Towards understanding the brittle–ductile transition in the extreme manufacturing

The brittle–ductile transition(BDT) widely exists in the manufacturing with extremely small deformation scale, thermally assisted machining, and high-speed machining. This paper reviews the BDT in extreme manufacturing. The factors affecting the BDT in extreme manufacturing are analyzed, including the deformation scale and deformation temperature induced brittle-to-ductile transition, and the reverse transition induced by grain size and strain rate. A discussion is arranged to explore the mechanisms of BDT and how to improve the machinability based on the BDT. It is proposed that the mutual transition between brittleness and ductility results from the competition between the occurrence of plastic deformation and the propagation of cracks. The brittleness or ductility of machined material should benefit a specific manufacturing process, which can be regulated by the deformation scale, deformation temperature and machining speed.

EFFECTS OF INTERPARTICLE DISTANCE,TEMPERATURE AND INTERFACIAL ADHESION ON BRITTLE-DUCTILE TRANSITION FOR NYLON 6/ABS BLENDS

The toughness of blends composed of nylon 6 and acrylonitrile-butadiene-styrene(ABS) compatibilized by using styrene-maleic anhydride(SMA) as a compatibilizer was measured over a wide temperature region.Results reveal that the combining effects of particle size and volume fraction of ABS on the toughness of nylon 6/ABS/SMA blends can be described through plotting brittle-ductile transition of the impact strength versus the interparticle distance(ID) on the assumption that ABS domains relieve the triaxial te...

RANDOM-FUZZY MODEL FOR THE DUCTILE/BRITTLE TRANSITION

Based on a large experimental sample, the influence of stress triaxiality and temperature have been studied on the growth of micro voids and the ductile/brittle transition (DBT) of 40Cr steel. Ductile and brittle fractures have been investigated simultaneously. The experiments show that the ductile fracture is controlled by the micro void mechanism,and the critical void growth ratio can be used as the criterion of ductile fracture. The brittle fracture is modeled by an embedded penny crack, and a micro stress intensity with a characteristic length can be used as the criterion of the brittle fracture. The DBT is the result of the competition of the two mechanisms. Which exists in the fracture of all specimens simultaneously. The distributions of model parameters were measured experimentally. A random model and a random-fuzzy model for DBT were presented. The comparison between the calculated and experimental results shows that the random-fuzzy model can model the DBT satisfactorily.

Smoothed-Particle Hydrodynamics Investigation on Brittle-Ductile Transition of Quartz Glass in Single-Grain Grinding Process

The smoothed-particle hydrodynamics(SPH)method was introduced to simulate the quartz glass grinding process with a single grain under micrp-nano scale.To investigate the mechanism of brittle-ductile transition,such factors as the machin-ing depth,grinding force,maximum equivalent stress,and residual stress were analyzed.The simulation results indicate that quartz glass can be machined in a ductile mode under a certain condition.In this paper,the occurrence and propaga-tion of cracks in quartz glass at different grinding depths(0.1-1μm)are observed,and the critical depth of brittle-ductile transformation is 0.36 pum.At different grinding depths,the grinding force ratio is greater than 1.When the cutting depth is 0.4 um,the crack propagation depth is about 1.2μm,which provides a basis for the prediction of subsurface damage depth.In addition,the correctness of the simulation result was verified by carrying out scratch experiments of varying cutting depth on optical quartz glass.

Low Temperature Impact Toughness and Fracture Analysis of EN-GJS-400-18-LT Ductile Iron under Instrumented Impact Load

The impact toughness of EN-GJS-400-18-LT ductile iron was measured by Charpy V-notch impact test at temperature between-80 and 20℃.The fracture properties were tested under instrumented impact loading.Total impact fracture energy,crack initiation and propagation energy,dynamic loads and the ductile to brittle temperature were measured.Three-dimensional reconstruction of impact fracture morphology was accomplished by confocal laser scanning microscope.The results of quantitative fractography indicate that cleavage fracture produces flatter fracture surfaces accompanying with less absorbed energy during the impact fracture process.It indicates that fracture roughness has a close relationship with crack propagation energy at low temperature.

Effect of Rare Earth and Cooling Process on Microstructure and Mechanical Properties of an Ultra-Cleaned X80 Pipeline Steel

In order to explore the eff ect of a small amount of rare earth addition in ultra-cleaned pipeline steel and the influence of the cooling process on the tensile and impact properties,three API X80 pipeline steels were fabricated by varying RE addition and the cooling process at the same time.Three microstructures with different features for a low C high Nb microalloyed high-strength pipeline steel and the corresponding mechanical properties were investigated.The results showed that even in the ultra-cleaned steel with O and S contents less than 10 ppm,the addition of RE would still cause an increase in the volume fraction of inclusions consisting of complicated RE oxysulfide and RE sulfide.More inclusions formed in the 112 ppm RE steel were harmful to the low temperature toughness,while few inclusions formed in the 47 ppm RE steel had almost no influence on the low temperature toughness.The two RE additions had no effect on strength of the steels.As the finishing cooling temperature was increased and the cooling rate was decreased within a certain range,the volume fractions of polygonal ferrite and quasi-polygonal ferrite as well as the number density and size of martensite–austenite islands were increased.Under such combined effect,the strength of the steels had almost no change.As the finishing cooling temperature was increased from 481 to 584℃and the cooling rate was reduced from 20 to 13℃/s,for the steel with 112 ppm addition of RE,there was an obvious decrease in the low temperature toughness.The reduced value(about 33 J)of the USE of steel consisted of two parts including the influence(about 18 J)of more inclusions formed due to 112 ppm addition of RE and the eff ect(about 15 J)of the lower high-angle grain boundaries.