Experimental Investigation of Fracture Performances of SBHS500, SM570 and SM490 Steel Specimens with Notches

Round 1

Reviewer 1 Report

REPORTS ON: metals-1647366

 

 

Dear Authors;

The proposed manuscript is well organized and reasonably well discussed. Novelty seems to be provided and a great number of experimentations are carried out. Based on the results and contribution, the manuscript seems to DESERVES its final publication after a MINOR (Obligatory) REVISION, as indicated.

 

1. Firstly, in the Abstract, a simple past tense should be used. At least three distinctive tenses are used. Besides, Grammar and Spelling should meticulously be revised.
2. Although these three distinctive steel are reasonably important, it is hardly suggested that a new sentence be proposed in order to elucidate:
3. Where can these steel be applied? Or are commonly be utilized?
4. At least a recognized standard or similar ASTM or uNS procedure should be mentioned/correlated wih each steel examined.
5. Error ranges should be included in Table 1, 2, 3 and 4.
6. Although, the experimental reproducibility seems to be carried out (e.g. “…three tensile coupons...”), it is not clearly detailed/mentioned/discussed. In this sense, each experimental procedure should be revised and duplicate or triplicate mentioned/evidenced.
7. In line 81, the follow sentence is equivocate: “…were loaded at a rate of 0.02 to 0.05 mm/s.”. This mentioned physical component is speed selected, and a strain rate (e.g. 2x10-4 s-1) should be mentioned and adopted.
8. Besides, it seems that the “extensometer” information is irrelevant.
9. In introduction when it is detailed each proposed steel, it is suggested that at least a new sentence be included. This in order to elucidate what kind of the resulting microstructure and its microconstituents constitute each sample examined. Also, it should also be mentioned that the microstructural array has a very important hole upon the mechanical behavior. The follow sentences and references can be included:

 

“It is remarked that from the metallurgical point of view, both the grain sizes and microstructural arrays of distinctive materials and alloys have important roles upon the resulting material’s properties (e.g. mechanical and corrosion behaviors), as previously reported [AA-FF].

[AA] N. J. Petch. The cleavage strength of polycrystals. J. Iron Steel Inst. 174 (1953) 25-31.

 

[BB] P. Donelan, Modelling microstructural and mechanical properties of ferritic ductile cast iron", Mater. Sci. Technol.16 (2000) 261-269.

 

[CC] W. R. Osório, C. A. Santos, J. M. V. Quaresma, A. Garcia. Mechanical properties as a function of thermal parameters and microstructure for Zn-Al castings. J. Mater. Proc. Technol. 143 (2003) 703-709.

 

[DD] D.J. Lloyd, S Court. Influence of grain size on tensile properties of Al-Mg alloys. Mater. Sci. Technol. (2003) 1349-1354.

 

[EE] W.R. Osório, N. Cheung, J.E. Spinelli, P.R. Goulart, A. Garcia. The effects of a eutectic modifier on microstructure and surface corrosion behavior of Al-Si hypoeutectic alloys. Journal of Solid State Electrochemistry 11 (2007) 1421-1427.

 

[FF] D.M. Rosa. J.E. Spinelli, W.R. Osório, A. Garcia. Effects of cell size and macrosegregation on the corrosion behavior of a dilute Pb-Sb alloy. Journal of Power Sources 162 (2006) 696-705.

 

 

8. Figs. 2 and 12 should be revised and scale bar included.
9. Fig. 3 should be reworked in order to evidence each important parameter obtained. For instance, a “zoom” (another inside Figure or optionally other figure) can be used to depict the 0.2 yield strength lines. THe values shown in Table 2 are very similar to tjose two firstly steels shown. With this “zoom”, it can be elucidate a possible “difference” with determining their corresponding values. This is a reason showing that error range and error bars have its importance to compare experimental results.
10. In line 127, the term “obvious” can be replaced with another term more appropriate. It is understood that the experimental result can be reasonably expected, but the term “obvious” is very “strong”. Please, revise it.
11. Figs. 6 and 8 need urgently of “scale bars”.
12. If into the Conclusion section, the chemical composition is not mentioned, it seems that their section can be omitted from the revised version of the manuscript. On the other hand, if there exists some possibility to included another “bullet” in Conclusion concerning to chemical composition, this section can be revised.
13. From those 24 References cited into the list, at least 16 (~70%) are dating between 2018 and 2022. This is a great academic merit and surely will contribute significantly with future researchers. However, at least two or three paper/articles published in METALS journal should be mentioned. This is not an obligatory action, but it is a commonly movement provided. Please, revise it.

 

Author Response

The authors would like to thank the reviewer for providing valuable comments and professional suggestions. Feedback from reviewer significantly improved the paper. Furthermore, reply to each of the issues raised by the reviewer is provided below. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper studies fracture performance of HSS with artificially introduced notches. Flat specimens with single sided notches are loaded in tension, while specimen elongation is measure over a whole gage length. Then, the measured mormalized “strain at crack initiation” is related to reciprocal value of Nishitani’s stress concentration factor to obtain linear relation. Crack initiation in the notch stress field, its stable propagation and final shear ruptures are quantified using fractography.  The article needs clarification in several major aspects and some minor corrections for the improvement of readability. Some theoretical and experimental information has to be added to make the paper self-contained. The results presentation should reworked to be more systematic and clear. Therefore MAJOR revision is recommended:
Major comments
-    The paper needs to be put into wider context of standard fracture mechanics, i.e. it needs to be explained, that the standard fracture toughness approach using sharp crack starters is not representative for the bridge structures and the basic motivation for measuring the stages of crack life should be given
-    The method used to detect ductile crack initiation should be  specified
-    The strain at crack initiation should be defined, is it the nominal strain from the xtensometer ?
-    “relatively faster ductile crack propagation compared to those of SM570  and SM490 steels” needs further explanation, was the crack length measured during the test i.e by unloading ? How can the authors separate the effect of plasticity and crack growth ?
-    stress definition for notched geometries should be given (nominal stresses ?) 
-    l123 and figure 5,  displacement of 1mm for 20mm specimen represents nominal 5% deformation,it is unlikely that any steel is in elastic range at that strain !!! The data in figure 5 more likely represent the growth of a plastic zone ahead of the crack tip and start to deviate from the straight line when the plastic zone reaches the sensor. Note that the elastic difference caused by the notch will be small 5mm distance. Also please infclude specification of the strain gage as the mesured strain above 2% is usually higher than the maximum strain accepted by most strain gages.  
-    a clear definition of yield stress should be given, usually it is defined as the intersection of offset line at a defined amount of plastic deformation (usually, 0.2%). 
-    the paper lacks clear conclusions summarizing the performance of the three steels using objective measured values
Minor comments:
l31, remove “in-which”
l32 remove “on the other hand:
l46 rephrase “into soften stage”
l48 remove “on the other hand”
l60 the “different stress trixialities” require reference
l77 rephrase “are totally prepared” 
l80 “were subjected” -> “were tested using”
l82 what is omega extensometer
l83 what is “the load N”, F, or P is usually used for applied load
l91 “0.2% of” remove off, rephrase to slerly describe the yield stress
Table 1 can be omitted and the tolerance of thickness given in text
l108 “of the two specimens” -> add “of same type and material”, rephrase the rest oof sentence to make it more clear
l113 what is meant by “ductile crack propagation becomes slow ?” how was the propagation measured/estimated ?
l114 “the strain-displacement curves” need definition of displacement (by extensometer) and strain (by strain gage) to lead the reader
I suggest to transform table 3 to figure analogously to Fig. 12
Used equipment should be cited in a standard way type (make, country)
codes c1c2c3 in fig 3 need explanation
l109-111 needs rephrasing such as „of the two specimens of identical material with identical notches..“ 
l154 „The linear notch mechanics“ needs some introduction as the cited source is in japanese and it is extremely difficult to find any  other source of information
l158: displacement -> notch radius ????
l208-211 the presented data call for a chart or table 
l213- clearly define the yield stress, its mesurement method (extensometer) ?, After the methodology is clear, it may be clear why the „yield strength“ of specimen with longer notch is higer.
l222-228 –not sure what the paragraph is abotu. Is it is defining yet anothe methods of yiled stress determinanition. Elastic modulus does not decrease by plasticity !!!! How is neutra axis define in uniaxial bending ???
par 3.6 has tu be put in cotext with th rest of the paper
 

Author Response

The authors would like to thank the reviewer for providing valuable comments and professional suggestions. Feedback from reviewer significantly improved the paper. Furthermore, reply to each of the issues raised by the reviewer is provided below. Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors carefully adressed reviewers comments. Still the paragraph 3.6, estimating weldability from chemical composition needs to be put in context of the paper. It is clear that weldability of structural steel is and important propertyespecially in bridge construction, however this should be state explicitly in introduction as one aim of the paper. Also I suggest to rename par 3.6 to 'Weldability', istead of 'Chemical Composition' as the composition is solely used to estimate the property of intrest - weldability

I also recommend to write a short comment on strain gage type, as strain gage measurement of 10% deformation is a rather demanding task

Based on the above minor comment I suggest minor revision. Alternatively, the minor change can be incorporated at the proofing stage.

Author Response

The authors would like to thank the reviewer for providing valuable comments and professional suggestions. Feedback from reviewer significantly improved the paper. We have substantially revised our manuscript after reading the comments provided by the reviewer. Furthermore, the authors express our many thanks to the editor for your professional and efficient work. Please see the attachment.

Author Response File: Author Response.pdf