Behavior of Aramid Fiber/Ultrahigh Molecular Weight Polyethylene Fiber Hybrid Composites under Charpy Impact and Ballistic Impact

The aramid fiber礥HMWPE (ultrahigh molecular weight polyethylene) fiber hybrid composites (AF礑F) were ma-nufactured. By Charpy impact, the low velocity impact behavior of AF礑F composite was studied. And the high velocity impact behavior under ballistic impact was also investigated. The influence of hybrid ratio on the performances of low and high velocity impact was analyzed, and hybrid structures with good impact properties under low velocity impact and high velocity were optimized. For Charpy impact, the maximal impact load increased with the accretion of the AF layers for AF礑F hybrid composites. The total impact power was reduced with the decrease of DF layers and the delamination can result in the increase of total impact power. For ballistic impact, the DF ballistic performance was better than that of the AF and the hybrid ratio had a crucial influence. The failure morphology of AF礑F hybrid composite under Charpy impact and ballistic impact was analyzed. The AF礑F hybrid composites in suitable hybrid ratio could attain better performance than AF or DF composites.

Comparative Study of Tensile and Charpy Impact Properties of X70 and X80 Linepipe Steels After Ultra Fast Cooling Processing

Ultra fast cooling（UFC） processing after hot deformation was conducted on X70 and X80 linepipe steels. Tensile and charpy impact properties of both steels have been investigated in this work. The results have shown that the mechanical properties satisfy all the standard requirements of the X70 and X80 steels. UFC results in a presence of microstructure containing quasi polygonal（QF）, acicular ferrite（AF） and granular bainite（GB）. The alloying elements and UFC enhance the strengthening contribution caused by solid solution, dispersion, dislocation and precipitation strengthening. The size and distribution of precipitates in the linepipe steels are fine and dispersed. MA is also homogeneously dispersed due to UFC. Average grain size in the X80 steel is finer than that in the X70 steel. The volume fractions of secondary phases in the X80 steel are greater than those in the X70 steel. The X80 steel remains finer and more dispersed precipitates compared to the X70 steel. As a result, the tensile properties of X80 steel are higher than those of X70 steel. The Charpy absorbed energies of X70 and X80 steels at-10 ℃ reached 436 and 460 J, respectively. They reached 433 and 461 J at-15 ℃, respectively. This is mainly attributed to the presence of larger amounts of AFs in the X80 steel. A microstructure of AF for the X80 steel results in combining high strength and high toughness.

Nonlinear Impact Damage Evolution of Charpy Type and Analysis of Its Key Influencing Factors

The current research of Charpy impact mainly focuses on obtaining the ductile brittle transition temperature of materials by experiments.Compared with experiments,numerical simulation can study many problems with harsh conditions.However,there are still few studies on the influence of geometric factors such as side grooves.In this paper,the geometry of standard Charpy impact test is designed.Specimens with different widths and side grooves are tested.The finite element model of Charpy impact was established by ABAQUS software.Use test results and simulation results to verify each other.The effects of sample width,side groove depth and side groove bottom fillet on the impact fracture resistance of the sample were studied.The results show that the specimen width is positively correlated with the impact toughness of the specimen.The side groove greatly reduces the impact toughness of the material;the toughness of side groove decreases with the increase of depth;the fracture toughness of side groove decreases with the increase of fillet at the bottom of side groove.The proportion of toughness energy to impact energy of samples was analyzed.The results show that the toughness energy accounts for about 70%of the impact energy of the sample,which has little to do with the geometric characteristics of the sample.This study presents a reliable method for studying Charpy impact tests.The influence of geometric parameters is obtained,which provides a reference method for the study of impact toughness of high toughness materials.

Improved data-driven performance of Charpy impact toughness via literature-assisted production data in pipeline steel

Pipeline transportation is one of the most economical ways to transport crude oil and natural gas over long distances.High toughness is one of the important qualities of pipeline steel to ensure safe transportation,wherein a key factor characterizing toughness is Charpy impact toughness(CIT).In this work,according to the production line data provided by a steel mill and the experimental data collected in literature,two machine learning model construction strategies were proposed.One was based solely on the production line dataset,and the other was based on the production line dataset together with the literature dataset.In these two strategies,the random forest model displayed the best prediction results,the accuracy of strategy I was 0.58,and the accuracy of strategy II was 0.90,wherein literature data effectively improved the CIT prediction accuracy.Finally,an optimized CIT model based on machine learning algorithms was established.The proposed strategy of literature data-assisted production line data provides a new perspective for optimizing and predicting the performance of traditional structural materials.

Identifying facile material descriptors for Charpy impact toughness in low-alloy steel via machine learning

High toughness is highly desired for low-alloy steel in engineering structure applications,wherein Charpy impact toughness(CIT)is a critical factor determining the toughness performance.In the current work,CIT data of low-alloy steel were collected,and then CIT prediction models based on machine learning(ML)algorithms were established.Three feature construction strategies were proposed.One is solely based on alloy composition,another is based on alloy composition and heat treatment parameters,and the last one is based on alloy composition,heat treatment parameters,and physical features.A series of ML methods were used to effectively select models and material descriptors from a large number of al-ternatives.Compared with the strategy solely based on the alloy composition,the strategy based on alloy composition,heat treatment parameters together with physical features perform much better.Finally,a genetic programming(GP)based symbolic regression(SR)approach was developed to establish a physical meaningful formula between the selected features and targeted CIT data.

Effect of TiN Particles and Grain Size on the Charpy Impact Transition Temperature in Steels

The toughness of ferritic steels is influenced by the grain size distribution, second phase, precipitates and coarse inclusions. In this work an examination of the effect of coarse TiN particles （〉0.5 μm） and ferrite grain size on the Charpy impact transition temperature in high strength low alloyed steels has been carried out. Steels with high Ti content （up to 0.045 wt%）, have been heat-treated and furnace cooled to obtain a ferrite-pearlite microstructure with different ferrite grain sizes. Coarse TiN particle size and ferrite grain size distributions have been measured and Charpy impact testing has been carried out. Scanning electron microscopy （SEM） analysis has been used to measure the grain boundary carbide thickness and to determine if the coarse TiN particles are acting as cleavage initiation sites by fractographic analysis. The Charpy ductile-brittle transition temperatures （DBTT） have been predicted using standard literature equations, and compared to the measured values. The relationship between the ferrite grain size and coarse TiN particle size and number density in terms of whether the coarse TiN particles act as effective cleavage initiation sites is discussed in this paper.

A New Analytical Expression for the Relationship Between the Charpy Impact Energy and Notch Tip Position for Functionally Graded Steels

The effect of the distance between the notch tip and the position of the middle phase in the FGSs on the Charpy impact energy is investigated in the present paper. The results show that when the notch apex is close to the middle layer, the Charpy impact energy reaches its maximum value. This is due to the increment of the absorbed energy by plastic deformation ahead of the notch tip. On the other hand, when the notch tip is far from the middle layer, the Charpy impact energy strongly decreases. Another fundamental motivation of the present work is that for crack arrester configuration, no accurate mathematical or analytical modelling is available up to now. By considering the relationship between the Charpy impact energy and the plastic volume size, a new theoretical model has been developed to link the Charpy impact energy with the distance from the notch apex to the middle phase. This model is a simplified one and the effect of different shapes of the layers and the effect of microstructureon the mechanical properties and plastic region size will be considered in further investigation. The results of the new developed closed form expression show a sound agreement with some recent experimental results taken from the literature.

Effects of Craddition on Charpy impact energy in austenitic 0.45C-24Mn-(0,3,6)Cr steels

Effects of Cr addition(0,3,and 6 wt%) on Charpy impact properties of Fe-C-Mn-Cr-based steels were studied by conducting dynamic compression tests at room and cryogenic temperatures.At room temperature,deformation mechanisms of Charpy impacted specimens were observed as twinning induced plasticity(TWIP) without any transfo rmation induced plasticity(TRIP) in all the steels.At cryogenic temperature,many twins were populated in the Cr-added steels,but,interestingly,fine ε-martensite was found in the OCr steel,satisfying the Shoji-Nishiyama(S-N) orientation relationship,{111}γ//{0002}ε and <101>γ//<1120>ε.Even though the cryogenic-temperature staking fault energies(SFEs) of the three steel were situated in the TWIP regime,the martensitic transformation was induced by Mn-and Cr-segregated bands.In the OCr steel,SFEs of low-(Mn,Cr) bands lay between the TWIP and TRIP regimes which were sensitively affected by a small change of SFE.The dynamic compressive test results well showed the relation between segregation bands and the SFEs.Effects of Cr were known as not only increasing the SFE but also promoting the carbide precipitation.In order to identify the possibility of carbide formation,a precipitation kinetics simulation was conducted,and the predicted fractions of precipitated M23C6 were negligible,0.4-1.1×10-5,even at the low cooling rate of 10℃/s.

Effect of hot rolling on the microstructure and impact absorbed energy of the strip steel by CSP

The microstructures and impact absorbed energies at various temperatures were investigated for steel strips hot rolled to thickness reductions of 95.5%, 96.0%, 96.5%, 97.0%, and 97.5%. Results indicate that grain refinement can be realized with an increase in hot rolling reduction. Besides, finer precipitates can be achieved with an increase in hot rolling reduction from 95.5%to 97.0%. The impact absorbed energy decreases with a decrease in testing temperature for steel strips hot rolled to 95.5%, 96.0%, and 96.5%reductions in thickness. However, in the case of steel strips hot rolled to 97.0%and 97.5%reductions in thickness, the impact absorbed energy remained almost constant with a decrease in testing temperature.

Investigation on the process parameters of TIG-welded aluminum alloy through mechanical and microstructural characterization

Multi-pass TIG welding was conducted on plates(15×300×180 mm^(3))of aluminum alloy Al-5083 that usually serves as the component material in structural applications such as cryogenics and chemical processing industries.Porosity formation and solidification cracking are the most common defects when TIG welding Al-5083 alloy,which is sensitive to the welding heat input.In the experiment,the heat input was varied from 0.89 kJ/mm to 5 kJ/mm designed by the combination of welding torch travel speed and welding current.Tensile,micro-Vicker hardness and Charpy impact tests were executed to witness the impetus response of heat input on the mechanical properties of the joints.Radiographic inspection was performed to assess the joint’s quality and welding defects.The results show that all the specimens displayed inferior mechanical properties as compared to the base alloy.It was established that porosity was progressively abridged by the increase of heat input.The results also clinched that the use of medium heat input(1-2 kJ/mm)offered the best mechanical properties by eradicating welding defects,in which only about 18.26% of strength was lost.The yield strength of all the welded specimens remained unaffected indica ted no influence of heat input.Partially melted zone(PMZ)width also affected by heat input,which became widened with the increase of heat input.The grain size of PMZ was found to be coarser than the respective grain size in the fusion zone.Charpy impact testing revealed that the absorbed energy by low heat input specimen(welded at high speed)was greater than that of high heat input(welded at low speed)because of low porosity and the formation of equiaxed grains which induce better impact toughness.Cryogenic(-196℃)impact testing was also performed and the results corroborate that impact properties under the cryogenic environment revealed no appreciable change after welding at designated heat input.Finally,Macro and micro fractured surfaces of tensile and impact specimens were analyzed using Stereo and Scanning Electron Microscopy(SEM),which have supported the experimental findings.

THE INVESTIGATION OF FRACTURE PROPERTIES OF SISAL TEXTILE REINFORCED POLYMERS

Sisal filbre is a kind of natural filbre which possesses high specic strength and modu- lus, low price, recycalability, easy availability in some countries. Using sisal filbre as reinforcement to make sisal filbre reinforced polymer composites has aroused great interest of materials scientists and engineers all over the world. Many researches have been done in recent years which include the study of mechanical properties of the composites, nding an ecient way to improve the inter- facial bonding properties between sisal bre and polymeric matrices and bre surface treatment on the mechanical performance of the composites. Though many researches on sisal bre reinforced composites have been done so far, none deals with the fracture properties of this novel composite which is crucial for the actual application of this material. In this research, Charpy impact test and compact tension test were employed to study the fracture toughness of sisal bre reinforced vinyl ester and epoxy composites. The eect of bre surface treatment on the fracture properties of these composites by permanganate and silane was evaluated. The initiation and propagation of the crack were observed with optical microscopy (OM). The fracture morphologies revealed by OM explains the fracture phenomenon of sisal bre reinforced composites.

Effects of Al addition and cryogenic cyclic treatment on impact toughness of phase-transformable Ti-based bulk metallic glass composites

Developing bulk metallic glass composites(BMGCs)with high toughness is vital for their practical application.However,the influence of different microstructures on the impact toughness of BMGCs is still unclear.The effects of Al addition and cryogenic cyclic treatment(CCT)on the Charpy impact toughness,a K,at 298 and 77 K of a series of phase-transformable BMGCs are investigated in this work.It is found that deformation-induced martensitic transformation(DIMT)of theβ-Ti dendrites is the dominant toughening mechanism in the phase-transformable BMGCs at 298 K,but at 77 K,the toughness of BMGCs is primarily determined by the intrinsic toughness of the glass matrix.The addition of Al can moderately tune theβ-Ti phase stability,which then affects the amount of DIMT and impact toughness of the BMGCs at 298 K.However,at 77 K,Al addition causes a monotonic decrease in the toughness of the BMGCs due to the embrittlement of the glass matrix.It is found that CCT can effectively rejuvenate the phase-transformable BMGCs,which results in an enhanced impact toughness at 298 K.However,the toughness at 77 K monotonously decreases with increasing the number of CCT cycles,suggesting that the rejuvenation of the glass matrix affects the toughness at both 298 and 77 K of BMGCs,but in dramatically different ways.These findings reveal the influence of microstructures and CCT on the impact toughness of BMGCs and provide insights that could be useful for designing tougher BMGs and BMGCs.

Characterization of Impact Deformation Behavior of a Thermally Aged Duplex Stainless Steel by EBSD

The effect of thermal aging on phase transformation and impact toughness of an as-cast duplex stainless steel was investigated at room temperature. After long-term thermal aging, the impact toughness decreases significantly and the cracks initiate and propagate more easily. The plastic deformation ability of the ferrite phase decreases after thermal aging,which leads to the degradation of impact toughness. High stress concentration occurs on the grain boundaries of the austenite phase in the aged materials. Meanwhile, high-stress concentration areas are also observed in the austenite phase near the grain boundaries. After long-term thermal aging, pinned dislocations in ferrite and along phase boundaries lead to the high stress concentration. Micro-cracks preferentially initiate in the ferrite phase and propagate via separation of phase boundaries. The blocking influences of spinodal decomposition precipitates and G-phase precipitates are stronger than the effect of grain boundaries and phase boundaries on the dislocation movement.

Effects of cryogenic temperature on tensile and impact properties in a medium-entropy VCoNi alloy

Multi-principal element alloys usually exhibit outstanding strength and toughness at cryogenic temperatures,especially in CrMnFeCoNi and CrCoNi alloys.These remarkable cryogenic properties are attributed to the occurrence of deformation twins,and it is envisaged that a reduced stacking fault energy(SFE)transforms the deformation mechanisms into advantageous properties at cryogenic temperatures.A recently reported high-strength VCoNi alloy is expected to exhibit further notable cryogenic properties.However,no attempt has been made to investigate the cryogenic properties in detail as well as the underlying deformation mechanisms.Here,the effects of cryogenic temperature on the tensile and impact properties are investigated,and the underlying mechanisms determining those properties are revealed in terms of the temperature dependence of the yield strength and deformation mechanism.Both the strength and ductility were enhanced at 77 K compared to 298 K,while the Charpy impact toughness gradually decreased with temperature.The planar dislocation glides remained unchanged at 77 K in contrast to the CrMnFeCoNi and CrCoNi alloys resulting in a relatively constant and slightly increasing SFE as the temperature decreased,which is confirmed via ab initio simulations.However,the deformation localization near the grain boundaries at 298 K changed into a homogeneous distribution throughout the whole grains at 77 K,leading to a highly sustained strain hardening rate.The reduced impact toughness is directly related to the decreased plastic zone size,which is due to the reduced dislocation width and significant temperature dependence of the yield strength.

Effect of Mn content on microstructure, tensile and impact properties of SA508Gr.4N steel for reactor pressure vessel

The effect of manganese(Mn)on the microstructure,tensile and impact properties of SA508Gr.4N steel has been experimentally investigated.The influence of Mn content on the substructure of SA508Gr.4N steel was investigated using the scanning electron microscope,electron back-scattered diffractometer and transmission electron microscope.It was found that the increased Mn content had a beneficial effect on both strength and toughness.Examination of microstructure revealed smaller size of block and larger number of high-angle grain boundaries with higher Mn content.The change of the ultimate tensile strength and toughness with increasing Mn content was attributed to the increased hardenability,the number of high-angle grain boundaries and the crack propagation path by the block refining.

Microstructure Evolution during Friction Stir Welding of Aluminum Alloy AA2219

The characterization of microstructure evolution in friction stir welded aluminum alloy was carried out by optical microscopy （OM） and transmission electron microscopy （TEM） and electron backscatter diffraction （EBSD）. The weld nugget consisted of very fine equiaxed grains and experienced dissolution of nearly half of metastable precipitates into the matrix during welding. Thermomechanically affected zone （TMAZ） also experienced dissolution of precipitates but to a lesser extent whereas coarsening of precipitates was observed in heat affected zone （HAZ）. Grain boundary misorientation measurements using EBSD indicated continuous dynamic recrystallization as the underlying mechanism for the fine equiaxed nugget grains. The yield and tensile strength of the weld decreased with comparison to base material. But due to the decrease of grain size and the dissolution of second phase precipitates, an increased Charpy energy value was observed in the weld n u gget.

First Results of Characterization of 9Cr-3WVTiTaN Low Activation Ferritic/Martensitic Steel

Ferritic/martensitic steels with Cr of 9%-12% （in mass percent） are favourable candidates for fuel cladding tube and in-core components of supercritical water-cooled reactor. 9Cr-3WVTiTaN low activation ferritic/martensitic steel, designated as China Nuclear Steel- I （CNS- I ）, was patterned after T91 steel （modified 9Cr-lMo） for the reactor. The idea of low activation material and microalloy technology was introduced into the design of the steel. The hardening, tempering and transformation behaviour of CNS- I steel was investigated. The steel has advantages in tensile properties at elevated temperature relative to zircaloy that has been widely used as cladding material for conventional light water reactors. CNS- I steel exhibits tensile properties and impact toughness comparable to T91 steel which exhibits availability in the present fission reactors and fast breeder reactor but includes undesired radioactive elements such as molybdenum and niobium.

Mechanical property comparisons between CrCoNi medium-entropy alloy and 316 stainless steels

We systematically compared the mechanical properties of CrCoNi,a recently emerged prototypical medium-entropy alloy(MEA)with face-centered-cubic(FCC)structure,with hallmark FCC alloys,in particular,the well-known austenitic 316 L and 316 LN stainless steels,which are also concentrated singlephase FCC solid solutions and arguably next-of-kin to the MEAs.The tensile and impact properties,across the temperatures range from 373 K to 4.2 K,as well as fracture toughness at 298 K and 77 K,were documented.From room temperature to cryogenic temperature,all three alloys exhibited similarly good mechanical properties;CrCoNi increased its tensile uniform elongation and fracture toughness,which was different from the decreasing trend of the 316 L and 316 LN.On the other hand,the stainless steels showed higher fracture toughness than CrCoNi at all temperatures.To explain the differences in macroscopic mechanical properties of the three alloys,microstructural hardening mechanisms were surveyed.CrCoNi MEA relied on abundant mechanical twinning on the nanoscale,while martensitic transformation was dominant in 316 L at low temperatures.The deformation mechanisms in the plastic zone ahead of the propagating crack in impact and fracture toughness tests were also analyzed and compared for the three alloys.

Improving toughness of medium-Mn steels after friction stir welding through grain morphology tuning

This work demonstrated the viability of friction stir welding for the welding of medium-Mn steels when used as cryogenic vessel materials for liquefied gas storage.We used an intercritically annealed Fe-7 Mn-0.2 C-3 Al(wt.%)steel with a dual-phase(α'martensite andγ_(R) retained austenite)nanolaminate structure as a base material and systematically compared its microstructure and impact toughness after friction stir and tungsten inert gas welding.The friction stir welded specimen exhibited a large amount ofγ_(R) phase owing to a relatively low temperature during welding,whereas the tungsten inert gas welded specimen comprised only theα'phase.Furthermore,the friction stir welded steel exhibited a tuned morphology of nanoscale globular microstructure at the weld zone and did not exhibit any prior austenite grain boundary due to active recrystallization caused by deformation during welding.The preserved fraction ofγ_(R) and morphological tuning in the weldment improved the impact toughness of the friction stir welded steel at low temperatures.In the steel processed by tungsten inert gas welding,the notch crack propagated rapidly along the prior austenite grain boundaries-weakened by Mn and P segregations-resulting in poor impact toughness.However,the friction stir welded steel exhibited a higher resistance against notch crack propagation due to the slow crack propagation along the ultrafine ferrite/ferrite(α/α)interfaces,damage tolerance by the active transformation-induced plasticity from the large amount ofγR,and enhanced boundary cohesion by suppressed Mn and P segregations.