• Advances in aircraft and spacecraft science
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• 제2권3호
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• pp.249-261
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• 2015

The mechanical characterization of composite materials is nowadays a major interest due to their increasing use in the aeronautic industry. The design of most of these materials is based on their stiffness, which is mainly obtained by means of tensile tests with strain gauge measurement. For thin laminated composites, this classical method requires adequate samples with specific orientation and does not provide all the independent elastic constants. Regarding ultrasonic characterization, especially immersion technique, only one specimen is needed and the entire determination of the stiffness tensor is possible. This paper presents a study of different methods to determine the mechanical properties of transversely isotropic carbon fibre composite materials (gauge and correlation strain measurement during tensile tests, ultrasonic immersion technique). Results are compared to ISO standards and manufacturer data to evaluate the accuracy of these techniques.

• International Journal of Korean Welding Society
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• 제2권1호
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• pp.29-32
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• 2002

In previous study, the decrease and recovery of total stiffness in welded structure was discussed on the basis of experimental examination through tensile loading and unloading test of welded specimen. The recovery of structure stiffness was caused by the release of welding residual stress through mechanical loading. In this study, analysis model that is indispensable for the effective application of MSR method was established on the basis of test and measurement result. Thermal elasto-plastic analysis for welding process was performed by non- coupled analysis. Analysis results of welding process were transfer to elasto-plastic model for tensile loading & unloading by restart technique. In elasto-plastic analysis model for mechanical loading & unloading, hardening appearance of weld metal was considered by rezoning technique and tying technique was used for JIG condition of test machine.

• 대한통합의학회지
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• 제9권1호
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• pp.193-202
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• 2021

Purpose : The purpose of this study is to examine inter-and intra-rater reliabilities of myotonometric measurements of tone, elasticity and stiffness for the erector spinae muscles of the young and the elderly populations. Methods : A total of 102 (69 young adults from K university and 33 older adults from the D community center in Daejeon) were enrolled in this study. The two different raters measured each side of the erector spinae muscles at prone position. After each rater performed first measurement for a subject, 30 minutes of rest was given. The same rater then repeated the second myometric measurement on the subject. The collected data on the tone, elasticity, and stiffness of the erector spinae were analyzed using intraclass correlation coefficient (ICC) to determine inter- and intra- rater reliabilities. Results : The inter-and intra-rater reliabilities of the myotonometric measurement of the erector spinae for the total subjects were excellent (ICC > 0.9, p < 0.001). Within each of the elderly group and the young group, inter- and intra-rater reliabilities were also excellent (ICC > 0.8~0.9 / p < 0.001, ICC > 0.75~0.9 / p < 0.001, each). Conclusion : The measurement of muscle tone, elasticity, and stiffness for the erector spinae muscles using the myotonometer had excellent reliability. It was confirmed that a highly reliable myometric measurement on the erector spinae can be obtained regardless of whether it is from young or elderly people. This suggests that the myotonometer can be a useful tool to measure muscular properties of the erector spinae of the young and old as an evaluative instrument.

• Structural Engineering and Mechanics
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• 제26권3호
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• pp.315-341
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• 2007

A sudden change of stiffness in a structure, associated with the events such as weld fracture and brace breakage, will cause a discontinuity in acceleration response time histories recorded in the vicinity of damage location at damage time instant. A new damage index is proposed and implemented in this paper to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. The proposed damage index is suitable for online structural health monitoring applications. It can also be used in conjunction with the empirical mode decomposition (EMD) for damage detection without using the intermittency check. Numerical simulation using a five-story shear building under different types of excitation is executed to assess the effectiveness and reliability of the proposed damage index and damage detection approach for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also examined. The results from this study demonstrate that the damage index and damage detection approach proposed can accurately identify the damage time instant and location in the building due to a sudden loss of stiffness if measurement noise is below a certain level. The relation between the damage severity and the proposed damage index is linear. The wavelet-transform (WT) and the EMD with intermittency check are also applied to the same building for the comparison of detection efficiency between the proposed approach, the WT and the EMD.

• 대한토목학회논문집
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• 제28권4A호
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• pp.475-485
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• 2008

이 논문은 국내 탄성받침의 성능과 신뢰성 향상을 위한 일환으로, 탄성받침의 설계/제작/품질평가 기준인 KS F 4420의 강성 관련 개선방향을 제안하였다. 이를 위하여 KS F 4420의 압축탄성계수, 강성측정방법, 성능평가방법을 Eurocode, 일본 도로교지승편람, ISO 기준과 비교 분석하였으며, KS F 4420의 강성 제안식과 실측치와의 차이를 알아보기 위하여 국내 일반적인 탄성받침을 대상으로 수직강성과 전단강성 측정 실험을 실시하였다. 실측된 수직강성은 강성정의 방법에 따라 20%정도 차이를 나타냈으며, 전단강성은 13%정도 차이를 나타냈다. 또한 실측된 강성은 KS F 4420의 제안식과의 편차도 큰 것으로 나타났다. 교량받침이 요구되는 수직강성을 가지지 못하는 경우 교량 상부 구조물의 부등침하 및 응력집중 현상을 야기할 수 있다. 따라서 국내 받침이 설계에서 요구되는 성능을 갖기 위해서는 다양한 형상, 형상계수를 갖는 받침의 성능평가를 통하여 국내 실정에 맞는 압축탄성계수식과 성능평가기준의 마련이 필요하다고 판단된다.

• 센서학회지
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• 제18권1호
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• pp.42-47
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• 2009

In this paper we propose a microfluidic chip that measures the mechanical stiffness of cell membrane using impedance measurement. The microfluidic chip is composed of PDMS channel and a glass substrate with electrode. The proposed device uses patch-clamp technique to capture and deform a target cell and measures impedance of deformed cells. We demonstrated that the impedance increased after the membrane stretched and blocked the channel.

• 한국산업융합학회 논문집
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• 제21권2호
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• pp.63-70
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• 2018

In this paper, the design of a novel 6-axis compliance device with force/torque sensing capability and the experiment results on force measurement are presented. Unlike the traditional control methods using a force/torque sensor with very limited compliance, the force control method employs a compliant device to provide sufficient compliance between an industrial robot and a rigid environment for more stable force control. The proposed compliance device is designed to have a diagonal stiffness matrix at the tip and uses strain gauge measurement which is robust to dust and oil. The measurement circuit is designed with low-cost IC chips however the force resolution is 0.04N.

• 한국정밀공학회지
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• 제32권5호
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• pp.415-422
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• 2015

Ballscrews are important motion transfer and positioning units of industrial machinery and precision machines. Positioning accuracy of the feed drive system depends upon axial stiffness of ballscrew systems. As the nut stiffness depends upon preload and operating conditions, analytical modeling of the stiffness is performed through the contact and body deformation analysis. For accurate contact analysis, the contact angle variation between balls and grooves is incorporated in the developed model. To verify the developed mathematical stiffness model, experiments are conducted on the test-rig. Through the uncertainty analysis according to GUM (Guide to the expression of Uncertainty in Measurement), it is confirmed that the formulated stiffness model has over 85% estimation accuracy. After constructing the ballscrew DB, a quick turnaround system for the nut stiffness estimation has been developed in this research.

• 한국생산제조학회지
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• 제19권6호
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• pp.797-803
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• 2010

A method has been developed to tune the static stiffness at a rotation joint considering the whole machine tool system by interactive use of finite element method and experiment. This paper describes the procedure of this method and shows the results. The method uses the static experiment on measurement model which is set-up so that the effects of uncertain factors can be excluded. For FEM simulation, the rotation joint model is simplified using only spindle, bearing and spring. At the rotation joint, the damping coefficient is ignored, The spindle and bearing is connected by only spring. By static experiment, 500 N is forced to the front and behind portion of spindle and the deformation is measured by capacitive sensor. The deformation by FEM simulation is extracted with changing the static stiffness from the initial static stiffness considering only rotation joint. The tuning static stiffness is obtained by exploring the static stiffness directly trusting the deformation from the static experiment. Finally, the general tuning method of the static stiffness of machine tool joint is proposed using the force stream and the modal analysis of machine tool.

• 대한의용생체공학회:의공학회지
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• 제29권2호
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• pp.151-158
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• 2008

To evaluate aortic wall stiffness without influence of different background blood pressure, a new technique was developed and verified. At eight swine descending aortae, volume-pressure measurement was performed using custom-made system. Based on averaged pressure-volume curve, aortic distensibility index was formulated to evaluate aortic wall stiffness regardless of variable blood pressure and aortic size. The variability of aortic distensibility index by pressure change was compared with other parameters for wall stiffness evaluation. Subsequently, the aortic distensibility index was calculated at 100 contrast-enhanced EBCT data sets of normal volunteers in regular health screening program. The measured aortic distensibility index was compared with age, coronary calcium score, and aortic calcium score. Between 50 and 360 mmHg of blood pressure, the coefficient of variance of aortic distensibility index was 22.00% as comparing with 88.99% of classical compliance. Based on age, aortic distensibility index showed correlation coefficient of 0.55, whereas classical compliance showed 0.26. The correlation coefficient with modified aortic calcification was 0.43. Linear regression study revealed statistical significance of correlation coefficients. The aortic distensibility index, the method to evaluate aortic wall stiffness free from variable blood pressure and aortic size, was developed and verified with significant practical feasibility.