A numerical modelling study for determining ideal size and geometry of dog bone shaped direct tensile strength test rock specimens

Mat Design & Process Comms

2020

Drilled core specimens including a reaming and two loading holes were investigated with both numerical and experimental studies to assess its usability to determine direct tensile strength values of rock materials. A new loading apparatus with rods to insert into the loading holes has been designed and manufactured to supply tension. Elimination of the gluing in the standard direct tensile strength test method is a significant advantage to make both hard and soft rocks possible to be tested. The cylindrical specimens with the diameter of NX size and length to diameter ratio of 3 were used in the tests. In this test method, reaming holes with higher diameter than that of the loading holes were drilled at the middle length of the specimens as the target location for the crack initiation. However, the drilled discs were determined to fail because of the crack initiation at sidewalls of loading holes, instead of the reaming hole. Therefore, loading with inserted rods was not found applicable. The test method and its failure mechanism were discussed for the aim of contributing to relevant studies.

Section: Discussionmentioning

confidence: 89%

Investigation of a new drilling design for loading core specimens with triple holes to determine direct tensile strength values of rock materials

Komurlu

Mat Design & Process Comms

2020

“…(1) is suggested for determination of the DTS values of rock materials in the case of 20 mm drill diameter, NX size disc diameter and specimen length to diameter ratio of 0.5. Since stress distribution in the drilled disc specimens can vary with the change of geometry and size parameters, the findings of this study should be considered for only the relevant case written above [22][23][24].…”

Section: Discussionmentioning

confidence: 99%

Determination of Direct Tensile Strength Values of Rock Materials by a New Test Method of Drilled Disc Tension

Komurlu

Period. Polytech. Civil Eng.

2019

Use of drilled disc specimens was investigated with both numerical and experimental studies to determine direct tensile strengths of rock materials. A new loading apparatus with rods to insert into the drill holes of discs has been designed and manufactured to supply tension by using the compression test presses. In addition to the use of popular compressive presses for direct tension, elimination of the gluing in the standard direct tensile strength test method is a significant advantage to make possible both hard and soft rocks to be tested. The Brazilian test discs with the diameter of NX size and length to diameter ratio of 0.5 were used in tests. Different loading apparatus designs were analyzed and ideal angle of contact between rock and the loading rods was assessed to be 50° within various choices investigated in this study. The drilled discs were determined to fail due to the crack initiation under the condition of uniaxial tensile stress distribution at sidewalls of the hole. In addition to the drilled disc tension test, standard direct tensile strength tests were also carried out to take as reference and compare the results obtained from different methods. According to the results of both numerical and experimental studies, an equation was suggested to determine uniaxial tensile strengths of drilled disc specimens with 20 mm hole diameter and the contact angle of 50°.

“…2is suggested to determine UTS values of rock materials in the case of 11 mm drill diameter, NX size rock core diameter and specimen length to diameter ratio of 3. Since stress distribution in the core specimens varies with the change of geometry and size parameters, the findings of this study should be considered for only the relevant case written above [18][19][20]. The hole drilling location is another important point that can make a significant change in the stress distribution.…”

Section: Discussionmentioning

confidence: 99%

Drilled Core Specimen Testing Method for Determination of Tensile Strength Values of Rock Materials

Komurlu¹,

Period. Polytech. Civil Eng.

2018

In this study, a new direct tensile strength determination method of drilled core specimen testing was investigated with numerical and experimental studies. Effect of different drill diameters of holes of the rock specimens was analysed to assess the ideal drill-hole design. The aim of drilling process is decreasing the failure load and stress concentration at the adhesive part to prevent invalid failures. Drilled specimens were determined to fail due to the start of cracking under the condition of uniaxial tensile stress distribution at sidewalls of holes. It was found that drill bits with the diameter of 11 mm is usable for a practical specimen drilling process to make a significant decrease in the failure load of the core specimens with the NX size (@54 mm) diameter. According to the results obtained from numerical and experimental analyses, an equation was suggested to determine uniaxial tensile strength values of drilled core specimens with the hole diameter of 11 mm.