Compressive Behaviour of 3D-Printed PETG Composites

Round 1

Reviewer 1 Report

The manuscript reported the compressive properties of PETG and PETG reinforced with carbon and aramid fibres were analysed in terms of static properties and viscoelastic behaviour. Moreover, a study on stress relaxation and creep behaviour based on viscoelastic behaviour of these materials for long loadbearing periods is evaluated and some conclusions are drawn. The article is clear and well detailed in the parts that more interest scientific researcher to understand the characteristics of the model and probably in compressive behaviour of 3D printed PETG composites.  This kind of paper is what is necessary for our scientific community in order to understand and spread the knowledge about mechanical properties for design criteria. However, there are some issues in the manuscript and hope the author can improve it.

1. Abstract/Conclusion :

To give the reader a briefly introduction of the manuscript and helps readers decide whether they want to read the rest of the paper. Usually includes: 1) the overall purpose of the study and the research problem(s) you investigated; 2) the basic design of the study; 3) major findings or trends found as a result of your analysis; and, 4) a brief summary of your interpretations and conclusions.Please rewrite them precisely and concisely. 

    2. Literature review:

Please give a summary of the references and state why this study is needed and how it contributes to the academic research.

    3. Materials and Methods :

• The study is purely experimental and has no mathematical approach.
• Only one size of specimens dimensions is considered for the study which is not sufficient as different dimensions are used through the industry.
• The absence of mathematical modelling of the experiments limits its scope to extend the study for different material constructions.
• Addition the properties of materials for each printing material (PETG, PETG+CF, PETG+KF), and listed in table. 

4. References :

• Add references to standard printed ASTM D695-15 and Compressive tests standard ASTM D695-15
• The reason for selecting the sizes of specimens dimensions is not supported by any reference.

Author Response

The manuscript reported the compressive properties of PETG and PETG reinforced with carbon and aramid fibres were analysed in terms of static properties and viscoelastic behaviour. Moreover, a study on stress relaxation and creep behaviour based on viscoelastic behaviour of these materials for long loadbearing periods is evaluated and some conclusions are drawn. The article is clear and well detailed in the parts that more interest scientific researcher to understand the characteristics of the model and probably in compressive behaviour of 3D printed PETG composites. This kind of paper is what is necessary for our scientific community in order to understand and spread the knowledge about mechanical properties for design criteria. However, there are some issues in the manuscript and hope the author can improve it.

Response: Thank you for your comments and appreciation of our work.

1. - Abstract/Conclusion: To give the reader a briefly introduction of the manuscript and helps readers decide whether they want to read the rest of the paper. Usually includes: 1) the overall purpose of the study and the research problem(s) you investigated; 2) the basic design of the study; 3) major findings or trends found as a result of your analysis; and, 4) a brief summary of your interpretations and conclusions. Please rewrite them precisely and concisely.

Response: The text was improved according to the reviewer’s suggestion “Abstract: 3D printed PETG composites reinforced with carbon or Kevlar fibres are materials that can be suitable for specific applications in the aeronautical and/or automotive sector. However, for this purpose, it is necessary to understand its mechanical behaviour, which is not yet fully understood in terms of compression. Therefore, this study intends to increase the knowledge in this domain, especially in terms of static behaviour, as well as with regard to creep and stress relaxation due to the inherent viscoelasticity of the matrix. In this context, static, stress relaxation and creep tests were carried out, in compressive mode, using neat PETG and PETG composites reinforced with carbon and Kevlar fibres. From the static tests, it was found that the yield compressive strength decreased in both composites compared to the neat polymer. Values around 9.9% and 68.7% lower were found, respectively, when carbon and Kevlar fibres were added to the PETG. Similar behaviour was observed for compressive displacement, where a reduction of 20.4% and 46.3% were found, respectively. On the other hand, the compressive modulus, increased by 12.4% when carbon fibres are added to the PETG matrix and decreased by 39.6% for Kevlar fibres. Finally, the stress relaxation behaviour revealed a decrease in compressive stresses over time for neat PETG, while the creep response promoted greater compressive displacement. In both situations, the response was very dependent on the displacement/stress level used at the beginning of the test. However, when the fibres were added to the polymer, higher stress relaxations and compressive displacements were observed.”.

2. Literature review: Please give a summary of the references and state why this study is needed and how it contributes to the academic research.

Response: The text was improved according to the reviewer’s suggestion for “… Therefore, from the literature [2–7] it is evident that PETG and PETG-based composites have applications in many industries due to their resistance to heat, impact and solvents. In terms of compressive properties, the focus of the present study, literature is not abundant on this topic and what exists is not enough to establish a consolidated knowledge [13–17], because most of the available studies focus essentially on the tensile mode. On the other hand, as consequence of the inherent viscoelasticity of the matrix phase, polymer composites are prone to creep and stress relaxation, making it a great challenge when used in long-term applications. However, in terms of creep and stress relaxation behaviour these subjects are totally absent in the open literature for PETG and PETG-based composites, limiting their use in many applications due to lack of knowledge. In this context, the novelty of this study is related to the effect of fibre type on the compression properties of PETG-based composites, to consolidate knowledge, but essentially at level of creep and stress relaxation behaviour due to the absence of studies in this domain. For this purpose, an experimental study will be developed to characterize the compressive properties of PETG and PETG reinforced with carbon and aramid fibres, as well as the stress relaxation and creep behaviour of these materials …”.

3. Materials and Methods: The study is purely experimental and has no mathematical approach.

Only one size of specimens dimensions is considered for the study which is not sufficient as different dimensions are used through the industry.

The absence of mathematical modelling of the experiments limits its scope to extend the study for different material constructions.

Addition the properties of materials for each printing material (PETG, PETG+CF, PETG+KF), and listed in table.

Response: The authors designed the article for the mechanical characterization of the materials. For this purpose, the procedure, equipment and respective dimensions of the specimens are in accordance with ASTM standards. In this context, what we intend to disclose are the mechanical properties and not mechanical behavior for industrial applications. The industry has in this case the mechanical properties of the materials and if they are useful for the development of certain applications, it does not invalidate that the component produced is tested for the purposes for which they are proposed. In other words, we aim to provide mechanical properties and not mechanical performance of components. In terms of mathematical models, we intend to offer in the future a tool that can serve as a prediction, but, at the moment, this work only focuses on experimental characterization. Finally, this article aims to present the compression properties of different PETG-based materials. They are summarized in Table 2. Regarding the mechanical properties of the filaments, they are outside the focus of this work.

4. References: Add references to standard printed ASTM D695-15 and Compressive tests standard ASTM D695-15. The reason for selecting the sizes of specimens dimensions is not supported by any reference.

Response: The text has been improved according to the reviewer's suggestion. The ASTM standard has been included in the references section and the dimensions of the specimens are in accordance with the ASTM D695-15 standard, which was conveniently referred to in the text. However, authors improved the text to be clearer for “… Using this equipment and methodology (see Figure 1), specimens with dimensions of 12.7×12.7×25.4 mm³ were printed, values that are recommended by the ASTM D695-15 standard …”.

Author Response File: Author Response.docx

Reviewer 2 Report

The article 'Compressive behavior of 3D Printed PETG composites' presents the results and discussion of compression tests on printed PETG composites. The article does not contain relevant data for the scientific area. However, it is possible to enrich the manuscript with some additional evidence and information.

introduction section

The authors could add other studies and analyses on 3D printed composites and their study in terms of viscoelasticity. Please review the article Characterization of 3D Printing on Jute Fabrics published in Polymers 2021, 13 (19), 3202; https://doi.org/10.3390/polym13193202

materials section

The authors do not explain where they obtained the PETG and PETG + CF and PETG + KF composites. Are these materials commercial? Were the materials prepared in the laboratory? Please complete the information.

Table 1, authors should add the second decimal (40?) In layer height.

Table 2, authors should include the std dev values ​​as ± in the average values. Please eliminate the second row (average value - std dev)

The manuscript is explained correctly. However, it is necessary to add some photographs of the printing process, specimens, materials, and compression tests. Do the materials deform during the test? Please add these photos and discuss them

Throughout the manuscript and in the conclusions section '… PETG and PETG reinforced with carbon and aramid fibers were analyzed in terms of static properties and viscoelastic behavior…'. The word viscoelasticity is highlighted, but I consider that the correct analysis of viscoelastic properties could be performed in the DMA instrument, not just with a creep test. The authors should modify these sentences or perform the DMA tests. Pay attention to the third paragraph as well and the entire manuscript.

Author Response

The article 'Compressive behavior of 3D Printed PETG composites' presents the results and discussion of compression tests on printed PETG composites. The article does not contain relevant data for the scientific area. However, it is possible to enrich the manuscript with some additional evidence and information.

Response: Thank you for your comments and appreciation of our work.

1. - Introduction section: The authors could add other studies and analyses on 3D printed composites and their study in terms of viscoelasticity. Please review the article Characterization of 3D Printing on Jute Fabrics published in Polymers 2021, 13 (19), 3202; https://doi.org/10.3390/polym13193202.

Response: The text was improved according to the reviewer’s suggestion for “… Therefore, from the literature [2–7] it is evident that PETG and PETG-based composites have applications in many industries due to their resistance to heat, impact and solvents. In terms of compressive properties, the focus of the present study, literature is not abundant on this topic and what exists is not enough to establish a consolidated knowledge [13–17], because most of the available studies focus essentially on the tensile mode. On the other hand, as consequence of the inherent viscoelasticity of the matrix phase, polymer composites are prone to creep and stress relaxation, making it a great challenge when used in long-term applications. However, in terms of creep and stress relaxation behaviour these subjects are totally absent in the open literature for PETG and PETG-based composites, limiting their use in many applications due to lack of knowledge. In this context, the novelty of this study is related to the effect of fibre type on the compression properties of PETG-based composites, to consolidate knowledge, but essentially at level of creep and stress relaxation behaviour due to the absence of studies in this domain. For this purpose, an experimental study will be developed to characterize the compressive properties of PETG and PETG reinforced with carbon and aramid fibres, as well as the stress relaxation and creep behaviour of these materials. …”.

2. Materials section: The authors do not explain where they obtained the PETG and PETG + CF and PETG + KF composites. Are these materials commercial? Were the materials prepared in the laboratory? Please complete the information.

Table 1, authors should add the second decimal (40?) In layer height.

Table 2, authors should include the std dev values as ± in the average values. Please eliminate the second row (average value - std dev).

The manuscript is explained correctly. However, it is necessary to add some photographs of the printing process, specimens, materials, and compression tests. Do the materials deform during the test? Please add these photos and discuss them.

Response: The text was improved according to the reviewer’s suggestion. For example, authors included the supplier of the materials used “Therefore, given the benefits reported for these materials, PETG, PETG+CF and PETG+KF were the filaments selected to obtain the specimens used in this study. While PETG composites containing fibres were supplied by Nanovia (Louargat, France), neat PETG was supplied by FilTech (Baesweiler, Germany)”.

In Table 1, authors included the second decimal place (0.40) in the layer height.

In Table 2, authors included the std dev values as ± in the average values and eliminated the second row.

Finally, authors included some photographs related with the experimental work and respective comments.

3. Throughout the manuscript and in the conclusions section '… PETG and PETG reinforced with carbon and aramid fibers were analyzed in terms of static properties and viscoelastic behavior…'. The word viscoelasticity is highlighted, but I consider that the correct analysis of viscoelastic properties could be performed in the DMA instrument, not just with a creep test. The authors should modify these sentences or perform the DMA tests. Pay attention to the third paragraph as well and the entire manuscript.

Response: As suggested by the reviewer, authors changed the term “viscoelastic behavior” to “creep and stress relaxation behavior”.

Author Response File: Author Response.docx

Reviewer 3 Report

I have reviewed the paper entitled “Compressive behaviour of 3D Printed PETG composites”. The study investigates the compressive properties of components manufactured Additive Manufacturing procedures like Fused Deposition Modelling. The feedstock material that was employed was a neat PETG and PETG reinforced with carbon and Kevlar fibres. In general, the research is interesting and I would like to congratulate the authors for their work. The paper is well written, the results are promising, although I have some comments that should be addressed:

1. The need for the study and novelty of this work should be added in the Introduction Section with more clarity.
2. You could include clear figures from the experimental procedures that you applied in the study.
3. Why did you not use the same printing parameters in each investigated case? Print speed and layer height could influence the mechanical behavior of the printed components, hence the attained results.
4. The explanation of the attained results should be described in more depth concerning the alterations on the fixed strain (25%, 50% and 75%).
5. Can the results and the conclusions of your study be employed in situations where other printing parameters will be utilized? Please validate your answer with experimental results.

Author Response

I have reviewed the paper entitled “Compressive behaviour of 3D Printed PETG composites”. The study investigates the compressive properties of components manufactured Additive Manufacturing procedures like Fused Deposition Modelling. The feedstock material that was employed was a neat PETG and PETG reinforced with carbon and Kevlar fibres. In general, the research is interesting and I would like to congratulate the authors for their work. The paper is well written, the results are promising, although I have some comments that should be addressed.

Response: Thank you for your comments and appreciation of our work.

1. - The need for the study and novelty of this work should be added in the Introduction Section with more clarity.

Response: The text was improved according to the reviewer’s suggestion for “… Therefore, from the literature [2–7] it is evident that PETG and PETG-based composites have applications in many industries due to their resistance to heat, impact and solvents. In terms of compressive properties, the focus of the present study, literature is not abundant on this topic and what exists is not enough to establish a consolidated knowledge [13–17], because most of the available studies focus essentially on the tensile mode. On the other hand, as consequence of the inherent viscoelasticity of the matrix phase, polymer composites are prone to creep and stress relaxation, making it a great challenge when used in long-term applications. However, in terms of creep and stress relaxation behaviour these subjects are totally absent in the open literature for PETG and PETG-based composites, limiting their use in many applications due to lack of knowledge. In this context, the novelty of this study is related to the effect of fibre type on the compression properties of PETG-based composites, to consolidate knowledge, but essentially at level of creep and stress relaxation behaviour due to the absence of studies in this domain. For this purpose, an experimental study will be developed to characterize the compressive properties of PETG and PETG reinforced with carbon and aramid fibres, as well as the stress relaxation and creep behaviour of these materials. …”.

2. You could include clear figures from the experimental procedures that you applied in the study.

Response: Authors included some photographs related with the experimental work and respective comments.

3. Why did you not use the same printing parameters in each investigated case? Print speed and layer height could influence the mechanical behavior of the printed components, hence the attained results.

Response: Yes, authors agree with the reviewer. However, the criterion of maximum mechanical performance was adopted, because in any structural application we expect, in general, to maximize the mechanical properties. It was on this assumption that the paper was designed and for this purpose, previous studies were carried out to obtain the parameters that maximize the properties for each material and, consequently, it was with these values that the study was prepared. However, to clarify the readers, the following text has been included “… Different printing parameters were used, and Table 1 shows those that maximized the mechanical properties of these materials. For this purpose, a study was previously carried out. The criterion of maximum mechanical performance was adopted, because in any structural application we expect, in general, to maximize the mechanical properties …”.

4. The explanation of the attained results should be described in more depth concerning the alterations on the fixed strain (25%, 50% and 75%).

Response: The text was improved according to the reviewer’s suggestion for “… layers can also contribute for the observed decrease. Regarding the displacement effect (correspondent to 25%, 50% and 75% of the yield compressive stress), it is possible to observe that its increase promotes higher stress relaxation due to a change in the mechanisms mentioned above. For example, at lower displacement levels, stress relaxation is mainly induced by the molecular rearrangements and/or chain scission, while for higher displacement levels it is due to damage and its propagation. This is line with the studies developed by Mirzae et al [30], where these authors also observed that increasing the strain level promotes more stress relaxation … motion in backbone polymer arrangement [31–34]. It is also possible to notice that the stress levels significantly influence the creep displacement of the material. This behaviour agrees with what has been described for stress relaxation and is also justified by the change in the previously reported mechanisms. In this case, at lower stress levels, creep is mainly induced by molecular movements, while at higher stress levels, creep is dominated by damage and its propagation. For the highest stress levels, the load transfer on the interface regions is significantly affected and, inclusively, some debonding are expected [22]. However, as displacement is held constant in stress relaxation, any mechanism reported above will have a lower severity than in creep, because the deflection is always increasing [22] …”.

5. Can the results and the conclusions of your study be employed in situations where other printing parameters will be utilized? Please validate your answer with experimental results.

Response: Obviously, the results obtained will be different for other printing parameters. Once again, the authors mention that the present article was designed to maximize mechanical properties because, in general, these are what govern most structural applications. However, what the reviewer requests would be another work similar to this one that would take too long for the available review period. Nevertheless, authors intend to carry out this study in order that the results obtained can be used in very specific applications. However, to alert readers to the different print parameters used, the following sentence has been included “… Different printing parameters were used, and Table 1 shows those that maximized the mechanical properties of these materials. For this purpose, a study was previously carried out. The criterion of maximum mechanical performance was adopted, because in any structural application we expect, in general, to maximize the mechanical properties …”.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The article covers the modifications suggested.