Achieving High Strength and Tensile Ductility in Pure Nickel by Cryorolling with Subsequent Low-Temperature Short-Time Annealing

Ultra fine-grained pure metals and their alloys have high strength and low ductility.In this study,cryorolling under different strains followed by low-temperature short-time annealing was used to fabricate pure nickel sheets combining high strength with good ductility.The results show that,for different cryorolling strains,the uniform elongation was greatly increased without sacrificing the strength after annealing.A yield strength of 607 MPa and a uniform elongation of 11.7%were obtained after annealing at a small cryorolling strain(ε=0.22),while annealing at a large cryorolling strain(ε=1.6)resulted in a yield strength of 990 MPa and a uniform elongation of 6.4%.X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),and electron backscattered diffraction(EBSD)were used to characterize the microstructure of the specimens and showed that the high strength could be attributed to strain hardening during cryorolling,with an additional contribution from grain refinement and the formation of dislocation walls.The high ductility could be attributed to annealing twins and micro-shear bands during stretching,which improved the strain hardening capacity.The results show that the synergistic effect of strength and ductility can be regulated through low-temperature short-time annealing with different cryorolling strains,which provides a new reference for the design of future thermo-mechanical processes.

The Early Mesozoic NE-SW Extensional Model and Exhumation Processes at the Southeastern Margin of the Central Asian Orogenic Belt:Insights from the Strain and Kinematic Vorticity Analysis of the Sonid Zuoqi Ductile Detachment Zone

The Sonid Zuoqi ductile detachment zone is located at the southeastern margin of the Central Asian orogenic belt(CAOB),striking EW and dipping to the S.The major rock type of the Sonid Zuoqi ductile detachment zone is mylonite derived from granite.The sequence of mylonite features is:(1)S and C foliations of mylonite,and(2)extensional crenulation cleavage(ecc)or C′and the kinematic vorticity(Wk)value changed from 0.70 to 0.95 and from 0.37 to 0.69,respectively;the strain type of the mylonites within the Sonid Zuoqi ductile detachment zone is compressional to planar strain.The strong deformation mylonite and Halatu plutons yielded a zircon U-Pb age of 244 Ma and a zircon(U-Th)/He age of 214 Ma,respectively.Based on the strain and kinematic vorticity analysis,together with the zircon U-Pb and zircon(U-Th)/He ages and the regional tectonic background,the study area experienced three stage evolution:tangential simpleshear(244 Ma),simple-shear-dominated general shear represented by upper crustal extension(224 Ma)and pure-shear-dominated general shear represented by the Halatu pluton doming(214 Ma),which constrained the early Mesozoic NE-SW crustal extension at the southeastern margin of the CAOB.This NE-SW extension probably originated from the postorogenic extensional collapse of the CAOB,subsequent exhumation being controlled by the far afield effects of the closure of the Mongol-Okhotsk belt.

Deformation characteristics of granitic rocks in Erguna ductile shear zone,NE China

The Erguna ductile shear zone is situated in the Erguna Massif,which has been exposed along the eastern bank of the Erguna River in northeastern China.The authors present comprehensive study results on the macro-and micro-structures,finite strain and kinematic vorticity,quartz electron backscatter diffraction(EBSD)fabrics,and geochronology of granitic rocks in the Erguna ductile shear zone.The deformed granitic rocks have experienced significant SE-trending dextral strike-slip shearing.Finite strain and kinematic vorticity in all deformed granitic rocks indicate that the deformation is characterized by simple sheardominated general shearing with S-L tectonites.Mineral deformation behaviors and quartz C-axis textures demonstrate that the deformed granitic rocks developed under greenschist to amphibolite facies conditions at deformation temperatures ranging from 450 to 550℃.New LA-ICP-MS zircon U-Pb ages indicate that these granitic rocks were formed in Early Triassic(~248.6 Ma)and Early Cretaceous(~136.7 Ma).All the evidence indicates that this deformation may have occurred in Early Cretaceous and was related to the compression resulting from the final closure of the Mongol-Okhotsk Ocean.

Influence of grain size on the tensile ductility and deformation modes of rolled Mg–1.02 wt.%Zn alloy

The influence of grain size on the tensile deformation and ductility for Mg–1.02%Zn(wt.%)alloy was investigated.The uniform elongation is nearly insensitive to the increase of grain size,but the post-uniform elongation is significantly decreased with increasing grain size.The high ductility in the fine-grained samples is due to the lower frequency of twins and increased dynamic recovery from the enhanced activation of prismatic<a>slip.

EVOLUTION OF VOIDS IN DUCTILE POROUS MATERIALS AT HIGH STRAIN RATE

In the present work, a dynamic damage model in ductile materials under the application of dynamic general stresses loading is presented. The evolution equation of ductile voids has the closed form, in which work-hardening, the change of surface energy of voids, rate-dependent, inertial effects are taken into account. The expressions of critical stresses for the growth and compaction of voids are directly obtained from the evolution equations of voids. Numerical analysis of the model indicates that the growth of voids is sensitive to the strain rates. The voids grow quickly as the increase of strain rates. It is also shown that the influence of the inertial effects on the void growth is great at high loading rates. It appears to resist the growth of voids. In addition, a dynamic collapse model of ductile voids is also proposed, which can be applied to study the problems of compaction in powder and other materials.

Tensile behaviors of ecological high ductility cementitious composites exposed to interactive freeze-thaw-carbonation and single carbonation

To explore the tensile property parameters in the structural design of bridge deck link slabs made by ecological high ductility cementitious composites (Eco-HDCC), the tensile properties of Eco-HDCC exposed to interactive freeze-thaw-carbonation cycles and single carbonation cycles were studied. The carbonation front of Eco-HDCC was determined by X-ray diffraction and differential scanning calorimetry-thermal gravimetric methods. Results indicate that the carbonation front of Eco-HDCC after interaction tests is deeper than that of Eco-HDCC after single carbonation tests. In addition, the ultimate tensile strength for Eco-HDCC shows an increasing trend after the interaction of 1 to 5 cycles compared with that of virgin specimens, while the ultimate tensile strength decreases after the interaction of 10 to 15 cycles. For single carbonation tests, the ultimate tensile strength of Eco-HDCC increases as cycles increase. After being subjected to interaction and single carbonation environments, both the ultimate tensile strain and tensile strain energy of Eco-HDCC decrease as cycles increase, and the decrease degrees of Eco-HDCC after interaction cycles are larger than those of Eco-HDCC after single carbonation. For general consideration, the tensile stress-strain relationship of Eco-HDCC after the interaction of 15 cycles can be adopted in the design of bridge deck link slabs for the purpose of safety.

Achieving high strength and high ductility in nanostructured metals: Experiment and modelling

Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong, Chinagrains to a^1-martensite nanograins with bimodal grain size distribution for lower strain rates to nanotwins in the ultrafine/coarse grained austenite phase for higher strain rates. Meanwhile, we will further address the mechanism-based plastic models to describe the yield strength, strain hardening and ductility in nanostructured metals with bimodal grain size distribution and nanotwinned polycrystalline metals. The proposed theoretical models can comprehensively describe the plastic deformation in these two kinds of nanostructured metals and excellent agreement is achieved between the numerical and experimental results. These models can be utilized to optimize the strength and ductility in nanostructured metals by controlling the size and distribution of nanostructures.

Effect of Strain Rate on Tensile Behavior of Sn-9Zn-xAg-ySb;{(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} Lead-Free Solder Alloys

The tensile properties of Sn-9Zn-xAg-ySb;{(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} lead-free solders were investigated. All the test samples were annealed at 150°C for 1 hour. The tests are carried out at room temperature at the strain rate of 4.17 × 10-3 s-1, 20.85 × 10-3 s-1, and 208.5 × 10-3 s-1. It is seen that the tensile strength increases and the ductility decrease with increasing the strain rate over the investigated range. From the strain rate change test results, the strain sensitivity values are found in the range of 0.0831 to 0.1455 due to the addition of different alloying elements.

四种典型球墨铸铁应变释放系数及其塑性修正研究

盲孔法是工程中测量残余应力最普遍的方法,其中材料的应变释放系数是该方法中的关键参数,目前国内外对球墨铸铁的应变释放系数研究相对较少。本文采用盲孔法对四种常用球墨铸铁QT450-10、QT550-6、QT600-3和QT700-4的应变释放系数进行了标定,得到应变释放系数与应力的关系曲线,发现低牌号的球墨铸铁由于铁素体含量多,对应力集中更为敏感,在标定试验中易产生局部的塑性变形。使用基于形状改变比能S的修正方法对四种球墨铸铁的应变释放系数进行修正,发现和其他均质金属材料不同,球墨铸铁应变释放系数与■之间存在良好的线性关系,因此提出了球墨铸铁应变释放系数关于■的修正公式,可直接应用于盲孔法测量球墨铸铁的残余应力。

延性铜合金颈缩后力学响应工程修正方法

液体火箭发动机中大量采用延性铜合金,严苛载荷导致其普遍工作于大塑性变形状态。由于无法有效处理拉伸试验颈缩后数据,传统工程强度分析所用材料本构无法充分反映出材料的真实承载能力。针对某延性铜合金开展常温单轴拉伸试验,并从工程强度分析的角度提出通用修正函数与参数拟合原则,随后通过有限元颈缩仿真拟合得到加权因子w=0.75和指数修正因子n=2.4。研究表明,有限元颈缩仿真的载荷-位移响应对模型参数和网格具有收敛性,指数修正方法可更好地描述铜合金试件颈缩后响应,选取n=2.4可得到偏保守的材料性能估计。

应变率与短纤维掺量对TR-HDC单轴拉伸力学性能影响试验研究

为研究纤维织物增强高延性混凝土(TR-HDC)在不同应变率和短纤维掺量下的单轴拉伸力学性能,该文设计了25组TR-HDC薄板试件进行单轴拉伸试验,研究应变率(10^(−5) s^(−1)~10^(−1) s^(−1))和短纤维掺量(0%~2%)对TR-HDC开裂模式、破坏机理和抗拉强度的影响。结果表明:TR-HDC在单轴拉伸荷载作用下具有多缝开裂特征,随应变率的增大,试件裂缝间距略有增大趋势,同时短纤维掺量越高,多缝开裂模式越稳定;应变率和短纤维掺量增加可显著改善界面性能,抑制纤维织物的滑移失效;随应变率的提升,TR-HDC的力学性能呈现出一定的应变率敏感性,同时增加短纤维掺量,其开裂和峰值强度也呈现出显著的增长趋势。基于线性对数关系和多因素耦合提出的预测模型可统一TR-HDC静态与动态抗拉强度计算方法,为其工程应用提供了理论依据。

高锁螺母用7075T73铝合金韧性断裂准则研究

通过单向拉伸试验,获取高锁螺母用7075T73铝合金的力学性能和应力应变曲线,拟合求解其Swift/Hockett-Sherby硬化模型参数。设计了2种缺口拉伸试样、3种缺口压缩试样,并结合相应的有限元模型分析,获取不同应力状态下材料的断裂应变、平均应力三轴度和平均罗德参数。以预测值和试验值的误差最小为目标,求解得到7075T73铝合金的Cockroft&Latham、Brozzo、Rice&Tracy三种韧性断裂准则参数,为7075T73铝合金高锁螺母收口成形工艺有限元仿真分析以及收口成形工艺优化提供理论支持。

Research progress of heterogeneous structure magnesium alloys:A review

In recent years,a new class of metallic materials featuring heterogeneous structures has emerged.These materials consist of distinct soft and hard domains with significant differences in mechanical properties,allowing them to maintain high strength while offering superior ductility.Magnesium(Mg)alloys,renowned for their low density,high specific strength,exceptional vibration damping,and electromagnetic shielding properties,exhibit tremendous potential as lightweight and functional materials.Despite their advantageous properties,high-strength Mg alloys often suffer from limited ductility.However,the emergence of heterogeneous materials provides a fresh perspective for the development of Mg alloys with both high strength and ductility.This article provided a fundamental overview of heterostructured materials and systematically reviewed the recent research progress in the design of Mg alloys with strength-ductility balance based on heterostructure principles.The review encompassed various aspects,including preparation methods,formation mechanisms of diverse heterostructures,and mechanical properties,both within domestic and international contexts.On this basis,the article discussed the challenges encountered in the design and fabrication of heterostructured Mg alloys,as well as the urgent issues that require attention and resolution in the future.

液态乙烷管道的韧脆转变及环焊接头可靠性研究

针对液态乙烷管道运行的安全性和可靠性问题,采用力学性能试验和失效评估分析的方法,对液态乙烷管道泄漏失压下的低温脆性、外载作用下的环焊接头应变能力变化进行了研究和分析,结果表明:当液态乙烷由液相转变为气相时,管壁温度高于管材的韧脆转变温度,管道发生低应力下的脆性断裂可能性较低。环焊接头失效模式主要为裂纹扩展失效时,拉伸应变与材料的断裂韧性高低有关;失效模式转变为颈缩失效时,拉伸应变与焊缝、母材的拉伸性能相关。裂纹尺寸较大时,环焊接头会发生断裂失效;裂纹尺寸较小时,失效模式则会转变为焊缝、母材的塑性失效,轴向拉伸应变较高。

Mechanical and Electrical Properties of Some Sn-Zn Based Lead-Free Quinary Alloys

Although there are many lead-free soldering alloys on the market, none of them have ideal qualities. The researchers are combining binary alloys with a variety of additional materials to create the soldering alloys’ features. The eutectic Sn-9Zn alloy is among them. This paper investigated the mechanical and electrical properties of Sn-9Zn-x (Ag, Cu, Sb);{x = 0.2, 0.4, and 0.6} lead-free solder alloys. The mechanical properties such as elastic modulus, ultimate tensile strength (UTS), yield strength (YS), and ductility were examined at the strain rates in a range from 4.17 10−3 s−1 to 208.5 10−3 s−1 at room temperature. It is found that increasing the content of the alloying elements and strain rate increases the elastic modulus, ultimate tensile strength, and yield strength while the ductility decreases. The electrical conductivity of the alloys is found to be a little smaller than that of the Sn-9Zn eutectic alloy.

高延性水泥基复合材料研究进展

文中介绍了人类使用纤维增强材料的历史和高延性水泥基材料(英文简称ECC)的发展过程,分析了普通混凝土、纤维混凝土和高延性水泥基材料的性能特点和区别,详细地阐述了ECC的设计理论、力学特征,以及其在欧洲、日本、美国和中国的研究和应用情况,展望了ECC的应用前景。

TiO_(2)光催化高延性水泥基材料拉伸性能和光催化性能研究

随着大气污染给建筑物及居住环境带来的恶劣影响日益严重,TiO_(2)光催化水泥基材料广受关注。利用光催化剂纳米TiO_(2)颗粒制备光催化高延性水泥基材料(PC-ECC),研究其单轴拉伸应力作用下力学性能和光催化性能;结合微观力学模型及孔结构分析纳米TiO_(2)颗粒对PC-ECC延性的作用机理。结果表明:掺0~15%纳米TiO_(2)颗粒的PC-ECC在龄期28 d时均具有显著的应变硬化特征和优异的多缝开裂能力,拉伸应变在掺1%纳米TiO_(2)颗粒时出现最低值3.48%,之后升至4.55%;宏观拉伸应变随纳米TiO_(2)颗粒掺量变化趋势与应变硬化指标J_(b)’/J_(tip)一致,且后者与孔结构等微观结构紧密相关;掺5%纳米TiO_(2)颗粒的PC-ECC经72 h紫外光照后光降解亚甲基蓝效率达95%,符合一级反应动力学模型。

Damage evolution model of strain hardening cementitious composites under the uniaxial stress state

The deformation and damage behaviors of strain hardening cementitious composites （SHCC） under the uniaxial stress state were investigated in this paper. Two ductile failure-based constitutive models were introduced to describe the uniaxial tension and compression properties of SHCC only using a few parameters. The computation method of model parameters was developed to ease the simulation procedures. Damage evolution of the SHCC was simulated by the formulation of continuum damage mechanics subsequently. The results show that the proposed models fit the stress-strain curves reasonably well, and the damage variables show different growth rules under uniaxial tension and compression. It is concluded that the proposed method can not only simply simulate the constitutive behavior of SHCC with the reasonable accuracy but also capture the characteristic of material degradation.

Unified analytical stressstrain curve for quasibrittle geomaterial in uniaxial tension, direct shear and uniaxial compression

Considering strain localization in the form of a narrow band initiated just at peak stress, three analytical expressions for stressstrain curves of quasibrittle geomaterial (such as rock and concrete) in uniaxial tension, direct shear and uniaxial compression were presented, respectively. The three derived stressstrain curves were generalized as a unified formula. Beyond the onset of strain localization, a linear strain-softening constitutive relation for localized band was assigned. The size of the band was controlled by internal or characteristic length according to gradient-dependent plasticity. Elastic strain within the entire specimen was assumed to be uniform and decreased with the increase of plastic strain in localized band. Total strain of the specimen was decomposed into elastic and plastic parts. Plastic strain of the specimen was the average value of plastic strains in localized band over the entire specimen. For different heights, the predicted softening branches of the relative stressstrain curves in uniaxial compression are consistent with the previously experimental results for normal concrete specimens. The present expressions for the post-peak stressdeformation curves in uniaxial tension and direct shear agree with the previously numerical results based on gradient-dependent plasticity.

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.