scholarly journals Investigation of Fracture Behavior and Mechanism in High-Speed Precise Shearing for Metal Bars with Prefabricated Fracture-Start Kerfs

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4073
Author(s):  
Yuanzhe Dong ◽  
Jinqiang Ning ◽  
Peng Dong ◽  
Yujian Ren ◽  
Shengdun Zhao
Keyword(s):  
Numerical Simulation ◽  
Fracture Mechanism ◽  
High Speed ◽  
Fracture Behavior ◽  
Equivalent Plastic Strain ◽  
Fractographic Analysis ◽  
Fracture Plane ◽  
Second Phase ◽  
Steel Bars ◽  
The Impact

A laser-assisted high-speed shearing (LAHSS) method has been proposed for metal bars, which prefabricates equally spaced fracture-start kerfs by Nd:Yag laser to make stress concentration, and applies a high-speed load to complete fracture separation. Comparative tests were conducted for Q235, 40Cr, and 304 steel bars, and the effects of fracture-start kerfs and axial clearance were investigated on the fracture section. Moreover, the fracture behavior was demonstrated by numerical simulation, and the micro-fracture mechanism was revealed by fractographic analysis. The numerical simulation results show that the material damage concentrates along with the kerf tips with peak equivalent plastic strain, and the corresponding stress triaxiality drops to almost zero at the kerf tip, which reveals that the material is subjected to pure shearing at kerf tip; the Max. loading force is reduced by 15.2%–29.6%, and the impact energy is decreased by 29.8%–46.9% for the three types of bar material. The experimental results showed that the fracture-start kerfs effectively inhibited the plastic deformation stage, and higher precision blanks were obtained in the LAHSS test: roundness error improved from 2.7%–10.9% to 1.1%–2.6%, Max. bending deflection decreased from 1.3–3.4 mm to 0.4–1.0 mm, and flatness error dropped from 0.9–3.3 mm to 0.3–0.7 mm. The fractographic analysis reveals that the crack initiation is related to alternative V-shape micro-notches at the laser-affected zone; the predominant fracture mechanism involves mode II microvoid coalescence at the main fracture plane; smaller and less elongated dimples were formed in 40Cr steels due to higher number density of grains and pinning effect of second-phase particles compared to Q235 and 304 steel bars.

scholarly journals Numerical simulation and experimental research of cavitation nozzle based on equation curve

2021 ◽  
Author(s):  
Lifu Wang ◽  
Dongyan Shi ◽  
Zhixun Yang ◽  
Guangliang Li ◽  
Chunlong Ma ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Flow Field ◽  
High Speed ◽  
Quadratic Equation ◽  
Outer Contour ◽  
Study Results ◽  
Fluent Software ◽  
The Impact ◽  
Better Than

Abstract To further investigate and improve the cleaning ability of the cavitation nozzle, this paper proposes a new model that is based on the Helmholtz nozzle and with the quadratic equation curve as the outer contour of the cavitation chamber. First, the numerical simulation of the flow field in the nozzle chamber was conducted using FLUENT software to analyze and compare the impact of the curve parameters and Reynolds number on the cleaning effect. Next, the flow field was captured by a high-speed camera in order to study the cavitation cycle and evolution process. Then, experiments were performed to compare the cleaning effect of the new nozzle with that of the Helmholtz nozzle. The study results demonstrate that effective cavitation does not occur when the diameter of the cavitation chamber is too large. For the new nozzle, with the increase of the Reynolds number, the degree of cavitation in the chamber first increases and then decreases; the cleaning effect is much better than that of a traditional Helmholtz nozzle under the same conditions; the nozzle has the best cleaning effect for the stand-off distance of 300 mm.

scholarly journals Field Test Research and Numerical Simulation on Aerodynamic Deloading Characteristics of V-Shaped Noise Barrier

2019 ◽  
Vol 24 (4) ◽  
pp. 764-773
Author(s):  
Ji Zhao ◽  
Ning Zhi ◽  
Lu Ming
Keyword(s):  
Numerical Simulation ◽  
Impact Strength ◽  
Field Test ◽  
High Speed ◽  
Rapid Development ◽  
Research Work ◽  
Load Shedding ◽  
Aerodynamic Load ◽  
Noise Barrier ◽  
The Impact

With the rapid development of the high-speed railway in China, the problems of the noise pollution induced by passing trains emerge. Theoretically, the V-shaped noise barrier is of pretty good performance of noise-reduction and load-shedding. To assess the practical aerodynamic deloading characteristics of the V-shaped noise barrier, a full-scale field test was carried out at three measuring-sections equipped with noise barriers of different heights. In order to quantify the research work, the impact strength and deloading rate were selected as indicators. The effects of train speeds, train types and barrier heights are studied. This study includes the variations of impact strength and deloading rate in vertical directions. Meanwhile, 2D numerical simulation research is conducted to analyze the experimental results from the angle of mechanism. It is observed that the aerodynamic load acting on the surface of the V-shaped noise barrier was weaker and more uniform compared with conventional barrier. The flow field distribution influenced the deloading characteristics of the V-shaped noise barrier significantly. Moreover, the load-shedding effect of V-shaped noise barrier, when CRH380AM passed by, was slightly better than CRH380A. The deloading rate improved with the increasing of the noise barrier height in general.

PENGEMBANGAN MODEL COMPUTER-BASED E-LEARNING UNTUK MENINGKATKAN KEMAMPUAN HIGH ORDER MATHEMATICAL THINKING SISWA SMA

2011 ◽  
Vol 16 (2) ◽  
pp. 71
Author(s):  
Jarnawi Afgani Dahlan ◽  
Yaya Sukjaya Kusumah ◽  
Mr Heri Sutarno
Keyword(s):  
High Speed ◽  
Teaching And Learning ◽  
Mathematical Thinking ◽  
Computer Software ◽  
High Order ◽  
Learning Activity ◽  
Second Phase ◽  
E Learning ◽  
Computer Based ◽  
The Impact

The focus of this research is on the development of mathematics teaching and learning activity which is based on the application of computer software. The aim of research is as follows : 1) to identify some mathematics topics which feasible to be presented by computer-based e-learning, 2) design, develop, and implement computer-based e-learning on mathematics, and 3) analyze the impact of computer-based e-learning in the enhancement of SMA students’ high order mathematical thinking. All activity in this research achieved in 2 phases. In the first phase, the following activities are conducted: analysis theoretically topics which are difficult to be delivered by conventional methods, need too many repetitions, need high accuracy, need high speed process, and can be presented more interestingly. In the second phase, the following activities are conducted: designing, developing, and implementing a number of teaching and research instruments; implementing computer-based e-learning on mathematics for SMA students’, and analyzing the impact of computer-based e-learning in the enhancement of SMA students’ high- order mathematical thinking. Key words: computer-based e-learning model, high-order mathematical thinking

An experimental and numerical investigation on impact spot welding of metallic plates using gas mixture detonation technique

2020 ◽  
pp. 146442072098232
Author(s):  
Sedigheh Hosseinzadeh ◽  
Hashem Babaei ◽  
Tohid Mirzababaie Mostofi
Keyword(s):  
Numerical Simulation ◽  
Shear Stress ◽  
Plastic Strain ◽  
Spot Welding ◽  
Equivalent Plastic Strain ◽  
Welding Process ◽  
Gas Mixture ◽  
The Impact ◽  
Base Plates ◽  
Metallic Plates

In this paper, the impact spot welding of metallic plates was investigated both experimentally and numerically using a single-stage gas mixture detonation apparatus. The impact spot welding process was carried out on aluminum alloy and steel materials using rigid steel projectiles. In this process, the mixture of oxygen and acetylene was detonated in a combustion chamber to launch the projectile. The masses of flat- and spherical-nosed projectiles were 270 and 230 g, respectively. The impact velocity was measured in all experiments. The cross-sections of the weld spots were inspired by a scanning electron microscope to assess the quality of welding. For several experiments, wavy interfaces were observed showing there is a good bonding. For numerical simulation of the process, Abaqus/Explicit software was used and the deformation and failure mechanisms of impact spot-welded specimens were further investigated. The Johnson–Cook thermoplasticity model along with its failure model was utilized to predict the behavior of metallic materials. The numerical simulation results were in good agreement with those obtained from experiments in terms of the deformation mode and failure pattern. The propagation of the wave on the surface of the flyer plate was further studied. The results showed that the stress waves start from the center and propagate to the corners of the plate. To numerically evaluate the welding quality, two parameters of the shear stress at the collision point as well as the equivalent plastic strain for the flyer and target plates were obtained in the numerical simulation. The numerical results showed opposite directions of shear stress for flyer and base plates at the contact point, which can be used as proof for good bonding. Besides, the magnitudes of the equivalent plastic strain for both flyer and base plates were higher than those reported values in the open literature that confirms successful welding.

Numerical study of theanti-penetration performance of sandwich composite armor containing ceramic honeycomb structures filled with aluminum alloy

2021 ◽  
pp. 154851292199592
Author(s):  
Hongwei Zhu ◽  
Changfang Zhao
Keyword(s):  
Numerical Simulation ◽  
Aluminum Alloy ◽  
High Speed ◽  
Penetration Resistance ◽  
Sandwich Composite ◽  
Honeycomb Structures ◽  
Rigid Projectile ◽  
Composite Armor ◽  
Ceramic Honeycomb ◽  
The Impact

The aim of this work was to study the anti-penetration effect of sandwich composite armor with ceramic honeycomb structures filled with aluminum alloy under the impact of high-speed projectiles. The finite element software ABAQUS was used to conduct numerical simulation research on the process of a standard 12.7-mm projectile penetrating sandwich composite armor. The armor-piercing projectile model was simplified as a rigid body. The numerical simulation models were applied to three different sandwich composite armor structures (A, B, and C), each with a total armor thickness of 25 mm. The penetration resistance of the three kinds of composite armor was studied. We obtained velocity curves for the rigid projectile penetrating the different structures. The failure forms and penetration resistance characteristics of the three composite armor structures adopted in this paper were analyzed. In addition, the velocity reduction ratio is proposed as an index to evaluate the penetration resistance performance of the armor. The simulation results revealed decreasing rates of projectile speed in the structures A, B, and C of 69.6%, 91.1%, and 100%, respectively. The third composite armor (structure C) designed here has excellent penetration resistance and can block the penetration of a high-speed (818m/s) rigid projectile. This study can provide some reference for the application of laminated armor material in anti-penetration protection structures.

scholarly journals Study on Microstructure and Properties of Tailored Hot-Stamped U-shaped Parts Based on Temperature Field Control

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 593
Author(s):  
Xiangji Li ◽  
Limei Xiao ◽  
Qifeng Zheng ◽  
Huan Zhang ◽  
Yanjiao Gu
Keyword(s):  
Tensile Strength ◽  
Temperature Field ◽  
Brittle Fracture ◽  
Automotive Industry ◽  
Fracture Mechanism ◽  
High Speed ◽  
Fracture Behavior ◽  
Hot Stamping ◽  
Micro Hardness ◽  
Field Control

In order to meet the needs of the automotive industry, it is necessary to produce “tailored” parts. The U-shaped die equipped with a high-speed airflow device was designed to conduct the hot stamping experiments. The microstructure, micro-hardness, tensile properties, and fracture behavior of the parts were analyzed. The experimental results showed that the quenched phase of the hardened section was mainly martensite, and the micro-hardness and tensile strength could reach 445 HV and 1454 MPa, respectively. The fracture mechanism was brittle fracture. For the toughness section, as the tool temperature increased from 300 to 600 °C, both micro-hardness and tensile strength decreased. Meanwhile, the area fractions of bainite and ferrite increased, and the area fraction of martensite reduced. The fracture behavior was plastic fracture.

Experimental and Numerical Investigation of Quick Closing Buffer Performance of Steam Turbine Admission Valve

2016 ◽  
Author(s):  
Lei Xiao ◽  
Sihua Xu ◽  
Jin He ◽  
Zhiqiang Hu ◽  
Xiaogang Zhou
Keyword(s):  
Numerical Simulation ◽  
Steam Turbine ◽  
Dynamic Characteristic ◽  
Impact Energy ◽  
Dynamic Characteristics ◽  
High Speed ◽  
Buffer System ◽  
Characteristic Analysis ◽  
Cfd Numerical Simulation ◽  
The Impact

One of the main functions of the steam turbine admission valve is to provide a very fast closing to intercept the supply of mass flow rapidly from the steam entering the turbine and cause destructive overspeed. In order to quickly close the admission valve, at the beginning of the stroke the moving parts of the valve should be accelerated to a high speed; when the stroke ends, a lot of kinetic energy is converted to impact energy. To prevent damage to valve parts, a quick closing buffer system is required to absorb the most of the impact energy. The quick closing buffer system plays an important role in the admission valve as an influencing factor of the dynamic characteristics of the valve. In the past, considering the complex internal structure, the research about quick closing buffer system relied on confirmatory experimental study or analytic method to get a quick closing buffer process. This paper focus on the quick closing process of a high pressure steam admission valve of Shanghai Turbine Plant. The dynamic characteristic of the quick closing buffer system is investigated by means of method of CFD numerical simulation for the first time, in order to find a more convenient and effective way to get the key factors that affect the dynamic characteristics, and the accuracy of the of CFD numerical simulation is verified by test, which are valuable for building an accurate dynamic characteristic analysis model of steam turbine admission valve.

Numerical Simulation of Green Water and the Safety Analysis Research on Structures and Equipments

2016 ◽  
Author(s):  
Xu Wang ◽  
Huilong Ren ◽  
Xiaolong Lu ◽  
Guoqing Feng
Keyword(s):  
Numerical Simulation ◽  
High Speed ◽  
Impact Force ◽  
Wave Model ◽  
Calculation Model ◽  
Green Water ◽  
Ship Building ◽  
Oil Platforms ◽  
The Impact ◽  
Rough Sea

With the high speed development of ship building and the widely use of the deep-sea oil platforms in severe sea conditions, green water have attracted more and more attention. Based on the relative motion of ship and wave, a numerical simulation of the distribution of green water on the wet deck of ship is achieved according to the dam break model and flood wave model, and the strength of local structure is calculated. In addition, the calculation model of the impact force on the objects of wet deck is got through the momentum theorem in hydrodynamics, which is used to analyze the safety of the equipment on the wet deck. The research is significant to the safety of the ship and the platform in rough sea.

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