反应堆贯穿件J形焊缝残余应力研究

焊接残余应力是引起应力腐蚀开裂的主要原因,准确地掌握残余应力的分布是对结构完整性评定的关键.为了探明反应堆压力容器顶盖控制棒驱动机构(control rod drive mechanism,CRDM)贯穿件J形焊缝残余应力的分布,本研究加工两个CRDM贯穿件实验模拟件,采用盲孔法测试两个J形接头的焊接残余应力.通过实验探明了CRDM贯穿件焊缝残余应力的分布规律,为反应堆压力容器结构完整性的研究提供必要参考.     

爆炸处理消除大型柱壳结构环焊缝残余应力实验研究

为探讨大型耐压柱壳结构对接环焊缝焊接残余应力消除方法,根据耐压柱壳结构环焊缝焊接工艺,设计并制作了大型耐压柱壳结构对接环焊缝模拟焊接模型,并采用沿焊缝条状布药,分别进行了单、双面布药爆炸处理消除大型耐压柱壳结构对接环焊缝焊接残余应力模型实验。结果表明:大型耐压柱壳结构对接环焊缝存在较大的焊接残余应力;单、双面爆炸处理均能有效调整、消除焊接残余应力,残余应力分布明显均匀化;焊后残余应力越大,爆炸处理效果越明显,当焊接残余应力大于0.5s时,单面爆炸处理后残余应力m下降幅度在40%以上,双面爆炸处理后残余应力m下降幅度在60%以上;采用沿焊缝条状布药,爆炸处理能有效消除沿焊缝的纵向残余应力;双面爆炸处理效果优于单面爆炸处理效果。     

焊管的残余应力测试与研究

通过小孔法与分割法对φ272mm螺旋埋弧焊管和φ380mm对接焊管的残余应力测试,分析探讨了螺旋焊缝、环焊缝以及焊缝热影响区的残余应力分布。研究结果表明,不同工艺焊接成型的圆管,其焊缝纵向均匀为拉应力分布,焊缝横向均为压应力分布,焊缝热影响区的残余应力分布各异。     

云纹干涉与钻孔法测量搅动摩擦焊接头的残余应力

搅动摩擦焊是90年代出现的一种新型焊接技术,特别适用于熔化焊接性差的有色金属等材料.搅动摩擦焊接头的残余应力分别具有高应力梯度的特点,传统的应变片钻孔法不能满足测量要求.本文结合云纹干涉法与钻孔法的技术,得到了铝合金薄板搅拌摩擦焊接头残余应力沿深度和沿垂直焊缝方向的分布.     

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。     

考虑焊接残余应力的波形钢腹板PC梁关键细节疲劳可靠度研究

焊接残余应力对波形钢腹板细节疲劳寿命的影响不可忽略，本文以头道河大桥为工程背景，基于ABAQUS有限元软件，建立波形钢腹板焊接构件数值模型，提出不同波折角度的波形钢腹板残余应力模型。采用瞬态分析方法，分析6种典型车辆作用下波折角区域焊缝细节的应力时程。在此基础上，构建考虑焊接残余应力和车辆荷载共同作用下的波形钢腹板细节疲劳极限状态方程，讨论不同波折角度和交通增长率对疲劳可靠度指标的影响规律。研究表明，翼缘板-波形钢腹板焊接构件斜边两侧的纵向残余应力呈对称分布，焊接细节转角区域圆弧外侧的纵向残余应力整体高于圆弧内侧，随着波折角度的增加，两侧焊缝附近的纵向残余应力变大；在桥梁设计基准期取100年时，30°波折角度焊缝细节疲劳可靠度是60°波折角度的1.05倍；交通量的线性增长对头道河大桥焊缝细节的疲劳可靠度影响较大，不考虑交通增长率的焊缝细节疲劳可靠度是α=5%的1.84倍。     

基于多因素的焊接结构疲劳裂纹扩展速率分析

以Donahue等提出的疲劳裂纹扩展速率计算模型为基础,通过引入形状系数、张开比和残余应力等参数,建立了适用于焊接结构的疲劳裂纹扩展速率计算模型,分析了多种因素对焊接结构疲劳裂纹扩展速率的影响规律。结果表明,焊板厚度和焊缝余高的变化均会对焊接结构疲劳裂纹的扩展速率产生影响,在对焊接结构表面形状进行设计时应保有一定的焊缝余高;有效应力比的增大会降低焊接结构疲劳裂纹的扩展速率,且裂纹深度的变化不会改变有效应力比对焊接结构疲劳裂纹扩展速率的影响;残余应力的增大会提高焊接结构疲劳裂纹的扩展速率,且残余应力对疲劳裂纹扩展速率的促进作用随着裂纹深度的增加而增大,在对焊接结构的疲劳性能进行设计时须考虑残余应力对结构性能的影响。     

爆炸法消除焊接残余应力

随着工业的发展,焊接技术在工业生产中的地位显得越来越重要。但是,由于焊接是局部加热,温度梯度很大,使焊件内部产生了很大的焊接残余应力。因为焊接残余应力的存在,致使焊件的静强度、刚度、稳定性及抗疲劳、抗脆性破坏、抗应力腐蚀等性能均低于同类材料的非焊接件。这就造成了它的使用寿命大大降低。在许多结构的破坏事故中,不少是由于焊接残余应力的存在所造成。为此研究消除焊接残余应力,对生产和科学实验都具有很大的意义。     

CTOD试验焊缝表面开缺口试样裂纹前沿平直度研究

对于裂纹尖端张开位移(CTOD)试验,焊缝试样中预制疲劳裂纹前沿平直度直接影响了试样制备的合格率,是试验的关键难题之一．试验中常对试样进行预处理以提高裂纹前沿平直度,但由此也使试验结果与实际情况产生一定差异．本文深入研究规范BS7448: Part2中对焊缝试样取样方向的规定,对表面开缺口试样裂纹尖端焊接残余应力进行分析,运用大型有限元软件ANSYS模拟90mm厚钢板焊接过程,求解了横向残余应力沿板厚方向及焊缝方向的分布规律,研究出横向残余应力分布是影响焊缝试样预制裂纹前沿平直度的主要原因,并通过试验进行验证．试验结果表明,表面开缺口试样可不经过局部韧带压缩等预处理而得到合格的裂纹前沿平直度,试验不改变原焊缝残余应力,可测得更加接近焊缝实际情况的CTOD韧度值,给CTOD试验中合理选取焊缝试样取样方向提供了新思路．     

残余应力对压力容器破坏模式的影响分析

破前漏(简称LBB)是压力容器、核电站设备结构设计与评价中的一个重要准则.表面裂纹准静态扩展的几何形貌变化规律的预测是破前漏(LBB)评判十分重要的课题之一.本文对特定焊接残余应力场加载作用下,含三维表面裂纹的压力容器模型,用有限元软件(ABAQUS)进行了表面裂纹准静态扩展模拟计算,得到在此残余应力场作用下应力强度因子沿裂纹前缘的分布规律.结合外载引起的应力强度因子,就可以判别裂纹的扩展形貌,从而判断结构是否满足LBB要求.     

不同坡口形状铍环激光钎焊温度场和应力场分析

本文对不同坡口形状镀环焊接过程进行了数值模拟,分析了坡口形状和焊接速度对铍环钎焊温度场和应力场的影响,结果表明:开坡口后铍环焊接的熔深和熔宽增大,而热影响区的焊接残余应力相对降低,特别是对于降低铍和AlSi12熔合面处的应力集中具有明显的效果;同时,坡口角度的增加主要对铍环热影响区的应力分布也有一定的影响.因此,铍环接头处开坡口不仅能够降低焊缝区的残余应力,还能减少铍材熔化引起的开裂.     

Effect of compressibility on the hypervelocity penetration

We further consider the effect of rod strength by employing the compressible penetration model to study the effect of compressibility on hypervelocity penetration. Meanwhile, we define different instances of penetration efficiency in various modified models and compare these penetration efficiencies to identify the effects of different factors in the compressible model. To systematically discuss the effect of compressibility in different metallic rod-target combinations, we construct three cases, i.e., the penetrations by the more compressible rod into the less compressible target, rod into the analogously compressible target, and the less compressible rod into the more compressible target. The effects of volumetric strain, internal energy, and strength on the penetration efficiency are analyzed simultaneously. It indicates that the compressibility of the rod and target increases the pressure at the rod/target interface. The more compressible rod/target has larger volumetric strain and higher internal energy. Both the larger volumetric strain and higher strength enhance the penetration or anti-penetration ability. On the other hand, the higher internal energy weakens the penetration or anti-penetration ability. The two trends conflict, but the volumetric strain dominates in the variation of the penetration efficiency, which would not approach the hydrodynamic limit if the rod and target are not analogously compressible. However, if the compressibility of the rod and target is analogous, it has little effect on the penetration efficiency.     

Fatigue crack growth through residual stress fields—theoretical and experimental studies on thick-walled cylinders

Experiments are described which determined the effects of various residual stress distributions on the growth rate of fatigue cracks. For each stress distribution, the contribution (K_RS) to the net stress intensity at the crack tip is determined, and a comparison is then made with the behaviour predicted using a fracture mechanics approach based on a weight function analysis and a simple crack closure model. The example studied is a thickwalled pressure vessel containing a longitudinal crack which grows radially from the inner surface; fatigue cracks were grown under laboratory conditions in ring test specimens. sectioned from vessels which had been cold-expanded by different amounts to increase their pressure limits, and so contained various complex residual stress distributions. The experiments provide direct evidence that the effects of residual stress (and by extension, thermal stress) on the crack tip stress intensity may be modelled conveniently using weight function techniques, and can be incorporated satisfactorily in fatigue crack growth analyses.     

在椭圆横截面弹体正侵彻下有限厚铝靶的破坏模式及响应特性

基于30 mm口径弹道炮平台,开展了3种不同椭圆横截面弹体在200~600 m/s撞击速度范围内正侵彻2A12铝靶的实验,获得了2A12铝靶的破坏形貌及弹体的剩余速度。在此基础上,建立了相应的数值模型,结合实验结果验证了所建模型的有效性,并系统分析了弹体横截面长短轴长度比对靶体的破坏情况及响应特性的影响。研究结果表明:弹体最大横截面面积是影响弹体剩余速度的主要因素,而弹体横截面长短轴长度比对弹体剩余速度的影响较弱;在圆形横截面弹体侵彻下靶体背部形成的花瓣大小和形状一致,空间分布均匀,而在椭圆横截面弹体侵彻下,随着弹体横截面长短轴长度比的增大,靶体背部形成的花瓣数量增加、尺寸变小,且在短轴方向的花瓣数量和靶体表面隆起高度均大于长轴方向的;靶体在圆形横截面弹体侵彻下的径向位移、径向应力和切向应力与其在椭圆横截面弹体侵彻下的显著不同,前者沿周向方向各点的变化规律基本一致,靶体处于简单的压缩状态,切向应力为零,而后者各点的应力状态与弹体横截面长短轴长度比和周向角密切相关,靶体受到压缩和剪切应力的耦合作用。     

80%钨纤维增强锆(Zr)基块体金属玻璃复合材料长杆弹侵彻钢靶实验研究

本文在765~1766m/s速度范围内,对钨纤维体积分数为80%的增强锆(Zr)基块体金属玻璃复合材料长杆弹进行侵彻Q235钢靶的穿甲试验,对残余弹体进行宏、细观观测,研究弹体材料的失效破坏模式。穿甲试验表明,在大于1000m/s速度侵彻时,钨纤维非晶弹拥有头形自锐能力,表现出优秀的侵彻能力。弹材变形和破坏主要发生于弹体头部边缘层,呈局域化和尖锐化特点,而且边缘层厚度在整个高速穿甲过程中保持动态平衡。由于非晶基体作用,弹体材料易发生剪切断裂等破坏,通过流动形成质量侵蚀并导致弹体头部边缘层形成自锐。     

控制棒驱动机构步跃提升碰撞的动力学建模

控制棒驱动机构(CRDM)在步跃提升时,钩爪部件会与承压壳体上的提升磁极发生面面碰撞。本文基于混合坐标法建立控制棒驱动机构有限元离散的刚-柔耦合动力学方程,用罚函数法计算了钩爪部件与承压壳体之间的碰撞力和应力分布情况。结果表明,刚柔耦合多体方法在仿真小变形碰撞时可以提高计算效率,同时又能达到与有限元方法同等的精度。进一步对碰撞模型不同区域的网格疏密和尺寸大小做了定量分析,得到了降低有限元网格数量的方法,可为工程中碰撞模型的网格划分提供参考。     

Measurement of thermal stresses within an experimental nuclear-reactor vessel head

This paper describes certain tests and techniques employed in measuring stresses within an experimental nuclear-reactor head of unusual design. The incorporation of certain desired design features necessitated that the head be extremely thick. Due to the thickness and its complex geometry, it was considered desirable to determine stress distribution within the head under conditions of steady-state pressure combined with rapid heating and cooling transients within the reactor, in order to determine safe limits for the operation of the head. A photoelastic study of a three-dimensional model of the reactor head was completed in 1956; this study permitted prediction of the stress distribution throughout the head as a function of internal pressure, but it was not possible to assimilate the head thermal stresses by photoelastic means. It is the purpose of this paper to describe the technique employed in measuring thermal stresses in the interior of the head, under simulated operating conditions of steady-state pressure and temperature transients.     

Assessment by comparison and experimental verification of VVER reactor pressure vessel integrity

This work is concerned with assessing the lifetime integrity of VVER (water-water power reactor) reactor pressure vessel. Results based on the Soviet Code are compared with those of the ASME Code, Section III and XI. Similarities and discrepancies are illustrated and discussed in connection with numerical results of a typical RPV (reactor pressure vessel) under operational conditions. Involved are data for fracture toughness, crack initiation and crack arrest conditions. Considerations are also given for possible adoption of the ASME Code for VVER reactors.     

P91钢中厚壁管焊接残余应力分析

针对管道试件规格不同所要求的焊接工艺不一致问题,讨论P91钢中厚壁管对接接头所要求的双人对称焊形式下的焊接残余应力分布规律．基于ANSYS分析软件,以双移动高斯热源结合单元生死技术,利用顺序耦合方法得到P91钢中厚壁管焊接残余应力．讨论热处理工艺对于P91钢中厚壁管焊接残余应力的影响．结果表明,由于焊接工艺在环向位置上的结构反对称性使得焊接残余应力在环向上呈反对称分布;即便经过较高温度的预热处理,没有焊后热处理时最大等效应力仍超过屈服极限;进行焊后整体热处理的P91钢中厚壁管焊接残余应力得到了有效的改善,平均应力数值下降了60%~70%．     

An investigation of the use of strain gages to measure welding-induced residual stresses

The measurement of weld-induced residual stress is important in structures that are subjected to cyclic loading during their service life. Depending on their magnitude, stresses can influence the rate of crack growth under cyclic loading and hence affect the life of the structure. Because the level of residual stress may change during service, measurement of these changes is necessary for accurate life prediction of the structures. The measurement of welding-induced residual stress using strain gages poses significant problems, the most important being the potential damage to the gages by high temperatures generated in the welding process. This laboratory study was undertaken to assess the suitability and signal stability of commercially available resistive strain gages for the measurement of postweld residual stresses in a submarine hull structure. Adhesively bonded and weldable-type strain gages were attached to the surface of a 35 mm thick steel plate, which was then subjected to thermal cycles similar to those encountered during welding construction of a submarine pressure hull. This paper describes the strain gage application procedure, changes in the strain gage output at end of each experimental stage and the history of changes in the residual stress.