Effects of thawing-induced softening on fracture behaviors of frozen rock

Due to the presence of ice and unfrozen water in pores of frozen rock,the rock fracture behaviors are susceptible to temperature.In this study,the potential thawing-induced softening effects on the fracture behaviors of frozen rock is evaluated by testing the tension fracture toughness(KIC)of frozen rock at different temperatures(i.e.-20℃,-15℃,-12℃,-10℃,-8℃,-6℃,-4℃,-2℃,and 0℃).Acoustic emission(AE)and digital image correlation(DIC)methods are utilized to analyze the microcrack propagation during fracturing.The melting of pore ice is measured using nuclear magnetic resonance(NMR)method.The results indicate that:(1)The KIC of frozen rock decreases moderately between-20℃ and-4℃,and rapidly between-4℃ and 0℃.(2)At-20℃ to-4℃,the fracturing process,deduced from the DIC results at the notch tip,exhibits three stages:elastic deformation,microcrack propagation and microcrack coalescence.However,at-4℃e0℃,only the latter two stages are observed.(3)At-4℃e0℃,the AE activities during fracturing are less than that at-20℃ to-4℃,while more small events are reported.(4)The NMR results demonstrate a reverse variation trend in pore ice content with increasing temperature,that is,a moderate decrease is followed by a sharp decrease and-4℃ is exactly the critical temperature.Next,we interpret the thawing-induced softening effect by linking the evolution in microscopic structure of frozen rock with its macroscopic fracture behaviors as follow:from-20℃ to-4℃,the thickening of the unfrozen water film diminishes the cementation strength between ice and rock skeleton,leading to the decrease in fracture parameters.From-4℃ to 0℃,the cementation effect of ice almost vanishes,and the filling effect of pore ice is reduced significantly,which facilitates microcrack propagation and thus the easier fracture of frozen rocks.

Large-Scale Preparation of Mechanically High-Performance and Biodegradable PLA/PHBV Melt-Blown Nonwovens with Nanofibers

Biodegradable polylactic acid(PLA)melt-blown nonwovens are attractive candidates to replace nondegradable polypropylene melt-blown nonwovens.However,it is still an extremely challenging task to prepare PLA melt-blown nonwovens with sufficient mechanical properties for practical application.Herein,we report a simple strategy for the large-scale preparation of biodegradable PLA/poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV)melt-blown nonwovens with high strength and excellent toughness.In this process,a small amount of PHBV is added to PLA to improve the latter’s crystallization rate and crystallinity.In addition,when the PHBV content increases from 0 to 7.5 wt%,the diameters of the PLA/PHBV melt-blown fibers decrease significantly(with the proportion of nanofibers increasing from 7.7%to 42.9%).The resultant PLA/PHBV(5 wt%PHBV)melt-blown nonwovens exhibit the highest mechanical properties.The tensile stress,elongation,and toughness of PLA/PHBV(5 wt%PHBV)melt-blown nonwovens reach 2.5 MPa,45%,and 1.0 MJm3,respectively.More importantly,PLA/PHBV melt-blown nonwovens can be completely degraded into carbon dioxide and water after four months in the soil,making them environmentally friendly.A general tensile-failure model of melt-blown nonwovens is proposed in this study,which may shed light on mechanical performance enhancement for nonwovens.

Cardo poly (ether sulfone) toughened E51/DETDA epoxy resin and its carbon fiber composites

A toughener that can effectively improve the interlaminar toughness in carbon fiber composites is crucial for various applications.We investigated,the toughening effects of phenolphthalein-based cardo poly(ether sulfone)(PES-C)on E51/DETDA epoxy and its carbon fiber composites(CFCs).Scanning electron microscopy showed that the phase structures of PES-C/epoxy blends change from island(of dispersed phase)structures to bi-continuous structures(of the matrix)as the PES-C content increased,which is associated with reaction-induced phase separation.After adding 15 phr PES-C,the glass transition temperature(T_(g))of the blends increased by 51.5℃,and the flexural strength,impact strength and fracture toughness of the blends were improved by 41.1%,186.2%and 42.7%,respectively.These improvements could be attributed to the phase separation structure of the PES-C/epoxy sys-tem.A PES-C film was used to improve the mode-II fracture toughness(G_(IIC))of CFCs.The G_(IIC) value of the 7μm PES-C film toughened laminate was improved by 80.3%compared to that of the control laminate.The increase in G_(IIC) was attributed to cohesive failure and plastic deformation in the interleaving region.

Hydraulic fracturing behaviors of shale under coupled stress and temperature conditions simulating different burial depths

Fracture propagation in shale under in situ conditions is a critical but poorly understood mechanical process in hydraulic fracturing for deep shale gas reservoirs. To address this, hydraulic fracturing experiments were conducted on hollow double-wing crack specimens of the Longmaxi shale under conditions simulating the ground surface(confining pressure σ_(cp)=0, room temperature(Tr)) and at depths of 1600 m(σ_(cp)=40 MPa, Ti=70 ℃) and 3300 m(σ_(cp)=80 MPa, high temperature Ti=110 ℃) in the study area.High in situ stress was found to significantly increase fracture toughness through constrained microcracking and particle frictional bridging mechanisms. Increasing the temperature enhances rather than weakens the fracture resistance because it increases the grain debonding length, which dissipates more plastic energy and enlarges grains to close microdefects and generate compressive stress to inhibit microcracking. Interestingly, the fracture toughness anisotropy in the shale was found to be nearly constant across burial depths, despite reported variations with increasing confining pressure. Heated water was not found to be as important as the in situ environment in influencing shale fracture. These findings emphasize the need to test the fracture toughness of deep shales under coupled in situ stress and temperature conditions rather than focusing on either in situ stress or temperature alone.

Recent Advances in Instrumented Scratching

The instrumented scratch test,which has the advantages of simple sample preparation,high test efficiency,and low cost,has become an effective technique to investigate contact mechanisms(e.g.,contact-induced surface deformation,single-asperity contact,sliding contact,reciprocating sliding,elastic recovery,stick-slip behaviors,damage/cracking,buckling failure of films,mechanical glass frosting,abrasive machining mechanism,cutting,wear,grinding and polishing)and a large quantity of mechanical properties(e.g.,scratch resistance,tribological behavior,friction coefficient,structural integrity,hardness,strength,and fracture toughness)of various solids(e.g.,multilayer coatings,single crystals,bones,gels,polymers,ceramics,glasses,semiconductors,metals,concreates,shales,rocks,and composites)based on the measured scratch variables such as penetration depth and lateral force.

Recent Advances in Instrumented Scratching

The instrumented scratch test,which has the advantages of simple sample preparation,high test efficiency,and low cost,has become an effective technique to investigate contact mechanisms(e.g.,contact-induced surface deformation,single-asperity contact,sliding contact,reciprocating sliding,elastic recovery,stick-slip behaviors,damage/cracking,buckling failure of films,mechanical glass frosting,abrasive machining mechanism,cutting,wear,grinding and polishing)and a large quantity of mechanical properties(e.g.,scratch resistance,tribological behavior,friction coefficient,structural integrity,hardness,strength,and fracture toughness)of various solids(e.g.,multilayer coatings,single crystals,bones,gels,polymers,ceramics,glasses,semiconductors,metals,concreates,shales,rocks,and composites)based on the measured scratch variables such as penetration depth and lateral force.The application of instrumented scratch to characterization of mechanical properties of materials based on the quantitative relationships linking macroscopic mechanical properties of materials with characteristic values of measured variables during scratching under different conditions(e.g.,different geometries of indenters)has great potential in the fields of materials science and engineering.

Toughening ultrastrong low-density steel by textured δ-ferrite lamellas

By both the Charpy V-notched impact and the projectile tests, we here investigated the dynamic fracture behavior of a recently developed ultrastrong lightweight steel comprising a hierarchical martensitic matrix, dispersed ultra-fine-retained austenite grains and oriented δ-ferrite lamellas, the latter being due to high Al and Si contents employed for low-density design. This steel shows a superior combination of specific ultimate tensile strength and impact toughness to other ultrastrong steels and has successfully arrested a real steel-cored bullet shot. These are attributed to the densely textured δ-ferrite lamellas that can deflect the propagating cracks until they are trapped and enclosed besides austenite-to-martensite transformation crack closure, leading to more energy consumed before failure. These results suggest a new pathway for toughening ultrastrong lightweight steels.

Constructing high-toughness polyimide binder with robust polarity and ion-conductive mechanisms ensuring long-term operational stability of silicon-based anodes

Silicon-based materials have demonstrated remarkable potential in high-energy-density batteries owing to their high theoretical capacity.However,the significant volume expansion of silicon seriously hinders its utilization as a lithium-ion anode.Herein,a functionalized high-toughness polyimide(PDMI) is synthesized by copolymerizing the 4,4'-Oxydiphthalic anhydride(ODPA) with 4,4'-oxydianiline(ODA),2,3-diaminobenzoic acid(DABA),and 1,3-bis(3-aminopropyl)-tetramethyl disiloxane(DMS).The combination of rigid benzene rings and flexible oxygen groups(-O-) in the PDMI molecular chain via a rigidness/softness coupling mechanism contributes to high toughness.The plentiful polar carboxyl(-COOH) groups establish robust bonding strength.Rapid ionic transport is achieved by incorporating the flexible siloxane segment(Si-O-Si),which imparts high molecular chain motility and augments free volume holes to facilitate lithium-ion transport(9.8 × 10^(-10) cm^(2) s^(-1) vs.16 × 10^(-10) cm^(2) s~(-1)).As expected,the SiO_x@PDMI-1.5 electrode delivers brilliant long-term cycle performance with a remarkable capacity retention of 85% over 500 cycles at 1.3 A g^(-1).The well-designed functionalized polyimide also significantly enhances the electrochemical properties of Si nanoparticles electrode.Meanwhile,the assembled SiO_x@PDMI-1.5/NCM811 full cell delivers a high retention of 80% after 100 cycles.The perspective of the binder design strategy based on polyimide modification delivers a novel path toward high-capacity electrodes for high-energy-density batteries.

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.

The Boundary Element Method for Ordinary State-Based Peridynamics

The peridynamics(PD),as a promising nonlocal continuum mechanics theory,shines in solving discontinuous problems.Up to now,various numerical methods,such as the peridynamic mesh-free particlemethod(PD-MPM),peridynamic finite element method(PD-FEM),and peridynamic boundary element method(PD-BEM),have been proposed.PD-BEM,in particular,outperforms other methods by eliminating spurious boundary softening,efficiently handling infinite problems,and ensuring high computational accuracy.However,the existing PD-BEM is constructed exclusively for bond-based peridynamics(BBPD)with fixed Poisson’s ratio,limiting its applicability to crack propagation problems and scenarios involving infinite or semi-infinite problems.In this paper,we address these limitations by introducing the boundary element method(BEM)for ordinary state-based peridynamics(OSPD-BEM).Additionally,we present a crack propagationmodel embeddedwithin the framework ofOSPD-BEM to simulate crack propagations.To validate the effectiveness of OSPD-BEM,we conduct four numerical examples:deformation under uniaxial loading,crack initiation in a double-notched specimen,wedge-splitting test,and threepoint bending test.The results demonstrate the accuracy and efficiency of OSPD-BEM,highlighting its capability to successfully eliminate spurious boundary softening phenomena under varying Poisson’s ratios.Moreover,OSPDBEMsignificantly reduces computational time and exhibits greater consistencywith experimental results compared to PD-MPM.

Instrumented oscillographic study on impact toughness of an axle steel DZ2 with different tempering temperatures

Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the strength and toughness of a DZ2 axle steel at various tempering temperatures and the cause of the improvement in impact toughness was evaluated.The tempering process dramatically influenced carbide precipitation behavior,which resulted in different aspect ratios of carbides.Impact toughness improved along with the rise in tempering temperature mainly due to the increase in energy required in impact crack propagation.The characteristics of the impact crack propagation process were studied through a comprehensive analysis of stress distribution,oscilloscopic impact statistics,fracture morphology,and carbide morphology.The poor impact toughness of low-tempering-temperature specimens was attributed to the increased number of stress concentration points caused by carbide morphology in the small plastic zone during the propagation process,which resulted in a mixed distribution of brittle and ductile fractures on the fracture surface.

A modified 3D mean strain energy density criterion for predicting shale mixed-mode Ⅰ/Ⅲ fracture toughness

The fracture toughness of rocks is a critical fracturing parameter in geo-energy exploitation playing a significant role in fracture mechanics and hydraulic fracturing.The edge-notched disk bending(ENDB)specimens are employed to measure the entire range of mixed-modeⅠ/Ⅲfracture toughness of Longmaxi shale.To theoretically interpret the fracture mechanisms,this research first introduces the detailed derivations of three established fracture criteria.By distinguishing the volumetric and distortional strain energy densities,an improved three-dimensional mean strain energy density(MSED)criterion is proposed.As the critical volumetric to distortional MSED ratio decreases,the transition from tensiondominated fracture to shear-dominated fracture is observed.Our results indicate that both peak load and applied energy increase significantly with the transition from pure mode I(i.e.,tension)to pure modeⅢ(i.e.,torsion or tearing)since mode-Ⅲcracking happens in a twisted manner and mode-Ⅰcracking occurs in a coplanar manner.The macroscopic fracture signatures are consistent with those of triaxial hydraulic fracturing.The average ratio of pure mode-Ⅲfracture toughness to pure mode-Ⅰfracture toughness is 0.68,indicating that the obtained mode-Ⅲfracture resistance for a tensionbased loading system is apparent rather than true.Compared to the three mainstream fracture criteria,the present fracture criterion exhibits greater competitiveness and can successfully evaluate and predict mixed-modeⅠ/Ⅲfracture toughness of distinct materials and loading methods.

Effect of B_(2)O_(3) enrichment on microstructural inhomogeneity of high strength steel weldments

The present work attributes the role of boron on the high strength steel submerged arc weld using an undermatching filler wire.Mild steel filler wire was used for welding in constant machine parameters setting to evaluate the joint strength due to the enrichment of boron.To change the chemical composition of the weld metal,boron trioxide powder was blended with virgin flux in various proportions(2.5%−12.5%),which led to an increase in boron weight percentage in the range of 0−0.0065.The results show that weld metals(WM)optical micrographs depict the various types of ferrites,pearlites and secondary phases like martensite-austenite(M-A).Acicular ferrite content was influenced by the boron trioxide addition.Heat affected zone(HAZ)micrographs were not showing appreciable changes with oxide enrichment.Hardness and toughness of weld metals showed the mixed trend with B_(2)O_(3) enrichment whereas,small reduction in ultimate tensile strength(UTS)and yield strength(YS)was observed.

MAGAZINE REVIEW

World Cinema Issue 3(Bimonthly),2024 Film as Painting:Nollywood's Philosophical Understanding of the Photographic Medium This issue focuses on national films,with three articles analyzing one or more representative flms from three countries.Film as Painting:Nollywood's Philosophical Understanding of the Photographic Medium explores thephilosophical roots of photography in Nigerian film;Stalkers in Istanbul:Silence,Urban Space,and Damaged Masculinity in Nuri Bilge Ceylan's UZAK shows the decaying male image on Turkish film screens as opposed to the tough guy;The Broken Frame:The Non-Creative WaysofAbbasKiarostami in 24 FRAME Sprovides a frame-by-frame analysis of the lranian director's use of off-screen space to activate the imagination of the audience.

大自然的调色盘

主题语境:人与自然篇幅:379词关键词:structural color1 Scientists at the University of Central Florida(UCF)have created a new kind of paint thats super light and super tough.The colors in the new paint arent at all like those in most paints.Instead,theyre more like the colors on a butterflys wings.

ITMF gains momentum in 2023

In 2023,unfavorable macro-economic conditions such as high inflation and interest rates currently combine with unfavorable industry specific aspects such as high inventories at brand and retail level,creating pressure on textile manufacturers from both supply and demand sides.When the textile industry is going through a tough phase,ITMF helps the industry to change its growth pattern with an innovative and responsible attitude,actively promotes international trade and investment,plays its full role in promoting the economic growth of the industry and strives to build an open global textile economy.At the same time,ITMF advocates diversity and inclusion,implements the United Nations"The 2030 Agenda for Sustainable Development"and promotes the realisation of the industry’s development outcomes.

Ministry of Commerce:Full of confidence,clear direction,strong motivation

On March 12,the official account of the International Business Daily of the Ministry of Commerce published an article titled“Foreign trade enterprises:full of confidence,clear direction,strong motivation”.The content is as follows:This year,China is still facing a tough foreign trade situation.On the one hand,many international organizations predict that global economic growth in 2024 will still be lower than the historical average and the pressure on external demand will increase;on the other hand,trade protectionism and unilateralism are on the rise,geopolitical conflicts,the global“super election year”and other spillover factors have created many uncertainties.

坚持不懈的旅程

如何在逆境中坚持不懈,将失败转化为通往成功的阶梯?让我们一起到文章中寻找答案!Life is like a big picture, and every part of it stands for a choice, a hard time,or a win. Making your own way isn't just about getting where you want to go;it's about keeping on trying, even when things get tough.

Product Development of High Strength and Toughness Spring Flat Steel

With the continuous development of mechanical industry,higher requirements are put forward for the comprehensive properties of spring steel.The chemical composition and production process of spring flat steel are designed to meet the requirements of high strength and high toughness of spring flat steel,through the test,the product surface quality and internal quality all meet the national standards,the performance indicators to meet user requirements.

储层和开采参数对天然气水合物开采产能的影响分析

开展储层参数和开采参数对天然气水合物开采产能影响的研究有助于其实际开采场址和开采方法的选择。以中国南海神狐海域SH7站位的地质参数为背景,采用TOUGH+HYDRATE软件系统地分析了储层压力、温度、孔隙度、水合物饱和度、渗透率、上覆层和下伏层渗透率等储层参数,以及降压幅度、降压井长度和出砂堵塞(通过改变井周网格渗透率反映出砂堵塞)等开采参数对天然气水合物降压开采产能的影响。数值模拟结果表明:①随着储层渗透率的增大,产气量有明显的增加;随着储层压力、孔隙度的增大以及上覆层和下伏层渗透率的减小,产气量有较大的增加;随着储层温度的增大,产气量有一定的增加;产气量随饱和度的增大先增大后减小。因此,实际开采时可优先选择渗透率大、上覆层和下伏层渗透率小、孔隙度大、温度较高、水合物饱和度适中的储层。②随着降压幅度的增大以及降压井长度增大,产气量有明显的增加;而随着出砂堵塞程度的加剧,产气量有非常明显的减少。因此,实际开采时可以通过增大降压幅度和降压井长度以及采取减轻出砂堵塞的措施来提高产气量。研究结果可以为我国将来天然气水合物开采区域及开采方式的选择和确定提供参考。