Modeling and Simulation of Adiabatic Shear Bands in AISI 4340 Steel Under Impact Loads

2012 ◽  
Author(s):  
Gbadebo Owolabi ◽  
Daniel Odoh ◽  
Akindele Odeshi ◽  
Horace Whitworth
Keyword(s):  
Finite Element ◽  
Strain Rate ◽  
Shear Bands ◽  
Adiabatic Shear ◽  
Experimental Results ◽  
Strain Rates ◽  
Adiabatic Shear Bands ◽  
Aisi 4340 Steel ◽  
4340 Steel ◽  
Aisi 4340

In this study, the effects of microstructure and strain rate on the occurrence and failure of adiabatic shear bands in AISI 4340 steel under high velocity impact loads are investigated using finite element analysis and experimental tests. The shear band generated due to impact load was divided into some set of elements separated by nodes using finite element method in ABAQUS environment with initial and boundary conditions specified. The material properties were assumed to be lower at the second element set in order to initialize the adiabatic shear bands. The strain energy density for each successive node was calculated successively starting from the first element where initial boundary condition, initial strain hardening constant, and stress resistance had been specified. As the load time is increased, its corresponding effect on the localized shear deformation and width of the adiabatic shear band was also determined. The finite element model was used to determine the maximum stress, the strain hardening, the thermal softening, and the time to reach critical strain for formation of adiabatic shear bands. Experimental results show that deformed bands were formed at low strain rates and there was a minimum strain rate required for formation of transformed band in the alloy. The experimental results also show that cracks were initiated and propagated along transformed bands leading to fragmentation under the impact loading. The susceptibility of the adiabatic shear bands to cracking was markedly influenced by strain-rates and the initial material microstructures. The numerical results obtained were compared with the experimental results obtained for the AISI 4340 steel under high strain-rate loading in compression using split impact Hopkinson bars. A good agreement between the experimental and simulation results are also obtained.

Dynamic Deformation Response of G33 Steel under High Temperature

2015 ◽  
Vol 782 ◽  
pp. 61-70
Author(s):  
You Jing Zhang ◽  
Hong Nian Cai ◽  
Xing Wang Cheng ◽  
Shuang Zan Zhao
Keyword(s):  
High Temperature ◽  
Flow Stress ◽  
Strain Rate ◽  
Shear Bands ◽  
Shear Zones ◽  
Adiabatic Shear ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Strain Rates ◽  
Adiabatic Shear Bands

The high temperature deformation and fracture behavior of ultra-high strength G33 steel under high strain rate compression are investigated by means of a split Hopkinson p ressure bar. Impact tests are performed at strain rates of 1000/s and 2200/s and at temperatures ranging from 25°C to 700°C. The SEM and TEM techniques are also used to analyze the microstructure evolution of the adiabatic shear band (ASB) and fracture characteristics of the deformed specimens at high temperature. The experimental results indicate that the flow stress of G33 steel is significantly dependent on temperatures and strain rates. The flow stress of G33 steel increases with the increase of strain rates, but decreases with the increase of temperatures. The strain rate sensitivity is more pronounced at the low temperature of 25°C. In addition, G33 steel is more liable to fracture at high temperatures than at 25°C. Observations of microstructure show two well-developed symmetric parabolic adiabatic shear bands on the longitudinal cross-section of the cylindrical specimen deformed at the temperature of 700°C and at the strain rate of 2200/s. Within the ASB, the width of the fine equiaxed grain structure is about 7μm. The size of those equiaxed grains is approximately 100nm. The fracture analysis results indicate that the ASBs are the predominant deformation and the specimens fracture along adiabatic shear bands. The fracture surfaces of the deformed G33 steel specimens are characterized by two alternating zones: rough dimple zone and relatively smooth shear zone. Further observations reveal that smooth shear zones consist of severely sheared dimples.

A Micromilling Experimental Study on AISI 4340 Steel

2009 ◽  
Vol 407-408 ◽  
pp. 335-338 ◽  
Author(s):  
Jin Sheng Wang ◽  
Da Jian Zhao ◽  
Ya Dong Gong
Keyword(s):  
Experimental Study ◽  
Surface Roughness ◽  
Cutting Force ◽  
Spectrum Analysis ◽  
Chip Thickness ◽  
Experimental Results ◽  
Minimum Chip Thickness ◽  
Aisi 4340 Steel ◽  
4340 Steel ◽  
Aisi 4340

A micromilling experimental study on AISI 4340 steel is conducted to understand the micromilling principle deeply. The experimental results, especially on the surface roughness and cutting force, are discussed in detail. It has been found the minimum chip thickness influences the surface roughness and cutting force greatly. Meanwhile, the material elastic recover induces the increase of the axial micromilling force. The average cutting force and its spectrum analysis validate the minimum chip thickness approximation of AISI 4340 is about 0.35μm.

Modelling of Formation of Adiabatic Shear Bands

2014 ◽  
Vol 566 ◽  
pp. 92-96
Author(s):  
Nabil Bassim ◽  
Jeffrey Delorme
Keyword(s):  
Strain Hardening ◽  
Dimensional Analysis ◽  
Shear Bands ◽  
Hopkinson Bar ◽  
Thermal Softening ◽  
Adiabatic Shear ◽  
Large Strains ◽  
Strain Rates ◽  
Adiabatic Shear Bands ◽  
Impact Compression

Adiabatic shear bands are microstructural features that appear when metals, and some non-metals are subjected to impact loading at strain rates in excess of 103 s-1 and large strains. The formation of these bands is generally attributed to several competing mechanisms, among them is an initial strain hardening followed by adiabatic thermal softening that may lead to crack initiation within the bands. The authors have developed a model for formation of adiabatic shear bands in metallic materials as they are formed during testing using a torsional Hopkinson Bar. The model relies on a one dimensional analysis which predicts accurately the two steps of forming adiabatic shear bands in terms of strain hardening followed by thermal softening. In this current research, the model is extended to a two-dimensional analysis which would be suitable for application in either a two bar compression Split Hopkinson Bar or in a direct impact compression system developed by the author (Nabil Bassim) to produce high strain rates and large strains. The algorithm relies on applying the concept of dynamic recrystallization in order to determine the onset or initiation of the adiabatic shear bands.

Inspection of Adiabatic Shear Bands in High Manganese TRIP Steels

2013 ◽  
Vol 753 ◽  
pp. 72-75 ◽  
Author(s):  
Hui Zhen Wang ◽  
Xiu Rong Sun ◽  
Ping Yang ◽  
Wei Min Mao
Keyword(s):  
Shear Failure ◽  
High Strain ◽  
Shear Bands ◽  
Adiabatic Shear ◽  
Strain Rates ◽  
Trip Effect ◽  
Adiabatic Shear Bands ◽  
High Manganese ◽  
High Strain Rates ◽  
Trip Steels

Adiabatic shear bands (ASBs) develop generally during high strain rates. This paper investigates the transformation induced plasticity (TRIP) effect during ASBs formation at high strain rates in high manganese TRIP steels containing initial austenite and ferrite by EBSD technique. Results show that TRIP effect takes place mainly before the formation of ASBs. After ASBs formation, TRIP effect is strongly restricted by the size effect, the increase of stacking fault energy (SFE) and even inverse martensitic transformation due to the rise of temperature. The TRIP effect before ASBs formation contributes to the resistance of adiabatic shear failure. Dynamic recrystallization driven by subgrains rotation occurs within ASBs, and ultrafine grains often show strong shear textures with twin relationship owing to slip mechanism.

On the Catastrophic Shear Instability in High-Speed Machining of an AISI 4340 Steel

1982 ◽  
Vol 104 (2) ◽  
pp. 121-131 ◽  
Author(s):  
R. Komanduri ◽  
T. Schroeder ◽  
J. Hazra ◽  
B. F. von Turkovich ◽  
D. G. Flom
Keyword(s):  
Titanium Alloys ◽  
Shear Zone ◽  
Chip Formation ◽  
High Speed ◽  
Shear Bands ◽  
Shear Instability ◽  
Aisi 4340 Steel ◽  
4340 Steel ◽  
Cutting Speeds ◽  
Aisi 4340

An AISI 4340 Steel (325 BHN) was machined at various speeds up to 2500 m/min (8000 SFPM). Longitudinal midsections of the chips were examined metallurgically to delineate the differences in the chip formation characteristics at various speeds. Chips were found to be continuous at 30 to 60 m/min (100 to 200 SFPM) but discontinuous below this speed. Instabilities in the cutting process, leading to different types of cyclic chip formations, were observed at cutting speeds above 60 m/min (200 SFPM). Fully developed catastrophic shear bands separated by large areas (segments) of relatively less deformed material, similar to that when machining titanium alloys, were observed in the chips at cutting speeds above 275 m/min (800 SFPM). The intense shear bands between the segments appeared to have formed subsequent to the localized intense deformation of the segment in the primary shear zone. As the cutting speed increases, the extent of contact between the segments is found to decrease rapidly. At speeds of 1000 m/min (3200 SFPM) and above, due to rapid intense, localized shear between the segments, these segments were found to separate completely as isolated segments instead of being held intact as a long chip. The speed at which this decohesion occurs was found to depend upon the metallurgical state of the steel machined and its hardness. As in the case of machining titanium alloys, the deformation of the chip as it slides on the tool face, i.e., “secondary shear zone,” appeared to be negligible when machining this AISI 4340 steel at high speed. Based on the metallurgical study of the chip and the similarities of machining this material at high speed and that of titanium alloys at normal speed, a cyclic phenomenon in the primary shear zone is identified as the source of instability responsible for the large-scale heterogeneity and a mechanism of chip formation when machining AISI 4340 steel at high speed is proposed.

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