ISOCHRONOUS STRESS-STRAIN CURVES OF LOW ALLOY STEEL CROSS-WELD-SPECIMEN AT HIGH TEMPERATURE

In this work, a parametric approach is presented and utilized to determine the creep properties of weldments; then the model of creep strain for cross weld specimen is given. On the basis of the experimental results, attempt has been made to establish equations of the isochronous stress-strain for weld joint that can predict the function of loading and service time in use of the creep data of base metal and weld metal.

Numerical simulation of the stress-strain curve and the stress and strain distributions of the titanium-duplex alloy

The stress-strain curve of an α-β Ti-8Mn alloy was measured and then it was calculated with finite element method （FEM） based on the stress-strain curves of the single α and β phase alloys. By comparing the calculated stress-strain curve with the measured one, it can be seen that they fit each other very well. Thus, the FE model built in this work is effective. According to the above mentioned model, the distributions of stress and strain in the α and β phases were simulated. The results show that the stress gradients exist in both α and β phases, and the distributions of stress are inhomogeneous. The stress inside the phase is generally higher than that near the interface. Meanwhile, the stress in the α phase is lower than that in the β phase, whereas the strain in the α phase is higher than that in the β phase.

The Complete Stress-strain Curve of Recycled Aggregate Concrete under Uniaxial Compression Loading

The mechanical performance of recycled aggregate concrete （RAC） is investigated. An experiment on the complete stress-strain curve under uniaxial compression loading of RAC is carried out. The experimental results indicate that the peak stress, peak strain, secant modulus of the peak point and original point increase with the strength grade of RAC enhanced. On the contrary, the residual stress of RAC decreases with the strength grade enhancing, and the failure of RAC is often broken at the interface between the recycled aggregate and the mortar matrix. Finally, the constitutive model of stress-strain model of RAC has been constituted, and the results from the constitutive model of stress-strain meet the experiment results very well.

Charactersitics of Stress-strain Curve of High Strength Steel Fiber Reinforced Concrete under Uniaxial Tension

A whole of 110 specimens divided into 22 groups were tested with varying the volume fraction of steel fibers and the matrix strength of these specimens. The stress-strain behaviors of four types of steel fiber reinforced concrete （SFRC） under uniaxial tension were studied experimentally. When the matrix strength and the fiber content increase, the tensile stress and tensile strain vary differently according to the fiber type. The mechanisms of reinforcing effect for different types of fiber were analyzed and the stress-strain curves of the specimens were plotted. Some experimental factors for stress or strain of SFRC were given. A tensile toughness modulus Re0.5 was introduced to evaluate the toughness characters of SFRC under uniaxial tension. Moreover, the formula of the tensile stress-strain curve of SFRC was regressed. The theoretical curve and the experimental ones fit well, which can be used for references in construction.

On the calibration of a shear stress criterion for rock joints to represent the full stress-strain profile

Conventional numerical solutions developed to describe the geomechanical behavior of rock interfaces subjected to differential load emphasize peak and residual shear strengths.The detailed analysis of preand post-peak shear stress-displacement behavior is central to various time-dependent and dynamic rock mechanic problems such as rockbursts and structural instabilities in highly stressed conditions.The complete stress-displacement surface(CSDS)model was developed to describe analytically the pre-and post-peak behavior of rock interfaces under differential loads.Original formulations of the CSDS model required extensive curve-fitting iterations which limited its practical applicability and transparent integration into engineering tools.The present work proposes modifications to the CSDS model aimed at developing a comprehensive and modern calibration protocol to describe the complete shear stressdisplacement behavior of rock interfaces under differential loads.The proposed update to the CSDS model incorporates the concept of mobilized shear strength to enhance the post-peak formulations.Barton’s concepts of joint roughness coefficient(JRC)and joint compressive strength(JCS)are incorporated to facilitate empirical estimations for peak shear stress and normal closure relations.Triaxial/uniaxial compression test and direct shear test results are used to validate the updated model and exemplify the proposed calibration method.The results illustrate that the revised model successfully predicts the post-peak and complete axial stressestrain and shear stressedisplacement curves for rock joints.

Relations of complete creep processes and triaxial stress-strain curves of rock

Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stress and time,but also it has the corresponding relations to the triaxial stress-strain curves of rock.The deformation properties of soften-strain,harden-strain and ideal plasticity presented by conventional triaxial compressive test curves under the different stress states were utilized,and the creep characteristics,the creep starting stress and the different entire creep process curves of rock were studied systematically according to creep experiment results,and the relations of the triaxial stress-strain curves to the creeping starting stress,the terminating curve,the different creep processes,and the different creep fracture properties were established.The relations presented in this paper were verified partially by the creep experiment results of five types of rock.

MODELLING OF TENSILE STRESS-STRAIN CURVE OF WOVEN FABRICS

A general shape of tensile stress-strain curves of woven fabrics is first recognised by puttingtested and predicted results together.An exponential function with two parameters is then selectedfor the prediction of tensile stress-strain relationship.The predicted results by using the proposedfunction show excellent agreement with experimental data.

Ideal Drift Response Curve for Robust Optimal Damper Design for Elastic-Plastic MDOF Structures under Multi-Level Earthquakes Dedicated to Professor Karl S.Pister for his 95th birthday

A new method of robust damper design is presented for elastic-plastic multi-degree-of-freedom(MDOF)building structures under multi-level ground motions(GMs).This method realizes a design that is effective for various levels of GMs.The robustness of a design is measured by an incremental dynamic analysis(IDA)curve and an ideal drift response curve(IDRC).The IDRC is a plot of the optimized maximum deformation under a constraint on the total damper quantity vs.the design level of the GMs.The total damper quantity corresponds to the total cost of the added dampers.First,a problem of generation of IDRCs is stated.Then,its solution algorithm,which consists of the sensitivity-based algorithm(SBA)and a local search method,is proposed.In the application of the SBA,the passive added dampers are removed sequentially under the specified-level GMs.On the other hand,the proposed local search method can search the optimal solutions for a constant total damper quantity under GMs’increased levels.In this way,combining these two algorithms enables the comprehensive search of the optimal solutions for various conditions of the status of the GMs and the total damper quantity.The influence of selecting the type of added dampers(oil,hysteretic,and so on)and the selection of the input GMs on the IDRCs are investigated.Finally,a robust optimal design problem is formulated,and a simple local search-based algorithm is proposed.A simple index using the IDRC and the IDA curve of the model is used as the objective function.It is demonstrated that the proposed algorithm works well in spite of its simplicity.

Investigation into the stress-strain curves of deformation-induced ferrite transformation in a low carbon steel

A series of tests of deformation-induced ferrite transformation （DIP-T） in a low carbon steel were carried out by the Gleeble-3500 hot simulation machine at a temperature range of Ae3-Ar3. The overall stress-strain curves during DIFT can be divided into three typical types： ＂double-humped＂,＂ single-humped＂ and ＂transitional＂. The peaks exhibited in the curve are involved with deformation-induced transformation which happened in grains or at the grain boundaries. According to the stress-time curve and strain-time curve, strain capacity dramatically postponed the strain-induced transformation, which leads to the start of the transformation right ahead of the finish of deformation and the majority of the ferrite transformation process mainly happened after the deformation. Deformation-induced transformation is a metadynamic transformation process with dynamic nucleation.

High temperature stress–strain curves of MnS and their applications in finite element simulation

A novel method for testing stress–strain curves of non-metallic materials was presented.The high temperature stress-strain curves of MnS were preliminarily obtained and corrected to account for the influence of friction.Using the finite element method,the influence of deformation parameters on the deformation evolution of MnS inclusions was investigated based on the experimental reference data.The corresponding physical experiment was designed for comparative analysis.The results indicate that the experimental high-temperature deformation data of MnS are highly reliable.In the process of matrix deformation,the shapes of MnS inclusions change from spherical to ellipsoidal and even to lamellar.There are some differences in the morphological deformation of MnS inclusions located at different positions.With the increase in the initial size of MnS inclusions,the risk of failing the inclusion-flaw inspection increases and the forging quality further deteriorates.

On Two Problems About Isogenies of Elliptic Curves Over Finite Fields

Isogenies occur throughout the theory of elliptic curves.Recently,the cryptographic protocols based on isogenies are considered as candidates of quantum-resistant cryptographic protocols.Given two elliptic curves E1,E2 defined over a finite field k with the same trace,there is a nonconstant isogeny b from E2 to E1 defined over k.This study gives out the index of Homk(E1,E2)b as a nonzero left ideal in Endk(E2)and figures out the correspondence between isogenies and kernel ideals.In addition,some results about the non-trivial minimal degree of isogenies between two elliptic curves are also provided.

Finite Element Modeling of Stress Strain Curve and Micro Stress and Micro Strain Distributions of Titanium Alloys— A Review

Most of the alloys like titanium, steel, brass, copper, etc., are used in engineering applications like automobile, aero- space, marine etc., consist of two or more phases. If a material consists of two or more phases or components it is very difficult to predict the properties like mechanical and other properties based on simple laws such as rule of mixtures. Titanium alloys are capable of producing different microstructures when it subjected to heat treatments, so much of money and time are squandering to study the effect of microstructure on mechanical properties of titanium alloys. This squandering can be reduced with the help of modeling and optimization techniques. There are many modeling tech- niques like Finite element method, Mat lab, Mathematical modeling etc. are available. But Finite element method is widely used for prediction because of capable of producing distributions of stresses and strains at any different loads. From the literature it is observed that there is a good agreement between the calculated and measured stress strain curves. This review paper describes the effect of volume fraction and grain size of alpha phase on the stress strain curve of the titanium alloys. It also can predict the effect of strength ratio on stress strain curve by using FEM. This informa- tion will be of great use in designing and selecting the titanium alloys for various engineering applications.

考虑嵌固段桩前土体弹塑性变形的锚索微型桩群计算模型研究

锚索微型桩群在中小型边坡治理及边坡紧急抢险工程中的应用越来越广泛,但现有的计算模型对嵌固段桩前土体塑性变形及桩侧土体受力变形连续性考虑较少。针对这一问题,首先根据锚索微型桩群加固土质边坡的特点,以潜在滑裂面位置为分界线,将微型桩群分为受荷段与嵌固段进行分析。对于受荷段,将桩间土简化为水平土弹簧,有效考虑桩间土力的传递作用;对于嵌固段,采用理想弹塑性p-y曲线分析桩-土相互作用。其次,将冠梁处预应力锚索简化为弹性支座,将其作用力转移至后排桩桩顶,再由桩顶冠梁重分配至各排桩桩顶处,从而达到对桩顶位移的约束作用。最后,以帕斯捷尔纳克(Pasternak)双参数地基梁法为基础,建立考虑嵌固段桩前土体弹塑性变形及桩侧土体受力变形连续性的锚索微型桩群有限差分计算模型,并迭代求解得到该结构的水平位移与内力。利用该计算模型分别对微型桩群与锚索微型桩群加固土质边坡进行算例计算,与试验、数值模拟结果对比分析,验证该模型的合理性,并探讨土体剪切刚度、锚索束及桩径对该锚索微型桩群水平位移与内力的影响。研究表明:嵌固段桩前土体塑性变形及桩侧土体受力变形连续性对微型桩的水平位移与内力有较大影响;随着锚索束的增加,桩身最大正弯矩及水平位移均不断减小,可通过增设锚索束达到控制桩身变形与内力的目的。

基于暗特性曲线提取辐伏转换器件特性参数的算法

开展辐伏电池理论研究需要计算辐伏转换器件的特性参数,通过特性参数即可预测辐照条件下辐伏转换器件的输出特性,为辐伏电池设计提供重要理论参考。本研究算法基于辐伏转换器件暗特性曲线,计算辐伏转换器件的特性参数,并通过统计学方法分析计算特性参数的优劣。并利用提取出的特性参数预测转换器件在源辐照条件下的特性曲线并与实际测量的辐照特性曲线对比,以证明算法的有效性。结果表明,计算结果在曲线拟合和输出特性预测上均取得了良好的效果。此算法能够在不辐照器件的基础上,通过暗特性曲线预测电池输出特性,可为辐伏电池的设计提供指导。

恶意模型下集合交集问题的保密计算

研究集合问题是安全多方问题的基础,当前已有的协议在处理集合问题时,不能保证集合运算的隐私性和正确性,且都是在全集范围下取值,导致应用范围受限,容易受到恶意敌手的攻击,安全性较低。因此,将集合是否存在交集问题转化为集合元素相减问题,并且基于高效的椭圆曲线加密方案,设计了一种半诚实模型下无全集限制求集合交集的保密计算协议。然后借助密码学工具设计了恶意模型下无全集限制求集合交集的保密计算协议。协议可以更好地抵御恶意攻击,且参与方无法通过观察结果推断出其他参与方的信息。这有助于提高整个协议的安全性。此外,该协议的计算复杂度和通信复杂度也低于其它现有同类型协议。

Stress-strain Model of Corroded Concrete under Uniaxial Compressive Loading

The prism specimens of corroded concrete were subjected to uniaxial compressive load to develop the stress-strain model. Compared to the un-corroded concrete, the mechanical prop- erties of corroded concrete, such as peak strength, Young＇s modulus, and residual deformation, et al are degraded. The concrete, which were subjected to the aggressive media in the environment, were resulted in randomly distributed pre-loading flaws and defects. The propagation of these corrosion flaws during the procedure of loading was the main reason of degradation of corroded concrete properties. By the application of the statistic theory of continuum damage, the compressive stress-strain curve of corroded concrete was simulated. The initial damage factor was introduced to represent the corrosive effects of different media. The present damage constitutive model agreed well with the test results.

Stress-strain analysis of loess triaxial shear test by PFC^(3D)

In order to compensate for limitations of microscopic study on loess triaxial tests, taking the loess in Longxi area as an example, the authors established the loess triaxial test model by using PFC3D software and simulating tfiaxial shear test under the different confining pressures in 0 kPa, 50 kPa and 300 kPa. Compared with laboratory triaxial shear test, the numerical simulation test has a guiding role in loess mechanical strength analysis.

基于RBF神经网络的舰载稳定平台控制系统

舰载稳定平台是一个非线性时变系统,采用传统PID控制难以达到较好的控制性能指标要求。对基于RBF神经网络整定PID参数的控制策略进行研究,针对液压缸突然起动或停止产生的液压冲击问题,根据活塞杆运行距离设计理想速度曲线,建立舰载稳定平台控制系统的数学模型,并在此基础上搭建Simulink仿真模型。仿真结果表明,基于RBF-PID控制的舰载稳定平台较传统PID控制有更快的响应速度、更好的适应能力,在调平开始阶段的超调量降低了16%,到达稳态的时间缩短了1.6s。

Mechanical behaviour of wood compressed in radial direction-part I.New method of determining the yield stress of wood on the stress-strain curve

A test equipment was developed,which allows for real time observation of the deformation behav-ior of wood cellular structure under a compression load applied in radial direction.Compression tests were performed on jack pine(Pinus banksiana)and balsam poplar(Populus balsamifera)spec-imens to explore the relationship between the yield stress and the first failure occurring in wood cell layers during radial compression.The microstructural changes for P.banksiana and P.bal-samifera wood below and above the yield point were analyzed.The study results showed that for P.banksiana the first failure of wood cells occurred at the first earlywood layer,while for P.balsamifera it occurred at the layer with the largest vessels.The first failure of wood cell layer for each species tested was found to correspond to the yield point on the stress-strain curve.A new method of determining the yield stress for wood specimens under radial compression was developed.

Full-Range Compressive Stress-Strain Curves for Cold-Formed 304 Stainless Steel Circular Hollow Sections After Exposure to Vacuum Brazing

With the rapid development of microscale cellular structures, the small-diameter cold-formed welded stainless steel tubes have recently been used for creating the metallic lat- tice topologies with high mechanical properties. In this paper, to obtain the accurate material properties of the circular hollow section （CHS） under pure compression, a series of concentric compression tests are conducted on the millimeter-scale cold-formed 304 stainless steel circu- lar tubular stub columns after exposure to a vacuum brazing process. The tests cover a total of 18 small-diameter stub tubes with measured thickness-to-diameter ratios （t/D） from 0.023 to 0.201. A generalized three-stage nominal stress-strain model is developed for describing the compressive behavior of the post-brazing CHSs over the full strain range. This mechanical model is especially applicable to computer code implementation. Hence, an interactive computer pro- gram is developed to simultaneously optimize three strain hardening exponents （n1, n2, n3） in the expression of the model to produce the stress-strain curve capable of accurately replicating the test data. To further reduce the number of the model and material parameters on which this model depends, this paper also develops five expressions for determining the 2.5% proof stress （ap2）, n2, the ultimate compressive strength （σp3）, n3, and the ultimate plastic strain （p3%） for given experimental values of three basic material parameters （E0, σ0.01, σ0.2）. These expressions are validated to he effective for the CHSs with t/D 〉_ 0.027. The analytically predicted full-range stress-strain curves have generally shown close agreement with the ones obtained experimentally.