scholarly journals STUDY ON BRITTLE FRACTURE OF STEEL UNDER PLASTIC STRAIN BASED ON LOCAL FRACTURE APPROACH

2000 ◽  
Vol 65 (536) ◽  
pp. 151-156 ◽  
Author(s):  
Tadao NAKAGOMI ◽  
Susumu MINAMI ◽  
Hiroshi SHIRASAKI ◽  
Satoru ARAI
Keyword(s):  
Brittle Fracture ◽  
Plastic Strain ◽  
Local Fracture

Full Scale Reeling Simulation Tests of Girth Welded X60 HFW Linepipe

2016 ◽  
Author(s):  
Teruki Sadasue ◽  
Satoshi Igi ◽  
Kenji Oi ◽  
Satoru Yabumoto
Keyword(s):  
Brittle Fracture ◽  
Plastic Strain ◽  
Yield Strength ◽  
Tensile Properties ◽  
Local Buckling ◽  
Full Scale ◽  
The Other ◽  
Simulation Test ◽  
Other Hand ◽  
Girth Welds

The reel-lay method is a fast and cost efficient installation process for offshore rigid steel pipelines. Pipelines installed by the reel-lay method are plastically deformed due to reeling, unreeling, aligning and straightening during pipeline installation. Therefore, local buckling is one of the major concerns from a view point of integrity in linepipes, especially around girth welds where strength mismatching arises due to adjacent pipes with different yield strength. One the other hand, the change in mechanical properties of linepipes during reel-lay, including coating process (e.g. 250°C) and long time exposure (e.g. 250°C aging) after installation is also important in order to guarantee safety of linepipes. Furthermore fracture toughness at girth weld Coarse-grain HAZ (CGHAZ) after reeling and aging should be clear to prevent brittle fracture of offshore linepipes in service. In this study, full scale reeling simulation tests of girth welded X60 HFW (High Frequency electric resistance Welded) linepipes with OD; 323.9mm and WT;15.9mm after full body heat treatment (coating simulation) were conducted at 5cycles and 2cycles reeling and straightening situations when yield strength mismatches are present between adjacent pipes around girth welds. Localized strain concentration was observed near girth welds by strength mismatching of adjacent pipes. DNV ovality increased with increasing reeling and straightening cycles, however the ovality did not exceed 10%, which was a criterion value for local buckling, after 5cycles reeling simulation test. The change ratio of wall thickness after full scale reeling simulation tests were about ±2% (within DNV-OS-F101 tolerance) regardless of circumferential and longitudinal direction of pipes. Longitudinal tensile properties could be characterized by axial last introduced plastic strain. That is, in the positive number of last introduced plastic strain, YS and Y/T increased, while uEl decreased by work hardening effect. On the other hand YS and Y/T decreased, while uEl increased at the negative number of last introduced plastic strain by Bauschinger effect. Circumferential tensile properties could be also characterized by axial last introduced plastic strain. Yield strength and Y/T slightly increased while uniform elongation slightly decreased by aging at longitudinal and circumferential direction. Tensile properties did not change irrespective of the number of cycles of reeling simulation tests. After 5cycles reeling simulation test and aging, girth welded CGHAZ CTOD values were over 0.4mm at −20°C and Charpy absorbed energy were over 200J at −30°V, therefore, it was considered that the brittle fracture of the girth welded linepipe unlikely occur at reeling and aging situation in this study.

Plastic Strain Distribution as a Precursor for Transition From Ductile to Brittle Failure in Lead-Free Solder Joints

2009 ◽  
Author(s):  
Feng Gao ◽  
Jianping Jing ◽  
Frank Z. Liang ◽  
Richard L. Williams ◽  
Jianmin Qu
Keyword(s):  
Brittle Fracture ◽  
Plastic Strain ◽  
Solder Joint ◽  
Failure Mode ◽  
Strain Distribution ◽  
Solder Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Loading Rates ◽  
Free Solder

One of the major failure modes in lead-free solder joints is the brittle fracture at the solder/Cu pad interface under dynamic loading conditions. Such brittle fracture often leads to catastrophic premature failure of portable electronic devices. Therefore, it is desirable to design the package and the solder joints in such a way that brittle interfacial fracture can be avoided during drop test. To develop such design guidelines, we studied in this paper the dynamic failure of a single solder joint (SSJ). The SSJs with different geometry and substrate surface finish were prepared by laser-cutting from a BGA package assembled on a printed circuit board (PCB). The SSJs were tested under various shear loading rates, ranging from 5 mm/s to 500 mm/s. In conjunction with the experimental tests, finite element analyses (FEA) of these SSJ samples subjected to various loading rates were also conducted. Results from both experimental testing and numerical simulations show that the distribution of plastic strain near the solder/IMC interface is a key indictor of the failure mode. For a given sample geometry and loading rate, if the maximum solder plastic strain lies near the solder/IMC interface, the failure will be more likely to be ductile failure within the solder alloy. On the other hand, if the maximum plastic strain is mainly located at the edge of the interface between solder and the IMC layer with very little plasticity within the solder near the interface, brittle fracture of the IMC/Cu interface will be more likely to occur. Since numerically computing the plastic strain distribution in a solder joint is much easier than predicting joint failure, results of this study provide us with an effective means to predict the type of failure mode of a solder joint under dynamic loading.

scholarly journals Structure of fracture under the joint operation of two mechanisms of local destruction

2020 ◽  
pp. 49-58
Author(s):  
Николай Михайлович Осипенко
Keyword(s):  
Brittle Fracture ◽  
Joint Action ◽  
Ice Sheet ◽  
Compression Axis ◽  
Mechanism Of Formation ◽  
Local Fracture ◽  
Joint Operation ◽  
Model Situation ◽  
Local Destruction ◽  
A Chain

Рассмотрены примеры сценариев хрупкого разрушения, в которых участвуют два механизма локального разрушения - развитие трещин нормального разрыва и компактирование, либо торошение, при сжатии. Работа является продолжением исследований структур разрушения в условиях сжатия [1]. Показано, что в модельной ситуации с цепочкой отверстий в пластине выбор механизма формирования локальных очагов разрушения или их совместного действия зависит от ориентации системы отверстий относительно оси сжатия. Другой пример относится к процессу разрушения ледяного покрова при его сжатии под действием течений и ветровой нагрузки. Рассмотрен вариант разрушения, в котором происходит взаимодействие двух видов разрушения - локализованное в виде трещиноподобного дефекта разрушение при сжатии (торошении) и формирование сопутствующих поперечных разрывов, разбивающих нагружаемый участок ледяного покрова на ряд полос вдоль напряжений сжатия. Examples of brittle fracture scenarios are considered, in which two mechanisms of local fracture participate - the development of normal fracture cracks and compaction, or hummocking, under compression. The work is a continuation of studies of fracture structures under compression [1]. It is shown that in a model situation with a chain of holes in a plate, the choice of the mechanism of formation of local fracture centers or their joint action depends on the orientation of the system of holes relative to the compression axis. Another example relates to the process of destruction of the ice cover when it is compressed under the influence of currents and wind load. The fracture variant is considered, in which two types of fracture interact: the fracture localized in the form of a crack-like defect during compression (hummocking) and the formation of accompanying transverse ruptures dividing the loaded ice sheet section into a series of bands along the compression stresses.

Effect of Raw Material Purity on Structure and Properties of Metallic Glasses

2021 ◽  
Vol 1035 ◽  
pp. 759-767
Author(s):  
Rui Xian Ding ◽  
Sheng Zhong Kou ◽  
Jian Jun Fan ◽  
Ye Jiang
Keyword(s):  
Adverse Effect ◽  
Compressive Strength ◽  
Brittle Fracture ◽  
Plastic Strain ◽  
Metallic Glass ◽  
Metallic Glasses ◽  
Raw Material ◽  
Structure And Properties ◽  
Compression Process ◽  
Strength And Plasticity

Zirconium base metallic glasses [Zr0.73(Cu0.59Ni0.41)0.27]87Al13 was fabricated by industrial zirconium with low purity and high purity zirconium according to different quality ratios in order to study the effect of raw material purity on the structure and properties of metallic glasses. The results showed that the complete metallic glasses was failed to be fabricate with low purity zirconium. And the compression process was typical brittle fracture with low compressive strength and without plastic strain. The glasses forming ability of low purity zirconium metallic glass with different purity was significantly improved after the addition of yttrium element. The compression experiments showed that the compressive strength and plasticity of metallic glasses were improved, and the microhardness was also increased. It indicates that yttrium element can eliminate the adverse effect of impurity in low purity zirconium on the glasses forming ability of the alloy and improve the structural properties of the metallic glasses.

scholarly journals Brittle fracture in structural steels: perspectives at different size-scales

2015 ◽  
Vol 373 (2038) ◽  
pp. 20140126 ◽  
Author(s):  
John Knott
Keyword(s):  
Brittle Fracture ◽  
Fracture Stress ◽  
Structural Integrity ◽  
Materials Testing ◽  
Local Fracture ◽  
Cooperative Movement ◽  
Test Pieces ◽  
Conclusion Section ◽  
Local Fracture Stress ◽  
Size Scales

This paper describes characteristics of transgranular cleavage fracture in structural steel, viewed at different size-scales. Initially, consideration is given to structures and the service duty to which they are exposed at the macroscale , highlighting failure by plastic collapse and failure by brittle fracture. This is followed by sections describing the use of fracture mechanics and materials testing in carrying-out assessments of structural integrity. Attention then focuses on the microscale , explaining how values of the local fracture stress in notched bars or of fracture toughness in pre-cracked test-pieces are related to features of the microstructure: carbide thicknesses in wrought material; the sizes of oxide/silicate inclusions in weld metals. Effects of a microstructure that is ‘heterogeneous’ at the mesoscale are treated briefly, with respect to the extraction of test-pieces from thick sections and to extrapolations of data to low failure probabilities. The values of local fracture stress may be used to infer a local ‘work-of-fracture’ that is found experimentally to be a few times greater than that of two free surfaces. Reasons for this are discussed in the conclusion section on nano -scale events. It is suggested that, ahead of a sharp crack, it is necessary to increase the compliance by a cooperative movement of atoms (involving extra work) to allow the crack-tip bond to displace sufficiently for the energy of attraction between the atoms to reduce to zero.

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