基于电阻的冻结砂砾土孔隙冰压融效应研究

为验证冻结砂砾土压缩过程中是否存在压融效应,对不同含水(冰)状态与不同冻结温度的砂砾土进行无侧限压缩试验和电阻测试,通过核磁共振测定饱和砂砾土的未冻水含量。结果表明:(1)砂砾土压缩过程电阻均先快速降低后趋缓,仅有干燥样品在应力峰值点后出现电阻增大的现象;(2)电阻快速降低阶段干燥样品的电阻降低率小于饱和冻结样品,−4℃饱和样品该值为26.8%,其值为相同温度下干燥样品的4倍;(3)随温度降低,电阻快速降低阶段的降低率先增加后减小;(4)随温度降低,自由水与毛细水的相对含量快速减小,吸附水的相对含量先小幅增加后缓慢降低。分析认为:冻结砂砾土压缩过程中存在压融效应,这导致样品在受荷过程中高应力区未冻水含量增大,而融水会沿未冻水膜向低应力区的孔隙迁移、复冰进而改变孔隙结构;冻结温度在−2~−4℃区间附近,压融效应更容易发生。

冻结盐渍土三轴剪切试验过程中的损伤及压融分析

三轴剪切过程中损伤及压融等力学性质对冻结盐渍土的强度及变形影响显著。通过对-15℃德令哈含盐砂土进行一系列的三轴剪切循环试验及CT扫描试验,分析冻结盐渍土在三轴试验过程中的损伤演化以及压融量变化规律。研究发现,在三轴剪切中损伤变量随静水压力的变化而改变,在本文条件下当静水压力在1~12 MPa之间时,损伤变量随围压的增加而增加,当静水压力超过12 MPa时,损伤变量反而呈现减小趋势。同时,定义压融阈值ps以及压融量达到最大值时对应的静水压力值pm,研究表明：当静水压力小于ps时,试样内部几乎不存在压融现象;当静水压力大于ps且小于pm时试验内部的压融量可用二次函数描述;当静水压力超过pm时,试样中的压融量达到最大值λm,且压融极值点与损伤变量极值点对应的静水压力值基本一致。

软黏土带压冻融循环下不固结力学特性试验研究

人工冻结法和季节性冻土地区土体通常在一定围压下经历冻融循环作用。受到冻融围压和不排水条件影响,融化后土体残存超孔压,并非完全固结状态,开展此工况下土体不排水力学性能研究具有重要工程和科学意义。通过自主改进的温控三轴仪,对重塑软黏土开展冻融后未完全固结不排水三轴剪切和微观试验,分析了冻融围压、次数和冻结温度对冻融后软黏土力学特性影响。结果表明:与零围压相比,带围压冻融后土体中絮凝结构和孔隙数量增大,加剧了冻融对土体强度和模量的弱化作用;随着冻结温度降低和冻融次数增大,土体力学性能弱化效应越明显。

带围压冻融循环下滨海重塑软土力学特性试验研究

滨海软土地区人工冻结工程中土体通常在一定围压下受到冻融作用进而力学性能发生改变,因此开展带围压冻融作用下土体力学特性研究具有重要意义。以天津滨海地区典型淤泥质土为研究对象,通过自主改进的温控应力路径仪,对比分析了常规无围压冻融和带围压冻融下淤泥质土力学特性差异,揭示了冻融围压、冷端温度、冻融循环次数对其超孔隙水压力、应力-应变曲线、强度及变形指标的影响,并通过电镜扫描试验揭示了冻融围压对其力学特性的影响机制。在此基础之上,采用指数函数建立了淤泥质土冻融循环作用下抗剪强度和弹性模量折减系数与上述因素的关系。结果表明:冻融围压降低了冻融后土体内孔隙大小和数量,能够在一定程度上减弱冻融对土体结构的破坏,但对其应力-应变曲线模式影响较小;随着冷端温度的降低和冻融循环次数的增加,冻融后土体强度和模量均大幅度降低;超孔隙水压力随冻融围压和冷端温度的升高及冻融次数的降低而降低。

冻结砂土三轴试验中颗粒破碎研究

压力作用下颗粒发生破碎是引起砂土力学特性变化的重要因素之一,冻结砂土也是如此。对冻结砂土进行了不同温度和围压下的三轴剪切试验,并筛分得到三轴试验前后的颗粒大小分布曲线。通过引入Hardin定义的颗粒破碎率Br,分析了围压与颗粒破碎的关系及颗粒破碎对冻土抗剪强度的影响。结果表明:在温度为-0.5℃,-1℃,-2℃,-5℃和围压为0.5,2,5,10 MPa的条件下,三轴剪切过程中会产生较为可观的颗粒破碎;颗粒破碎率Br随围压增大,到达一定围压后Br不再随着围压的增大发生明显变化,即存在一个颗粒不再发生明显破碎的临界围压σr。结合前人研究发现,-5℃下一般工程关心的围压范围内压融对冻土力学特性没有显著影响,而颗粒破碎起控制性作用。分析表明:-5℃条件下在不同的围压范围颗粒破碎对抗剪强度具有不同的影响。试验所采用的围压范围内,随着围压的增大,颗粒破碎率增大使得冻土的抗剪强度降低;破碎率达到极限以后,由于破碎的颗粒重排列又导致抗剪强度有所提高。

Microstructure and mechanical properties of melt-conditioned high-pressure die-cast Mg-Al-Ca alloy

A new shape casting process,melt-conditioned high-pressure die-casting(MC-HPDC) was developed.In this process,liquid metal was conditioned under intensively forced convection provided by melt conditioning with advanced shear technology(MCAST) unit before being transferred to a conventional cold chamber high-pressure die-casting(HPDC) machine for shape casting. The effect of melt conditioning was investigated,which was carried out both above and below the liquidus of the alloy,on the microstructure and properties of a Mg-Al-Ca alloy(AZ91D+2%Ca(mass fraction) ,named as AZX912) .The results show that many coarse externally-solidified crystals(ESCs) can be observed in the centre of conventional HPDC samples,and hot tearing occurs at the inter-dendritic region because of the lack of feeding.With the melting conditioning,the MC-HPDC samples not only have considerably refined size of ESCs but also have significantly reduced cast defects,thus provide superior mechanical properties to conventional HPDC castings.The solidification behaviour of the alloy under different processing routes was also discussed.

冻压条件下冻融软土孔隙特征与动力特性分析

杭州软土地区地铁联络通道建设多采用冻结法施工,在整个冻结范围内,不同区域的土体冻融期间承受不同冻结温度与冻融压力。通过自主研发土样制作仪器,得到不同组合冻结条件的试样,再基于核磁共振试验,研究冻融土在不同冻结压力、冻结温度以及加载情况下精确孔径分布特征曲线变化规律,并结合动三轴试验深入探究以孔压、应变以及刚度为代表的动力特性。最终,建立以一次对数为基础的动孔压预测模型,该模型参数物理意义清晰,能较好地预测不同冻融条件下软土动孔压发展。研究结果表明:随着冻结温度的降低,孔隙中的水冻胀效果更为明显;冻融期间围压可有效使融土骨架结构更为紧密,从而减少融土在循环荷载下的变形;循环荷载作用下,小孔隙尺寸大幅度减小,尺寸分布范围增大,中等孔隙进一步向次级孔隙发展;不同冻融压力作用下,孔压极限值与冻融完成后中等孔隙的面积呈类线性相关。研究成果可作为冻结法施工条件下,预测冻融土结构损伤程度与循环荷载下孔压发展的可靠依据。

Effect of Freeze-Thaw Cycles on Mechanical Properties and Permeability of Red Sandstone under Triaxial Compression

Geological disasters will happen in cold regions because of the effects of freeze-thaw cycles on rocks or soils, so studying the effects of these cycles on the mechanical characteristics and permeability properties of rocks is very important. In this study, red sandstone samples were frozen and thawed with o, 4, 8 and 12 cycles, each cycle including 12 h of freezing and 12 h of thawing. The P-wave velocities of these samples were measured, and the mechanical properties and evolution of the steady-state permeabilities were investigated in a series of uniaxial and triaxial compression tests. Experimental results show that, with the increasing of cyclic freeze-thaw times, the P-wave velocity of the red sandstone decreases. The number of freeze-thaw cycles has a significant influence on the uniaxial compressive strength, elastic modulus, cohesion, and angle of internal friction. The evolution of permeability of the rock samples after cycles of freeze-thaw in a complete stress-strain process under triaxial compression is closely related to the variation of the microstructure in the rock. There is a highly corresponding relationship between volumetric strain and permeability with axial strain in all stages of the stress-strain behaviour.

Freeze-thaw damage mechanism of elastic modulus of soil-rock mixtures at different confining pressures

As a frequently-used roadbed filler,soil-rock mixture is often in the environment of freeze-thaw cycles and different confining pressures.In order to study the freeze-thaw damage mechanism of elastic modulus of soil-rock mixtures at different confining pressures,the concept of meso-interfacial freeze-thaw damage coefficient is put forward and the meso-interfacial damage phenomenon of soil-rock mixtures caused by the freeze-thaw cycle environment is concerned;a double-inclusion embedded model for elastic modulus of soil-rock mixtures in freezing-thawing cycle is proposed.A large triaxial test was performed and the influences of confining pressure and experimental factors on elastic modulus of soil-rock mixtures were obtained,and then the accuracy of the double-inclusion embedded model to predict the elastic modulus of soil-rock mixtures in freezing-thawing cycle is verified.Experiment results showed that as to soil-rock mixtures,with the increase of confining pressure,the elastic modulus increases approximately linearly.The most crucial factors to affect the elastic modulus are rock content and compaction degree at the same confining pressure;the elastic modulus increases with the increase of rock content and compactness;as the number of freeze-thaw cycles increases,the freeze-thaw damage coefficient of meso-structural interface and the elastic modulus decrease.

The General Design and Technology Innovations of CAP1400

A historical review of in-vessel melt retention （IVR） is given, which is a severe accident mitigation mea- sure extensively applied in Generation III pressurized water reactors （PWRs）. The idea of IVR actually originated from the back-fitting of the Generation 11 reactor Loviisa WER-440 in order to cope with the core-melt risk. It was then employed in the new deigns such as Westinghouse APIO00, the Korean APR1400 as well as Chinese advanced PWR designs HPRIO00 and CAP1400. The most influential phe- nomena on the IVR strategy are in-vessel core melt evolution, the heat fluxes imposed on the vessel by the molten core, and the external cooling of the reactor pressure vessel （RPV）. For in-vessel melt evolution, past focus has only been placed on the melt pool convection in the lower plenum of the RPV; however, through our review and analysis, we believe that other in-vessel phenomena, including core degradation and relocation, debris formation, and coolability and melt pool formation, may all contrib- ute to the final state of the melt pool and its thermal loads on the lower head. By looking into previous research on relevant topics, we aim to identify the missing pieces in the picture. Based on the state of the art, we conclude by proposing future research needs.

Effects of spinneret structure on poly-ether-ether-ketone fibers by screw extrusion

According to the characters of poly-ether-ether-ketone (PEEK) plastic, the spinnerets with three kinds of different structure were designed. The effects of spinneret structure on the melt spinning conditions, melt flow instability of the screw extrusion, and the performance of PEEK fibers were studied. The results show that the appropriate screw extrusion temperature is 370 385℃. The PEEK fibers extruded using the spinnerets with L/D=6, 8holes and 0.5mm in diameter have better performances. The performances of PEEK fibers are related to the dia- meter of the spinneret hole. Increasing the L/D value of the spinnerets can not always improve the surface quality and the performances of PEEK fibers. The extrusion pressure is about 50% of that of the spinneret with 12holes and 0.3mm in diameter.

PM-3母料在吹塑加工中的应用

试验中添加定量PM-3母料吹塑薄膜制品,通过对加工过程中记录下的实验数据,以及对不同时段采集的薄膜样品进行力学性能和光学性能分析,表明:在相同的加工工艺条件下,添加PM-3母料后,初始5个小时内,薄膜的性能与未添加PM-3母料前的薄膜相比,发生无规律变动,10个小时后,薄膜的性能与未添加PM-3母料前的薄膜相比,有了明显的改善,并且挤出机内物料融压下降,从而挤出机电流下降,有效降低了设备的能耗。

Multi-voltage X-ray image sequence fusion based on selection of valid region

A key step is to extract valid information region in the fusion of multi-voltage X-ray image sequence for complicated components. To improve the self-adaption of extraction, a method is presented in this paper. In this paper, the valid informa-tion region is selected by the grey level interval, which is computed by the optimization of image quality evaluation model. The model is based on the histogram equalization and the grey level interval. Then, every valid region of images at different voltages is extracted and they are fused according their grey level transformation function. The fusion image contains completed struc-ture information of the component. The fusion experiment of a cylinder head shows the effectiveness of the presented method.

Application of enhanced recovery after surgery program for posterior lumbar decompression and fusion

Objective: To establish and optimize an enhanced recovery after surgery (ERAS) program, for the classic posterior lumbar decompression and fusion (PLDF).Methods: 1.An ERAS for PLDF procedure during the perioperative period had been designed. 2.A total of 155 patients (73 in the ERAS group and 82 in the traditional health care group) were analyzed, and their clinical outcomes were compared. The evaluation indexes included physiological function, postoperative visual analogue scale (VAS), pain score, postoperative complications. Results: ERAS significantly promoted early food-taking (7.93±2.15h vs 24.54 ± 5.72h, P < 0.00), early catheter removal (36.31 ± 8.42h vs 71.48 ± 13.75h, P < 0.00), early defecation (3.80 ± 1.3 days vs 5.3±1.41 days, P < 0.00);reduced the incidence of urinary tract infection (2.7% vs 9.7% P = 0.01) and shorter hospital stay (3.80 ± 1.04 days vs 7.29±1.62 days, P < 0.00), while no difference between the two groups in vomiting, lung infection, wound bleeding and infection. Conclusion: ERAS for PLDF can facilitate the recovery of physiological function, reduce postoperative pain, reduce operative complications and morbidity after surgery and contribute to a shorter hospital stay. Further research is needed to optimize the process.

Mechanical and electrical properties of coarse-grained soilaffected by cyclic freeze-thaw in high cold regions

To evaluate the geotechnical properties of coarse-grained soil affected by cyclic freeze-thaw,the electrical resistivity and mechanical tests are conducted.The soil specimens are prepared under different water contents,dry densities and exposed to 0?20 freeze-thaw cycles.As a result,the stress?strain behavior of the specimen(w=14.0%andρd=1.90 g/cm^3)changes from strain-hardening into strain-softening due to the freeze-thaw effect.The electrical resistivity of test specimen increases with the freeze-thaw cycles change,but the mechanical parameters(the unconfined compressive strength qu and the deformation modulus E)and brittleness index decrease considerably at the same conditions.All of them tend to be stable after 7?9 cycles.Moreover,both the dry density and the water content have reciprocal effects on the freeze-thaw actions.The failure and pore characteristics of specimens affected by freeze-thaw cycles are discussed by using the image analysis method.Then,an exponential function equation is developed to assess the electrical resistivity of specimens affected by the cyclic freeze-thaw.Linear relations between the mechanical parameters and the electrical resistivity of specimens are established to evaluate the geotechnical properties of the soil exposed to freeze-thaw actions through the corresponding electrical resistivity.

The Coolibility of Melt Pool in PWR Lower Head - Results of LIVE Experiments

The LIVE （Late In-Vessel Phase Experiments） test program investigates in-vessel melt pool behaviour and cooling strategies for in-vessel corium retention during severe accidents in light water reactors （LWR）. The main part of the LIVE facility is a 1：5 scaled semi-spherical lower head of a typical pressurized water reactor. Up to now, LIVE experiments have been performed in different initial external cooling conditions, melt volumes and internal heat generations. At present the well-known simulant material KNO3-NaNO3 in non-eutectic composition （80 mole% KNO3-20 mole% NaNO3） and in eutectic composition （50 mole% KNO3- 50 mole% NaNO3） is used in the live program. The 3D heat flux distribution through vessel wall, melt pool temperature, crust thickness and the pool melt composition can be measured or determined. Extensive results have been obtained concerning the melt pool thermal hydraulic behaviour in transient and in steady state conditions.

Modelling and Control of Pressurized Molten Metal in Press Casting

This paper presents a modeling and control of molten metal＇s pressure in pressing process using an innovative iron casting developed by our group. In this method, molten metal is directly poured into a lower mold, and then pressed to fill cavity by an upper mold being lowered down. For complex liquid flow during pressing, the liquid＇s pressure changing inside vertical path with various contraction and expansion geometries is newly modeled via the unstationary Bernoulli equation. The mathematical model is derived for a control design of pressing. To conduct the pressing velocity design algorithm, an unknown parameter of proposed model considering viscous flow is identified by using CFD （Computational Fluid Dynamics） with heat flow calculation. Control performance using a multi-switching velocity pattern is confirmed as an effective control design using the pressure model, because the pressure fluctuation has discontinuous variation points. Substituting detailed information for mold shape, poured volume and initial temperature into a developed control input generator, an optimum pressing velocity design and a robust design for defect-free production are proposed by the design algorithm based on the construction of an inverse system comprised of the sequential switching from higher to lower speed. Consequently, the effectiveness of the pressing control with reasonable pressure suppression has been demonstrated through CFD.

不同冻融模式下淤泥质土力学及微观结构特性研究

通过改进的温控三轴仪,考虑冻融围压、次数和冻结温度组合影响,对淤泥质土开展冻融后固结不排水剪切试验(FC模式)和固结后冻融不固结不排水剪切试验(CF模式),分析上述因素对淤泥质土力学特性的影响,并通过电镜扫描试验揭示冻融围压对其力学特性的影响机制。结果表明:FC模式中,冻融围压会减少冻融后土体内孔隙数量,进而降低冻融对土体强度和模量的弱化作用;而CF模式中,冻融围压使得冻融后土体内孔隙增多,土体融化时土体内超孔压增大且无消散过程,进而加剧了冻融对土体强度和模量的弱化作用;两种模式中,随着冻结温度越低和冻融次数越多,淤泥质土强度弱化效应越明显,土体破坏时的超孔隙水压力越高。淤泥质土力学指标劣化系数随冻融围压、次数和冻结温度的变化规律可用生长函数描述。

Gradient-based compressive image fusion

We present a novel image fusion scheme based on gradient and scrambled block Hadamard ensemble （SBHE） sam- piing for compressive sensing imaging. First, source images are compressed by compressive sensing, to facilitate the transmission of the sensor. In the fusion phase, the image gradient is calculated to reflect the abundance of its contour information. By com- positing the gradient of each image, gradient-based weights are obtained, with which compressive sensing coefficients are achieved. Finally, inverse transformation is applied to the coefficients derived from fusion, and the fused image is obtained. Information entropy （IE）, Xydeas＇s and Piella＇s metrics are applied as non-reference objective metrics to evaluate the fusion quality in line with different fusion schemes. In addition, different image fusion application scenarios are applied to explore the scenario adaptability of the proposed scheme. Simulation results demonstrate that the gradient-based scheme has the best per- formance, in terms of both subjective judgment and objective metrics. Furthermore, the gradient-based fusion scheme proposed in this paper can be applied in different fusion scenarios.