• Journal of the Korean Society of Safety
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• v.25 no.6
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• pp.14-21
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• 2010

A miniature single solder ball joint is designed to mimic the actual solder joints used in the micro-electric industries. Shear tests were conducted to evaluate the mechanical behavior of miniature single solder joints at intermediate strain rates from $0.019\;s^{-1}$ to $2.16\;s^{-1}$ at room temperature. The shear fracture strength of the present solder ball joints generally increased with increasing shear strain rate, ranging from 32 to 51MPa. This behavior is affected by the sensitivity of bulk solder strength to strain rate. Shear fracture mode changed from brittle to partial ductile (failure inside the bulk solder) with an increase of shear speed. The unloading shear fracture toughness is generally consistent with the measure of the amount of bulk solder on the fractured surface.

• International Journal of Concrete Structures and Materials
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• v.10 no.3
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• pp.307-323
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• 2016

The nonlinear behaviors of recycled aggregate concrete (RAC) frame structure are investigated by numerical simulation method with 3-D finite fiber elements. The dynamic characteristics and the seismic performance of the RAC frame structure are analyzed and validated with the shaking table test results. Specifically, the natural frequency and the typical responses (e.g., storey deformation, capacity curve, etc.) from Model 1 (exclusion of strain rate effect) and Model 2 (inclusion of strain rate effect) are analyzed and compared. It is revealed that Model 2 is more likely to provide a better match between the numerical simulation and the shaking table test as key attributes of seismic behaviors of the frame structure are captured by this model. For the purpose to examine how seismic behaviors of the RAC frame structure vary under different strain rates in a real seismic situation, a numerical simulation is performed by varying the strain rate. The storey displacement response and the base shear for the RAC frame structure under different strain rates are investigated and analyzed. It is implied that the structural behavior of the RAC frame structure is significantly influenced by the strain rate effect. On one hand, the storey displacements vary slightly in the trend of decreasing with the increasing strain rate. On the other hand, the base shear of the RAC frame structure under dynamic loading conditions increases with gradually increasing amplitude of the strain rate.

• Journal of Pharmaceutical Investigation
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• v.39 no.3
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• pp.185-199
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• 2009

Using a strain-controlled rheometer [Advanced Rheometric Expansion System (ARES)], the steady shear flow properties and the dynamic viscoelastic properties of $Antiphlamine-S^{(R)}$ lotion have been measured at $20^{\circ}C$ (storage temperature) and $37^{\circ}C$ (body temperature). In this article, the temperature dependence of the linear viscoelastic behavior was firstly reported from the experimental data obtained from a temperature-sweep test. The steady shear flow behavior was secondly reported and then the effect of shear rate on this behavior was discussed in detail. In addition, several inelastic-viscoplastic flow models including a yield stress parameter were employed to make a quantitative evaluation of the steady shear flow behavior, and then the applicability of these models was examined by calculating the various material parameters. The angular frequency dependence of the linear viscoelastic behavior was nextly explained and quantitatively predicted using a fractional derivative model. Finally, the strain amplitude dependence of the dynamic viscoelastic behavior was discussed in full to elucidate a nonlinear rheological behavior in large amplitude oscillatory shear flow fields. Main findings obtained from this study can be summarized as follows : (1) The linear viscoelastic behavior is almostly independent of temperature over a temperature range of $15{\sim}40^{circ}C$. (2) The steady shear viscosity is sharply decreased as an increase in shear rate, demonstrating a pronounced Non-Newtonian shear-thinning flow behavior. (3) The shear stress tends to approach a limiting constant value as a decrease in shear rate, exhibiting an existence of a yield stress. (4) The Herschel-Bulkley, Mizrahi-Berk and Heinz-Casson models are all applicable and have an equivalent validity to quantitatively describe the steady shear flow behavior of $Antiphlamine-S^{(R)}$ lotion whereas both the Bingham and Casson models do not give a good applicability. (5) In small amplitude oscillatory shear flow fields, the storage modulus is always greater than the loss modulus over an entire range of angular frequencies tested and both moduli show a slight dependence on angular frequency. This means that the linear viscoelastic behavior of $Antiphlamine-S^{(R)}$ lotion is dominated by an elastic nature rather than a viscous feature and that a gel-like structure is present in this system. (6) In large amplitude oscillatory shear flow fields, the storage modulus shows a nonlinear strain-thinning behavior at strain amplitude range larger than 10 % while the loss modulus exhibits a weak strain-overshoot behavior up to a strain amplitude of 50 % beyond which followed by a decrease in loss modulus with an increase in strain amplitude. (7) At sufficiently large strain amplitude range (${\gamma}_0$>100 %), the loss modulus is found to be greater than the storage modulus, indicating that a viscous property becomes superior to an elastic character in large shear deformations.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1992.03a
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• pp.83-102
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• 1992

As shear localization is observed in different deformation modes, an attempt is made to understand the conditions for shear localization in general deformation modes. Most emphasis in put upon the effects of pre-localization deformation mode on the onset of shear localization and all the other well-recognized effects of subtle constitutive features and imperfection sensitivity studied elsewhere are not investigated here. Rather, an approximate perturbation stability analysis is performed for simplified isotropic rigid-plastic solids subjected to general mode of homogeneous deformation. Shear localization is possible in any deformation mode if the material has strain softening. The incipient rate of shear localization and shear plane orientations are strongly dependent upon the pre-localization deformation mode. Significant strain softening is necessary for shear localization in homogeneous axisymmetric deformation modes while infinitesimal strain softening is necessary for shear localization in plane strain deformation mode. In any deformation mode, there are more than one shear plane orientation. Except for homogeneous axisymmetric deformation modes, there are two possible shear plane orientations with respect to the principal directions of stretching. Some well-known examples are discussed in the light of the current analysis.

• Structural Engineering and Mechanics
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• v.64 no.4
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• pp.461-472
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• 2017

The dynamic tests of recycled aggregate concrete (RAC) are carried out, the rate-dependent mechanical models of RAC are proposed. The dynamic mechanical behaviors of RAC frame structure are investigated by adopting the numerical simulation method of the finite element. It is indicated that the lateral stiffness and the hysteresis loops of RAC frame structure obtained from the numerical simulation agree well with the test results, more so for the numerical simulation which is considered the strain rate effect than for the numerical simulation with strain rate excluded. The natural vibration frequency and the lateral stiffness increase with the increase of the strain rate. The dynamic model of the lateral stiffness is proposed, which is reasonably applied to describe the effect of the strain rate on the lateral stiffness of RAC frame structure. The effect of the strain rate on the structural deformation and capacity of RAC is analyzed. The analyses show that the inter-story drift decreases with the increase of the strain rate. However, with the increasing strain rate, the structural capacity increases. The dynamic models of the base shear coefficient and the overturning moment of RAC frame structure are developed. The dynamic models are important and can be used to evaluate the strength deterioration of RAC structure under dynamic loading.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.1
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• pp.48-53
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• 2006

A methodology is described for predicting the fatigue life of the resistance spot weldment including strain rate effect. Because it is difficult to perform a physical failure test with high strain rate, an analytical method is necessary to get the mechanical properties of various strain rate, To this end, quasi-static tensile-shear tests at several strain rate were performed on spot weldments of SPC. These test provided the empirical data with the strain rate. With these results, we formulated the function of fatigue life prediction using the lethargy coefficient which is the global material property from tensile test. And, we predicted the fatigue life of spot weldment at dynamic strain rate. To confirm this method for fatigue life prediction, analytical results were compared with the experimental fatigue data.

• Geomechanics and Engineering
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• v.10 no.6
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• pp.827-836
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• 2016

The rate of softening is an important factor to determine whether the failure occurs along localized shear band or in a more diffused manner. In this paper, strength loss and softening rate effect depending on sensitivity are investigated for weakly cemented clays, for both artificially cemented high plasticity San Francisco Bay Mud and low plasticity Yolo Loam. Destructuration and softening behavior for weakly cemented sensitive clays are demonstrated and discussed through multiple vane shear tests. Artificial sensitive clays are prepared in the laboratory for physical modeling or constitutive modeling using a small amount of cement (2 to 5%) with controlled initial water content and curing period. Through test results, shear band thickness is theoretically computed and the rate of softening is represented as a newly introduced parameter, ${\omega}_{80%}$. Consequently, it is found that the softening rate increases with sensitivity for weakly cemented sensitive clays. Increased softening rate represents faster strength loss to residual state and faster minimizing of shear band thickness. Uncemented clay has very low softening rate to 80% strength drop. Also, it is found that higher brittleness index ($I_b$) relatively shows faster softening rate. The result would be beneficial to study of physical modeling for sensitive clays in that artificially constructed high sensitivity (up to $S_t=23$) clay exhibits faster strain softening, which results in localized shear band failure once it is remolded.

• Geomechanics and Engineering
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• v.34 no.2
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• pp.197-208
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• 2023

Rate-dependent mechanical response of sand, subjected to loading of medium to high strain rate range, is of interest for several civilian and military applications. Such rate-dependent response can vary significantly based on the initial density state of the sand, applied confining pressure, considered strain rate range, drainage condition and sand morphology. A numerical study has been carried out employing a recently proposed visco-plastic constitutive model to explore the rate-dependent mechanical behaviour of Toyoura sand under drained triaxial loading condition. The model parameters have been calibrated using the experimental data on Toyoura sand available in published literature. Under strain rates higher than a reference strain rate, the simulation results are found to be in good agreement with the experimentally observed characteristic shearing behaviour of sand, which includes increased shear strength, pronounced post-peak softening and suppressed compression. The rate-dependent response, subjected to intermediate strain rate range, has further been assessed in terms of enhancement of peak shear strength and peak friction angle over varying initial density and confining pressure. The simulation results indicate that the rate-induced strength increase is highest for the dense state and such strength enhancements remain nearly independent of the applied confinement level.

• Korea-Australia Rheology Journal
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• v.15 no.2
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• pp.63-73
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• 2003

An experimental technique was developed to determine the strain-rate in a tensile specimen. Then one can calculate the transient isothermal elongational viscosity. Both shear and elongational viscosities were measured to study the effect of shear and elongational fields on the flow properties. The comparison between these viscosities shows that the onset of rapid viscosity growth as crystallization solidification proceeds occurs at about the same value of time at very small deformation rates (0.0028 and 0.0047 $s^{-1}$). The comparison of these measured viscosities as functions of shear and elongational Hencky strains also reveals that the onset of rapid viscosity growths starts at critical Hencky strain values. The behaviour of steady shear viscosity as function of temperature sweep was also explored at three different low shear rates. Finally, the influence of changing oscillatory frequencies and strain rates was also investigated.

• Korean Journal of Metals and Materials
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• v.47 no.7
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• pp.397-405
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• 2009

The high strain rate deformation behavior of ultra-fine grained 5083 aluminum alloys prepared via equal channel angular (ECA) extrusion was investigated in this study. The microstructure of ECA extruded specimens consisted of ultra-fine grains, and contained a considerable amount of second phase particles, which were fragmented and distributed homogeneously in the matrix. According to the dynamic torsion test results, the maximum shear stress and fracture shear strain of the route A (no rotation) specimen were lower than those of route C ($180^{\circ}$ rotation) specimen since that adiabatic shear bands of $100{\mu}m$ in width were formed in the route A specimen. The formation of adiabatic shear bands was addressed by concepts of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity associated with ECA operations.