正应力对7150铝合金剥蚀行为的影响

针对老龄飞机7150铝合金结构普遍存在的剥蚀问题,在海洋性盐雾环境下,通过T73时效态不受载和悬臂梁加载剥蚀试验,以及T77时效态波音737CL龙骨梁下缘条不受载和受载剥蚀试验,研究了正应力对7150铝合金剥蚀的影响。结果表明:T73时效态剥蚀,L轴向拉应力作用表面最轻,其次为不受载表面,L轴向压应力作用表面最严重。T77时效态龙骨梁下缘条剥蚀,在L轴向压应力作用下的产生和扩展速度,比不受载状态下快得多。由此认为:L轴向压应力可以加速7150铝合金剥蚀的形成和扩展,而L轴向拉应力可以抑制剥蚀的形成和扩展。     

7075铝合金真空电子束焊接残余应力场数值分析

针对7075铝合金中厚板真空电子束焊接过程,采用非线性有限元法,对焊接接头的残余应力分布进行了数值模拟。结果表明,沿焊缝方向,纵向残余应力均为拉应力,一般在焊缝中间处最大;沿垂直焊缝方向递减。焊缝上表面的横向残余应力多为压应力,沿焊缝方向呈递增趋势。垂直焊缝方向,焊板处的横向残余应力多在零值附近变动。焊缝处沿厚度方向残余应力变化不大。     

黄铜应力腐蚀裂纹与应力分量的关系SCIEI

利用黄铜Ⅱ型和Ⅲ型试样研究了应力腐蚀裂纹形核位置和扩展方向与应力分量的关系。结果表明,裂纹在最大正应力处形核,扩展方向与最大正应力相垂直.在Ⅲ型试样中,氨浓度对裂纹扩展形态有影响,氨浓度较高时,由于均匀腐蚀的作用,在45°面上的裂纹很不明显;在氨浓度较低时,则可看到沿试样圆周有许多45°面裂纹,裂纹间隔在10—150μm之间,而在具有最大剪应力的扭转面上则没有裂纹形成。     

7075铝合金真空电子束焊接残余应力场数值分析

针对7075铝合金中厚板真空电子束焊接过程，采用非线性有限元法，对焊接接头的残余应力分布进行了数值模拟。结果表明，沿焊缝方向，纵向残余应力均为拉应力，一般在焊缝中间处最大；沿垂直焊缝方向递减。焊缝上表面的横向残余应力多为压应力，沿焊缝方向呈递增趋势。垂直焊缝方向，焊板处的横向残余应力多在零值附近变动。焊缝处沿厚度方向残余应力变化不大。     

300M钢电子束预热与焊接复合加工后的残余应力测试

采用盲孔法测量了电子束预热与焊接复合加工300M超高强度钢板的残余应力分布。结果表明,垂直于焊缝方向的纵向残余应力以拉应力为主,横向残余应力以压应力为主,焊缝中心的最大纵向和横向残余应力分别为34.3和9.2 MPa;最大残余拉应力峰值出现在母材区,其应力值约为208.3 MPa,远低于母材屈服强度。沿焊接方向残余应力变化不大,可近似认为其分布基本稳定。     

2219铝合金FSW接头残余应力分布特点

采用压痕应变法测量2219-T87高强铝合金FSW试板与筒体结构上典型位置的残余应力. 结果表明,在试板上接头残余应力呈不对称分布,焊缝上的纵向残余应力数值高于横向残余应力,纵向应力的最大拉应力出现在焊缝中心位置,最大压应力出现在后退侧轴肩外侧,横向残余应力的最大压应力出现在前进侧轴肩边缘;筒体结构的环缝上,纵向残余应力呈较大拉应力,横向残余应力的数值较小,纵缝接头处残余应力关于焊缝中心呈对称分布,纵向残余应力在焊缝上呈拉应力,横向残余应力在焊缝上呈压应力;压力试验使结构件上部分应力释放,应力数值略有下降.     

高强度钢压剪疲劳裂纹扩展的实验研究

滚珠轴承接触点附近的高压剪应力是引起轴承疲劳破坏的原因。为获得高强度钢在压剪疲劳加载下的断裂性态,通过轴向裂纹薄壁圆筒的压剪疲劳加载试验,研究了这类材料的疲劳破坏规律。结果表明,复合疲劳加载时门槛值对压应力分量并不敏感,但对扩散速率和临界扩展角却有明显影响。裂纹扩展速率随压应力增加而提高,裂纹较快达到失稳;裂纹扩散角则随压应力增加而减小,疲劳裂纹将向有利于Ⅰ型断裂的方向扩展。这表明轴承滚道内,任何平行于压应力的缺陷、微裂纹都将是十分危险的。     

2195-F态铝锂合金TIG焊和FSW焊后残余应力分析

采用盲孔法和压痕法,分别对2195-F态铝锂合金手工TIG焊和FSW焊后残余应力进行测量. 结果表明,盲孔法的测量值普遍高于压痕法. 两种焊接方法,近焊缝区的纵向应力均高于横向应力;横向应力整体表现为压应力或小于50 MPa的拉应力;纵向应力在热影响区附近表现为大于焊缝的拉应力. 焊缝区附近,手工TIG焊纵向残余应力大于FSW,且纵向残余应力表现为较大的拉应力,最大值接近于接头的屈服强度;焊缝区外,手工TIG焊和FSW残余应力值相差不大,其横向残余应力基本表现为很小的拉应力或者压应力.     

TA12钛合金电子束焊接组织性能及残余应力分析

采用电子束焊接TA12钛合金薄板焊缝表面成形良好,焊缝区以马氏体组织为主,细小的稀土相呈均匀弥散分布状态;随着距焊缝距离的增加,稀土相尺寸逐渐增大,数量逐渐减少,并逐渐趋于球形,沿接头呈一定的规律性分布.小孔法残余应力测试结果表明,垂直于焊缝方向残余应力以纵向应力主,应力呈梯度分布,横向应力较低;焊缝区为纵向拉应力区,应力峰值低于其屈服强度,横向应力为较小的压应力;沿焊缝试板中心区(±20 mm范围内)焊接残余应力分布趋于稳定.     

2397合金高周疲劳性能及裂纹萌生扩展行为

研究了2397-T87铝锂合金的高周疲劳性能及裂纹萌生扩展行为。结果表明:在应力比R=0.1时,2397-T87铝锂合金L方向、LT方向和ST方向光滑试样(K_t=1.0)的疲劳寿命极限分别约为192,243和151 MPa;缺口试样(K_t=3.0)的疲劳寿命极限分别约为72,78和70 MPa。其疲劳裂纹主要萌生于试样表面,以及氧化物、夹杂等脱落形成的空洞,Al(CuFeMn)第二相杂质粒子。驻留滑移带(PSB)和晶粒取向对其疲劳裂纹早期扩展有重要影响。     

受力的LY12和LC4铝合金在中国西部盐湖大气环境中的腐蚀行为

通过现场大气暴露实验,利用金相显微镜和SEM等手段分析试样表面和截面形貌,研究了U弯受力状态下包铝与无包铝的LY12和LC4两种铝合金在我国西部盐湖大气环境中的腐蚀行为。结果表明,包铝的两种铝合金的腐蚀主要发生在包铝层,以点蚀为主,未观察到包铝层被穿透现象。无包铝的铝合金试样都发生了明显的沿晶应力腐蚀开裂,其中LY12铝合金在拉应力和压应力下都有较多的应力腐蚀裂纹,LC4铝合金只在拉应力下观察到了裂纹;两种铝合金在压应力下都发生了剥层腐蚀,拉应力下剥层腐蚀受到抑制。     

CORRELATION BETWEEN STRESS COMPONENTS AND STRESS CORROSION CRACKS IN BRASS Lecturer,Department of Materials Physics,University of Science and Technology Beijing,Beijing 100083,China

The effects of stress components on nucleation sites and propagation directions of stress cor-rosion cracks in brass were investigated with specimens under mode Ⅱ and mode Ⅲ loadings.The results indicated that under mode Ⅱ loading,stress corrosion cracks nucleated on the sitewith maximum normal stress component and propagated along the plane perpendieular to themaximum normal stress,under mode Ⅲ loading,the stress corrosion crack was not evident onthe 45°plane due to the general corrosion in aqueous solution with high NH_4OH concentra-tion,while stress corroded in aqueous solution with low NH_4OH concentration, numerouscracks with spacings of 10—150μm were found on the 45°plane with maximum normalstress and no stress corrosion cracks was observed on the plane with maximum shear stress.     

Mechanic treatment of fastener holes: The influence of compressive residual stress on the corrosion behaviour of aluminium alloys

Corrosion has a significant impact on the life cycle cost of military aircraft. Fleet experiences show that structural areas around joining elements (rivets, bolts) and faying surfaces are particularly sensitive to corrosion. During the repair currently performed the corrosion usually is blended out, the surface protection applied, the fastener inserted and a new top coat applied. Blending out corrosion often results in a reduction of fatigue life. To restore fatigue life the induction of compressive stress in the area affected is common practice. It is generally accepted that the induction of compressive residual stress extends fatigue life but its impact on the overall corrosion behaviour of alloys is discussed controversially in the literature. For this reason the influence of compressive residual stress on the corrosion behaviour was investigated in a joint experimental project. The compressive residual stress was introduced in different ways on laboratory scale and the specimens artificially weathered to simulate the effect of corrosion.     

预渗氢对Zr-4合金在360℃/LiOH水溶液中耐腐蚀性能的影响

核反应堆运行时,锆合金包壳的腐蚀和吸氢相伴发生,被锆合金吸收的氢不但会影响锆合金的力学性能,同时对锆合金的耐腐蚀性能也会产生一定的影响,其影响程度与合金成分和腐蚀条件密切相关.氢对Zr-4合金(Zr-1.3Sn-0.2Fe-0.1Cr,质量分数,％)在LiOH水溶液中的耐腐蚀性能影响机理尚不完全清楚.本工作开展了预渗氢...     

不同应力条件下不锈钢局部腐蚀行为的研究进展

不锈钢因具有良好的耐腐蚀性能而倍受重视,在众多工业领域内被广泛使用,但在实际应用中,由于受到腐蚀环境和应力的共同作用,不可避免地会产生点蚀或裂纹,导致服役性能下降,甚至引发各类安全事故.所以,应力条件下不锈钢的腐蚀行为一直是不锈钢材料腐蚀领域的重要研究课题.总结了部分代表性的不锈钢材料在应力作用下局部腐蚀行为的研究进展...     

Influence of shot peening and thermal ageing treatment on resistance to intergranular corrosion in shielded metal arc weld metal for type 600 nickel base alloy

Shielded metal arc weld metal for type 600 nickel base alloy (alloy 182) is used for weld components in nuclear power plants. To evaluate the intergranular corrosion resistance of alloy 182 after application of shot peening and subsequent thermal ageing treatment at 593–793 K, we conducted the corrosion test (immersed in boiled 16% sulphuric acid +5.7% copper sulphate aqueous solution at 57.6 ks) using specimens of alloy 182. The results show that the intergranular corrosion resistance of alloy 182 subjected to heat treatment at 893 K for 72 ks was improved by shot peening. Also, the intergranular corrosion resistance was not changed by thermal ageing treatment at 593–793 K subsequent to shot peening. Because remaining chromium depletion layers along grain boundaries were still observed by transmission electron microscope (TEM) after shot peening, disappearance of chromium depletion layers cannot be a factor in the improvement of the intergranular corrosion resistance. The results of measurement of surface residual stress by the X-ray diffraction method show that the compressive residual stress introduced by shot peening still remained on the surface of the specimens. Based on these observations, we assumed that chromium depletion layers along grain boundaries near the surface were dissolved by the environment of the corrosion test, the dissolved regions were closed by the compressive residual stress on the surface, and then the remaining chromium depletion layers were protected from the corrosive environment. This assumption explains why the intergranular corrosion resistance was improved although chromium depletion layers remained.     

不同时效态对7150铝合金剥蚀行为的影响

针对老龄飞机7150合金飞机结构普遍存在的剥蚀问题,采用海洋性环境腐蚀试验、透射电子显微镜观测等手段,研究了T6、T73和T77时效态7150合金剥蚀行为。研究结果表明：T77时效态抗剥蚀性能最好,T6时效态抗剥蚀性能最差,T73 时效态介于T77和T6时效态之间。7150-T77合金晶界腐蚀产物的锲力,尚不足以提供其剥蚀扩展所需动力。7150合金时效后的晶界微观组织结构,是抗剥蚀性能的重要决定因素。     

Relationship between alloy composition, microstructure and exfoliation corrosion in Al–Zn–Mg–Cu alloys

The exfoliation corrosion (EFC) susceptibility of several 7000 Aluminium alloys has been studied after a variety of heat treatments using two independent corrosion tests (standard EXCO test and an electrochemical test based on potential transients analysis), together with detailed microstructural examinations. It is proposed that depending on heat treatment EFC may occur via two different mechanisms: inter-granular dissolution induced damage (IDD) or inter-granular fracture induced damage (IFD). The coexistence of these two mechanisms, leading to EFC, and their relative predominance explain the influence of alloy composition and heat treatment on EFC susceptibility via the confrontation of the two corrosion tests.     

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 利用多晶X射线面探测器衍射系统对304奥氏体不锈钢板在拉伸状态下的应力及其分布进行了检测分析。结果表明，在受到单向拉伸时原有的表面平均压应力σxx减小，σyy增加；在受到双向拉伸时，原有的表面平均压应力σxx和σyy均减小；最大压应力也是如此变化；缺陷（人为制造的方孔和圆孔）对平均应力影响不大，对最大应力影响较大。通过有限元模拟计算，实验结果和模拟结果的应力分布和变化趋势符合较好。