scholarly journals Investigation of Notch-Induced Precise Splitting of Different Bar Materials under High-Speed Load

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2461 ◽  
Author(s):  
Yuanzhe Dong ◽  
Yujian Ren ◽  
Shuqin Fan ◽  
Yongfei Wang ◽  
Shengdun Zhao
Keyword(s):  
Crack Initiation ◽  
High Speed ◽  
Splitting Method ◽  
Equivalent Plastic Strain ◽  
Stress Triaxiality ◽  
Initiation Zone ◽  
New Type ◽  
Notch Tip ◽  
Maximum Impact Force ◽  
1045 Steel

A notch-induced high-speed splitting method was developed for high-quality cropping of metal bars using a new type of electric-pneumatic counter hammer. Theoretical equations and FE models were established to reveal the crack initiation and fracture mode. Comparative tests were conducted for notched and unnotched bars of four types of steels, i.e., AISI 1020, 1045, 52100, and 304, and the section quality and microfracture mechanism were further investigated. The results show that damage initiates at the bilateral notch tips with peak equivalent plastic strain, and propagates through the plane induced by the notch tip; the stress triaxiality varies as a quasi-sine curve, revealing that the material is subjected to pure shearing at the notch tip, and under compression at the adjacent region. High precision chamfered billets were obtained with roundness errors of 1.1–2.8%, bending deflections of 0.5–1.5mm, and angles of inclination of 0.7°–3.4°. Additionally, the notch effectively reduced the maximum impact force by 21.6–23.9%, splitting displacement by 7.6–18.6%, and impact energy by 27.8–39.1%. The crack initiation zone displayed quasi-parabolic shallow dimples due to shear stress, and the pinning effect was larger in AISI 52100 and 1045 steel; the final rupture zone was characterized by less elongated and quasi-equiaxial deeper dimples due to the combination of shear and normal stress.

Ductile Crack Initiation Behavior of Prestrained Steels

2011 ◽  
Author(s):  
Takehisa Yamada ◽  
Yoichi Yamashita
Keyword(s):  
Crack Initiation ◽  
Void Nucleation ◽  
Equivalent Plastic Strain ◽  
Stress Triaxiality ◽  
Ductile Crack ◽  
Round Bar ◽  
Point Bend ◽  
Materials Used ◽  
Cracked Specimens ◽  
Triaxiality Factor

Ductile crack initiation behaviors were experimentally and analytically investigated using compressively prestrained notched round bar specimen (lower stress triaxiality condition) and four point bend specimen (higher stress triaxiality condition). The materials used were SM400B and HT780. It was observed that ductile crack initiation of notched round bar specimen occurred at the center of specimen and was caused by coalescence of micro voids. Ductile limit curves, which are the relationships between equivalent plastic strain and stress triaxiality factor at ductile crack initiation, were obtained using FE-analyses and experimental results. Ductile crack initiation of four point bend specimens as cracked specimens could be evaluated using ductile crack initiation limit curves obtained from notched round bar specimens if the positions of void nucleation at crack tip are properly considered. It has been found that ductile crack initiation limits can be evaluated using ductile limit curves under both low and high constraint conditions (stress triaxiality conditions.

Two-Parameter Criteria for Ductile Crack Initiation and Propagation in High-Grade Line Pipes

2007 ◽  
Vol 348-349 ◽  
pp. 493-496
Author(s):  
Yoichi Kayamori ◽  
P.S.J. Crofton ◽  
Roderick A. Smith
Keyword(s):  
Crack Initiation ◽  
Plastic Strain ◽  
Driving Force ◽  
Equivalent Plastic Strain ◽  
Stress Triaxiality ◽  
High Grade ◽  
Ductile Crack ◽  
Force Curve ◽  
Crack Driving Force ◽  
The Relationship

Full-scale burst test data of high-grade line pipes for high-pressure gas pipelines were referred to, and 3-D elastic-plastic finite element analysis was carried out using the test data for the calculation of fracture parameters. Ductile crack initiation was evaluated by the intersection of a toughness locus and a crack driving force curve, where the toughness locus was indicated by the relationship between the critical equivalent plastic strain and the stress triaxiality, and the crack driving force curve was shown by a history of the equivalent plastic strain and the stress triaxiality at characteristic distance. In addition, ductile crack rapid propagation was assessed by the relationship between the critical CTOA and the global constraint factor, where the critical CTOA remained almost constant because of high constraint.

Application of Ductile Cracking Criterion to the Assessment of Girth Weld Integrity for High Strength Linepipe

2005 ◽  
Author(s):  
Nobuyuki Ishikawa ◽  
Shigeru Endo ◽  
Satoshi Igi ◽  
Teruki Sadasue
Keyword(s):  
Crack Initiation ◽  
Plastic Strain ◽  
Large Deformation ◽  
Material Properties ◽  
Equivalent Plastic Strain ◽  
High Strength ◽  
Small Scale ◽  
Pipeline System ◽  
Ductile Crack ◽  
Notch Tip

Fracture behavior of high strength linepipes with weld defects is of great interest for the integrity of pipeline system. Especially, in the seismic or permafrost area, where large ground displacement can be expected, linepipe materials need to have sufficient resistance against brittle and ductile fracture under large deformation. Wide plate tensile test with surface flaw in the girth weld metal of X100 linepipe demonstrated that tensile limit is dominated by ductile crack initiation and its propagation. Conditions for ductile crack initiation for the base materials and girth weld joints of Grade X80 and X100 linepipes were investigated in this study. It was shown that ductile cracking occurs in the notch tip region of the wide plate specimen when notch tip equivalent plastic strain reaches the same critical value as determined by the small-scale tests. Therefore, “the equivalent plastic strain” in the critical regions can be used as a transferable parameter to predict ductile crack initiation behavior. Assessment methodology for tensile limit of high strength linepipe girth weld with respect to preventing ductile cracking was proposed. The effect of strength matching of girth weld and base metal Y/T ratio on limit remote strain as well as allowable defect size was investigated analytically. Increasing strength matching and lowering Y/T ratio of base material can lead to higher limit strain to ductile cracking of girth weld. These effects of material properties were validated by weld wide plate tensile tests. Therefore, careful selection of material properties should be important to improve resistance against ductile cracking of linepipe girth welds under large deformation field.

Effect of Strength Mismatch on Ductile Crack Initiation Behavior from Notch Root under Static Loading

2005 ◽  
Vol 297-300 ◽  
pp. 756-761 ◽  
Author(s):  
Gyu Baek An ◽  
Mitsuru Ohata ◽  
Masahito Mochizuki ◽  
Han Sur Bang ◽  
Masao Toyoda
Keyword(s):  
Crack Initiation ◽  
Static Loading ◽  
Notch Root ◽  
Equivalent Plastic Strain ◽  
Stress Triaxiality ◽  
Critical Conditions ◽  
Ductile Crack ◽  
Surface Cracking ◽  
Triaxial Stresses ◽  
Ductile Fractures

It has been well known that ductile fractures of steels are accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameter criterion based on equivalent plastic strain and stress triaxiality. It has been demonstrated by authors using round-bar specimens with circumferential notch in single tension that the critical strain to initiate ductile crack from specimen center depends considerably on stress triaxiality, but surface cracking of notch root is in accordance with constant strain condition. This study fundamentally clarifies the effect of strength mismatch, which can elevate plastic constraint due to heterogeneous plastic straining under static loading, on critical conditions for ductile cracking from the pre-notch root. In order to evaluate the stress/strain state in the pre-notch root of specimens, a thermal elastic-plastic finite element (FE) analysis has been carried out.

Light Railways as the Basic for Transport Infrastructure Development in Northern Territories of Russia

2020 ◽  
pp. 97-101
Author(s):  
P.I. Tarasov
Keyword(s):  
High Speed ◽  
Road Transport ◽  
Transport Infrastructure ◽  
The Arctic ◽  
Infrastructure Development ◽  
Capital Costs ◽  
New Type ◽  
The Republic ◽  
Northern Territories ◽  
Mode Of Transport

Research objective: studies of economic and transport infrastructure development in the Arctic and Northern Territories of Russia. Research methodology: analysis of transport infrastructure in the Republic of Sakha (Yakutia) and the types of railways used in Russia. Results: economic development of any region is proportional to the development of the road transport infrastructure and logistics. When a conventional railway is operated in the Arctic conditions, it is not always possible to maintain a cargo turnover that would ensure its efficient use, and transshipment from one mode of transport to another is very problematic. A new type of railway is proposed, i.e. a light railway. Conclusions: the proposed new type of transport offers all the main advantages of narrow gauge railroads (high speed of construction, efficiency, etc.) and helps to eliminate their main disadvantage, i.e. the need for transloading when moving from a narrow gauge to the conventional one with the width of 1520 mm, along with a significant reduction in capital costs.

Effects of Cooling Conditions on Thermal Crack Initiation of Brittle Cutting Tools during Intermittent Cutting

2015 ◽  
Vol 656-657 ◽  
pp. 237-242
Author(s):  
Kenji Yamaguchi ◽  
Tsuyoshi Fujita ◽  
Yasuo Kondo ◽  
Satoshi Sakamoto ◽  
Mitsugu Yamaguchi ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Thermal Shock ◽  
High Speed ◽  
Cutting Tools ◽  
Cutting Speed ◽  
Cutting Condition ◽  
Thermal Crack ◽  
Cooling Conditions ◽  
Cutting Operation ◽  
Intermittent Cutting

It is well known that a series of cracks running perpendicular to the cutting edge are sometimes formed on the rake face of brittle cutting tools during intermittent cutting. The cutting tool is exposed to elevated temperatures during the periods of cutting and is cooled quickly during noncutting times. It has been suggested that repeated thermal shocks to the tool during intermittent cutting generate thermal fatigue and result in the observed thermal cracks. Recently, a high speed machining technique has attracted attention. The tool temperature during the period of cutting corresponds to the cutting speed. In addition, the cooling and lubricating conditions affect the tool temperature during noncutting times. The thermal shock applied to the tool increases with increasing cutting speed and cooling conditions. Therefore, to achieve high-speed cutting, the evaluation of the thermal shock and thermal crack resistance of the cutting tool is important. In this study, as a basis for improving the thermal shock resistance of brittle cutting tools during high-speed intermittent cutting from the viewpoint of cutting conditions, we focused on the cooling conditions of the cutting operation. An experimental study was conducted to examine the effects of noncutting time on thermal crack initiation. Thermal crack initiation was found to be restrained by reducing the noncutting time. In the turning experiments, when the noncutting time was less than 10 ms, thermal crack initiation was remarkably decreased even for a cutting speed of 500 m/min. In the milling operation, the number of cutting cycles before thermal crack initiation decreased with increasing cutting speed under conditions where the cutting speed was less than 500 m/min. However, when the cutting speed was greater than 600 m/min, thermal crack initiation was restrained. We applied the minimal quantity lubrication (MQL) coolant supply to the intermittent cutting operation. The experimental results showed that the MQL diminished tool wear compared with that under the dry cutting condition and inhibited thermal crack initiation compared with that under the wet cutting condition.

Ductile Crack Extension Analysis for X80 Bending Deformation Using Damage-Based Model

2014 ◽  
Author(s):  
Satoshi Igi ◽  
Mitsuru Ohata ◽  
Takahiro Sakimoto ◽  
Kenji Oi ◽  
Joe Kondo
Keyword(s):  
Plastic Strain ◽  
Simulation Model ◽  
Crack Growth ◽  
Crack Extension ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Crack Growth Behavior ◽  
Ductile Crack ◽  
Ductile Crack Growth ◽  
Notch Tip

This paper presents experimental and analytical results focusing on the strain limit of X80 linepipe. Ductile crack growth behavior from a girth weld notch is simulated by FE analysis based on a proposed damage model and is compared with the experimental results. The simulation model for ductile crack growth accompanied by penetration through the wall thickness consists of two criteria. One is a criterion for ductile crack initiation from the notch-tip, which is described by the plastic strain at the notch tip, because the onset of ductile cracking can be expressed by constant plastic strain independent of the shape and size of the components and the loading mode. The other is a damage-based criterion for simulating ductile crack extension associated with damage evolution influenced by plastic strain in accordance with the stress triaxiality ahead of the extending crack tip. The proposed simulation model is applicable to prediction of ductile crack growth behaviors from a circumferentially-notched girth welded pipe with high internal pressure, which is subjected to tensile loading or bending (post-buckling) deformation.

scholarly journals Investigation on the Crack Initiation of V-Shaped Notch Tip in Precision Cropping

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Lijun Zhang ◽  
Shengdun Zhao ◽  
Zhenwei Wang
Keyword(s):  
Crack Initiation ◽  
Equivalent Stress ◽  
Initiation Time ◽  
Initiation Point ◽  
Change Rate ◽  
Crack Initiation Angle ◽  
Notch Tip ◽  
Crack Initiation Life ◽  
Microscopic Measurement ◽  
Displacement Extrapolation Method

The crack initiation of V-shaped notch tip has a very important influence on the cross-section quality and the cropping time for every segment of metal bar in course of low stress precision cropping. By the finite element method, the influence of machining precision of V-shaped notch bottom corner on the crack initiation location is analyzed and it is pointed out that the crack initiation point locates in the place at the maximal equivalent stress change rate on V-shaped notch surface. The judgment criterion of the crack initiation direction is presented and the corresponding crack initiation angle can be calculated by means of the displacement extrapolation method. The factual crack initiation angle of the metal bar has been measured by using the microscopic measurement system. The formula of the crack initiation life of V-shaped notch tip is built, which mainly includes the stress concentration factor of V-shaped notch, the tensile properties of metal material, and the cyclic loading conditions. The experimental results show that the obtained theoretical analyses about the crack initiation location, the crack initiation direction, and the crack initiation time in this paper are correct. It is also shown that the crack initiation time accounts for about 80% of the cropping time for every segment of the metal bar.

A Fiber Optic Probe for Gas Total Temperature Measurement in Turbomachinery

1995 ◽  
Vol 117 (4) ◽  
pp. 635-641 ◽  
Author(s):  
S. R. Kidd ◽  
J. S. Barton ◽  
P. Meredith ◽  
J. D. C. Jones ◽  
M. A. Cherrett ◽  
...  
Keyword(s):  
Fiber Optics ◽  
High Speed ◽  
Gas Temperature ◽  
Fiber Optic Probe ◽  
Sensing Element ◽  
Unsteady Temperature ◽  
High Bandwidth ◽  
New Type ◽  
Total Temperature ◽  
Optic Probe

This paper describes the design, operation, construction, and demonstration of a new type of high-bandwidth unsteady temperature sensor based on fiber optics, and capable of operating in a high-speed multistage research compressor with flow representative of jet engine conditions. The sensing element is an optical coating of zinc selenide deposited on the end of an optical fiber. During evaluation in aerodynamic testing, a 1 K gas temperature resolution was demonstrated at 9.6 kHz and an upper bandwidth limit of 36 kHz achieved.

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