STUDY OF THREE-SHEAR STRESS UNIFIED STRENGTH THEORY

材料强度理论研究是高等材料力学的一个重要研究领域,200多年来,各国学者提出了许多强度理论及试验研究结果.这些理论都是从不同的假设和力学模型出发,推导出不同的数学表达式,但一般只适用于某一类特定的材料.各种强度理论之间是否有联系?是否可能建立一个广泛适用的统一强度理论?自19世纪末以来,世界各国学者都在努力寻求建立统一强度理论,但一直没有成功.本文应用理论研究和试验验证相结合的方法,提出并验证了三剪应力统一强度理论。认为当作用于菱形十二面单元体上的三个主剪应力及其作用面上的三个正应力的函数达到某一极限值时,材料发生破坏.三剪应力统一强度理论是全应力理论,它用一个统一的线性表达式包含或逼近了现有的和其他新的各种单一和统一、线性和非线性、外凸和非凸的强度理论,形成了以单剪强度理论为下限、而以三剪应力强度理论为上限的一系列强度理论的新体系,实现了外凸强度理论和非凸强度理论的高度统一,使强度理论从适用于某一类材料、某种应力状态的单一强度理论发展为可以适用于各种材料及不同应力状态的统一强度理论,并能更大程度地发挥材料的强度潜力.通过与大量试验结果的对比分析表明：三剪应力统一强度理论可以广泛适用于各种材料及其不同的应力状态.     

A simulation-based analysis of the effect of a reflecting surface on aeroacoustic time-reversal source characterization and comparison with beamforming

This paper presents a simulation-based analysis of the effect of a reflecting surface on aeroacoustic Time-Reversal (TR) source localization/characterization and compares the results of TR with those obtained using cross-spectral Conventional Beamforming (CB). The TR technique is shown to require the use of at least two line arrays of microphones to accurately characterize the nature of aeroacoustic sources. This work, however, shows that in the presence of a rigid surface, only one line array of microphones is sufficient to accurately localize and characterize idealized aeroacoustic sources. Forward simulations were carried out using the 2-D Linearized Euler Equations on a rectangular domain with a rigid bottom boundary (modeling a 2-D semi-infinite space) for the test-cases of stationary idealized tonal aeroacoustic (monopole, dipole and lateral quadrupole) sources located in a fully-developed mean shear flow field wherein the acoustic pressure time–history was stored at the computational boundaries. A set of TR simulations are implemented that show for each test-case that only the top line array is required to accurately characterize the idealized aeroacoustic sources in the presence of a reflecting bottom boundary, thereby suggesting the redundancy of acoustic pressure measurement at the rigid surface. The test-case of convecting (moving) idealized aeroacoustic source was also considered and the TR simulation using only the top line array in the presence of reflecting bottom boundary was able to accurately retrieve the source trajectory and simultaneously characterize its nature. This numerical experiment demonstrates in principle that when a rigid surface is mounted on the floor of an Anechoic Wind Tunnel, the use of only one (top) line array of microphones should be sufficient to characterize the nature and location of experimental flow-induced noise source. Acoustic source maps were also obtained using the CB method based on the Method of Images (to model the reflecting surface) and incorporation of the Ray-Tracing algorithm necessary to account for the effect of mean flow. The CB results were found to be highly comparable to those obtained using TR for the test-cases of non-convecting sources; thereby demonstrating the conceptual equivalence of the Method of Images and directly implementing the rigid-wall condition during TR for source localization/characterization.     

基于Oda裂隙结构张量的流纹岩各向异性试验研究

岩石内天然存在长度、倾角和形态不同的裂隙,造成岩石的各向异性特征。为揭示岩石内天然随机裂隙发育特征对岩石物理力学特性的影响规律,以泥巴山隧址区采集裂隙性流纹岩为研究对象,首先对试样裂隙进行素描统计分析;然后基于Oda裂隙结构张量,获得天然随机分布裂隙的几何统计参数;最后对裂隙性流纹岩试样分别进行单轴和常规三轴压缩试验,得到不同应力路径下流纹岩的应力-应变曲线及物理力学参数。分析Oda裂隙结构张量定义的各向异性参数与试验获得的力学参数之间的规律,研究结果表明:(1)Oda裂隙结构张量适用于天然随机分布裂隙的几何统计分析,各向异性参数A(F)越大,裂隙优势方向越明显;(2)单轴压缩下,随着各向异性参数I1和A(F)的增大,流纹岩各向异性程度增大,弹性模量减小,泊松比增大;(3)常规三轴压缩下,流纹岩弹性模量和泊松比随各向异性参数改变的规律较不明显,Oda裂隙结构张量不再适用。     

πg9/2(⊕)vh11/2 doublet bands in A～100 mass region

Using the model with one particle and one hole coupled with a triaxial rotor, the πg(-1)(9/2)(⊕)vh11/2 doublet bands in the A ～ 100 mass region are studied, and compared with the πh11/2(⊕)vh(-1)(11/2) doublet bands.It is found that the calculated results for the configuration of πg(-1)(9/2)(⊕)vh11/2 are very similar the results for a pure h11/2 proton particle and a neutron quasiparticle with λn =ε5. After including the pair correlation, the model describes the candidate chiral doublet bands in 106Rh successfully, which supports the interpretation of chirality geometry.     

Lifetime measurements in chiral nucleus 130Cs

The level lifetimes in partner bands of 130Cs have been measured using the Doppler Shift Attenuation method. The high-spin states of 130Cs were populated via fusion evaporation reaction 124Sn(11B,5n)130Cs at a beam energy of 65 MeV. The absolute M1 and E2 transition probabilities have been deduced. The results indicate that the partner bands of 130Cs manifest the chiral properties.     

Interactions between cationic gemini/conventional surfactants with polyvinylpyrrolidone: Specific conductivity and dynamic light scattering studies

The interaction between bis(hexadecyldimethylammonium)hexane dibromide (16-6-16), bis(tetradecyldimethylammonium)hexane dibromide (14-6-14), their conventional counterparts cetyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB) with polyvinylpyrrolidone (PVP) was investigated using the conductivity technique. The results show that gemini surfactants interact strongly with PVP as compared to conventional surfactants. The results also reveal that the surfactants with shorter hydrocarbon chain interact weakly as those of longer hydrocarbon chain. The interactions of 16-6-16 and 14-6-14 and their conventional counterparts with PVP were also studied using dynamic light scattering (DLS) measurements. We have also highlighted the effect of surfactant–polymer interactions on the dispersion force in the solution. Critical aggregation concentration (cac) and critical micelle concentration (cmc) were obtained using the conductivity data. The degrees of micelle ionization and free energies associated with aggregation, micellization, and transfer have also been evaluated and discussed.     

Selectivity differences between alkyl and polar‐modified alkyl phases in reversed phase high performance liquid chromatography

Compared to conventional C18 phases, polar‐modified phases have distinct differences with regards to chromatographic behavior. In the present study, ODS phases and polar‐modified phases were synthesized. The columns containing these new packings demonstrated satisfactory stability under both acidic (pH 1.5) and basic (pH 10) conditions. We evaluated the selectivity differences between alkyl and polar‐modified alkyl RP columns by using a range of neutral analytes. The polar‐modified alkyl phases showed excellent peak shapes for almost all compounds. We also compared the selectivity differences between them for separating nucleotides by using 100% aqueous mobile phase and tricyclic antidepressants in the intermediate pH mobile phases. The results demonstrated that polar‐modified phases display a significantly reduced hydrophobic nature and a significantly reduced silanol activity compared to the conventional C18 phases.     

On the performance of a virtual user pairing scheme to efficiently utilize the spectrum of unpaired users in NOMA

This paper evaluates the performance of a virtual user pairing scheme that efficiently utilizes the spectrum of unpaired users in non-orthogonal multiple access (NOMA), termed as VP-NOMA. The scheme aims at utilizing the frequency bands of those users which remain unpaired due to the non-uniform distribution of users in a cellular area. We consider a case where the cell edge users are more than the cell center users, so that complete one-to-one correspondence does not exist between all cell center and cell edge users to be accommodated/paired using conventional NOMA (C-NOMA) user pairing. Thus, some cell edge users remain unpaired, and are served using conventional multiple access (OMA) schemes. In such scenario, VP-NOMA pairs a single cell center user with two or more clustered (closely located) cell edge users over non-overlapping frequency bands, thus enabling the cell center user to efficiently use the frequency bands of these previously unpaired cell edge users. Performance of VP-NOMA in terms of ergodic sum capacity (ESC), outage probability (OP), and outage sum capacity (OSC), is analyzed through comprehensive mathematical derivations and simulations for a generalized system model. Moreover, the mathematical analysis is validated through close concordance between analytical and simulation results of ESC, OP, and OSC.     

基于三维Hopkinson杆的混凝土动态力学性能研究

混凝土、岩石类材料在复杂应力状态下的动态力学性能研究一直备受关注,但鉴于动态实验的复杂性,对真三轴应力状态下材料的动态加载一直未曾实现。本文中研制了一套真三轴静载作用下混凝土、岩石类材料的“三维Hopkinson杆”动态力学实验系统,为冲击载荷作用下材料动态各向异性特性的研究提供了一种有效的实验测试技术。该系统采用液压伺服控制对立方体试件施加三向独立的0~100 MPa真三轴静载,再利用分离式Hopkinson压杆对试件施加冲击动载,具体研究了C30混凝土材料在不同真三轴静载条件下的动态压缩性能,得到了不同条件下X、Y、Z方向上的动态应力应变关系。     

三轴应力下花岗岩加载破坏的能量演化和损伤特征

为揭示不同围压下硬岩在破坏过程中的力学性质和能量演化规律,基于RMT-150B岩石力学试验系统对花岗岩试样进行不同围压条件下常规三轴压缩试验。研究结果表明:岩样的峰值应力和围压具有较强的线性关系,利用Mohr-Coulomb强度准则求出花岗岩的黏聚力为23.548 MPa,内摩擦角为57.629°。围压对花岗岩加载破坏过程中能量演化的影响显著,岩石的峰值能量、弹性应变能以及耗散能都随着围压的增大而增大,且两者呈线性增加关系。根据岩石的线性储能规律,提出了确定岩石应力阈值的方法。围压越大,起裂应力和扩容应力越大,且岩样起裂点处与扩容点处的能量也越大;当围压较低时,岩石破坏前储存的能量较少,破坏时能量释放速率低,岩样表现为典型低劈裂破坏;在高围压情况下,能量快速释放,岩样表现为剪切破坏。基于能量演化规律,提出了岩石损伤演化模型,得到了花岗岩的损伤变量D在不同围压下加载破坏过程中的演化规律。