多轴载荷作用下表面裂纹的疲劳扩展

通过对圆柱体直前缘表面裂纹在循环拉伸与循环扭转载荷共同作用下的扩展规律进行实验研究,分析了不同载荷曲线相位差、以及拉扭应力幅度对表面裂纹扩展路径、疲劳寿命和裂纹扩展速率的影响。结果表明:不同的相位差对裂纹扩展行为有着非常重要的影响。初始阶段的裂纹扩展主要受到剪应力幅度的影响,后继扩展则依赖于轴向应力幅度。拉应力和剪应力的增加均会增加裂纹扩展速率,但轴向应力幅度变化的影响大于剪切应力幅度。     

钛合金裂纹尖端氢扩散影响因素分析

为了获得氢在钛合金裂纹尖端的扩散行为,提出了一种力学与氢扩散的耦合模型。在COMSOL软件中建立了含单边椭圆裂纹的氢扩散模型,并分析了钛合金类型、载荷和裂纹长度对裂纹尖端氢扩散的影响。结果表明：在容易发生氢脆的环境中,α型钛合金的服役时间远大于β型钛合金;施加载荷对氢扩散有促进作用;裂纹长度与氢浓度成正比,与扩散区域的面积成反比。     

十字焊接接头疲劳试验与宏观断口分析

疲劳断口的宏观分析是焊接结构疲劳试验和失效分析的有效手段,但一直未获得应得的重视,原因在于较难出现肉眼可识别的海滩条带。基于勾线法原理,研究了标记载荷对生成海滩条带的影响,制定了3种标记载荷谱,开展了十字焊接接头的拉伸疲劳试验。试验结果表明,标记载荷的幅值、平均值和循环次数是影响海滩条带生成效果的重要因素,保留载荷最大值的半幅标记载荷谱容易获得较明显的疲劳海滩条带。宏观断口分析发现了3种基本的裂纹演变形态,揭示了初始裂纹萌生位置及其数量是影响裂纹演变形态的主要因素。     

考虑焊趾形貌的T形焊接接头三点弯疲劳试验

针对弯曲载荷作用下焊趾疲劳裂纹的萌生与扩展问题，考虑焊趾形貌的影响，开展了T形焊接接头的三点弯疲劳试验。试验前，观察和测量试件双侧焊趾的形貌，得到系列形貌不规则的特征点，通过在部分特征点设置FBG应变传感器测量焊趾局部的应变时间变化。施加了2级载荷谱块的循环载荷，在疲劳断口获得了清晰的海滩条带，结合断口形貌和焊趾形貌对焊趾裂纹的萌生和扩展行为进行了分析。结果表明，受弯焊接接头更易在焊趾形貌更恶劣的一侧萌生裂纹，且复杂的焊趾形貌容易导致多裂纹的产生，多裂纹的萌生位置与焊趾形貌特征点有较强的对应关系。     

船体结构钢腐蚀疲劳裂纹扩展行为研究

针对船体结构钢16 Mn处于海水腐蚀与交变载荷的交互作用,并且在阴极保护作用下工作的实际工况,研究了阴极保护对16 Mn船体结构钢在海水和3.5%NaCl水溶液中的腐蚀疲劳裂纹萌生和裂纹扩展的行为。结果表明裂纹扩展速率不仅受阴极电位的影响而且受环境介质的影响。     

采用CCCD-SHPB试验系统确定岩石的动态断裂韧度

鉴于目前岩石动态断裂韧度在研究方法上没有统一的标准,有必要对其进行研究。使用花岗岩制作中心裂纹圆盘试件,预制裂纹的宽度控制在1mm左右,在SHPB试验系统下进行动态冲击,得出试件两端的平均载荷带入到推广的中心裂纹圆盘试件应力强度因子计算公式算出动态断裂韧度。     

检测输电线内部钢芯损伤的漏磁传感器设计

由于电流的集肤效应,涡流检测法主要适用于管、棒材表面裂纹及近表面裂纹的检测．高压输电线的内部钢芯只用于承受拉力和各种外界载荷,而基本无电流通过,所以检测钢芯缺陷的传感器最好采用漏磁检测法．文章介绍了这种漏磁传感器的设计方法．     

弹塑性断裂的内参量热力学分析——Ⅰ.线弹性裂纹体的裂纹扩展

本文在内参量热力学的理论框架内详细讨论了线弹性裂纹体的裂纹扩展问题。对线弹性断裂力学中所涉及到的各种能量关系作了统一的整理,其中包括Irwin的弹性能释放率——裂纹扩展力,Griffith的脆性断裂准则,以及Irwin-Kies的柔度公式和Paris的位移公式。本文以中心裂纹体为例,详细计算了裂纹扩展的稳定性,并区分恒载荷和恒位移两种情况,对材料断裂韧性测试中所遇到的失稳扩展,稳定扩展以及进发现象提供了理论说明。     

基于SINTAP方法的热影响区裂纹的安全评定

采用欧共体的结构完整性评定方法SINTAP(Structural Integrity Assessment Procedure)的一级评定标准,对高频电阻焊热影响区裂纹进行安全评定,用极限载荷法和CTOD(裂纹尖端张开位移)实验结果进行评定。采用SINTAP一级评定,评定点在评定曲线范围内,说明该结构是安全的。     

携表面割痕的压电陶瓷柱体裂纹前缘奇异行为

研究了同时处于机械与电学载荷之下的压电陶瓷柱体表面裂纹前缘的应力场和电位移场。求得了应力及电位移的奇异性阶数和相应的两个强度因子。     

荷载对称性与连续梁三弯矩方程

应用广义图乘法分析荷载与连续梁三弯矩方程关系.若杆内有对称荷载,则三弯矩方程简单;简支梁弯矩图的面积能表示荷载对连续三个支座弯矩的作用.任意荷载的作用含反对称荷载分量的图乘剪力的作用.若杆内荷载是同方向,则反对称荷载比弯矩图面积的影响小.     

How sequencing and fading affects the relationship between intrinsic and germane cognitive loads

Scaffolding techniques, such as sequencing and fading, used in online video lectures may help mitigate the negative relationship between complex contents represented by intrinsic load and content understanding represented by germane load. This study analyzed survey responses from university students (n = 2365) who participated in online classes in South Korea, and looked at the relationships between sequencing and fading and germane load, intrinsic load and germane load, and the moderating effect of sequencing and fading on the relationship between intrinsic load and germane load. Results showed a positive relationship between sequencing and fading and germane load and a negative relationship between intrinsic load and germane load. Furthermore, sequencing and fading moderated the negative relationship between intrinsic load and germane load. This article examines conflicting evidence on the topic and provides explanations as to why sequencing and fading reduces the negative impact of complex contents found in the current study.     

Learners Emphasize Their Intrinsic Load if Asked About It First: Communicative Aspects of Cognitive Load Measurement

Cognitive load measurement is an important aspect of educational research. Current cognitive load surveys differentiate between intrinsic cognitive load (resulting from the complexity of learning materials) and their extraneous cognitive load (which is increased by a demanding design). In two studies, order effects of cognitive load subscales are demonstrated. Asking learners regarding their intrinsic load first increases their responses concerning this type of load, with little effect on extraneous load ratings. This effect can be replicated even when extraneous load is intentionally induced. This finding has important implications for cognitive load research, as the order of surveys appears to bias cognitive load ratings. As most cognitive load research is conducted to find ways of reducing extraneous load, it may be reasonable to carefully consider whether and when intrinsic load items are included in studies. Generally, the results show that study participants seem to emphasize certain demands, similar to a dialogue.     

Cognitive Load Theory: How Many Types of Load Does It Really Need?

Cognitive load theory has been traditionally described as involving three separate and additive types of load. Germane load is considered as a learning-relevant load complementing extraneous and intrinsic load. This article argues that, in its traditional treatment, germane load is essentially indistinguishable from intrinsic load, and therefore this concept may be redundant. Contrary to extraneous and intrinsic load, germane cognitive load was added to the cognitive load framework based on theoretical considerations rather than on specific empirical results that could not be explained without this concept. The design of corresponding learning activities always required methods and techniques external to the theory. The article suggests that the dual intrinsic/extraneous framework is sufficient and non-redundant and makes boundaries of the theory transparent. The idea of germane load might have an independent role within this framework if (as recently suggested by John Sweller) it is redefined as referring to the actual working memory resources devoted to dealing with intrinsic rather than extraneous load.     

论体育课的心理负荷

体育课的心理负荷是指心理负荷量和心理负荷强度.文章在分析体育教学中心理负荷所包括的主要因素及其作用规律的基础上,揭示体育课中心理负荷不适现象存在的原因,强调重视体育课心理负荷的重要性,并提出合理把握体育课心理负荷的建议.     

基于NAT的Free BSD负载均衡网关研究

为了达到最佳的负载均衡效果，将负载分给多个服务器分担，负载控制器需要根据网络流量状态和服务器资源来分配负载，这就需要应用优化的负载分配策略，达到平均分配负载的目的，本文讨论了特定流量条件下网关数目的计算模型，分布式路由策略实现负载分配的策略的方法，并研究了基于网络地址转换在Free BSD unix环境下实现负载均衡网关的方法。     

Element Interactivity and Intrinsic,Extraneous, and Germane Cognitive Load

In cognitive load theory, element interactivity has been used as the basic, defining mechanism of intrinsic cognitive load for many years. In this article, it is suggested that element interactivity underlies extraneous cognitive load as well. By defining extraneous cognitive load in terms of element interactivity, a distinct relation between intrinsic and extraneous cognitive load can be established based on whether element interactivity is essential to the task at hand or whether it is a function of instructional procedures. Furthermore, germane cognitive load can be defined in terms of intrinsic cognitive load, thus also associating germane cognitive load with element interactivity. An analysis of the consequences of explaining the various cognitive load effects in terms of element interactivity is carried out.     

混部负载场景下离线负载资源调度策略研究

混部负载是当前业界提高数据资源利用率的重要手段,其原理是将在线负载和离线负载共同放置于同一数据中心、共享资源,在保证在线负载服务质量的前提下,将空闲资源分配给离线负载。当前针对混部负载中离线负载的资源调度采用传统的公平或者短作业优先等策略,并未考虑在线负载资源需求波动对离线负载运行的影响。为了达到进一步提升资源利用率和作业吞吐率的目的,提出基于负载完成时间预判的模拟退火资源分配策略。结果表明,该策略比公平策略和短作业优先策略在平均资源利用率上分别提高了7.8%和15.5%,在吞吐率上分别提高了38.2%和29.1%。     

Neuroimaging of cognitive load in instructional multimedia

This paper reviews research literature on cognitive load measurement in learning and neuroimaging, and describes a mapping between the main elements of cognitive load theory and findings in functional neuroanatomy. It is argued that these findings may lead to the improved measurement of cognitive load using neuroimaging. The paper describes how current measures of cognitive load cannot accurately show the distinction between different types of cognitive load in different learning conditions, and existing approaches to cognitive load assessment are limited in terms of their precision and methodology. A literature review discusses the conceptual framework of Sweller's [Sweller, J. (1994). Cognitive load theory, learning difficulty, and instructional design. Learning and Instruction 4, 295-312; Sweller, J. (1999). Instructional design in technical areas. Camberwell, Australia: ACER Press] cognitive load theory, and describes various approaches to load measurement and their limitations. The paper then describes how the core components of cognitive load - intrinsic, extraneous, and germane load - may be observable using neuroimaging techniques, and argues for the exploration of new links between education research and neuroscience.     

放大电路负载线的研究与理解

从负载线的内涵出发,诠释了负载线的概念,列举了几类负载线,并总结了有载交流负载线的方程,提出了两点法画交流负载的办法。