解理裂缝过界扩展模型

根据对低碳钢解理断裂显微特征分析的结果,以相邻解理系统失配作为裂纹过界扩展的阻力源,建立了解理裂纹过界扩展的临界条件,并根据解理系统的空间分布的统计特性,对裂缝试样的解理断裂行为进行了计算模拟。计算结果与实验结果一致。     

氢促进解理裂纹形核的机制

求出了有氢和无氢条件下稳定解理裂纹核尺寸ａｃ（Ｈ）和ａｃ，由于氢促进部塑性变形，氢降低表面能以及裂纹核中存在氢压，故ａｃ（Ｈ）＜ａｃ，这就表明，氢能促进解理裂纹的形核稳定化。     

IN-SITU OBSERVATION OF CRACK PROPAGATION IN PST CRYSTALS OF Ti-49% AlALLOY

１ＩＮＴＲＯＤＵＣＴＩＯＮγＴｉＡｌｂａｓｅａｌｏｙｈａｓｂｅｅｎｏｆｍｕｃｈｉｎｔｅｒｅｓｔａｓｓｔｒｕｃｔｕｒａｌｍａｔｅｒｉａｌｓｆｏｒｅｌｅｖａｔｅｄｔｅｍｐｅｒａｔｕｒｅａｅｒｏｓｐａｃｅａｐｐｌｉｃａｔｉｏｎｓｂｅｃａｕｓｅｏｆｉｔｓｌ...     

TiAl型金属间化合物解理断口的纳米尺度研究

采用隧道扫描显微镜（ＳＴＭ）对Ｔｉ３Ａｌ及Ｔｉ－２４Ａｌ－１１Ｎｂ试样在空气中拉伸的解理断口进行了研究。结果表明，ＳＴＭ可以揭示出解理断口上存在许多纳米尺度的细节，如纳米尺度的微台阶、微孔洞（微韧窝）及空位等。     

腐蚀疲劳裂缝扩展的韧带模型

采用４３４０、１５和Ａ５０８三种结构钢,八种热处理状态;测定了它们在空气、海水和蒸馏水中的疲劳、应力腐蚀和腐蚀疲劳裂缝扩展速率,并进行了定量断口分析。在比较了叠加模型、竞争模型与实验结果的差异之后,提出了腐蚀疲劳裂缝扩展的韧带模型,拟出了该模型的计算程序。结果表明,尽管这个模型还比较粗糙,某些常数的决定还有点勉强,但由此估算的腐蚀疲劳扩展曲线,无论在形状和数值上,都与实验吻合;而它的简单方便,为工程应用提供了有利条件。     

RELATIONSHIP BETWEEN M-A CONSTITUENT AND CLEAVAGE FRACTURE BEHAVIOUR OF GRANULAR BAINITIC WELD METAL

The cleavage fracture mechanism of granular bainitie weld metal in 15MnVN steel has beeninvestigated.SEM observation of a special specimen for revealing simultaneously fracture sur-face and microstructure shows that the cleavage of the weld is initiated by M-A constituent.The 95th percentile equivalent diameter of M-A constituent controls the cleavage fracturestress of the weld metal.     

C—Si—Mn—B贝氏体钢的疲劳裂纹扩展特性

本文研究了C－Si-Mn-B贝氏体钢的疲劳裂纹扩展特性。结果表明,在强度相近的情况下,含1．8％Si钢的门槛值△Kth较0．6％Si钢的低,而且钢中的残余奥氏体对提高△Kth值并非有利。1．8％Si钢的△Kth值随钢的屈服强度降低而提高,然而450℃回火后,虽然△Kt提高,但裂纹扩展速率也显著提高,这表明450℃回火贝氏体脆性促进了疲劳裂纹的扩展。在应力强度因子较高的范围内,疲劳裂纹扩展速率受钢的断裂韧性影响,断裂韧性高,裂纹扩展速率低。     

HIGH TEMPERATURE CRACK PROPAGATION AND FRACTUREOF SUPERALLOYS

１．ＩｎｔｒｏｄｕｃｔｉｏｎＨｉｇｈｓｐｅｅｄｒｏｔａｔｉｎｇｄｉｓｋｓａｒｅｃｏｎｓｉｄｅｒｅｄａｓｍｏｓｔｉｍｐｏｒｔａｎｔｈｏｔｃｏｍｐｏｎｅｎｔｓｆｏｒｔｕｒｂｏｃｈａｒｇｅｒｓ,ｅｘｐａｎｄｅｒｓ,ｃｏｍｐｒｅｓｓｏｒｓ,ｌａｎｄｂａ...     

腐蚀疲劳裂纹扩展的断裂模型

将修正的疲劳裂纹扩展静态断裂模型和裂尖腐蚀溶解相结合,提出了腐蚀疲劳裂纹扩展(CFCP)的腐蚀-钝化-断裂模型.根据该模型和断裂力学原理,导出了CFCP速率的定量表达式,它揭示了CFCP速率与力学条件,裂尖表面腐蚀率、加载频率、假设的裂尖材料元临界断裂应力之间的定量关系,并能说明氢脆对CFCP率的影响规律。实验结果表明,应用所提出的模型可很好地描述铝合金在35％NaCI中CFCP的一般规律。     

腐蚀疲劳裂纹扩展的机理

针对高强度低合金钢、钛合金和镁合金进行了腐蚀疲劳裂纹的扩展FCG、外加电压对于腐蚀疲劳裂纹扩展速率的影响以及断裂表面的研究。在外加电压对于腐蚀疲劳裂纹扩展速率影响的研究过程中,在一段时间内发生极化,可以根据此期间内的开路电压记录裂纹扩展速率,并测量极化情况下的裂纹增长速率。由于裂纹扩展测量技术的进步,测量的时间很少超过300s,这使观测非独立模式阴极极化对于腐蚀疲劳裂纹扩展速率的影响成为可能。当最大应力强度（Kmax）超过给定材料--溶液组合的特定临界特征值时,阴极极化会加速裂纹的扩展。当Kmax低于临界值,而所有其他条件（试件、溶液、pH值、载荷频率、应力比率、温度等）不变时,同样的阴极极化会妨碍裂纹扩展,或者对于裂纹扩展无影响。断口显微分析结果显示,阴极极化下加速裂纹的扩展是由于氢致腐蚀(HIC)。因此,根据氢致腐蚀机理以及KHIC和△ KHIC的显示,Kmax的临界值,以及应力范围（△ K）是由相应的腐蚀疲劳裂纹扩展的症状所确定的。当Kmax > KHIC（△ K > △ KHIC）时,腐蚀疲劳裂纹扩展的主要机理是HIC。对于大多数的材料--溶液组合的研究表明,当Kmax < KHIC（△ K < KHIC）时,应力协助扩散在腐蚀疲劳裂纹扩展中起决定性作用。     

基于有限元计算的金属断裂准则的应用与分析

为获得金属各种断裂行为的有限元分析与实际情况的符合度,论述了金属材料在有限元分析中常见断裂的判断方法.介绍了断裂行为有限元分析关键技术和常见延性断裂准则,并提出一种获得金属断裂准则的方法,以及此方法在断裂行为有限元分析中的成功应用.介绍了断裂行为有限元分析过程中有限元网格的调整和重划分,有限元技术在挤压、金属切削、切断和精冲工艺中断裂行为的成功分析,得出断裂行为有限元分析中的关键因素.     

FATIGUE CRACK PROPAGATION OF Ni-BASE SUPERALLOYS

Time-dependent Fatigue Crack Propagation (FCP) behaviors of five Ni-base superalloys were investigated at various temperatures under fatigue with various holding times and sustained loading conditions. The new concept of damage zone is defined and employed to evaluate the alloys‘ resistance to hold-time FCP. A special testing procedure is designed to get the maximum damage zone of the alloys. Udimet 720 and Waspaloy show shorter damage zones than alloys 706 and 718. The fractographieal analyses show that the fracture surfaces of the specimens under hold-time fatigue conditions are mixtures with intergranular and transgranular modes. As the extension of holding time per cycle, the portion of intergranular fracture increases, The effects of loading stress intensity, temperature, holding time, alloy chemisty, and alloy microstructure on damage zone and the crack growth behaviors are studied. Hold-time usually increases the alloy‘s FCP rate, but there are few exemptions. For instance, the steady, state hold-time FCP rate of Waspaloy at 760℃ is lower than that without hold-time. The beneficial effect of hold-time was attributed to the creep caused stress relaxation during the hold-time.     

M-A组元与粒状贝氏体焊缝的解理断裂

研究了15MnVN钢粒状贝氏体焊缝的解理断裂机制。对断口-金相直接对照试样的观察表明,粒状贝氏体焊缝的解理是由M-A组元引发的。M-A组元等效直径的分布控制了粒状贝氏体焊缝的解理断裂应力。     

SLOW PROPAGATION OF FATIGUE CRACK NEAR THRESHOLD

The effect of pearlite interlamellar spacing(d)from 0.31 to 0.77 μm of T8 steel on fatiguecrack propagation near threshold has been investigated at different stress ratios(R).Theclosure stress intensity factor(K_(cl)),the threshold value(ΔK_(th))and crack tip opening dis-placement range(ΔCOD)were measured.The results show that pearlite interlamellar spac-ing in this range has no effect on K_(cl),but has effect on the threshold value in low stress ratio.The threshold value is higher for materials with larger interlamellar spacing.No matter whatthe stress ratio is,during the propagation near threshold,the propagation rate will be thesame,provieded the crack tip opening displacement range is the same.Metallurgical examinations were also carried out to show that the crack propagationpath is sensitive to mierostructure.The crack always propagates along either boundary ofpearlite colony or ferrite lamellar in pearlite.     

加载速率、缺口几何和加载方式对16MnR钢解理断裂行为的影响

通过实验和有限元(FEM)计算研究了加载速率、缺口几何和加载方式对16MnR钢解理断裂行为的影响. 结果表明, 该钢的解理断裂机理及相应测得的细观解理断裂应力σ_f和宏观解理断裂应力σ_F不随加载速率、缺口几何和加载方式发生变化. 不同缺口几何和加载方式试样的缺口韧性随加载速率的变化可以通过判据 σ_yymax≧σ_F预测. σ_yymax为缺口前的最大正应力, 可通过有限元计算得到. σ_F可作为一个工程缺口韧性参数用于含缺口类缺陷的结构完整性评定中.钢的σ_F值可用Griffiths--Owen缺口试样在一个温度和加载速率下获得.     

FATIGUE CRACK PROPAGATION RATE OF ZG35 STEEL WITH SEMI－ELLIPTICAL SURFACE CRACK

ＦＡＴＩＧＵＥＣＲＡＣＫＰＲＯＰＡＧＡＴＩＯＮＲＡＴＥＯＦＺＧ３５ＳＴＥＥＬＷＩＴＨＳＥＭＩ－ＥＬＬＩＰＴＩＣＡＬＳＵＲＦＡＣＥＣＲＡＣＫ￥Ｃｈｅｎ，Ｆａｎｇｊｕｎ；Ｘｕ，Ｚｈｅｎｘｉ；Ｌｉｕ，Ｙａｏｄｏｎｇ；Ｃｈｅｎ，Ｙｉｊｕｎ；Ｇｕｏ，Ｚｈａｏｈ...     

矢量渐近边界条件在涡流检测微扰模型中的应用

根据低频电磁场在导体中的集肤效应及基准模型中激励线圈相对较小的特点,     

Na,K杂质及微量Ce对8090合金裂纹扩展阻力的影响

研究了含0.05%Ce及不同Na,K杂质含量的8090合金薄板裂纹扩展阻力,探讨了合金断裂韧性及裂纹起始扩展阻力随(Na+K)含量变化的规律和微量Ce的作用,结果指出:随(Na+K)含量增加,合金裂纹扩展阻力下降;若(Na+K)含量处于一定范围内时,合金中加入0.05%Ce会改善其断裂韧性及裂纹起始扩展抗力;当(Na+K)含量过高,Ce的这种有益作用便被掩盖,Na,K对合金韧性造成危害的原因之一是可以促使T_1等相沿晶界或亚晶界析出,并促使再结晶晶粒异常长大。     

屈强比对高强钢断裂韧性的影响

通过控制组织形态，对化学尬发相同，屈强比不同的两种钢材进行三点弯曲ＣＴＯＤ试验，并利用三维有限元法分析裂纹法端的应力应变分布。结果表明，高屈强比的材料，由于裂纹尖端应力水平高，脆性启裂ＣＴＯＤ值δｃ明显低于低屈强比的材料；而对有延性裂纹扩展的ＣＴＯＤ临界值δｕ和δｍ，高屈强比的材料同于低屈强比双相钢，这是因为低屈强比材料内部存在微观组织非均质，有应变集中所致。     

MICROFRACTOGRAPHY OF NEAR-THRESHOLD FATIGUE CRACK PROPAGATION IN DUAL-PHASE STEELS

SEM microfractography of near-threshold fatigue crack propagation were carried out in thedual-phase steels of 3 martensite morphologies and 6 volume fractions of martensite (V_m).All of them are featured by cyclic cleavage characteristics in near-threshold region,i.e.,main-ly controlled by mode Ⅱ stress.In the higher ΔK regions,the fracture surfaces are character-ized by mixed modes including cyclic cleavage facets,two types of secondary cracks andstriations,etc..The roughness-induced crack closure of fracture surface is attributedprimarily to extreme high fatigue crack growth threshold values.