?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=http%3A%2F%2Fd-scholarship-dev.library.pitt.edu%2F19090%2F&rft.title=Considerations+for+Discrete+Element+Modeling+of+Rock+Cutting&rft.creator=Mendoza+Rizo%2C+Jorge+Alejandro&rft.description=This+study+attempts+to+build+a+framework+within+the+Discrete+Element+Method+(DEM)+to+produce+a+reliable+predictive+tool+in+rock+cutting+applications%2C+such+that+the+cutting+forces+and+fragmentation+process+are+reasonably+estimated.+The+study+is+limited+to+shallow+depth+cutting%2C+often+the+mode+of+cutting+involved+in+drilling+operations.%0D%0ARock+cutting+requires+the+consideration+of+tool-rock+interaction+and+the+damage+or+fracture+of+rocks.+With+respect+to+modeling%2C+rock+cutting+becomes+a+sequence+of+difficult+problems%3A+A+contact+problem+first+arises+as+a+cutter+advances+and+interacts+with+a+target+rock.+This+is+followed+by+the+problem+of+determining+the+location+and+nature+of+the+rock+failure.+In+the+event+of+rock+failure%2C+a+modeler+must+then+consider+modeling+the+initiation+of+the+fragmentation+process.+The+adopted+approach+utilizes+the+intrinsic+capability+of+DEM+to+adequately+consider+contacts+and+model+fractures.+The+commercial+DEM+codes+PFC2D+and+PFC3D+from+Itasca+were+used.%0D%0AThis+modeling+effort+focuses+on+the+rock+cutting+that+occurs+during+rock+scratching+tests.+Two+primary+reasons+provide+the+impetus+of+this+investigation%3A+first%2C+a+rock+scratching+test+possesses+all+essential+characteristics+of+a+general+rock+cutting+problem%3B+second%2C+available+test+data%2C+particularly+data+obtained+by+Richard+%5B1%5D%2C+provide+a+basis+for+validation.+Modeling+the+scratch+test+also+served+another+purpose+for+understanding+the+mechanics+of+drilling+into+rock+because+the+cutting+action+is+very+similar+to+that+of+a+single+polycrystalline+diamond+compact+(PDC)+bit.%0D%0AThe+validation+of+the+present+modeling+effort+utilizes+an+observation+made+by+Richard+and+Dagrain+%5B2%5D+during+shallow+cuts+that+the+specific+energy+obtained+in+a+scratch+test+is+approximately+equal+to+the+uniaxial+strength+of+the+rock.+Rocks+were+represented+as+bonded+particles+%5B3%5D.+This+study+first+explores+the+sensitivity+of+the+essential+parameters+that+affect+rock+behavior+and+parameter+selection+necessary+to+realistically+represent+a+rock.+Extensive+two-dimensional+analyses+were+first+completed+and+followed+by+three-dimensional+analyses%2C+all+of+which+were+conducted+under+an+ambient+pressure+environment.%0D%0AThis+study+also+addressed+an+important+question+regarding+rock+porosity.+The+current+practice+often+implicitly+considers+porosity.+Essentially%2C+a+porosity+that+is+computationally+simple+and+advantageous+but+ultimately+unrealistic+is+used+and+other+DEM+parameters+are+consequently+adjusted+until+the+desired+modulus+and+strength+are+produced.+This+sample+is+then+considered+mechanically+equivalent.+The+ability+to+substitute+rock+materials+of+low+porosities+with+higher+values+is+extremely+beneficial+for+computational+efficiency.+Samples+with+small+porosity+values+were+generated+by+solving+the+Apollonius%E2%80%99+problem+to+fill+voids+with+particles%2C+and+therefore%2C+the+influence+of+initial+sample+microstructure+could+be+studied.%0D%0AThe+Unconfined+Compressive+Strength+(UCS)+for+most+rocks+is+generally+about+ten+times+greater+than+that+of+the+tensile+strength+%5B4%5D.+This+ratio%2C+considered+to+be+realistic+rock+behavior%2C+has+been+historically+difficult+to+obtain+in+similar+models.+In+order+to+achieve+this+strength+ratio%2C+microdefects+were+also+introduced+into+the+sample.+This+study+was+able+to+implicitly+model+porosity+by+introducing+optimal+microdefects+percentages+in+order+to+create+equivalent+rock+samples+with+varying+porosity+values.+Moreover%2C+a+connection+between+two-dimensional+and+three-dimensional+samples+was+also+established+by+finding+an+appropriate+porosity+to+match+the+two+models.%0D%0AThis+study+presented+a+validated+and+simplified+framework+for+modeling+rock+cutting%2C+and+should+be+useful+for+general+applications+for+a+wide+variety+of+fields.+Preliminary+work+on+cutting+under+high+pressure+was+also+initiated+and+yielded+results+that+would+be+useful+for+subsequent+studies.%0D%0A&rft.date=2013-09-25&rft.type=University+of+Pittsburgh+ETD&rft.type=PeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=http%3A%2F%2Fd-scholarship-dev.library.pitt.edu%2F19090%2F1%2FMendozaRizoJA_etd2013.pdf&rft.identifier=++Mendoza+Rizo%2C+Jorge+Alejandro++(2013)+Considerations+for+Discrete+Element+Modeling+of+Rock+Cutting.++Doctoral+Dissertation%2C+University+of+Pittsburgh.++++(Unpublished)++