An experimental study of temperature and moisture content of wet porous materials under short-pulsed laser heating

The measurements of temperature and moisture content of a wet porous material were accomplished on the micro-seconds scale. The temperature wave was observed when the wet porous material was heated by short-pulsed laser with high power. It firstly revealed that the moisture content of wet porous material rapidly rises twice in one laser irradiation. The influences of laser parameters, the thickness and initial moisture content of the wet porous material on its temperature and moisture content were investigated.     

CO_2 permeability of fractured coal subject to confining pressures and elevated temperature: Experiments and modeling

The CO_2 permeability of fractured coal is of great significance to both coalbed gas extraction and CO_2 storage in coal seams, but the effects of high confining pressure, high injection pressure and elevated temperature on the CO_2 permeability of fractured coal with different fracture extents have not been investigated thoroughly. In this paper, the CO_2 permeability of fractured coals sampled from a Pingdingshan coal mine in China and artificially fractured to a certain extent is investigated through undrained triaxial tests. The CO_2 permeability is measured under the confining pressure with a range of 10–25 MPa, injection pressure with a range of 6–12 MPa and elevated temperature with a range of 25–70°C. A mechanistic model is then proposed to characterize the CO_2 permeability of the fractured coals. The effects of thermal expansion, temperature-induced reduction of adsorption capacity, and thermal micro-cracking on the CO_2 permeability are explored. The test results show that the CO_2 permeability of naturally fractured coal saliently increases with increasing injection pressure. The increase of confining pressure reduces the permeability of both naturally fractured coal and secondarily fractured coal. It is also observed that initial fracturing by external loads can enhance the permeability, but further fracturing reduces the permeability. The CO_2 permeability decreases with the elevation of temperature if the temperature is lower than 44°C, but the permeability increases with temperature once the temperature is beyond 44°C. The mechanistic model well describes these compaction mechanisms induced by confining pressure, injection pressure and the complex effects induced by elevated temperature.     

Microstructural evolution and mechanism of grain growth in magnesia ceramics prepared by high pressure and temperature with ultra-high heating rate

The fast densification method of combustion reaction plus quick pressing was adopted to prepare nanocrystalline ceramics.The densification process of magnesia compact with a particle size of 100 nm was investigated,under the applied pressure of up to 170 MPa,and the temperature range of 1740–2080 K with ultra-high heating rate(above 1700 K/min).High-purity magnesia ceramics with a relative density of 98.8%and an average grain size of 120 nm was obtained at 1740 K,and the grain growth during the densification process was effectively restrained.The characteristic morphology of evaporation-condensation was observed in the compact prepared at 2080 K,which revealed the actual process of mass transfer by gas diffusion.Moreover,the investigation on the microstructure evolution and mechanism of grain growth was carried out,on the basis of as-preserved nanocrystalline ceramics.The result indicated that the grain growth of the nanocrystalline MgO was controlled by the mechanism of evaporation-condensation rather than surface diffusion.Furthermore,the pressure had an influence of restraining the grain growth based on solid diffusion and strengthening the effect of gas diffusion with the increasing temperature.Under the particular conditions,there existed an appropriate temperature for the densification of nanocrystalline magnesia,while the excessive temperature would exaggerate grain growth and impede densification.     

满堂扣件式钢管脚手架应力传递规律试验研究

满堂扣件式钢管脚手架在混凝土工程模板施工中有着广泛的应用,具有拆装方便、周转次数多、经济效益显著等诸多优点。本文通过3×3跨的满堂式扣件钢管脚手架加载实验,在施加不同荷载的情况下,研究脚手架某一立杆扣件处的应力传递规律。采用数值模拟和现场监测等分析方法,分析在不同的荷载作用下,架体内部钢管立柱的应力传递规律,其结论和研究方法可为研究类似架体的受力性能提供借鉴和参考,同时为现场关键点监控和远程安全预警系统开发提供相应的理论依据。     

冻融环境下混凝土力学性能试验及损伤演化

在我国西部寒区,冻融作用往往是导致混凝土破坏的主要因素之一。通过对饱水状态下的多组混凝土试样进行冻融循环试验,并对试验后的试样进行了单轴压缩试验,从损伤和能量耗散的角度对试样进行了力学性能的分析;运用CT细观试验的方法初步对经历不同冻融循环次数下的试样进行了细观结构分析。通过试验研究,得到了饱水状态下混凝土材料的冻融破坏特征,以及不同冻融循环次数下试样质量、单轴应力-应变全过程曲线、抗压强度、能量耗散和细观结构的变化特征,系统研究了冻融循环下混凝土主要物理力学性能及损伤演化规律,为寒区重大工程冻融灾变预测提供较可靠的基础依据。     

Theoretical and experimental study on surface tension and dynamic surface tension of aqueous lithium bromide and water with additive

Heat and mass transfer of LiBr absorption chiller can be enhanced significantly through addi-tion of trace amounts of additives, such as 2-ethyl-1-hexanol (2EH) and 1-octanol. This enhance-ment is apparently due to the interfacial convection, i.e. Marangoni convection. However, the formation mechanism of Marangoni convection is still not clear[1]. Accurate static and dynamic surface tension data are necessary for studying the formation mechanism of Marangoni convection. Unfortunately, the e…     

高低温交变湿热环境下外加载荷对不同孔隙率CFRP拉伸力学性能影响

通过高低温交变加速湿热循环试验及有限元模拟,研究了孔隙率和外加载荷对CFRP层合板湿热拉伸力学性能及界面破坏机理的影响.通过控制模压压力,制备出3种孔隙率的层合板;加载载荷分别为层合板最大弯曲载荷的30%、40%和60%.结果表明,孔隙率的增大是导致CFRP层合板湿热老化后拉伸性能大幅下降的主要原因,孔隙率越大,湿热拉伸强度下降越多.外加载荷能加速纤维与树脂基体界面脱粘,使材料湿热拉伸性能进一步下降,而且对不同孔隙率的层合板影响程度不一样,其中影响最大的是孔隙率为0.08的层合板,其次是孔隙率0.04的层合板,影响最小的是孔隙率为0.11的层合板.并且载荷越大,影响也越大,但其对材料湿热拉伸性能的影响远不如孔隙率的影响大.使用ABAQUS软件建立有限元模型,计算得到了层合板的各层拉伸应力分布,结果发现湿热循环导致90°层承受的拉伸应力上升,因此容易发生基体开裂及纤维/基体界面脱粘,导致力学性能下降,这一结果与试验结果相一致.计算得到的拉伸力学强度变化趋势与试验结果相一致.     

An experimental and modeling study of n-hexadecane autoignition under low-to-intermediate temperatures

N-hexadecane is a potential candidate of diesel surrogate fuels and is also the largest linear alkane (n-alkanes) with known chemical kinetic models. The o     

高地应力下砂岩力学参数和波速变化规律试验研究

基于波动方程,提出一种砂岩的纵波波速与静水围压关系的数学模型。在岩石常规三轴试验的基础上得到不同静水围压下砂岩的静弹性模量、静泊松比和纵波波速,并分别拟合得到静弹性模量-静水围压和静泊松比-静水围压关系的拟合曲线和拟合公式。试验结果表明,砂岩的静弹性模量和静泊松比随静水围压的增大而增加,且静弹性模量增加速率缓慢减少。基于波动方程求解得到纵波波速-静水围压关系的数学模型,利用数学模型计算得到的纵波波速可知,砂岩的纵波波速随静水围压的增大而增大,且增加速率逐渐变缓。计算得到的纵波波速与试验测得的纵波波速进行对比验证,误差范围为7.0%~8.3%,故基于波动方程求解的砂岩纵波波速-静水围压关系的数学模型可靠性和准确性较高,对高地应力下岩石的物理力学参数和波速变化规律的分析判定具有指导意义。     

CO<Subscript>2</Subscript> permeability of fractured coal subject to confining pressures and elevated temperature: Experiments and modeling

The CO₂ permeability of fractured coal is of great significance to both coalbed gas extraction and CO₂ storage in coal seams, but the effects of high confining pressure, high injection pressure and elevated temperature on the CO₂ permeability of fractured coal with different fracture extents have not been investigated thoroughly. In this paper, the CO₂ permeability of fractured coals sampled from a Pingdingshan coal mine in China and artificially fractured to a certain extent is investigated through undrained triaxial tests. The CO₂ permeability is measured under the confining pressure with a range of 10–25 MPa, injection pressure with a range of 6–12 MPa and elevated temperature with a range of 25–70°C. A mechanistic model is then proposed to characterize the CO₂ permeability of the fractured coals. The effects of thermal expansion, temperature-induced reduction of adsorption capacity, and thermal micro-cracking on the CO₂ permeability are explored. The test results show that the CO₂ permeability of naturally fractured coal saliently increases with increasing injection pressure. The increase of confining pressure reduces the permeability of both naturally fractured coal and secondarily fractured coal. It is also observed that initial fracturing by external loads can enhance the permeability, but further fracturing reduces the permeability. The CO₂ permeability decreases with the elevation of temperature if the temperature is lower than 44°C, but the permeability increases with temperature once the temperature is beyond 44°C. The mechanistic model well describes these compaction mechanisms induced by confining pressure, injection pressure and the complex effects induced by elevated temperature.     

An experimental study of the incipient bed shear stress partition in mobile bed channels filled with emergent rigid vegetation

This paper investigates the bed shear stress based on the condition of the incipient motion of sediment in a uniform-flow flume covered with emergent rigid vegetation,which is represented by arrays of circular cylinders arranged in a regular pattern.A total of 148 tests are performed to observe the influence of the vegetation density,bed slope,flow depth and sediment size on the bed shear stress.The tests reveal that when the sediment is in incipient motion,the resistances acting on the flow passing the rigid vegetation contain the vegetation resistance and the bed shear stress.This shear stress could be divided into two parts:the grain shear stress and the shear stress caused by sand dunes,which are the deformed bedform with the sediment incipient motion.An empirical relationship between the shear stress of the sand dune and vegetation density,the Froude number,the apparent vegetation layer velocity is developed.     

Comparative study of mechanical-electrical-thermal responses of pouch,cylindrical, and prismatic lithium-ion cells under mechanical abuse

In the study, mechanical abuse tests mainly in the form of indentation were performed on the cylindrical cell, pouch cell, and prismatic cell. The mechanical force-displacement response, open circuit voltage (OCV), and temperature distribution were recorded and compared. In spherical head indentation tests of the pouch and prismatic cell and lateral indentation of the cylindrical cell, the peak force is strongly correlated with OCV drop and local temperature increase. However, in flat-end cylinder indentation tests, the internal mechanical damage is progressively developed, and the OCV drop and the temperature increase occur before the peak force. The fracture surfaces of the post-mortem samples were examined to investigate the correlation between fracture patterns and internal short circuit (ISC) behaviors (OCV and temperature distribution). Two distinct fracture patterns were observed that the in-plane fracture induced by biaxial stretching and inter-layers’ fracture induced by shearing. A strong correlation is observed between the number of shear fractures and OCV drop. An increase in the number of inter-layers’ fractures increases the rate of OCV drop. Additionally, the fracture patterns influence the ISC area and location, thereby affecting the heat generation and conduction as well as the temperature distribution.     

An experimental study on thermal characteristics of nanofluid with graphene and multi-wall carbon nanotubes

High-thermal conductivity enhancement of nanofluid is one of the promising topics of the nanoscience research field. This work reports the experimental study on the preparation of graphene(GN) and multi-walled carbon nanotubes(MWCNTs) based nanofluids with the assistance of sodium dodecyl benzene sulfonate(SDBS) and sodium dodecyl sulfate(SDS) surfactants, and their thermal behaviors. The present work suggests not a solution, but a solution approach and deduces a new conclusion by trying to resolve the agglomeration problem and improve the dispersibility of nanoparticles in the base fluid. The analysis results of FESEM, thermal conductivity, diffusivity, effusivity and heat transfer coefficient enhancement ratio of nanofluid with surfactants SDS and SDBS expose strong evidence of the dispersing effect of surfactant on the making of nanofluid.     

KMnO4和MnSO4联用处理微污染原水试验研究

KMnO4和MnSO4联用处理微污染原水在一定程度上解决了单纯使用KMnO4在高投量时残余量产生的色度问题和低投量时处理效果不理想的问题，KMnO4和MnSO4联合使用能有效的去除水中有机物和浊度，并对KMnO4投量，KMnO4／MnSO4的最佳投量摩尔比，KMnO4预氧化时间，混合药剂反应时间以及投量对处理效果的影响等进行了一定的研究。     

盐-干湿循环作用下低温养护纤维水泥土的力学性能试验研究

为探明玄武岩纤维水泥土在盐溶液(Na2SO4)和干湿循环耦合作用下的力学特性,将玄武岩纤维按一定比例掺入水泥土中,试块分批分次放入不同浓度的盐溶液中浸泡,而后放入烘干箱中烘干,如此实现若干次干湿循环,并基于无侧限抗压强度试验,研究低温和常温养护条件下纤维水泥土的强度变化规律,在此基础上,探讨盐溶液浓度和干湿循环次数对试...     

Theoretical and experimental study of initial cracking mechanism of an expansive soil due to moisture-change

Swelling and shrinkage due to moisture-change is one of the characteristics of the expansive soil, which is similar to the behavior of most materials under thermal effect. If the deformation is restricted, stress in expansive soil is caused by the swell-shrinking. The stress is defined as “moisture-change stress” and is adopted to analyze swell-shrinkage deformation based on the elasticity mechanics theory. The state when the total stress becomes equal to the soil tensile strength is considered as the cracking criterion as moisture-change increases. Then, the initial cracking mechanism due to evaporation is revealed as follows: Different rates of moisture loss at different depths result in greater shrinkage deformation on the surface while there is smaller shrinkage deformation at the underlayer in expansive soil; cracks will grow when the nonuniform shrinkage deformation increases to a certain degree. A theoretical model is established, which may be used to calculate the stress caused by moisture-change. The depth of initial cracks growing is predicted by the proposed model in expansive soil. A series of laboratory tests are carried out by exposing expansive soil samples with different moisture-changes. The process of crack propagation is investigated by resistivity method. The test results show good consistency with the predicted results by the proposed theoretical model.     

Experimental study on the mechanical and failure behaviors of deep rock subjected to true triaxial stress: A reviewOA

It has become an inevitable trend of human development to seek resources from the deep underground.However, rock encountered in deep underground engineering is usually in an anisotropic stress state(σ₁>σ>σ₃) due to the influences of geological structures and engineering disturbances. It is therefore essential to study the mechanical, seepage, and dynamic disaster behaviors of deep rock under true triaxial stress to ensure the safe operation of deep rock engineering an...     

Strength failure and crack coalescence behavior of sandstone containing single pre-cut fissure under coupled stress,fluid flowand changing chemical environment简

In order to study the strength failure and crack coalescence characteristics of cracked rocks, uniaxial compression experiments were conducted on cylindrical sandstone specimens, sampled from Longyou Grottoes of Zhejiang Province, China, with a single pre-cut crack soaking in different chemical solutions. Based on the results of uniaxial compressive test under different chemical solutions and velocities of flow, the effect of strength and deformation characteristics and main modes of crack coalescence for cracked rocks under chemical corrosion were analyzed. The results show that the pH value and velocity of the chemical solutions both have great influence on the sandstone sample＇s uniaxial compressive strength and deformation characteristics. Cracked sandstone samples are tension-destructed under uniaxial compression, and the crack propagation directions are consistent with the loading direction. The phenomena of crack initiation, propagation and coalescence of sandstone are well observed. Four different crack types are identified based on the crack propagation mechanism by analyzing the ultimate failure modes of sandstone containing a single pre-cut fissure. The failure process of specimen in air is similar with the specimen under chemical solutions, however, the initial time of crack occuring in specimen under chemical solutions is generally earlier than that in the natural specimen, and the crack propagation and coalescence process of specimen under chemical solutions are longer than those of the natural specimen due to softening of structure of rock caused by hydro-chemical action. Immersion velocity of flow and chemical solutions does not have influence on the ultimate modes of crack coalescence.     

舰船敷设抗冲瓦后的阻力计算与试验研究

为了研究舰船敷设抗冲瓦后的阻力性能,采用RNG湍流模型和有限体积法求解RANS方程对船模三维粘性绕流进行了数值模拟,兴波阻力计算则采用基于格林定理的时域边界元法.开展了敷设抗冲瓦前后的阻力性能拖曳水池对比试验.理论计算与试验结果表明:舰船敷设抗冲瓦后阻力在低速时基本保持不变,中高速时会由于兴波阻力的增加使得舰船的阻力有所增加,但不超过1%.计算与试验结果的比较验证了数值方法的有效性.