共查询到20条相似文献,搜索用时 46 毫秒
1.
A. Nazari J. Aghazadeh Mohandesi 《Journal of Materials Engineering and Performance》2010,19(7):1058-1064
Charpy impact energy of functionally graded steels produced by electroslag remelting composed of graded ferrite and austenite
layers together with bainite or martensite intermediate layer in the form of crack arrester configuration has been investigated.
The results obtained in the present study indicate that the notch tip position with respect to bainite or martensite layer
significantly affects the impact energy. The closer the notch tip to the tougher layer, the higher the impact energy of the
composite due to increment of energy absorbed by plastic deformation zone ahead of the notch and vice versa. Empirical relationships
have been determined to correlate the impact energy of functionally graded steels to the morphology of layers. 相似文献
2.
《Acta Materialia》2003,51(10):2933-2957
The R-curve and fracture toughness behavior of single-edge notch beams of Ti–Al3Ti metallic–intermetallic laminate (MIL) composites has been investigated. Composites with 14, 20, and 35% volume fraction Ti, with a corresponding intermetallic layer thickness of ~540, ~440, and ~300 microns, respectively, were tested in crack arrester and crack divider orientations. In the arrester orientation, the R-curve could not be determined for the two highest Ti volume fraction compositions as the main crack could not be grown through the test samples. In the divider orientation, R-curves were determined for all three Ti volume fractions tested. The laminate composites were found to exhibit more than an order of magnitude improvement in fracture toughness over monolithic Al3Ti. Crack bridging and crack deflection by the Ti layers were primarily responsible for the large-scale bridging conditions leading to the R-curve behavior and enhanced fracture toughness. Estimates of steady-state toughness under small-scale bridging conditions were in close agreement with experimental results. 相似文献
3.
本文研究了蠕变断裂韧性对二种低合金耐热钢蠕变裂纹开裂和扩展的影响。试验表明:随着蠕变断裂韧性提高,抗蠕变裂纹开裂和扩展能力增加。材料呈韧性或脆性状态时,蠕变裂纹萌生和扩展过程不同。韧性状态时,裂纹为穿晶和晶界二种混合形式:穿晶裂纹可在晶内碳化物处发生,或在晶界上形核后向晶内扩展,晶界裂纹仍是由晶界上空洞形成和相互连接而成,裂纹可沿晶界和晶内扩展,但不连续。脆性状态时,裂纹沿晶界发生,它是由晶界形成空洞和相互连接而成,扩展仅沿晶界发生。 相似文献
4.
采用高温高压气相热充氢方法将氢充入SA508-3钢,采用J积分方法比较不同载荷速率下未充氢与充氢钢的断裂韧性,考察氢对SA508-3钢断裂韧性的影响。结果表明,在相同载荷速率下,与未充氢SA508-3钢相比,充氢钢断裂韧性明显降低,充氢断口均为韧性和脆性混合断口形貌。随着载荷速率的降低,断裂韧性损失逐渐增加,准解理所占面积增加,脆性提高。在三向应力的作用下,氢与静水应力的交互作用能大于氢与可动位错的交互作用能,静水应力更易捕获到氢。SA508-3钢断裂韧性测试过程中,在三向应力的诱导下会促进氢富集在裂纹尖端碳化物和基体的界面处,从而降低了碳化物和基体的结合强度,致使阻碍裂纹扩展的能力减弱,因此钢充氢后断裂韧性降低。随着载荷速率的降低,三向应力作用在裂纹尖端的时间增加,氢富集在碳化物和基体界面浓度增加,氢压增强,加速裂纹扩展,钢的脆性提高,断裂韧性损失增加。 相似文献
5.
X70管线钢不同温度下断裂韧性实验研究 总被引:6,自引:0,他引:6
以三维弹塑性断裂理论为基础,对有限厚度板裂纹端部应力场、三维应力约束进行了分析,通过对不同厚度、不同初始裂纹长度在不同温度下三点弯曲试件的断裂韧性测试断口观测和理论分析获得如下结果:离面约束对裂尖应力场及断裂韧性有强烈的影响;断口均产生分层裂纹,其位置、大小和数量与试样厚度、温度和裂纹初始长度有关;温度较低时,分层裂纹距主裂纹根部一定距离,分层裂纹宽度较小,对厚度效应影响较小;温度较高时,分层裂纹首先出现在主裂纹根部,分层裂纹宽度较大且充分张开,降低了试样的有效厚度,对X70管线钢进行性能评价时必须考虑管道壁厚、层裂和环境温度的耦合作用。 相似文献
6.
选用Gleeble-1500试验机模拟了两种成分Q690CFD高强钢的焊接粗晶热影响区(CGHAZ),测试了CGHAZ的冲击韧性,并通过三点弯曲试样,测试了CGHAZ的CTOD特征值. 利用SEM对CTOD试样断口及近断口区裂纹扩展行为进行了分析. 结果表明,示波冲击止裂功及CTOD特征值δm/c/u(8)随温度降低呈明显下降趋势;将CTOD特征值δm用Boltzmann函数拟合后所得脆韧转变温度与示波冲击变化规律相对应;两种成分钢的CTOD失稳裂纹扩展路径与近断口区组织亚结构中大角度晶界和M/A分布位置有关. 相似文献
7.
研究了不同组织状态的15Mn钢在3.5%氯化钠水溶液中的疲劳裂纹扩展行为,测定了裂尖区的平均氢含量和裂纹闭合力,发现外部条件(力学及环境)和材料的显微组织对腐蚀疲劳有重要影响。结合断口和裂纹走向观察,提出了15Mn钢腐蚀疲劳断裂的复合机制和断裂机制图。 相似文献
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9.
EFFECT OF CREEP FRACTURE TOUGHNESS ON CRACK INITIATION AND PROPAGATION UNDER CREEP FATIGUE INTERACTION 总被引:4,自引:0,他引:4
本文研究了蠕变断裂韧性对三种低合金Cr-Mo-V钢在蠕变一疲劳交互作用下裂纹开裂和扩展的影响.试验表明,材料韧性对裂纹开裂和扩展起重要作用,脆性状态时,裂纹开裂时间比蠕变时短,二者间的裂纹扩展速度无明显差别;韧性状态时,裂纹开裂时间不仅比蠕变时短,而且其裂纹扩展速度比蠕变时大得多.此外,低合金Cr-Mo-V钢经蠕变一疲劳交互作用后有脆化倾向,其脆性程度取决于钢的原始韧性值.韧性状态时,蠕变-疲劳交互作用显著促使三种Cr-Mo-V钢由韧性向脆性转变;而在脆性状态时,这种脆性转变不明显。 相似文献
10.
Influence of nonmetallic inclusion characteristics on the mechanical properties of rail steel 总被引:1,自引:0,他引:1
S. K. Dhua Amitava Ray S. K. Sen M. S. Prasad K. B. Mishra S. Jha 《Journal of Materials Engineering and Performance》2000,9(6):700-709
An extensive investigation has been carried out on six commercial heats of pearlitic rail steel to study the influence of
nonmetallic inclusion characteristics on the tensile, fatigue, and fracture toughness properties. The steels investigated
were made through the basic oxygen furnace (BOF)-continuous casting route and rolled in the rail and structural mill into
90 kg/mm2 ultimate tensile strength (UTS) grade rails. While tensile properties (yield strength [YS], UTS, and elongation) of the rail
steels investigated were found to be insensitive to inclusion type and volume fraction at their present level (0.23 to 0.45%),
the fracture toughness and high-cycle fatigue properties were found to be inclusion sensitive. The fracture toughness values
of the steels were found to range between 42.33 and 49.88 MPa √m; higher values, in general, were obtained in heats exhibiting
lower volume fractions (0.15 to 0.19%) of sulfide inclusions. The high-cycle fatigue limit, i.e., stress corresponding to 107 cycles, was found to be higher in cleaner steels, particularly in those with lower volume fractions of oxide inclusions.
This phenomenon was corroborated by scanning electron microscopy (SEM) observations of fracture surfaces, where oxide inclusions
in particular were found to be instrumental in crack initiation. Although fatigue life did not show any direct correlation
with the volume fraction of sulfides, elongated MnS inclusions were sometimes observed at crack initiation sites of fatigue-tested
specimens. 相似文献
11.
《Science & Technology of Welding & Joining》2013,18(2):252-258
AbstractThe use of high strength low alloy steels for high performance structures (e.g. pressure vessels and pipelines) requires high strength consumables to produce an overmatched welded joint. This globally overmatched multipass welded joint contains two significantly different microstructures, as-welded and reheated. In this paper, the influence of weld metal microstructure on fracture behaviour is estimated in comparison with the fracture behaviour of composite microstructures (as-welded and reheated). The lower bound of fracture toughness for different microstructures was evaluated by using the modified Weibull distribution. The results, obtained using specimens with crack front through the thickness, indicated low fracture toughness, caused by strength mismatching interaction along the crack front. In the case of through thickness specimens, at least one local brittle microstructure is incorporated in the process zone at the vicinity of the crack tip. Hence, unstable fracture occurred with small, or without, stable crack propagation. Despite the fact that the differences between the impact toughness of a weld metal and the that of base metal are insignificant, the fracture toughness of a weld metal can be significantly lower. 相似文献
12.
Influence of the environment on the cracking toughness and crack propagation in high-strength steels The crack toughness of four fine grained steels and one high strenght steel of different heat-treatments are investigated in 3% NaCl solution depending from the electrochemical polarisation. The steels are of commerical compositions, their strengths are in the range of 635 to 1460 N/mm2. The stress intensity factors, KISCC for slow crack growth are determined by a method of fracture mechanics. For these investigations the DCB-specimen with an incipient crack is used. The KISCC-values generally decrease with increasing strength of the steels, but they show different susceptibility for crack growth under cathodic and anodic polarisation. Outdoor experiments conducted in seawater covering a period of one year confirm the results of laboratory. 相似文献
13.
The present paper demonstrates the effect of switching stresses on domain evolution and fracture toughening during quasi-static crack growth in elastically isotropic ferroelastic single crystals with transversally isotropic ferroelastic strains. With a simple switching algorithm and crack propagation procedure, domain evolution is simulated in an exemplary material with semi-infinite crack under mode I loading, starting from a mono-domain configuration. Domain reorientation is found to be strongly affected by switching stresses, which therefore have to be considered in the context of domain evolution modelling and fracture toughening. Before the onset of crack growth a needle-like domain is formed at the tip of the stationary crack, but this does not effect the crack tip stress intensity factor. Elongation of this domain during the onset of crack growth causes a large increase of the fracture toughness. Domain separation in a later stage results in toughness reduction. The subsequent domain evolution indicates a periodic formation of needle-like domains as observed in soft ferroelastic materials. 相似文献
14.
1. IntroductionCr12MoV steel is used widely as an important high wear resistallt cold die steel aroundthe world[1]. It is well known that Cr12MoV steel has networked carbide in the solidification structure, which leads to the intergranular brittleness. Moreover. The networkcarbide is too stable to be changed during heat treatment even at high temperaturely]. Inthe conventional process, forging is needed to break etwork carbide into a granular form.However, partly owing to Cr12MoV steel hav… 相似文献
15.
Suwat Ploypech Yuttanant Boonyongmaneerat Petch Jearanaisilawong 《Surface & coatings technology》2012
Crack initiation and propagation behaviors in the intermetallic layers of galvanized coatings subjected to bending loads are characterized and numerically simulated. Coating structure of galvanized steel prepared by hot dipping at 450 °C is a laminate composite consisting of δ, ζ, and η phases, with an infinitesimal layer between the coating and steel article speculatively representing a Γ phase. The specimens were deformed in a four-point bending configuration, and the evolution of cracks was investigated as a function of bending angles. Through-cracks were found to develop in the δ layer of the coatings after thermal cooling due to thermal stresses and propagate toward the outer surface under increments of bending loads. Finite element simulations of galvanized steels were subsequently developed with an initial crack tip located in the δ layer to determine the controlling parameters of the crack propagation and to assess the coatings' fracture parameter, critical far field stress, and stress distributions. The analysis highlights the enhancement of fracture resistance of the galvanized coatings owing to the presence of the ζ layer. 相似文献
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17.
Majid Pouranvari 《Science & Technology of Welding & Joining》2018,23(6):520-526
The failure of advanced high-strength steels’ spot welds is a critical issue for automotive crashworthiness. This paper deals with understanding the underlying factors of the tensile-shear strength of automotive steels’ resistance spot welds during interfacial failure. It was found that the ratio of the fracture toughness to the hardness of the fusion zone is the critical factor governing the interfacial failure mechanism: ductile shear failure (controlled by the fusion zone hardness) vs. cleavage crack propagation (controlled by the fracture toughness). This clarification could pave the way for more accurate modelling of interfacial failure of advanced steel resistance spot welds and shed light on the design of proper post-weld heat treatment for improving the weld mechanical performance. 相似文献
18.
A model of heating a flux-cored wire in arc metallizing and analysis of the structure of the coating
Yu.S. Korobov A.A. Belozertsev M.A. Filippov V.I. Shumyakov 《Welding International》2013,27(7):546-551
Summary This paper describes HAZ‐notched CTOD tests of multipass welds in SMYS = 420–460 MPa class high‐strength steels for offshore structural applications. The weld metal strength overmatch causes different fracture behaviour depending on the actual CGHAZ toughness. When the CGHAZ is completely embrittled, the weld metal strength overmatch leads to the lower bound critical CTOD value. This is due to elevation of the local stress in the CGHAZ caused by the restraint effect of the overmatched weld metal. The fracture surface is generally flat, and brittle fracture originates from the CGHAZ sampled by the fatigue crack front. A larger fraction of the CGHAZ along the crack front gives a smaller critical CTOD value. When the CGHAZ has moderate toughness, however, the weld metal strength overmatch may produce a higher critical CTOD value at brittle fracture initiation. This is due to crack growth path deviation towards the base metal. Plastic deformation preferentially accumulates to a greater extent on the softer base metal side before the critical stress conditions for brittle fracture initiation occur in the CGHAZ. This asymmetrical plastic deformation promotes deviation of ductile crack growth from the crack tip CGHAZ. In this case, the critical CTOD value does not always reflect the CGHAZ toughness itself. A notch location nearer the weld metal sometimes causes fracture initiation in the weld metal if the fatigue crack tip samples the CGHAZ. Such experimental data do not reflect the real CGHAZ toughness. The significance of the critical CTOD value obtained in the tests must be determined in the fracture toughness evaluation of the weld CGHAZ. This paper presents a procedure for evaluation of CTOD test results obtained for HAZ‐notched welds that considers the strength mismatch effect. 相似文献
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