Nondestructive Hardness Assessment of Chemically Strengthened Glass

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors

Thank you for submitting an interesting paper.

 

I would like to make the following comments after reviewing the paper.

- Confirm the normality of Vickers Hardness and NER data

- The type of correlation analysis varies depending on the normality of the above data, so it needs to be clearly stated.

1) If the normality of the data is secured, Pearson correlation analysis should be applied,

2) If the normality of the data is not secured, Spearman correlation analysis should be used.

- The statistical tool for correlation analysis should be disclosed.

- Although the graph in Figure 4 is meaningful, a scatter plot of only Vickers Hardness and NER data should be presented.

- The value of R2 = 0.8±0.1 in line 211 is very important, but the p value, which is the result of the significance test, should also be presented.

- In supplementary file, I need to explain how to measure the elastic modulus,
  and I don't think the elastic modulus can decrease as the hardness increases.
  Please explain why this phenomenon occurs.
  (ref. Journal of Non-Crystalline Solids 664 (2025) 123596)

Author Response

The responses to the reviewer’s comments and questions are provided in the attached PDF file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The main question addressed by the research:

Hardness is a decisive property of chemically strengthened glass e.g. in display applications. Long term performance and even high strength require high hardness. The compressive stress introduced into the surface by ion exchange is supposed to affect nonlinear ellipse rotation NER of polarized light. The authors investigate whether there is a correlation between classical indentation tests for hardness and the NER signal.

Up to date, reliable data on hardness result from destructive examination of random samples. Any hints on hardness by tests that do not imply hurting the surface would be of great help. The proposed method does not even touch the surface of interest. For sufficient local resolution, however, it has to be shown that the caustic of the laser allows for discerning the exchanged zone from the center of the panes. The thickness of the zone under compressive stress is in the range of a few ten µm. Brillouin spectroscopy, e.g., has been shown to assess the refractive index changes in thermally strengthened glass, but in this case the altered zones are much wider, in the range of 1/6 of the thickness on both sides. Other alternative method are quoted and described in appropriate form in the manuscript.

In contrast to other proposed methods, the sample is irradiated in z-direction, observed in transmission and moved along the z-axis. There are other optical methods that observe in the xy plane and require perfect edge preparation. Here, nonlinear effects are exploited, which are also relevant for upcoming applications of strengthened glass in nonlinear optics.

Specific improvements should the authors consider regarding the methodology

It is mentioned that thermally strengthened glass has also been investigated. In many cases, lower hardness has been reported for tempered glass, compared to untreated glass. The maximum stress in the surface is typically lower than for chemically strengthened glass. In future, the methodology could be improved by measuring more of such glasses, glasses with different thicknesses and other types than Gorilla® to gain a better explanation of structure related changes of index, nonlinear effects and compressive stress. Within the frame of the presented study, the methodology supports the given statements well.

• Additional comments on the tables and figures are given in the pdf file

- Figure 4 must have been confused with a version containing an insert that is described in the text.

- Improvement for line 34: "...replacing smaller alkali ions in the glass surface..."

- Improvement for line 93: in the explanation of the parameters in (1), I intensity of laser is missing, ε0 vacuum permittivity is quoted, but not contained in (1)

- Line 212, Fig. 4: legend does not fit image: red dots = black dots?, no insert on correlation , no pink area. Question: would [% m] be the correct unit for the cumulative NER signal?

- Correction for line 287, [6]: "aluminosilicate glass..."

Comments for author File: Comments.pdf

Author Response

The responses to the reviewer’s comments and questions are provided in the attached PDF file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is devoted to evaluation of microhardness by use of NER. In general, it's interesting idea, authors shown the correlation between non-linear refractive index and harndess of ion-exchanged glass. In the same time, authors claimed that the method can be used as altenative way to hardness test, for example Vickers microharness. But as it can be seen from the results, only qualitative correlation is shown, which is more or less obviuos. If authors want to replace Vickers hardness method by NER, they should make an experiment, when they measure nonlinear refractive index and then predict hardness value, and then prove it by Vickers harndess method. Also, in NER method ultrafast laser is used, which is more of less expensive. If we talk about qulitative correlation between hardness and NER, what not use another method, for example, birefringence measurement, which cheeper?

Author Response

The responses to the reviewer’s comments and questions are provided in the attached PDF file.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The paper can be accepted in the present form.