A Novel Methodology to Investigate Critical Depth for Ductile-to-Brittle Transition During Scratch Testing

2021 ◽  
Author(s):  
Mohammad Rasheed Khan ◽  
Guenther Glatz ◽  
Devon Chikonga Gwaba ◽  
Gallyam Aidagulov
Keyword(s):  
Brittle Failure ◽  
Morphological Analysis ◽  
Test Method ◽  
Depth Of Cut ◽  
Response Analysis ◽  
Critical Depth ◽  
Micro Ct ◽  
Scratch Testing ◽  
Rock Interaction ◽  
Critical Depth Of Cut

Abstract More than two decades have passed since the introduction of the scratch testing method for rock strength determination. The test method typically involves dragging a rigid-shaped cutter across the rock surface at a fixed cutting depth. This depth determines the failure mechanism of the rock, ductile for shallow depths and brittle for deeper. In the ductile mode, intrinsic specific energy is primarily a measure of the unconfined-compressive-strength (UCS), which is pivotal for rate of penetration (ROP) during drilling and for borehole stability analysis. On the contrary, brittle failure can lead to permanent core damage and is usually not desired as it impacts interpretation of the scratch testing results. Consequently, it is imperative to identify the critical depth, and at which transition from ductile to brittle failure occurs which will help optimize rock testing and tool designs. In this study, a novel methodology is proposed utilizing micro-computed tomography (CT) imaging to determine critical depth through morphological analysis of scratch test cuttings. Scratch tests are carried out on Indiana limestone core samples with the cutter-rock interaction geometry characterized by a cutter width of 10mm and a back-rake angle of 15°. The sample is scratched in the range of 0.05mm to 0.40mm with increments of 0.05mm. Scratch powder is carefully collected after each scratch increment and stored for further analysis. This powder is then loaded into slim rubber tubes and imaged at a high resolution of 1 µm with a helical micro-CT scanner. The scans are then reconstructed using a computer program to initiate the visualization of individual grains from each cutter depth including evaluation of grain morphologies. Finally, the results from this morphological analysis are corroborated and compared with three other methods: force response analysis, force inflection point analysis, and the size effect law (SEL). Based on shape analysis, it was found that the transition from ductile to brittle regime occurs at a depth of 0.25mm. Elongation and appearance of the enhanced degree of angularity of the grains as the depth of cut (DOC) increases past 0.25mm was observed. Moreover, large grain sizes were detected and are representative of formation of chips (typical brittle regime response). Furthermore, it is illustrated that the image analysis helps eliminate the ambiguity of force signal analysis and in combination can aid in the critical depth of cut determination. The other methods involving force alone and the SEL are not able to pin-point onset of brittle regime. Using a similar methodology, creation of a database for various rock types is recommended to develop a guide for the depth of cut selection during scratch testing. This novel methodology utilizing micro-CT analysis and comparative study with other techniques will put in place an accurate strategy to determine the critical depth of cut when designing rock scratch testing programs.

Study of Ductile-to-Brittle Transition in Single Grit Diamond Scribing of Silicon: Application to Wire Sawing of Silicon Wafers

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Hao Wu ◽  
Shreyes N. Melkote
Keyword(s):  
Hydrostatic Pressure ◽  
Silicon Wafers ◽  
Depth Of Cut ◽  
Critical Depth ◽  
External Hydrostatic Pressure ◽  
Tensile Stresses ◽  
Brittle Transition ◽  
Ductile Mode Cutting ◽  
Critical Depth Of Cut ◽  
Ductile To Brittle Transition

The ductile-to-brittle cutting mode transition in single grit diamond scribing of monocrystalline silicon is investigated in this paper. Specifically, the effects of scriber tip geometry, coefficient of friction, and external hydrostatic pressure on the critical depth of cut associated with ductile-to-brittle transition and crack generation are studied via an eXtended Finite Element Method (XFEM) based model, which is experimentally validated. Scribers with a large tip radius are shown to produce lower tensile stresses and a larger critical depth of cut compared with scribers with a sharp tip. Spherical tipped scribers are shown to generate only surface cracks, while sharp tipped scribers (conical, Berkovich and Vickers) are found to create large subsurface tensile stresses, which can lead to nucleation of subsurface median/lateral cracks. Lowering the friction coefficient tends to increase the critical depth of cut and hence the extent of ductile mode cutting. The results also show that larger critical depth of cut can be obtained under external hydrostatic pressure. This knowledge is expected to be useful in optimizing the design and application of the diamond coated wire employed in fixed abrasive diamond wire sawing of photovoltaic silicon wafers.

Study on Chip Breaking Behavior of 3-D Complex Groove Insert in Machining Carbon Constructional Steel at High Cutting Speeds

2008 ◽  
Vol 375-376 ◽  
pp. 206-210
Author(s):  
Hui Ping Zhang ◽  
Zhen Jia Li ◽  
Er Liang Liu ◽  
Guo Liang Wei
Keyword(s):  
High Speed ◽  
Mathematic Model ◽  
Constructional Steel ◽  
Depth Of Cut ◽  
Critical Depth ◽  
Chip Breaking ◽  
Critical Depth Of Cut ◽  
On Chip ◽  
Cutting Experiments ◽  
Cutting Speeds

This paper deals with chip breaking behaviour of 3-D complex groove inserts in machining carbon constructional steel-45 steel at high cutting speeds .Cutting experiments were performed at eleven different cutting speeds. Firstly, the results showed that by increasing cutting speeds, the changes of the critical feedrate and chip breaking scopes at high cutting speeds machining with 3-D complex groove inserts were nonlinear and not monotonous function relations. Then, mathematic models were built. Secondly, the results showed that the critical depth of cut was a constant value at various cutting speeds. And, the curves of the critical depth of cut were perpendicular lines. For this purpose, the critical depth of cut mathematic model has been built. The study above lays a theory and basis for future investigation of the mechanism of chip breaking with 3-D groove insert in high speed machining.

An Experimental Approach to Determine the Critical Depth of Cut in Brittle-to-Ductile Phase Transition During End Milling of Soda-Lime Glass

2016 ◽  
Vol 41 (11) ◽  
pp. 4553-4562 ◽  
Author(s):  
A. K. M. Nurul Amin ◽  
Mst. Nasima Bagum ◽  
Noor Fathiah ◽  
Mohamed Konneh ◽  
Tasnim Firdaus Bt. Mohamed Ariff
Keyword(s):  
Phase Transition ◽  
Experimental Approach ◽  
End Milling ◽  
Soda Lime ◽  
Depth Of Cut ◽  
Soda Lime Glass ◽  
Critical Depth ◽  
Ductile Phase ◽  
Critical Depth Of Cut

Research on the Influence of Cutting Fluids on the Critical Depth of Cut in Diamond Cutting of Optical Glass BK7

2010 ◽  
Vol 431-432 ◽  
pp. 126-129 ◽  
Author(s):  
Ming Zhou ◽  
Peng Jia ◽  
Min Li
Keyword(s):  
Boric Acid ◽  
Optical Glass ◽  
Cutting Fluid ◽  
Depth Of Cut ◽  
Cutting Fluids ◽  
Critical Depth ◽  
Diamond Cutting ◽  
Brittle Ductile Transition ◽  
Fluid Properties ◽  
Critical Depth Of Cut

In diamond cutting of optical glasses, the magnitude of critical depth of cut for brittle-ductile transition is an important factor affecting the machinability of the work material in terms of production rate and surface quality. In this work, scratching tests with increasing depths of cut were conducted on glass BK7 to evaluate the influence of the cutting fluid properties on the critical depth of cut. Boric acid solutions of different concentrations were selected as cutting fluids in the tests. The resulting scratches were examined utilizing a white light interferometer and the values of the critical depth of cut were determined based on the observations of the micro-morphology of the scratch surfaces produced. Experimental results indicated that compared with the process without cutting fluid action, the critical depth of cut in diamond cutting of glass BK7 can be increased by using boric acid solution as the cutting fluid.

scholarly journals Modeling and Experiment of the Critical Depth of Cut at the Ductile–Brittle Transition for a 4H-SiC Single Crystal

Micromachines ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 382 ◽  
Author(s):  
Peng Chai ◽  
Shujuan Li ◽  
Yan Li
Keyword(s):  
Single Crystal ◽  
Lateral Displacement ◽  
Tangential Force ◽  
Test System ◽  
Depth Of Cut ◽  
Critical Depth ◽  
Berkovich Indenter ◽  
Nose Radius ◽  
Brittle Transition ◽  
Critical Depth Of Cut

In this paper, a theoretical model of the critical depth of cut of nanoscratching on a 4H-SiC single crystal with a Berkovich indenter is proposed, and a series of scratch tests in a nanomechanical test system was performed. Through nanoindentation experimentation on fused quartz, the Berkovich indenter nose radius was indirectly confirmed using least squares. The range of critical depths of cut at the ductile–brittle transition was obtained by SEM observation, and the size of cracks was amplified with increasing scratching depth. The theoretical result of the critical depth of cut at the ductile–brittle transition for a 4H-SiC single crystal is 91.7 nm, which is close to the first obvious pop-in point of the relation curve between tangential force and lateral displacement. Repeated experimental results show good consistency and good agreement with other references.

Indentation and Scratching Experimental Research on Brittle-Ductile Transition of Optical Glass SF6

2013 ◽  
Vol 589-590 ◽  
pp. 480-484 ◽  
Author(s):  
Peng Jia
Keyword(s):  
Boric Acid ◽  
Optical Glass ◽  
Cutting Fluid ◽  
Depth Of Cut ◽  
Critical Depth ◽  
Diamond Cutting ◽  
Brittle Ductile Transition ◽  
Fluid Properties ◽  
Critical Depth Of Cut ◽  
Micro Morphology

In diamond cutting of optical glasses, the magnitude of critical depth of cut for brittle-ductile transition is an important factor affecting the machinability of the work material in terms of production rate and surface quality. In this work, scratching tests with increasing depths of cut were conducted on glass BK7 to evaluate the influence of the cutting fluid properties on the critical depth of cut. Boric acid solutions of different concentrations were selected as cutting fluids in the tests. The resulting scratches were examined utilizing a white light interferometer and the values of the critical depth of cut were determined based on the observations of the micro-morphology of the scratch surfaces produced. Experimental results indicated that compared with the process without cutting fluid action, the critical depth of cut in diamond cutting of glass BK7 can be increased by using boric acid solution as the cutting fluid.

The Effect of Multiple Dynamic Absorbers on Regenerative Chatter and Resonance in End Milling Process

2012 ◽  
Author(s):  
Yutaka Nakano ◽  
Hiroki Takahara ◽  
Kengo Yasue ◽  
Ryutaro Asaga
Keyword(s):  
Natural Frequency ◽  
Phase Difference ◽  
Forced Vibration ◽  
End Milling ◽  
Rotation Frequency ◽  
Spindle Speed ◽  
Depth Of Cut ◽  
Critical Depth ◽  
Spindle Rotation ◽  
Critical Depth Of Cut

The present study investigates the effect of multiple dynamic absorbers on regenerative chatter and resonance caused by forced vibration generated in the end milling operations. Regenerative chatter is caused by the cutting force variation due to the phase difference between the wave left by the previous cutting edge and the wave left by the current one. This phase difference is expressed as the product of the tooth passing period and chatter frequency [1]. The tooth passing period depends on the spindle rotation frequency and the number of teeth. Chatter frequency is related to the natural frequency of the tool and spindle system. If the integral multiple of the spindle rotation frequency approaches to the natural frequency, the phase difference gets smaller and the critical depth of cut at the onset of chatter is increased. Therefore the critical depth of cut varies with the spindle speed and stable cutting conditions are plotted on the chatter stability lobe, which is a chart that represents the boundary between stable and unstable cuts as a function of the spindle speed and the depth of cut. The chatter stability lobe is widely employed to find the axial depth of cut and the spindle speed in which chatter doesn’t occur. Meanwhile, the cutting force variation by the intermittent cutting with an end milling tool causes the forced vibration. The excitation frequency is determined by the spindle rotation frequency and the number of teeth. When the integral multiple of the excitation frequency approaches to the natural frequency of the tool and spindle system, resonance can be caused by the forced vibration. The resonance occurs in the spindle speed resistant to chatter. Therefore, there is a need for a countermeasure against not just the chatter but also the resonance caused by the forced vibration. In the present study, the cutting conditions which can lead to the chatter and the resonance are investigated by the direct numerical integration method. It is made clear that the optimum tuning parameters of the absorbers to maximize the critical depth of cut vary with the spindle speed. Furthermore, a significant suppression effect on the chatter and the resonance by using the absorbers mounted in a rotating collet holder with a spindle is confirmed.

Numerical Investigation on Effect of Rounded Cutting Edge Radius in Milling of Ultra-High-Strength Steel 30Cr3SiNiMoVA

2013 ◽  
Vol 797 ◽  
pp. 202-207
Author(s):  
Chang Ying Wang ◽  
Jia Jin Tian ◽  
Qing Long An ◽  
Ming Chen
Keyword(s):  
Cutting Forces ◽  
High Strength Steel ◽  
High Strength ◽  
Cutting Edge ◽  
Depth Of Cut ◽  
Critical Depth ◽  
Cutting Edge Radius ◽  
Edge Radius ◽  
Ultra High Strength Steel ◽  
Critical Depth Of Cut

Ultra-high-strength steel 30Cr3SiNiMoVA (30Cr3) which has excellent mechanical properties is usually used to manufacture the key parts in aviation industry. Precision hard milling is an efficiency way to machine 30Cr3 instead of grinding. Rounded cutting edge radius has important influence on the machining process due to small depth of cut. In order to better understanding the influence of rounded cutting edge radius, cutting forces, cutting temperature, critical depth of cut, etc., is analyzed by using finite element method (FEM). The results show that cutting forces in theydirection are more sensitively to the rounded cutting edge radii. Ploughing effect is also observed at the end of the climb milling process and it has significant influence on the quality of the machined surface. Simulation reveals that the increment of rounded cutting edge radius can lead to the increment of critical depth of cut correspondingly and the proportionality factor is about 14%.

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