Fatigue Crack Initiation Potential from Defects in terms of Local Stress Analysis

The competition of surface and subsurface crack initiation induced failure is critical to understand very high cycle fatigue（VHCF） behavior, which necessitates the elucidation of the underlying mechanisms for the transition of crack initiation from surface to interior defects. Crack initiation potential in materials containing defects is investigated numerically by focusing on defect types, size, shape, location, and residual stress influences. Results show that the crack initiation potency is higher in case of serious property mismatching between matrix and defects, and higher strength materials are more sensitive to soft inclusions（elastic modulus lower than the matrix）. The stress localization around inclusions are correlated to interior crack initiation mechanisms in the VHCF regime such as inclusion-matrix debonding at soft inclusions and inclusion-cracking for hard inclusions（elastic modulus higher than the matrix）. It is easier to emanate cracks from the subsurface pores with the depth 0.7 times as large as their diameter. There exists an inclusion size independent region for crack incubation, outside which crack initiation will transfer from the subsurface soft inclusion to the interior larger one. As for elliptical inclusions, reducing the short-axis length can decrease the crack nucleation potential and promote the interior crack formation, whereas the long-axis length controls the site of peak stress concentration. The compressive residual stress at surface is helpful to shift crack initiation from surface to interior inclusions. Some relaxation of residual stress can not change the inherent crack initiation from interior inclusions in the VHCF regime. The work reveals the crack initiation potential and the transition among various defects under the influences of both intrinsic and extrinsic factors in the VHCF regime, and is helpful to understand the failure mechanism of materials containing defects under long-term cyclic loadings.

Extended Kantorovich method for local stresses in composite laminates upon polynomial stress functions

The extended Kantorovich method is employed to study the local stress concentrations at the vicinity of free edges in symmetrically layered composite laminates subjected to uniaxial tensile load upon polynomial stress functions. The stress fields are initially assumed by means of the Lekhnitskii stress functions under the plane strain state. Applying the principle of complementary virtual work,the coupled ordinary differential equations are obtained in which the solutions can be obtained by solving a generalized eigenvalue problem. Then an iterative procedure is established to achieve convergent stress distributions. It should be noted that the stress function based extended Kantorovich method can satisfy both the traction-free and free edge stress boundary conditions during the iterative processes. The stress components near the free edges and in the interior regions are calculated and compared with those obtained results by finite element method（FEM）. The convergent stresses have good agreements with those results obtained by three dimensional（3D） FEM. For generality, various layup configurations are considered for the numerical analysis. The results show that the proposed polynomial stress function based extended Kantorovich method is accurate and efficient in predicting the local stresses in composite laminates and computationally much more efficient than the 3D FEM.

Local Stress Field in Wafer Thinning Simulations with Phase Space Averaging

From an ingot to a wafer then to a die,wafer thinning plays an important role in the semiconductor industry.To reveal the material removal mechanism of semiconductor at nanoscale,molecular dynamics has been widely used to investigate the grinding process.However,most simulation analyses were conducted with a single phase space trajectory,which is stochastic and subjective.In this paper,the stress field in wafer thinning simulations of 4H-SiC was obtained from 50 trajectories with spatial averaging and phase space averaging.The spatial averaging was conducted on a uniform spatial grid for each trajectory.A variable named mask was assigned to the spatial point to reconstruct the shape of the substrate.Different spatial averaging parameters were applied and compared.The result shows that the summation of Voronoi volumes of the atoms in the averaging domain is more appropriate for spatial averaging.The phase space averaging was conducted with multiple trajectories after spatial averaging.The stress field converges with increasing the number of trajectories.The maximum and average relative difference(absolute value)of Mises stress was used as the convergence criterion.The obtained hydrostatic stress in the compression zone is close to the phase transition pressure of 4H-SiC from first principle calculations.

Conditional Generative Adversarial Network Enabled Localized Stress Recovery of Periodic Composites

Structural damage in heterogeneousmaterials typically originates frommicrostructures where stress concentration occurs.Therefore,evaluating the magnitude and location of localized stress distributions within microstructures under external loading is crucial.Repeating unit cells(RUCs)are commonly used to represent microstructural details and homogenize the effective response of composites.This work develops a machine learning-based micromechanics tool to accurately predict the stress distributions of extracted RUCs.The locally exact homogenization theory efficiently generates the microstructural stresses of RUCs with a wide range of parameters,including volume fraction,fiber/matrix property ratio,fiber shapes,and loading direction.Subsequently,the conditional generative adversarial network(cGAN)is employed and constructed as a surrogate model to establish the statistical correlation between these parameters and the corresponding localized stresses.The stresses predicted by cGAN are validated against the remaining true data not used for training,showing good agreement.This work demonstrates that the cGAN-based micromechanics tool effectively captures the local responses of composite RUCs.It can be used for predicting potential crack initiations starting from microstructures and evaluating the effective behavior of periodic composites.

Coupling damage and reliability model of low-cycle fatigue and high energy impact based on the local stress–strain approach

Fatigue induced products generally bear fatigue loads accompanied by impact processes,which reduces their reliable life rapidly. This paper introduces a reliability assessment model based on a local stress–strain approach considering both low-cycle fatigue and high energy impact loads.Two coupling relationships between fatigue and impact are given with effects of an impact process on fatigue damage and effects of fatigue damage on impact performance. The analysis of the former modifies the fatigue parameters and the Manson–Coffin equation for fatigue life based on material theories. On the other hand, the latter proposes the coupling variables and the difference of fracture toughness caused by accumulative fatigue damage. To form an overall reliability model including both fatigue failure and impact failure, a competing risk model is developed. A case study of an actuator cylinder is given to validate this method.

WAVE LOCALIZATION IN RANDOMLY DISORDERED PERIODIC PIEZOELECTRIC RODS WITH INITIAL STRESS

The elastic wave localization in disordered periodic piezoelectric rods with initial stress is studied using the transfer matrix and Lyapunov exponent method. The electric field is approximated as quasi-static. The effects of the initial stress on the band gap characteristics are investigated. The numerical calculations of localization factors and localization lengths are performed. It can be observed from the results that the band structures can be tuned by exerting the suitable initial stress. For different values of the piezoelectric rod length and the elastic constant, the band structures and the localization phenomena are very different. Larger disorder degree can lead to more obvious localization phenomenon.

Effect of local wound infiltration with ropivacaine on postoperative pain relief and stress response reduction after open hepatectomy

AIM To prospectively evaluate the effect of local wound infiltration with ropivacaine on postoperative pain relief and stress response reduction after open hepatectomy.METHODS A total of 56 patients undergoing open hepatectomy were randomly divided into two groups:a ropivacaine group(wound infiltration with ropivacaine solution)and a control group(infiltration with isotonic saline solution).A visual analog scale(VAS)at rest and on movement was used to measure postoperative pain for the first 48 h after surgery.Mean arterial pressure(MAP),heart rate(HR),time to bowel recovery,length of hospitalization after surgery,cumulative sufentanil consumption,and incidence of nausea and vomiting were compared between the two groups.Surgical stress hormones(epinephrine,norepinephrine,and cortisol)were detected using enzyme-linked immunosorbent assay,and the results were compared. RESULTS VAS scores both at rest and on movement at 24 h and48 h were similar between the two groups.Significantly lower VAS scores were detected at 0,6,and 12 h in the ropivacaine group compared with the control group(P<0.05 for all).MAP was significantly lower at 6,12,and 24 h(P<0.05 for all);HR was significantly lower at 0,6,12,and 24 h(P<0.05 for all);time to bowel recovery and length of hospitalization after surgery(P<0.05 for both)were significantly shortened;and cumulative sufentanil consumption was significantly lower at 6,12,24,and 36 h(P<0.05 for all)in the ropivacaine group than in the control group,although the incidence of nausea and vomiting showed no significant difference between the two groups.The levels of epinephrine,norepinephrine,and cortisol were significantly lower in the ropivacaine group than in the control group at 24 and 48 h(P<0.01 for all). CONCLUSION Local wound infiltration with ropivacaine after open hepatectomy can improve postoperative pain relief,reduce surgical stress response,and accelerate postoperative recovery.

锦屏一级水电站库区中小地震震源机制解与局部应力场特征

利用四川及邻区数字地震台网2013—2018年的波形资料,基于CAP和HASH方法反演得到锦屏一级水电站(以下简称锦屏水库)库区及周边M_(L)≥2.5地震的震源机制解,根据DRSSI方法计算得到库区局部应力场信息,结合该区域的地质资料,从震源机制参数和局部应力场变化等方面讨论了水库加卸载对该区域地震活动的影响.取得的主要认识如下:(1)库区地震活动类型以走滑型为主,不同加卸载阶段震源机制类型存在一定差异,库区蓄水前期震源机制类型呈现多样性,蓄水后期与区域背景场趋于一致;(2)库区应力场最大主应力方向以NNW-SSE向为主,分时段结果显示,蓄水后期局部应力场最大主应力方向由NNW向逐渐发生偏转至NW向;(3)库区周边的地质构造和岩性条件有利于库水的渗透,蓄水后重力载荷和流体渗透的共同作用导致岩体断层面库仑应力的变化,从而呈现出库区蓄水前后中小地震活跃程度的显著差异特征.

Localized corrosion of LY12CZ under stress in chloride media

Electrochemical methods were applied to investigate the corrosion behaviour of LY12CZ under applied stress in 3% sodium chloride aqueous solution. The experimental results indicate that LY12CZ shows two breakdown potentials on its polarization curve: one is related to the dissolution of the intermetallic particles and the other is related to the cracking of oxidation film and the dissolution of the matrix. When the stress is applied, it varies both breakdown potentials and makes the intermetallic particles and matrix dissolute at lower potentials. The relationship between the variation of the two breakdown potentials and applied stress was summarized. At the same time the influence of stress on the pitting and intergranular corrosion sensitivity of LY12CZ was also investigated. From the results it can be concluded that the stress can significantly affect the localized corrosion behaviour of LY12CZ in 3% NaCl solution.

小麦倒春寒响应基因TaJAZ6的克隆、表达模式及亚细胞定位分析

JAZ蛋白在植物生长发育和胁迫信号通路中具有关键作用。为探究JAZ蛋白在小麦倒春寒中的调控机制,从小麦幼穗中克隆了TaJAZ6基因,并对其分子特征、表达特性与亚细胞定位进行分析。结果表明,该基因CDS序列全长为549 bp,编码178个氨基酸,预测编码蛋白质的分子质量为18.376 ku,理论等电点为9.37,不稳定系数为62.44,属于不稳定蛋白。该基因编码蛋白质具有1个TIFY结构域和1个CCT_2结构域。系统进化树分析发现,该蛋白质与野生二粒小麦和乌拉尔图小麦TIFY 11b蛋白亲缘关系最近。TaJAZ6基因启动子区除含有CAAT-box、TATA-box等基础作用元件外,还含有激素类响应元件、光响应元件、低温响应元件、防御和应激反应元件等。实时荧光定量PCR分析发现,TaJAZ6基因在根、茎、叶和幼穗中均有表达,根系中表达量最高。TaJAZ6基因还受低温和茉莉酸甲酯(MeJA)的诱导表达,低温胁迫下,TaJAZ6在矮抗58(耐倒春寒)和郑麦366(倒春寒敏感)根、茎和叶中表达趋势相同,均显著升高;喷施300,350μmol/L的MeJA之后再低温处理TaJAZ6在2个小麦品种中表达量均显著下降。TaJAZ6在低温胁迫后的幼穗中表达量出现相反的趋势,在矮抗58幼穗中表达量显著下降,在郑麦366幼穗中则显著上升,推测该基因可能负调控了小麦倒春寒胁迫防御反应。通过喷施MeJA显著降低了低温胁迫下2个小麦品种幼穗中TaJAZ6基因的相对表达量,同时提高了小麦的结实粒数。亚细胞定位试验显示,TaJAZ6蛋白定位于细胞核中。以上研究结果表明,TaJAZ6可能在小麦响应倒春寒胁迫过程中发挥重要作用。

ANALYSIS OF THE LOCALIZATION OF DAMAGE AND THE COMPLETE STRESS-STRAIN RELATION FOR MESOSCOPIC HETEROGENEOUS BRITTLE ROCK SUBJECTED TO COMPRESSIVE LOADS

A micromechanics-based model is established. The model takes the interaction among sliding cracks into account, and it is able to quantify the effect of various parameters on the localization condition of damage and deformation for brittle rock subjected to compressive loads. The closed-form explicit expression for the complete stress-strain relation of rock containing microcracks subjected to compressive loads was obtained. It is showed that the complete stress-strain relation includes linear elasticity,nonlinear hardening,rapid stress drop and strain softening.The behavior of rapid stress drop and strain softening is due to localization of deformation and damage. Theoretical predictions have shown to be consistent with the experimental results.

NUMERICAL ANALYSIS OF RESIDUAL STRESSES IN TITANIUM ALLOY DURING ELECTRON BEAM LOCAL POST-WELD HEAT TREATMENT

The distributions of temperature and residual stresses in thin plates of BT20titanium alloy are numerically analyzed by three-dimensional finite element software duringelectron beam welding and electron beam local post-weld heat treatment (EBLPWHT). Combined withnumerical calculating results, the effects of different EBLPWHT mode and parameters, including heattreating position, heating width and heating time, on the distribution of welding residual stressesare analyzed. The results show that, the residual tensile stresses in weld center can be largelydecreased when the weld is heat treated at back preface of the plate. The numerical results alsoindicated that the magnitude of the residual longitudinal stresses of the weld and the zone vicinityof the weld is decreased, and the range of the residual longitudinal stresses is increased alongwith the increase of heating width and heating time.

ANALYSIS OF THE LOCALIZATION OF DAMAGE AND THE COMPLETE (STRESS-STRAIN) RELATION FOR MESOSCOPIC HETEROGENEOUS ROCK UNDER UNIAXIAL TENSILE LOADING

The mechanical behavior of rock under uniaxial tensile loading is different from that of rock under compressive loads. A micromechanics-based model was proposed for mesoscopic heterogeneous brittle rock undergoing irreversible changes of their microscopic structures due to microcrack growth. The complete stress-strain relation including linear elasticity, nonlinear hardening,rapid stress drop and strain softening was obtained. The influence of all microcracks with different sizes and orientations were introduced into the constitutive relation by using the probability density function describing the distribution of orientations and the probability density function describing the distribution of sizes. The influence of Weibull distribution describing the distribution of orientations and Rayleigh function describing the distribution of sizes on the constitutive relation were researched. Theoretical predictions have shown to be consistent with the experimental results.

玉米逆境胁迫响应基因ZmbZIP84的克隆与功能验证

碱性亮氨酸拉链(Basic leucine zipper,bZIP)转录因子是真核生物中分布最广泛、结构极其保守的家族之一,在植物生长进程中发挥重要作用。为验证bZIP转录因子在逆境胁迫中发挥的作用,本研究通过分析转录组数据,筛选到27个参与干旱-复水胁迫的bZIP基因,计算相关性系数、构建共表达网络图发现ZmbZIP84(Zm00001d053988)是核心节点基因;该基因位于玉米第4号染色体,具有高度保守的bZIP结构域;分析理化性质,发现该基因是亲水性蛋白且属于不稳定蛋白;构建系统发育树,发现该基因与柳枝稷和高粱的亲缘关系最近;实时荧光定量PCR(qRT-PCR)结果显示,ZmbZIP84在玉米各组织中均有表达,成熟根中的表达量最高;设置20%聚乙二醇(PEG)-6000、42℃高温、200 mmol·L^(-1)NaCl以及缺乏铵态氮等模拟试验,发现该基因在高温、干旱、氮处理下表达量显著上调,而在NaCl处理下表达量下调,说明ZmbZIP84基因积极参与并响应非生物胁迫;利用CRISPR/Cas9技术获得ZmbZIP84基因的拟南芥同源基因缺失型纯合突变体,发现在高温、干旱胁迫处理下突变体植株生长受到严重抑制、叶片萎蔫、甚至干死,而野生型植株影响较小,说明在干旱、高温胁迫处理下,ZmbZIP84基因敲除后抗旱、耐高温能力下降;亚细胞定位发现该基因编码的蛋白位于细胞核。本研究结果可为后续研究ZmbZIP84基因的功能及下游靶基因的调控机制奠定基础,为培育抗逆性玉米新品种提供参考。

四季秋海棠BsMYB62的抗旱性功能研究

【目的】以前期从四季秋海棠叶片中克隆得到的R2R3型MYB转录因子BsMYB62为研究对象,分析其在干旱胁迫下的功能。【方法】对四季秋海棠MYB62蛋白进行亚细胞定位,并通过实时荧光定量PCR方法明确BsMYB62基因在四季秋海棠根、茎、叶、雄花和雌花5个组织部位中的表达情况;构建BsMYB62基因的过表达载体转化到拟南芥,观察过表达转基因株系与野生型植株在萌发期和幼苗期遭受干旱胁迫时的生长表型、种子萌发和根长情况,测定各株系在幼苗期干旱胁迫处理时的叶绿素荧光参数PSⅡ最大光化学效率(F_(v)/F_(m)),叶绿素、丙二醛(MDA)、脯氨酸(Pro)含量,抗氧化酶(SOD、POD、CAT)活性以及转基因株系中BsMYB62基因的相对表达量变化。【结果】BsMYB62定位于四季秋海棠的细胞核,其在根、茎、叶和雌雄花中均有表达,其中以根和茎中的表达水平较高。在MS培养基中,野生型拟南芥和3个BsMYB62过表达转基因株系(OE1、OE2和OE3)的发芽率和长势均无显著差异,而在200 mmol/L甘露醇(模拟干旱胁迫)培养基中,OE1、OE2和OE3在胁迫处理后前2 d的发芽率及主根长均显著高于野生型拟南芥,幼苗长势也明显优于野生型。置于培养土中干旱胁迫1 d时,OE1、OE2和OE3的BsMYB62即被显著诱导;干旱胁迫13 d时,OE1、OE2和OE3的F_(v)/F_(m)、叶绿素含量、Pro含量以及SOD、POD和CAT活性均显著高于野生型拟南芥,而MDA含量则显著低于野生型拟南芥。【结论】BsMYB62基因通过提高转基因拟南芥的光合潜能和抗氧化能力,显著增强其对干旱胁迫的抗性。

Exploring the Interplay between Local Chain Structure and Stress Distribution in Polymer Networks

The mechanical behavior of polymer networks is intrinsically correlated with the local chain topology and chain connectivity.In this study,we delve into this relationship through the lens of coarse-grained molecular dynamics(CG-MD)simulations.Our aim is to illuminate the intricate interplay between local topology and stress distribution within polymer monomers,cross-linkers,and various components with distinct cross-link connections,thereby elucidating their collective impact on the mechanical properties of polymer networks.We mainly focus on how specific local structures contribute to the overall mechanical response of the network.In particular,we employ local stress analysis to unravel the mechanics of these structures.Our findings reveal the diverse responses of individual components,such as junctions,strands,cross-linkers between junctions,and dangling chain ends,when subjected to stretching.Notably,we observe that these components exhibit varying degrees of deformation tolerance,underscoring the significance of their roles in determining the mechanical characteristics of the network.Our investigations highlight junctions as primary contributors to stress accumulation,and particles with higher local stress showing a stronger correlation between stress and Voronoi volume.Moreover,our results indicate that both strands and cross-linkers between junctions exhibit heightened stress levels as strand lengths decrease.This study enhances our understanding of the multifaceted factors governing the mechanical attributes of cross-linked polymer systems at the microstructural level.

发动机摇臂断裂原因分析

材料为QT600-3球墨铸铁的摇臂在发动机试车过程中断裂。对断裂的摇臂进行了断口的宏观和微观检验及能谱分析、化学成分分析、硬度检测和金相检验。结果表明:摇臂中有疏松和大面积夹渣,破坏了基体的连续性,并产生局部应力集中,从而导致裂纹萌生和扩展及摇臂断裂。此外,组织的球化不良也在一定程度上促进了摇臂的脆性断裂。

蒺藜苜蓿MtMYB16基因克隆、表达及转录自激活分析

植物中MYB转录因子数量众多,功能多样,在植物生长发育、逆境响应等多方面发挥着重要作用。为研究MYB转录因子在蒺藜苜蓿中的功能,本研究采用PCR技术从蒺藜苜蓿中克隆MtMYB16基因,该基因开放阅读框1074 bp,共编码357个氨基酸。进化树分析结果显示,MtMYB16蛋白与白花草木樨中MYB蛋白同源性最高。亚细胞定位结果显示,MtMYB16蛋白定位在细胞核中。酵母自激活检测结果显示,MtMYB16蛋白具有自激活活性,自激活结构域位于C端。表达分析结果显示,MtMYB16在蒺藜苜蓿根、茎、叶、花、果实中均有表达,在根中表达水平最高;IAA、MeJA能够降低MtMYB16表达水平;盐胁迫和干旱胁迫下,MtMYB16表达量在1.0 h时迅速增加,说明MtMYB16可能具有响应盐及干旱胁迫的功能。

山药块茎膨大期DoCDPK1基因生物信息学及低温胁迫下的表达分析

钙依赖性蛋白激酶(CDPK)在植物的生长发育及逆境胁迫方面发挥着重要作用。以大和长芋和毕克齐山药为试验材料,克隆钙依赖性蛋白激酶基因DoCDPK1,并对其进行生物信息学分析,为DoCDPK1基因的功能研究奠定基础。采用生物信息学方法分析DoCDPK1基因结构,构建瞬时表达载体,对DoCDPK1蛋白进行亚细胞定位;采用qRT-PCR分析DoCDPK1基因在不同山药品种的不同发育阶段及低温胁迫处理下的表达模式。结果表明(:1)DoCDPK1基因序列长度为2023 bp,编码521个氨基酸。(2)DoCDPK1与几内亚薯蓣CDPK蛋白序列的一致性为97%,且DoCDPK1存在STKc_CAMK结构域。(3)瞬时表达分析表明,DoCDPK1蛋白定位于细胞核与细胞膜。(4)大和长芋山药中的CDPK活性更高,DoCDPK1可能参与调控山药块茎膨大后期的生长发育。(5)经4℃低温胁迫后,CDPK活性降低,DoCDPK1表达量上调,且表达水平在不同时间处理下存在差异。综上所述,DoCDPK1可能参与调控山药块茎膨大后期的生长发育及低温胁迫响应过程。

大跨连续梁拱组合体系桥拱脚结合段局部应力分析

大跨连续梁拱组合体系桥拱脚结合段的构造和受力复杂,需要对此处进行局部应力分析。结合工程实例,采用有限元法对拱脚结合段进行建模,提出了局部模型边界力的施加方法,并对其施加整体模型计算出的内力进行细部计算,分析局部应力状态。计算和分析结果表明,拱脚结合段的应力总体上满足设计规范要求,横隔板分别与顶板、底板和腹板相连接的倒角位置出现应力集中现象,建议对倒角设置平顺过渡段;在拱肋插入处的顶板和支座位置处的底板存在应力集中现象,建议对这些位置加强布置构造钢筋。