HRR理论的近似解析解

本文根据文献[3]给出的HRR 解的角函数数值表,利用数值拟合方法,给出了HRR理论的近似解析解.本文结果不仅形式简单,而且和精确解符合得很好.对幂硬化指数n在0和1之间的任何弹塑性材料均适用.给进一步研究裂纹尖端附近的弹塑性应力应变场以及工程安全评定提供了一个方便的解析工具.为了计算方便,我们把应力、应变、位移无量纲化,它们与实际应力、应变、位移的关系为     

海底管线钢焊接缺陷裂纹尺寸容许值研究

裂纹尖端张开位移(CTOD)作为评定海洋工程用钢断裂韧性的重要指标,已广泛应用于现代工业中.根据BS7448:part4标准,采用多式样法对海底管线钢X70进行低温韧度试验,分别建立了焊缝和热影响区的CTOD-R阻力曲线,从而确定了焊缝和热影响区的CTOD启裂值.考虑到铺设之后的安全性问题,采用较小的焊缝CTOD启裂值为参考依据.以此为基础,分别采用SINTAP标准中的一级评定和三级评定对其埋藏裂纹进行安全评估(ECA)考虑铺设环境和残余应力影响,分别得出在铺设条件下的一级评定和三级评定埋藏裂纹容许尺寸.以试验数据为依托,以BS7448和SINTAP规范为理论指导,为海底管线铺设工程中的焊接缺陷验收和拒收提供了依据,为海底管线钢质量的优劣提供参考.     

铝制容器焊缝超声阵列成像方法研究

针对铝制容器焊缝内部缺陷检测问题,本文提出一种基于斜入射的超声阵列全聚焦成像方法。基于斯涅尔定律,研究了超声波在界面中的传播特性,确定了引入楔块下声束的传播路径,并将提出的斜入射超声阵列全聚焦成像技术用于铝制容器焊缝缺陷检测。仿真和实验结果表明,利用该方法可很好地实现焊缝中缺陷的检测。本文研究工作为焊接构件安全评价提供了可行的技术方案。     

弹性矩形板问题的Hamilton正则方程

为了采用辛算法求出弹性矩形板问题的解析解，中直接从弹性矩形板的控制方程出发推导了弹性矩形板，其中包括弹性矩形薄板和厚板问题以及弹性地基上矩形薄板和厚板问题的Hamilton正则方程，为利用辛几何方法求出任意边界条件下这类问题的理论解奠定了基础．     

用非局部弹性场论研究圆盘状裂纹问题

本文采用非局部弹性理论。用Love位移函数导出三维轴对称问题的非局部弹性应力的一般形式解,并求解了圆盘裂纹问题。得到了裂纹尖端区的应力是有界的,再次证实了非局部理论模型求解断裂力学问题的正确性。     

爆炸法消除焊接接头残余应力的数值模拟

利用非线性动力有限元法对爆炸处理消除焊接接头残余应力的全过程进行了数值模拟。首先，采用温度场与位移场的间接耦合方法计算了钢板对接焊的焊后冷却及残余应力的生成过程，求得焊接接头处由高温冷却到室温由于变形受到阻碍而产生的不均匀的残余塑性变形和应力。然后，在焊缝区引入移动的爆炸载荷，计算了爆炸波作用下该钢板焊接接头附近应力的变化。计算结果表明，爆炸处理可引起板内应力的重新分布，从而有效地释放超过塑性极限的残余应力。利用炸药爆炸消除大型焊接结构残余应力是一种经济有效的方法，本文的数值模拟为研究炸药爆炸消除焊接结构残余应力的机理提供了有力的工具。     

移动集中力作用下的局部脱空地基梁的振动

利用分离变量法导出了局部脱空地基梁在移动集中力作用下的振动解析解。通过应用例子讨论局部脱空地基梁振动的频幅特征,为分析和评估局部脱空地基梁的工程问题提供理论依据和手段。     

等厚双层涂层材料受集中力作用的平面问题理论解

界面应力的正确评价是分析薄膜涂层材料力学特性的难题之一。利用镜像点法和Dirichlet等值性原理，本文推导了等厚双层薄膜涂层材料受表面集中力作用的平面问题理论解。该显式理论解是以固定在各镜像点上的局部坐标系下的Goursat应力函数的形式给出的。对应于高阶镜像点的应力函数，可通过递推的方法，从对应于低阶镜像点的应力函数求得，而且也易于计算机编程。随着镜像点阶数的增大，它与界面的距离也越来越大，因而相对应的应力函数对界面应力的影响越来越小。最后的算例表明，只需考虑前面有限个镜像点，便可获得足够精度的解。该理论解可作为格林函数，以求解复杂问题的理论解，也可用作边界元法的基本解，提高数值计算的精度和效率。     

基础滑移隔震体系的地震响应计算

利用随机振动理论求出了基础滑移隔震房屋在无频谱过程的白噪声过程作用下的响应特性，探讨了基础滑移隔震的振动时最佳阻尼系数取值，提出了基础最大滑移量在白噪声过程作用下的计算公式，并进行了基础滑移隔震位移量的试验测定。计算结果与试验结果表明，本文提出的基础滑移隔震体系的计算公式是可行的，为滑移隔震房屋设计证结构安全、合理提供了理论依据。     

设导流墩排沙漏斗清水流场的测试研究

经过多年的理论与实践研究，螺旋流排沙已被广大的水利工作者所认可．本文首次利用毕托球测速系统测试了由新疆农业大学最新推出的带导流墩排沙漏斗的三维螺旋流流场，对其时均流特性进行了分析和研究．其次，文中还分析了其对输沙过程所产生的影响，为进一步优化此类型排沙漏斗流态打下了基础     

拉压循环载荷下正交异性钢桥面板肋-面板焊缝裂纹扩展分析

采用四步法计算了考虑循环载荷中压应力影响的正交异性钢桥面板的肋-面板焊缝表面裂纹扩展。第一步是基于正交异性钢桥面板的疲劳分析模型,计算肋-面板焊缝处的应力,第二步是通过肋-面板焊缝的三维局部模型,用Schwartz-Neumann交替法计算焊缝表面裂纹的应力强度因子分布,第三步是用二维断裂力学模型和增量塑性损伤模型,计算循环载荷中的压应力对裂纹扩展的影响,第四步是用第二步中的三维裂纹分析结果和第三步中的二维断裂力学模型得到的裂纹扩展公式,计算钢桥面板的肋-面板焊缝表面裂纹扩展。计算结果表明,对应于正交异性钢桥面板肋-面板焊缝处的循环应力,本文所用模型的裂纹尖端反向塑性区导致裂纹扩展率增加50%以上。研究结果为正交异性钢桥面板肋-面板焊缝裂纹的疲劳寿命分析提供了研究基础。     

双螺旋辊式新型磨浆机螺旋套磨损机理的研究

利用金相组织分析和电子显微分析技术,结合生产实际,对已磨损的输料段和磨浆段的螺旋套进行磨损表面形貌分析,探讨螺旋套磨损机理.结果表明:输料段正螺旋套能够将纸浆料旋转送入机壳内,不承受较大的挤压应力,但由于纸浆料中含有腐蚀介质,其主要的磨损失效形式以腐蚀磨损为主,磨料磨损为辅;磨浆段反螺旋套本身无正输送能力,浆料在正输送组件作用下形成高压区,纤维与浆料之间产生较大摩擦力,导致纤维分离,进而使之分丝帚化和压溃,浆料水分降低,其主要的磨损失效形式为高应力磨料磨损,并伴有腐蚀磨损.     

焊接接头超高周疲劳实验研究

本文基于超声疲劳振动技术,设计了三种焊接接头试样(圆形对接焊接试样及其喷丸处理试样和板状十字焊接试样),并利用超声疲劳试验系统测定了其超高周疲劳性能,实验应力比为-1,频率20kHz,实验在室温条件下进行。实验结果表明,圆形对接焊接接头的疲劳性能高于板状十字焊接接头,喷丸处理能提高焊接接头的疲劳强度。将焊接接头的疲劳性能与对应形状的母材进行对比分析,发现焊接接头的疲劳性能远低于母材。在相同疲劳寿命的条件下,圆形焊接接头试件的疲劳强度仅为母材的45%,十字焊接接头试件仅为母材的29%;圆形对接接头在5×106周次以后,试件仍然发生疲劳断裂,而板状十字焊接接头在超高周区域(107～109周次)存在疲劳极限。超声疲劳断口的扫描电子显微镜分析结果显示,圆形焊接接头试件断口位置主要位于熔合区的焊趾处或焊接接头表面几何非连续处,十字接头试件断口位于焊趾处;焊接接头试件裂纹萌生于焊接缺陷、试样表面夹杂或熔合区的不连续处;喷丸处理对焊接接头的裂纹萌生机制没有显著影响。     

A phenomenological model for anisotropic creep in a multipass weld metal

Creep strength of welded joints can be estimated by continuum damage mechanics. In this case constitutive equations are required for different constituents of the welded joint: the weld metal, the heat-affected zone, and the parent material. The objective of this paper is to model the anisotropic creep behavior in a weld metal produced by multipass welding. To explain the origins of anisotropic creep, a mechanical model for a binary structure composed of fine-grained and coarse-grained constituents with different creep properties is introduced. The results illustrate the basic features of the stress redistribution and damage growth in the constituents of the weld metal and agree qualitatively with experimental observations. The structural analysis of a welded joint requires a model of creep for the weld metal under multiaxial stress states. For this purpose the engineering creep theory based on the creep potential hypothesis, the flow rule, and assumption of transverse isotropy is applied. The outcome is a coordinate-free equation for secondary creep formulated in terms of the Norton–Bailey–Odqvist creep potential and three invariants of the stress tensor. The material constants are identified according to the experimental data presented in the literature.     

考虑塑性和刚度不匹配的焊接残余应力估算

现有残余应力计算方法未能考虑材料塑性变形和焊接接头刚度不匹配的影响,使得焊接残余应力计算结果和实际残余应力存在较大偏差.在2219-T87铝合金钨极氩弧焊焊接头残余应力测试基础上,提出一种基于非线性有限元和材料弹性模量分区的残余应力—释放应变曲线的残余应力计算方法,研究了材料塑性变形和接头刚度不匹配对焊接残余应力计算的影响.结果表明,焊接接头中非均质材料塑性不匹配可以引起对于残余应力计算的较大误差;材料塑性变形对残余应力的影响大于接头刚度不匹配对残余应力的影响.所提出方法修正了传统方法在焊接接头的残余应力计算中由于未考虑接头非均质材料塑性不匹配而引起的误差.     

A new theoretical approach for structural modelling of riveted and spot welded multi-spot structures

A general theoretical approach based on theory of elasticity is presented in order to define the structural behaviour of riveted and spot welded joints. The new closed form solutions lead to the definition of a joint element useful to FE models of riveted or spot welded multi-spot structures. The objective is an accurate evaluation of the local elastic stiffness of spot joints in FE analysis, which is fundamental to perform a reliable simulation of multi-joint structures and, consequently, a good estimate of loads acting on spots; this makes it possible to introduce structural stress or new general criteria allowing, for example, to predict fatigue behaviour. On the other hand, a low entry of degrees of freedom is needed when several spot joints are present in a complex structure. The goal is to reach a reliable spot region model which can be used as the basis to develop a spot element in FE analysis. In the present paper, based on new closed form solutions, a spot element is introduced, so as to precisely evaluate both local and overall stiffness both of spot welded joints and riveted joints. Based on the stress function approach and the Kirchhoff plate theory in linear elastic hypotheses, closed-form in-plane stress, displacement, moment and transverse shear force solutions are derived for a new bidimensional model, subjected to various types of loads. The capability to simulate spot welds or rivets depends on the definition of two elastic parameters intrinsic in closed form solutions, that tunes the theoretical model according to actual joint behaviour.The proposed joint element combines the precision in the simulation with a very limited number degrees of freedom in the overall finite element model of an actual multi-spot structure.The results obtained using the introduced theoretical framework and spot element approach perfectly match those obtained using very refined FE models and experimental data.     

Fatigue growth prediction of elliptical cracks in welded joint structure: Hybrid and energy density approach

A hybrid weight function approach (HWFM) is presented for the fatigue life prediction of infinite body and welded joint structure containing elliptical cracks. A self-containing computer code has been developed for this purpose. Numerical computations were first conducted on cracked infinite body showing a physical fact, that the elliptical shape of the crack becomes circular during its evolution. The prediction of the fatigue crack growth shows that the present results are in perfect concordance with those reported in the literature. Then, numerical tests were carried out on two types of specimens of welded joint structure. The present results were compared to the experimental and predicted ones of other authors, demonstrating that the hybridization method is a powerful numerical technique, and that the SEDF approach (using the Sih’s law) is more valid for the critical cases of welded joints than the SIF approach (using the Paris law). A parametric study has been conducted on the stress ratio “R” showing that the fatigue life to failure decreases with the increase of “R”.     

QFP结构中引脚焊缝界面端的奇异性热应力问题研究

由于引脚、印制电路板和焊接剂的热-机材料属性不同,在受到热载荷或机械载荷时,引脚焊接界面端会产生奇异性应力,有可能产生界面开裂.为了基于界面端奇异场来评价QFP结构引脚界面端力学行为,本文拟采用数值方法求解引脚焊缝任意角度尖劈界面端的应力强度系数.具体步骤为:首先,基于高次内插有限元特征分析法确定两相任意角度尖劈界面端的奇异性指数和应力角分布函数,并引入常数热应力项,获得热-机耦合奇异性应力场表达式;采用有限元分析技术和最小二乘拟合法来获得应力强度系数的数值解.文中考察了热-机材料属性对热载荷下焊接剂/印制电路板界面端应力强度系数的影响,并给出改善界面端热应力状态的建议.     

焊趾表面裂纹的形态发展曲线与疲劳寿命预测

以作者建立的焊地椭圆表面裂纹应力强度因子数据库以及复杂应力场中焊践半随圆表面裂纹前缘应力强度因子分布计算的基本模式法为基础上,给出了复杂应力场中焊践表面表纹在疲劳扩展过程中形态变化规律及寿命的工程分析方法。     

Mechanical response of thin SMAW arc welded structures: Experimental and numerical investigation

The mechanical response of thin welded plates made of Ck45 steel during shielded metal arc welding (SMAW) is investigated by employing data from numerical results using the finite element method and laboratory experimental measurements. The aim of this paper is to investigate the effect of the thermal uncertainty encountered during the thermal numerical analysis on the out-of-plane angular distortion of the welded panels. For this purpose a comparison between the numerical mechanical response (using the calibrated and as-predicted thermal history) and the experimental results is carried out. The effect of the microstructural transformations on the angular out-of-plane distortion is also investigated by introducing the material transformation within the numerical analysis by the simplest means in order to clearly demonstrate its influence. The same strategy is followed in order to investigate the effect of low-temperature martensitic transformation on the longitudinal residual stress field by properly combining experimental and numerical results and analyzing an idealized welding fabrication. Discussion is, finally, carried out regarding the design process of welded marine structures.