Expansion of spherical cavity of strain-softening materials with different elastic moduli of tension and compression

An expansion theory of spherical cavities in strain-softening materials with different moduli of tension and com-pression was presented. For geomaterials,two controlling parameters were introduced to take into account the different moduli and strain-softening properties. By means of elastic theory with different moduli and stress-softening models,general solutions cal-culating Tresca and Mohr-Coulomb materials' stress and displacement fields of expansion of spherical cavity were derived. The effects caused by different elastic moduli in tensile and compression and strain-softening rates on stress and displacement fields and development of plastic zone of expansion of cavity were analyzed. The results show that the ultimate expansion pressure,stress and displacement fields and development of plastic zone vary with the different elastic moduli and strain-softening prop-erties. If classical elastic theory is adopted and strain-softening properties are neglected,rather large errors may be the result.

Dynamic Similarity of Six Bar Ball Tensegrity Structure in Compression and Expansion Processes

Tensegrity structures have identical members in an orientation that have correlated dynamics under external force.To study this interdependent dynamics in different members in compression and expansion processes,it is vital to analyze the dynamics of the whole structure.In this study,six bar tensegrity structure was studied under compression and expansion,and interdependent movement of different members of the structure in both processes was obtained.First,the relationship between external force and members force densities was analytically developed based on the assumption that each bar moves with the same distance when an external force is applied on the six bar tensegrity ball structure along one plane that either compresses or expands the structure.Then,two individual simulations were carried out to analyze the movement of each bar in compression and expansion under the effect of external force,and elongation in all strings was studied in both processes.Finally,comparative dynamic study of different members in compression and expansion of the structure with the effect of external force was performed,which were categorized according to dynamic symmetry.

A Novel Multichannel Audio Signal Compression Method Based on Tensor Representation and Decomposition

Multichannel audio signal is more difficult to be compressed than mono and stereo ones.A novel multichannel audio signal compression method based on tensor representation and decomposition is proposed in this paper.The multichannel audio is represented with 3-order tensor space and is decomposed into core tensor with three factor matrices in the way of channel,time and frequency.Only the truncated core tensor is transmitted which will be multiplied by the pre-trained factor matrices to reconstruct the original tensor space.Objective and subjective experiments have been done to show a very noticeable compression capability with an acceptable output quality.The novelty of the proposed compression method is that it enables both high compression capability and backward compatibility with limited signal distortion to the hearing.

Measurement Method of Compressibility and Thermal Expansion Coefficients for Density Standard Liquid at 2329 kg/m^3 based on Hydrostatic Suspension Principle

The accurate measurement on the compressibility and thermal expansion coefficients of density standard liquid at 2329kg/m3（DSL-2329） plays an important role in the quality control for silicon single crystal manufacturing. A new method is developed based on hydrostatic suspension principle in order to determine the two coefficients with high measurement accuracy. Two silicon single crystal samples with known density are immersed into a sealed vessel full of DSL-2329. The density of liquid is adjusted with varying liquid temperature and static pressure, so that the hydrostatic suspension of two silicon single crystal samples is achieved. The compression and thermal expansion coefficients are then calculated by using the data of temperature and static pressure at the suspension state. One silicon single crystal sample can be suspended at different state, as long as the liquid temperature and static pressure function linearly according to a certain mathematical relationship. A hydrostatic suspension experimental system is devised with the maximal temperature control error ±50 μK; Silicon single crystal samples can be suspended by adapting the pressure following the PID method. By using the method based on hydrostatic suspension principle, the two key coefficients can be measured at the same time, and measurement precision can be improved due to avoiding the influence of liquid surface tension. This method was further validated experimentally, where the mixture of 1, 2, 3-tribromopropane and 1,2-dibromoethane is used as DSL-2329. The compressibility and thermal expansion coefficients were measured, as 8.5′10–4 K–1 and 5.4′10–10 Pa–1, respectively.

Low-frequency data analysis and expansion

The use of low-frequency seismic data improves the seismic resolution, and the imaging and inversion quality. Furthermore, low-frequency data are applied in hydrocarbon exploration; thus, we need to better use low-frequency data. In seismic wavelets, the loss of low-frequency data decreases the main lobe amplitude and increases the first side lobe amplitude and results in the periodic shocking attenuation of the secondary side lobe. The loss of low frequencies likely produces pseudo-events and the false appearance of higher resolution. We use models to examine the removal of low-frequency data in seismic data processing. The results suggest that the removal of low frequencies create distortions, especially for steep structures and thin layers. We also perform low-frequency expansion using compressed sensing and sparse constraints and develop the corresponding module. Finally, we apply the proposed method to real common image point gathers with good results.

Reduction of the residual stresses in cold expanded thick-walled cylinders by plastic compression

We suppose that in order to maintain high accuracy of holes and to lower residual stresses after cold expansion of thick-walled cylinders, which undergo cross-section plastic deformation, it is necessary to perform axial plastic compression and subsequent cold expansion with small interferences. To test this hypothesis, we studied hoop, radial and axial residual stresses in cylinders made of carbon steel AISI 1050 with hole diameter of 5 mm, outer diameter of 15 mm and length of 30 mm by Sachs method as well as accuracy of expanded holes. It is found that double cold expansion with total interference equal to 5.1% generates hoop residual stresses with largest absolute value equal to 284 MPa and ensures high holes accuracy(IT7). After plastic compression with strain equal to 0.5 and 1% the mentioned stresses reduced to 120 and 75 MPa respectively,and accuracy of the holes reduced as well. Subsequent cold expansion with small interference equal to 0.9% helps to restore holes accuracy(IT7)gained by double cold expansion and ensure that absolute value of hoop residual stresses(177 MPa) is lower compared to double cold expansion.

Molar volume, thermal expansivity and isothermal compressibility of trans-decahydronaphthalene up to 200MPa and 446K

The molar volume isotherms of trans-decahydronaphthalene （C10H18） between 293 and 446 K and at pressures from 10 to 200 MPa have been determined. A modified Tait equation of state is used to fit each experimental molar volume isotherm with a maximum average deviation of 0.029%. The thermal expansivity （cubic expansion coefficient） α and isothermal compressibility κ were determined by fitting the slopes of the isobaric curves and isotherms, respectively. The coefficients in the equation Vm=C1＋C2T＋C3T^2-C4p-C5pT have been fitted with an average deviation of 1.03%.

Experimental Study on the Expansion Uniformity of Armature

A measurement system has been developed based on high-precision printed probes in printed circuit board （PCB） and steep rising-time probe adapters, which can be applied to study the expansion uniformity of armature in a helical magnetic flux compression generator （HFCG）. The influences of wall thickness and initiation position on the expansion uniformity of armature in HFCG were experimentally investigated. The results show that the armature with thinner wall thickness will easily rupture due to the high pressure of detonation products inside, the armature with larger wall thickness will easily crack due to the tensile stress on the outer surface of the wall, the influence of the end effect on the expansion uniformity can be ignored if the distance between the first group of probe and the initiation point is more than 3 times the armature diameter.

Study and Comparison of Swelling and Compressibility Characteristics of Crumb Marl, Flaky Marl with Attapulgite and Sandy Clay from the Diamniadio Urban Pole at the Oedometer

In Senegal, the Diamniadio, Sebikhotane and Bargny sector contains clay soils that are problematic for construction. In order to have more information on the behavior of the clay soils of Diamniadio, free swelling tests followed by load-discharge cycles were carried out according to standard NF P 94-090-1. These tests were carried out using an Oedometric device on the three samples from the study site (sandy clays with calcareous concretion, marls with crumbs and laminated marls with attapulgite) to apprehend their swelling aspects in saturated conditions. For the free swelling test, a determination of the different swelling phases will be carried out followed by a comparison of the rate of evolution of the phases for the three samples from the site. In the same vein, the compressibility characteristics of the samples will also be provided from load-unload Oedometric tests. Thereafter, we proceed to a comparison of the void index at the initial state of the samples after two charge-discharge cycles and the influence of the cycles on the reorganization of the internal structure of the samples. These studies will provide more information on the swelling behavior of Diamniadio soils in the presence of water.

宝兰客专第三系泥岩物性参数与力学特性研究

研究目的:膨胀性地层中隧道施工是一个较难的工程问题,本文以宝兰客专北二十里铺隧道的膨胀性及地下水情况测试为基础,对泥岩膨胀特性等展开深入的研究,有利于明确泥岩膨胀对隧道内轨道变形的影响,完善隧道设计理论。研究结论:(1)第三系泥岩具有弱膨胀性;(2)膨胀岩的弹性模量和单轴抗压强度、单轴抗拉强度、三轴抗压强度在浸水后都呈现出明显的降低,随着浸泡时间的增加,各强度降低的速率逐渐下降;(3)单轴压缩试验表明,平均单轴抗压强度由29.18 MPa减少为4.65 MPa,衰减了84%,平均弹性模量由2.32 GPa减小为0.85 GPa,减小了63%;巴西劈裂试验表明,膨胀岩的平均抗拉强度由2.66 MPa减少为0.36 MPa,衰减了86.5%;三轴压缩试验表明,随着浸水时间的不断增加,膨胀岩的内聚力出现大幅的降低,尤其是在浸水初期下降迅速,由5.82 MPa降至1.34 MPa,减小了77%,膨胀岩的内摩擦角虽有所降低,但下降幅度不大,浸水15 d内总共降低4.07%;(4)本研究成果可为类似膨胀性泥岩铁路隧道设计提供参考。

涡轮压缩膨胀机的设计与性能分析

随着人们环境保护意识的加强,天然工质制冷剂重新受到研究人员的关注。空气是一种安全且对环境绝对友好的天然制冷剂,未来,压缩空气制冷循环有望成为传统蒸气压缩制冷循环的潜在替代品。压缩膨胀机作为压缩空气制冷的核心部件,其工作效率对机组性能有直接影响。为了设计出能够配合膨胀机高效工作的离心压缩机,需要对传统的设计方法进行一些修正。本文将质量、动量、能量守恒与射流尾迹区理论相结合,并将传统的离心压缩机相关参数推广到较低压力的范围中,提出了一种与现有的涡轮膨胀机相匹配的离心压缩机几何参数的设计方法。使用该方法为现有的膨胀机设计了对应的离心压缩机,并利用其他学者分析过的离心压缩机模型对该方法进行验证,利用计算流体力学方法(CFD)对压缩膨胀机变工况下的工作性能及对膨胀功的利用率进行模拟分析。按本方法设计的离心压缩机在设计工况下能够以高于92%的效率利用膨胀机的输出功。在变工况条件下能够以高于88%的效率利用膨胀机的输出功,并且在设计质量流量附近能够顺利运行。

钢纤维对自密实混凝土工作性能和抗压韧性影响的试验研究

纤维掺量是影响钢纤维增强自密实混凝土(SFRSCC)性能的重要因素之一.为研究钢纤维掺量对SFRSCC性能的影响,设计制作6组不同纤维掺量的试块,进行工作性能和轴心受压力学性能试验.结果表明,钢纤维能够有效延缓裂缝发展,提高混凝土峰值应变,等效抗压韧性指数随纤维掺量的增加而增大.钢纤维的掺加使得新拌合混凝土流动性降低,与流变特性相关的SFRSCC形状因子λ值低于普通自密实混凝土(SCC).钢纤维的掺加对SFRSCC抗压强度的影响不大,且随着纤维掺量增加,抗压强度呈现先减小后增大的特征.

基于响应面法的复合改良膨胀土无侧限抗压强度研究

为提高膨胀土的无侧限抗压强度,降低工程危害。在木质素改良膨胀土的研究基础上,通过单因素试验研究纤维长度、纤维掺量及木质素掺量对膨胀土抗压强度的影响规律,基于单因素试验结果,通过BBD (BOX-Behnken design)响应面设计法进行响应面试验,建立二次回归模型,研究了双因素交互作用对膨胀土无侧限抗压强度的影响。结果表明:单因素作用时,膨胀土无侧限抗压强度在各因素作用下均呈现先增大后减小的趋势;双因素交互作用时,木质素掺量和聚丙烯掺量二者交互作用显著性最好。由BBD响应面法得到的最优组合为:聚丙烯纤维长度为9 mm、纤维掺量为0.3%、木质素掺量为3%,该变量下平行试验组的平均抗压强度为552.48 kPa,相比于素膨胀的抗压强度提升了76.97%,可见此方案下对素膨胀土的无侧限抗压强度提升效果最好。研究成果为新乡地区弱膨胀土的改良提供了借鉴,为复合改良土的试验设计提供了新思路。

石灰-高炉矿渣改良膨胀土强度特性试验研究

因膨胀土具有吸水膨胀、失水收缩等不稳定性特征,使用高炉矿渣作为新型固化剂,并与无机材料石灰组合对膨胀土进行改良。对改良膨胀土开展自由膨胀率、液塑限、无侧限抗压强度和抗剪强度等指标的研究,探讨并分析了石灰-高炉矿渣(L-BLS)改良膨胀土在不同养护龄期以及不同改良剂掺量下的无侧限抗压强度变化规律。结果表明:使用L-BLS改良膨胀土能够显著提高膨胀土的早期强度;改良膨胀土的强度随养护龄期及改良剂掺量的增加而增强;当掺入6%石灰及9%高炉矿渣时,对应龄期的无侧限抗压强度最大,材料的有效利用率最佳。

基于朗肯热力循环模型修正的热电厂热耗改进分析与实践

朗肯循环是热力发电厂的典型热力循环之一,主要包括等熵压缩、等压加热、等熵膨胀以及等压冷凝4个热力过程。在分析朗肯循环的基础上,结合实际工程案例,对4个热力过程进行优化和修正,提高了发电厂朗肯循环的效率,并结合《ASME PTC46电厂整体性能试验标准》,运用简单的Excel软件开发了机组效率分析软件,对发电厂蒸汽循环过程进行了详细的分析诊断,找出机组效率折损点以及优化提升方向。通过检修工作逐一落实热耗改进方案,实现了机组高效运行,节省热耗支出约2263万美元。

颈椎后路单开门椎管扩大成形术与颈椎后路双开门椎管扩大成形术治疗多节段压迫性颈脊髓病的效果分析

目的:比较颈椎后路单开门椎管扩大成形术与颈椎后路双开门椎管扩大成形术治疗多节段压迫性颈脊髓病的效果。方法:选取2018年2月—2023年1月北京丰台医院收治的84例多节段压迫性颈脊髓病患者作为研究对象,随机分为单开门组和双开门组,各42例。单开门组采用单开门椎管扩大成形术治疗,双开门组采用双开门椎管扩大成形术治疗。比较两组治疗效果。结果:双开门组手术时间短于单开门组,术中出血量少于单开门组,差异有统计学意义(P<0.001)。术前、术后,两组上肢运动功能、下肢运动功能、感觉功能、膀胱功能评分及总分比较,差异无统计学意义(P>0.05);术后,两组上肢运动功能、下肢运动功能、感觉功能、膀胱功能评分及总分高于术前,差异有统计学意义(P<0.001)。术前、术后,两组颈椎曲度、疼痛评分比较,差异无统计学意义(P>0.05);术后,两组颈椎曲度小于术前,疼痛评分低于术前,差异有统计学意义(P<0.001)。结论:颈椎后路单开门椎管扩大成形术与颈椎后路双开门椎管扩大成形术治疗颈脊髓病均可取得较好效果,但颈椎后路双开门椎管扩大成形术手术时间更短,术中出血量更少。

硫酸亚铁对铝酸盐水泥浆体性能及水化产物的影响

铁相对水泥混凝土耐久性具有显著的积极作用,为拓宽铁相来源,本文研究了铁盐对铝酸盐水泥性能及水化产物的影响。通过将铝酸盐水泥和硫酸盐(二水石膏和硫酸亚铁)复合,使铝酸盐水泥水化生成以钙矾石为主的产物,在此基础上,研究了硫酸盐中硫酸亚铁比例对铝酸盐水泥浆体凝结时间、抗压强度以及体积稳定性的影响规律,并采用XRD和SEM分析水化产物类型以及微观形貌,阐明硫酸亚铁对水泥浆体性能的影响机理。结果表明:适量的硫酸盐可提升铝酸盐水泥浆体的抗压强度;硫酸亚铁对铝酸盐水泥表现出轻微的促凝作用,对膨胀率具有显著的抑制作用;硫酸亚铁对钙矾石的形成具有明显的抑制作用,适量的硫酸亚铁使得所生成的钙矾石尺寸较小,且分布均匀,有利于提升硬化浆体的抗压强度。

压合衬套冷挤压强化的残余应力的数值模拟

孔用衬套冷挤压强化的残余应力分布对实现优异的挤压效果起到重要的作用,而被挤压件材料和挤压量对挤压残余应力分布的影响显著。根据非线性接触摩擦理论,建立了基于压合衬套冷挤压强化的三维有限元模型,模拟获得了TB6钛合金、7050铝合金及TC4钛合金材料耳片孔强化的切向残余应力分布情况,并通过残余应力检测实验验证了有限元模拟的有效性;同时,研究了挤压量对耳片孔冷挤压强化残余应力状态的影响,揭示了切向残余应力沿着挤入面、中间面、挤出面以及衬套厚度方向的分布规律。研究结果表明:冷挤压孔强化后的残余应力在沿孔壁厚度方向上分布不均匀,切向残余压应力在中间面的分布区域最广;增大挤压量可以在一定程度上扩大压应力的分布范围,且能够提高区域压应力数值,但是也会引入部分拉应力,易产生褶皱现象;在相同的挤压条件下,TB6钛合金耳片冷挤压后所产生的切向残余压应力在应力数值和分布区域上都具有明显的优势。

基于响应面法的膨胀性充填体强度演化规律及配比优化

针对某铁矿采场充填接顶率低和接顶效果差的问题,通过添加复合膨胀剂可实现采场主动接顶.采用响应面法,借助Design-Expert软件中的Box-Behnken design(BBD)方法,开展了膨胀性充填体强度配比试验,研究了料浆质量分数、胶固粉质量分数和复合膨胀剂质量分数对膨胀性充填体抗压强度的影响规律.结果表明,单一因素及各因素间交互作用对膨胀性充填体抗压强度均有显著影响,其中胶固粉质量分数影响最大,复合膨胀剂质量分数次之,料浆质量分数最小;料浆质量分数与胶固粉质量分数的交互作用对充填体的早、中期抗压强度影响最为显著,胶固粉质量分数与复合膨胀剂质量分数的交互作用对充填体的后期抗压强度影响最为显著.通过目标规划法确定了膨胀性充填体最优配比:料浆质量分数为69%,胶固粉质量分数为10%,复合膨胀剂质量分数为3×10^(-4).利用X射线衍射(XRD)和扫描电镜(SEM)分析发现,复合膨胀剂可使充填体的内部结构疏松而引起膨胀,提高充填接顶率.

考虑初始饱和度影响的冻结渠坡膨胀土力学特性

为探究初始饱和度对渠坡膨胀土低温力学特性的影响,以不同初始饱和度渠坡膨胀土为研究对象,通过开展试验温度分别为-2℃、-5℃、-10℃和-15℃下的无侧限抗压强度试验,研究温度与初始饱和度对渠坡膨胀土强度及变形特征的影响。试验结果表明:试样的应力-应变曲线随初始饱和度的增加逐渐从软化型过渡到硬化型,两种不同类型的应力-应变关系可分别采用双曲线方程和复合指数本构方程来描述;试样的破坏形态根据其破坏特征可划分为垮塌破坏、鼓胀破坏和整体压缩破坏3种形式;-2℃下,试样的抗压强度整体随初始饱和度的增加而减小,但在-5℃、-10℃和-15℃下,试样的抗压强度随着初始饱和度的增加先增大后减小,也即存在一个“临界饱和度”使得试样的抵抗破坏能力最强,并且该“临界饱和度”随着试验温度的降低而减小;此外,随着试验温度的降低,试样的弹性模量和抗压强度均逐渐增大,但试样的硬化模量却呈现出先增大后减小的变化规律。