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.

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.

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.

经济周期波动与菲利普斯曲线形态变异:兼论经济回升的路径选择

厘清菲利普斯曲线形态变异的本质机理对于准确把握经济运行规律和确保宏观调控精准施策具有重要意义。为此,文章全面识别了中国菲利普斯曲线在经济周期不同阶段下的形态特征,并就如何采取合意的宏观经济政策引导经济回升展开了深入探讨。研究发现:第一,经济增速放缓、通胀单边异动以及全球化向逆全球化转变是导致“产出—通胀”型菲利普斯曲线出现形态变异的核心原因;第二,中国菲利普斯曲线在经济周期不同阶段的表现为:在经济周期上升或是平稳运行阶段,斜率较为陡峭,而在经济周期下行阶段则呈现出扁平化趋向;第三,不同宏观经济政策对经济回升路径的影响存在显著差异,现阶段以价格型货币政策搭配财政政策的渐进调控方式不失为一种引导经济平稳复苏的有益尝试。面对当下产出端与通胀端的双重紧缩压力,适度地矫正“产出—通胀”权衡关系,塑造陡峭的菲利普斯曲线斜率具有重要意义,这不仅有利于引导经济沿着安全的路径回升,同时也能在最大限度上避免古典经济危机重现。

基于宏程序的数控车削非圆曲线的刀具轨迹拟合研究

通过对比分析几种非圆曲线车削方法的功能特定,分析确定宏程序车削加工非圆曲线零件的应用优势,并结合车削复合循环指令编程思路以抛物线、椭圆曲线组合零件车削加工为例,进行数控仿真加工实验。实验验证了编程程序的可行性,同时编程过程的简便快捷以及参数指令可手动修改替换的特点,也为类似复杂类零件轮廓车削加工提供了借鉴。

基于MACRO的非圆二次旋转曲线轮廓的数控加工研究

针对常规手工编程中难以加工非圆二次旋转曲线的问题,对华中数控系统中典型的非圆二次函数公式曲线轮廓的车削加工进行研究。首先根据加工轮廓确定中心在坐标原点,且不倾斜的曲线方程,在solidworks软件中创建表达式,应用规律曲线参数模块绘制出曲线图形;然后将表达式中的方程进行坐标旋转及平移转换,绘制出与加工图纸一致的曲线轮廓;最后采用分析归纳法得出二次旋转曲线的宏程序模块,并给出该宏程序在旋转双曲线和椭圆曲面零件加工中的编程应用。实践表明,该宏程序对数控编程基础人员灵活应用非圆二次旋转曲线轮廓的编程方法与技巧有实际的指导意义。

二次曲线零件的宏车削研究

针对二次曲线零件的加工难点,结合葫芦零件工艺结构,编制其宏程序,并进行刀轨模拟检验,总结出宏编程的一般思路和方法,为企业中数控车加工其他非圆曲线提供了有益的参考。

基于MACRO的非圆二次旋转曲线轮廓的数控加工研究

针对常规手工编程中难以加工非圆二次旋转曲线的问题,对华中数控系统中典型的非圆二次函数公式曲线轮廓的车削加工进行了研究。首先根据加工轮廓确定中心在坐标原点,且不倾斜的曲线方程,在solidworks软件中创建表达式,应用规律曲线参数模块绘制出曲线图形,然后将表达式中的方程进行坐标旋转及平移转换,绘制出与加工图纸一致的曲线轮廓,最后采用分析归纳法得出二次旋转曲线的宏程序模块,并给出该宏程序在旋转双曲线和椭圆曲面零件加工中的编程应用。实践表明,该宏程序对有一定数控编程基础的人员更加灵活应用非圆二次旋转曲线轮廓的编程方法与技巧有实际的指导意义。

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.

轻骨料混凝土单轴受压性能细观模拟

从细观角度出发,将轻骨料混凝土看作由轻粗骨料、基体砂浆及两者间的界面过渡区组成的复合材料。采用塑性损伤本构模型,建立了含3种等效粒径的轻骨料混凝土二维数值模型,对其在单轴受压条件下破坏时的损伤分布和宏观应力-应变曲线关系进行了细观数值模拟。研究了不同轻粗骨料体积含量、表观密度、最大粒径及其随机分布对轻骨料混凝土单轴受压损伤分布及宏观应力-应变曲线关系的影响。结果表明,轻骨料混凝土受压破坏时轻粗骨料颗粒会破裂,轻粗骨料体积含量与表观密度对轻骨料混凝土力学性能的影响较大,轻粗骨料最大粒径对轻骨料混凝土单轴受压强度有轻微的影响,轻粗骨料的随机分布对轻骨料混凝土单轴受压应力-应变曲线的非线性段有一定影响,且对损伤分布影响明显。

应用宏程序和VERICUT实现非圆曲线数控仿真加工技术研究

非圆曲线在航空航天、汽车和医疗等需要复杂几何形状和精密加工的各个行业中必不可少。探讨了宏程序和VERICUT软件在非圆曲线数控(NC)仿真加工技术开发中的应用。该研究以非圆曲线正弦曲线槽为例,应用宏程序编程以及使用VERICUT进行精确仿真和优化,实现非圆曲线正弦曲线槽数控仿真加工。通过案例研究和分析,验证了宏程序和VERICUT在提高类似非圆曲线的加工精度、减少误差和优化整体制造过程方面的有效性。

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.