Some micromechanical models of elastoplastic behaviors of porous geomaterials

Some micromechanics-based constitutive models are presented in this study for porous geomaterials.These micro-macro mechanical models focus on the effect of porosity and the inclusions on the macroscopic elastoplastic behaviors of porous materials. In order to consider the effect of pores and the compressibility of the matrix, some macroscopic criteria are presented firstly for ductile porous medium having one population of pores with different types of matrix(von Mises, Green type, Misese Schleicher and Druckere Prager). Based on different homogenization techniques, these models are extended to the double porous materials with two populations of pores at different scales and a Druckere Prager solid phase at the microscale. Based on these macroscopic criteria, complete constitutive models are formulated and implemented to describe the overall responses of typical porous geomaterials(sandstone,porous chalk and argillite). Comparisons between the numerical predictions and experimental data with different confining pressures or different mineralogical composites show the capabilities of these micromechanics-based models, which take into account the effects of microstructure on the macroscopic behavior and significantly improve the phenomenological ones.

A phenomenological model for plastic flow behavior of rotating band material with a large temperature range

The plastic flow behavior of the rotating band material is investigated in this paper. The rotating band material is processed from H96 brass alloy, which is hardened to a much higher yield strength compared to the annealed one. The dynamically uniaxial compression behavior of the material is tested using the split Hopkinson pressure bar(SHPB) with temperature and strain rate ranging from 297 to 1073 K and500 to 3000 s^(-1), respectively, and a phenomenological plastic flow stress model is developed to describe the mechanical behavior of the material. The material is found to present noticeable temperature sensitivity and weak strain-rate sensitivity. The construction of the plastic flow stress model has two steps. Firstly, three univariate stress functions, taking plastic strain, plastic strain rate and temperature as independent variable, respectively, are proposed by fixing the other two variables. Then, as the three univariate functions describe the special cases of flow stress behavior under various conditions, the principle of stress compatibility is adopted to obtain the complete flow stress function. The numerical results show that the proposed plastic flow stress model is more suitable for the rotating band material than the existing well-known models.

PLASTIC BEHAVIOR AND CONSTITUTIVE MODELING OF ARMOR STEEL OVER WIDE TEMPERATURE AND STRAIN RATE RANGES

Plastic behavior of 603 armor steel is studied at strain rates ranging from 0.001 s-1 to 4500 s-1, and temperature from 288 K to 873 K. Emphasis is placed on the effects of temperature, strain rate, and plastic strain on flow stress. Based on experimental results, the JC and the KHL models are used to simulate flow stress of this material. By comparing the model prediction and the experimental results of strain rate jump tests, the KHL model is shown to have a better prediction of plastic behavior under complex loading conditions for this material, especially in the dynamic region.

Behavioral plasticity is not significantly associated with head volume in a wild Chestnut Thrush(Turdus rubrocanus) population

Background: The drivers of intraspecific variation in behavioral plasticity are poorly known. A widely held hypothesis is that brain size is positively correlated with behavioral plasticity.Methods: A total of 71 Chestnut Thrushes(Turdus rubrocanus) were caught in the wild population. We quantified behavior plasticity of activity of individuals measured in the same cage across two contexts(common and with a novel object stimulation), using a random regression analysis. We then investigated whether head volume(a proxy for brain size) was associated with behavioral plasticity in activity level using Spearman rank-order correlation.Results: We found no significant evidence that activity plasticity was associated with relative head volume. There was no sex difference in head volume or in variance in head volume.Conclusions: We speculate that the absence of an association between brain volume and activity behavior plasticity may result from the inaccuracy of using external skull measurements to estimate brain size, or from a particular part of the brain being responsible for plasticity in activity level.

Plastic deformation behavior of ZK60 magnesium alloy with addition of neodymium

The hot deformation simulation of a ZK60 magnesiuln alloy at different temperatures from 373 to 673 K and different strain rates of 0.1, 0.01 and 0.002 s^-1 was studied by using the Gleebe-1500 simulator. The plastic deformation behavior was measured and the deformation activation energy was calculated. The microstructures of ZK60 magnesium alloy with an addition of neodymium during the deformation process were observed by using Polyvar-MET optical microscope and Tecnai G^2 20 TEM. The results show that the working hardening, the dynamic recovery and the dynamic recrystallization occur during the plastic deformation process at different temperatures and strain rates. The dynamic recrystallization starts when the temperature is over 473 K and the DRX grain size after hot deformation is only 5-10 μm. So the refined grains improve both the tensile strength and the elongation of alloys at room temperature. Neodymium is added into the alloy and a precipitate phase Mg12Nd that impedes the movement of dislocations is formed, which benefits to increasing mechanical properties of ZK60 magnesium alloy.

ANOMALOUS BEHAVIOR REVISITED:DYNAMIC RESPONSE OF ELASTIC-PLASTIC STRUCTURES

Based on the minimum principle of acceleration in the elastic-plastic continua under finite def ormation, the dynamic response of an elastic-perfectly plastic pin-ended beam subjected to rectangular impulse loading is studied with the help of a numerical approach. The calculated results once again show the anomalous behavior of the beam during its response process, which was previously found in [1]. By carefully analyzing the instantaneous distribution of the bending moment, the membrane force, the curvature and displacement during the response process, it is concluded that the interactive effect between the geometry and materials nonlinearities of the structure is the key reason for leading to the anomalous behavior. This will be helpful for clarifying some misunderstandings in explaining the problem before.

Tribological Behavior of Diamond Coatings against Carbon Fiber Reinforced Plastics under Dry Conditions

The frictional resistance and machining quality when cutting carbon fiber reinforced plastics (CFRP) laminates are associated with tribological behavior of tool materials. In the present study, the tribological properties of three types of monolayer microcrystalline diamond (MCD) coatings, nanocrystalline diamond (NCD) coatings and dual-layer MCD/NCD coatings sliding against CFRP are investigated under dry lubricated conditions using the rotational friction tester. The coefficients of friction (COF), wear rate and worn surfaces of the contacted surfaces are analyzed for the MCD-CFRP, NCD-CFRP and MCD/NCD-CFRP contacting pairs. The results show that compared with the monolayer MCD and NCD, the bilayer of MCD/NCD coating displays the lowest COF with the value of ~0.13, it is 42% and 55% of the values for MCD and NCD coatings. Due to the rough surfaces of MCD, the wear debris of CFRP on MCD samples exhibits the plowing effect. While for the NCD and MCD/NCD samples, the wear fragments display the planar shapes. The wear rate of CFRP against MCD is more than twice that of CFRP against NCD, due to the excellent loading capacity. While the wear rate of CFRP against MCD/NCD is about twice than that of CFRP-NCD pairs. The bilayer of MCD/NCD combines the excellent advantages of high hardness of MCD and the smooth surface of NCD. It shows the broad application potential for the bilayer coatings.

Efficiency of employing fiber-based finite-length plastic hinges in simulating the cyclic and seismic behavior of steel hollow columns compared with other common modelling approaches

The accuracy and effi ciency of the modelling techniques utilized to model the nonlinear behavior of structural components is a signifi cant issue in earthquake engineering. In this study, the suffi ciency of three diff erent modelling techniques that can be employed to simulate the structural behavior of columns is investigated. A fi ber-based fi nite length plastic hinge (FB-FLPH) model is calibrated in this study. In order to calibrate the FB-FLPH model, a novel database of the cyclic behavior of hollow steel columns under simultaneous axial and lateral loading cycles with varying amplitudes is used. By employing the FB-FLPH model calibrated in this study, the interaction of the axial force and the bending moment in columns is directly taken into account, and the deterioration in the cyclic behavior of these members is implicitly considered. The superiority of the calibrated FB-FLPH modelling approach is examined compared with the cases in which conventional fi ber-based distributed plasticity and concentrated plasticity models are utilized. The effi ciency of the enumerated modelling techniques is probed when they are implemented to model the columns of a typical special moment frame in order to prove the advantage of the FB-FLPH modelling approach.

基于离散位错动力学的纳米层状铜异质结构诱导协同强化研究

利用三维多尺度离散位错动力学(DDD)方法对粗/细晶交替的纳米层状铜力学行为及其变形机制进行了研究。在多尺度DDD框架内分别构筑了粗/细晶叠层的多晶模型和对应的粗晶、细晶多晶模型,并采用基于粗粒化方法的位错穿透晶界模型描述了位错与晶界之间的相互作用。单轴拉伸模拟结果表明,层状材料的屈服应力和应变硬化均大于混合法则预测值,表明层状结构诱导了额外强化。进一步的微观结构演化分析表明,在层状材料中,位错在粗晶和细晶中激活并滑移,细晶中位错开动以后很快就会被晶界阻碍,而粗晶中的位错则会滑过整个粗晶层产生更大的塑性应变,从而诱发粗晶层和细晶层间产生应变分配。界面处的应变梯度促进几何必需位错累积,并产生异质变形诱导(HDI)强化。因此,纳米层状铜表现出更强的包辛格效应。

强剪切对单层晶极薄带轧制变形行为的影响

为确定最优的极薄带轧制工艺,本研究深入分析了强剪切对轧制单层晶极薄带微观变形行为和晶体转动演化的影响。采用基于位错滑移机制的晶体塑性有限元模型进行模拟,最大异速比达到1.5。建立了晶粒取向随机分布的单层晶极薄带轧制模型,以探究少晶组织的晶界作用特性。结果表明:强剪切导致单层晶极薄带轧制微观变形和晶体转动表现出显著的局部化。强剪切促进了晶粒的剪切变形,使得晶界的协调变形能力增强。在轧制区施加强剪切变形,可使已启动滑移得到扩展,主滑移带缩窄分散形成新的次滑移带,滑移更加集中和各向异性。变形后晶粒取向主要绕箔材宽度方向发生转动和分散,强剪切使转动角度增大和分散点更加集中稳定。模拟表明强剪切严重影响单层晶极薄带轧制变形的各向异性,进而导致择优取向、滑移局部化以及非均匀应力-应变分布。

基于KAP理论的跟踪式指导在眼睑美容整形术后的作用探讨

目的探讨基于知识-信念-行为(KAP)理论的跟踪式指导在眼睑美容整形术后的作用。方法随机抽样法选取2021年1月~2023年1月本院106例行眼睑美容整形手术的患者,分为对照组与研究组,各53例。对照组术后行常规随访护理,研究组术后行基于KAP理论的跟踪式指导。比较两组干预前后焦虑自评量表(SAS)、抑郁自评量表(SDS)、一般自我效能感量表(GSES)及自我护理能力量表(ESCA)评分,统计两组术后并发症发生情况。结果干预后,研究组SAS、SDS评分低于干预前及对照组(P<0.05);研究组GSES、ESCA评分高于干预前及对照组(P<0.05);研究组术后并发症发生率为3.85%,低于对照组的21.15%(P<0.05)。结论眼睑美容整形术后实施基于KAP理论的跟踪式指导可改善患者情绪状况、自我效能感及自我护理能力,减少术后并发症。

衬塑钢管海水海砂混凝土组合构件受弯性能研究

对12根衬塑钢管海水海砂混凝土(seawater sea-sand concrete filled plastic-lined steel tube, SSC-PLST)试件进行了受弯加载试验和有限元建模分析,研究该类构件的受弯性能及内衬塑料层对组合构件承载变形能力的影响规律。研究结果表明:SSC-PLST受弯构件的破坏形态具体表现为受压区钢管外凸屈曲、对应位置混凝土被压碎,受拉区钢管屈服、核心混凝土弯曲裂缝细而密,与普通钢管混凝土类似;试件的弯矩-挠度曲线呈三阶段特征,表现出良好的承载与变形性能。SSC-PLST构件不同部分之间的接触应力较小,且分布不均匀。内衬塑料对SSC-PLST构件受弯承载力的影响程度主要与塑料层厚度有关,受钢材强度和混凝土强度的影响较小。最终提出了SSC-PLST受弯构件承载力的简化计算公式,可为该结构构件的工程应用提供参考。

梯度晶粒结构材料拉伸断裂行为的晶体塑性有限元模拟

梯度晶粒结构材料通过在材料内部构筑由纳米晶、细晶渐进过渡至粗晶的微结构,使其展现出诸多优异的力学性能,如高强度、高韧性和抗疲劳性等.工程材料在长期服役过程中,不可避免会发生疲劳和断裂,严重威胁材料的服役安全和使用寿命.相关实验研究报道了纳米晶材料具有沿晶断裂的特点,且抗断裂性能与晶粒尺寸相关,然而梯度晶粒结构材料具有复杂的晶粒尺寸分布,其断裂机理仍需进一步揭示.为此,基于晶体塑性有限元方法,将Cohesive单元植入有限元模型的多晶晶界处,分别模拟了均匀晶粒结构铜和梯度晶粒结构铜的单拉力学性能,并研究了预制裂纹对梯度晶粒结构材料裂纹扩展的影响.结果表明,所提出的晶体塑性本构模型结合晶界损伤机制可以有效模拟梯度晶粒结构材料的塑性变形以及裂纹扩展过程.在单轴拉伸变形下,梯度晶粒结构材料展现了应力与塑性应变的梯度分布特征.一方面,由于晶粒尺寸效应,尽管基体细晶区具有相对较低的流动应力,但是表层纳米晶强度高.此外,由于应变硬化能力的不同,尽管纳米晶区域表现出较低的塑性应变,但细晶区域呈现较高的塑性变形能力.因此,梯度晶粒结构通过强度与应变硬化能力的差异,有效地优化了强度与韧性的协同作用,从而增强了抵抗裂纹扩展的能力.纳米晶区域预制裂纹对梯度晶粒结构材料的强度影响较大,因此抑制纳米晶区域的裂纹萌生有助于晶粒结构材料的安全服役.

高硫塑料模具钢中硫稳定性控制基础研究

基于高硫塑料模具钢典型缺陷检测和MnS析出行为研究,结合热力学计算和工业试验探索了高硫塑料模具钢精炼过程硫稳定性控制手段。结果表明,MnS夹杂是裂纹产生的原因之一。MnS在1708 K开始析出,且优先发生位错形核。MnS发生晶界形核的最快沉淀析出温度为1573 K,并在铸坯加热过程明显长大。综合高硫塑料模具钢精炼顶渣物化性质、硫容量和硫分配比的理论研究,确定最优精炼顶渣成分范围:1.55≤(w(CaO)/w(SiO_(2)))≤1.7、24%≤w(Al 2O 3)≤28%、1.4≤(w(CaO)/w(Al 2O 3))≤2.3、7%≤w(MgO)≤9%和2.5%≤∑w(FeO+MnO)≤4.0%。精炼顶渣成分与精炼工艺优化后,VD出站到中包钢中硫平均降低质量分数由108×10-6减少至30×10-6,平均Al s损由24.9×10-6减少至14.2×10-6,实现了模具钢中硫稳定性和VD至中包Al s损的大幅度改善。

基于行为分阶段转变理论的护理干预在四肢大面积烧伤后瘢痕整形患者中的应用

目的:探究基于行为分阶段转变理论的护理干预在四肢大面积烧伤后瘢痕整形患者中的应用效果。方法:选取2019年5月-2022年5月于笔者医院行瘢痕整形修复的四肢大面积烧伤后瘢痕患者作为研究对象,根据基于行为分阶段转变理论护理干预在笔者医院实施时间,将2019年5月-2020年12月收治的46例患者纳入对照组,给予常规干预;2021年1月-2022年5月收治的44例患者纳入观察组,给予基于行为分阶段转变理论的护理干预。比较干预前和干预3个月后两组患者恐动症信念[恐动症信念评分量表(Kinesiophobia causes scale,KCS)]、恐惧回避信念[恐惧-回避信念问卷(Fear-avoidance beliefs questionnaire,FABQ)]、健康行为[健康行为能力自评量表(Self-rated abilities for health practices scale,SRAHP)]、创面愈合情况[创面愈合时间、温哥华瘢痕量表(Vancouver scar scale,VSS)、瘢痕美容评估与评级量表(Scar cosmesis assessment and rating,SCAR)]、生活质量[烧伤专用健康量表(Burn specific health scale,BSHS-A)]。结果:干预3个月后,两组KCS、FABQ、VSS、SCAR评分均较干预前降低,且观察组低于对照组(均P<0.05);观察组创面愈合时间短于对照组(P<0.05);两组SRAHP、BSHS-A评分较干预前升高,且观察组高于对照组(均P<0.05)。结论:基于行为分阶段转变理论的护理干预可减弱四肢大面积烧伤后瘢痕整形术患者恐动和恐惧回避信念,促进患者健康行为及创面愈合,提高患者生活质量。

金属层状复合材料的力学行为及微观变形机理

金属层状复合材料作为一种典型的非均质材料,通过调控其内部的多尺度微结构特性,可以实现金属结构材料强度-韧性的协同提升,在高端先进制造领域具有潜在的应用前景。金属层状复合材料的宏观力学性能显著依赖于各组元层的性能、厚度和异质界面的结构特性。变形过程中材料内部的微观应力/应变在异质界面处的协调特性对组元金属的形变微观机制产生重要影响,进而影响复合材料整体的性能。因此,探索金属层状复合材料的“微观结构-力学行为-变形机制-宏观力学性能”的内在关联并揭示其对应的微观形变机理,对设计具有优异综合力学性能的金属层状复合材料有重要的理论指导意义和实际应用价值。聚焦于晶态金属层状复合材料的微观力学行为及变形机理,介绍了其力学行为的尺寸与界面效应,着重讨论了室温下材料的微观形变物理过程,阐明了非均匀金属层状复合体强韧化的机理。最后,对金属层状复合材料力学行为的研究进行了简要展望。

合理情绪行为护理对烧伤整形患者负性情绪及生活质量的影响

目的:探究合理情绪行为护理对烧伤整形患者负性情绪及生活质量的影响。方法:选取2020年5月—2022年7月联勤保障部队第九九〇医院收治的82例烧伤整形患者作为研究对象,按照随机数表法分为两组,每组各41例。对照组予以常规护理干预,观察组在对照组基础上实施合理情绪行为护理干预,均持续护理1个月。比较两组患者负性情绪、生活质量、护理满意度情况。结果:护理后,观察组SCL-90中各维度评分均较对照组低,差异有统计学意义(t=19.419、31.071、29.515、29.454、8.188、19.607、26.052、23.163、34.031,P<0.05);护理后,观察组SF-36中各维度评分均较对照组高,差异有统计学意义(t=9.611、9.827、14.138、10.165、10.602、14.582、11.337、9.532,P<0.05);观察组护理满意度较对照组高,差异有统计学意义(χ^(2)=5.145,P<0.05)。结论:在烧伤整形患者中实施合理情绪行为护理干预,可有效缓解患者不良情绪,促进生活质量改善,进而获得较高护理满意度。

行为转变理论指导下康复护理在颜面部烧伤后瘢痕整形患者中的应用

目的探讨行为转变理论指导下康复护理在颜面部烧伤后瘢痕整形患者中应用效果。方法选取焦作市人民医院皮肤烧伤整形科2021年2月至2022年6月收治的40例颜面部烧伤后瘢痕整形患者为研究对象,在常规护理的基础上采用行为转变理论指导下的康复护理。采用伤残接受度量表(ADS-R)调查患者干预前后的伤残接受程度,采用医学应对方式问卷(MCMQ)调查患者干预前后的应对方式变化,并采用简烧伤健康量表(BSHS-B)调查患者干预前后的生活质量,同时调查患者的护理满意度。结果该组患者干预后的ADS-R量表评分高于干预前,MCMQ中的积极应对评分干预前,消极应对评分低于干预前,差异有统计学意义(P<0.05)。该组患者干预后的BSHS-B量表评分高于干预前,差异有统计学意义(P<0.05)。该组患者的整体护理满意度为100%(40/40)。结论行为转变理论指导下的康复护理能够转变颜面部烧伤整形患者的应对方式,提高伤残接受程度和生活质量,提升护理满意度。

环境丰容技术在鱼类增养殖中的应用研究进展

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