THE HYSTERESIS LOOP 2. AN ANALYSIS OF THE LOOP SHAPE

Abstract— Hysteresis loops of a low carbon steel measured at various temperatures and plastic strain amplitudes are analysed using the statistical theory of the hysteresis loop. It is shown that the parameters of the statistical theory characterizing the saturated hysteresis loop, i.e. the probability density function and effective saturated stress, can be obtained from experiments. The probability density function is influenced mainly by strain amplitude; the effective saturated stress mainly by temperature.     

THE HYSTERESIS LOOP 1. A STATISTICAL THEORY

Abstract— Starting from a knowledge of inhomogeneous dislocation structures observed in cyclically strained metals, a model for cyclic straining is developed. A distribution of volumes with different internal critical flow stresses is assumed characterized by a probability density function. A generalization which includes a thermally activated component of the flow stress is derived assuming that the saturated microscopic effective stress, μ_es, is equal in all volumes. The relations to obtain the probability density function from experimental data are derived. The theory yields the macroscopic internal stress, σ_e and the macroscopic effective stress, σ_e, along the hysteresis loop. Experimental observations on cyclically strained metals can be explained using this statistical theory.     

T300/LD2热循环时产生滞后环原因及改善方法探讨

T300/LD2复合材料在热循环时产生滞后环并留下很大的残留应变。本文对T300/LD2试样在热循环时产生滞后环和残留应变的原因进行分析和探讨。实验结果表明,基体在热循环时大量的塑性变形是产生滞后环和残留应变的主要原因,并通过在界面预设不同应力和缩短热循环温度区间来研究界面应力状态和热循环温度区间跟热循环时滞后环和残留应变之间的关系。提出了改善残留应变和滞后的方法(1)尽量减少复合材料的使用环境中的温度变化,(2)根据材料的使用环境,经过各种预处理使复合材料在工作时基体处于弹性变形状态,(3)提高基体的屈服强度。     

一种低频下测量电滞回线的新方法

本文通过对以Ｓａｗｙｅｒ－Ｔｏｗｅｒ电路为基础的电滞回线测量方法进行仔细分析后，指出传统的测量方法是以饱和区只存在线性极化这一物理概念为基础的，但由于漏导和损耗的影响，在实际测量中以它为依据往往是不可靠的。同时本文通过分析流过铁电试样的电流，与传统测量方法对比，发现了寻找补偿电阻的有效简便方法，提出以电流采样代替传统的电荷采样，借助微机数值处理功能得到电滞回线，并以此为基础建立了一套电滞回线测量系     

持久蠕变试验自动巡回测温软件设计

通过对持久蠕变试验测温软件系统的设计，使原测试设备控温的精度和可靠性得到了提高，同时也提高了试验员的劳动效率，减轻了劳动强度。     

反应磁控溅射工艺中的滞后效应研究

研究了反应磁控溅射的动力学过程。理论分析与试验结果表明:反应气体流量随其压力的变化呈滞后效应,最佳镀膜工艺位于滞后区域。给出了金属靶阴极表面溅射清洗效果的伏安特性评价法,为克服"靶中毒"提供了有效的技术途径。     

往复荷载下钢筋混凝土柱受力性能的数值模拟

准确预测地震荷载下钢筋混凝土柱的受力性能,对评估震后混凝土框架结构及桥梁结构的安全性和震害损失具有重要意义。由于复杂的材料性能和受力行为,地震作用下钢筋混凝土柱受力性能的准确计算目前仍需主要借助数值模拟,并且对数值模型中混凝土和钢筋材料的滞回本构关系提出了更高的精度要求。该文基于纤维分析模型,采用更加完善的反复荷载下钢筋和混凝土的本构,编制了可精确分析钢筋混凝土杆系结构及构件在往复荷载下受力性能的计算程序,并对不同轴压比和不同配筋率的2根压弯柱试件进行了数值模拟,计算结果与试验结果吻合良好。     

THE DETERMINATION OF HYSTERESIS LOOPS IN THERMO-MECHANICAL FATIGUE USING ISOTHERMAL STRESS-STRAIN DATA

Abstract— Thermo-mechanical fatigue stress-strain data on ferritic/austenitic steels and superalloys from a variety of sources are analysed with regard to hysteresis loop stress asymmetry. This arises from a decoupling of the thermal and mechanical strain signals in the test technique so that many tension-compression load combinations are possible. Data from simplified isothermal and bithermal tests are also examined. Taking a typical example of an "out-of-phase" thermo-mechanical loop on a 1/2 CrMoV steel cycled between 200 and 550°C, isothermal stress-strain data were generated at 50°C intervals on material from the same cast and, used in conjunction with the elastic characteristics of the apparatus, an attempt was made to re-create this loop. The methods employed were (i) a graphical construction between appropriate isothermal yield contours (ii) a tangent modulus calculation (iii) a secant modulus calculation. Method (i) appeared to give the closest agreement in the present case.     

往复何荷载下钢筋混凝土柱受力性能的数值模拟

准确预测地震荷载下钢筋混凝土柱的受力性能,对评估震后混凝土框架结构及桥梁结构的安全性和震害损失具有重要意义.由于复杂的材料性能和受力行为,地震作用下钢筋混凝土柱受力性能的准确计算目前仍需主要借助数值模拟,并且对数值模型中混凝土和钢筋材料的滞回本构关系提出了更高的精度要求.该文基于纤维分析模型,采用更加完善的反复荷载下钢筋和混凝土的本构,编制了可精确分析钢筋混凝土杆系结构及构件在往复荷载下受力性能的计算程序,并对不同轴压比和不同配筋率的2根压弯柱试件进行了数值模拟,计算结果与试验结果吻合良好.     

铱钵起爆系统的安全性分析与试验

介绍了一种具有高安全性和孔内可编程延期功能的隆芯1号数码电子雷管及其铱钵起爆系统。分析了系统的安全性和可靠性技术,进行了系统可靠性试验和300发雷管网路同步起爆实验测试。实测数据表明,系统具有耐高压、耐交直流、免疫非法起爆的安全性能,系统可编程延期范围达到1¹5000ms,编程增量为1ms间隔。系统安全可靠、延期精度高、操作使用方便,在未来大规模、高水平的复杂工程爆破中将具有很好的应用前景。     

铱钵起爆系统的安全性分析与试验

介绍了一种具有高安全性和孔内可编程延期功能的隆芯1号数码电子雷管及其铱钵起爆系统。分析了系统的安全性和可靠性技术,进行了系统可靠性试验和300发雷管网路同步起爆实验测试。实测数据表明,系统具有耐高压、耐交直流、免疫非法起爆的安全性能,系统可编程延期范围达到1~15000ms,编程增量为1ms间隔。系统安全可靠、延期精度高、操作使用方便,在未来大规模、高水平的复杂工程爆破中将具有很好的应用前景。     

一次泵冷冻水系统直接应用变频的模拟分析及工程应用

通过理论分析，模拟计算和实际应用。指出在风机盘管加新风机组的空调一次泵冷冻水系统中，由于实际大多数建筑的新风机组水阀目前不控制。在这样的系统中如果直接对一次泵进行变频改造和取消冷机旁通管，不仅仍然能够满足室内的空调要求，而且可以大量节约冷却水泵的电耗。     

氟聚合物表面接触角滞后的研究

研究了几种含氟聚合物粉末和６０Ｃｏ辐照ＰＴＦＥ粉末压块的表面粗糙度以及辐照剂量对接触角滞后的影响，得出了辐照ＰＴＦＥ粉末的接触角滞后随粗糙度和辐照剂量的增加而下降。ＰＴＦＥ粉末辐照表面处理剂量在２×１０３～２×１０４Ｇｙ时，其使ＰＴＦＥ表面的性质发生了很大变化，而ＰＴＦＥ本体性能改变较小。     

CONSTRAINT BASED EVALUATION OF CRACK GROWTH EXPERIMENTS IN THE TRANSITION REGION

Abstract— A large number of experiments has been performed over a wide temperature range in the transition region of a ferritic steel with the aim of studying its fracture behaviour and assessing the applicability of a two parameter fracture mechanics approach for such situations.
The experimental results clearly show a constraint effect, reflected in a decrease of the transition temperature with a decrease in specimen size and in a narrower transition region for shallow cracks. The results also show that the J - Q model, in conjunction with a fracture criterion (like the RKR criterion for cleavage fracture) is a promising approach for predicting the cleavage fracture event even in the transition region. No constraint effect could be detected for ductile initiation. The cleavage stress has been measured directly by testing. This reduces the number of fracture tests needed for the construction of the critical J - Q locus and improves the accuracy of the predictions.