Effect of NaCl Concentration on the Cumulative Strain and Pore Distribution of Clay under Cyclic Loading

Clay,as the most common soil used for foundationfill,is widely used in various infrastructure projects.The phy-sical and mechanical properties of clay are influenced by the pore solution environment.This study uses a GDS static/dynamic triaxial apparatus and nuclear magnetic resonance experiments to investigate the effects of cyclic loading on clay foundations.Moreover,the development of cumulative strain in clay is analyzed,and afitting model for cumulative plastic strain is introduced by considering factors such as NaCl solution concentration,con-solidation stress ratio,and cycle number.In particular,the effects of the NaCl solution concentration and con-solidation stress ratio on the pore distribution of the test samples before and after cyclic loading are examined,and the relationship between microscopic pore size and macroscopic cumulative strain is obtained accordingly.Our results show that as the consolidation stress ratio grows,an increasing number of large pores in the soil samples are transformed into small pores.As the NaCl solution concentration becomes higher,the number of small pores gradually decreases,while the number of large pores remains unchanged.Cyclic loading causes the disappearance of the large pores in the samples,and the average pore size before cyclic loading is posi-tively correlated with the axial cumulative strain after cyclic loading.The cumulative strain produced by the soil under cyclic loading is inversely proportional to the NaCl solution concentration and consolidation stress ratio.

Effect of Strain Ratio on Fatigue Model of Ultra-fine Grained Pure Titanium

The ultra-fine grained(UFG)pure titanium was prepared by equal channel angular pressing(ECAP)and rotary swaging(RS).The strain controlled low cycle fatigue(LCF)test was carried out at room temperature.The fatigue life prediction model and mean stress relaxation model under asymmetrical stress load were discussed.The results show that the strain ratio has a significant effect on the low cycle fatigue performance of the UFG pure titanium,and the traditional Manson-coffin model can not accurately predict the fatigue life under asymmetric stress load.Therefore,the SWT mean stress correction model and three-parameter power curve model are proposed,and the test results are verified.The final research shows that the threeparameter power surface model has better representation.By studying the mean stress relaxation phenomenon under the condition of R≠-1,it is revealed that the stress ratio and the strain amplitude are the factors that significantly afiect the mean stress relaxation rate,and the mean stress relaxation model with the two variables is calculated to describe the mean stress relaxation phenomenon of the UFG pure titanium under different strain ratios.The fracture morphology of the samples was observed by SEM,and it was concluded that the final fracture zone of the fatigue fracture of the UFG pure titanium was a mixture of ductile fracture and quasi cleavage fracture.The toughness of the material increases with the increase of strain ratio at the same strain amplitude.

Specimen aspect ratio and progressive field strain development of sandstone under uniaxial compression by three-dimensional digital image correlation

The complete stress-strain characteristics of sandstone specimens were investigated in a series of quasistatic monotonic uniaxial compression tests.Strain patterns development during pre-and post-peak behaviours in specimens with different aspect ratios was also examined.Peak stress,post-peak portion of stress-strain,brittleness,characteristics of progressive localisation and field strain patterns development were affected at different extents by specimen aspect ratio.Strain patterns of the rocks were obtained by applying three-dimensional(3D) digital image correlation(DIC) technique.Unlike conventional strain measurement using strain gauges attached to specimen,3D DIC allowed not only measuring large strains,but more importantly,mapping the development of field strain throughout the compression test,i.e.in pre-and post-peak regimes.Field strain development in the surface of rock specimen suggests that strain starts localising progressively and develops at a lower rate in pre-peak regime.However,in post-peak regime,strains increase at different rates as local deformations take place at different extents in the vicinity and outside the localised zone.The extent of localised strains together with the rate of strain localisation is associated with the increase in rate of strength degradation.Strain localisation and local inelastic unloading outside the localised zone both feature post-peak regime.

Effects of Strain Ratio on Fatigue Behavior of G20Mn5QT Cast Steel

Due to traffic and wave actions, cast steel joints are subjected to variable-amplitude fatigue loading, which may cause fatigue problems. The ratio of the minimum strain to the maximum strain(strain ratio)can be employed to analyze the influence of variable-amplitude fatigue both in the elastic and plastic ranges. To evaluate the effect of the strain ratio on G20Mn5 QT cast steel, the fatigue tests of smooth specimens were carried out at the strain ratio of 0.1. The cyclic deformation and the relationships between the strain amplitude, the stress amplitude, the Smith, Watson and Topper(SWT)parameter and fatigue life were studied and compared with those at the strain ratio of-1. Compared with other methods, Basquin formula and Solonberg formula provide reliable and appropriate ranges of S-N curve and fatigue limit at different strain ratios respectively. The SWT parameter can be used to predict the fatigue life at other strain ratios accurately.

Real time endoscopic ultrasound elastography and strain ratio in the diagnosis of solid pancreatic lesions

AIM To evaluate the accuracy of the elastography score combined to the strain ratio in the diagnosis of solid pancreatic lesions(SPL). METHODS A total of 172 patients with SPL identified by endoscopic ultrasound were enrolled in the study to evaluate the efficacy of elastography and strain ratio in differentiating malignant from benign lesions. The semi quantitative score of elastography was represented by the strain ratio method. Two areas were selected, area(A) representing the region of interest and area(B) representing the normal area. Area(B) was then divided by area(A). Sensitivity, specificity, positive predictive value(PPV), negative predictive value(NPV), and accuracy were calculated by comparing diagnoses made by elastography, strain ratio and final diagnoses.RESULTS SPL were shown to be benign in 49 patients and malignant in 123 patients. Elastography alone had a sensitivity of 99%, a specificity of 63%, and an accuracy of 88%, a PPV of 87% and an NPV of 96%. The best cut-off level of strain ratio to obtain the maximal area under the curve was 7.8 with a sensitivity of 92%, specificity of 77%, PPV of 91%, NPV of 80% and an accuracy of 88%. Another estimated cut off strain ratio level of 3.8 had a higher sensitivity of 99% and NPV of 96%, but with less specificity, PPV and accuracy 53%, 84% and 86%, respectively. Adding both elastography to strain ratio resulted in a sensitivity of 98%, specificity of 77%, PPV of 91%, NPV of 95% and accuracy of 92% for the diagnosis of SPL. CONCLUSION Combining elastography to strain ratio increases the accuracy of the differentiation of benign from malignant SPL.

IMPROVEMENT ON THE CALCULATION OF PLASTIC STRAIN RATIO IN BCC MONOCRYSTALS

Two improvements have been made on the calculation of plastic strain ratio (r value) in BCC monocrystals by considering the differences in the critical shear stresses among the three slip systems and the rotation of crystal lattice. It is found that the results calculated by the improved method are more rational.

STRAIN-DEPENDENCE OF PLASTIC STRAIN RATIO OF DEEP-DRAWING ALUMINIUM-KILLED STEEL SHEET

The change of width and length of an aluminium-killed(AK)steel sheet was measured in detail at various tensile strain levels.The effects of tensile strain on the conventional strain ratio,rc-value,and the instantaneous strain ratio,r^(1)-value,were analyzed.It was shown that the strain ratio of the AK steel sheet had obvious strain-dependency.The individual r^(c)-values for all tested directions tended to unity with increasing strain so that the planar anisotropy decreased with increasing strain.The r^(1)-value had overall straidenpendency similar to that of r^(c)-value,though it was overly sensitive to the experimental errors and showed significant variation with strain.In the representation of average strain ratio.the linear regression strain ratio,r^(r)-value,which was obtained by fitting a straight line to the εw vs εt curve,is preferable to the r^(c)-value measured at some specfic extension.

Physical meaning and prediction efficiency of the load/unload response ratio of rocks in strain-weakening phase before failure

Rock experiment results indicate that the load/unload response ratio (LURR) of rocks expressed via strain energy may have singular or negative value after the stress in the rock reaches its maximum before rock failure or when the rock goes into the strain-weakening phase. The universality of this phenomenon is discussed. Expressed via strain or strain energy and the travel time of P wave, the variation form of the reciprocal of LURR during the process of rock failure preparation is derived. The results show that after a sharp decrease the reciprocal of LURR reaches its minimum when the main fracture of the rock is about to appear. This feature can be taken as an indication that the rock main fracture is impending.

The correlation between the ultrasonic elastic strain ratio of thyroid cancer and the malignant biological characteristics of cancer cells in the lesions

Objective:To study the correlation between the ultrasonic elastic strain ratio of thyroid cancer and the malignant biological characteristics of cancer cells in the lesions.Methods:A total of 90 patients with thyroid cancer who accepted surgical treatment in our hospital between March 2015 and September 2016 were selected as the observation group, and 50 patients who received surgery in our hospital during the same period and were with clear pathological diagnosis of thyroid adenoma were selected as the control group. According to the median of ultrasonic elastic strain ratio, the observing group were further divided into high elastic strain ratio group and low elastic strain ratio group (n=45). RT-PCR was used to determine the mRNA expression of proliferation genes, invasion genes and autophagy genes in lesions of all groups of patients.Results: The mean elastic strain ratio of observation group was significantly lower than that of control group. Proliferation gene FOXA1 mRNA expression in lesions of low elastic strain ratio group and high elastic strain ratio group were higher than those of control group while PP4R1 and Smac mRNA expression were lower than those of control group, and as the elastic strain ratio decreased, the FOXA1 mRNA expression increased while PP4R1 and Smac mRNA expression decreased;invasion genes BCORL1, SATB1, Twist1 and CXCR4 mRNA expression in lesions of low elastic strain ratio group and high elastic strain ratio group were higher than those of control group, and as the elastic strain ratio decreased, the BCORL1, SATB1, Twist1 and CXCR4 mRNA expression increased;autophagy genes ARHI, Beclin1, LC3 and PTEN mRNA expression in lesions of low elastic strain ratio group and high elastic strain ratio group were lower than those of control group, and as the elastic strain ratio decreased, the ARHI, Beclin1, LC3 and PTEN mRNA expression decreased.Conclusion:The ultrasonic elastic strain ratio of thyroid cancer is negatively correlated with tumor cell proliferation and invasion activity, and positively correlated with autophagy activity.

EFFECT OF THE POISSON RATIO ON THE PERFECTLY PLASTIC STRESS FIELD AT A STATIONARY PLANE-STRAIN CRACK TIP

Under the condition that all the perfectly plastic stress components at a crack tip are the functions of ? only, making use of equilibrium equations and Von-Mises yield condition containing Poisson ratio, in this paper, we derive the generally analytical expressions of perfectly plastic stress field at a stationary plane-strain crack tip. Applying these generally analytical expressions to the concrete cracks, the analytical expressions of perfectly plastic stress fields at the stationary tips of Mode I, Mode II and Mixed-Mode I-II plane-strain cracks are obtained. These analytical expressions contain Poisson ratio.

Research on the Distribution Features of the Benioff Strain Ratio in the North-South Seismic Belt after the Two Yutian M_S7.3 Earthquakes

In view of the correlation between tectonic activity and seismicity,the strong earthquake risk in the North-South Seismic Belt aroused wide concern after the 2014 Yutian M_S7.3 earthquake. Using the seismic catalog of the China Earthquake Networks Center,the Benioff strain ratio in the North-South Seismic Belt is calculated in 30 days before and after the March 21,2008 and February 12,2014 Yutian M_S7.3 earthquakes. Results show that in a year after the 2008 Yutian M_S7.3 earthquake,M > 5. 0 earthquakes all occurred near the high strain ratio area or the junction between the low and high strain ratio areas,the activity of strong earthquakes obviously coincides with the high strain ratio area,which indicates that these areas have a higher stress level. The Yutian earthquakes promoted the release of small earthquakes in the high stress areas. This research is of certain indicating significance to the study of subsequent strong earthquakes of this region.

颗粒表面粗糙度对材料小应变动力特性的影响

土体的小应变剪切模量和阻尼比是表征土体动力学特性的重要参数,不仅受到土体密实度和应力状态的影响,还受到土体颗粒级配、形状等颗粒特征的影响。颗粒表面粗糙度是重要的土体颗粒特征之一,然而关于颗粒表面粗糙度对土体小应变动力特性影响的研究较为匮乏。利用能量注入式虚拟质量共振柱设备,系统地测试了颗粒表面粗糙度不同的玻璃珠所成试样的小应变剪切模量和阻尼比;采用三维干涉显微镜测量了玻璃珠的表面粗糙度,并量化表征粗糙度对试样小应变剪切模量和阻尼比的影响。试验结果表明,在相同孔隙比和有效应力条件下,试样的小应变剪切模量随颗粒表面粗糙度增大而减小,而小应变阻尼比受颗粒表面粗糙度影响的规律不明显。研究结果表明,当材料的颗粒形状、级配等因素相近时,颗粒表面粗糙度对材料小应变剪切模量的影响不应被忽略。

甲状腺结节射频消融术后复发预测模型的构建与应用

目的探讨甲状腺结节射频消融术后复发的影响因素,构建列线图预测模型,以期指导临床诊治。方法选取2019年1月至2021年1月郑州大学第二附属医院收治的398例甲状腺结节作为研究对象,其中16例于生化复发前接受内分泌治疗,12例无术后2年随访信息,均予以剔除,经筛选后259例纳入训练集用于建立模型,111例纳入验证集用于验证模型,采用COX比例风险回归方程确定甲状腺结节射频消融术后复发影响因素,采用R软件可视化处理获得列线图预测模型,行内外部验证。结果术后2年,甲状腺结节射频消融术后复发率为15.14%(56/370);COX比例风险回归方程显示,体质量指数(BMI)(OR:6.873)、热休克蛋白70(HSP70)(OR:5.380)、弹性应变率比值(SR)(OR:3.872)、结节成分(OR:5.880)、结节内部血流(OR:6.944)、结节钙化(OR:3.764)是甲状腺结节射频消融术后复发影响因素(P<0.05);基于COX比例风险回归方程结果构建甲状腺结节射频消融术后复发列线图预测模型,该模型在训练集、验证集中曲线下面积(AUC)分别为0.856、0.874,且其预测效能与实际吻合较理想。结论基于SR、BMI、HSP70、结节成分、结节内部血流、结节钙化构建列线图预测模型对甲状腺结节射频消融术后复发具有良好区分度、精准度,有助于实现个体化预测,帮助临床医师识别高风险人群,确定合理防治措施。

重塑黄土的往返加卸载真三轴试验研究

针对不同应力路径往返加卸载条件下黄土累积塑性应变发展特性,以重塑黄土为研究对象,利用真三轴仪开展不同应力路径的往返加卸载试验研究,探究不同应力路径、应力幅值下黄土的循环应力时程曲线、滞回曲线、骨干曲线及累积塑性应变曲线的影响规律。揭示了应力路径对重塑黄土力学特性的影响,描述了各主应力与中主应力比b和应力幅值的相关性,提出了重塑黄土的滞回曲线近似呈椭圆形,长轴斜率随中主应力比b值的增大而增大,随应力幅值的增大而减小;随着中主应力比b值的增大,循环应力-应变骨干曲线随之硬化,累积塑性应变曲线依次降低,且累积塑性应变发展更早的进入平缓阶段,为解决相关黄土工程问题提供了参考。

基于能量转化机制的岩石强度的演化机理研究

针对岩石强度的演化机理是提高强度准则计算精度与适用性的前提,基于能量转化是物质物理过程的本质属性,弹性应变能是材料破坏的内在机理,通过试验与理论研究,探究了围压、中间主应力及泊松比对岩石强度演化规律的影响.结果表明:岩石破坏与应力状态及岩石变形特性有关,忽略泊松比的影响是中间主应力效应提出的理论依据,并指出围压效应与中间主应力效应忽略变形影响,既与试验结果不一致,又是据此建立的强度理论精度较差的内在原因.岩石强度的演化是围压、中间主应力及泊松比共同作用的结果,并据此研究了静水应力状态下材料破坏特性、围压区间性及三轴拉伸强度恒大于三轴压缩强度条件.理论及试验表明,体现了围压、中间主应力及泊松比影响的强度理论具有较高计算精度与适用性.研究成果对于精准地描述岩石破坏特性,建立普遍适用的强度理论具有重要意义.

风机荷载作用下频率比对砂土动力响应的影响

海上风机在运行过程中风荷载与波浪荷载频率耦合作用对土体动力特性的影响不容忽略,为了探究这种影响,采用多向循环动单剪系统(VDDCSS)对砂土进行了一系列试验研究,分析了双向剪切频率比f_(r)对砂土动应变、动孔压比以及动强度的影响。试验结果表明:剪应变发展受双向频率耦合及应力组合效应的影响。循环应力比(C_(SR))为0.15时,双向频率耦合效应大于应力组合作用;随着应力水平的增加(C_(SR)=0.20或0.25),频率耦合效应和应力组合作用均得到了加强。在低应力水平时,破坏试样的孔压曲线呈“上凹型”且频率比对试样孔压发展影响不大。而随着应力水平增加(C_(SR)=0.20或0.25),孔压最终值u_(max)随之增大。除f_(r)=1.00与10.00对应试样外,土体动强度随f_(r)与C_(SR)值增大而减少。f_(r)=5.00对应试样应变大、孔压值高、强度低的原因与此比值下土体受双向频率耦合与应力组合的叠加效果增强有关。

基于声发射特征的不同高径比矸石胶结充填柱单轴压缩损伤演化

为研究高径比对矸石胶结充填柱单轴压缩性能的影响,本实验制备了高径比为0.5~4.0的5组圆柱体试件进行单轴压缩试验,同时利用数字图像相关技术(DIC)和声发射进行监测,探讨了不同高径比充填柱的破坏特征.研究表明:矸石胶结充填柱的峰值应力和峰值应变都会随着高径比的增大而减小,并与高径比呈指数关系;充填柱的破坏形式在高径比大于2.0后从整体破坏转为局部破坏,局部应变大于16%可以导致充填柱整体失稳;充填柱的高径比从1.0升高到4.0,损伤程度下降到11%;充填柱在累计振铃计数快速上升区中的破坏占总破坏的比例随高径比的增大从22.6%增加到72.3%,高径比大于2.0时该比例达到40.9%且上升速度加快,破坏的集中程度较高;声发射最终累积振铃计数先随着高径比增大而增大,在高径比为2.0以后开始减小,且高径比对振铃集中出现的位置有较大影响;用声发射能量与振铃计数的比值(E/C)反应能量释放剧烈程度,平均E/C随高径比增大从1.26增大到2.76,高径比大于2.0时峰后能量释放较为剧烈.试验结果可以为结构充填开采中充填柱高径比的选取提供参考.

部分排水条件下静力触探试验力学机理研究

在自然状态下,大部分土体的约束条件介于完全排水和不排水两者之间。在孔压静力触探试验(piezocone penetrationtest,CPTU)的贯入过程中,受探头尺寸、贯入速度和岩土材料等因素的影响,将发生部分排水现象。为研究排水条件对CPTU试验数据的影响,开展三轴压缩试验。引入应变增量比,建立考虑渐近状态的修正剑桥(Modified Cam-Clay,MCC)模型。推导考虑渐近状态MCC模型的柱孔扩张理论,提出CPTU测试数据的力学模型。通过数值模拟和模型槽试验,研究归一化贯入速度与排水系数的规律。结合CPTU数据的力学模型,获得应变增量比与排水系数的数理关系。最后以上海市苏州河地区深层排水调蓄管道系统工程的测试数据为背景,验证力学模型的正确性。结果表明:在部分排水条件下,利用考虑渐近状态的MCC模型,能够描述土体的应力-应变关系,合理解释CPTU贯入的力学机理。

多频段循环荷载下海洋黏土动力特性试验研究

为探究海洋土的动力特性及动力影响因素,采取原状黄海海洋黏土,利用GCTS动三轴试验系统开展室内试验研究,探讨偏应力水平、动应力幅值和动荷载频率对海洋土动应力应变关系和动孔压的影响规律,分析动剪切模量和阻尼比的变化特征。试验结果表明:海洋黏土的动应变随偏应力水平提高和动应力幅值增大而增大,且具有显著的频率效应,低频段动荷载(0.02~0.1 Hz)引起的动应变累积量高于高频段动荷载(1~10 Hz)的应变累积量;在低频段动荷载作用下,土样内超静动孔压显著上升,而在高频段下,动孔压的累积变化量很小;土样的动剪切模量对动荷载的频率反应不十分明显,仅在低频段,动剪切模量会随动荷载频率的提高略有下降,但是会随动应力幅值增加而显著提高,随偏应力水平提高而显著下降;土样的阻尼比对动荷载频率也很敏感,在低频段,阻尼比随频率的增大而降低,在0.1 Hz时的阻尼比最低;在高频段,土样的阻尼比随动荷载频率增加明显提高,提高幅度可达到1倍以上;阻尼比会随动应力幅值增长而略有减小,随偏应力水平提高而略有增加。

冻融循环作用下黄土累积塑性应变演变规律

为探究黄土路基在冻融循环和交通荷载耦合作用下的累积塑性应变变化规律,选取西宁地区重塑黄土为研究对象,采用GDS双向动三轴测试系统对其进行一系列动三轴试验,研究不同冻融循环次数、围压、动应力幅值以及频率对累积塑性应变的影响规律,并通过引入拟合参数建立考虑多因素的累积塑性应变预测模型。结果表明:累积塑性应变随冻融循环次数的增大而增大,在6次冻融循环后增长速率减缓且趋于稳定;减小动应力幅值和增大围压能显著抑制累积塑性应变的发展;加载初期累积塑性应变随频率变化不明显,随着振次的增加,频率作用凸显,累积塑性应变随着频率的增大而减小;基于试样的累积塑性应变演变规律,分别采用幂指数模型和对数模型进行拟合,发现后者拟合效果好;综合考虑4种因素对累积塑性应变的影响,建立累积塑性应变预测模型,并对试验的实测值与预测值进行对比,验证模型的可行性。研究成果可为季冻区黄土路基永久变形的计算提供理论参考依据。