EXPERIMENTAL PLASTIC DEFORMATION ANALYSIS BY MEANS OF THERMOPLASTIC EFFECT

This paper proposes a new experimental method of quantitative plastic deformation analysis by means of the thermoplastic effect. The incremental plastic strain distribution for a single shear specimen was obtained by using this method.

INFLUENCES OF MICROSCOPE SIZE EFFECT OF MATRIX ON PLASTIC POTENTIAL AND VOID GROWTH OF POROUS MATERIALS

Based on approximate theoretical analyses on a typical spherical cellcontaining a spherical rnicrovoid, the influences of matrix materials' microscopic scale on themacroscopic constitutive potential theory of porous material and microvoid growth have beeninvestigated in detail. By assuming that the plastic: deformation behavior of matrix materialsfollows the strain gradient (SG) plastic theory involving the stretch and rotation gradients , theratio (λ = l/a) of the matrix materials' intrinsic characteristic length l to the micro-void radiusa is introduced into the plastic constitutive potential and the void growth law. The presentresults indicate that, when the radius a of microvoids is comparable with the intrinsiccharacteristic length l of the matrix materials, the influence of microscopic size effect on neitherthe constitutive potential nor the micro-void evolution predicted can be ignored. And when the voidradius a is much lager than the intrinsic characteristic length l of the matrix materials, thepresent model can retrogress automatically to the improved Gur-son model that takes into account thestrain hardening effect of matrix materials.

Characterization of the Elastic-plastic Region Based on Magnetic Memory Effect

Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further research to evaluate stress concentration quantitatively due to ambiguous physical mechanism, though it has potential to detect early defects in ferromagnetic materials. Mild Q235 steel defective specimens in demagnetization state were loaded in tension up to visible necking, with magnetic memory signals measurement made at increasing stress levels. Magnetic signals varied greatly under first several loadings and subsequently tended to stability in the elastic region, which showed that the magnetization always approaches the anhysteretic magnetization curve and was explained by the theory of magnetomechanical effect. In the plastic stage, an abnormal wave occurred in the stress concentration zone and its height value was sensitive to plastic deformation levels and dependent on the distance between the probe and defect, in accordance with the simulation results based on the magnetic dipole model. Different magnetic signal characteristics in the elastic-plastic region indicate that the magnetic memory technique can identify macroyielding and early damage, which is of profound significance for ensuring safe operation of equipment in service.

Effects of Plastic Deformation and Stresses on Dilatation duringthe Martensitic Transformation in a B-bearing Steel

To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel were investigated. It was found that plastic deformation of austenite at high temperatures enhances ferrite formation significantly, and consequently, the dilatation decreases markedly even at a cooling rate of 280'C/s. The created ferritic-martensitic microstructure possesses clearly lower hardness and strength than the martensitic structure. Elastic stresses cause the preferred orientation in martensite to be formed so that diametric dilatation can increase by nearly 200% under axial compression.

Bauschinger and size effects in thin-film plasticity due to defect-energy of geometrical necessary dislocations

The Bauschinger and size effects in the thinfilm plasticity theory arising from the defect-energy of geometrically necessary dislocations （GNDs） are analytically investigated in this paper. Firstly, this defect-energy is deduced based on the elastic interactions of coupling dislocations （or pile-ups） moving on the closed neighboring slip plane. This energy is a quadratic function of the GNDs density, and includes an elastic interaction coefficient and an energetic length scale L. By incorporating it into the work- conjugate strain gradient plasticity theory of Gurtin, an energetic stress associated with this defect energy is obtained, which just plays the role of back stress in the kinematic hardening model. Then this back-stress hardening model is used to investigate the Bauschinger and size effects in the tension problem of single crystal Al films with passivation layers. The tension stress in the film shows a reverse dependence on the film thickness h. By comparing it with discrete-dislocation simulation results, the length scale L is determined, which is just several slip plane spacing, and accords well with our physical interpretation for the defect- energy. The Bauschinger effect after unloading is analyzed by combining this back-stress hardening model with a friction model. The effects of film thickness and pre-strain on the reversed plastic strain after unloading are quantified and qualitatively compared with experiment results.

DETERMINATION OF EFFECTIVE MODULI FOR FOAM PLASTICS BASED ON THREE PHASE SPHEROIDAL MODEL

The relations of bulk modulus, shear modulus, Young's modulus and the Poisson's ratio with porosity of foam plastics are determined by a three phase spheroidal model commonly used in Composite Mechanics. The results are compared with those using differential scheme. It is shown that the material properties derived from the present model normally are larger than those obtained by differential scheme for foam plastics with identical porosity. The differences in shear moduli and Young's moduli obtained by the two methods are small but they are larger for bulk moduli of incompressible matrix and Poisson's ratios. The Young's moduli of high density foam plastics derived by the present model agree better with experimental ones.

Effects of ultrasonic vibration on plastic deformation of AZ31 during the tensile process

An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration（with a frequency of 15 kHz and a maximum output of 2 kW） during the process of tension at room temperature was conducted to reveal the volume effect of the vibrated plastic deformation of AZ31.The characteristics of mechanical properties and microstructures of AZ31 under routine and vibrated tensile processes with different amplitudes were compared.It is found that ultrasonic vibration has a remarkable influence on the plastic behavior of AZ31 which can be summarized into two opposite aspects：the softening effect which reduces the flow resistance and improves the plasticity,and the hardening effect which decreases the formability.When a lower amplitude or vibration energy is applied to the tensile sample,the softening effect dominates,leading to a decrease of AZ31 deformation resistance with an increase of formability.Under the application of a high-vibrating amplitude,the hardening effect dominates,resulting in the decline of plasticity and brittle fracture of the samples.

Effects of Metal Absorber Thermal Conductivity on Clear Plastic Laser Transmission Welding

In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.

A STUDY ON THE EFFECT OF RADIAL INERTIA ON THE ELASTO-PLASTIC COMBINED STRESS WAVE PROPAGATION IN THIN-WALLED TUBES

An in-depth analysis of propagation characteristics ofelasto-plastic combined stress waves in circular thin-walled tubeshas been made. In obtaining the simple-wave solution, however, mostresearches have ignored the influence of the circumferential stressrelated to the radial inertial ef- fect in the tubes. In this paperthe incremental elasto-plastic constitutive relations which areconve- nient for dynamic numerical analysis are adopted, and thefinite-difference method is used to study the evolution adpropagation of elasto-plastic combined stress waves in a thin-walledtube with the radial inertial effect of the tube considered. Thecalculation results are compared with those obtained when the radialinertial effect is not considered. The calculation results show thatthe radial inertial effect of a tube has a fairly great influence onthe propagation of elasto-plastic combined stress waves.

ELASTIC EFFECT IN DYNAMIC RESPONSE OF PLASTIC CANTILEVER BEAMS TO IMPACT

A lumped masses-springs model is proposed to analyze the dynamic response of an elastic-plastic cantilever beam resulting from impact. The numerical results are in good agreement with those by finite-element approaches. The simplified model can catch the most essential features of elastic-plastic response of beams; in particular, it demonstrates the effect of elastic deformation on the distribution of bending moment and energy dissipation, and provides valuable quatitative results.

THE VOID-SIZE EFFECT ON PLASTIC FLOW LOCALIZATION IN THE GURSON MODEL

Recent studies have shown that the size of microvoids has a significant effect on the void growth rate.The purpose of this paper is to explore whether the void size effect can influence the plastic flow localization in ductile materials.We have used the extended Gurson's dilatational plasticity theory,which accounts for the void size effect,to study the plastic flow localization in porous solids with long cylindrical voids.The localization model of Rice is adopted,in which the material inside the band may display a different response from that outside the band at the incipient plastic flow localization.The present study shows that it has little effect on the shear band angle.

Correlation between the cumulative analgesic effect of electroacupuncture intervention and synaptic plasticity of hypothalamic paraventricular nucleus neurons in rats with sciatica

In the present study, a rat model of chronic neuropathic pain was established by ligation of the sciatic nerve and a model of learning and memory impairment was established by ovariectomy to investigate the analgesic effect of repeated electroacupuncture stimulation at bilateral Zusanfi （ST36） and Yanglingquan （GB34）. In addition, associated synaptic changes in neurons in the paraventricular nucleus of the hypothalamus were examined. Results indicate that the thermal pain threshold （paw withdrawal latency） was significantly increased in rats subjected to 2-week electroacupuncture intervention compared with 2-day electroacupuncture, but the analgesic effect was weakened remarkably in ovariectomized rats with chronic constrictive injury. 2-week electroacupuncture intervention substantially reversed the chronic constrictive injury-induced increase in the synaptic cleft width and thinning of the postsynaptic density. These findings indicate that repeated electroacupuncture at bilateral Zusanfi and Yanglingquan has a cumulative analgesic effect and can effectively relieve chronic neuropathic pain by remodeling the synaptic structure of the hypothalamic paraventricular nucleus.

ANALYSIS OF SIZE EFFECT,SHEAR DEFORMATION AND DILATION IN DIRECT SHEAR TEST BASED ON GRADIENT- DEPENDENT PLASTICITY

The paper concerns the issue of size law,localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single shear band,and based on gradient-dependent plasticity,an analytical solution on size effect or snap-back is obtained. The results show that the post peak response becomes steeper and even exhibits snap-back with increasing of length. For small specimen,the relative shear displacement when specimen failure occurs is lower than that of larger specimen and the shear stress-relative displacement curve becomes steeper. The theoretical solution on non-uniformity of strains in shear band is obtained and evolution of the relative shear displacement is represented. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain,the dilation and compaction within shear band are analyzed. Relation between apparent shear strain and apparent normal strain and relation between shear displacement and vertical displacement are established.

微塑料在黄河流域的污染现状与治理研究进展

我国是世界最大的塑料制品生产和消费国,而黄河流域人口密集,其水质安全极其重要。针对黄河流域水体中微塑料,通过调研大量黄河流域微塑料污染相关文献,从微塑料的来源特征、形状与粒径、空间与季节分布特征等方面系统归纳了黄河流域微塑料污染现状,结合不同地区人口密度、地理环境和季节变化进行深入分析,进一步对比了黄河流域和国内其他主要河流微塑料污染状况,结果表明:微塑料在黄河流域的丰度整体呈现西低东高的态势,黄河流域干流微塑料粒径大部分集中在200μm以下,黄河流域枯水期微塑料丰度大于丰水期的。此外,还系统阐述了微塑料的生物毒性及治理技术研究进展。

负压封闭引流术治疗烧伤整形患者的效果分析

目的 探究对烧伤整形患者实施负压封闭引流术的效果。方法 选取2022年2月—2023年1月本院收治的60例烧伤整形患者作为研究对象,用随机数字表分为对照组和实验组,每组30例。对照组的患者采取常规的烧伤处理方式治疗,实验组的患者采取负压封闭引流术进行治疗,对比两组治疗效果。结果 实验组患者的植皮成活率高于对照组(P<0.05);实验组患者的疼痛评分低于对照组(P<0.05);实验组患者的植皮时间低于对照组(P<0.05);实验组局部治疗费用高于对照组(P<0.05);实验组治疗后的满意度高于对照组(P<0.05)。结论 为烧伤整形患者使用负压封闭引流术进行治疗,患者治疗后的满意度更高,治疗效果更好。因此,负压风引流术治疗烧伤整形患者值得在临床上推广和使用。

酸枣仁皂苷A对抑郁小鼠行为及突触可塑性相关蛋白的作用

该文探究了酸枣仁皂苷A(Jujuboside A,JuA)对抑郁模型小鼠行为及神经突触可塑性相关蛋白表达的作用。通过悬尾实验、强迫游泳实验、旷场实验、Morris水迷宫实验评价小鼠的抑郁状态,免疫组织化学染色法检测小鼠海马组织中脑源性神经营养因子(Brain Derived Neurotrophic Factor,BDNF)的表达水平,Western blot实验检测小鼠海马组织酪氨酸激酶受体B(Tyrosine Kinase Receptor B,TrkB)、cAMP反应元件结合蛋白(cAMP Responsive Element Binding,CREB)、突触后密度蛋白95(Postsynaptic Density Protein 95,PSD95)、自噬效应蛋白Beclin1(Autophagy Effector Protein Beclin1,Beclin1)的表达水平。结果表明,JuA显著改善抑郁模型小鼠的抑郁状态。同时,JuA作用后海马组织BDNF、TrkB、CREB、PSD95、Beclin1的表达水平较模型组分别上调了190.23%、137.24%、76.29%、169.32%、82.53%。综上所述,JuA对抑郁模型小鼠具有显著的抗抑郁作用,并能明上调BDNF、TrkB、CREB、PSD95、Beclin1等神经突触可塑性相关蛋白的表达。实验结果为JuA在抑郁症临床治疗方面的应用提供理论依据,并为探究抑郁症药物治疗靶点提供参考。

自体鼻中隔软骨联合耳软骨对鼻扁平患者整形效果及安全性分析

目的分析自体鼻中隔软骨联合耳软骨对鼻扁平患者的整形效果及安全性。方法选取灵宝市第二人民医院2019年10月至2021年8月收治的115例拟行鼻整形术的鼻扁平患者作为研究对象,根据选择的整形填充材料不同,分为假体填充组(57例)和自体组织填充组(58例),假体填充组接受L形硅胶鼻假体植入隆鼻,自体组织填充组接受自体的鼻中隔软骨、耳软骨进行隆鼻,比较两组矫正成功率、整形效果、并发症、整形效果满意度。结果术后6个月,自体组织填充组矫正成功率(96.55%)高于假体填充组(82.46%),差异具有统计学意义(P<0.05);两组鼻部形态较术前均得到改善,与假体填充组对比,自体组织填充组鼻尖角较小,鼻长较长,鼻尖高度较高,差异具有统计学意义(P<0.05);自体组织填充组并发症发生率(3.45%)低于假体填充组(22.81%),差异具有统计学意义(P<0.05);自体组织填充组对鼻头、鼻背、鼻根部的整形效果满意度均高于假体填充组,差异具有统计学意义(P<0.05)。结论采用自体鼻中隔软骨联合耳软骨进行鼻扁平整形术,具有较高的矫正成功率和整形效果满意度,能改善患者的鼻部形态,并发症较少,安全性较高。

蜂窝梁柱子结构抗连续性倒塌性能研究

目的研究蜂窝梁柱子结构的抗连续性倒塌性能,为工程应用提供设计依据。方法基于拆除构件法,应用ABAQUS有限元分析软件建立蜂窝梁柱子结构与实腹梁柱子结构模拟模型,研究在中柱失效作用下的结构性能,分析孔型、开孔率和首孔距离等参数对蜂窝梁柱子结构抗连续性倒塌性能的影响。结果蜂窝梁柱子结构相比于实腹梁柱子结构的峰值承载力增长64.26%,所对应的位移增长73.57%;蜂窝梁良好的成铰机制使悬链线效应发展更充分;孔型、开孔率、首孔距离对其破坏模式、峰值荷载、悬链线效应发展程度均具有一定影响。结论蜂窝梁柱子结构具有良好的抗连续性倒塌能力,孔型宜为圆形或六边形,开孔率宜取40%~60%,首孔距离宜取0.75~1.0倍梁截面高度。

水压-应力作用下井筒围岩的破坏机理与控制研究

本研究结合曹家滩煤矿井筒围岩在穿越地层时受到了水压弱化作用的实际情况,采用查阅资料、现场查勘、理论分析、公式计算、数值模拟等研究方法,开展了该煤矿主斜井围岩在水压-应力作用下的变形破坏与控制研究。利用半圆拱形井筒断面等效表示的当量半径法,结合地层水压、侧压系数、埋深、内聚力、内摩擦角、巷道尺寸等因素,优化建立了井筒围岩塑性区分布的数学表达式,并进行了模型的数值模拟验证与公式的敏感性分析,针对层位岩性差异及水压弱化作用等主要控制因素,从抑制围岩剪切破坏发生、提高围岩内聚力及内摩擦角、开孔泄水降压、注浆驱替水源、加强原有支护的角度进行了井筒的水害治理与围岩控制。对掌握井筒周边围岩在水压-应力作用下的变形破坏规律、开展相关的数值模拟研究、进行井筒的加固与水害防治工作具有一定的参考意义。

应用^(15)N自然丰度值揭示不同氮源对设施土壤氨挥发的贡献

【目的】我国设施蔬菜生产中普遍存在着氮肥施用过量、氨气(NH_(3))挥发损失严重等问题。通过^(15)N自然丰度法,研究不同肥料类型对土壤NH_(3)挥发的影响,并定量分析其贡献率,为实现降低氮素损失的氮肥科学管理提供依据。【方法】开展为期40天的番茄盆栽培养试验,供试土壤为棕壤,未施过肥也未种植过作物,供试作物为番茄。试验设置4个处理,即不施氮肥(CK)和等量施氮(N3 g/pot)条件下单施鸡粪有机肥(M)、单施尿素(U)、有机肥半量替代尿素(MU)处理。利用被动采样器测定了土壤NH_(3)挥发速率和累积排放量,并借助^(15)N自然丰度方法估算肥料和土壤氮对NH_(3)挥发的贡献。【结果】基肥施用后3~6天内,NH_(3)挥发速率迅速增加并达到高峰,之后逐渐降低,直至第33天恢复到施肥前水平。与MU和U处理相比,M处理的净NH_(3)挥发累积量分别显著降低了60.8%和63.1%(P<0.05),MU较U处理的NH_(3)减排效果不显著(4.62%),相应的NH_(3)挥发系数分别为1.37%(U)、1.29%(MU)及0.51%(M)。施肥处理中,δ^(15)N-NH_(3)值随NH_(3)挥发的进行而迅速降低,然后逐渐增加至施肥前水平,M处理的δ^(15)N-NH_(3)均值高于MU和U处理。^(15)N同位素混合方程计算显示,在番茄生产中肥料对NH_(3)挥发的贡献比例为:M处理中鸡粪贡献30.5%,U处理中尿素贡献53.1%,MU处理中鸡粪和尿素分别贡献28.6%和56.6%。【结论】等量施氮条件下,单施鸡粪产生的NH_(3)挥发量远低于尿素,鸡粪和尿素等量氮配施对NH_(3)挥发的减排效果不显著。根据同位素分馏效应计算结果,单施鸡粪、尿素对土壤NH_(3)挥发源的贡献比例分别为30.5%、53.1%,鸡粪和尿素配施时二者对土壤NH_(3)挥发源的贡献比例分别为28.6%、56.6%,贡献比例与单施差异不大。因此,控制化肥氮施用量是减少NH_(3)挥发的关键。