Experimental and Analytical Study on Local Failure of Structure Subjected to High Temperature and Pressure

2019 ◽  
Author(s):  
Yoshiki Tsunemoto ◽  
Takashi Sakaguchi ◽  
Takuya Sato ◽  
Naoto Kasahara
Keyword(s):  
Fracture Surface ◽  
Analytical Study ◽  
Failure Modes ◽  
Hydrostatic Stress ◽  
Plastic Region ◽  
Local Failure ◽  
Elastic Plastic ◽  
Creep Region ◽  
Temperature And Pressure ◽  
Failure Location

Abstract In our past paper, the new fracture surface was proposed considering the effects of hydrostatic stress in an elastic-plastic region and in a creep region. In this paper, the mechanism the dominant factors of local failure were studied in an elastic-plastic region. Experimental and analytical study were made using circular plate specimens with a nozzle. The material was a lead alloy (99% Pb-1% Sb). The fracture test was performed in an elastic-plastic region at room temperature. Both ductile fracture and local failure were observed at structural discontinuities, based on the stiffness differences between attached nozzles and plates. In this study, the proposed fracture surface in an elastic-plastic region showed the fracture location accurately, for the both failure modes. It was concluded that the proposed fracture surface is available and useful in order to predict the failure mode and the failure location.

Proposal of the Local Failure Evaluation Method With Stress Parameters

2018 ◽  
Author(s):  
Takashi Sakaguchi ◽  
Mizuki Yoshida ◽  
Takuya Sato ◽  
Naoto Kasahara
Keyword(s):  
Fracture Surface ◽  
Evaluation Method ◽  
Hydrostatic Stress ◽  
Notch Root ◽  
Local Failure ◽  
Dominant Factor ◽  
Multiaxial Stress ◽  
Minimum Diameter ◽  
Nuclear Plants ◽  
New Criterion

The failure mode known as local failure could occur at structure discontinuities with multiaxial stress conditions. Experiments and analyses of notched bars, which generate multiaxial stress, were conducted. The experiments showed that the tensile strength of a notched bar was stronger than that of a smooth bar. The ratio of the maximum and minimum diameter has become the important factor of this notch strengthening. In addition, the initiation of failure was observed at the inner location from the notch root. According to the analysis results, the Mises-stress became the maximum at the notch root. On the other hand, hydrostatic stress became the maximum at the inner location from the notch root, and this location corresponded to the initiation of fracture. The maximum hydrostatic stress has good correlation with the notch strengthening ratio. These facts reveal that hydrostatic stress must be taken into account for strength evaluation as a dominant factor in addition to the Mises-stress. However, only Mises-stress is considered in the present structural design code of nuclear plants. From above results, the new criterion based on fracture surface, where the coordinate plane consists of hydrostatic stress and Mises-stress, was proposed for local failure. Furthermore, this fracture surface was extended to an isochronous fracture surface in a creep region based on isochronous stress-strain curves.

Structural Integrity Research for Reactor Pressure Vessel Under In-Vessel Retention of a Core Melt

2016 ◽  
Author(s):  
Yongjian Gao ◽  
Yinbiao He ◽  
Ming Cao ◽  
Yuebing Li ◽  
Shiyi Bao ◽  
...  
Keyword(s):  
Pressure Vessel ◽  
Material Properties ◽  
Power Plants ◽  
Structural Integrity ◽  
Plastic Material ◽  
Plastic Region ◽  
Reactor Pressure Vessel ◽  
Elastic Plastic ◽  
Elastic Plastic Material ◽  
Reactor Pressure

In-Vessel Retention (IVR) is one of the most important severe accident mitigation strategies of the third generation passive Nuclear Power Plants (NPP). It is intended to demonstrate that in the case of a core melt, the structural integrity of the Reactor Pressure Vessel (RPV) is assured such that there is no leakage of radioactive debris from the RPV. This paper studied the IVR issue using Finite Element Analyses (FEA). Firstly, the tension and creep testing for the SA-508 Gr.3 Cl.1 material in the temperature range of 25°C to 1000°C were performed. Secondly, a FEA model of the RPV lower head was built. Based on the assumption of ideally elastic-plastic material properties derived from the tension testing data, limit analyses were performed under both the thermal and the thermal plus pressure loading conditions where the load bearing capacity was investigated by tracking the propagation of plastic region as a function of pressure increment. Finally, the ideal elastic-plastic material properties incorporating the creep effect are developed from the 100hr isochronous stress-strain curves, limit analyses are carried out as the second step above. The allowable pressures at 0 hr and 100 hr are obtained. This research provides an alternative approach for the structural integrity evaluation for RPV under IVR condition.

Crack Propagation and Local Failure Simulation of Reinforced Concrete Subjected to Projectile Impact Using RBSM

2016 ◽  
Author(s):  
Yoshihito Yamamoto ◽  
Soichiro Okazaki ◽  
Hikaru Nakamura ◽  
Masuhiro Beppu ◽  
Taiki Shibata
Keyword(s):  
Reinforced Concrete ◽  
Crack Propagation ◽  
High Velocity ◽  
Failure Modes ◽  
Concrete Structures ◽  
Constitutive Models ◽  
Local Failure ◽  
High Velocity Impact ◽  
Velocity Impact ◽  
Projectile Impact

In this paper, numerical simulations of reinforced mortar beams subjected to projectile impact are conducted by using the proposed 3-D Rigid-Body-Spring Model (RBSM) in order to investigate mechanisms of crack propagation and scabbing mode of concrete members under high-velocity impact. The RBSM is one of the discrete-type numerical methods, which represents a continuum material as an assemblage of rigid particle interconnected by springs. The RBSM have advantages in modeling localized and oriented phenomena, such as cracking, its propagation, frictional slip and so on, in concrete structures. The authors have already developed constitutive models for the 3D RBSM with random geometry generated Voronoi diagram in order to quantitatively evaluate the mechanical responses of concrete including softening and localization fractures, and have shown that the model can simulate cracking and various failure modes of reinforced concrete structures. In the target tests, projectile velocity is set 200m/s. The reinforced mortar beams with or without the shear reinforcing steel plates were used to investigate the effects of shear reinforcement on the crack propagation and the local failure modes. By comparing the numerical results with the test results, it is confirmed that the proposed model can reproduce well the crack propagation and the local failure behaviors. In addition, effects of the reinforcing plates on the stress wave and the crack propagation behaviors are discussed from the observation of the numerical simulation results. As a result, it was found that scabbing of reinforced mortar beams subjected to high velocity impact which is in the range of the tests is caused by mainly shear deformation of a beam.

Failure Modes of Tapered Suction Caissons Under Vertical Pull-Out Loads

2007 ◽  
Author(s):  
Mahmood Nabipour ◽  
Mostafa Zeinoddini ◽  
Mahmood R. Abdi
Keyword(s):  
Failure Modes ◽  
Numerical Approach ◽  
Local Failure ◽  
Superior Performance ◽  
Soil Plug ◽  
Pull Out ◽  
Modes Of Failure ◽  
Numerical Studies ◽  
Second Mode ◽  
Suction Caissons

The pull-out performance of conventional upright suction caissons has been investigated by different researchers. However, no attention has been formerly paid to tapered suction caissons. Some numerical studies already conducted by the authors demonstrated that tapered caissons exhibit pull-out capacities well above than that from their corresponding upright caissons. This paper deals with different failure mechanisms of tapered suction caissons and discusses some reason for their superior performance. A numerical approach has been used and different combinations of caisson types/ soil categories have been examined. With tapered suction caissons two different modes of failure have been discerned. The first mode has been noticed to develop in weak clays and sands under drained conditions. This mode corresponds to a shear sliding failure in the soil plug along the caisson’s interior wall. Concurrently a soil wedge is formed in the soil body adjacent to the caisson. The second mode of failure has been observed in higher strength drained clays and undrained clays and sands. With this failure mode a local failure at the bottom of the soil plug has been noticed to happen. At the same time the failure is extended to the lower surfaces of a soil wedge outside of the caisson. The detached soil plug accompanies the caisson in its movement upward following the local failure.

Identification of Failure Modes Under Design Extension Conditions

2015 ◽  
Author(s):  
Naoto Kasahara ◽  
Izumi Nakamura ◽  
Hideo Machida ◽  
Hitoshi Nakamura ◽  
Koji Okamoto
Keyword(s):  
High Temperature ◽  
Nuclear Power ◽  
Failure Modes ◽  
Low Cycle Fatigue ◽  
External Pressure ◽  
Lessons Learned ◽  
Local Failure ◽  
Severe Accident ◽  
Mitigation Measures ◽  
Loading Mode

As the important lessons learned from the Fukushima-nuclear power plant accident, mitigation of failure consequences and prevention of catastrophic failure became essential against severe accident and excessive earthquake conditions. To improve mitigation measures and accident management, clarification of failure behaviors with locations is premise under design extension conditions such as severe accidents and earthquakes. Design extension conditions induce some different failure modes from design conditions. Furthermore, best estimation for these failure modes are required for preparing countermeasures and management. Therefore, this study focused on identification of failure modes under design extension conditions. To observe ultimate failure behaviors of structures under extreme loadings, new experimental techniques were adopted with simulation materials such as lead and lead-antimony alloy, which has very small yield stress. Postulated failure modes of main components under design extension conditions were investigated according three categories of loading modes. The first loading mode is high temperature and internal pressure. Under this mode, ductile fracture and local failure were investigated. At the structural discontinuities, local failure may become dominant. The second is high temperature and external pressure loading mode. Buckling and fracture were investigated. Buckling occurs however hardly break without additional loads or constraints. The last loading is excessive earthquake. Ratchet deformation, collapse, and fatigue were investigated. Among them, low-cycle fatigue is dominant.

scholarly journals Repeated alternating loading of a elastoplastic three-layer plate in a temperature field

2021 ◽  
Vol 21 (1) ◽  
pp. 60-75
Author(s):  
Eduard I. Starovoitov ◽  
◽  
Denis V. Leonenko ◽  
Keyword(s):  
Temperature Field ◽  
Differential Equations ◽  
Boundary Value Problem ◽  
Boundary Conditions ◽  
Nonlinear Differential Equations ◽  
Boundary Value ◽  
Plastic Region ◽  
Local Load ◽  
Natural State ◽  
Elastic Plastic

Axisymmetric deformation of a three-layer circular plate under repeated alternating loading from the plastic region by a local load is considered. To describe kinematics of asymmetrical on the thickness of the plate pack is adopted the hypothesis of a broken line. In a thin elastic-plastic load-bearing layers are used the hypothesis of Kirchhoff. A non-linearly elastic relatively thick filler is incompressible in thickness. It is taken to be a hypothesis of Tymoshenko regarding the straightness and the incompressibility of the deformed normals with linear approximation of the displacements through the thickness layer. The work of the filler in the tangential direction is taken into account. The physical relations of stress-strain relations correspond to the theory of small elastic-plastic deformations. The effect of heat flow is taken into account. The temperature field in the plate was calculated by the formula obtained by averaging the thermophysical parameters over the thickness of the package. The system of differential equations of equilibrium under loading of the plate from the natural state is obtained by the Lagrange variational method. Boundary conditions on the plate contour are formulated. The solution of the corresponding boundary value problem is reduced to finding the three desired functions: deflection, shear and radial displacement of the shear surface of the filler. A non-uniform system of ordinary nonlinear differential equations is written for these functions. Its analytical iterative solution is obtained in Bessel functions by the method of elastic solutions of Ilyushin. In case of repeated alternating loading of the plate, the solution of the boundary value problem is constructed using the theory of variable loading of Moskvitin. In this case, the hypothesis of similarity of plasticity functions at each loading step is used. Their analytical form is taken independent of the point of unloading. However, the material constants included in the approximation formulas will be different. The cyclic hardening of the material of the bearing layers is taken into account. The parametric analysis of the obtained solutions under different boundary conditions in the case of a local load distributed in a circle is carried out. The influence of temperature and nonlinearity of layer materials on the displacements in the plate is numerically investigated.

Application of the Cyclic Strain Approach to the Fatigue Failure of Ship Structural Details

1987 ◽  
Vol 31 (03) ◽  
pp. 177-185
Author(s):  
Wolfgang Fricke ◽  
Hans Paetzold
Keyword(s):  
Fatigue Life ◽  
Plastic Region ◽  
Steel Structure ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Damage Parameter ◽  
Elastic Plastic ◽  
Strain Behavior ◽  
Structural Details ◽  
The Relationship

The cyclic strain approach is useful for determining the fatigue life of notches strained in the elastic-plastic region. Examples are the flame-cut edges of cutouts in the ship steel structure. After the description of the cyclic stress-strain behavior of the usual mild steel, the individual elements of the approach are described: the probability distribution of load amplitudes, the relationship between load and local elastic-plastic strain, the relationship between the damage parameter and fatigue life, and finally the damage accumulation law. The approach is illustrated by two examples of longitudinal/transverse web intersections. In the first, the predicted life is confirmed by experimental results. The second example shows the approach for complicated load combinations. It is hoped that this paper will contribute to sound and crack-free ship structural details, particularly if unusual loads are applied to well-tried details or if simplified designs are introduced.

The Microscopic Analysis on the Crankshaft Fracture Surface of the Compressor

2014 ◽  
Vol 912-914 ◽  
pp. 837-840
Author(s):  
Wei Dong Chen
Keyword(s):  
Heat Treatment ◽  
Brittle Fracture ◽  
Fracture Surface ◽  
Grain Refinement ◽  
Stress Fracture ◽  
Failure Modes ◽  
Microscopic Analysis ◽  
Dendritic Segregation ◽  
Micro Analysis

Fracture is the most common failure modes of the crankshaft, under normal circumstances often result in serious consequences. So study the reasons for the crankshaft fracture, thus achieving the purpose of controlling and reducing accidents, is very realistic. In this paper, for example, a factory break 4M16 compressor crankshaft. Through micro-analysis of the crankshaft fracture, the 4M16 compressor crankshaft is a low stress fracture of brittle fracture .The fracture is mainly due to dendritic segregation cause tissue caused by uneven. Solution to the problem is to increase the ratio of forging the forging, heat treatment when the grain refinement.

Contribution to Safety Enhancement for BDBE in Structure and Material Fields

2018 ◽  
Author(s):  
Naoto Kasahara ◽  
Takuya Sato ◽  
Andrei Blahoianu
Keyword(s):  
Failure Mode ◽  
Failure Modes ◽  
Stress Test ◽  
Relative Strength ◽  
Research Issues ◽  
Best Estimate ◽  
Safety Function ◽  
Risk Approach ◽  
Failure Location ◽  
Safety Enhancement

This paper proposes research issues on contribution to safety enhancement for BDBE in structure and material fields. There are large difference between DBE and BDBE. Objective of DBE is prevention of accident and conservative approach is adopted such as prevention of all assumed failure modes. As for BDBE, objectives are prevention of safety function loss and mitigation of accident consequences, risk approach is expected. Since DEC is a part of BDBE, approach against DEC is different from DBE. DEC requires best estimate. Probabilistic Risk Assessment consists of best estimate plus uncertainty. For stress test, identification of the weakest portions and cliff edges become important. To realize above approach, prediction of realistic failure modes is essential. Furthermore, relative strength evaluation becomes important to predict order of failure location and their mode, even though absolute strength is not clear. After Fukushima daiichi nuclear accident, there is a tendency to apply DBE design criteria to BDBE, however, conservative criteria for design are inappropriate for best estimate. Therefore, authors proposes failure mode maps to identify realistic failure mode and its application to mitigation to accident sequences such as fracture control.

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