Strain Rate Evaluation of Some Typical Nuclear Power Plant Components During Plant Operation

2010 ◽  
Author(s):  
Koji Dozaki ◽  
Hiromasa Chitose ◽  
Hiroshi Ogawa ◽  
Hideo Machida
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Strain History ◽  
Strain Rates ◽  
Peak Strain ◽  
Plant Operation ◽  
Thermal Transients ◽  
Reactor Water ◽  
Rate Evaluation ◽  
Reactor Internals

The dynamic aspects of loading conditions for reactor internals, piping and the like, are thought to play important roles in the initiation of failures due, for example, to stress corrosion cracking (SCC) and fatigue. Some reports show that a strain rate on the order of 10−7 s−1 most affects susceptibility to SCC in the BWR reactor water environment. Environmental fatigue, which exhibits a shorter fatigue life in reactor water than that in air, is considered to have a remarkable correlation with strain rate and its affect on fatigue life. Despite its significant affect on SCC and fatigue, the actual strain rate of components is not known and practical evaluation methods have not been developed; consequently, such failure modes as SCC and fatigue are not evaluated in design. For this paper, strain rates induced by dynamic loading during such operations as plant start-up were calculated at typical points, such as reactor internals, piping and so on. The finite element method was applied to calculate the strain history of each point, and the strain rate was evaluated. The strain rate evaluation results clearly demonstrated that thermal transients provide greater peak strain rate values than pressure transients. Strain rates on the order of 10−7 s−1 were obtained for most points of major components during such thermal transients as plant start-ups. The major factors determining the strain rate magnitude were discussed, based on the calculation results. It was shown that the rate of temperature rise was the most important parameter, because it exhibited much larger sensitivity than the other parameters on the strain rate and could be controlled by plant operation procedures. In addition, a simple strain rate evaluation method based on Green’s function was developed for a specific point with a given design condition.

Effects of Strain Holding and Continuously Changing Strain Rate on Fatigue Life Reduction of Structural Materials in Simulated LWR Water

2007 ◽  
Author(s):  
Makoto Higuchi ◽  
Katsumi Sakaguchi ◽  
Yuichiro Nomura
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Sine Wave ◽  
Fatigue Tests ◽  
Wave Form ◽  
Peak Strain ◽  
Strain Wave ◽  
Strain Rate Change ◽  
Thermal Transients ◽  
Fatigue Life Reduction

The fatigue life reduces remarkably with reduction in strain rate in simulated light water reactor (LWR) water but the effects of strain wave form on this reduction are still not clear. This paper provides fatigue life data obtained from stepwise strain rate change tests, sine wave tests and strain holding tests. The effects of varying strain rate on fatigue life reduction can be estimated very well by the modified rate approach (MRA) method in the case of the step wise strain rate changing as shown in authors’ previous papers [1, 2, 3, 4, 5]. In the case of sine wave, however, the fatigue life reduction is much less compared to that predicted by the MRA method. The mechanism of such difference is not clear and the quantitative assessment of the fatigue life reduction caused by irregular strain wave form in actual transient seems impossible. The current MRA method gives always conservative assessment for sine wave straining and thus it is judged that this method need not be revised any more. The fatigue life reduction caused by strain holding at the peak of straining cycle in simulated BWR water had been reported in the previous paper [6]. In actual thermal transients, however, strain is not usually held at the peak of straining cycle but at the point somewhat reduced from the peak after the stabilization of temperature. In considering this phenomenon, additional fatigue tests in which the strain was held at the point somewhat reduced from the peak were carried out. In such conditions, the fatigue life reduction caused by strain holding disappeared. The similar fatigue tests with peak strain holding were also carried out in simulated PWR water and no fatigue life reduction can be observed. Considering the effects of strain holding on fatigue, the model for evaluating fatigue life reduction in LWR water was revised.

scholarly journals Experimental Study on Biaxial Dynamic Compressive Properties of ECC

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1257
Author(s):  
Shuling Gao ◽  
Guanhua Hu
Keyword(s):  
Strain Rate ◽  
Lateral Pressure ◽  
Deformation Modulus ◽  
Strain Curve ◽  
Peak Stress ◽  
Pressure Level ◽  
Strain Rates ◽  
Peak Strain ◽  
Stress Strain Curve ◽  
Toughness Index

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength applied laterally to the static compressive strength of the specimen), and three strain rates of 10−4, 10−3 and 10−2 s−1. The failure mode, peak stress, peak strain, deformation modulus, stress-strain curve, and compressive toughness index of ECC under biaxial dynamic compressive stress state are obtained. The test results show that the lateral pressure affects the direction of ECC cracking, while the strain rate has little effect on the failure morphology of ECC. The growth of lateral pressure level and strain rate upgrades the limit failure strength and peak strain of ECC, and the small improvement is achieved in elastic modulus. A two-stage ECC biaxial failure strength standard was established, and the influence of the lateral pressure level and peak strain was quantitatively evaluated through the fitting curve of the peak stress, peak strain, and deformation modulus of ECC under various strain rates and lateral pressure levels. ECC’s compressive stress-strain curve can be divided into four stages, and a normalized biaxial dynamic ECC constitutive relationship is established. The toughness index of ECC can be increased with the increase of lateral pressure level, while the increase of strain rate can reduce the toughness index of ECC. Under the effect of biaxial dynamic load, the ultimate strength of ECC is increased higher than that of plain concrete.

scholarly journals Dynamics and Structure of Griesgletscher, Switzerland

1980 ◽  
Vol 25 (92) ◽  
pp. 215-228 ◽  
Author(s):  
M. J. Hambrey ◽  
A. G. Milnes ◽  
H. Siegenthaler
Keyword(s):  
Strain Rate ◽  
Flow Line ◽  
Compressive Strain ◽  
Local Deformation ◽  
Strain History ◽  
Strain Rates ◽  
Shear Strain Rate ◽  
Maximum Shear Strain ◽  
Alpine Valley ◽  
Ablation Area

AbstractA detailed investigation has been carried out on the dynamics of an Alpine valley glacier of relatively simple shape and the results are considered in relation to the development of secondary structures. Ice velocity reaches a maximum near the top of a small ice fall (40 m a−1) which also coincides approximately with the equilibrium line. Flow lines converge in the accumulation area but are roughly parallel in the ablation area. The “regional” strain-rate pattern is rather complex. Approximate longitudinal extension is evident in the accumulation area and strain-rates reach high values at the south margin and in the ice fall (up to 0.12 a−1). In the ablation area, strain-rates are comparatively small and in general indicate longitudinal compression. “Local” deformation rates obtained in the area beneath the ice fall and along a flow line near one of the margins reveal complex patterns of deformation within small areas.There is no clear relationship between foliation and strain-rates (and by analogy stresses), except in the case of longitudinal foliation in marginal areas which, if actively developing, lies approximately parallel to a direction of maximum shear strain-rate. It is more important to consider the relationship of this structure to strain history. Results from this study indicate that, regardless of the initial orientation of the foliation in relation to the strain ellipse, it attains approximate parallelism with the long axis of the ellipse as deformation progresses.It is also shown that many foliations originate from pre-existing layered structures such as stratification or crevasse traces. This problem is discussed particularly with reference to an arcuate foliation which originates in the ice fall and is believed to represent tensional veins, subsequently subjected to compressive strain within and below the ice fall.

Effects of Continuous Strain Rate Changing on Environmental Fatigue for Stainless Steels in PWR Environment

2010 ◽  
Author(s):  
Yuichiro Nomura ◽  
Seiji Asada ◽  
Takao Nakamura ◽  
Masakazu Tanaka
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Water Environment ◽  
Sine Wave ◽  
Fatigue Tests ◽  
Integral Model ◽  
Strain Rates ◽  
Test Results ◽  
Approach Method ◽  
The Difference

The strain rates in actual transients of operating plants are not constant and changing momentarily. A large number of fatigue tests under stepwise strain rate changing conditions were performed to develop a method for evaluating fatigue life under varying strain rate conditions. Based on these test results, a strain base integral model known as the named the modified rate approach method was developed and verified. However it was reported recently that in the case of sine wave fatigue tests in BWR environment, the fatigue life was two to six times longer than the fatigue life predicted by the modified rate approach method. For this paper, in order to confirm whether the same tendency is observed in PWR environment, fatigue tests of sine wave were performed of SS316 in simulated PWR water environment. As the result, the difference of fatigue life by sine wave test reported in BWR environment was not observed between experimental and predicted life in PWR environment and the modified rate approach method was applicable under continuous strain rate changing condition.

High Strain Rate Behavior of Graphene Reinforced Polyurethane Composites

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Sanjeev K. Khanna ◽  
Ha T. T. Phan
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Peak Load ◽  
Peak Stress ◽  
Strain Rates ◽  
Peak Strain ◽  
Plateau Stress ◽  
Dynamic Mechanical ◽  
Stress Peak

A compressive split Hopkinson pressure bar (SHPB) was used to investigate the dynamic mechanical behavior of graphene (GR) reinforced polyurethane (PU) composites (GR/PU) at high strain rates ranging from approximately 1500 s−1 to 5000 s−1. Four types of GR/PU composites with different GR contents: 0.25% GR, 0.5% GR, 0.75% GR, and 1% GR were prepared by the solution mixing method and divided into two groups of unheated and postheated specimens. Experimental results show that the GR/PU composite is a strong strain rate dependent material, especially in the high strain rate regime of 3000 s−1–5000 s−1. The dynamic mechanical properties of GR/PU composite in terms of plateau stress, peak stress, and peak load carrying capacity are better than that of pristine PU at most of the applied strain rates. Among the four different GR concentrations used, the 0.5 wt.%-GR specimen shows the highest peak stress, and the 1 wt.% GR specimen has the highest plateau stress; while no significant change in peak strain with changing GR weight fraction was observed. Compared to unheated specimens, the plateau stress, peak stress, and peak strain of postheated specimens are significantly higher.

scholarly journals Viscoelastic characteristics of the canine cranial cruciate ligament complex at slow strain rates

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e10635
Author(s):  
Rosti Readioff ◽  
Brendan Geraghty ◽  
Ahmed Elsheikh ◽  
Eithne Comerford
Keyword(s):  
Extracellular Matrix ◽  
Knee Joint ◽  
Strain Rate ◽  
Viscoelastic Properties ◽  
Strain History ◽  
Strain Rates ◽  
Cruciate Ligaments ◽  
Test Protocol ◽  
Stifle Joint ◽  
Viscoelastic Characteristics

Ligaments including the cruciate ligaments support and transfer loads between bones applied to the knee joint organ. The functions of these ligaments can get compromised due to changes to their viscoelastic material properties. Currently there are discrepancies in the literature on the viscoelastic characteristics of knee ligaments which are thought to be due to tissue variability and different testing protocols. The aim of this study was to characterise the viscoelastic properties of healthy cranial cruciate ligaments (CCLs), from the canine knee (stifle) joint, with a focus on the toe region of the stress-strain properties where any alterations in the extracellular matrix which would affect viscoelastic properties would be seen. Six paired CCLs, from skeletally mature and disease-free Staffordshire bull terrier stifle joints were retrieved as a femur-CCL-tibia complex and mechanically tested under uniaxial cyclic loading up to 10 N at three strain rates, namely 0.1%, 1% and 10%/min, to assess the viscoelastic property of strain rate dependency. The effect of strain history was also investigated by subjecting contralateral CCLs to an ascending (0.1%, 1% and 10%/min) or descending (10%, 1% and 0.1%/min) strain rate protocol. The differences between strain rates were not statistically significant. However, hysteresis and recovery of ligament lengths showed some dependency on strain rate. Only hysteresis was affected by the test protocol and lower strain rates resulted in higher hysteresis and lower recovery. These findings could be explained by the slow process of uncrimping of collagen fibres and the contribution of proteoglycans in the ligament extracellular matrix to intra-fibrillar gliding, which results in more tissue elongations and higher energy dissipation. This study further expands our understanding of canine CCL behaviour, providing data for material models of femur-CCL-tibia complexes, and demonstrating the challenges for engineering complex biomaterials such as knee joint ligaments.

Fatigue Initiation of 304L Stainless Steel Subject to Thermal Shock Loading in a PWR Environment

2019 ◽  
Author(s):  
Peter Gill ◽  
Peter Brown ◽  
David Tice ◽  
Norman Platts ◽  
Chris Currie
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Strain Rate ◽  
Thermal Shock ◽  
Constant Strain Rate ◽  
304L Stainless Steel ◽  
Strain Rates ◽  
Complex Load ◽  
Evaluation Procedures ◽  
Fatigue Initiation

Abstract The evaluation procedures for fatigue initiation of nuclear class 1 components are defined in ASME BPVC Section III NB-3200 (Design by Analysis) and NB-3600 (Piping Design). Design fatigue curves are provided to establish the suitability of a component for cyclic service and define the allowable number of cycles as a function of applied stress amplitude (S-N curves). The number of load cycles at a particular strain range is then divided by the cycles to failure to obtain a partial usage factor., and the cumulative usage factor (CUF) for the component site, calculated from the sum of the partial usage factors, must be less than one. The original fatigue evaluation procedures did not include the effects of the PWR or BWR coolant environments, but laboratory test data indicate that significant fatigue life reductions can occur under such conditions, depending on strain rates and temperatures. These observations led to the formulation of modified procedures, originally published in NUREG-CR/6909 which required the usage factors to be increased by an additional environmental factor, Fen, which accounts for the deleterious effects of high temperature water. An ASME Code Case N-792-1 has now been included in ASME Section III which is based on the NUREG-CR/6909 equations, with some minor modifications. The Fen factors are derived from testing of membrane-loaded solid round tensile or tubular specimens at different strain rates and temperatures. The data were obtained using simple triangular waveforms, i.e. at constant strain rate, and the temperature was also constant for each test. However, for components subject to plant loading, the situation is significantly more complicated, with most major transients being thermal in origin. For a thermal shock transient some key characteristics become apparent. These are (i) temperature is out-of-phase with strain (ii) strain rate and temperature vary through the cycle with a faster strain rate at the top of the cycle (iii) stress decays through the wall of the component. Several assumptions need to be made in order to simplify the assessment of these sorts of transients. Examples of such assumptions include the choice of temperature for the calculation (e.g. maximum or average through the transient) and the method of strain rate calculation (e.g. assumption of constant strain rate, or integration through the cycle, i.e. the modified strain rate approach). These assumptions can be overly conservative and hence very restrictive for plant operators when making safety justifications. Improved models have been developed which weight fatigue damage through the cycle, which is consistent with recent observations from testing under complex load cycles. Although these models can more accurately predict fatigue life for loading that is representative of PWR transients, they still assume membrane loading which is unrealistic for thermal shock transients in thin walled components. Details of a testing capability at Wood (formerly Amec Foster Wheeler) or thermal shock testing in a PWR environment were presented in a previous paper (ASME PVP2018-84923). The predictions of fatigue initiation indicated test durations of 2–3 months based on the latest fatigue models for austenitic stainless steel. The current paper presents the results of the first thermal shock tests carried out on a type 304L stainless steel. The predictions are compared with experimental observations and the accuracy of the models are assessed.

A Procedure for Low Cycle Fatigue Life Prediction for Various Temperatures and Strain Rates

1990 ◽  
Vol 112 (4) ◽  
pp. 422-428 ◽  
Author(s):  
Ange Zhang ◽  
T. Bui-Quoc ◽  
R. Gomuc
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Low Frequency ◽  
Strain Range ◽  
Strain Rates ◽  
Total Strain Range ◽  
Wide Range ◽  
Experimental Values

This paper describes a procedure that permits the calculation of the fatigue life over a wide range of temperatures and strain rates. The isothermal fatigue life is expressed in terms of the total strain range by an equation previously obtained from a continuous damage concept. Additional new terms are introduced to take into account the effect of the temperature and of the strain rate. For a given material, a multiple regression analysis is carried out using some experimental results in order to evaluate the material constants involved. Once these constants are known, the life prediction can be made for other specified values of temperature and strain rate. The approach is applied to available data obtained from several stainless steels (AISI 304, 316, 348, and some SUS materials) under several combinations of temperatures and strain rates. The deviation of the calculated lives from the experimental values is reasonably acceptable. The extension of the proposed procedure to cases of cycling with a very low frequency, usually involving hold times, is examined and discussed.

scholarly journals Uniaxial Dynamic Mechanical Properties Of Tunnel Lining Concrete Under Moderate-Low Strain Rate After High Temperature

2015 ◽  
Vol 61 (2) ◽  
pp. 35-52 ◽  
Author(s):  
L. X. Xiong
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Strain Rate ◽  
High Temperatures ◽  
Concrete Specimen ◽  
Tunnel Lining ◽  
Strain Rates ◽  
Peak Strain ◽  
Increasing Temperature

AbstractTo investigate the mechanical properties of tunnel lining concrete under different moderate-low strain rates after high temperatures, uniaxial compression tests in association with ultrasonic tests were performed. Test results show that the ultrasonic wave velocity and mass loss of concrete specimen begin to sharply drop after high temperatures of 600 °C and 400 °C, respectively, at the strain rates of 10-5s-1 to 10-2s-1. The compressive strength and elastic modulus of specimen increase with increasing strain rate after the same temperature, but it is difficult to obtain an evident change law of peak strain with increasing strain rate. The compressive strength of concrete specimen decreases first, and then increases, but decreases again in the temperatures ranging from room temperature to 800 °C at the strain rates of 10-5s-1 to 10-2s-1. It can be observed that the strain-rate sensitivity of compressive strength of specimen increases with increasing temperature. In addition, the peak strain also increases but the elastic modulus decreases substantially with increasing temperature under the same strain rate.

scholarly journals Study on Dynamic Mechanical Properties of Full Tailings Cemented Backfilling Impacted by Cement-Sand Ratio

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Shan Yang ◽  
Zhiyong Zhou ◽  
Yifei Zhao ◽  
Wei Yang
Keyword(s):  
Compressive Strength ◽  
Growth Factor ◽  
Strain Rate ◽  
Dynamic Strength ◽  
Peak Stress ◽  
Strain Ratio ◽  
Dynamic Mechanical Properties ◽  
Strain Rates ◽  
Peak Strain ◽  
Dynamic Compressive Strength

In order to study the effect of cement-sand ratio on the dynamic mechanical properties of the full tailings cemented backfilling, three sets of full tailings cemented backfilling specimens with different cement-sand ratios were prefabricated. The uniaxial impact of the prefabricated specimens was performed by the Ф50 mm SHPB test system. Test results showed that full tailings cemented backfilling had strong reflection and damping effects on elastic wave propagation. At lower strain rates, specimens presented strength hardening, and at higher strain rates, the test specimens presented rapid-softening strength; the strength-hardened specimen reached the peak stress at 40 μs, and the softening specimen reached the peak stress at about 18 μs; with the increase of strain rate, dynamic compressive strength, growth factor of dynamic strength, peak strain, and dynamic-static strain ratio of specimens increased totally. When the cement-sand ratio increased, ultimate dynamic compressive strength, limit dynamic strength growth factor, and ultimate peak strain of the specimen were higher; at the same strain rate, with the increase of cement content, the dynamic compressive strength, dynamic strength growth factor, and dynamic-static strain ratio of the test piece all decreased. The failure mode of the specimen was crushing failure. Under the same strain rate, when the cement content decreased, there was a higher damage degree of specimens.

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