Prediction of Ductile-to-Brittle Transition Under Different Strain Rates in Undermatched Welded Joints

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Masahito Mochizuki ◽  
Masao Toyoda
Keyword(s):  
Strain Rate ◽  
Dynamic Loading ◽  
Welded Joints ◽  
Welded Joint ◽  
Material Behavior ◽  
Stress Strain ◽  
Fracture Characteristics ◽  
Brittle Transition ◽  
Tension Tests ◽  
Ductile To Brittle Transition

A welded joint generally has heterogeneity of strength, material, and fracture toughness. It is important to understand the characteristics of the strength and fracture of welded joints while considering the heterogeneous effect. In particular, the material behavior becomes more complicated when the welded joint with strength heterogeneity is subjected to dynamic rapid loading; for example, the welded heat-affected zone of pipeline steels is softened and welded underground pipelines are affected by a rapid ground sliding in an earthquake. In this paper, the characteristics of the strength and fracture of an undermatched joint under dynamic loading are studied by round-bar tension tests and thermal elastic-plastic analyses. The results show that the strength and fracture characteristics of the undermatched joints should be evaluated based on the effects of the strain rate and the temperature, including the temperature rise during dynamic loading. The tensile strength and the yield stress of the undermatched joints increase with the strain rate and with the decreasing temperature. The strength of the undermatched zone approaches that of the base metal when the thickness of the undermatched zone becomes smaller, and it does not depend on the strain rate. Finally, it is found that the stress-strain distribution affects fracture characteristics such as ductile-to-brittle transition behavior. The fracture characteristics are explained and predicted from the results of stress-strain relations obtained by numerical analysis.

Effect of Plastic Constraint and Strain Rate on Characteristics of Strength and Fracture in Undermatched Joints

2002 ◽  
Author(s):  
Masahito Mochizuki ◽  
Gyu-Baek An ◽  
Masao Toyoda
Keyword(s):  
Strain Rate ◽  
Dynamic Loading ◽  
Welded Joint ◽  
Material Behavior ◽  
Material Strength ◽  
Constraint Effect ◽  
Plastic Constraint ◽  
Tension Tests ◽  
Strength Material ◽  
Rapid Plastic Deformation

Welded joint generally has heterogeneity of strength, material, and fracture toughness. It is important to understand the characteristics of material strength and fracture in welded joint considering plastic constraint effect due to material heterogeneity. Furthermore, the material behavior becomes more complicated when welded joint receives dynamic loading like as earthquake. In this paper, the characteristics of strength and fracture in undermatched joints with strength heterogeneity under dynamic loading were studied by round-bar tension tests and thermal elastic-plastic analysis. These strength and fracture in undermatched joints are evaluated by considering the effects of strain rate and temperature including temperature rise due to rapid plastic deformation. The differences of fracture characteristics such as ductile-to-brittle transition behavior are considered from the plastic constraint effect and strain rate effect, and they are precisely explained in terms of the stress-strain distribution obtained by numerical analysis.

scholarly journals Investigation of the Mechanical Properties of St. Lawrence River Ice

1971 ◽  
Vol 8 (2) ◽  
pp. 163-169 ◽  
Author(s):  
L. W. Gold ◽  
A. S. Krausz
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Yield Stress ◽  
Power Law ◽  
River Ice ◽  
Stress Strain ◽  
Strain Behavior ◽  
Brittle Transition ◽  
Ductile To Brittle Transition ◽  
St Lawrence River

Observations are reported on the stress–strain behavior at −9.5 ± 0.5 °C of four types of ice obtained from the St. Lawrence River. The ice was subject to nominal rates of strain covering the range 2.1 × 10−5 min−1 to 5.8 × 10−2 min−1. A ductile-to-brittle transition was observed for strain rate of about 10−2 min−1. In the ductile range the four types had an upper yield stress that increased with strain rate according to a power law.

Development of a Methodology for Model Testing of Utor Welded Joints of a Vertical Cylindrical Tank

2021 ◽  
pp. 21-27
Author(s):  
D.A. Neganov ◽  
◽  
A.E. Zorin ◽  
O.I. Kolesnikov ◽  
G.V. Nesterov ◽  
...  
Keyword(s):  
Welded Joints ◽  
Strain State ◽  
Welded Joint ◽  
Design Parameters ◽  
Cylindrical Tank ◽  
Stress Strain ◽  
The Real ◽  
Stress Strain State ◽  
Hydraulic Machines ◽  
Wide Range

The methodology of laboratory modeling of the loading of utor welded joint of the tank is presented. The methodology is based on testing of the special design sample. It allows under uniaxial tension on the typical servo-hydraulic machines to reproduce in the zone of a utor welded joint the combined action of bending and shear forces, similar to that which occurs during the operation of a vertical cylindrical tank. To assess the distribution of the stress-strain state in the proposed design of the sample under its loading, the finite element modeling was performed in the ANSYS software package. It showed the fundamental correspondence of the stress distribution in the zone of the utor node in the sample and in the real tank. The experimental studies consisted in carrying out tests for the durability of a series of 16 samples loaded with the maximum force in the cycle, causing the calculated stresses in the zone of the welded utor node in the range of 100–200 % from the maximum permissible ones. The obtained results showed that the maximum loaded zone, where the destruction of the samples occurred, is the near-seam zone of the utor welded joint on the inside of the tank. This corresponds to the statistics of the real tank failures. It is established that the developed methodology ensures the possibility of carrying out correct resource tests of the tank utor welded joints. It is also possible to vary the stress-strain state scheme within a wide range in the area of the utor welded joint by changing the design parameters of the test sample. In compliance with the regulated welding technologies and the absence of unacceptable defects in the welded joint, the utor node has a high resource, which significantly exceeding 50 years of the tank operation.

Creep Strength Evaluation of a New and a Used Grade 91 Welded Joints by Using a Miniature Specimen

2018 ◽  
Author(s):  
Takashi Ogata
Keyword(s):  
Weld Metal ◽  
Strain Rate ◽  
Creep Strain ◽  
Base Metal ◽  
Welded Joints ◽  
Welded Joint ◽  
Creep Damage ◽  
Creep Strain Rate ◽  
Standard Size ◽  
Grade 91

Grade 91 is widely used for steam pipes and tubes in high temperature boilers of ultra-super critical power plants in Japan. It was reported that creep damage may initiate at the fine grain region within the heat affected zone (HAZ) in welded joints prior to the base metal, so called “Type IV” damage, which causes steam leakage in existing power plants. Therefore, development of creep damage assessment methods is not only an important but also an urgent subject to maintain operation reliability. In order to evaluate creep damage of welded joints based on finite element analyses, creep deformation properties of a base metal, a weld metal and a HAZ have to be obtained from creep tests. However, it is difficult to cut a standard size creep specimen from the HAZ region. Only a miniature size specimen is available from the narrow HAZ region. Therefore, development of creep testing and evaluation technique for miniature size specimens is highly expected. In this study, a miniature tensile type solid bar specimen with 1mm diameter was machined from a base metal, a weld metal and a HAZ of a new and a used Grade 91 welded joints, and creep tests of these miniature specimens were conducted by using a special developed creep testing machine. It was found that creep deformation property is almost identical between the base metal and weld metal, and creep strain rate of the HAZ is much faster than that of these metals in the new welded joint. Relationships between stress and creep strain rates of the base metal and the HAZ in the used welded joint are within scatter bands of those in the new material. On the other hand, creep strain rate of the weld metal in the used welded joint became much faster than that in the new one. Then both the standard size and the miniature size cross weld specimens were machined from the new and the used welded joints and were tested under the same temperature and stress conditions. Rupture time of the miniature cross weld specimen is much shorter than that of the standard size cross weld specimen. The finite element creep analysis of the specimens indicates that higher triaxiality stress yields within the HAZ of the standard size specimen than that of the miniature specimen causing faster creep strain rate in the HAZ of the miniature cross weld specimen.

Effect of Strain Rate on Ductile-to-Brittle Transition Temperature of a Free-Standing Pt-Aluminide Bond Coat

2011 ◽  
Vol 42 (6) ◽  
pp. 1431-1434
Author(s):  
Md. Zafir Alam ◽  
D. Chatterjee ◽  
K. Muraleedharan ◽  
T. K. Nandy ◽  
S. V. Kamat ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Strain Rate ◽  
Bond Coat ◽  
Free Standing ◽  
Brittle Transition ◽  
Brittle Transition Temperature ◽  
Ductile To Brittle Transition

scholarly journals Experimental Study on Damage and Failure of Coal-Pillar Dams in Coal Mine Underground Reservoir under Dynamic Load

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Qiangling Yao ◽  
Liqiang Yu ◽  
Ning Chen ◽  
Weinan Wang ◽  
Qiang Xu
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Strain Rate ◽  
Water Content ◽  
Dynamic Loading ◽  
Coal Pillar ◽  
Strain Curve ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Underground Reservoir

The stability of coal-pillar dams in underground hydraulic engineering works is affected not only by long-term water erosion but also by dynamic loading induced, for example, by roof breaking or fault slipping. In this paper, the water absorption characteristics of coal samples from western China were studied by nondestructive immersion tests, and a high-speed camera was used to monitor SHPB tests on samples of varying water content and subjected to various strain rates. Besides, the coal-pillar dam is numerically simulated based on the experimental data and the actual engineering conditions. The results show that, given low strain rate and high water content, the compaction stage accounts for most of the stress-strain curve, whereas the elastic stage accounts for only a relatively small fraction of the stress-strain curve. The dynamic compressive strength and elastic modulus follow exponential and logarithmic functions of strain rate, respectively, exhibiting a significant positive correlation. As the water content increases, the dynamic elastic modulus increases almost linearly, and the compressive strength decreases gradually. Under the same impact load, samples with greater water content fail more rapidly, and the failure is exacerbated by the propagation of parallel cracks to staggered cracks. The average size of coal fragments decreases linearly with increasing strain rate and water content. Simulations indicate that dynamic loading increases the stress concentration on both sides of the dam and expands the high-stress area and plastic zone. The results provide guidance for designing waterproof coal pillars and underground reservoir dams.

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