Influences of Different Habitats on Asexual Propagation of Wild Gastrodia elata f. glauca being Domesticated in Ganzi

[Objective] The influences of different habitats on asexual propagation of wild Geg(abbreviation for Gastrodia elata Bl. f. glauca S. Chow) being domesticated in Ganzi prefecture was studied. [Method] The research trial was carried out in the following three kinds of habitats at the same time: the plastic greenhouses, the birch forest of shady slope and the shrubbery of sunny slope, and the results were analyzed with group data average hypothesis test method. [Result] The overall tuber(the juvenile tuber, the immature tuber and the mature tuber) yield and the mature tuber yield were both very significantly higher in the plastic greenhouses than in the other two types of habitats, and respectively reached 9.52 and 6.70 kg/m2; the mature tuber drying rate was dramatically or very dramatically lower in the plastic greenhouses than in the other two types of habitats, and was 23.84%; the stabilities of the overall tuber yield, the mature tuber yield and the drying rate were all reduced in the order of greenhouses, birch forest and shrubbery; and the dry mature tuber yield of the plastic greenhouses was the highest in the three kinds of habitats, and was 1.60 kg/m2. [Conclusion] A good habitat had to be created or chosen in the domesticating cultivation of the wild Geg in Ganzi prefecture. The preferred choice was the plastic greenhouse, the alternative one was the deciduous broadleaved forest of shady slope. The imitating wild planting of the wild Geg should be done in the warm moist deciduous broad-leaved forest of shady slope.

Effect of Tree Species and Dosage of Rhizomorph Wood on Asexual Propagation of Wild Gastrodia elata. Bl. f. glauca S. Chow in Ganzi

The effects of the tree species and the dosages of Armillariella mellea rhizomoph wood on asexual propagation of wild Gastrodia elata Bl. f. glauca S. Chow were studied in Ganzi prefecture. The results showed that tree species had a very significant effect on asexual reproduction yield of wild Gastrodia elata Bl. f. glauca S. Chow. The drying rate and yield of Gastrodia elata Bl. f. glauca S. Chow cultured by close grained woods such as Quercus spinosa David ex Fr. was extremely significant higher than that cultured by coarse grained wood such as Betula platyphylla Suk. The dosage had a very significant effect on the yield of wild Gastrodia elata Bl. f. glauca S. Chow whereas it had no influence on the drying rate.

Vibration and wave propagation analysis of twisted micro-beam using strain gradient theory

In this research, vibration and wave propagation analysis of a twisted micro- beam on Pasternak foundation is investigated. The strain-displacement relations （kine-matic equations） are calculated by the displacement fields of the twisted micro-beam. The strain gradient theory （SGT） is used to implement the size dependent effect at micro-scale. Finally, using an energy method and Hamilton＇s principle, the governing equations of motion for the twisted micro-beam are derived. Natural frequencies and the wave prop- agation speed of the twisted micro-beam are calculated with an analytical method. Also, the natural frequency, the phase speed, the cut-off frequency, and the wave number of the twisted micro-beam are obtained by considering three material length scale parameters, the rate of twist angle, the thickness, the length of twisted micro-beam, and the elastic medium. The results of this work indicate that the phase speed in a twisted micro-beam increases with an increase in the rate of twist angle. Moreover, the wave number is in- versely related with the thickness of micro-beam. Meanwhile, it is directly related to the wave propagation frequency. Increasing the rate of twist angle causes the increase in the natural frequency especially with higher thickness. The effect of the twist angle rate on the group velocity is observed at a lower wave propagation frequency.

Wave propagation responses of porous bi-directional functionally graded magneto-electro-elastic nanoshells via nonlocal strain gradient theory

This study examines the wave propagation characteristics for a bi-directional functional grading of barium titanate(BaTiO_(3)) and cobalt ferrite(CoFe_(2)O_(4)) porous nanoshells,the porosity distribution of which is simulated by the honeycomb-shaped symmetrical and asymmetrical distribution functions.The nonlocal strain gradient theory(NSGT) and first-order shear deformation theory are used to determine the size effect and shear deformation,respectively.Nonlocal governing equations are derived for the nanoshells by Hamilton's principle.The resulting dimensionless differential equations are solved by means of an analytical solution of the combined exponential function after dimensionless treatment.Finally,extensive parametric surveys are conducted to investigate the influence of diverse parameters,such as dimensionless scale parameters,radiusto-thickness ratios,bi-directional functionally graded(FG) indices,porosity coefficients,and dimensionless electromagnetic potentials on the wave propagation characteristics.Based on the analysis results,the effect of the dimensionless scale parameters on the dispersion relationship is found to be related to the ratio of the scale parameters.The wave propagation characteristics of nanoshells in the presence of a magnetoelectric field depend on the bi-directional FG indices.

Crack evolution behavior of rocks under confining pressures and its propagation model before peak stress

The understanding of crack propagation characteristics and law of rocks during the loading process is of great significance for the exploitation and support of rock engineering.In this study,the crack propagation behavior of rocks in triaxial compression tests was investigated in detail.The main conclusions were as follows:1)According to the evolution characteristics of crack axial strain,the differential stress?strain curve of rocks under triaxial compressive condition can be divided into three phases which are linear elastic phase,crack propagation phase,post peak phase,respectively;2)The proposed models are applied to comparison with the test data of rocks under triaxial compressive condition and different temperatures.The theoretical data calculated by the models are in good agreement with the laboratory data,indicating that the proposed model can be applied to describing the crack propagation behavior and the nonlinear properties of rocks under triaxial compressive condition;3)The inelastic compliance and crack initiation strain in the proposed model have a decrease trend with the increase of confining pressure and temperature.Peak crack axial strain increases nonlinearly with the inelastic compliance and the increase rate increases gradually.Crack initiation strain has a linear relation with peak crack axial strain.

FATIGUE CRACK PROPAGATION FOR BIAXIAL STRESS CYCLING

Based on the experimental study of complex biaxial mode Ⅰ fatigue crack growth and the discussion on Von Mises'theory,a new approach is proposed for correlating crack propaga- tion rate under both in-phase and out-of-phase biaxial stress cycling.The results emphasize the contribution of plasticity to fatigue crack growth.

Integrating Test Data and ATBM Simulations into Dose Propagation Uncertainty Formulation for Bone Fracture Risk Assessment

We consider the problem of assessing bone fracture risk for a subject hit by a blunt impact projectile. We aim at constructing a framework for integrating test data and Advanced Total Body Model (ATBM) simulations into the risk assessment. The ATBM is a finite element model managed by the Joint Non-Lethal Weapons Directorate for the purpose of assessing the risk of injury caused by blunt impacts from non-lethal weapons. In ATBM simulations, the quantity that determines arm bone fracture is the calculated maximum strain in the bone. The main obstacle to accurate prediction is that the calculated strain is incompatible with the measured strain. The fracture strain measured in bending tests of real bones is affected by random inhomogeneity in bones and uncertainty in measurement gauge attachment location/orientation. In contrast, the strain calculated in ATBM simulations is based on the assumption that all bones are perfectly elastic with homogeneous material properties and no measurement uncertainty. To connect test data and ATBM simulations in a proper and meaningful setting, we introduce the concept of elasticity-homogenized strain. We interpret test data in terms of the homogenized strain, and build an empirical dose-injury model with the homogenized strain as the input dose for predicting injury. The maximum strain calculated by ATBM has randomness due to uncertainty in specifications of ATBM setup parameters. The dose propagation uncertainty formulation accommodates this uncertainty efficiently by simply updating the shape parameters in the dose-injury model, avoiding the high computational cost of sampling this uncertainty via multiple ATBM runs.

A new mixed-mode phase-field model for crack propagation of brittle rock

Study on crack propagation process of brittle rock is of most significance for cracking-arrest design and cracking-network optimization in rock engineering.Phase-field model(PFM)has advantages of simplicity and high convergence over the common numerical methods(e.g.finite element method,discrete element method,and particle manifold method)in dealing with three-dimensional and multicrack problems.However,current PFMs are mainly used to simulate mode-I(tensile)crack propagation but difficult to effectively simulate mode-II(shear)crack propagation.In this paper,a new mixed-mode PFM is established to simulate both mode-I and mode-II crack propagation of brittle rock by distinguishing the volumetric elastic strain energy and deviatoric elastic strain energy in the total elastic strain energy and considering the effect of compressive stress on mode-II crack propagation.Numerical solution method of the new mixed-mode PFM is proposed based on the staggered solution method with self-programmed subroutines UMAT and HETVAL of ABAQUS software.Three examples calculated using different PFMs as well as test results are presented for comparison.The results show that compared with the conventional PFM(which only simulates the tensile wing crack but not mode-II crack propagation)and the modified mixed-mode PFM(which has difficulty in simulating the shear anti-wing crack),the new mixed-mode PFM can successfully simulate the whole trajectories of mixed-mode crack propagation(including the tensile wing crack,shear secondary crack,and shear anti-wing crack)and mode-II crack propagation,which are close to the test results.It can be further extended to simulate multicrack propagation of anisotropic rock under multi-field coupling loads.

Characteristics and mechanisms of strain waves generated in rock by cylindrical explosive charges

A superposing principle, by suitably adding the strain waves from a number of concentrated explosive charges to approximate the waves generated by a cylindrical charge based on the strain wave of a point or small spherical explosive charge generated in rock, is used to further study the triggering time of strain gauges installed in radial direction at same distances but different positions surrounding a cylindrical explosive charge in rock. The duration of the first compression phase and peak value of strain wave, and furthermore, their differences are analyzed and some explanations are given. Besides that, the gauge orientation in which the maximum peak value occurs is also discussed. At last, the effect of velocity of detonation(V.O.D.) of a cylindrical explosive charge on the strain waves generated in the surrounding rock is taken as key research and the pattern of peak amplitude of a strain wave varies with the V.O.D. is likely to have been found.

THE ASYMPTOTIC SOLUTION TO THE ANTIPLANE SHEAR DYNAMICCRACK-TIP FIELD IN AN ELASTIC STRAIN-SOFTENING VISCOPLASTIC MATERIAL

The elastic strain softening-viscoplastic model is given in this paper. Using this model, the asymptotic stress and strain equations surrounding the tip of a propagating crock are given and numerical results ale obtained under antiplane shear. The analysis and calculation show that at the crack tip the strain possesses logarithmic singularity (ln(R/r))(1/(n+1)) while the stress is like (ln(R/r))(-n/(n+1)), therefore the asymptotic behaviour of the elastic strain-softening viscoplastic field is revealed under the antiplane shear.

STRAIN-GRADIENT STRESS ANALYSIS IN SAINT-VENANT BENDING

Light beam deflections caused by stress or strain gradients are inves- tigated analytically and experimentally in homogeneous beam specimens which are subjected to a particular case of flexure with shear. This study is a generalization of the prior an alytical-experimental examination of strain-gradient light deflections produced in stressed plates, which had concentrated on the simplest case where in- formation of interest is collected along a line of symmetry of the stress field. Main purpose of the present investigation is to document the efficacy of the strain-gradient method in analysis of the general case of stress state. The most interesting stress state is that in a beam subjected to the Saint-Venant bending, where the transversal and the longitudinal axes of the beam are in pure shear. The obtained results are compared with the predictions of the developed analytical models and with the pre- dictions of Filon's stress function. The procedures of evaluating the photoelastic and material coefficients using strain-gradient techniques were tested positively.

干湿循环作用下压实黄土裂隙演化特征

为了解干湿循环作用下压实黄土裂隙演化规律,通过自制装置开展考虑不同干密度和干湿循环路径的干湿循环裂隙试验,获取土样表面裂隙发育图像。采用PCAS软件对土样裂隙进行定量化分析,获得裂隙形态特征参数,并结合数字图像相关(DIC)法获得土样应变场。结果表明:①压实黄土裂隙发育随干湿循环次数的增长可划分为裂隙缓慢发展、快速增长和裂隙缓滞发展3个阶段;②裂隙发育程度受干密度、干湿循环路径共同影响,干密度越大,裂隙越难发育,干湿循环幅度越大、下限含水量越低,裂隙发育越充分;③裂隙中心线部位第一主应变随距起裂点距离的增大呈线性减小趋势,裂隙尖端、裂隙临近区块土体所受挤压作用随远离裂隙程度增大而减弱。研究成果可为压实黄土裂隙演化特征分析提供参考。

氯离子质量浓度对Inconel 740H合金应力腐蚀开裂性能的影响

采用慢应变速率拉伸试验和应力腐蚀裂纹扩展试验方法,研究了630~700℃高参数先进超超临界机组候选镍基合金Inconel 740H在0、1、20 mg/L氯离子水环境中的应力腐蚀开裂性能及规律,并探讨了高质量浓度氯离子促进应力腐蚀裂纹的萌生和扩展的相关机理。结果表明:高质量浓度氯离子促进740H合金的应力腐蚀开裂,合金应力腐蚀敏感性指数断后伸长损失I_(scc(δ))随氯离子质量浓度升高而增大;当氯离子质量浓度升高至20 mg/L时,断口中部和断口边缘均呈沿晶脆性断裂特征,断口附近有大量沿晶二次裂纹,此时合金发生了应力腐蚀开裂。在20 mg/L氯离子水环境中裂纹平均扩展速率达1.15×10^(–6) mm/s,是高纯水中裂纹平均扩展速率的111.7倍。

不同含水状态砂岩裂纹稳定扩展阶段损伤特征

为深入揭示裂纹稳定扩展阶段的岩石损伤状态,以干燥、自然和饱水状态砂岩为研究对象,采用体积应变法测定起裂应力和损伤应力值,进一步通过增量循环加卸载试验,综合分析了裂纹稳定扩展阶段的残余应变、变形模量和能量演化规律。结果表明:轴向残余应变随轴向应力水平增加而增加,其增幅表现为先减小、后稳定、再增大,且增幅稳定阶段对应于裂纹稳定扩展阶段;在裂纹稳定扩展阶段,加载过程和卸载过程变形模量均呈线性减少趋势,而耗散能密度呈线性增加趋势。上述演化规律适用于不同含水状态砂岩,但其具体数值与含水率有关。对于裂纹稳定扩展阶段,加载过程变形模量可有效表征砂岩损伤状态,基于含水率和轴向应力水平的线性数学模型可用于评价工程岩体的实际损伤状态。

单轴压缩过程中冻结砂岩的损伤局部化规律研究

损伤局部化是岩石受荷破坏过程中的必经阶段和破坏前兆特征。本文研究冻结岩石受荷破坏过程中的损伤局部化规律,并探讨初始饱和度的影响。在-20℃下对具有不同初始饱和度的冻结砂岩试样进行单轴压缩试验,并采用数字图像相关(DIC)和声发射(AE)系统采集试验过程中的表面变形和声发射信号,分析了试样表面应变局部化模式与内部微裂纹扩展类型。结果表明:(1)初始饱和度令试样的单轴抗压强度产生阶段性变化,并改变了试样各加载阶段占比和破裂过程中的声发射振铃计数分布特征;(2)以40%初始饱和度为转折点,试样的表面应变局部化模式由拉应变为主变为剪应变为主,初始饱和度超过90%时出现了拉、剪应变同时发展的混合模式,并能与试样的最终破坏形态对应;(3)损伤局部化过程中,试样内部的微裂纹扩展类型与表面应变局部化模式基本吻合。最后,结合不同初始饱和度下冻结岩石孔隙中的相组成分变化,分析了其对冻结岩石损伤局部化模式的影响。本研究有助于加深研究人员对冻结岩石力学性质的认识,为寒区岩石工程破坏与失稳预测提供重要参考。

粘弹性基底上功能梯度压电纳米梁波传播特性

本文利用非局部应变梯度理论(NSGT)探究了含粘弹性基底的功能梯度压电(FGP)纳米梁的波传播特性.基于NSGT,建立含粘弹性基底的Euler梁波传播模型及考虑剪切效应的Timoshenko梁模型,利用哈密顿原理推导出波传播控制方程;通过引入两种梁变形理论对应的波传播通解方程,对运动方程组进行求解,探讨了剪切效应、尺度参数、粘弹性参数、FG指数等对波传播频率及相速度的影响.研究表明:尺度参数对波传播频率的影响与波数密切相关;电压与梯度指数对两种梁波传播特性影响程度不同;粘弹性基底参数对波传播频率有明显的影响,且其影响程度与波数密切相关.

平面拉伸下聚氨酯裂纹板的裂纹扩展研究

聚氨酯(PU)因具有优异的物理化学性能,常用于一般工业与民用建筑中的屋面、地下室、浴室、卫生间地面等防水工程,但在长期服役过程中,难免会产生裂纹或微孔等缺陷,裂纹地萌生与扩展将劣化材料的使用性能,降低材料构件的承载力,甚至导致结构失效或安全事故。本文通过平面拉伸试验,探究了不同拉伸速率下聚氨酯裂纹板的力学性能及其裂纹扩展规律,研究结果表明,拉伸速率对裂纹板的应力应变关系、断裂失效时间以及裂纹扩展规律均有一定影响。

莓叶委陵菜叶插繁殖技术研究

莓叶委陵菜(Potentilla fragarioidis)作为我国北方地区极具开发潜力的乡土地被植物,存在着有性繁殖材料不易获得且繁殖系数较低的问题。而扦插繁殖作为一种无性繁殖手段,能为莓叶委陵菜的快速繁殖提供新的途径。本研究以莓叶委陵菜生长健壮、无病虫害的叶为试验材料,通过正交试验针对不同扦插基质、激素种类及其浓度对莓叶委陵菜叶插生根效果的影响进行探究。结果表明,莓叶委陵菜插穗在扦插45 d后能够形成根系,不同处理水平的扦插基质、激素种类及其浓度间的交互效应对插穗生根效果的影响具有显著差异(P<0.05)。扦插基质是影响莓叶委陵菜叶插生根率的主导因子,而激素种类是影响平均单株生根数、平均单株总根长、最长根长和根系效果指数的主要因素。以草炭+珍珠岩+蛭石(1:1:1)为基质,扦插前使用300 mg·L^(-1)的IBA对插穗进行处理生根效果最佳,该处理方式下扦插生根率达63.33%,平均单株生根数为6.90条,平均单株总根长为27.98 cm,最长根长13.83 cm,根系效果指数达20.50。本研究结果可为莓叶委陵菜无性系繁殖体系的快速建立提供理论依据。

多孔功能梯度压电纳米壳中波传播特性

基于非局部应变梯度理论,探究了含孔隙的功能梯度压电陶瓷纳米壳中波传播特性.利用Hamilton原理和一阶剪切理论推导了控制方程.结合非局部应变梯度理论和谐波解得到了尺度依赖的特征方程.数值讨论了尺度参数、波数、梯度指数、壳厚、孔隙率及电压对波传播特性的影响.研究表明:非局部参数和应变梯度参数对波传播频率的影响与波数密切相关,在一定范围内波数越大,尺度参数对频率的影响越大;另外,孔隙和梯度指数对频率具有耦合作用.

仿生柔性抗缺陷材料研究进展

在众多人造材料中,强度和韧性是相互制约的,如何使材料在具有高强度的同时兼具较高的韧性,其关键在于通过结构设计赋予材料较强的抗缺陷能力。大自然中存在很多种能够兼顾高强度和高韧性的材料,而这类材料往往具有独特的天然抗缺陷结构,为合成材料的设计与制造提供了丰富灵感。本文介绍了材料抗缺陷特性的主要机理,综述了仿生高性能抗缺陷材料特别是柔性材料相关的研究进展。在天然抗缺陷原型的启发下,相关仿生材料也能兼顾高强度与高韧性等力学性能,进而实现材料承载能力和使用可靠性的提升。同时,本文对该领域的未来研究方向进行了展望。