解理裂缝过界扩展模型SCIEI

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。     

钛合金防弹材料的设计与性能

研究了Ｔｉ－６．５Ａｌ－３．５Ｍｏ－１．５Ｚｒ－０．３Ｓｉ合金细观结构对裂纹扩展特性的影响。发现当△Ｋ值小于ｄａ／ｄＮ－△Ｋ曲线上转折点处△Ｋ值时，合金出现解理断裂，表明转折点是解理断裂向条纹机制断裂的过渡；大量试验又进而证明，解理断裂与裂尖塑性区大小和裂纹穿过的晶粒或晶域尺寸有关。由此，作者提出了钛合金在裂纹扩展过程中形成解理断裂的一种新的断裂机制。     

TiAl基合金弯曲疲劳的断裂机制

通过对弯曲疲劳断裂宏观试验结果以及相应的卸载表面观察和断口观察分析研究,发现在疲劳加载的过程中,首先在缺口根部产生裂纹,裂纹在应力循环的作用下不断扩展,直至疲劳裂纹的长度达到与疲劳外加力所匹配的临界裂纹长度时,突然发生整体解理断裂.在一定应力下的疲劳弯曲加载试验中,随着循环次数的增加,产生的裂纹变长,即产生的损伤严重,疲劳区域变宽,其断裂机制是疲劳区各裂纹单向扩展,解理区起裂源分散扩展直至断裂.对于循环次数较小的材料,其断裂机制是具有发散扩展路径的起裂源直接产生于缺口根部,然后分散扩展直至断裂,在其扩展的路径上并不因疲劳区与解理区而有任何的不同.     

A STUDY OF FRACTURE CHARACTERISTICS OF DUAL PHASE STEEL

本文研究了双相钢的断裂特性。用缺口试棒四点弯曲试验法测定了双相钢的解理断裂应力σ_f;根据解理断裂温度下断口形貌、微裂纹萌生和扩展以及显微组织的观察结果,得出了双相钢的裂纹扩展途径;根据σ_f与开裂单元的测定结果,并考虑到微裂纹的形状对解理断裂应力的影响,计算了双相钢的有效表面能。提出了双相钢解理断裂的应力扩展控制模型,并得出了σ_f=(0.33+19.33-c~(·1/2))kgf/mm~2的回归关系式。提高双相钢解理断裂应力的途径是:降低铁素体的晶粒尺寸,尽可能使马氏体岛细化,分布均匀和增加马氏体岛中板条马氏体的比例。     

双相钢断裂特性的研究

本文研究了双相钢的断裂特性。用缺口试棒四点弯曲试验法测定了双相钢的解理断裂应力σ_f;根据解理断裂温度下断口形貌、微裂纹萌生和扩展以及显微组织的观察结果,得出了双相钢的裂纹扩展途径;根据σ_f与开裂单元的测定结果,并考虑到微裂纹的形状对解理断裂应力的影响,计算了双相钢的有效表面能。提出了双相钢解理断裂的应力扩展控制模型,并得出了σ_f=(0.33 19.33-c~(·1/2))kgf/mm~2的回归关系式。提高双相钢解理断裂应力的途径是:降低铁素体的晶粒尺寸,尽可能使马氏体岛细化,分布均匀和增加马氏体岛中板条马氏体的比例。     

铸造Ti-6Al-4V钛合金疲劳裂纹扩展特性的研究

按照GB6398-1986试验标准,采用紧凑拉伸试样(CT)测定了铸造Ti-6Al-4V钛合金疲劳裂纹扩展速率da/dN,采用扫描电镜(SEM)等现代技术对断口形貌进行观察,分析了不同应力比(R值)条件下的疲劳裂纹扩展特性。结果表明,应力比R对铸造Ti-6Al-4V钛合金的裂纹扩展速率影响较大,应力比R越大,裂纹扩展速率越大。在裂纹预裂区和快速扩展区的断裂机理主要是以微区解理断裂为主,稳态扩展区主要是以疲劳条带扩展机制为主,同时也存在微区解理断裂机制。     

应力比对Mg-3Al-2Sc合金疲劳行为的影响

在不同应力比条件下对热挤压变形的Mg-3Al-2Sc合金进行了疲劳试验,分析了应力比对合金裂纹扩展行为和断裂机制的影响。结果表明:在应力幅Δσ=60 MPa时,随应力比的增加,Mg-3Al-2Sc合金疲劳寿命显著降低,裂纹扩展速率提高。在裂纹萌生区和扩展区疲劳断裂机制主要表现为解理断裂,而在瞬断区主要表现为准解理和沿晶断裂的复合断裂机制。     

近全层组织γ-TiAl基合金的室温拉伸断裂机理

通过对直缺口近全层组织的扫描电镜原位拉伸实验以及相应的断裂表面观察，结合有限元计算了TiAl基合金近全层组织拉伸的断裂机理。研究表明：许多裂纹在塑性变形前沿着层间起裂和扩展，断裂过程的驱动力是拉应力。在直缺口试样中，许多裂纹直接起裂于缺口根部，并且沿着层间扩展。随着拉应力的增加，主裂纹和新裂纹也可以通过障碍晶粒的穿层解理断裂来连接。通过有限元计算得沿层断裂强度大约为50MPa，穿层断裂强度大约为120MPa。     

Ti_3Al金属间化合物氢致解理断裂及其机理

Ｔｉ－２４Ａｌ－１１Ｎｂ合金在室温下恒载荷动态充氢以及交变载荷动态充氢时，氢通过促进裂纹在滑移面上的解理，促进了裂纹扩展。不连续的氢致解理裂纹优先在α_２相形核，α_２／β相界面是裂纹扩展的有效障碍。氢通过促进裂尖位错的发射、解理微裂纹在无位错区（ＤＦＺ）的形核以及解理裂纹的扩展，导致氢致解理断裂     

含B2相TiAl金属间化合物的室温韧化机理研究（英文）

通过三点弯曲断裂和卸载试验对含B2相TiAl金属间化合物的韧化机理进行研究,通过双缺口四点弯曲试验确定解理断裂的临界事件。通过扫描电子显微镜和能谱分析观察断口形貌和裂纹扩展路径。结果表明:(1)3PB试验的载荷位移曲线为线性关系,B2相对裂纹的起裂无影响;(2)块状B2相对裂纹的扩展有一定的阻碍作用,裂纹遇到B2相停止或绕过B2相继续扩展;(3)解理断裂的临界事件为沿缺口根部开裂裂纹的扩展,穿层断裂对临界事件起着重要的作用;(4)这种材料的韧化机理包括:块状B2相韧化,裂纹偏转,穿层断裂和剪切韧带韧化。     

MODEL OF CLEAVAGE CRACK PROPAGATION ACROSS BOUNDARY

In the light of analysis of the features of cleavage fractographs of low carbon steel,the stresscriterion for cleavage crack propagation across ferrite grain boundary was established on thesupposition that resistance to the propagation results from an arbitrary mutual orientation ofthe cleavage plans in the neighbouring grains.On the basis of concept of statistical distribu-tion of cleavage plane in space,the probabilistic characteristic of cleavage process was ex-pounded,and the fracture stress of the cracked specimen over temperature range in whichfracture is initiated by cleavage mechanism was calculated by means of finite element analysisprogram and the calculated result was found to be in agreement with that measured.     

Micromechanism of Cleavage Fracture of Weld MetalsEI北大核心CSCD

Cleavage fracture is the most dangerous form of fracture. Cleavage fracture usually happens well before general yielding at low nominal fracture stress and strain. Cleavage fracture is often spurred by low temperature and determines the toughness in the lower shelf temperature region. This paper describes a new framework for the micromechanism of cleavage fracture of high strength low alloy (HSLA) steel weld metals. Cleavage fracture not only determines the impact toughness in the lower shelf but also plays a decisive role on the impact toughness in the transition temperature region. The toughness is determined by the extending length of a preceding fibrous crack which is terminated by cleavage fracture. Three non-stop successive stages, i.e. crack nucleation, propagation of a second phase particle-sized crack across the particle/grain boundary, propagation of a grain-sized crack across the grain/grain boundary are explained. The "critical event" of cleavage fracture is emphasized which offers the greatest difficulty during crack formation and controls the cleavage process. The critical event indicates the weakest microstructural component and its critical size which specifies the local cleavage fracture stress sigma(f) for cleavage fracture. In toughness-study it is paramount important to reveal the critical events for various test specimens. Three criteria for crack nucleation, for preventing crack nucleus from blunting and for crack propagation are testified. An active region specified by these criteria is suggested where the combined stress and strain are sufficient to trigger the cleavage fracture. It can be used in statistical analyses. A case study, using the new framework of micromechanism for analyzing toughness of 8% Ni steel welding metals is presented to analyze the experimental results.     

ON THE TEMPERATURE DEPENDENCE OF CLEAVAGE FRACTURE TOUGHNESS OF SILICON STEEL

以实验事实说明了RKR模型应用于硅钢所遇到的严重困难。引入了Weibull统计分布来描述硅钢解理断裂应力的体积效应。运用HRR理论和Rice-Johnson关于钝化区的应力分析,结合Weibull统计模型,导出了硅钢解理断裂韧性K_(Ⅰc)与温度的依赖关系,与实验结果符合得较好。     

Investigation of fatigue crack initiation in Ti-6Al-4V during tensile-tensile fatigue

Fatigue crack initiation in Ti-6Al-4V has been investigated in high cycle fatigue (HCF) and low cycle fatigue (LCF) regimes at stress ratio R=0.1 using the replication technique. In all four tested α/β microstructures, the crack was initiated by fracture of equiaxed alpha grain. Fractured alpha grains are seen on the fracture surface as flat facets with features characteristics of cleavage fracture. In the regime of low stress amplitudes and in the absence of reverse loading, cleavage fracture contributes to crack initiation and early stages of crack growth in Ti-6Al-4V. This mechanism is discussed in relation to the anomalous mean stress fatigue behavior exhibited by this alloy.     

Effects of X (V, W, Mo, Hf, Ta, Zr) additions on the ideal cleavage fracture of Cr2Nb: First-principles determination

The effects of the additive elements X (V, W, Mo, Hf, Ta and Zr) on the ideal cleavage fracture of the C15 Cr₂Nb were investigated using the first-principles method. The brittle cleavage energy G_c and critical stress σ_c were calculated. The results show that V on Cr sites and X (W and Zr) on Nb sites can increase the cleavage strength of Cr₂Nb, while X (W and Mo) on Cr sites and X (Mo, Ta and Hf) on Nb sites can reduce the cleavage strength of Cr₂Nb. Our results are consistent with available experimental ones. We also find that the effect of the element W on the cleavage strength of Cr₂Nb strongly depends on its site preference in Cr₂Nb. The charge densities induced by the additive elements X were also calculated in order to reveal the origin of the effects of X on the ideal cleavage fracture of Cr₂Nb.     

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.     

2.25Cr-1Mo钢连铸圆坯端面缺陷分析和预防

通过对 2.25Cr-1Mo钢连铸圆坯锯切面出现的裂纹和“花样”缺陷进行了研究分析，发现这两种缺陷均属于解理断裂。通过对解理断裂机理的研究并结合实际情况，提出了防止解理断裂的措施：铸坯高温入坑、降低冷却速度；实施去应力退火，实现原子重排、推进位错行动并消除位错聚集。     

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。     

First-principles study of the ideal cleavage fracture of Cr2Nb microalloyed by X (Al,Ni, Co,Ti)

The structural properties and elastic constants of the pure Cr₂Nb, the ideal cleavage fracture properties of the Cr₂Nb with the elements X (Al, Ni, Co and Ti) and site preference of the elements X were investigated using the first-principles method. Our calculated lattice parameters and elastic constants of the pure Cr₂Nb are in agreement with the experimental data. Moreover, our calculated results show that the elements X (Al, Ni and Co) occupy the Cr site, and Ti the Nb site in Cr₂Nb. The cleavage energies G_c and critical cleavage stress σ_c with and without the additive elements in the cleavage planes were calculated. The results demonstrate that the elements X (Al, Ni, Co and Ti) could be used to improve the cleavage properties of Cr₂Nb. Finally, the electronic mechanism behind the effects of the additive elements on the ideal cleavage properties of Cr₂Nb was investigated by calculating the electronic structure.