分级循环加卸载下砂岩损伤力学特性研究

通过选取陕西省略阳市某滑坡表层的中风化砂岩进行静态单轴压缩试验与三轴循环加卸载试验,研究低围压循环加卸载条件下岩石的损伤力学特性,得到力学参数、损伤参数、滞回环面积等随循环过程的演化规律及循环荷载作用下砂岩的变形破坏机制。结果表明：循环加卸载试验过程中,围压增强砂岩抵抗变形破坏能力,随着围压增大,动弹性模量明显增大而动泊松比逐渐降低,砂岩试样内凹现象逐渐“模糊”;滞回环面积受围压与轴向载荷影响明显,与围压变化呈负相关,与轴向载荷变化呈正相关,轴向载荷增大时,不可逆应变逐渐累积,砂岩损伤加剧;砂岩内部原始裂隙在初始较低循环荷载作用下压密,后过渡到弹性变形与裂纹稳定扩展阶段,随着试验进行,裂纹加速演化不稳定扩张,岩样逐渐变形失稳破坏。     

混凝土循环加卸载动态损伤特性研究

利用大型多功能动静力三轴仪对混凝土试件进行了5种应变速率下的动态循环加卸载压缩试验。对混凝土的物理力学参数的变化规律进行了统计分析。结果表明：峰值应力和弹性模量随加载速率的提高而增大,但峰值应变随加载速率的变化表现出较大的离散性。在此基础上,进一步研究了混凝土在不同加载速率下的刚度退化规律。最后,选用基于Weibull统计理论的分段式动态损伤本构模型对试验数据进行拟合。经验证,此模型能够较好的模拟混凝土材料的本构特性。     

大质量砝码量值传递智能化自动加卸载砝码的实现

为了提高大质量砝码检定的准确性及检定效率,本装置通过对等臂电磁天平改造、加卸载砝码及传运机构、中央智能控制软件的设计,实现了大质量砝码检定从加卸标准砝码、加卸被检砝码、数据处理、出具检定记录等全过程的智能化操作.     

工程爆破中卸载波与加载波互相作用的初步讨论

初步讨论了工程爆破中卸载波和加载波互相作用的基本过程、特征和表现形式。卸载波在一些爆、破条件下有可能加强或削弱加载波。为了提高爆破的精确度,应对卸载波的作用予以重视,在可能的条件下做进一步的研究。     

2D-SiC/SiC复合材料拉伸加卸载行为

为了研究国产2D-SiC/SiC复合材料的拉伸损伤行为以及低周循环载荷作用下的力学性能,通过试验和建立加卸载细观力学模型,对其拉伸加卸载行为进行了探讨。建立了单向连续纤维增强陶瓷基复合材料加卸载细观力学模型,得到了初始加载、卸载和重新加载时的应力-应变关系;利用断裂统计方法得到了基体裂纹数随应力变化的关系和复合材料失效判断条件。经过应力转化,将该模型应用于国产二维编织SiC/SiC复合材料。对单向加载试件,采用正交试验方法和最小二乘法得到基体Weibull模量和界面剪切阻力,通过控制材料失效强度与试验结果一致,得到纤维Weibull模量。由上述参数确定的2D-SiC/SiC复合材料拉伸循环加卸载应力-应变曲线与实测曲线吻合很好。通过Matlab编程得到2D-SiC/SiC复合材料单向加载时基体开裂过程图。结果表明,2D-SiC/SiC复合材料失效时,基体裂纹分布相对比较均匀;基体裂纹数随应力单调增加,未出现持平段,表明材料失效时,基体裂纹还没有达到饱和。     

循环冲击下风化花岗岩渗透性演化规律

针对低渗透离子型稀土矿体回采效率低的缺点,提出利用爆炸应力波改变岩体内部孔隙结构进而提高渗透性的设想,并通过试验进行验证。选取赣南某离子型稀土矿弱风化层花岗岩为研究对象,利用改进的SHPB装置进行等速循环冲击,结合GDS-VIS三轴渗流试验,分析风化花岗岩循环冲击后的破坏模式,并研究有效孔隙度对循环动荷载前后岩石渗透性变化规律的影响。研究结果表明:随着冲击次数的增加,风化花岗岩抗冲能力逐渐减弱,其破碎程度与冲击速度呈正相关;冲击速度为4 m/s和5 m/s的等速循环冲击会使风化花岗岩渗透性呈现先减后增的趋势,而冲击速度为6 m/s的等速循环冲击会使风化花岗岩渗透性持续增大至岩样损坏;岩体渗透性受其有效孔隙度的影响,随有效孔隙度的增大整体呈现上升趋势,同时风化花岗岩初始有效孔隙度越大,冲击后其内部孔隙结构更易发生改变,后续循环冲击荷载下增渗效果更明显。     

循环冲击下风化花岗岩渗透性演化规律

针对低渗透离子型稀土矿体回采效率低的缺点,提出利用爆炸应力波改变岩体内部孔隙结构进而提高渗透性的设想,并通过试验进行验证。选取赣南某离子型稀土矿弱风化层花岗岩为研究对象,利用改进的SHPB装置进行等速循环冲击,结合GDS-VIS三轴渗流试验,分析风化花岗岩循环冲击后的破坏模式,并研究有效孔隙度对循环动荷载前后岩石渗透性变化规律的影响。研究结果表明:随着冲击次数的增加,风化花岗岩抗冲能力逐渐减弱,其破碎程度与冲击速度呈正相关;冲击速度为4 m/s和5 m/s的等速循环冲击会使风化花岗岩渗透性呈现先减后增的趋势,而冲击速度为6 m/s的等速循环冲击会使风化花岗岩渗透性持续增大至岩样损坏;岩体渗透性受其有效孔隙度的影响,随有效孔隙度的增大整体呈现上升趋势,同时风化花岗岩初始有效孔隙度越大,冲击后其内部孔隙结构更易发生改变,后续循环冲击荷载下增渗效果更明显。     

不同应力路径下辉绿岩能量演化与破坏机制研究EI北大核心CSCD

以灵宝矿区辉绿岩为研究对象,开展了单轴及三轴循环加卸载试验和恒轴压卸围压试验,分析了应力-应变曲线及破坏形态,研究了辉绿岩在不同应力路径下的能量演化过程与破坏机制。研究表明:在三轴循环加卸载变形破坏过程中,随着循环次数的增加,滞回环的面积逐渐增大,岩样耗散能与弹性能均增大,耗散能的增长速率逐渐变大,弹性能的增长速率逐渐变小,且围压越大耗能比越大,岩样内部的裂隙扩展和汇合现象显著增加;在恒轴压卸围压变形破坏过程中,围压对辉绿岩的抗压强度和横向变形影响较大;在相同初始围压下,相比较循环加卸载应力路径,卸围压应力路径下试件破坏时弹性能密度更大。     

循环载荷下再生混凝土损伤声发射特性

在地震多发地,混凝土结构常常承受循环荷载作用,为了研究循环加卸载作用下再生混凝土的受压损伤特性,对不同再生粗骨料取代率的混凝土试件进行单轴抗压试验.基于声发射技术,对受压损伤全过程进行了动态分析.研究表明:循环荷载作用下,再生混凝土声发射振铃计数存在Kaiser效应,该效应反映了材料损伤程度,同时揭示了不同掺量再生混凝土的损伤机制;随着应力水平的增加,Felicity比逐渐减小,以Felicity比小于1作为混凝土损伤严重的标志;将每次循环声发射振铃图进行分形计算,循环荷载作用下再生混凝土声发射振铃分形维数随着循环次数的增加而增加,证明了声发射应用于损伤预测的可行性;应用响应比理论对声发射累计事件的研究得出:再生混凝土加卸载声发射数响应比Y随着试件承受的应力水平的增高而减小,且将Y减小至1左右时作为再生混凝土破坏前兆特征,为工程损伤预测及安全评估提供参考.     

缝合式三维编织C/SiC复合材料拉伸加卸载力学行为

本文通过开展缝合式三维编织C/SiC复合材料的准静态单轴拉伸及循环加卸载试验,研究加卸载行为对复合材料的损伤及材料内部能量耗散的影响。通过对材料的断口分析,探究加卸载对材料破坏强度的影响规律。结果表明,加卸载行为会消耗材料内部的能量,对纤维束与基体之间的界面造成损伤,进而降低材料的承载能力;材料滞回曲线的面积随着卸载点应力的增大而增大;材料的整体失效属于脆性破坏,复合材料断口表现出明显的分层现象,且单轴拉伸时断口相对于循环加卸载更整齐。      

高周疲劳载荷下6061-T6铝合金的温度演化

为了研究金属材料在疲劳载荷下的温度变化,采用红外热像系统对高周疲劳载荷下6061-T6铝合金的温度演化进行分析,用热像图对疲劳裂纹尖端的塑性区进行测量.结果显示,疲劳加载作用下,循环次数达到107次时6061-T6铝合金试样表面温度的变化分为四个阶段:初始温升阶段、温度缓降阶段、温度二次缓慢上升阶段和温度快速上升阶段.结合热弹性理论、铝合金塑性变形的微观机制分析并预测疲劳载荷下温度的演化和宏观裂纹扩展时裂纹尖端塑性区域大小.宏观裂纹开始扩展时,裂纹尖端的塑性区域可达3.6 mm2,红外热像仪测得结果为3.46 mm2,测试结果与理论结果吻合.     

AZ31B镁合金压-压循环载荷下变形行为及变形机制演化EI北大核心CSCD

为探讨AZ31B挤压态镁合金棒材沿径向取样的循环变形特征,开展了0.75%,1.0%,2.0%和4.0%应变幅下应变控制的非对称压-压循环变形实验。结果表明:在小应变幅(0.75%,1.0%)下,循环变形的滞回曲线表现出较好的对称性;在大应变幅(2.0%,4.0%)下,滞回曲线对称性差,且在滞回曲线上出现拐点;随着循环周次增加,塑性应变幅呈现下降趋势,材料均表现出循环硬化行为,在小应变幅下循环拉伸阶段对材料硬化率远大于压缩阶段的硬化率,而在大应变幅下这种区别并不明显。分析表明,沿径向取向的〈1120〉丝织构镁合金,小应变幅下位错滑移在整个寿命周期内作用更大;大应变幅下,随着塑性变形的增加,循环过程中变形机制发生演化,较低临界剪切应力(critical resolved shear stress,CRSS)的基面位错和拉伸孪生不能完全满足变形要求,较高CRSS滑移系启动及残余孪晶使得滞回曲线出现拐点;循环变形过程中不完全的孪生-去孪生过程使基体中存在大量残余孪晶,影响了循环变形过程的硬化率,同时降低了疲劳寿命。     

High-temperature creep and long-term strength of structural elements under cyclic loading

We present a method for solving problems of high-temperature cyclic creep and damage accumulation in structural elements. The asymptotic expansion and averaging techniques both over the period of forced vibrations of a body and that of slowly varying loads are used for the set of equations describing the creep and damage processes in thin-walled structural elements. __________ Translated from Problemy Prochnosti, No. 5, pp. 45–53, September–October, 2008.     

Life estimation for high-strength materials under cyclic loading in the multiaxial stress state

The life of high-strength materials under cyclic loading in the multiaxial stress state is experimentally estimated using the deformation-kinetic criterion. Translated from Problemy Prochnosti, No. 2, pp. 139–143, March–April, 2009.     

基于Flexsim的自动化立体仓库出入库仿真与优化

对某制造企业的自动化立体仓库出入库进行了仿真和优化。首先在对该仓库的实际作业进行测录的情况下,收集了各类仿真对象的数据并记录了该自动化立体仓库的出入库及存取作业程序;然后使用Flexsim软件进入仿真,并对仿真运行数据进行分析,写出相应的改善方案;最后再使用Flexsim仿真软件对优化后的仓库进行仿真建模,与优化前的仿真模型输出的数据进行对比分析。结果表明,各个操作台的利用率都比优化前的提高了10%~15%,巷道堆垛机的利用率提高了3%,高层货架货位库存量、货位利用率得到明显提高,各个缓存区的堆积现象明显减少,从而验证了优化方案的可行性。     

High-temperature behaviour of IN 738 LC under isothermal and thermo-mechanical cyclic loading

The temperature dependence of the cyclic behavior of IN 738 LC was studied. Cyclic iso- and non-isothermal tests were performed with proportional and non-proportional tension/torsion strain paths. It was shown that maximum and minimum stress values measured in isothermal strain controlled tests correspond quite well with results of non-isothermal tests. Thermal-mechanical constitutive equations based on the viscoplastic Chaboche model were used to describe the non-isothermal stress-strain behavior.     

A study of stress concentration zones under cyclic loading by thermal imaging method

A method is put forward for detection of stress concentration zones in structures under repeated cyclic loading. It is proposed that prior to cyclic loading the temperature characteristics of a structure should be stabilized, and then in the course of loading the temperature fields in the structure should be measured by instruments with subsequent analysis and processing of the thermograms. Translated from Problemy Prochnosti, No. 3, pp. 134–142, May–June, 2009.     

Experimental and theoretical investigation on mechanical behaviors of TB991 weld sealant under cyclic loading

The mechanical behaviors of TB991 weld sealant under cyclic loading conditions were experimentally investigated. The evolution of relaxation stress, cyclic softening, and dissipated energy was evaluated with the effect of strain amplitude and mean strain. The experimental results showed that the stress–strain response curves of the first loading-unloading and cyclic loading-unloading were significantly different. The phenomenon of stress relaxation and cyclic softening occurred under cyclic strain loading conditions. Furthermore, the relaxation stress and dissipated energy decreased rapidly during the initial cyclic loading and then steadily decreased with the increase of cycle number, while the cyclic softening increased rapidly at first and then steadily. Besides, a viscoelastic constitutive model was proposed which can describe the different shapes of stress–strain curve between the initial loading-unloading and the cyclic loading-unloading and also considers the cyclic stress relaxation and cyclic softening of the materials under cyclic loading condition. Comparisons between the numerical results and the experimental data demonstrated that the proposed model can better describe the mechanical behavior of TB991 weld sealant under cyclic loading conditions.     

Notch fatigue life prediction considering nonproportionality of local loading path under multiaxial cyclic loading

An innovative numerical methodology is presented for fatigue lifetime estimation of notched bodies experiencing multiaxial cyclic loadings. In the presented methodology, an evaluation approach of the local nonproportionality factor F for notched specimens, which defines F as the ratio of the pseudoshear strain range at 45° to the maximum shear plane and the maximum shear strain range, is proposed and discussed deeply. The proposed evaluation method is incorporated into the material cyclic stress‐strain equation for purpose of describing the nonproportional hardening behavior for some material. The comparison between multiaxial elastic‐plastic finite element analysis (FEA) and experimentally measured strains for S460N steel notched specimens shows that the proposed nonproportionality factor estimation method is effective. Subsequently, the notch stresses and strains calculated utilizing multiaxial elastic‐plastic FEA are used as input data to the critical plane‐based fatigue life prediction methodology. The prediction results are satisfactory for the 7050‐T7451 aluminum alloy and GH4169 superalloy notched specimens under multiaxial cyclic loading.