• Structural Engineering and Mechanics
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• v.72 no.4
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• pp.469-477
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• 2019

The understanding of tool-rock interaction mechanism is of high essence for improving the rock breaking efficiency and optimizing the drilling parameters in mechanical rock breaking. In this study, the tool-rock interaction models of indentation and cutting are carried out by employing the discrete element method (DEM) to examine the rock failure modes of various brittleness rocks and critical indentation and cutting depths of the ductile to brittle failure mode transition. The results show that the cluster size and inter-cluster to intra-cluster bond strength ratio are the key factors which influence the UCS magnitude and the UCS to BTS ratio. The UCS to BTS strength ratio can be increased to a more realistic value using clustered rock model so that the characteristics of real rocks can be better represented. The critical indentation and cutting depth decrease with the brittleness of rock increases and the decreasing rate reduces dramatically against the brittleness value. This effort may lead to a better understanding of rock breaking mechanisms in mechanical excavation, and may contribute to the improvement in the design of rock excavation machines and the related parameters determination.

• Geomechanics and Engineering
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• v.16 no.2
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• pp.195-204
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• 2018

Based on theories of rock mechanics, rock fragmentation, mechanics of elasto-plasticity, and energy dissipation etc., a method is presented for evaluating the rock fragmentation efficiency by using plastic energy dissipation ratio as an index. Using the presented method, the fragmentation efficiency of rocks with different strengths (corresponding to soft, intermediately hard and hard ones) under indentation is analyzed and compared. The theoretical and numerical simulation analyses are then combined with experimental results to systematically reveal the fragmentation mechanism of rocks under indentation of indenter. The results indicate that the fragmentation efficiency of rocks is higher when the plastic energy dissipation ratio is lower, and hence the drilling efficiency is higher. For the rocks with higher hardness and brittleness, the plastic energy dissipation ratio of the rocks at crush is lower. For rocks with lower hardness and brittleness (such as sandstone), most of the work done by the indenter to the rocks is transferred to the elastic and plastic energy of the rocks. However, most of such work is transferred to the elastic energy when the hardness and the brittleness of the rocks are higher. The plastic deformation is small and little energy is dissipated for brittle crush, and the elastic energy is mainly transferred to the kinetic energy of the rock fragment. The plastic energy ratio is proved to produce more accurate assessment on the fragmentation efficiency of rocks, and the presented method can provide a theoretical basis for the optimization of drill bit and selection of well drilling as well as for the selection of the rock fragmentation ways.

• Tribology and Lubricants
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• v.37 no.4
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• pp.144-150
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• 2021

The most cost-effective method of reducing abrasive wear in mechanical parts is increasing their hardness with thin hard coatings. In practice, the composite hardness of the coated substrate is more important than that of the substrate or coating. After full unloading of the load applied to an indenter, its indentation hardness evaluated based on the dent created on the test piece was almost dependent on plastic deformation of the substrate. Following the first part of this study, which proposes a new Brinell hardness test method for a coated surface, the remainder of the study is focused on practical application of the method. Indentation analyses of a rigid sphere and elastic-perfect plastic materials were performed using finite element analysis software. The maximum principal stress and plastic strain distributions as well as the dent shapes according to the substrate yield stress and coating thickness were compared. The substrate yield stress had a significant effect on the dent size, which in turn determines the Brinell hardness. In particular, plastic deformation of the substrate produced dents regardless of the state of the coating layer. The hardness increase by coating behaved differently depending on the substrate yield stress, coating thickness, and indentation load. These results are expected to be useful when evaluating the composite hardness values of various coated friction surfaces.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.2
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• pp.305-316
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• 1997

A more efficient method for obtaining the fatigue life enhancement of a structure member with fastener holes is described. It is based on the combined process of cold-expansion and ring-indentation. Residual stresses were induced onto premachined holes using ring-indentation process near the fastener hole combined with cold-expansion. And residual stresses at the vicinity of a hole were evaluated using a fracture mechanics approach. The compressive residual stresses were larger using the combined process than is in the case of simple cold-expansion. Fatigue testing of aluminum specimens showed that the fatigue crack growth retardation emanating from a circular hole was greater for the combined process than for a simple cold-expansion alone.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.61-66
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• 2008

This study is performed to compare characteristics of various measurement technique for weld residual stress. AISI 304 plate with one path weld on the surface was manufactured for this study. Hole drilling method, X-ray diffraction method and instrumented indentation method were used to measure the residual stress before and after welding. All the results were compared and analyzed.

• Journal of the Korean GEO-environmental Society
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• v.16 no.11
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• pp.29-37
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• 2015

Non-excavation method is needed to secure the stability of existing structures during construction. Therefore, prediction of ground settlement is essential. Causes of settlement when using steel pipe indentation method are leading pipe-steel pipe gap, excessive excavation and soil-steel pipe friction etc. Also they are similar to the causes of settlement when using Shield TBM during construction. In this study, ground settlement during steel pipe indentation is predicted by the Gap Parameter Method and Volume Loss Method which are kinds of Shield TBM prediction Method. and compared with those of prediction methods by conducting field test. As a result, Volume Loss Prediction Method is the most similar to the field tests. However, It is needed to additional studies, such as decision of the factors and adaptability for total settlement predictions of non-excavation method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.2
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• pp.185-192
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• 1988

Computation of the elasto-plastic solution of ball indentation was carried out by the quadratic programming method. The problem was formulated as an elasto-plastic contact problem under the assumption of small displacement and small deformation and then transformed into a minimization problem. Finite element approximation resulted in a quadratic programming problem. Numerical and experimental study were done with aluminium Al 2024-T351 and commercially pure copper. The computed load-displacement curves were in good agrement with those obtained from experiments. Tabor's relationship for representative strains was also examined. Stress distributions were found to resemble closely those results available in the literature.

• Journal of the Korean Ceramic Society
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• v.30 no.6
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• pp.469-477
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• 1993

Residual stresses is one of the major factors to degrade the magnetic properties of VCR magnetic heads. Vicker's indentation technique was adapted to estimate the residual stresses Residual stresses and distribution in the glass and ferrite were obtained after bonding ferrite with glass, varing the cooling rate. The compressive and tensile stresses were developed in the interface and gradually decreased with increasing distance from the interface. The stresses were decreased with a cooling rate. The mean values of residual stress in ferrite were 10MN/㎡, 8MN/㎡, 5MN/㎡ with cooling rate 10℃/min, 5℃/min, 1℃/min respectively. When the bonded sample was annealed above the glass transition temperature followed by cooling at 5℃/min cooling rate, the residual stress was reduced to 6MN/㎡.

• Advances in materials Research
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• v.7 no.3
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• pp.185-194
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• 2018

The mechanism of biological materials structure is very complex and has optimal properties compared to engineering materials. Top Neck mollusks shells, as an example of biological materials, have hierarchical structure, which 95 percent of its structure is Aragonite and 5 percent organic materials. This article detected mechanical properties of the Top Neck mollusks shell as a Nano composite using Nano-indentation method in different situations. Research findings indicate that mechanical properties of the Top Neck mollusks shell including elastic modulus and hardness are higher than a fresh one preserved in -50 centigrade and also a Top Neck mollusks shell preserved in environmental conditions. Nano-indentation test results are so close in range, overall, that hardness degree is 3900 to 5200 MPa and elastic modulus is 70 to 85 GPa.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.212-214
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• 2004

It is widely recognized that the residual stress of weldment affects steel construction and causes fracture initiation of welded structures. It is necessary to know since the power plants adopt a variety of welding processes distribution and magnitude of residual stresses. Therefore the purpose of present study is to investigate the validity of the indentation method to measure residual stresses of steel plates by residual stresses measured form the specimens of hot reheater pipes, cold reheater pipes and feed water lines used in power plants.