A refined deviatoric hardening plastic model for sand

The classical deviatoric hardening models are capable of characterizing the mechanical response of granular materials for a broad range of degrees of compaction.This work finds that it has limitations in accurately predicting the volumetric deformation characteristics under a wide range of confining/consolidation pressures.The issue stems from the pressure independent hardening law in the classical deviatoric hardening model.To overcome this problem,we propose a refined deviatoric hardening model in which a pressure-dependent hardening law is developed based on experimental observations.Comparisons between numerical results and laboratory triaxial tests indicate that the improved model succeeds in capturing the volumetric deformation behavior under various confining/consolidation pressure conditions for both dense and loose sands.Furthermore,to examine the importance of the improved deviatoric hardening model,it is combined with the bounding surface plasticity theory to investigate the mechanical response of loose sand under complex cyclic loadings and different initial consolidation pressures.It is proved that the proposed pressure-dependent deviatoric hardening law is capable of predicting the volumetric deformation characteristics to a satisfactory degree and plays an important role in the simulation of complex deformations for granular geomaterials.

A hardening load transfer function for rock bolts and its calibration using distributed fiber optic sensing

Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior,yet only a few experimental works and analytical models have been reported,most of which are based on the global rock bolt response evaluated in pull-out tests.This paper presents a laboratory experimental setup aiming to capture the rock formation effect,while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level.It is shown that the behavior along the sample itself varies,with certain points exhibiting stress drops with crack formation.Some edge effects related to the kinematic freedom of the grout to dilate are also observed.Regardless,it was found that the mid-level response is quite similar to the average response along the sample.The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations.The paper also offers a plasticity-based hardening load transfer function,representing a"slice"of the anchor.The paper describes in detail the development of the model and the calibration/determination of its parameters.The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.

Effect of aging treatment on the precipitation transformation and age hardening of Mg-Gd-Y-Zn-Zr alloy

In this study, the precipitation transformation and age hardening of solution-treated Mg-9Gd-4Y-2Zn-0.5Zr(wt.%) alloy were investigated at different aging treatment parameters. The precipitation sequences of the alloy aged at 200℃, 250℃ and 300℃ are β’’(DO19) → β’(BCO) → β(FCC), β’’(DO19) → β’(BCO) → β_(1)(FCC) → β(FCC) and β(FCC), respectively. The streaks sequences of the alloy aged at 200℃, 250℃ and 300℃ are SF, SF → 14H-LPSO and SF → 14H-LPSO, respectively. For the alloy aged at 200℃ and 250℃, the increase in hardness with increasing aging time is contributed from the increase in precipitate volume fraction and the transformation from β’’ to β’ phase with basal → prismatic and spherical → spindle-like precipitate changes. The decrease in hardness after the peak-aging stage is attributed to the appearance of micro-sized β precipitates. Because of the smaller size of precipitates and the triangular arrangement of β’ precipitate, the hardness of the alloy aged at 200℃ is higher than that aged at 250℃. For the alloy aged at 300℃, the appearance of only micro-sized β precipitate and its coarsening with increasing aging time leads to the lowest hardness and an overall decrease in hardness with the aging time.

Microstructure,Texture Evolution,and Strain Hardening Behaviour of As-extruded Mg-Zn and Mg-Y Alloys under Compression

Microstructure,texture evolution and strain hardening behaviour of the Mg-1Y and Mg-1Zn(wt%)alloys were investigated under room temperature compression.Microstructural characterization was performed by optical microscopy,scanning electron microscopy,electron back scattered diffraction and transmission electron microscopy.The experimental results show that Mg-1Zn alloy exhibits conventional three-stage strain hardening curves,while Mg-1Y alloy exhibits novel six-stage strain hardening curves.For Mg-1Y alloy,rare earth texture leads to weak tensile twinning activity in compression and consequently results in a moderate evolution to<0001>texture.Moreover,inefficient tensile twinning activity and weak slip-twinning interaction give rise to excellent ductility and high hardening capacity but low strain hardening rate.For Mg-1Zn alloy,basal texture leads to pronounced tensile twinning activity in compression and consequently results in rapid evolution to<0001>texture.The intense tensile twinning activity and strong slip-twinning interaction lead to high strain hardening rate but poor ductility and low hardening capacity.

Tribological behavior of ZK60Gd alloy reinforced by SiC particles after precipitation hardening

In this research, the effect of precipitation hardening on the tribological behavior of the ZK60Gd/SiC composite was studied. For this purpose, ZK60Gd alloy containing with 5 and 10 wt% SiC were produced with stir casting method. The microstructure characterization of the samples showed the wide distributions of Mg_(7)Zn_(3) and Gd(Mg_(0.5)Zn_(0.5)) precipitates were formed during casting. The results of hardness measurement after precipitation hardening at different temperatures showed that the hardness peck was obtained at 175 ℃. The wear tests with different loads(10, 40, 60, 90, and 120 N) and velocities(0.1, 0.3, 0.6, and 0.9 m/s) were performed on the as-cast and heat treated sample at 125, 175, and 225 for 12 h. Between the different precipitation hardening conditions, the precipitation hardened samples at 175 ℃ had the highest hardness values and least wear rate. The sample containing 10% reinforcement had the least wear rate between the unreinforced alloy and the composites. The results showed that abrasive, adhesive, delamination, MML, and fatigue wear mechanisms were the dominant wear mechanisms for the composite samples. In contrast, the dominant wear mechanism for the unreinforced samples was abrasive, adhesive,delamination, MML, and plastic deformation.

Hardening effects of sheared precipitates on {1121} twinning in magnesium alloys

The interactions between a plate-like precipitate and two twin boundaries(TBs)({1012},{1121}) in magnesium alloys are studied using molecular dynamics(MD) simulations. The precipitate is not sheared by {1012} TB, but sheared by {1121} TB. Shearing on the(110) plane is the predominant deformation mode in the sheared precipitate. Then, the blocking effects of precipitates with different sizes are studied for {1121} twinning. All the precipitates show a blocking effect on {1121} twinning although they are sheared, while the blocking effects of precipitates with different sizes are different. The blocking effect increases significantly with the increasing precipitate length(in-plane size along TB) and thickness, whereas changes weakly as the precipitate width changes. Based on the revealed interaction mechanisms, a critical twin shear is calculated theoretically by the Eshelby solutions to determine which TB is able to shear the precipitate. In addition, an analytical hardening model of sheared precipitates is proposed by analyzing the force equilibrium during TB-precipitate interactions. This model indicates that the blocking effect depends solely on the area fraction of the precipitate cross-section, and shows good agreement with the current MD simulations. Finally, the blocking effects of plate-like precipitates on the {1012} twinning(non-sheared precipitate), {1121} twinning(sheared precipitate) and basal dislocations(non-sheared precipitate) are compared together. Results show that the blocking effect on {1121} twinning is stronger than that on {1012} twinning, while the effect on basal dislocations is weakest. The precipitate-TB interaction mechanisms and precipitation hardening models revealed in this work are of great significance for improving the mechanical property of magnesium alloys by designing microstructure.

Mg-3Al-1Zn alloy deformed along different strain paths: Role of latent hardening

The mechanical properties of magnesium alloy AZ31 were investigated experimentally with visco-plastic self-consistent modeling. Tension,compression and plane strain compression(PSC) tests were performed along 3 directions of a hot rolled plate, and the material parameters input in the model were fitted with the uniaxial stress-strain curves. The critical resolved shear stress(CRSS) for tension twinning was modeled with a modified Voce hardening law first decreasing, and then increasing with strain, that could reproduce better the flow stress for twin-predominant deformation. Such CRSS evolution may better model twin nucleation, propagation and growth. Firstly simulations were carried out assuming latent hardening coefficients for slip by other slip systems equal to self-hardening. Then different heterogeneous latent hardening were used, whose values were based on dislocation dynamics simulations from the literature. This study shows that equal self and latent hardening can reproduce the stress strain curves and plastic anisotropy as well as heterogeneous mode on mode latent hardening.Discrepancies between simulations and experimental results from PSC are explained by an under-estimation of twinning for some PSC strain paths.

Strengthening the Security of Supervised Networks by Automating Hardening Mechanisms

In recent years, the place occupied by the various manifestations of cyber-crime in companies has been considerable. Indeed, due to the rapid evolution of telecommunications technologies, companies, regardless of their size or sector of activity, are now the target of advanced persistent threats. The Work 2035 study also revealed that cyber crimes (such as critical infrastructure hacks) and massive data breaches are major sources of concern. Thus, it is important for organizations to guarantee a minimum level of security to avoid potential attacks that can cause paralysis of systems, loss of sensitive data, exposure to blackmail, damage to reputation or even a commercial harm. To do this, among other means, hardening is used, the main objective of which is to reduce the attack surface within a company. The execution of the hardening configurations as well as the verification of these are carried out on the servers and network equipment with the aim of reducing the number of openings present by keeping only those which are necessary for proper operation. However, nowadays, in many companies, these tasks are done manually. As a result, the execution and verification of hardening configurations are very often subject to potential errors but also highly consuming human and financial resources. The problem is that it is essential for operators to maintain an optimal level of security while minimizing costs, hence the interest in automating hardening processes and verifying the hardening of servers and network equipment. It is in this logic that we propose within the framework of this work the reinforcement of the security of the information systems (IS) by the automation of the mechanisms of hardening. In our work, we have, on the one hand, set up a hardening procedure in accordance with international security standards for servers, routers and switches and, on the other hand, designed and produced a functional application which makes it possible to: 1) Realise the configuration of the hardening;2) Verify them;3) Correct the non conformities;4) Write and send by mail a verification report for the configurations;5) And finally update the procedures of hardening. Our web application thus created allows in less than fifteen (15) minutes actions that previously took at least five (5) hours of time. This allows supervised network operators to save time and money, but also to improve their security standards in line with international standards.

循环张拉作用下新型多节泡土钉抗拔性能现场试验研究

新型多节泡土钉具有拉拔硬化特征,相比传统土钉,其在土质边坡中抗拔性能更优。为了探究实际工况条件下新型多节泡土钉的边坡加固性能,并与传统土钉进行比较,开展7组新型多节泡土钉及传统土钉现场循环张拉试验,研究注浆工艺、节泡间距及埋深对土钉抗拔力及其发挥速率的影响规律,进而探明了每一循环下土钉弹、塑性拉拔位移占比,并分析其内在机理。试验结果表明:循环张拉作用下,注浆工艺对土钉的抗拔力影响显著,采用改进式压密注浆工艺和直接压密注浆工艺的土钉抗拔力远远超出传统注浆工艺,且初期的拉拔硬化现象更明显。采用改进式压密注浆工艺的土钉抗拔力发挥速率最快,直接压密注浆工艺次之,传统注浆工艺最小。从总体趋势上看,新型多节泡土钉抗拔力发挥速率在降低,传统土钉抗拔力发挥速率在升高。采用改进式压密注浆工艺虽然不能提升土钉弹性拉拔位移的占比,却能显著提高极限抗拔力;节泡间距对多节泡土钉抗拔力和抗拔力发挥速率影响较小,主要受到土钉周围土体强度的影响;埋深影响多节泡土钉的极限抗拔力,埋深越大,极限抗拔力和初始抗拔力发挥速率越大,同时抗拔力发挥速率随拉拔位移递减的趋势也更加明显。研究成果对提高新型多节泡土钉加固性能和优化工程应用提供指导。

掺轻质砂超高性能混凝土的轴拉力学性能

为研究轻质砂对不同试件尺寸下超高性能混凝土(ultra high performance concrete,UHPC)拉伸应变强化性能的影响,采用轻质砂对原黄砂进行等体积替代,完成9组不同轻质砂体积率(0~35%)和不同试件厚度(30~100 mm)的单轴拉伸试验,并同步进行声发射实时探伤测试。结果表明:轻质砂体积率对UHPC弹性极限点对应应力和对应应变的影响较小,但轻质砂体积率由0增加到35%时,UHPC的极限抗拉强度和极限拉应变分别由10.6 MPa和2.35×10^(-3)提高到了19.4 MPa和4.3×10^(-3);轻质砂体积率大于15%时,UHPC的应变强化程度得到显著提升,试件内部产生的损伤点数更多且分布更均匀,展现出良好的裂缝控制能力;在相同轻质砂体积率下,UHPC的应变强化程度随试件厚度的增加而降低,且试件内部的损伤点趋于集中,表现出明显的尺寸效应。

金属材料瞬时拉伸应变硬化性能的标准化

随着用户使用技术的不断发展,现有的加工硬化性能测试标准已不能满足先进钢铁产品性能表征的需求,需增加结构钢圆形试样与3 mm厚度以上厚板试样的n值测定、拉伸瞬时应变硬化指数的测定、拉伸应变硬化率的测定方法。随着T/CSTM 00514—2022团体标准的颁布和实施,国内拉伸应变硬化性能的试验标准日趋完备与系统化。

一种星载高效率电源的样机研制

针对星载合成孔径雷达电源高效率抗辐射的需求,对适用于星载领域的各种电源拓朴结构进行了对比分析,提出一种同步整流正激变换器拓扑方案。该方案采用单管栅极电荷保持驱动拓扑,解决了变压器死区时间续流管驱动问题,并对电路原理以及抗辐射加固方法进行详细说明,给出电路组成、关键器件和参数计算方法。根据所提方案制作了一台输入50 V~70 V、输出5 V/6 A的样机。实验结果表明:该电源具有高效率和抗辐射的特点,验证了技术方案的准确性,可以满足星载电源的需求。

预见性干预在介入手术治疗儿童脉管畸形中的应用价值

目的 探讨预见性护理干预对脉管畸形患儿经介入治疗在预防或降低常见并发症、不良反应中的应用价值,患者及家属焦虑情绪改善和满意度评价。方法 选取河北省儿童医院2019~2022年介入治疗936例脉管畸形患儿,随机等分为对照组和观察组,每组468例。对照组采用一般护理方法,遵照医嘱执行治疗和护理至出院。观察组在一般护理基础上,采用预见性护理干预。比较2组患儿发热、腹泻、哭闹烦躁、疼痛、呕吐等不良反应发生情况;比较经血管栓塞剂,硬化剂注射治疗后发生感染、皮肤糜烂、局部组织缺损,穿刺部位出血等并发症发生情况;比较2组患儿及家属焦虑情绪状态;比较满意度问卷调查结果。结果 观察组患儿不良反应、并发症发生率低于对照组,差异有统计学意义(P<0.05);观察组患者及家属焦虑情绪明显好转,且满意度问卷调查结果,观察组满意度优于对照组,差异均有统计学意义(P<0.05)。结论 预见性护理干预在介入治疗儿童脉管畸形中能够降低不良反应/并发症发生率,患儿及家属摆脱焦虑情绪状态,满意度得到明显提升,有助提高介入治疗儿童脉管畸形的疗效。

DP900钢的成形性及预应变对烘烤硬化行为的影响

对汽车结构件用DP900钢的成形极限图进行了测试和研究,并运用数学模型进行了预测分析。利用内耗仪和透射电子显微镜从微观角度研究了预应变对烘烤硬化值的影响。结果表明:DP900钢室温下的力学性能为屈服强度604 MPa,抗拉强度935 MPa,均匀伸长率达到14%,断后伸长率为19%。冲压成形过程中,成形极限FLD0为0.245,基于Hollomon方程建立的成形极限数学模型的预测误差在0.2%~13.5%,平均误差为5.87%。预应变量的大小对BH值有显著的影响。随预应变增大,BH值先升高后降低,预应变为7%时达到最高值45 MPa。内耗峰值变化趋势与BH值一致。

三维弹塑性问题的比例边界有限元法

为了研究三维复杂结构的非线性硬化问题,在考虑关联流动准则的Von Mises塑性屈服准则和各向同性/随动硬化准则的本构模型中,引入一致切线模量,并基于比例边界有限元方法和平衡八叉树算法对本构模型进行求解。采用Newton-Raphson迭代法求解位移和应力的非线性方程,为了减少计算量,仅在比例中心点执行并储存迭代过程的变量,同时采用Fortran语言编制了求解程序。两个算例计算结果表明,该模型的计算结果具有较高的准确性。

梯度硬度A286高温合金的本构模型

构建了一种能够表征材料硬度对流动应力影响的本构模型以满足梯度硬度零件数值仿真的需要。开展了不同硬度(175~370 HV)A286高温合金的准静态压缩试验,构建了考虑硬度影响的改进Ludwik模型,基于该模型进行了梯度硬度薄壁管仿真。结果表明,随着硬度的增加,材料的流动应力也相应增加。相较于原始Ludwik模型,改进Ludwik模型R值增至0.996,e_(AARE)值降至2.6%,能有效预测不同硬度下的流动应力。仿真中薄壁管形成明显的鼓包,鼓包区域应力较小,非鼓包区域应力较大,验证了改进Ludwik模型可以较为准确地描述梯度材料在变形过程中的流动行为。

无水乙醇、泡沫硬化剂治疗儿童大型静脉畸形的疗效比较

目的探讨无水乙醇、泡沫硬化剂治疗儿童大型静脉畸形的临床疗效。方法回顾性分析60例大型孤立性静脉畸形患儿的临床资料。将先注射无水乙醇再注射泡沫硬化剂作为A组(n=30),先注射泡沫硬化剂再注射无水乙醇作为B组(n=30),对比两组患儿的临床疗效、并发症、注射次数及无水乙醇用量等。结果A、B两组的总有效率均为100%。A组显著有效率为63.33%(19/30),B组显著有效率为90%(27/30),差异有统计学意义(P<0.05)。无水乙醇用量A组为(10.30±3.19)mL,B组为(6.73±2.06)mL;注射次数A组为(3.57±1.01)次,B组为(2.63±0.61)次,差异均有统计学意义(均P<0.05)。两组均无严重并发症发生,水疱发生率A组30%(9/30),B组为6.67%(2/30),差异有统计学意义(P<0.05)。结论无水乙醇、泡沫硬化剂联合应用治疗儿童大型静脉畸形,可以增加疗效,减少无水乙醇用量,降低并发症;尤其先注射泡沫硬化剂再注射无水乙醇疗效更佳。

316L不锈钢非比例循环硬化特性的数值模拟

在等效应变范围为0.7%条件下,对316L不锈钢进行室温应变控制拉-扭疲劳试验,研究了比例应变路径(单轴路径和比例路径)和非比例应变路径(十字路径和圆路径)下的循环硬化特性;采用AF-OW随动硬化模型结合Chaboche各向同性硬化准则以及将非比例度嵌入到各向同性硬化准则中的改进模型对各路径下的循环特性进行模拟,并进行试验验证。结果表明:316L不锈钢在各路径下的循环初期均产生了循环硬化现象,在单轴、比例、十字和圆路径下的硬化率分别为5.2%,4.5%,38.2%,44.6%,在非比例应变路径下,该钢产生明显的附加强化;AF-OW模型结合各向同性硬化准则可以准确地模拟单轴和比例路径下的循环硬化特性,但对十字和圆路径下的模拟效果较差,模拟得到的正应力-正应变滞回环与试验结果之间的最大相对误差均大于20%;改进模型可以准确地描述十字和圆路径下的循环硬化特性,正应力-正应变滞回环的最大相对误差分别为1.3%和3.2%,最大等效峰值应力的相对误差分别为1.9%和1.2%。

集成电路和功率器件抗辐射工艺加固技术研究综述

随着我国空间装备的高速发展,尤其是深空探测器,微电子器件抗辐射性能得到广泛关注。抗辐射工艺加固是实现器件抗辐射性能提升的重要途径之一。本文围绕空间总剂量效应和单粒子效应,对近年来集成电路和功率器件辐射效应机理和工艺加固技术的研究进展进行了介绍和总结,为抗辐射工艺加固技术的发展与应用提供了有益参考。

离子改性对宽分子量分布聚丙烯黏弹性能影响

宽分子量分布聚丙烯(BMWDPP)PP1经离子改性剂处理后得到PP4。通过凝胶渗透色谱(GPC)与平板旋转流变、拉伸流变和熔体强度测试研究了PP1和PP4的分子结构与流变性能的变化。离子改性过程中的自由基诱发PP降解会降低BMWDPP的分子量大小及多分散性;虽未形成真正的长支链结构,但由于接枝在PP分子链上的金属盐之间靠离子相互作用造成“类长支链”效果,PP4可产生拉伸应变硬化现象;PP4因大分子量组分的降解削弱缠结及小分子量组分的降解增强塑化,导致黏弹性低于PP1。拉伸应变硬化对熔体强度增高的影响强于分子量降低对熔体强度削弱的影响,故PP4的熔体强度在不同的温度下皆高于PP1;在低温下呈现线形大分子量分子链PP特点,而在高温下呈现长支链PP特点。