关于焊接残余应力消除原理的探讨_王者昌

关于焊接残余应力消除原理的探讨 王者昌 (中国科学院金属研究所, 沈阳 � 110015) 摘 � 要: � 介绍了机械拉伸法、温差拉伸法、滚压法和低应力无变形焊接技术消除应力 原理的传统观点,认为焊接时焊缝产生压缩塑性变形, 消除应力的原理在于用拉伸塑性 变形抵消、补偿压缩塑性变形。本文提出新的应力应变发展过程, 指出焊缝不存在压缩 塑性变形, 一直受拉伸,熔合线附近处于脆性温度时承受较大的纵向拉伸应变, 随着远 离熔合线, 应变值陡降。焊缝消除应力的原理在于用塑性应变减少甚至抵消弹性应变, 在一般情况下是用拉伸塑性应变减少甚至抵消拉伸弹性应变。本文还阐述了各种消除 应力工艺的原理并很好地解释了横向液化裂纹分布在熔合线附近和裂纹很短的现象。 关键词: � 焊接残余应力; 应力消除; 塑性应变; 弹性应变; 液化裂纹 中图分类号: �TG404 � � 文献标识码: � A � � 文章编号: � 0253- 360X( 2000) 02- 55- 04 王者昌 0 � 序 � � 言 焊接应力和变形一直是焊接界关注的重要问 题 快递公司问题件快递公司问题件货款处理关于圆的周长面积重点题型关于解方程组的题及答案关于南海问题 之一。尼古拉也夫 � � 院士、关桥院士、田锡唐教 授等在此领域作了卓有成效的工作。机械拉伸法、 温差拉伸法和焊缝滚压法等也是消除焊接残余应力 和变形的有效方法。上述方法消除应力的原理虽有 报道,但有互相矛盾之处,载入�机械工程 手册 华为质量管理手册 下载焊接手册下载团建手册下载团建手册下载ld手册下载 �、�焊 接手册�中的一些权威性提法尚有商榷之处。因此 搞清楚焊接残余应力消除原理是必要的。 1 � 问题的提出 1. 1 � 机械拉伸法消除应力 文献[ 1, 2]指出: �对焊接结构进行加载,使焊接 压缩塑性变形区得到拉伸, 可减少由焊接引起的局 部压缩塑性变形量,使内应力降低。�文献[ 3]指出: �通过一次加载拉伸,拉应力区在外载的作用下产生 了拉伸塑性变形,它的方向与焊接时产生的压缩塑 性变形相反。因为焊接残余应力正是由于局部压缩 塑性变形引起的,加载应力越高,压缩塑性变形就抵 消的越多,内应力也就消除的越彻底。� 1. 2 � 温差拉伸法消除应力 文献[ 1, 2]指出: �两侧的金属受热膨胀对温度 较低的焊缝区进行拉伸, 使之产生的拉伸塑性变形 以抵消原来的压缩塑性变形, 从而消除内应力。� 1. 3 � 滚压法消除应力和变形 文献[ 4]指出: 用适当的压力滚压焊缝或近缝 收稿日期: 1999- 01- 12 区, �造成与焊接压缩塑性变形完全相等而方向相反 的延伸塑性变形(见图 1) , 这样在薄板构件上就可 以达到既消除应力又消除变形的目的。�文献[ 5]指 出: �在窄轮压力的作用下, 焊缝区产生相应延伸塑 性变形, 用以补偿焊后残余的压缩塑性变形(即不协 调应变量)。� 图 1� 滚压法消除应力原理示意图 Fig. 1� Schematic diagram of principle of relieving residual stress by rolling method 1. 4 � 低应力无变形焊接技术 关于动态低应力无变形焊接法消除应力的原 理, 文献[ 6]指出: �刚凝固的焊缝区中,已受到压缩 但仍处于高温的金属,由于强迫冷却射流热沉作用, 在温度低谷中受到极大的温差拉伸的作用, 随即得 到拉伸塑性变形的补偿。�文献[ 7]指出: �焊缝受冷 急剧收缩,产生很强的拉伸作用, 使仍处于高温状态 焊缝区的压缩塑性变形量得到补偿。� 第 21卷 � 第 2期 2 0 0 0 年 6 月 焊 接 学 报 TRANSACTIONS OF THE CHINA WELDING INSTITUTION Vol. 21 � �No. 2 June 2 0 0 0 上述文献都认为焊接时焊缝产生压缩塑性变 形,消除应力的原理在于设法使焊缝产生拉伸塑性 变形以抵消、补偿已产生的压缩塑性变形。焊缝是 否存在压缩塑性变形? 文献[ 3]提出另一种观点,认 为�对于焊缝金属来说,并不存在加热阶段。在冷却 过程中除相变外,都受到拉伸。�也就是说不存在压 缩,更不会出现压缩塑性变形。看来,焊接时焊缝是 否存在压缩塑性变形以及随之而来的消除应力原理 问题尚待研究。 2 � 焊接应力应变发展过程 尼古拉也夫 � � 院士 分析 定性数据统计分析pdf销售业绩分析模板建筑结构震害分析销售进度分析表京东商城竞争战略分析 了焊接应力应变发 展过程,原理图见图 2[ 8]。在 600 � 最宽截面即 I- I 截面,钢板中心区为压应力和压应变区,而板的两侧 为拉应力和拉应变区。在大约 200 � 以上的区域产 生压缩塑性变形,在 600 � 以上的区域, 压缩塑性变 形为常量, 其值为 ��600 � , 式中 �为线膨胀系数。 尼古拉也夫 � � 在文献[ 9]中将��600 � 改为 ��T , 式中 T 为温度,应力应变图则改为图 3。文献[ 2]引 用了后一观点。 图 2 � 低碳钢板焊接纵向应力应变分布 Fig. 2 � Longitudinal stress and strain distribution patterns in mild steel welded joint 在图 2和图 3中,作者忽略了一个最基本的事 实,即板中心区(焊缝及近缝区)处于冷却过程,而不 是加热过程,在这两个过程中,应力应变发展过程是 不同的。 下面分析一下薄板焊接应力应变发展过程。温 度场分布如图 4a所示。虚线将焊接板材分为升温 区和降温区两部分, 以焊接方向为准,虚线前为升温 图 3� 低碳钢板焊接纵向应力应变分布 Fig. 3� Lonitudinal stress and strain distribution patterns in the mild steel welded joint 图 4� 低碳钢板中心堆焊纵缝时横截面应力应变的变化 Fig. 4� Change of stress and strain distribution pattern of cross section of surfacing on center of mild steel sheet 区,虚线后为降温区, 可以看出, 焊缝处在降温区。 现取三个典型截面, 分析应力应变发展过程。截面 I取自熔池前沿。此截面全部在升温区, 中心区升 温很高, 两边升温很低, 中心区膨胀受阻产生压缩塑 性应变,应力应变分布见图 4b, 这与图 3类似。截 面 II取自熔池最宽处。截面 III取自熔池尾部后不 远处,其最高温度约为 1 450 � ,在图 4c中同时画出 截面 II和 III的温度分布。焊缝降温将产生收缩,两 侧的金属阻碍其收缩,结果将产生拉伸应变,温度高 于力学熔点处, 不会有应力存在, 因此没有弹性应 变, 全部拉伸应变为塑性应变, 其大小相应于图 4c 斜阴影高度, 在熔合线处拉伸塑性应变出现最大值。 离焊缝稍远处将引起升温,它的膨胀受阻, 将产生压 应变和压应力,板边则出现与压应力平衡的拉应力, 应力应变分布如图 4c所示。在随后的降温过程中, 焊缝一直承受拉伸应变,在温度降到力学熔点以前, 这种应变一直是拉伸塑性应变。当温度降到力学熔 56��� 焊 � 接 � 学 � 报 第 21卷 点以后,焊缝开始出现弹性拉伸应变和拉应力。可 以看出,焊缝从凝固温度降到室温的全过程中不存 在压应力和压应变, 更不存在压缩塑性变形。至于 熔池前沿升温膨胀产生的压缩塑性应变和变形,因 为焊缝尚未形成,故不能算作焊缝的压缩塑性变形。 3 � 讨 � � 论 3. 1 � 应力应变分布 从尼古拉也夫 � � 院士给出的图2、3所示的应 力应变分布可知,焊缝存在压缩塑性变形,这种传统 的观点一直被焊接界接受, 从而也形成了消除应力 的原理在于设法使焊缝产生拉伸塑性变形以抵消、 补偿已产生的压缩塑性变形的传统观点。图 2、3的 根本错误在于没有分清加热过程还是冷却过程,若 是加热过程, 图 2、3显然是正确的。但是对焊缝而 言,只有冷却过程。在冷却过程中,焊缝收缩受阻将 产生拉应力和拉伸变形, 不存在压缩塑性变形,因此 前述文献[ 3]的观点是正确的。焊接应力应变分布 是消除残余应力原理的基础, 基础变了,消除应力的 原理需要重新论述了。 3. 2 � 应变曲线出现拐点的原因 图4c中应变曲线在熔合线处出现拐点,这是由 于局部熔化所致。熔化时温度分布出现拐点, 这引 起应变分布出现拐点。如果加热温度未达熔化温 度,金属未熔化,则温度分布和应变分布都不会出现 拐点, 也不会出现图 4c所示的应变分布。此时的应 变分布应该是如图 3所示。看来图 3与图 4c 中相 反符号的塑性应变的出现是由于是否考虑金属熔化 现象造成的。 3. 3 � 焊件纵向变短的原因 焊件沿焊接方向缩短是持有焊缝受压缩观点的 一个理由, 即焊缝受压缩,产生压缩塑性变形, 因此 变短了。从上述分析可知, 焊缝沿纵向不存在压缩 塑性变形,并且一直受拉伸,并产生明显的拉伸塑性 变形。那么焊件沿焊缝方向为什么会变短呢? 焊缝 受拉伸,不等于此处的金属一直受拉伸,在熔池前沿 的金属受热产生明显的压缩塑性变形, 见图 4b。这 种压缩塑性变形量与焊缝冷却拉伸变形量相当。此 外,熔池凝固还会产生大约 3%收缩。三项合在一 起,总的结果是产生了收缩变形,焊件变短了。可以 说焊件变短主要是由于金属局部熔化随后凝固收缩 造成的。 3. 4 � 液化裂纹形成机制 某些高强钢焊接时, 在熔合线两侧容易产生横 向微裂纹, 长度一般不足 0. 5 mm, 具有晶间特征,示 意图见图 5[ 10] ,属于液化裂纹,是热裂纹的一种。拉 应力和拉应变是产生热裂纹的必要条件。从图 2和 图 3给出的应变分布可知,在高温阶段, 焊缝及近缝 区存在压缩塑性变形。如果放弃力学熔点的假设, 还会存在少量的压应力。这样, 图 5所示的液化裂 纹就失去了产生的条件。 图 5 � 液化裂纹示意图 Fig. 5� Schematic illustration of liquation cracks 按照作者给出的应力应变分布(图 4c) ,能够很 好地解释图 5所示的液化裂纹形成机制。当熔合线 附近处于脆性温度时,存在拉应力和拉应变,并且熔 合线处应变值最大,产生微裂纹。随着远离熔合线, 不管是焊缝一侧还是热影响区一侧,应变值陡降,裂 纹难以扩展。这就容易解释液化裂纹分布在熔合线 附近和裂纹很短的现象。 4 � 焊接残余应力消除原理 4. 1 � 机械拉伸法 焊缝及近缝区纵向残余拉应力一般为屈服应力 �s ,相应的弹性应变为 �s,加上拉伸载荷将产生工作 应力 �p 和应变 �p。因为原来的残余应力已达屈服 点, 故 �p 全部为拉伸塑性应变, 卸载后焊缝和近缝 区的弹性应变为 �s- �p ,最终的残余应力为 E ( �s- �p )。显然 E( �s- �p )< E�s ,即残余应力降低。若外 加载荷引起的工作应力 �p = �s, 则卸载后残余应力 全部消失。机械拉伸法消除应力的原理可以这样描 述: 通过加载拉伸,使焊缝及近缝区产生拉伸塑性应 变, 从而使拉伸弹性应变和拉应力减少。 4. 2 � 温差拉伸法和低应力无变形焊接法 低应力无变形焊接法, 不管是�静态�还是� 动 态�的,都是在焊接过程中建立一种焊缝温度低于两 侧的温度场, 与焊后进行的温差拉伸效果是一样的, 其原理在此一并叙述。 在建立两侧的温度高于焊缝及近缝区的温度场 时,两侧高温区的金属膨胀引起焊缝及近缝区拉伸 应力 �T 和拉伸应变 �T , �T 与原来的残余应力叠加, 引起材料屈服, 若原来的残余应力达到屈服应力 第2期 王者昌:关于焊接残余应力消除原理的探讨 57��� �s ,则产生的应变 �T 全部为拉伸塑性应变。最终残 余应力为 �s- �T ,残余应力减少了。若 �T= �S ,则残 余应力全部消除,若 �T> �S,则焊缝出现压应力。也 就是说,此法不仅可消除残余拉应力,还可产生残余 压应力。 温差拉伸法和低应力无变形焊接法消除应力的 原理可以这样描述: 在建立两侧温度高于焊缝的温 度场时,焊缝产生拉伸塑性应变,这与机械拉伸起到 类似作用,使应力降低。其原理也可这样描述:在建 立两侧温度高于焊缝的温度场后,在随后的均温过 程中, 两侧高温区的降温收缩将对焊缝及近缝区沿 纵向进行压缩, 抵消原来的拉应力, 使残余应力降 低。 4. 3 � 滚压法 滚压前焊缝的残余拉伸应力为 �S ,弹性应变为 �s,焊缝滚压时产生拉伸塑性变形和拉伸塑性应变 �p ,滚压后剩余的弹性应变为 �s- �p ,相应的残余应 力为 E( �s- �p ) ,显然 E( �s- �p) < E�s ,即残余应力 降低。若 �p= �s, 则残余应力全部消失。若 �p > �s , 则焊缝出现压应力。滚压法消除残余应力的原理可 以这样描述:焊缝滚压时产生拉伸塑性应变, 使最终 的残余弹性应变减少,从而降低了残余应力。 可以看出, 上述消除残余应力原理中,有一个共 同点,即产生拉伸塑性应变,消除应力的过程实质就 是将拉伸弹性应变转变为拉伸塑性应变的过程。 推而广之, 所有消除残余应力的过程都是将弹 性应变转变为塑性应变的过程。例如, 整体和局部 高温消除应力处理是利用金属屈服点的降低和保温 过程中应力松驰, 使弹性应变转变为塑性应变的。 锤击和爆炸消除应力分别是用锤击和爆炸的冲击力 使残余拉应力区产生拉伸塑性应变, 若这一应变小 于 �s , 则应力降低, 若等于 �s, 则应力全部消除, 若 大于 �s ,则产生压应力。振动消除应力时, 振动产 生的交变载荷与残余应力叠加,交变载荷中的拉伸 载荷与机械拉伸起到类似的作用,引起构件相应部 位拉伸塑性应变,残余应力降低。 5 � 结 � � 论 (1) 根据作者提出的应力应变分布 (图 4c)可 知,焊缝不存在压缩和压缩塑性变形,而是受到拉伸 和产生拉伸塑性变形。在接近熔点温度, 熔合线处 拉应变出现最大值,在熔合线两侧,随着到熔合线距 离的增加,拉应变激剧减少。 ( 2) 焊接时焊缝不存在压缩塑性变形, 消除焊 接残余拉应力的原理不是设法产生拉伸塑性变形来 抵消、补偿焊缝产生的压缩塑性变形, 而是产生塑性 应变抵消弹性应变。在一般情况下,焊缝和近缝区 产生拉伸塑性应变,抵消此处的拉伸弹性应变, 从而 减少焊缝及近缝区残余拉应力。 ( 3) 用传统的焊缝和近缝区存在压应变的观 点无法解释横向液化裂纹形成机制,用作者提出的 图 4c中应变分布则能很好的解释,并且由于高应变 区很窄, 所以液化裂纹很短。 参考文献: [ 1] � 机械工程手册编辑委员会.机械工程手册(第二版 ) [M ] .北京: 机械工业出版社, 1996, 6~ 20. [ 2] � 中国机械工程学会焊接学会.焊接手册(第三卷) [M ] .北京:机 械工业出版社, 1992. [ 3] � 田锡唐.焊接结构[M ] .北京:机械工业出版社, 1997. [ 4] � 关桥.推广应用焊接滚压工艺的几个问题[ J ] .航空工艺技术, 1980, (2) ; 21~ 26. [5] � 关桥.飞行器薄壳结构变形控制与焊接力学的发展[ C] . 第八 次全国焊接会议论文(第一册)北京:机械工业出版社, 1997, 51 ~ 57. [ 6] � 关桥,等.动态控制的低应力无变形焊接新技术[ J ] .焊接学报, 1994, 15( 1) : 8~ 14. [ 7] � 关桥,等.航宇薄壳结构的低应力无变形焊接新技术[ J ] .航空 工艺技术. 1996, 4; 4~ 7. [ 8] � �� !∀#∃% & ∋ ,�� !∀# ∃��%&∋ (∀)∗%∀%∗∗ ∗ +�(!%( #, ∃��%&∋ �� !∀#∃%&∀∀ [M] . �� !∀#∃%&∀∋(, 1965, 155~ 158. [ 9] � �� !∀#∃% & ∋, ��, �� !∀#∃ %&∀∋(!)%∗++ [ M ] . �� !∀#, 1982, 194~ 195. [ 10] � Savage W F.A mechanism for crack format ion in Hy- 80 steel weld� ments [ J] . Welding Journal, 1967, 46(2) : 94s~ 96s. 作者简介: � 王者昌,男, 1938年出生,研究员。兼任中国焊接学会 IXb专业委员会、中国宇航学会材料工艺专业委员会和中国空间科 学学会机械专业委员会委员,中国水机磨蚀中心理事。主要从事钛 合金焊接、焊接气孔、焊接热裂纹、堆焊材料和水轮机抗磨蚀用钢的 研究。研究成果曾获全国科学大会奖和国家特等奖各 1项、科学院 二等奖 2项、航天部二等奖 1项、水利部一等奖 1项。申请五项国家 发明专利。参与�机械工程手册�、�焊接手册�和�材料大词典�的编 审,发 表 关于同志近三年现实表现材料材料类招标技术评分表图表与交易pdf视力表打印pdf用图表说话 pdf 论文 80余篇。 58��� 焊 � 接 � 学 � 报 第 21卷 crack of stainless steels, namely the, st ress�strain f ield in the trail of molten� weld pool. First ly, the effect of the deformation in the molten�weld pool was eliminated after the element rebirth method was adopted. Secondly, the influ� ence of solidificat ion shrinkage was considered by increasing thermal expan� sion coefficients of the steels at elevated temperature. Finally, the stress� strain dist ributions of different condit ions have been got and analyzed. Fur� thermore, the driving force curves of the solidif ication crack of the steels have been obtained by convert ing strain�position curves into strain�t emperature ones which found a basis for predict ing welding solidification crack. Key words: w elding solidif ication crack; welding sol idificat ion crack driving force; stress�strain field; numerical simulation A Direct Assessing Method of Heated Widths During Local PWHT � � WANG Jian�hua(Shanghai Jiao tong University, Shanghai, China) , LU Hao, Hidekazu Murakawa. p39~ 42 Abstract: Local postweld heat treatment ( local PWHT ) is usually per� formed for tempering and relaxation of residual stresses. Many factors have an influence on PWHT procedures and the heatedwidth is the most important pa� rameter controlling the ef fectiveness of local PWHT. However, the determina� tion rules of this parameter are very different in the different codes. In this study, a direct method to assess the effectiveness of local PWHT was used based on the thermal�visco�elastic�plastic FEM with the consideration of creep phenomena. Thismethod clearly shows the whole history of stress relief during PWHT and a critical heated width can be obtained. The pipe with original welding residual st resses is analyzed under different condit ions of PWHT. In� vestigations show that the maximum residual st ress after PWHT decreases when the heated width increases. When the heated width becomes large e� nough, the residual stress after PWHT changes very slow ly and a crit ical heat� ed width can be foundwhich gives a residual stress close to the value obtained from th uniform PWHT. A series of diff erent PWHT condit ions are studied to f ind the critical heated width by using this method. It is found that a heated area of 5 rq centered on weld seems resonable from the view of st ress re� lief . Key words: postweld heat treatment ; residual stress; heated width; finite element method Influence of Processing Parameters on Geometrical Features of Powder Feeding Laser Cladding � � ZHANG Qing�mao( The Quartermaster Univer� sity of PLA, Changchun, China) , LIU Xi�ming, WANG Zhong�dong, GUAN Zhen� zhong. p43~ 46 Abstract:The influences of laser processing parameters with auto�f eed� ing on the geomet rical features of cladded coat ing by cladding Ni60A powders on steel Q235 plate have been invest igated. The rules of the combined param� eters ( such as laser energy density Pw , interaction t ime T , powder feeding rate and scanning speed Vs) on the sizes of the coatings have been amphat i� cally discussed. In order to express the relat ionship between the processing pa� rameters and the macroquality of cladded coat ing , the equation expressing the relationship between the covering rate and the processing parameters was de� rived . By varying the powder feeding rate and scanning speed under definite laser power and beam spot dimensions, coatings with different thickness were obtained . The covering rate was calculated approximately based on metallo� graphical measurement. The result s show that the cross�sect ion S , w idth vari� able and contact angle are mainly controlled by the laser energy density and interact ion time, they all become larger with the increase of laser energy den� sity and interaction time. Key words:metallographical measurement ; laser energy density ; cover� ing rate J�integral of Surface Crack in Overmatched Joint � � LI Ji�hong ( The Inst itute of Welding, Xi� an Jiaotong University, Xi� an, China) , ZHANG Jian� xun, PEI Yi. p47~ 50 Abstract:The part�through surface cracks exist widely in pract ical weld� ed structure, and the invest igation of the elast ic�plastic fracture mechanics parameters ( eg. J�integral) of this three�dimensional mechanical heterogene� ity is not enough. In this paper, the J�integral of surface cracks in over� matched weldment with different matching rat ios has been investigated by us� ing direct evaluat ionmethod. The influences of matching ratio of joint s on the crack driving force ( J� integral, crack mouth opening displacement CMOD) and strain distribut ions along the contour have been discussed in detail. The result s indicate that the comprehensive effect of crack position and the match� ing ratio of w elded joint dominate the distribution of strain. With the increas� ing of load, the obvious strain concentration may be produced in the parent metal zone close to weld. Moreover, with the decreasing of the matching ra� t io, the degree of the strain concentrat ion grows, the deformation of weldmet� al decreases to a certain extent , and the crack driving force increases. Key words:welded joint ; surface crack; J�integral Analysis of Metal Transfer and Usabili ty of High Cellulose Electrode� � LIU Hai�yun (Taiyuan University of Technology, Taiyuan, China) , WANG yong, WANG Bao. p51~ 54 Abstract: By using high�speed photographic method and usability exper� iments, the metal transfer form and usabil ity of high cellulose electrode have been analyzed. The results show that the metal transfer forms of high cellulose electrode contain spray transfer, explosive transfer and short circuiting trans� f er. The spatter forms include big and small droplet spatters. The transfer and spatter of big droplets show obviously periodic characteristic, and the small droplet spray t ransfer and spatter exist through whole welding. Strong and reg� ular spray transfer form is advantageous to the usability. The big droplet spat� t er is the main reason for bad usabil ity, e. g. low deposit ion efficiency, unsta� ble arc etc, . and it should be analyzed and prevented further. Key words: high cellulose elect rode; metal t ransfer; usabilit y Discuss on Principle of Relieving Welding Residual Stress � � WANG Zhe�chang ( Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China) . p55~ 58 Abstract:According to traditional viewpoint , for the mechanical stress rel ieving method, the low temperature stress relieving method, the rolling stress relieving method and Low�Stress Non�Distort ion Welding Technology, 2000, Vol. 21, No. 2 � � � � � � � TRANSACTIONS OF THE CHINA WELDING INSTITUTION � � � � � � � � � � � � � � the residual stress relieving principle is to compensate the compressive plast ic strain in the weld with tensile plast ic strain which is produced in the welding process. In this paper, a new stress and strain developing process is given. The w eld metal always bears tensile stress and there is no compressive plast ic strain being produced in the welding process. In the britt le temperature zone, the maximum tensile stress appears in the fusing line and it decreases sharply far from the fusing line. The stress�relief principle is to reduce or eliminate e� lastic strain w ith plast ic strain. In general case, the principle is to reduce or eliminate the original tensile elastic strain with tensile plast ic strain. In this paper, the principle of all kinds of residual stress relieving methods is also discussed. It also is sat isfactorily interpretedwhy the transverse l iquation crack appears in the adjacency to fusing line and it is very short . Key words:w elding residual stress; stress rel ieving; plast ic st rain; elast ic strain; liquation crack Investigation of an Engineering Simplification Approach for LOP� s J� integral Calculation � � MENG Xiang�feng( Ocean University of Qingdao, Qingdao, China) , WANG Wei�qiang, ZHANG Xua�li, GUO Jian�zhang. p59~ 62 Abstract: The lack of penetration (LOP) is a very common type of dis� continuit ies in welds, so that how to simplify it more scientifically and reason� able and therefore to conduct it s fracture analysis are a problem cont inuously interested to engineering and academic circles. In this paper, several common root shapeswere chosen among the photos of LOP� s root prof iles and five typ� ical sorts of notches with regular root shapes w ere obtained after some extent simplificat ion to the LOP� s root shapes. Based on this, the elast ic�plastic finite element method was adopted in the paper. The finite element calculat ions were conducted by taking the geomet rical shapes and sizes of nothch root as param� eters and a series of J�L r curvesw ere gotten. Through analyzing the curves, the main factors influencing the value of J� integral can be found, they were the notch wedth or the notch root curvature and the shapes of notch, and f inally the root shape with the maximum J� integral value was derived to be the flat end shape. Therefor, the values of LOP� s J� integral can be calculated simply and conservatively by adopting the notch with a flat end proposed in this pa� per, and furthermore the engineering calculat ions of LOP� s J�integral values can be realized. Key words: lack of penetration; J� integral; finite element analysis; engi� neering simplification method New Model Cu�Ni Alloy PTA Surfacing Material and Its Corrosion Re� sistance� � JI Jie( Tianjin University, Tianjin, China) , ZHANG Wen�yue, ZHANG Shu�sheng, LIU Li. p63~ 66 Abstract: By putting some alloy elements into white copper B30, through weldability examination, static corrosion trial and polarized curve test, a kind of corrosion resistance alloy powder to be used for plasma surfacing has been studied and prepared. The reason of reducing the corrosion�resisting property of the white copper alloy B30 after adding alloy elements has been also inves� tigated by means of SEM,AES,XPS. Key words: Cu�Ni alloy; powder plasma arc surfacing; corrosion Infrared Telecontrol of IGBT Arc Welding Inverter � � PI You�guo(The Automation Engineering E/ R Center of Guangdong Academy, Guangzhou, China) ,HU Dao�ming,HUANG Shi�sheng. p67~ 69 Abstract: The design of infrared telecontrol IGBT convert ing welder is presented in this paper and the designs of the system, power circuit, infrared system hardware and software are presented in detail also. The controlled dis� tance is as far as 10 meters and the control scope is as wide as � 45�. The welder has its output current 250A, both good static and dynamic characteris� t ics and can stably work in welding workshop Key words: infrared telecontrol; converting welder; IGBT Switching Welding Power Source Controlled by Microcomputer� � WU Wan�hua ( Shanghai Jiaotong University, Shanghai, China ) , YAO Shun, YU Hai�liong. p70~ 73 Abstract:The paper introduces the real value of the sw itching power source designed by authors and the systemic analysis of the principle and con� stitution of the power supply including the microcomputer controlling system . The authors put forward some viewpoints about the new welding power source . The power source which is controlled by the microcomputer system in this paper adopts the giant transistor (GTR) , and have it work in both the condi� t ion of � on� and� off� . Therefore , it overwhelms lower eff iciency of analogue transistor power source, and keeps a stable operat ion state. In the meant ime, the power source makes use of single chip microcomputer controlling technolo� gy and realizes the function of previous setting up the welding parameters . This power can also modify the welding voltage Uf through feedback control� ling so that gets constant voltage characteristic. Key words:microcomputer control; switching type; pulse width modula� t ion Measuring Normal Deformation Produced by Residual� stress in Friction Welding Joint Using Double�exposure Holography � � LIU Xiao�wen (Northwestern Polytechnical University, Xi� an, China) , DU Sui�geng, LIU Xiao�zhong, WANG Guo� zhi. p74~ 76 Abstract:The principle of measuring normal deformation of the surface of frict ion welding joint is analyzed. When the experimental system meets some condit ions, the interferometric fringe obtained from double�exposure hologram reflects the amplitude of normal deformation. In experiment , a Q� switched ruby laser is used as light source, and a double�exposure hologram of frict ionwelding joint is obtained. In this paper, the holographic interferomet� ric f ringe is collected through a CCD image process system and stored into computer. After using computer to process these data, the amplitude of nor� mal deformat ion of the surface of friction welding joint is obtained. Key words: double�exposure holography; frict ion welding joint; normal deformat io