Direct Assessment of Interlaminar Stresses in Composite Multilayered Plates Using a Layer-Wise Mixed Finite Element Model

An accurate determination of intedaminar transversal stresses in composite multilayered plates, especially near free-edge, is of great importance in the study of inter-ply damage modes, mainly in the initiation and growth of delamination. In this paper, interlaminar stresses are determined by layer-wise mixed finite element model. Each layer is analyzed as an isolated one where the displacement continuity is ensured by means of Lagrange multipliers （which represent the statics variables）. This procedure allows the authors to work with any single plate model, obtaining the interlaminar stresses directly without loss of precision. The FSDT （first shear deformation theory） with transverse normal strain effects included is assumed in each layer, but Lagrange polynomials are used to describe the kinematic instead of Taylor＇s polynomial functions of the thickness coordinates, as is common. This expansion allows the authors to pose the interlaminar displacements compatibility simpler than the second one. The in-plane domain of the plate is discretized by four-node quadrilateral elements, both to the field of displacement and to the Lagrange multipliers. The mixed interpolation of tensorial components technique is applied to avoid the shear-locking in the finite element model. Several examples were carried out and the results have been satisfactorily compared with those available in the literature.

Application of Nonlinear Lamb Wave Mixing Method for Residual Stress Measurement in Metal Plate

Harmonic nonlinear ultrasound can offer high sensitivity for residual stress measurements;however,it cannot be used for local stress measurements at a point in space and exhibits nonlinear distortions in the experimental system.This paper presents a feasibility study on the measurement of residual stress in a metal plate using a nonlinear Lamb wave-mixing technique.The resonant conditions for two Lamb waves to generate a mixing frequency wave are obtained via theoretical analysis.Finite element simulations are performed to investigate the nonlinear interactions between the two Lamb waves.Results show that two incident A0 waves interact in regions of material nonlinearity and generate a rightward S0 wave at the sum frequency.Residual stress measurement experiments are conducted on steel plate specimens using the collinear Lamb wave-mixing technique.By setting different delays for two transmitters,the generated sum-frequency component at different spatial locations is measured.Experimental results show that the spatial distribution of the amplitude of the sum-frequency component agrees well with the spatial distribution of the residual stress measured using X-rays.The proposed collinear Lamb wave-mixing method is effective for measuring the distribution of residual stress in metal plates.

A MIXED METHOD OF DETERMINING THETHERMAL STRESS FOR COLD ROLLER

A mixed method which combines the recent developed finite analytical method and the boundary fitting coordinate transformation method was used first to calculate the temperature field and thermal stress field of the cold roller in this paper. The following results are obtained by the calculation: thermal stresses σr=0, σθ=σz are maximum tension stress on the inner surface of the cold roller and σr=0, |σθ|=|σz| are maximum compression stress on the outer surface of the cold roller in the steady and unsteady case. Effectiveness and validity of the mixed method are checked with steady coil roller problems having theoretical solutions. The results show that good agreement is achived between the calculated value and theoretical solution,and the mixed method used in the paper is very workable. The mixed method is also useful in solving the steady and unsteady thermal stress field proplems of the hot -rolled for the reversing rolling mill and the continous rolling mill.

Effect of mixed-cropping and water-stress on macro-nutrients and biochemical constituents of rhizomatous medicinal plants in Central Himalaya,India

Plants in the alpine zone mainly depend on the reserved food materials stored in their rhizomes for the next growing season. We investigated the effect of mixed cropping （Phaseolus vulgaris L. var. Pinto） with four rhizomatous medicinal plants, i.e., Angelica glauca, Arnebia benthamii, Rheum emodi and Pleurospermum angelicoides as well as three levels of water stress treatment under two conditions （shade net and open field） on macronutrients （NPK） and biochemicals （carbohydrates and protein）. The experiment was conducted by completely randomized design （CDR）. The data were analyzed with ANOVA as well as CDR. The experimental results show that in all the species shade conditions with sever water stress （SSWS） increased the level of macronutrients （NPK）. However, （N） concentration was highest under shade with mixed cropping （SMIX）. Under SMIX, carbohydrate content was highest than open field control conditions （CONT）. This investigation results demon- strate that mixed cropping of medicinal plants with Phaseolus vulgaris could be a good livelihood option in the mountainous regions of Indian Central Himalaya. And the water-stress conditions along with mixed cropping could improve the biochemical constituents in the rhizome of these species.

Peierls stress for <110>{001} mixed dislocation in SrTiO_3 within framework of constrained path approximation

The core structure of （110）{001} mixed disloca- tion in perovskite SrTiO3 is investigated with the modified two-dimensional Peierls-Nabarro dislocation equation con- sidering the discreteness effect of crystals. The results show that the core structure of mixed dislocation is independent of the unstable energy in the （100） direction, but closely related to the unstable energy in the （110） direction which is the direction of total Burgers vector of mixed dislocation. Furthermore, the ratio of edge displacement to screw one nearly equals to the tangent of dislocation angle for differ- ent unstable energies in the （110） direction. Thus, the con- strained path approximation is effective for the （110）{001} mixed dislocation in SrTiO3 and two-dimensional equation can degenerate into one-dimensional equation that is only related to the dislocation angle. The Peierls stress for （110） {001 } dislocations can be expediently obtained with the one-dimensional equation and the predictive values for edge, mixed and screw dislocations are 0.17, 0.22 and 0.46 GPa, respectively.

Effects of Pressure Stress Work and Viscous Dissipation in Mixed Convection Flow Along a Vertical Flat Plate

The Effects of pressure stress work and viscous dissipation in mixed convection flow along a vertical fiat plate have been investigated. The results are obtained by transforming the governing system of boundary layer equations into a system of non-dimensional equations and by applying implicit finite difference method together with Newton＇s linearization approximation. Numerical results for different values of pressure stress work parameter, viscous dissipation parameter and Prandtl number have been obtained. The velocity profiles, temperature distributions, skin friction co-efficient and the rate of heat transfer have been presented graphically for the effects of the aforementioned parameters.

Impacts of a wind stress and a buoyancy flux on the seasonal variation of mixing layer depth in the South China Sea

The seasonal variation of mixing layer depth （MLD） in the ocean is determined by a wind stress and a buoy- ance flux. A South China Sea （SCS） ocean data assimilation system is used to analyze the seasonal cycle of its MLD. It is found that the variability of MLD in the SCS is shallow in summer and deep in winter, as is the case in general. Owing to local atmosphere forcing and ocean dynamics, the seasonal variability shows a regional characteristic in the SCS. In the northern SCS, the MLD is shallow in summer and deep in winter, affected coherently by the wind stress and the buoyance flux. The variation of MLD in the west is close to that in the central SCS, influenced by the advection of strong western boundary currents. The eastern SCS presents an annual cycle, which is deep in summer and shallow in winter, primarily impacted by a heat flux on the air-sea interface. So regional characteristic needs to be cared in the analysis about the MLD of SCS.

The stress-microstructure relationship in an evolving mixing layer of fiber suspensions

The equations for fiber suspensions in an evolving mixing layer were solved by the spectral method, and the trajectory and orientation of fibers were calculated based on the slender body theory. The calculated spatial and orientation distributions of fibers are consistent with the experimental ones that were performed in this paper. The relationship between the microstructure of fibers and additional stress was examined. The results show that the spatial and orientation distributions of fibers are heterogeneous because of the influence of coherent vortices in the flow, which leads to the heterogeneity of the additional stress. The degree of heterogeneity increases with the increasing of St number and fiber aspect ratio. The fibers in the flow make the momentum loss thickness of the mixing layer thicker and accelerate the vorticity dispersion.

Effects of salt-alkali stress on active oxygen metabolism in roots of Spiraea × bumalda 'Gold Mound' and Spiraea × bumalda 'Gold Flame'

Under artificially-simulated complex salt-alkali stress, the levels of active oxygen metabolism in roots were studied using three-year-old cutting seedlings of Spiraea × bumalda ‘Gold Mound＇ and Spiraea × bumalda ‘Gold Flame＇. The present study aimed at exploring the antioxidant capacity in roots of spiraeas and revealing their adaptability to salt-alkali stress. Results indicate that the oxygen free radicals contents, electrolyte leakage rates and MDA contents in roots of Spiraea × bumalda ＇Gold Mound＇ and Spiraea × bumalda ＇Gold Flame＇ show an increasing tendency with the increases of the salinity and pH value, whereas the activities of superoxide dismutase （SOD）, peroxidase （POD） and catalase （CAT） all increased firstly and then decreased. With the increase in intensity of salt-alkali stress, the CAT activity in roots of Spiraea × bumalda ‘Gold Flame＇ is higher and the increasing extents in the oxygen free radicals contents, electrolyte leakage rates as well as MDA contents are lower compared with Spiraea × bumalda ‘Gold Mound＇, indicating that Spiraea × bumalda ‘Gold Flame＇ has a stronger antioxidant capacity.

Spline Fictitious Boundary Element Alternating Method for Edge Crack Problems with Mixed Boundary Conditions

The alternating method based on the fundamental solutions of the infinite domain containing a crack,namely Muskhelishvili’s solutions,divides the complex structure with a crack into a simple model without crack which can be solved by traditional numerical methods and an infinite domain with a crack which can be solved by Muskhelishvili’s solutions.However,this alternating method cannot be directly applied to the edge crack problems since partial crack surface of Muskhelishvili’s solutions is located outside the computational domain.In this paper,an improved alternating method,the spline fictitious boundary element alternating method(SFBEAM),based on infinite domain with the combination of spline fictitious boundary element method(SFBEM)and Muskhelishvili’s solutions is proposed to solve the edge crack problems.Since the SFBEM and Muskhelishvili’s solutions are obtained in the framework of infinite domain,no special treatment is needed for solving the problem of edge cracks.Different mixed boundary conditions edge crack problems with varies of computational parameters are given to certify the high precision,efficiency and applicability of the proposed method compared with other alternating methods and extend finite element method.

Factors influencing the climatological mixed layer depth in the South China Sea:numerical simulations

The mixed layer depth （MLD） in the upper ocean is an important physical parameter for describing the upper ocean mixed layer. We analyzed several major factors influencing the climatological mixed layer depth （CMLD）, and established a numerical simulation in the South China Sea （SCS） using the Regional Ocean Model System （ROMS） with a high-resolution （1/12~x 1/12~） grid nesting method and 50 vertical layers. Several ideal numerical experiments were tested by modifying the existing sea surface boundary conditions. Especially, we analyzed the sensitivity of the results simulated for the CMLD with factors of sea surface wind stress （SSWS）, sea surface net heat flux （SSNHF）, and the difference between evaporation and precipitation （DEP）. The result shows that of the three factors that change the depth of the CMLD, SSWS is in the first place, when ignoring the impact of SSWS, CMLD will change by 26% on average, and its effect is always to deepen the CMLD; the next comes SSNHF （13%） for deepening the CMLD in October to January and shallowing the CMLD in February to September; and the DEP comes in the third （only 2%）. Moreover, we analyzed the temporal and spatial characteristics of CMLD and compared the simulation result with the ARGO observational data. The results indicate that ROMS is applicable for studying CMLD in the SCS area.

MIXED MODE SCC OF 18-8 STAINLESS STEEL IN BOILING 42% MgCl_2 SOLUTION

A series of mixed mode tests were carried out on 18-8 stainless steel in boiling 42% MgCl_2 solution.The results show that for any K_Ⅱ/K_Ⅰ ratio,the SCC direction coin- cides well with the crack tip maximum normal stress plane,while the SCC resistance of the material reduces as the ratio of K_Ⅱ/K_Ⅰ increases.The experimental results were discussed in the light of anode dissolving mechanism and the effect of mixed mode loading on crack tip stress and strain.It is concluded that for fracture analysis if mixed mode cracks were simply taken into account as mode Ⅰ cracks,and only mode Ⅰ testing results as mode Ⅰ fracture criter- ion were employed,it may not be safe.

Nonlinear simulation of arch dam cracking with mixed finite element method

This paper proposes a new, simple and efficient method for nonlinear simulation of arch dam cracking from the construction period to the operation period, which takes into account the arch dam construction process and temperature loads. In the calculation mesh, the contact surface of pair nodes is located at places on the arch dam where cracking is possible. A new effective iterative method, the mixed finite element method for friction-contact problems, is improved and used for nonlinear simulation of the cracking process. The forces acting on the structure are divided into two parts： external forces and contact forces. The displacement of the structure is chosen as the basic variable and the nodal contact force in the possible contact region of the local coordinate system is chosen as the iterative variable, so that the nonlinear iterative process is only limited within the possible contact surface and is much more economical. This method was used to simulate the cracking process of the Shuanghe Arch Dam in Southwest China. In order to prove the validity and accuracy of this method and to study the effect of thermal stress on arch dam cracking, three schemes were designed for calculation. Numerical results agree with actual measured data, proving that it is feasible to use this method to simulate the entire process of nonlinear arch dam cracking.

Numerical simulation of strain localization and damage evolution in large plastic deformation using mixed finite element method

An investigation of computer simulation is presented to analyze the effectsof strain localization and damage evolution in large plastic deformation. The simulation is carriedout by using an elastic-plastic-damage coupling finite element program that is developed based onthe concept of mixed interpolation of displacement/pressure. This program has been incorporated intoa damage mechanics model as well as the corresponding damage criterion. To illustrate theperformance of the proposed approach, a typical strain localization problem has been simulated. Theresults show that the proposed approach is of good capability to capture strain localization andpredict the damage evolution.

Computational Fracture Analysis of an AFM-Specimen under Mixed Mode Loading Conditions

Fracture processes in ship-building structures are in many cases of a 3-D character. A finite element （FE） model of an all fracture mode （AFM） specimen was built for the study of 3-D mixed mode crack fracture behavior including modes Ⅰ,Ⅱ, and Ⅲ. The stress intensity factors （SIFs） were calculated by the modified virtual crack closure integral （MVCCI） method, and the crack initiation angle assessment was based on a recently developed 3-D fracture criterion--the Richard criterion. It was shown that the FE model of the AFM-specimen is applicable for investigations under general mixed mode loading conditions, and the computational results of crack initiation angles are in agreement with some available experimental findings. Thus, the applicability of the FE model of the AFM-specimen for mixed mode loading conditions and the validity of the Richard criterion can be demonstrated.

MODE II AND MIXED MODE I-II ROCK FRACTURE RESEARCH

of PhD thesis For the mode I rock fracture toughness measurement,three standard methods have been recommended by the ISRM,but there has not been a standard method for the determination of mode II and mixed mode I-II rock fracture toughness. However mode II and mixed mode I-II fracturing of rock structures is more commonly observed than mode I in various geological and structural engineering settings. So it is of great important to thoroughly research these rock fracture problems and establish a standard method for determining the mode II or mixed mode I-II fracture toughness for rock materials. Based on the progress made for mode I rock fracture research,the cracked chevron notched Brazilian disk (CCNBD) specimen was also introduced for mode II and mixed mode I-II rock fracture toughness measurement. When the crack is orientated at an angle with respect to the diametrical loading,the crack of the CCNBD specimen is exposed to the mode II or mixed mode I-II stress distribution conditions. The solutions for stress intensity factors in the vicinity of the crack tip have been evaluated by the stepwise superimposition technique. In order to make sure that the theoretical analysis is correct,numerical calculation method has been employed to calibrate the theoretical results. It has been proved that the theoretical results yielded by the dislocation method are correct and reliable. According to the characteristic that the propagation of the crack in the CCNBD specimen is in its own plane and application of the energy superposition principle,the stress intensity factor of the mixed mode I-II has been defined in dimensionless terms as 212II2Imix])()[(***+=YYY. It was found that the curve of *mixY was concave. There exists a lowest point which corresponds to the maximum external load and indicates the crack has reached its critical state. Since the values of ***IIImix and YYY, are only dependent on the specimen geometry (qaaa and 10B,,),the critical values of ***IIImix and YYY, can be to known as long as the CCNBD specimen is prepared ready. It is only necessary to record the maximum load during the fracture tests. The fracture locus is very useful to know whether the crack in a rock structure has reached its critical condition. According to the amount of practical fracture testing data obtained,the rock fracturing locus was found to be 123IICII23ICI=+KKKK and the S-critical criterion was found to be more suitable for rock mixed mode I-II fracturing assessment.

乳酸菌的乙醇耐受机制及其在食醋生产中的应用

传统固态发酵食醋因其丰富的菌群在风味、品质等方面有着不可比拟的优势,乳酸菌作为固态食醋发酵中重要的功能微生物,广泛应用于食品、生物等领域。然而,食醋在发酵过程中乳酸菌会受到高乙醇环境的胁迫,因此探究乳酸菌如何在高乙醇环境下生存具有积极意义。该研究选择耐乙醇副干酪乳杆菌(PC-5)和不耐乙醇植物乳杆菌(PR-7)作为实验对比菌株,通过检测生物指标发现:在体积分数为8%的乙醇环境下,PC-5的多糖含量占比和细胞膜通透性分别提高至0.56%和75%,且显著高于PR-7。此外,代谢途径中的己糖激酶(Hexokinase,HK)、6-磷酸果糖激酶(6-Phosphofructokinase,PFK)、丙酮酸激酶(Pyruvate Kinase,PK)的活性均高于PR-7,并分别提高至99.82、2.78、3.43 U/mg。最后,在食醋不同发酵阶段中加入PC-5使其与酵母菌实现共同发酵,结果发现:共发酵食醋体系中多酚的生成和总抗氧化能力比单菌发酵分别提升了32.14%和55.56%。因此乳酸菌对食醋发酵有着良好的促进作用,为乳酸菌参与食醋共发酵提供了良好的理论依据。

Eco-physiological Characteristics of Alfalfa Seedlings in Response to Various Mixed Salt-alkaline Stresses

Soil salinization and alkalization frequently co-occur in nature, but little is known about the mixed effects of salt-alkaline stresses on plants. An experiment with mixed salts （NaCI, Na2SO4, NaHCO3 and Na2CO3） and 30 salt-alkaline combinations （salinity 24-120 mmollL and pH 7.03-10.32） treating Medicago sativa seedlings was conducted. The results demonstrated that salinity and alkalinity significantly affected total biomass and biomass components of seedlings. There were interactive effects of salt composition and concentration on biomass （P 〈 0.001）. The interactions between salinity and alkalinity stresses led to changes in the root activity along the salinity gradient （P 〈 0.001）. The effects of alkalinity on seedling survival rate were more significant than those of salinity, and the seedlings demonstrated some physiological responses （leaf electrolyte leakage rate and proline content） in order to adapt to mixed salt-alkaline stresses. It was concluded that the mixed salt-alkaline stresses, which differ from either salt or alkali stress, emphasize the significant interaction between salt concentration （salinity） and salt component （alkalinity）. Further, the effects of the interaction between high alkalinity and salinity are more severe than those of either salt or alkali stress, and such a cooperative interaction results in more sensitive responses of ecological and physiological characteristics in plants.

应力场常数项对Ⅰ型裂纹起裂扩展行为影响

对含裂纹材料与结构断裂力学评估中的最大环向应力准则(MTS)、最小应变能密度因子准则(SED)和平均应变能密度准则(ASED)以及在此基础上考虑应力场常数项影响修正的断裂准则进行介绍;基于考虑裂尖应力场奇异项和常数项的修正MTS准则、修正SED准则和修正ASED准则,对比分析了裂尖应力场常数项对Ⅰ型裂纹的起裂扩展行为,探究了裂纹尖端应力场常数项以及材料泊松比对Ⅰ型裂纹偏折、断裂极限的影响规律,掌握了应力场常数项对Ⅰ型裂纹偏折、起裂扩展影响阀值。研究结果表明,裂纹尖端应力场常数项T应力对Ⅰ型裂纹起裂扩展偏折角及断裂判据的影响不可忽略,研究结果可为含裂纹材料与结构断裂力学评估提供一定参考。

流变学参数表征湿喷混凝土工作性研究进展

为提高工作性对湿喷混凝土施工性能(可输送性、可喷性)的指导作用,归纳了现有各种技术规范的工作性要求,回顾了流变特性与可喷性相关性研究进展,探讨了流变性能时变机制,总结了时变模型发展现状。结果表明,坍落度无法协调可输送性与可喷性工作性需求矛盾,流变学参数应用效果优于坍落度;屈服剪切应力增加,一次喷射厚度变大,回弹率减小;塑性黏度降低,管道输送压力减小,可输送性变好,但屈服剪切应力、塑性黏度与密实度的相关性尚需深入研究;主流的流变性能时变模型为指数、对数、线性、幂函数等经验公式,应加强有物理意义的模型推导;时变预测模型缺乏有效验证手段,应重点研发速凝体系下湿喷混凝土流变性能的原位评估方法。