集装箱船用EH47高止裂钢的组织和性能北大核心CSCD

借助SEM,EBSD等显微组织分析手段及力学性能测试,研究了集装箱船用EH47级别高止裂韧性钢的显微组织与力学性能的关系。实验结果表明,针状铁素体+贝氏体的组织可满足集装箱船用EH47级别高止裂韧性钢对止裂韧性性能的严格要求。晶粒尺寸细小的针状铁素体+贝氏体相互配合具有较高的强度、止裂韧性性能;增大针状铁素体晶粒尺寸或引入多边形铁素体过多则会降低材料强度;而贝氏体体积分数过多、晶粒尺寸过大时,材料塑性和止裂韧性性能显著降低。     

集装箱船用EH47高止裂钢的组织和性能

借助SEM,EBSD等显微组织分析手段及力学性能测试,研究了集装箱船用EH47级别高止裂韧性钢的显微组织与力学性能的关系。实验结果表明,针状铁素体+贝氏体的组织可满足集装箱船用EH47级别高止裂韧性钢对止裂韧性性能的严格要求。晶粒尺寸细小的针状铁素体+贝氏体相互配合具有较高的强度、止裂韧性性能;增大针状铁素体晶粒尺寸或引入多边形铁素体过多则会降低材料强度;而贝氏体体积分数过多、晶粒尺寸过大时,材料塑性和止裂韧性性能显著降低。     

钢的动态断裂韧性及止裂韧性的研究现状

根据国内外关于动态断裂力学性能的研究文献，对动态断裂韧性KId(JId)及止裂韧性的研究现状进行了概括总结。     

脉冲放电裂纹止裂处的热处理研究

对含有裂纹的金属构件进行脉冲放电止裂时，裂纹尖端由于电流的绕流热集中效应，在瞬间使裂尖熔化形成焊口。由于裂尖附近超快速加热和冷却，金属材料完成了一次超高速冲击淬火。采用数值模拟计算了脉冲放电超快速加热时裂纹尖端温度、温度梯度场；通过脉冲放电止裂试验研究了裂尖超高速淬火全过程。通过对止裂后裂尖的金相组织观察和微观机理分析发现；超细化的条状马氏体、极少量残留奥氏体和细颗粒碳化物的出现明显提高了裂纹尖端的硬度、韧性和耐磨性。     

Cr12模具钢裂纹电磁热止裂的研究

采用脉冲电流发生装置对Cr12模具钢中裂纹进行了脉冲放电止裂。放电后,裂纹尖端金属熔化形成焊口和压应力区,使裂纹尖端钝化,达到了止裂的目的。同时在裂纹尖端处得到了超细化的隐晶马氏体和细粒碳化物等微观组织,极大提高了裂纹尖端处的硬度、强韧性和耐磨性。     

构件中半埋藏裂纹在线止裂及力学性能分析

依据热-电耦合数值分析结果选择合适的脉冲放电电压,应用ZL-2超强脉冲电流发生装置,对带有半埋藏裂纹的45号试件进行拉伸载荷下脉冲放电止裂研究。放电止裂后,裂纹尖端瞬间熔化、钝化,达到了裂纹止裂目的。止裂中,试件在拉伸载荷作用下没有瞬间开裂。对止裂前后的拉伸试件通过冲击试验机、扭转试验机进行了冲击和扭转力学性能测试。研究结果表明,电磁热裂纹止裂可以有效提高试件的抗冲击和抗扭力学性能。     

含全埋藏裂纹的T10钢焊接接头电磁热止裂分析

通过有限元分析方法,计算出含有圆形全埋藏裂纹的焊接接头电磁热止裂温度场分布,并通过ZL-2放电装置,对含圆形埋藏裂纹的T10钢焊接接头进行电磁热止裂试验。研究结果表明,止裂瞬间,焊接接头中埋藏裂纹裂尖处温升超过金属熔点,裂尖熔化、钝化,阻止了裂纹的进一步扩展;止裂后,在裂尖附近有白亮层组织出现。止裂前后的T10钢焊接接头力学性能测试表明,止裂后焊接接头所能承受的最大扭矩和抗扭强度提高了约17%。     

40GrNiMo试件单边裂纹在线止裂及组织分析

对带有单边裂纹的40GrNiMo金属薄板试件进行了脉冲放电在线止裂实验研究。在超强脉冲电流作用瞬间,单边裂纹尖端熔化、裂尖钝化,曲率半径增加了2～3个数量级,并在裂纹尖端处产生热压应力场,达到了遏制裂纹扩展的目的。止裂前后裂纹前缘的微观组织对比分析发现,止裂后裂尖处组织更加均匀细小,且裂尖处Cr原子数量增加,其他元素与Cr生成更多的合金组织,得到强韧性均高的微观组织,提高了止裂后构件的力学性能。     

3Cr2W8V热疲劳裂纹的止裂与修复

运用电磁效应理论最新研究成果,采用脉冲放电方法,对3Cr2W8V热挤压凸模的热疲劳裂纹实施了止裂试验。止裂后的裂纹尖端变得十分圆整。达到了钝化止裂的目的。显微组织分析证明：止裂处出现了强韧性极高的超细化组织,改善了裂尖处的机械性能。止裂也为热疲劳裂缝刷镀修复创造了理想的先决条件。     

45钢构件电磁热裂纹止裂后残余应力分析

对带有半埋藏裂纹的45钢金属构件进行电磁热止裂实验发现,止裂后,半埋藏裂纹裂尖处熔化、钝化,并有金属喷射现象;采用超声波对比测试法,分析了止裂前后试件内残余应力的变化情况,实验测得止裂后超声波声程减小,表明试件内部残余应力增大;通过ANSYS有限元软件,采用间接耦合方法,对半埋藏裂纹电磁热止裂过程进行数值分析,得到了止裂后构件内残余应力场的具体类型及分布情况。     

裂纹尖端塑性区对304不锈钢脉冲电流止裂的影响

分别对裂纹尖端附近有塑性区和无塑性区的304不锈钢脉冲电流止裂试样进行了显微观察和纳米压痕试验。结果表明,有裂纹尖端塑性区的304不锈钢,在脉冲电流止裂后,止裂处发生了相变和再结晶,在温度场和应力场共同作用下分别形成了凝固区、细晶区和形变诱发马氏体区;而无裂纹尖端塑性区的304不锈钢,裂纹止裂处只有凝固区。纳米压痕试验表明304不锈钢的疲劳裂纹尖端处具有较大的残余应力,且残余应力随着远离裂纹尖端而迅速衰减;经过脉冲电流止裂后,裂纹尖端形变诱发马氏体的产生导致该处体积膨胀,产生相变应力,增大了裂纹止裂处周边的压应力值,这有利于抑制裂纹的二次扩展。     

Controlled crack arrest in brittle thin films: The effect of embedded voids

Controlled crack arrest is useful for controlling self-assembled crack paths in micro-fabrication, as well as limiting crack length in toughening composites. Compliant inclusions and voids can effectively attract and arrest cracks, thereby controlling the crack pattern. Analytical stress solution indicates that when the inclusion is about 10 times more compliant than its matrix, it may be effectively modeled as a void. The crack arrest capability is expressed in terms of the critical angle of the initial crack path, as the inclusion size, shape, crack origin and film properties are varied. Simple criteria are established to maximize the crack arrest ability and to determine the critical crack angle. The effectiveness of using different void patterns to arrest cracks is also explored. The results are useful for both controlling and restricting cracks in brittle thin films, through the utilization of compliant or void-like inclusions as crack arrestors.     

单脉冲电流对高速钢裂纹的止裂效果

利用电磁热效应原理,探讨了超强度脉冲电流对高速钢裂纹止裂的可能性,结果表明,利用电磁效应可在裂纹尖端形成焊口,使裂纹尖端的曲率半径增大,抑制了裂纹扩展,同时,对裂纹尖端热影响区的组织进行了分析,讨论了裂地端的组织变化对止裂效果的影响。     

金属构件内埋藏椭圆形斜裂纹脉冲放电瞬间温度场的分析

采用数值分析的方法,研究了含埋藏椭圆形斜裂纹的金属构件放电瞬间的温度场,建立了带有空间裂纹的三维有限元分析模型。模拟了利用电磁热效应进行裂纹止裂的过程,得到埋藏椭圆形斜裂纹在不同倾斜角度情况下脉冲放电瞬间温度场的分布状态,给出了电流密度矢量图,分析了裂纹面倾斜角度对温度场的影响规律。计算结果表明,当通入的脉冲电流密度一定时,电流方向与裂纹面方向的夹角是影响止裂效果的关键因素。研究中同时采用ZL-2脉冲放电装置,完成了冷作模具钢模具中裂纹的电磁热止裂。     

Effect of toughness distribution in the thickness direction on long brittle crack propagation/arrest behaviour of heavy gauge shipbuilding steel

ABSTRACT

Brittle crack arrestability of the heavy gauge steel plates for shipbuilding is now an important issue for the recent mega container ships. In the present work, the brittle crack arrestability of the steel plate with different toughness distributions in thickness is examined in ultra-wide duplex ESSO tests. It is examined whether a running long brittle crack arrests or not in flat temperature condition in ultra-wide duplex ESSO test that are harder mechanical conditions similar to an actual ship hull condition. Test temperatures are selected at which arrest toughness, Kca, evaluated by temperature gradient type standard ESSO test is the same for two test plates. The steel plate with higher toughness in mid-thickness (t/2) than that in quarter thickness (t/4) could arrest a running long brittle crack although the plate with lower toughness in mid-thickness than that in quarter thickness could not arrest it. The typical split-nail shape appeared at the arrested crack front in the plate with higher toughness in mid-thickness than that in quarter thickness. The numerical analyses also demonstrate that the local stress intensity factor at the arrested crack tip is changing sensitively to the crack front shape. It suggests that the higher brittle crack arrestability appears due to the split-nail shape of the arrested crack front enhanced by the inhomogeneous toughness in thickness.     

电磁热效应对35钢裂纹尖端组织及止裂效果的影响

在自制的ZL－1型超强度脉冲电流发生装置上,对35钢的电磁势效应理裂纹止裂效果进行了初步研究。结果表明：利用电磁热效应可在放电瞬间在裂纹尖端形成焊口,使裂纹尖端曲率半径增大,达到抑制裂纹扩展的目的。对裂纹尖端热影响区的显微组织进行了分析。     

Crack arrest and velocity oscillations due to local fracture-plasticity effect in polymers

Nizhny Novgorod University, Nizhny Novgorod, 603600 Russia The nonisothermal dynamics of the unstable crack growth in polymers is investigated. The system of general equations (the heat conductivity equation and the crack propagation equation) is formulated taking into account the near-crack-tip plasticity, the specific geometry of the specimen (Chevron) and real temperature dependences of the material parameters (flow stress, critical stress intensity factor, specific heat, etc.). Numerical analysis of general equations reveals the existence of the high-frequency oscillations of the crack velocity and the crack-tip temperature in the course of the crack propagation. The stage of the oscillational crack advance is completed by the arrest. The conditions of crack arrest are discussed.     

Brittle crack arrestability of thick steel plate welds in large structure

Recently, there has been such a critical issue in shipbuilding industry that much larger and stronger ships are required to develop oil and gas in the Arctic region. Attention has been paid to obtaining high strength, good toughness at low temperature, and good weldability. An experimental study was performed to evaluate the brittle crack arrest toughness value (K_ca) and brittle crack arrest method of welded joints using EH40 grade steel with a thickness of 80 mm. The test specimens were made by both flux cored arc welding (FCAW) and combined welding (EGW+FCAW) processes. Temperature gradient ESSO test was performed to measure the Kca of the base metal. Also, a constant temperature (−10 °C) ESSO test was performed to establish a brittle crack arrest method using high toughness welding consumable with real structural specimens. The research aims in this study were to investigate the effect of joint design and welding consumable for the crack arrestability of thick steel plates using EH40 grade shipbuilding steel of straight block joint weld line with two kinds of welding processes.