Calibration of DEM for Cohesive Particles in the SLS Powder Spreading Process
Round 1
Reviewer 1 Report
In this paper, authors propsed a new DEM calibration procedure, based on two different types of pro-cedures to compare simulation with experiments. Both angle of repose and unconfined yield strength were tested and simualted. The experimental produces for angle of repose and unconfined yield strength were well descirbed and resultes were presened well. Meanwhile, the simualted valuse of both were correctely obtiained. The paper is meaningful for both powder properties evalution and DEM calibration. The paper is well prepared, so I think it can be accepated after some minor text editings corrected, such as the improvement of figures and tables and so on.
Author Response
All the improvements suggested by the Reviewer have been implemented.
Reviewer 2 Report
Paper title: Calibration of DEM for cohesive particles in the SLS powder spreading process
By Lupo et al
General comments are given as follows:
The paper content corresponds to a technical note.
The objective of this study consists in the use of DEM code for numerical simulation for modeled polymeric powder.
If the procedures used are well explained, results obtained are not convincing.
Comments are given versus the sections:
Title:
For some readers, SLS must be written with all letters.
After in the text, for any reader, all symbols must be written for the first appearing with all letters.
Abstract:
Line 15: what means “idolized”?
Introduction:
Line 87: is it justified to write “Linear cohesion” with L as capital letter?
Objectives of the present study are well presented and clear.
Materials and methods:
Experimental materials, apparatuses and procedure:
Materials:
Line 160: why authors did not control the solid particle density?
Line 165: the particles are clearly non-spherical and inhomogeneous.
Direct measurement of particle properties to be used in DEM:
Table 2 must be improved for the presentation.
Experimental setup used for the unconfined yield strength calibration method:
Line 194: authors must indicate on a scheme the main directions used with the ring shear (1, 2, 3 directions relative for example for stresses).
Lines 197-198: “consolidation stresses between 0.4 and 0.7 kg were carried out and 4-5 shear points were …”: stress unit is Pa! Authors must be rigorous, are these shear tests conducted without consolidation or on consolidated powder?
Modeling approach:
DEM:
Clear.
Model tuning for SLS applications and calibration procedures:
Many assumptions are listed in this subsection and nothing appears clearly about some of them:
- The shape of particles as shown in figure 1, is not “spherical” or “clumped spheres”; this kind of shape induces interpenetration of particles not considered in the simulation.
- About “consolidation”, even if stresses are very low, rearrangement of particles will be effective and porosity or void ratio depends on consolidation stresses;
- Authors must provide grain size distribution (cumulative and non-cumulative) graph to corroborate the gaussian distribution.
DEM Calibration methods:
DEM calibration using the static angle of repose:
Lines 322-323: Unclear. What is really inserted in the hopper?
Figure 2: some dimensions must be indicated (scale effect). Legend must be shortened.
DEM calibration using the unconfined yield strength:
Line 376: the slenderness here considered is 3. Usually for UCS test minimal slenderness is 2 for cylindrical sample (see international standard), why authors chose 3? Did authors test the slenderness scale effect?
Line 378: “desired consolidation stress” corresponds to prestressed the powder? What are really the initial conditions for porosity or void ratio?
Line 404: suppress “)” after 988Pa. Authors must provide reference of these tests.
Line 412: what is the effect on result of this procedure?
Line 428: it is figure 6a or b? Correct “time”.
Line 433: how to define clearly the plateau value?
Lines 435-438: for readers, figure 11 is not well placed or move this part of text.
Results and discussion:
Calibration according to the static angle of repose:
In this section, how authors are sure to get the optimal parameters? Why the αexp value is really obtained?
Figure 8: No explanation was given for the 2 figures a and b. Legend of figure partially repeats the text written in the section (lines 464-470). In figure b, what is the meaning of the linear fitting?
Lines 504-510: explanations given are not so convincing.
Calibration according to the unconfined yield strength:
Line 513: what are the corresponding stresses for the masses applied?
Figure 10: what about the evolution of fc and the increase till the 3rd point and decrease after this point?
Line 552: “shows…”.
Line 556: “pile simulation” is not adequate term.
Lines 557-567: authors state clearly the DEM use with the chosen models is not adapted to solve the problem investigated.
Conclusions:
Coherent with the paper content
References:
[48] this reference is not cited in the text.
Author Response
All the improvements suggested by the reviewer have been implemented. The changes file is attached below.
Author Response File: 
Author Response.docx
Round 2
Reviewer 2 Report
Paper title: Calibration of DEM for cohesive particles in the SLS powder spreading process-version R1
By Lupo et al
General comments on revised version:
The paper reports clearly results from a preliminary study. This explains that results obtained are not so convincing. But authors have mentioned these aspects in conclusions.
Comments are given versus the sections:
Materials and methods:
Direct measurement of particle properties to be used in DEM:
Table 2 has been improved but write all lines on one line, see line 6 of the table.
Also check with instructions for authors if you must insert the legend of each table.
Experimental setup used for the unconfined yield strength calibration method:
Line 204: put a space after “Pa” and “were”.
Modeling approach:
Model tuning for SLS applications and calibration procedures:
In fact, as said by authors, the JKR model considers the adhesion between the particles i.e. cohesive behaviour of the powder, but due to the shape of particles, is the phenomenon of interpenetration of particles occurred? This could be observed by means of SEM images and tomography.
DEM calibration methods:
DEM calibration using the static angle of repose:
Lines 348-349: Distinguish the legend of figure 3 and the following sentences that must be inserted in text.
Author Response
I reply to the comments in the attached file
Author Response File: Author Response.docx
