高钴钼不锈轴承钢疲劳裂纹萌生及扩展行为

采用高钴钼不锈轴承钢光滑圆柱形试样和缺口试样(理论应力集中系数K_t=3)进行旋转弯曲疲劳测试,研究了高合金轴承钢的裂纹萌生及裂纹扩展行为。用升降法和成组法分别测得轴承钢的疲劳极限和S-N曲线,利用扫描电镜对轴承钢旋转弯曲疲劳试样断口进行观察。结果表明,光滑试样起裂类型为单源萌生起裂,起裂源为表面缺陷和次表面夹杂物,表面缺陷为表面粗糙度、驻留滑移带和加工凹痕,次表面夹杂物为Al_2O_3-CaO-MgO-SiO_2复合夹杂;缺口试样疲劳极限显著下降,起裂类型为多源萌生起裂,计算得轴承钢的缺口敏感系数q_f为1.18。光滑试样疲劳破坏从以高应力幅粗糙度萌生表面裂纹的破坏向低应力幅驻留滑移带、加工凹痕、夹杂缺陷萌生裂纹转移。疲劳裂纹萌生寿命占整个疲劳寿命的94.1%以上。     

激光金属沉积TA15钛合金工字梁疲劳性能研究

激光金属沉积（LMD）是一种应用广泛的金属增材制造技术,可以快速成形复杂的结构件。以TA15钛合金粉末为原材料,采用激光金属沉积技术成形了TA15工字梁缩比件,进行了LMD TA15钛合金工字梁试样的疲劳试验和失效分析,研究了LMD TA15钛合金材料和结构的疲劳性能。对4件试样在应力比为0.06,载荷峰值为80%静力破坏载荷的交变载荷下进行四点弯曲疲劳试验,受成形缺陷影响,试样出现混合失效模式：两件试样无明显缺陷,裂纹形态为受拉缘条角裂纹,两件试样为内部气孔缺陷诱发失效,裂纹形态为受拉缘条半椭圆裂纹。起裂位置与缺陷和应力水平有关,存在明显的差异。为阐明试样疲劳失效行为,进行了有限元分析,获得起裂位置的应力水平,分析了缺陷和应力水平对疲劳寿命的影响。结果表明,缺陷是影响试样疲劳性能的主导因素,缺陷降低疲劳寿命50%以上,对于无明显缺陷试样,试样的疲劳行为受到应力水平控制。     

32Cr3MoVE轴承钢旋弯疲劳特性及裂纹萌生扩展行为

摘要：采用光滑漏斗状试样对32Cr3MoVE轴承钢进行旋转弯曲疲劳测试，研究了32Cr3MoVE轴承钢旋转弯曲疲劳性能及裂纹萌生扩展行为。采用升降法测得其疲劳极限为860MPa，疲劳断口SEM观察并统计破断试样结果表明：疲劳破坏68.7%是由于非金属夹杂起裂，18.8%由表面加工缺陷起裂，125%为表面粗糙度起裂。当加载应力低于980MPa时，疲劳断裂主要是由于内部非金属夹杂引起的，高于980MPa时，疲劳断裂主要是由于表面粗糙度引起的。表面加工缺陷和表面粗糙度引起的最大应力强度因子分别为3.05和2.97MPa·m1/2，容易引发疲劳裂纹。非金属夹杂物尺寸在5.30～5.90μm范围内，局部应力从859.35MPa升至977.75MPa时，疲劳寿命从1.96×105降低到1.58×105；非金属夹杂物局部应力在840～900MPa范围内，夹杂物尺寸从2.28μm升至5.83μm时，疲劳寿命从1.10×106降低到1.96×105。     

00Crl8Nil0N奥氏体不锈钢200 - 600℃高温疲劳性能的研究

试验用00Cr18Ni10N钢（/%:0.018C,0.41Si,1.68Mn,18.18Cr,10.38Ni,0.16N）经1t EAF-AOD-ESR冶炼,锻成Φ30 mm材和1 050℃固溶处理,进行了00Cr18Ni10N钢200～600℃光滑（K_t=1）、缺口（K_t=3）的轴向高周疲劳性能研究,绘制了疲劳S-N曲线、计算了疲劳极限,并对疲劳试样的典型断口进行了SEM观察。结果表明,光滑试样的疲劳极限随试验温度升高而降低,缺口试样的疲劳极限对试验温度变化不敏感。当应力集中系数由K_t=1提高到K_t=3时,00Cr18Ni10N钢的200、400、600℃下10⁷周次条件疲劳极限分别从530、506、410 MPa,降低到323、370、392 MPa。表明在高温下00Cr18Ni10N钢存在疲劳极限对应力集中敏感,且应力集中敏感性随着试验温度的升高而降低。疲劳试样的断口形貌由疲劳源区、疲劳裂纹扩展区和瞬断区组成,疲劳起源于表面加工刀痕的不连续位置,呈韧性断裂特征。     

表层改性及应力集中对18CrNiMo7-6合金钢疲劳分散性的影响

金属材料的疲劳试验数据常存在较大的分散性，这给材料疲劳寿命的预测带来一定的不确定性。引起疲劳数据分散性的因素是多样的，为了弄清表层改性及应力集中对疲劳数据分散性的影响，研究了光滑试样(K_t为1,K_t为应力集中系数)在3种状态下(淬火回火、渗碳表层改性、混合射流表层改性)及渗碳试样在2种应力集中系数下(K_t为2和4)的疲劳数据分散性，利用分散性指标(包括对数标准差和变异系数)对18CrNiMo7-6合金钢疲劳寿命分散性进行了定量描述；结合疲劳试验数据对淬火回火、渗碳和混合射流3种状态下不同应力水平的疲劳分散性展开分析；对不同应力水平下的试样进行断口失效分析，讨论了疲劳数据分散性与裂纹源的相关性。结果表明，淬火回火试样疲劳寿命分散性最大，渗碳试样次之，混合射流试样分散性最小，这说明表层改性工艺可有效降低疲劳寿命分散性和提升零部件服役可靠性。渗碳试样K_t为4时试样疲劳寿命分散性最大，K_t为2次之，K_t为1分散性最小，这说明随着应力集中的增加，疲劳分散性随之增加，...     

特厚EH47止裂钢板及焊接热影响区的组织性能

 为开发大型集装箱船用特厚EH47止裂钢板,提出了一种低碳微合金MnCrNiCu钢,研究了其变形奥氏体连续冷却相变规律,使用控轧控冷工艺(TMCP)试制出最大厚度为85 mm特厚EH47级钢板,使用埋弧焊(SMA)和药芯焊丝气保焊(FCAW)技术对最厚钢板进行焊接试验,研究钢板和焊接接头的显微组织和性能。通过系列V缺口Charpy(CVN)示波冲击试验研究钢板的韧脆转变行为,获得各部位的韧脆转变温度(DBTT)及其解理断裂强度σ_f;测试了钢板及热影响区粗晶区(CGHAZ)全厚度截面的组织和CVN韧性,测试了-10 ℃的裂纹张开位移(CTOD)及其启裂韧性(K_c);通过系列温度梯度宽板双重拉伸(DT)试验,获得了钢板的止裂韧性(K_ca)与温度之间的关系。结果表明,钢板的显微组织由铁素体(PF)、针状铁素体(AF)和弥散分布的马氏体奥氏体(MA)组成;随着精轧压下率和冷却速率逐渐提高,大角度晶界分数逐渐增大,DBTT随之降低;CVN试样和DT试样具有相同的解理断裂临界事件;FCAW CGHAZ由粒状贝氏体(GB)+MA组元为主,SMA CGHAZ由AF+准多边形铁素体(QPF)+MA组元为主,前者K_c低于后者,更容易萌生解理断裂;钢板-10 ℃的K_ca为7 140 N/mm3/2,具备止裂性能。     

1Cr17Ni1双相不锈钢室温旋转弯曲疲劳性能

在应力比R=-1,转速为5 000 r/min和室温环境下测试了1Cr17Ni1双相不锈钢光滑旋转弯曲疲劳试样和缺口旋转弯曲疲劳试样的数据,得到了2种试样的S-N曲线.并采用扫描电镜(SEM)分析了2种试样的断口形貌,研究了1Cr17Ni1双相不锈钢高周疲劳特性.结果显示,光滑旋转弯曲疲劳试样的疲劳极限为320 MPa,其疲劳裂纹萌生于试样的表面;缺口旋转弯曲疲劳试样的疲劳极限为137 MPa,其裂纹源萌生于缺口处.经计算得到1Cr17Ni1双相不锈钢的缺口敏感系数为0.67.     

表面加工方法对TC4钛合金表面完整性及高周疲劳性能的影响

研究了磨削、一次喷丸、二次喷丸3种表面加工方法对TC4钛合金表面完整性及高周疲劳性能的影响规律,采用白光干涉仪、X射线残余应力测试仪对经不同方法加工的试样的表面形貌、表面粗糙度和表面残余应力分布等表面完整性参数进行了表征。采用旋转弯曲疲劳试验机分别测试了不同方法加工的光滑试样(应力集中系数Kt=1)和缺口试样(Kt=2)的旋转弯曲疲劳S-N曲线。结果表明,相比磨削,一次喷丸和二次喷丸处理后TC4钛合金光滑试样和缺口试样的疲劳极限均显著提高,TC4钛合金的疲劳缺口敏感性下降。另外,二次喷丸的疲劳极限增益效果优于一次喷丸的,原因是二次喷丸在TC4钛合金表面形成了更优的残余压应力场分布和更低的表面粗糙度。     

压痕对车轴钢疲劳极限的影响

利用硬度计在光滑沙漏状车轴钢疲劳试样上制造压痕,同时利用电火花在试样上加工缺陷,通过疲劳试验研究两种缺陷尺寸与试样疲劳极限之间的关系.将两类试样的测试结果和基于材料硬度、缺陷投影面积的Murakami模型计算结果进行对比.利用扫描电镜观察试样疲劳断口.结果表明,与计算结果相比较,压痕局部塑性变形导致的加工硬化和残余应力对试样的疲劳强度没有影响,裂纹依然从应力集中最大的压痕底部起裂.电火花缺陷表面粗糙度较大引起二次缺口效应,表面硬脆的重铸白层上还有微孔和微裂纹存在,导致此类试样疲劳强度低于模型计算结果,裂纹从电火花缺口底部多处萌生.      

失效汽车催化剂中铂钯铑富集方法探讨

研究了硫镍试金法应用于失效汽车催化剂中铂、钯、铑富集的方法,探讨了小型硫镍试金应用于前处理失效汽车催化剂类样品的试金配方,结合正交试验法和控制变量法考察了熔炼温度、熔炼时间、硅酸度、捕集剂镍粉量、硫镍质量比例、助熔剂用量和助熔剂配比对样品前处理效果的影响。最佳试金配方为:熔炼温度为1 050 ℃;熔炼时间为30 min;硅酸度K=3.5;0.88 g镍;m(Ni)∶m(S)=0.9∶1;4 g助熔剂(m(Na₂CO₃)∶m(Na₂B₄O₇)=1∶2)。以硫镍试金-碲共沉淀-电感耦合等离子体原子发射光谱法(ICP-AES)测定失效汽车催化剂中的铂、钯、铑,方法中铂、钯、铑的检出限分别为0.008 9、0.005 1、0.002 4 μg/mL。按照实验方法对样品RM-1、RM-2、RM-3(企业内部质控样)和标准样品GYBW-CHJ-1中铂、钯、铑进行测定,结果的相对标准偏差(n=6)在0.14%～2.7%之间,测定值均与参考值/认定值相吻合。     

应力比对TC4钛合金超高周疲劳失效机理的影响

采用频率为100 Hz的电磁谐振疲劳试验机进行疲劳拉伸试验, 研究了两种应力比(R=0. 1和-1) 对TC4钛合金的超高周疲劳失效机理的影响.结果表明, 两种应力比下的S-N曲线都呈现"双线"型, 但各自表示的意义及失效机理不同.当R=0. 1时, TC4钛合金的疲劳失效形式有两种, 即由加工缺陷诱发的表面失效和内部鱼眼失效, 这两种失效形式都伴随着颗粒平面(Facet) 出现; 而当R=-1时, 仅存在表面失效, 且无Facet的出现.基于断裂力学的讨论可知, 在正应力比及真空环境下, 对应小裂纹扩展的门槛值更低, 更有利于裂纹扩展及Facet的形成. TC4钛合金的整个内部疲劳失效过程及机理可解释为: (1) 滑移线或滑移带在部分α晶粒上的出现; (2) 微裂纹的萌生和接合; (3) 颗粒亮区(GBF) 的形成; (4) 鱼眼的形成; (5) 鱼眼外的失稳裂纹扩展; (6) 最终的瞬时断裂.      

二次硬化超高强度钢的高周疲劳性能研究

研究了采用真空感应+真空自耗重熔工艺冶炼的高纯净二次硬化超高强度AF1410钢的高周疲劳和疲劳裂纹扩展性能.结果表明:高纯净度AF1410钢具有优异的强韧性配合和较高的抗疲劳裂纹扩展能力,应力比尺为0.1时,其光滑(Kt=1)和缺口(Kt=3)疲劳强度分别为1 375MPa和417MPa,且疲劳裂纹源均起始于试样表面缺...     

Fatigue crack initiation and propagation behavior of high cobalt molybdenum stainless bearing steel

The crack initiation and propagation behavior of high cobalt molybdenum stainless bearing steel was studied by rotating bending fatigue test with smooth cylindrical specimens and notched specimens (theoretical stress concentration factor Kt=3). The fatigue limit and S- N curve of bearing steel were measured by up- and- down method and group method, respectively. The fractures of the specimens were observed by scanning electron microscopy. The results show that the cracking type of the smooth specimens is single source initiation. The crack source is surface defects and subsurface inclusion. The surface defects are surface roughness, persistent slip band and machining dent, while the subsurface inclusion is Al2O3- CaO- MgO- SiO2 composite inclusion. The fatigue limit of notched specimens is significantly decreased. The cracking type of the notched specimens is multi- source initiation. The notch sensitivity factor qf of bearing steel is 1. 18. The fatigue failure of the smooth specimens is transferred from the surface roughness with high stress amplitude to the persistent slip bands, the machining dents and the inclusions with low stress amplitude. The fatigue crack initiation life accounts for more than 94. 1% of the whole fatigue life.     

V形缺口法硬质合金断裂韧性研究

V形缺口三点弯曲试样主要用于极脆性材料(如硬质合金、陶瓷等)平面应交断裂韧性(K_IC)的测试。这种试样与传统的断裂韧性(K_IC)试样相比,其优点是:(1)尺寸简单,易于加工;(2)不需用疲劳法预制裂纹;(3)不需测定裂纹长度(K_IC值可直接从载荷峰值计算而得);(4)其断裂韧性值分散性低,重复性好,可比性强。另外,本文还讨论了断裂韧性(K_IC)与硬质合金主要结构参数的关系。结果表明:硬质合金的K_IC值与其结构参数λ/D_WC1/2存在着良好的线性关系。     

Postrepair Fatigue Performance of FRP-Repaired Corroded RC Beams: Experimental and Analytical Investigation

This paper presents the results of an experimental and analytical study of the fatigue performance of corroded reinforced concrete (RC) beams repaired with fiber-reinforced polymer (FRP) sheets. Ten RC beam specimens (152×254×3,200?mm) were constructed. One specimen was neither strengthened nor corroded to serve as a reference; three specimens were corroded and not repaired; another three specimens were corroded and repaired with U-shaped glass FRP sheets that wrapped the cross section of the specimen; and the remaining three specimens were corroded and repaired with U-shaped glass FRP sheets for wrapping and carbon-fiber-reinforced polymer (CFRP) sheets for flexural strengthening. The FRP sheets were applied after the main reinforcing bars were corroded to an average mass loss of 5.5%. Following FRP repair, some specimens were tested immediately to failure, while the other repaired specimens were subjected to further corrosion before being tested to failure to investigate their postrepair (long-term) performance. Reinforcement steel pitting due to corrosion reduced the fatigue life significantly. The FRP wrapping had no significant effect on the fatigue performance, while using CFRP sheets for flexural strengthening enhanced the fatigue performance significantly. The fatigue results were compared to smooth specimen fatigue data to estimate an equivalent fatigue notch factor for the main reinforcing bars of the tested specimens.     

超声冲击对P355NL1钢焊接接头超高周疲劳性能影响

 通过超声疲劳试验探究超声冲击对P355NL1钢焊接接头超高周疲劳性能的影响。结果表明,由疲劳[S-N]曲线可知,在105～109寿命区间内,冲击态试样的疲劳性能要高于焊态试样,在1.0×108的疲劳寿命下,焊态试样的疲劳强度为139 MPa,冲击态的疲劳强度为217 MPa,冲击态疲劳强度相较于焊态提高了56%,这表明超声冲击可以明显提高焊接接头的疲劳强度。利用扫描电镜（SEM）观察断口形貌可以发现,裂纹源位于焊接接头焊根区表面。P355NL1钢焊接接头疲劳断裂为准解理断裂,超声冲击可以提高焊接接头的疲劳强度,但不会改变其疲劳失效机理。超声冲击可以降低焊根处应力集中,引入有益压应力和表面晶粒细化,从而提高焊接接头的疲劳强度。     

粉末冶金高强度烧结钢的疲劳特性

通过测定N-110烧结钢旋转弯曲疲劳下的S-N曲线、疲劳裂纹扩展速率da/dN以及疲劳门坎△K_th,对烧结材料的疲劳特性进行了探讨,初步阐明了孔隙的存在对各种疲劳性能的影响规律以及热处理状态与疲劳性能之间的关系。     

Fatigue Strength and Crack Initiation Mechanism of Very-High-Cycle Fatigue for Low Alloy Steels

The fatigue strength and crack initiation mechanisms of very-high-cycle fatigue (VHCF) for two low alloy steels were investigated. Rotary bending tests at 52.5?Hz with hour-glass type specimens were carried out to obtain the fatigue propensity of the test steels, for which the failure occurred up to the VHCF regime of 10⁸ cycles with the S-N curves of stepwise tendency. Fractography observations show that the crack initiation of VHCF is at subsurface inclusion with ??fish-eye?? pattern. The fish-eye is of equiaxed shape and tends to tangent the specimen surface. The size of the fish-eye becomes large with the increasing depth of related inclusion from the surface. The fish-eye crack grows faster outward to the specimen surface than inward. The values of the stress intensity factor (K _I ) at different regions of fracture surface were calculated, indicating that the K _I value of fish-eye crack is close to the value of relevant fatigue threshold (??K _th ). A new parameter was proposed to interpret the competition mechanism of fatigue crack initiation at the specimen surface or at the subsurface. The simulation results indicate that large inclusion size, small grain size, and high strength of material will promote fatigue crack initiation at the specimen subsurface, which are in agreement with experimental observations.