• Earthquakes and Structures
• /
• v.10 no.5
• /
• pp.989-1012
• /
• 2016

The structural dynamic behavior and yield strength considering both ductility and strain rate effects are analyzed in this article. For the single-degree-of-freedom (SDOF) system, the relationship between the relative velocity and the strain rate response is deduced and the strain rate spectrum is presented. The ductility factor can be incorporated into the strain rate spectrum conveniently based on the constant-ductility velocity response spectrum. With the application of strain rate spectrum, it is convenient to consider the ductility and strain rate effects in engineering practice. The modal combination method, i.e., square root of the sum of the squares (SRSS) method, is employed to calculate the maximum strain rate of the elastoplastic multiple-degree-of-freedom (MDOF) system under uniform excitation. Considering the spatially varying ground motions, a new response spectrum method is developed by incorporating the ductility factor and strain rate into the conventional response spectrum method. In order to further analyze the effects of strain rate and ductility on structural dynamic behavior and yield strength, the cantilever beam (one-dimensional) and the triangular element (two-dimensional) are taken as numerical examples to calculate their seismic responses in time domain. Numerical results show that the permanent displacements with and without considering the strain rate effect are significantly different from each other. It is not only necessary in theory but also significant in engineering practice to take the ductility and strain rate effects into consideration.

• Computers and Concrete
• /
• v.15 no.4
• /
• pp.607-642
• /
• 2015

The stress-strain relationship of concrete in flexure is one of the essential parameters in assessing the flexural strength and ductility of reinforced concrete (RC) columns. An overview of previous research studies revealed that the presence of strain gradient would affect the maximum concrete stress developed in flexure. However, no quantitative model was available to evaluate the strain gradient effect on concrete under flexure. Previously, the authors have conducted experimental studies to investigate the strain gradient effect on maximum concrete stress and respective strain and developed two strain-gradient-dependent factors k3 and ko for modifying the flexural concrete stress-strain curve. As a continued study, the authors herein will extend the investigation of strain gradient effects on flexural strength and ductility of RC columns to concrete strength up to 100 MPa by employing the strain-gradient-dependent concrete stress-strain curve using nonlinear moment-curvature analysis. It was evident from the results that both the flexural strength and ductility of RC columns are improved under strain gradient effect. Lastly, for practical engineering design purpose, a new equivalent rectangular concrete stress block incorporating the combined effects of strain gradient and concrete strength was proposed and validated. Design formulas and charts have also been presented for flexural strength and ductility of RC columns.

• Nuclear Engineering and Technology
• /
• v.50 no.6
• /
• pp.907-914
• /
• 2018

In this article, we conducted molecular dynamics simulations to investigate the effect of applied strain and temperature on irradiation-induced damage in alpha-zirconium. Cascade simulations were performed with primary knock-on atom energies ranging between 1 and 20 KeV, hydrostatic and uniaxial strain values ranging from -2% (compression) to 2% (tensile), and temperatures ranging from 100 to 1000 K. Results demonstrated that the number of defects increased when the displacement cascade proceeded under tensile uniaxial hydrostatic strain. In contrast, compressive strain states tended to decrease the defect production rate as compared with the reference no-strain condition. The proportions of vacancy and interstitial clustering increased by approximately 45% and 55% and 25% and 32% for 2% hydrostatic and uniaxial strain systems, respectively, as compared with the unstrained system, whereas both strain fields resulted in a 15-30% decrease in vacancy and interstitial clustering under compressive conditions. Tensile strains, specifically hydrostatic strain, tended to produce larger sized vacancy and interstitial clusters, whereas compressive strain systems did not significantly affect the size of defect clusters as compared with the reference no-strain condition. The influence of the strain system on radiation damage became more significant at lower temperatures because of less annealing than in higher temperature systems.

• Transactions of Materials Processing
• /
• v.8 no.2
• /
• pp.169-177
• /
• 1999

Different pass strains and rolling temperatures were applied to understand the effects of pass strain and rolling temperature on flow stress and flow strain of AA5083 alloy. The specimens were prepared by conventional casting process followed by hot rolling. Hot torsion tests were conducted at temperature ranges of 350 to 52$0^{\circ}C$ under a strain rate of 1.0/sec. During the process, hot-restoration mechanisms, dynamic recovery(DRV) or dynamic recrystallization (DRX), of the AA5083 alloy were analyzed from the flow curves and deformed microstructures. It was found that while the rolling strain per pass and rolling temperature have little effect on the folw stress, they have significant effect on the failure strain. The DRV was responsible for the hot restoration mechanism of the hot-rolled specimen. heavily elongated grains and small subgrains containing dislocations were obtaned during the hot deformation. This was due to the presence of Al6Mn precipitate in the alloy.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1990.04a
• /
• pp.78-83
• /
• 1990

The current analytical techniques for R/C elements under severe dynamic repeated loads, like earthquake or impact, has two major problems; one is that the effects of strain rate are not considered and the other one is the current model was developed based on flexural behavior only. Thus, this study develops a computer software that can idealize the flexural and shear behavior of R/C elements using several parameters and also can consider the effects of strain rate. The analytical results using the developed analytical technique were compared with several experimental results and were generally satisfied.

• Structural Engineering and Mechanics
• /
• v.19 no.2
• /
• pp.185-198
• /
• 2005

In the design of reinforced concrete beams, it is a standard practice to use the yield stress of the steel reinforcement for the evaluation of the flexural strength. However, because of strain hardening, the tensile strength of the steel reinforcement is often substantially higher than the yield stress. Thus, it is a common belief that the actual flexural strength should be higher than the theoretical flexural strength evaluated with strain hardening ignored. The possible increase in flexural strength due to strain hardening is a two-edge sword. In some cases, it may be treated as strength reserve contributing to extra safety. In other cases, it could lead to greater shear demand causing brittle shear failure of the beam or unexpected greater capacity of the beam causing violation of the strong column-weak beam design philosophy. Strain hardening may also have certain effect on the flexural ductility. In this paper, the effects of strain hardening on the post-peak flexural behaviour, particularly the flexural strength and ductility, of reinforced normal- and high-strength concrete beams are studied. The results reveal that the effects of strain hardening could be quite significant when the tension steel ratio is relatively small.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.29 no.3
• /
• pp.219-223
• /
• 2009

This paper prescribed the structural integrity of the API 5L X65 pipeline subjected to tensile pre-strain. The effects of pre-strain on the mechanical properties of API 5L X65 pipe were substantially investigated through a variety of the experimental procedures. Axial tensile pre-strain of 1.5, 5 and 10% was applied to plate-type tensile specimens cut from the pipe body prior to mechanical testing. Tensile test revealed that yield strength and tensile strength were increased with increasing tensile pre-strain. The increasing rate of the yield strength owing to the pre-strain is greater than that of the tensile strength. However, the pre-strain up to 5% had a little effect on the decreasing of the fracture toughness. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for service code.

• Structural Engineering and Mechanics
• /
• v.48 no.3
• /
• pp.415-434
• /
• 2013

This work is concerned with transverse vibrations of axially traveling nanobeams including strain gradient and thermal effects. The strain gradient elasticity theory and the temperature field are taken into consideration. A new higher-order differential equation of motion is derived from the variational principle and the corresponding higher-order non-classical boundary conditions including simple, clamped, cantilevered supports and their higher-order "offspring" are established. Effects of strain gradient nanoscale parameter, temperature change, shape parameter and axial traction on the natural frequencies are presented and discussed through some numerical examples. It is concluded that the factors mentioned above significantly influence the dynamic behaviors of an axially traveling nanobeam. In particular, the strain gradient effect tends to induce higher vibration frequencies as compared to an axially traveling macro beams based on the classical vibration theory without strain gradient effect.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.9 s.240
• /
• pp.988-996
• /
• 2005

Flame structure and extinction mechanism of counterflow methane/air non-premixed flame diluted with nitrogen are studied by NASA 2.2 s drop tower experiments and two-dimensional numerical simulations with finite rate chemistry and transport properties. Extinction mechanism at low strain rate is examined through the comparison among results of microgravity experiment, 1D and 2D simulations with a finite burner diameter. A two-dimensional simulation in counterflow flame especially with a finite burner diameter is shown to be very important in explaining the importance of multidimensional effects and lateral heat loss in flame extinction, effects that cannot be understood using a one-dimensional flamelet model. Extinction mechanism at low strain rate is quite different from that at high strain rate. Low strain rate flame is extinguished initially at the outer flame edge, the flame shrinks inward, and finally is extinguished at the center. It is clarified from the overall fractional contribution by each term in energy equation to heat release rate that the contribution of radiation fraction with 1D and 2D simulations does not change so much and the overall fractional contribution is decisively attributed to radial conduction ('lateral heat loss'). The experiments by Maruta et at. can be only completely understood if multi-dimensional heat loss effects are considered. It is, as a result, verified that the turning point, which is caused only by pure radiation heat loss, has to be shifted towards much lower global strain rate in microgravity flame.

• Safety and Health at Work
• /
• v.5 no.4
• /
• pp.186-190
• /
• 2014

Background: Physical exercise during leisure time is known to increase physical capacity; however, the long-term effects on work ability and work strain are inconclusive. The aim of this study was to investigate the effects of a 6-month physical exercise program on work ability and work strain after 6 months and 30 months, among women with menopausal symptoms at baseline. Methods: A questionnaire including questions on work ability and work strain was mailed in the beginning, at 6 months and after 30 months after the intervention to occupationally active women participating in a randomized controlled study on physical exercise and quality of life. The intervention included aerobic exercise training 4 times per week, 50 minutes per session. Work ability was measured with the Work Ability Index (WAI) and with questions about physical and mental work strain. Results: Women aged 47-62 years (N=89) who were occupationally active at baseline were included in the analyses. The increase in WAI from baseline to the end of the exercise intervention (6 months) was statistically significantly greater among the intervention group than among the control group (regression coefficient 2.08; 95% confidence interval 0.71-3.46). The difference between the groups persisted for 30 months. No significant short- or long-term effects on physical and mental work strain were found. Conclusion: A 6-month physical exercise intervention among symptomatic menopausal women had positive short-term as well as long-term effects on work ability.