• Journal of the Korean Society for Precision Engineering
• /
• v.2 no.2
• /
• pp.31-42
• /
• 1985

The metal flow and the strain distribution is investigated for the steady state and non-steady state bulk deformation processes by using an improved visioplasticity method which includes the effective smoothing scheme. The comparison of various smoothing schemes leads to the selection of the five- point least square smoothing method which is employed to reduce the measurement errors. As a steady state forming process experiments are carried out for axisy- mmetric forward extrusion through conical and curved dies of various area reduc- tions using Aluminum and steel billets. Axisymmetric backward extrusion is chosen for a nonsteady state forming process. In axisymmetric forward extrusion the results from visioplasticity show that the curved die of a fourth-order polynomial renders more uniform distribution of strain rates and strains. Higher reduction leads to greater strain rates at the outer side of the billet. The visioplastic observation for axisymmetric backward extrusion as a non-steady state deformation process shows the concentration of higher strain at the inner wall of the extruded product. The visioplastic results in forward extrusion are in agreement with the computed results by the finite element method. It is thus shown that the visio- plasticity combined with a smoothing technique is an effective method to determine the pattern and the distribution of strain rates and strains.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.1
• /
• pp.209-217
• /
• 1991

We have carried out a preliminary study to search for the new fracture mechanics parameter which can effectively estimate the fatigue life. In this study, the distribution of local fatigue strains near a fatigue crack tip was detailedly revealed using by fine dot grid strain measurement method. From these results, a single parameter (.DELTA.A), which characterize local fatigue strain field, was nearly proposed by the authors.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2004.05a
• /
• pp.409-412
• /
• 2004

Microstructures and mechanical properties of microalloyed cold forging steel and cold forged prototype automobile part are characterized. The work hardening according to the increase of plastic strain plays a major role in increasing the tensile strength of microalloyed cold forging steel during cold forming. On the other hand, inhomogeneous distribution of plastic strain causes variations in microstructure and mechanical properties. The relation between inhomogeneous distribution of plastic strain and variations in microstructure and mechanical properties is discussed. The variation of mechanical property in cold forged automobile part is analyzed using quantitative evaluation of plastic strain from finite element method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1999.03b
• /
• pp.269-272
• /
• 1999

It is still hard to measure the strain distribution over entire surface of a medium or large-size stamped part even by using an automated strain measurement system. Several methods which enable to enlarge the measurement range without losing accuracy and precision are suggested in this study, The superposition of images having different high-lightened or damaged part each other results in an enhanced image. A new method for constructing the element connectivity from a line-thinned image makes it possible to identify up to 1,000 elements. And the geometry assembling algorithm is proved very efficient in which the whole area to be measured is divided into several parts ; the coordinate transformation between every two adjacent parts is obtained from the concept of the least square error ; and the 3-D shape or strain distribution over the whole surface is assembled,

• The korean journal of orthodontics
• /
• v.31 no.3 s.86
• /
• pp.325-333
• /
• 2001

Optimal orthodontic treatment could be possible when a orthodontist can predict and control tooth movement by applying a planned force system to the dentition. The moment to force(M/F) ratio at the bracket, has been shown to be a primary determinate of the pattern of tooth movement. As various n/F ratios are applied to the bracket on the tooth crown, strain distribution in periodontium can be changed, and the center of rotation in tooth movement can be determined. It is, therefore, so important in clinicalorthodontics to know the strain distribution in a force system of a M/F ratio. The purpose of this study was to analyze the strain distribution in orthodontic force system by strain gauge attached to tooth root, and to evaluate the usage of the method. For this study, an experimental upper anterior arch model was constructed, where upper central incisors, on the root surface of which, 8 strain gauges were attached, were implanted In the photoelastic resin, as in the case of 4mm midline diastema. Three types of closing of upper midline diastema closure were compared : 1. with elastomeric chain(100g force) in no arch wire, 2. elastomeric chain in .016“ round steel wire, 3. elastomeric chain in .016”x.022“ rectangular steel wire. The results were as follows. 1. Strain distributions on labial, lingual, mesial and distal root surface of tooth were able to be evaluated with the strain gauge method, and the patterns of tooth rotation were understood by presuming the location of moment arm. 2. Extrusion and tipping movement of tooth was seen in closing in no arch wire, and intrusion and bodily movement was seen with steel arch wire inserted.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1997.03a
• /
• pp.213-216
• /
• 1997

The measurement of 3D surface strain using the image processing method is another approach for strain measurement. The advantage of this method is that strains at several points included in a captured image can be obtained automatically from only one process. In this study, the whole process of automated surface strain measurement is presented. The strain distribution on a LDH specimen is illustrated as a result of the trial to develope an automated strain measurement system.

• Korean Journal of Metals and Materials
• /
• v.47 no.6
• /
• pp.363-371
• /
• 2009

The effect of lubrication on the evolution of strain states during shape rolling in AA5052 sheet was studied by the finite element method (FEM) simulation. The strain states calculated by FEM were verified by texture analysis. Shape rolling with and without lubrication produces shape-rolled samples in fairly similar outer shapes, since the distribution of normal strain components is nearly independent of the lubrication condition. In contrast, the distribution of shear strain components strongly depends on the lubrication condition. Shape rolling without lubrication gives rise to the development of strong shear strain gradients leading to the formation of highly inhomogenous textures and microstructures. The {011}//ND fiber develops during rolling with the operation of plane strain plus ${\dot{\varepsilon}}_{22}$.

• Advances in nano research
• /
• v.12 no.5
• /
• pp.441-455
• /
• 2022

This study explores the linear and nonlinear solutions of sigmoid functionally graded material (S-FGM) nanoplate with porous effects. A size-dependent numerical solution is established using the strain gradient theory and isogeometric finite element formulation. The nonlinear nonlocal strain gradient is developed based on the Reissner-Mindlin plate theory and the Von-Karman strain assumption. The sigmoid function is utilized to modify the classical functionally graded material to ensure the constituent volume distribution. Two different patterns of porosity distribution are investigated, viz. pattern A and pattern B, in which the porosities are symmetric and asymmetric varied across the plate's thickness, respectively. The nonlinear finite element governing equations are established for bending analysis of S-FGM nanoplates, and the Newton-Raphson iteration technique is derived from the nonlinear responses. The isogeometric finite element method is the most suitable numerical method because it can satisfy a higher-order derivative requirement of the nonlocal strain gradient theory. Several numerical results are presented to investigate the influences of porosity distributions, power indexes, aspect ratios, nonlocal and strain gradient parameters on the porous S-FGM nanoplate's linear and nonlinear bending responses.

• The Journal of Engineering Geology
• /
• v.23 no.4
• /
• pp.353-361
• /
• 2013

To analyze the distribution of earthquake-induced strain data in rock masses, statistical analysis was performed on four-directional strain data obtained from a ground movement monitoring system installed in Korea. Strain data related to the 2011 Tohoku-oki earthquake and two aftershocks of >M7.0 in 2011 were used in x-MR control chart analysis, a type of univariate statistical analysis that can detect an abnormal distribution. The analysis revealed different dispersion times for each measurement orientation. In a more comprehensive analysis, the strain data were re-evaluated using multivariate statistical analysis (MSA) considering correlations among the various data from the different measurement orientations. $T_2$ and Q-statistics, based on principal component analysis, were used to analyze the time-series strain data in real-time. The procedures were performed with 99.9%, 99.0%, and 95.0% control limits. It is possible to use the MSA data to successfully detect an abnormal distribution caused by earthquakes because the dispersion time using the 99.9% control limit is concurrent with or earlier than that from the x-MR analysis. In addition, the dispersion using the 99.0% and 95.0% control limits detected an abnormal distribution in advance. This finding indicates the potential use of MSA for recognizing abnormal distributions of strain data.

• Steel and Composite Structures
• /
• v.36 no.6
• /
• pp.643-656
• /
• 2020

This article presents a comprehensive static analysis of simply supported cross-ply carbon nanotubes reinforced composite (CNTRC) laminated nanobeams under various loading profiles. The nonlocal strain gradient constitutive relation is exploited to present the size-dependence of nano-scale. New higher shear deformation beam theory with hyperbolic function is proposed to satisfy the zero-shear effect at boundaries and parabolic variation through the thickness. Carbon nanotubes (CNTs), as the reinforced elements, are distributed through the beam thickness with different distribution functions, which are, uniform distribution (UD-CNTRC), V- distribution (FG-V CNTRC), O- distribution (FG-O CNTRC) and X- distribution (FG-X CNTRC). The equilibrium equations are derived, and Fourier series function are used to solve the obtained differential equation and get the response of nanobeam under uniform, linear or sinusoidal mechanical loadings. Numerical results are obtained to present influences of CNTs reinforcement patterns, composite laminate structure, nonlocal parameter, length scale parameter, geometric parameters on center deflection ad stresses of CNTRC laminated nanobeams. The proposed model is effective in analysis and design of composite structure ranging from macro-scale to nano-scale.