattices across a combination of RD and RH while recording full-field strain and Poisson’s ratio via digital image correlation (DIC). Based on the above research, it is speculated that the negative Poisson’s ratio of each material varies with changes in RD and RH. However, whether this relationship is positive or negative still requires systematic investigation.”

 

Q2: Provide thickness-normalized diffusion analysis: plot M_t/M_∞ vs √t and estimate D (Fickian fit) per material; the current “three-phase” narrative needs quantification.

A2: Thank you for your suggestions and comments. Unfortunately, we did not measure the change of thickness during the water absorption test, so we regret that the thickness-normalized diffusion analysis cannot be provided and discussed. We sincerely hope the reviewer could give us more time to systematically studied the water absorption behavior of metamaterials through thickness-normalized diffusion analysis and present it in our future work. Besides, as you pointed out, “three-phase” need the quantification. We have realized that this kind of description in the abstract was a bit fuzzy. The “different stages” would be more suitable. We have modified the manuscript as follows:

 

From line #26 to #28:

“The water absorption process can generally be divided into different stages—rapid uptake (0–12 h), a plateau (12–60 h), and a late rebound (60–100 h)—with total uptake ranking Nylon > PETG > PLA≈ABS > TPU≈PEEK.”

 

From line #282 to #289:

“In general, a thickness-normalized diffusion analysis [52] and a Fickian fit per material are required to evaluate whether a material is more prone to water absorption. However, in this study, the water absorption test represents only a minor aspect of the work. The main focus is on the effects of different RH and RD conditions on the mechanical properties of the mechanical metamaterials. Therefore, only mass measurements and a calculation of  were conducted to quickly assess their water absorption behavior. A more systematic and detailed study on water absorption will be carried out in future work.”

 

Q3: Replace with in-chamber testing or a shroud and log RH at grips; alternatively, report weight just before/after testing to demonstrate negligible drift. Report time to equilibrium for each polymer at each RH (mass-change criterion and curve).

A3: We thank the reviewer for this important and practical suggestion. Unfortunately, due to the limited time and equipment, we were not able to repeat mechanical testing inside a humidity chamber or to install a shroud and log RH at the grips prior to submission. We are sorry that we cannot report the weight just before/after testing to demonstrate negligible drift. Instead, we have repeated three times for the test to report the error and verify the reproducibility. If the reviewer allows, we would like to further study about that and report them in our future work. We sincerely appreciate the reviewer could give us a chance to improve our work. In addition, samples were conditioned for 24 hours to reach each RH and monitored using renkforce Thermo-/Hygrometer. We are sorry that we do not have the curve for mass change criterion. Samples were weighed periodically on an analytical balance until the mass change between consecutive 24-hour measurements was almost unchanged, at which point the specimen was deemed to have reached equilibrium moisture content. We have modified the manuscript as follows:

 

From line #203 to #213:

“To evaluate the mechanical performance of various 3D‑printed polymer materials and to assess the behavior of negative Poisson’s ratio metamaterials fabricated from different materials, samples were conditioned at 45 % and 95 % RH for 24 hours using a program-mable Memmert HCP50 chamber and monitored using renkforce Thermo-/Hygrometer. Additionally, a separate batch of samples were also dried using a PrintDry and monitored using renkforce Thermo-/Hygrometer, with humidity controlled at 15% to serve as the dry control group. Therefore, three groups of samples conditioned at 15%, 45%, and 95% RH were prepared, respectively. Samples were periodically weighed using an analytical balance until the change in mass between consecutive 24-hour measurements became negligible, indicating that the specimen had reached its equilibrium moisture content.”

 

Q4: Include subset size, step, lens, calibration, gauge region definition, and strain window used to compute Poisson’s ratio; state whether ν is instantaneous (dε_trans/dε_ax) at small strain or averaged to a specified ε.

A4: Thank you for your comments. We used software GOM Correlate 2019 to quantify Poisson’s ratio. The subset size is set as 25 pixels, the step is set as 1 pixel. Imaging was performed with a 50 mm macro lens and a Blackmagic Design 4K camera. The gauge region for analysis was defined as the central 80% of the gauge length (axial direction) and the central 80% of the specimen width. Another approach was also employed to measure the Poisson’s ratio: first, four points were selected on the surface of the image and connected to form two perpendicular line segments. Then, by measuring the change in distance, the strain variations in the x and y directions were obtained, as shown in the upper-left corner of the image. Based on these results, Poisson’s ratio of the material can be determined. During this process, the points were positioned as close to the edges as possible, unless image quality caused slight displacement of the tracked points. In such cases, the selected points were placed slightly closer to the inner side, as shown in the image. However, this does not affect the calculated Poisson’s ratio, especially since the experiments were repeated multiple times, yielding consistent and reliable results. In addition, since strain in both directions’ changes during deformation, the average value was taken from the relatively stable middle region. The results obtained from the two methods were generally consistent.

 

We have modified the manuscript as follows:

 

From line #220 to #229:

“Prior to testing, all specimens were speckle‑coated with edding 5200 permanent black-and-white spray for DIC, and deformation was recorded using a Blackmagic Design 4K camera with a 50 mm macro lens and analyzed by GOM Correlate software. The subset size is set as 25 pixels, the step is set as 1 pixel. The gauge region for analysis was defined as the central 80% of the gauge length (axial direction) and the central 80% of the specimen width. Then, transverse and longitudinal strains of the samples during deformation can be measured precisely to facilitate the calculation of Poisson’s ratio (here the averaged value was adopted), and they also provide qualitative visual evidence of local instabilities and slip deformation.”

 

Q5: You claim “metamaterials are highly sensitive to structural changes” → support with references on humidity effects in printed lattices.

A5: Thank you for your comment. This inference is based on the results of the PLA metamaterial. At all RH levels, the stress was found to increase significantly with increasing RD. In this section, we only discussed the effect of RD, without involving any humidity-related factors. However, the original description was indeed ambiguous, so we have revised it to refer specifically to the change in RD in the manuscript as follows:

 

From line #381 to #384:

“This suggests that PLA metamaterials are highly sensitive to RD changes. Previous study [57] has also demonstrated that brittle lattice metamaterials (rigid 10k resin) with a Kelvin lattice structure exhibit significant variations in stress and fracture strength with changes in RD.”

 

Q6: State infill pattern, raster angle, nozzle size, perimeter count for tensile samples. Provide unit-cell dimensions for lattices (length, thickness, angle).

A6: Thank you for your suggestions. For tensile specimen, the infill pattern was a 45° grid along the X-direction. The nozzle size is 0.4 mm. The layer height is 0.3 mm. The perimeter count is set as 1. We have modified the manuscript as follows:

 

From line #176 to #177:

“The infill pattern was a 45° grid along the X-direction. The nozzle size is 0.4 mm. The layer height is 0.3 mm. The perimeter count is set as 1.”

 

The unit-cell dimensions for lattices (from left to right: RD 25%, 35%, 45%) are as follows:  please see the attachment

We have added the information to the manuscript:

 

On page #5:

Figure 2: please see the attachment

Figure 2. Sample structures used for compression testing of 3D‑printed mechanical metamaterials. The upper side shows the 3D‑printing models, from left to right at 25 %, 35 %, and 45 % RD. The lower side are the actual 3D‑printed samples at 25 %, 35 %, and 45 % RD, respectively, from left to right. The right side shows the unit-cell dimensions for lattices at 25 %, 35 %, and 45 % RD.

 

Q7: Clarify why tension at 0.05 mm/s and compression at 0.5 mm/s (rate sensitivity?).

A7: Thank you for your question. In this study, we did not intend to compare tension and compression. The tensile rate of 0.5 mm/s was selected specifically for the nylon and TPU samples, as these materials exhibit very large strains at fracture. Therefore, the testing rate was increased accordingly. Although the strain rate can also affect the mechanical properties of materials, all tests in this work were conducted within the quasi-static range. For PEEK, PLA, PETG, and ABS, the tensile rate was set to 0.05 mm/s; for Nylon and TPU, a higher rate of 0.5 mm/s was used to accommodate their large elongation at break. Compressive tests were performed at 0.03 mm/s.

 

Q8: Relate humidity effects to DMA data only if humidity-conditioned DMA is performed; otherwise restrict to dry baseline.

A8: We thank the reviewer for this precise and important point. We agree that direct correlation between humidity-driven mechanical changes and DMA data is only valid if DMA measurements are performed under the same humidity conditioning. We did not perform humidity-conditioned DMA for this revision. Accordingly, we have removed speculative correlations between humidity effects and DMA-derived viscoelastic parameters and limited the manuscript discussion to comparisons with the dry-baseline DMA results. We now explicitly state the conditions under which DMA was conducted (no humidity control) in the Methods, and we note that humidity-conditioned DMA will be performed in future work to directly probe the viscoelastic changes under controlled RH. We have modified the manuscript as follows:

 

From line #194 to #197:

“Dynamic Mechanical Analysis (DMA) was conducted one time on the original solid specimens without humidity conditioning with the dimension of 30×5×1 mm by DMA8000 PerkinElmer (USA) to characterize their inherent viscoelastic properties and establish a dry/ambient baseline for subsequent humidity studies.”

 

From line #247 to #251:

“The DMA data presented here represent the dry/ambient baseline viscoelastic response of the polymers and are used only to provide a baseline mechanical characterization. Direct correlation of humidity-driven mechanical behavior with DMA metrics requires DMA to be performed under the same humidity conditioning and will be conducted in future work.”

Author Response File: Author Response.docx

Round 2

Reviewer 4 Report (New Reviewer)

Comments and Suggestions for Authors

The paper titled "Experimental study on the effect of humidity on the mechanical properties of 3D printed mechanical metamaterials" has been evaluated after the revision performance. 
It can be seen that the authors performed the required revisions step by step. In this form, enhanced revised paper meets the necessary criteria's of the journal and can be accepted.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article investigates the tensile, compression, and water absorption behaviour of six common fused filament fabrication polymers at three different relative densities. Overall, the manuscript is well written, and the discussion is constructively developed with reference to relevant literature.

1. Could the authors clarify whether there was a specific reason for selecting a low heating rate during the DMA test.

2. What was the intended purpose of employing DIC technology as described in the methods section. "Prior to testing, all specimens were speckle-coated with edding 5200 permanent black-and-white spray for digital image correlation, and deformation was recorded using a Blackmagic Design 4K camera and analysed using GOM Correlate software.".

3. The presentation quality of all figures should be improved to enhance the overall clarity and impact of the article.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper does not tackle any novel research question: that moisture has a plasticization effect on polymers is well known. The polymers under study (PEEK, PLA, PETG, ABS, Nylon, and TPU) are all commercial, well known and well-studied polymers, concerning their mechanical properties ( https://doi.org/10.3390/polym16030403 https://doi.org/10.1016/j.matpr.2024.05.018) as well as their moisture uptake (seehttps://doi.org/10.1021/ma202719x https://doi.org/10.1002/adv.1989.060090206 https://doi.org/10.1080/19447024908659452 https://doi.org/10.1016/j.polymertesting.2023.107962 https://doi.org/10.1016/j.matdes.2009.05.038 https://doi.org/10.1177/002199838902300501https://doi.org/10.1021/acsapm.2c01515 https://doi.org/10.1177/002199838902300501  

https://doi.org/10.1002/app.1989.070370207 https://doi.org/10.1063/1.4949611 https://doi.org/10.1016/j.eurpolymj.2014.02.001

The behavior of cellular solids is governed mainly by the relative density as well as the properties of the constituent solid is well known (Gibson, L. J., & Ashby, M. F. (1988). Cellular solids. Structure and properties, 2.). Thus the obtained changes in the mechanical properties with relative density are as expected, and the changes in the mechanical properties of the lattices as the properties of the polymer change with relative humidity are as expected. No knew knowledge or unexpected result stems from the work.

Further, there are some aspects of the methodology that remain unclear: the samples are conditioned in an environmental chamber, but for how long is not stated. There are no sorption-desorption data or tests stated so it is unclear if the samples reached saturation under those conditions or not. If is unclear if the samples were tested at the stated relative humidity conditions (in-situ mechanical testing inside an environmental chamber) or if the samples were removed from the environmental chamber and tested in ambient room conditions, and if so, for how long were there samples out of the chamber, and how much of the moisture could have desorbed in that time. This is fundamental to know if the reported behavior at the stated relative humidity corresponds indeed to the actual conditions in the samples or not.

There are some misled interpretations in the work. Throughout different parts of the work, changes in the mechanical properties with moisture are allocated to filling of the pores. However, filling of the pores only occurs with liquid water, and not with humidity, see https://doi.org/10.1016/j.polymdegradstab.2022.110009.

To correctly interpretate the effect of moisture on the mechanical properties, the dry samples should be used as benchmark. However, the tensile properties of dry specimens are not reported, i.e. in Figure 6. Thus, while the authors state that Nylon and TPU are more sensitive to moisture than PEEK because there is a higher difference between the different levels of relative humidity. However, it could well be that at 15% relative humidity, PEEK is already saturated with moisture, thus increasing the humidity level does not have an increasing effect, whereas for Nilon and TPU, there as an increasing effect with increasing humidity because at 15% r.h., the polymer is not yet saturated. If PEEK already exhibits plastitization at 15% r.H and the others not, it seams like PEEK would be the most sensitive polymer towards moisture and not the other way round. The dry data is necessary in order to draw correct conclusions.

Because of all the above, I must reject the paper.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Please find below my comments on the research paper entitled “Experimental Study on the Effect of Humidity on the 2 Mechanical Properties of 3D Printed Mechanical Metamaterials”. The comparison of the human body environment to humidity is somewhat misleading. For biomedical applications, it would be more appropriate to test the samples in relevant physiological fluids, such as artificial blood or simulated body fluids, rather than under humid conditions. Given this fundamental misconception and the lack of adequate experimental validation, I regret to recommend rejection of the manuscript in its current form.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The authors show a study investigating the influence of moisture on the mechanical and related properties of 3d printer metamaterials. The study is of interest to the community, and I appreciate that several materials were tested.

Unfortunately, I have several questions and there is experimental information missing. Please find a detailed list of my questions attached. I hope that these will help to improve the paper. Please add information regarding all these question to the text of your paper.

 

 

Introduction: The application in the human body was highlighted as a relevant area of application of 3d-printed metamaterials. The examples shown in figure 1 will in most cases bring a contact to liquid water, when the 3d-printed metamaterial is used in the human body. You tested storage conditions up to 95% humidity. Can you give evidence, that the results at 95% humidity and in liquid water will be comparable? Or should all the tests have been done with samples stored in liquid water, too?

 

 

Introduction: There is a long passage motivating the usage of PEEK. But there is no motivation for the other tested materials. Please shorten the motivation for PEEK and add relevant motivation for the other materials, too.

 

 

Chapter 2.1.: What was the orientation of the tensile specimens in the printer? Upright standing or flat? In which angle to the printer's X- or Y-axis? What was the printing orientation/angle of the solid layers or solid infill, 45/45 or 0/90 degree to the X- or Y-axis?

 

 

Figure 2: PETG, PLA and Nylon: Unfortunately, the photographs are quite dark, and the reader cannot identify details. Please alter the lightness and perhaps contrast of these three images. Or take new photographs and take care of the camera settings, to be able to show more details of the black material.

 

 

Chapter 2.2: Moisture measurements: “The dimensions of each printed specimen used for water-absorption testing are listed” I’m sorry, but I did not find this list. Please add the information. And please state, if the samples were printed as solid parts or as metamaterial? How was a possible drying done before weighting the samples?

 

 

Chapter 2.2: DMA: Please add the dimension of the specimen and please state, if the samples were printed as solid parts or as metamaterial.

 

 

Chapter 2.2: Line 172: “all specimens were conditioned at” How long were they conditioned?

 

 

Chapter 3.1.: Line 188: “PLA sample contain noticeable impurities”: In table 1 you give the information that the PLA filament used is “Prusa Galaxy Black PLA”. The term “galaxy” refers to glitter particles. Why did you choose this material and not a standard black one? And in addition: Why did you choose filaments of different colors, as the coloring agents and possible needed modifier could influence the material properties. Why did you not choose “natural” or the same color for all materials?

 

 

Figure 3: What is the direction of view? Is this a view onto the top (=the last printed layers) of the printed parts or onto the bottom (=the first printed layers, in contact with the build plate)

 

 

Figure 3: The shown delamination is a real delamination of several printed layers leading to freestanding walls in parallel to each other? Or is it a gap visible only in the first printed layer, which was in contact to the build plate? This can occur, when the distance of nozzle and build plate were not set correct.

 

 

Figure 3: The strings will to some extent influence the water update (as the surface are of the part is bigger) and the mechanical properties (as bridging strings take a mechanical load). Why did you not optimize the printing settings for each material before printing the final test specimen?

 

 

General: Please state in Chapter 2 for each test method or in the figure captions of figure 4 to 10, how many specimens were printed and tested per parameter set. Please state, if the value shown is a mean or a representative example taken from all measured specimens. For e.g. figure 4 I assume only one sample was measured, and the result is shown? For figure 5 x samples were measured and the mean as well as standard deviation are shown? For Figure 6, for each material and RH, Y samples were tested, but one representative measurement is shown?

 

 

Chapter 3.2.: Please state the dimensions of the 3D-printed samples used for the water absorption testing. Were the samples printed as solid parts or as metamaterial? If the samples were printed as solid samples, please give an information regarding the density of the dry printed samples and compare them to the theoretical density or the density of the filament and compare both. If the 3D-printed samples are porous to some extent, this will influence the water absorption. And if samples from different materials show a different increase in porosity, this will influence the comparability of the results from different materials. E.g. the water uptake of 3d-printed and non-3d-printed PETG is stated to be different. This might be induced by a higher porosity of 3d-printed parts?

 

 

Figure 9 a: Thanks for that figure, it is very informative! Just a little hint: The stars indicating D, E and F in the lower left picture cannot be seen very good. Perhaps change their color?

 

 

Chapter 3.4: Poisson’s ratio: How did you get the information needed to calculate the Poisson’s ratio? I assume from the digital images using the GOM Correlate software? What was the region of interest for the calculation, or was it calculated for several areas and the greatest Poisson’s ratio was chosen? Please explain this here or in chapter 2 more in detail. Relating to this, the data given in figure 10 shows single values. Or are the data points mean values of several samples? Then please give an error.

 

 

Appendix A1: What does “repeated results” refer to? I assume there were several samples produced and tested? Or was one samples measured several times, which I would interpret into “repeated results”, but this is for sure not the case here?

 

 

Table A1: Please improve the formatting and hence the readability of the data.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf