Pull Test for Determination of Basic Friction Angle of Rock Joints

( Kook-hyun Lee ),( Gyn-young Jeong ),( Min-yong Sim ),( Hyun-sic Jang ),( Bo-an Jang ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

Although tilt test is the suggested by ISRM for basic friction angle measurement, basic friction angles measured by the tilt test are usually distributed in a wide range. Basic friction angles of granite, sandstone, marble, gneiss, and shale were measured by three different test methods, such as direct shear test, pull test and tilt test. Results are compared to determine the accuracy of measurement and the most convenient and accurate method for basic friction angle measurement. Samples were prepared as slab shape or disc shape, and sliding planes were polished by #100 grinding powders. Basic friction angles of granite, sandstone, marble, gneiss, and shale measured by direct shear test were 28.7º, 36.9º, 33.0º, 29.8º and 33.1º, respectively. Those measured by pull were almost identical with those measured by direct shear test within 2º. However, basic friction angles measured by the tilt test show a wide range. Pull test can be performed by a simple and convenient way, but results are more accurate than tilt test. These results indicate that pull test may be a better method to measure basic friction angle than the tilt test.

최적의 기본마찰각 측정법에 관한 실험적 연구

이국현,장현식,장보안 대한지질공학회 2019 지질공학 Vol.29 No.4

Basic friction angles of Hwangdeung granite, Berea sandstone, Jeongsun marble, Hongcheon gneiss, Pungam shale and Eumseong sandy shale were measured by direct shear test, tilt test and pull test. Characteristics of basic friction angle and the accuracy of test methods were compared and the optimal method in measuring basic friction angle was suggested. Although basic friction angles might be measured accurately by direct shear test, the test apparatus is expensive and procedures are complicated. Tilt tests which is the suggested method for measuring basic friction angle by International Association for Rock Mechanics also provided similar basic friction angles measured by direct shear test. However, the error measured for the same rock type is higher than 7° and values by repeated measurements in one sample show different trends, such as increasing or decreasing or almost constant as measurements continued. The difference measured in one gneiss sample is higher 12°, indicating that tilt test may be not a reliable method for measuring basic friction angle. Not only pull test provided accurate and consistent results under low normal stresses, but also test apparatus is simple and inexpensive and procedure is not complicated, indicating that pull test may be the optimal method for measuring basic friction angle. 황등 화강암, Berea 사암, 정선 대리암, 홍천 편마암, 풍암 셰일 및 음성 사질 셰일의 여섯 종류의 암석에대하여 직접전단시험, 기울임시험 그리고 당김시험을 이용하여 기본마찰각을 측정하고, 암종에 따른 기본마찰각의 특성, 시험방법의 정확성을 비교, 검토하여 기본마찰각 측정에 가장 정확하고 효율적인 시험방법을 제시하였다. 기본마찰각은 직접전단시험을 이용하면 정확하게 측정되지만, 비싼 장비와 복잡한 시험절차가 필요하다. 국제암반역학회에서 표준시험법으로 제안한 기울임시험은 직접전단시험에서측정된 기본마찰각과 유사한 값을 제시하나, 동일한 암석으로 제작된 3개의 시료에서 측정된 기본마찰각은 최대 7° 이상의 오차를 보이고, 1개의 시료에서 5회 측정된 미끄러짐 각 또한 시료에 따라서 증가하거나, 감소하거나, 유사한 값을 보이는 등 일정한 패턴을 보이지 않고 변할 뿐만 아니라, 편마암에서는 최대 12°의 오차를 보여 시험의 신뢰성에 상당한 의문이 든다. 간단한 시험장비와 비교적 낮은 수직응력하에서 실시되는 당김시험은 직접전단시험에서 구한 기본마찰각과 매우 유사한 값을 제공하고, 측정된 값들이 일관성을 보이고 시험절차 또한매우 간단하여 기본마찰각 측정에 가장 유용한 시험 방법으로 판단된다.

현장시험을 통한 기초 말뚝 부마찰력의 특성과 시공관리

홍석우 한국도로학회 2012 한국도로학회논문집 Vol.14 No.3

In this study the negative skin friction test of foundation pile was performed in order to monitor the negative skin frictional force acting on the steel pipe pile installed in soft soil. The monitored frictional stresses obtained from the long-term loading test. Through the long-term frictional stress monitoring test, the economical period for the construction of the superstructure was determined. The following conclusion were derived from this study: (1) In soft soil, negative skin friction increases with the increase in the rate of settlement. (2) In the friction relationship graph, the period where there is no frictional strain increase is verified and the time for the construction of the superstructure is determined. (3) The pile loading test was performed and the negative skin friction was compared with the test results. It was determined that the negative skin friction after driving was larger than the negative skin friction obtained from the loading test. 15 days after the construction, the monitored value was similar with the theoretical data. (4) It was determined that even during the occurrence of negative skin friction an economical construction management can be performed using the long-term monitoring method of negative skin friction. 본 연구에서는 교량기초 말뚝의 부주면마찰력 시험을 통하여 연약지반에 타설된 강관말뚝의 부주면마찰력을 측정하였으며장기적인 마찰응력의 관측시험을 통하여 경제적인 상부구조물 시공시기를 판단하였다. 본 연구의 결론은 다음과 같다. (1) 연약지반에서 부마착력의 크기는 침하속도가 클수록 크게 나타났다. (2) 마찰력의 관계 그래프에서 마찰응력의 증감이 없는 시기를확인하여 상부구조물 시공시기를 판단할 수 있었다. (3) 말뚝정재하시험결과와 부주면마찰력 시험결과를 비교해 본 결과 항타직후의 부주면마찰력은 재하시험 시의 마찰응력보다 크게 나오는 것으로 판단되며 15일 경과후의 측정값은 비슷하게 나오는것으로 판단되었고, 이론식에 의한 결과와도 비슷하였다. (4) 부주면마찰력의 장기관측기법을 사용하면 부주면마찰력이 발생하고 있는 중이라도 적절한 상부구조물의 시공시기를 파악할 수 있어 경제적인 시공관리가 가능한 것으로 판단된다.

진동대 시험에 의한 편평한 암석 절리면의 동적 마찰거동 특성

박병기(Byung-Ki Park),전석원(Seokwon Jeon) 한국암반공학회 2006 터널과지하공간 Vol.16 No.1

암반구조물의 규모가 점차 대형화됨에 따라 암반이 자유면에 노출되는 확률이 높아지고 있으며, 최근 들어 지진이나 발파, 고속철도의 운행에 의한 진동 등으로 야기되는 동적 하중의 발생빈도가 증가하는 추세이므로 동적 하중조건 하에서 암반 불연속면의 거동 특성 파악을 위한 연구의 필요성이 증대되고 있다. 본 연구에서는 자유면에 노출된 블록의 동적 거동을 모사할 수 있도록 경사면 진동대 시험장비를 제작하였고, 다양한 동적 하중 조건하에서 편평한 화강암 절리면의 마찰 거동 특성을 분석하였다. 경시시험을 통해서 구한 한계 경사각과 진동하중 하에서의 임계가속도로부터 역산한 정적 마찰각을 비교한 결과 동하중 하에서 정적마찰각이 4.5~8.2˚ 정도 낮게 산정되는 경향을 보였다. 이론적인 암석 블록의 마찰 거동을 표현하는 블록 거동 프로그램을 작성하고, 진동하중에 의해 미끄러지는 암석 블록의 기속도 및 변위 계측결괴를 개발된 프로그램에 의한 결과와 비교하여 임석 절리면의 동적 마찰각을 신정하였는데 동적 마찰각 역시 한계 경사각에 비해 2.0~7.5˚ 정도 감소하는 결과를 얻었다. 동하중 하에서 측정된 정적 마찰각과 동적 마찰각은 가해진 가속도의 크기나 진폭 등의 하중 특성과 기하조건에 따라 달라지는 경향을 보였다. 개별요소 프로그램을 이용하여 진동대 시험을 모사하였는데, 계측결과 및 개발된 프로그램에 의한 결과와 비교적 잘 일치하였다. 진동대 시험에 의한 동적, 정적 마찰각은 직접전단시험에 의한 기본 마찰각보다 현저히 작게 산정되었다. In recent years, not only the occurrences but the magnitude of earthquakes in Korea are on an increasing trend and other sources of dynamic events including large-scale construction, operation of high-speed railway and explosives blasting have been increasing. Besides, the probability of exposure for rock joints to free faces gets higher as the scale of rock mass structures becomes larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be investigated. In this study, a shaking table test system was set up and a series of dynamic test was carried out to examine the dynamic frictional behavior of rock joints. In addition, a computer program was developed, which calculated the acceleration and deformation of the sliding block theoretically based on Newmark sliding block procedure. The static friction angle was back-calculated by measuring yield acceleration at the onset of slide. The dynamic friction angle was estimated by closely approximating the experimental results to the program-simulated responses. As a result of dynamic testing, the static friction angle at the onset of slide as well as the dynamic friction angle during sliding were estimated to be significantly lower than tilt angle. The difference between the tilt angle and the static friction angle was 4.5 ~ 8.2° and the difference between the tilt angle and the dynamic friction angle was 2.0~7.5°. The decreasing trend was influenced by the magnitude of the base acceleration and inclination angle. A DEM program was used to simulate the shaking table test and the result well simulated the experimental behavior. Friction angles obtained by shaking table test were significantly lower than basic friction angle by direct shear test.

FE Analysis of the Sensitivity of Friction Calibration Curves to Dimensional Changes in a Ring Compression Test

Jeong Hoon Noh,Jeong Min Seo,황병복 대한금속·재료학회 2011 METALS AND MATERIALS International Vol.17 No.2

This paper is concerned with an analysis of the sensitivity of friction calibration curves to the frictional shear factor in a ring compression test. The main objective of this study is to examine the sensitivity of the FEA calibration curves of a ring compression test to the frictional shear factor. Different calibration curves were investigated by measuring dimensional changes at different positions of a ring specimen, including changes in the internal diameter at the middle and top section of the specimen, the outer diameter at the middle and top section, and the degree of surface expansion at the top surface. The initial ring geometries employed in the analysis maintain a fixed ratio of 6:3:2, i.e., the outer diameter : inner diameter : thickness ratio of the ring specimen, which is generally known as a ‘standard’ specimen, in order only to determine the sensitivity of the calibration curves for the measurement of dimensional changes at different positions to the frictional shear factor. A perfectly plastic material was modeled for the simulations using rigid-plastic finite element code. Analyses were performed within a definite range of friction as well as over the entire range of friction to uncover the different sensitivities of calibration curves to interfacial friction given different ranges of friction. The results of this investigation are summarized in terms of a dimensionless gradient. It was determined from the results that the friction calibration curves according to measurements of the dimensional changes at different positions of a ring specimen show different degrees of linearity and sensitivity to the frictional condition on the contact surface. Among these differences, the friction calibration curve upon changes in the degree of surface expansion at the contact boundary was found to be relatively linear and sensitive to the frictional condition over the entire range of friction.

Evaluation of Friction in Ultrasonic Vibration-assisted Press Forging Using Double Cup Extrusion Tests

Jung-Chung Hung,Chi-Chen Huang 한국정밀공학회 2012 International Journal of Precision Engineering and Vol. No.

Ultrasonic energy is applied to a die in an ultrasonic vibration-assisted metal forming process, and the die is used to deform the workpiece. The friction between die and workpiece decreases when ultrasonic vibration is applied in metal forming process. The friction plays a crucial role in metal forming; therefore, the friction force must be evaluated and quantified to obtain the optimal forming process. The ring compression test is widely used to evaluate the friction factor or coefficient of friction. However, the ring compression test is unsuitable to determine the friction condition in forging and extrusion processes. Therefore, this study evaluated the effect of ultrasonic vibration on the friction factor using double cup extrusion tests (DCET). The apparatus design for ultrasonic vibration-assisted DCET and experiments were conducted, and the commercial finite element software Marc was used to simulate the DECT to obtain the friction calibration curves. The results demonstrated that the evaluation of the interface friction factor using DCET is sensitive. Under no lubricant condition, the friction factors of traditional and ultrasonic vibration-assisted DCET were approximately 0.1 and 0.3, respectively. Under Blue Moly lubricant condition, the friction factors of traditional and ultrasonic vibration-assisted DCET were approximately 0.05 and 0.1, respectively.

Principles of Developing a Softness Evaluation Technology for Hygiene Paper

Young C. Ko,Jung Yoon Park,Jin Hee Lee,Hyoung Jin Kim 한국펄프·종이공학회 2017 펄프.종이技術 Vol.49 No.4

In developing objective tissue softness evaluation methods, reliable and reproducible subjective evaluation data are a prerequisite. A trade-off relationship generally exists between the relevance to a consumer’s in-use situations and the test variability. At present, sensory panel test (SPT) has been most widely used. It provides the least variable data, but it has the problem of being the least relevant to the real world. Recently we have developed a new sensory panel test which is referred to as new sensory panel test (NSPT). It performs like a HUT (home-user-test) for the relevance and like a physical test for the test variability. Since the pioneering work by Hollmark, it is now widely accepted that subjective tissue softness should primarily consist of the bulk softness component and the surface softness component. The bulk softness component can be determined by the tissue flexibility. The surface softness component can be determined by measuring the surface roughness and the surface friction. In the present study, the NSPT was performed on 7 commercial bathroom tissue products. For subjective softness evaluation, the Thurstone interval scale values have been determined for the 7 products. For the bulk softness component, the flexibilities of these samples were measured using a tensile tester (Criterion model-41, MTS, U.S.A.). For the surface softness component, the surface roughness and the surface friction were measured using the surface roughness/friction tester (KES-SESRU, Kato Tech., Japan). The result validates the hypothesis that the bulk flexibility and the surface roughness/friction should be sufficient for developing an objective tissue softness evaluation method.

동합금계 소결마찰재 싱크로나이저 링 개발

송준혁(Joon Hyuk Song),양성모(Sung Mo Yang),김은성(Eun Sung Kim),김경재(Kyung-Jae Kim),오제하(Je-Ha Oh),강신재(Shin Jae Kang) 한국자동차공학회 2013 한국자동차공학회 부문종합 학술대회 Vol.2013 No.5

Automotive engine has been improved with the requirements of customer for high speed, high torque, and horse power. These high performances of engine will create heat on the friction surface of synchronizer ring, and the temperature will rise to the limit, and because of this, the wear of synchronizer ring surface will rapidly increase by burn sticking. To solve this, it is studied the sintering process for friction materials. Sintering process is useful in the vehicle powertrain engineering with virtues of the net-shaping of complex component and high wear resistance at excessive friction temperature. This paper introduces an improved friction performance of Synchronizer system for high speed, high torque, and high horse power of automotive diesel engine. Copper based friction material is sintered to improve the friction performance and wear resistance. The friction coefficients and wear-weight were measured by Pin on disc Wear and friction test. And synchronizer rings were developed with diffusing ‘sintered friction material’ on the Fe-based mesh ring. Developed synchronizer ring were good to friction performance from the transmission dynamo.

Tests of the interface between structures and filling soil of mountain area airport

Wu, Xueyun,Yang, Jun Techno-Press 2017 Geomechanics & engineering Vol.12 No.3

A series of direct shear tests were conducted to investigate the frictional properties of the interface between structures and the filling soil of Chongqing airport fourth stage expansion project. Two types of structures are investigated, one is low carbon steel and the other is the bedrock sampled from the site. The influence of soil water content, surface roughness and material types of structure were analyzed. The tests show that the interface friction and shear displacement curve has no softening stage and the curve shape is close to the Clough-Duncan hyperbola, while the soil is mainly shear contraction during testing. The interface frictional resistance and normal stress curve meets the Mohr-Coulomb criterion and the derived friction angle and frictional resistance of interface increase as surface roughness increases but is always lower than the internal friction angle and shear strength of soil respectively. When surface roughness is much larger than soil grain size, soil-structure interface is nearly shear surface in soil. In addition to the geometry of structural surface, the material types of structure also affects the performance of soil-structure interface. The wet interface frictional resistance will become lower than the natural one under specific conditions.

Improving the Precision of Specifications by Evaluating the Influence of Test Parameters on Tribological Results

Mathias Woydt,Hartwig Weber 한국트라이볼로지학회 2003 한국트라이볼로지학회 학술대회 Vol.37 No.-

A series of cooperative interlaboratory tests (round robins) was conducted in 1997, 1998, 1999, 2000, 2001, 2002 and 2003 by the DIN 51834 Working Group on Tribological Tests in Translatory Oscillation Apparatus. The statistical analysis of these test results shows the influence of cleaning solvent, machine model and evaluation criteria on the tribological properties of the lubricants tested. Coefficients of friction and wear results are ranked according to the effects of ten different cleaning solvents, where isopropanol gave the lowest values and isoparaffin solvents the highest. The effect of machine model on coefficients of friction varied from about 0.2 % to 0.9 % of the mean. Wear results were not affected. The tests also showed that the seizure criteria and methods of measuring wear required for in the test procedure do not provide a suitable measure of the tribological properties of some lubricants. The precision was improved by introducing a grease apply caliper as well as an increased stroke to 1,5 mm and running-in. The temperature does not affect the precision of the oil test procedure.