GH4169合金电子束焊接接头CTOD断裂韧度

根据GB/T2358—94标准,分别在20℃和650℃下,对GH4169合金电子束焊接接头的裂纹尖端张开位移(CTOD)进行测试。取SE(B)试样进行三点弯曲试验,然后由所得到的20℃和650℃下母材和电子束焊缝的P-V曲线来计算CTOD值,比较两个温度下的试验结果,对试验结果进行了分析讨论。     

Comparison of methods to determine CTOD for SENB specimens in different strain hardening steels

Methods for determining crack tip opening displacement (CTOD) given in national and international standards are compared for steels with a range of strain hardening characteristics. Crack tip opening displacement measurements were made from single‐edge notched bend notches using a silicone rubber casting method. The finite element model produced good agreements with predictions of these CTOD measurements. The versatility of the finite element model enabled CTOD from the original crack tip and the 45° intercept method to be compared. The 45° CTOD generally underestimates the original crack tip CTOD, and is less useful for conditions with stable crack extension. Apart from the high strain hardening material, CTOD calculated using BS 7448‐1, WES 1108 (JWES), and ASTM E1820 was slightly lower than the values determined from silicone measurements and modelling, which is conservative. ASTM E1820 gave the largest underestimation of CTOD, whilst BS 7448‐1 may be unsuitable for higher strain hardening steels, where the standard predicts higher CTOD than measured from the replica. JWES gives the most consistent estimation of CTOD for steels with a wide range of strain hardening values.     

热输入对WEL—TEN780A高强钢焊接热影响区断裂性能和组织的影响

研究了焊接热输入对ＷＥＬ－ＴＥＮ７８０Ａ高强度钢热影响区断裂性能的影响。结果表明,通过控制焊接热输入可以获得理想的焊接热影响区断裂性能。     

结构钢材基于CTOD的裂纹扩展阻力曲线的低温试验研究

裂纹尖端张开位移(CTOD)是材料断裂分析的重要判据指标。在钢材韧性较好的时候,随着裂纹的扩展,构件的承载力也会有所提高,说明随着裂纹扩展,裂纹尖端的断裂韧度有所升高。裂尖断裂韧度与裂纹扩展量的关系曲线称为裂纹扩展阻力曲线。裂纹扩展阻力曲线反映了构件断裂过程与构件的断裂模式、承载力的有关系。本文根据结构钢材低温断裂试验的结果,分析了常用结构钢材的低温条件下基于CTOD指标的裂纹扩展阻力曲线,试验结果可为钢结构断裂设计提供依据。     

EQ70钢CTOD断裂韧度评估及允许值确定

采用传统方法评定EQ70钢断裂韧度CTOD值是否优良时,通常将基于英国BS7448规范测试的CTOD断裂韧度最小值与CTOD允许值δ_min进行比较,当EQ70钢CTOD断裂韧度最小值大于CTOD允许值δ_min时,则EQ70钢的CTOD断裂韧度优良,此方法局限于能够查阅到EQ70钢的CTOD允许值δ_min,但国内外规范中很少对CTOD允许值δ_min做明确规定。基于英国BS7910《金属结构缺陷可接受性评定方法指南》的失效评定曲线对EQ70钢的断裂韧度CTOD合格性进行评定,能够克服传统方法的不足。同时依据BS7910规范还可以推导出EQ70钢CTOD允许值δ_min,比传统的工程方法“母材参考法”和“类比法”具有优越性。     

基于CTOD与SINTAP的海洋用钢断裂韧度评定

裂纹尖端张开位移（CTOD）作为评定海洋工程用钢断裂韧性的重要指标,其临界值问题一直受到关注。针对这一问题,结合SINTAP《金属结构缺陷可接受性评定方法指南》的失效评定曲线对海工用钢几个钢种的CTOD值进行了评定。结合材料CTOD值和应力-应变曲线,采用SINTAP的3级评定方法得到海工用钢的CTOD的失效评定曲线（FAD）。通过分析材料CTOD值在失效评定曲线图上所处的位置,对海工用钢EQ70（60 mm）,EQ70（38 mm）,EQ56（38 mm）钢的断裂韧度进行了评定。结果表明,这三种钢的CTOD值均在失效评定曲线图中可接受区域内, 它们的断裂韧度均合格。     

低碳贝氏体钢低温CTOD试验断口分离分析

通过对低碳贝氏体钢在-20℃CTOD试验中出现的分离断口进行微观分析,研究了断口分离和失稳断裂的原因.结果表明,断口分离面均为脆性断裂,至主断面为韧性扩展,分离裂纹产生的主要因素不是夹杂物,而是材料内部的带状组织和成带状的硬相组织受三维应力作用的结果.拉伸材料的分离裂纹是在达到一定抗拉强度之后开始萌生和扩展,不影响材料的使用性能.在断裂韧度试验中,一方面分离裂纹能降低材料裂纹尖端的三维应力约束,提高材料的韧性;另一方面较大程度的分离裂纹,减小了裂纹形核功和扩展功,诱发主裂纹的失稳扩展.     

大厚度船用钢板焊接接头低温CTOD韧度试验研究

依据BS 7448-1997断裂韧度试验标准,对板厚为80 mm的大厚度船用钢板(ABS AB/EH36N)对接接头试样进行了-10℃下裂纹尖端张开位移(CTOD)试验,介绍了试件的制备、试验装置及试验步骤,对试验结果进行了分析。经测试,绝大部分试样的断裂韧性值是有效合格的,其CTOD值大于0.15 mm,符合DNV验收标准。由此判定,在给定的焊接工艺下,该钢种焊缝低温韧性好,可以在不进行焊后热处理的情况下使用,为指导海洋平台的施工建造提供了科学依据。     

Study of influence of notch root radius on fracture behaviour of extra deep drawn steel sheets

Fracture tests are carried out on extra deep drawn steel CT specimens containing notches with different values of notch root radius (ρ= 0.07–0.75 mm). Experimental findings clearly show a critical notch root radius (ρ_c) below which the fracture toughness remains independent of ρ and above which it varies linearly with ρ. The 3D finite element analysis shows that the location of maximum stress level causing crack initiation is in the vicinity of notch tip. The maximum stress level is independent of ρ; however, its location is shifted away from notch tip along unbroken ligament length with increase in ρ.     

Crack tip displacements of microstructurally small surface cracks in single phase ductile polycrystals

A planar double slip crystal plasticity model is applied to the evaluation of crack tip opening (CTOD) and sliding (CTSD) displacements for microstructurally small stationary cracks under monotonic loading for a material with nominal stress-strain behavior that is representative of a relatively high strength helicopter rotor hub material. Two-dimensional plane strain finite element calculations are presented for CTSD and CTOD of microstructurally small transgranular surface cracks in a polycrystal subjected to monotonic loading. The effects of crack length relative to grain size, orientation distribution of nearest neighbor grains, stress state and stress level are considered for nominal stress levels below the macroscopic yield strength. The CTOD and CTSD are computed for stationary crystallographic surface cracks with various realizations of crystallographic orientations of surrounding grains. It is found that (i) the opening displacement is dominant for remote tension even for crystallographic cracks oriented along the maximum shear plane in the first surface grain, (ii) there is a strong dependence of the CTOD on the proximity to grain boundaries, but lesser dependence of the CTSD, and (iii) that the elastic solutions for CTOD and CTSD are valid below about 30% of the 0.2% offset-defined yield strength.