铸钢焊接接头裂纹扩展行为研究

简要介绍了某深水气田开发项目中出现的高强度铸钢类型，针对该材料的焊接，选用气体保护药芯焊丝开发焊接工艺。测定了焊接接头区域疲劳裂纹扩展速率及疲劳裂纹扩展门槛值，结果表明：整体焊接接头疲劳裂纹扩展性能较好，耐裂纹性能按高低顺序为焊缝>热影响区>铸钢母材。     

疲劳裂纹随机扩展规律分析方法

针对较少试验试样（小子样），应用随机模拟方法，对焊接接头热影响区疲劳裂纹随机扩展规律进行随机模拟，并与试验值回归结果进行对比分析，结果表明即使在试验试样数较少的情况下，仍能得到较佳效果。同时对Ｐａｒｉｓ公式中参数ｃ和ｎ的相关性进行了分析。     

横向载荷对含表面裂纹对焊接头疲劳裂纹扩展速率影响的研究

研究了双向载荷作用下对焊接头表面裂纹的疲劳扩展规律。采用经精确标定应力强度因子幅值的双向十字形试样,在电液伺服双轴向疲劳试验机上对母材分别为16MnR 和 Q235-B 这两种钢的对焊试板进行了疲劳裂纹扩展试验。同时,将其结果分别与单向应力下对焊接头及母材的疲劳扩展速率进行了比较,为制定我国在役压力容器缺陷评定规范提供了参考数据。     

316H奥氏体不锈钢焊接接头裂纹失效分析

针对316H奥氏体不锈钢焊接接头出现裂纹的现象,对316H钢母材和热影响区的金相组织进行了观察。结果表明,材料组织不均匀且有夹杂物,晶界处有析出相。同时测试了裂纹附近材料的硬度,分析了裂纹产生的原因。焊接接头裂纹失效的分析为改善316H钢焊接质量提出了相应的措施。     

16MnR钢高温疲劳裂纹扩展行为试验研究

对16MnR钢在常温、150℃、300℃和425℃下的疲劳裂纹扩展速率进行了测试和分析,得到了四种温度下的疲劳裂纹扩展规律。结果表明：该材料在150℃和300℃的疲劳裂纹扩展速率比常温和425℃时低,425℃时疲劳裂纹扩展速率最高。     

水介质中4340钢超高压换热器疲劳裂纹扩展速率

针对超高压换热管常用的ＡＩＳＩ４３４０钢，对表面裂纹的试板采用浸水腐蚀的方法，研究了４３４０钢在水介质中表面裂纹的疲劳扩展速率，并与空气中的扩展速率进行了比较。试验结果表明，腐蚀介质的存在加速厂裂纹扩展，并随裂纹的扩展，其加速作用越来越明显。水中存在的氧是导致腐蚀和加速裂纹扩展的主要原因。     

高强度CrNiMoV钢裂纹疲劳扩展行为研究和水晶釜安全寿命评估

对高强度钢ＣｒＮｉＭｏＶ表面裂纹的疲劳扩展速率ｄａ／ｄＮ进行了测试和分析，并据此对某一超高压水晶釜的安全寿命作了评估。     

加氢反应器接管焊缝疲劳裂纹的扩展研究

对 2 .2 5Cr1Mo钢在室温和 42 0℃下的疲劳裂纹扩展速率进行了测试和分析 ,得到了两种温度下的疲劳裂纹扩展规律 ,并根据测试结果对一台加氢反应器接管连接焊缝裂纹的疲劳扩展进行了计算和安全评估 ,为该反应器的安全使用提供了理论依据。     

表面裂纹疲劳扩展形貌变化规律的研究

首先进行了１６Ｍｎ板材半椭圆表面裂纹疲劳扩展试验。试验结果表明，采用Ｎｅｗｍａｎ－ｒａｊｕ应力强度因子时，表面裂纹深度方向和表面方向的扩展速率均符合Ｐａｒｉｓ公式。在此基础上，从Ｎｅｗｍａｎ－Ｒａｊｕ应力强度因子计算式和Ｐａｒｉｓ疲劳裂纹扩展速率公式出发，通过理论和数值分析，建立了３类表面裂纹在受拉伸、弯曲、和拉弯组合加载下的疲劳扩展形貌统一表达式，并通过疲劳试验结果对其进行了考核。结果表明，采用统一表达式预测裂纹形貌的各项统计指标均优于其他两种表达式     

316L钢高温疲劳裂纹扩展的规律研究

对316L钢在常温、200℃、400℃和550℃。下的疲劳裂纹扩展速率进行了测试和分析，对疲劳断口形貌进行观察，得到了四种温度下的疲劳裂纹扩展规律。结果表明：裂纹扩展率随着温度的升高而增大；高温下氧化作用增强。     

桥梁用钢14MnNbq焊接接头的疲劳设计曲线

通过对 14Mn Nbq钢焊接接头的疲劳试验 ,得到了循环应力 -应变方程、应变寿命曲线以及疲劳设计曲线 ,并将 14Mn Nbq钢焊接接头疲劳设计曲线与 ASME、BS5 5 0 0中相应的曲线进行了比较。     

Analysis and design of adhesively bonded joints for fatigue and fracture loading: a fracture-mechanics approach

An experimental–computational fracture-mechanics approach for the analysis and design of structural adhesive joints under static loading is demonstrated by predicting the ultimate fracture load of cracked lap shear and single lap shear aluminum and steel joints bonded using a highly toughened epoxy adhesive. The predictions are then compared with measured values. The effects of spew fillet, adhesive thickness, and surface roughness on the quasi-static strength of the joints are also discussed. This fracture-mechanics approach is extended to characterize the fatigue threshold and crack growth behavior of a toughened epoxy adhesive system for design purposes. The effects of the mode ratio of loading, adhesive thickness, substrate modulus, spew fillet, and surface roughness on the fatigue threshold and crack growth rates are considered. A finite element model is developed to both explain the experimental results and to predict how a change in an adhesive system affects the fatigue performance of the bonded joint.     

0Cr18Ni9钢在低浓度NaCl溶液中腐蚀疲劳裂纹扩展特性

试验显示 Ｎａ Ｃｌ溶液的存在,其浓度增加及加载频率降低都加快 ０ Ｃｒ１８ Ｎｉ９ 钢在低浓度 Ｎａ Ｃｌ溶液中腐蚀疲劳裂纹的扩展速率。     

疲劳裂纹扩展速率的统计分析及疲劳寿命的概率预测

通过对Ｐａｒｉｓ模型的分析，得到ｍ和ｌｏｇＣ的线性关系。试验结果的数据分析表明了ｍ和Ｃ分别符合正态分布及对数正态分布，并运用统计结果对疲劳寿命进行了概率预测。     

Fatigue Crack Propagation in Ceria-Partially-Stabilized Zirconia (Ce-TZP)-Alumina Composites

Fatigue crack propagation rates in tension-tension load cycling were measured in ZrO₂-12 mol% CeO₂-10 wt% Al₂O₃ ceramics using precracked and annealed compact tension specimens. The fatigue crack growth behavior was examined for Ce-TZPs of different transformation yield stresses obtained by sintering for 2 h at temperatures of 1500°C (type A), 1475°C (type B), 1450°C (type C), and 1425°C (type D). The threshold stress-intensity range, ΔK_th, for initiation of fatigue crack propagation increased systematically with decreasing transformation yield stress obtained with increasing sintering temperature. However, the critical stress-intensity range for fast fracture, ΔK_c, as well as the stress-intensity exponent in a power-law correlation (log (da/d N ) vs log ΔK) were relatively insensitive to the transformation yield stress. The fatigue crack growth behavior was also strongly influenced by the history of crack shielding via the development of the crack-tip transformation zones. In particular, the threshold stess-intensity range, Δ K _th, increased with increasing size of the transformation zone formed in prior quasi-static loading. Crack growth rates under sustained peak loads were also measured and found to be significantly lower and occurred at higher peak stress intensities as compared to the fatigue crack growth rates. Calculations of crack shielding from the transformation zones indicated that the enhanced crack growth susceptibility of Ce-TZP ceramics in fatigue is not due to reduced zone shielding. Alternate mechanisms that can lead to reduced crack shielding in tension-tension cyclic loading and result in higher crack-growth rates are explored.     

Fatigue fracture of reaction injection molded (RIM) nylon composites

This study was undertaken to determine how milled glass fibers affect the fatigue resistance of reaction injection molded (RIM) nylon 6. Specifically the effects of glass content, fiber length, orientation, and surface treatment were investigated. The fatigue crack growth rates for unfilled and glass-filled samples were observed to follow the well-known Paris equation in terms of dependence on cyclic stress intensity factor. For the unfilled nylon a line shaped zone was observed in advance of the crack tip. Fractography results suggest that the zone was the projection of the actual crack tip profile through the thickness of the sample rather than a distinct plastic or deformation zone. The fatigue fracture surface exhibited a patchy type structure with features 50–150 μm in size, suggesting a void coalescence type of mechanism as has been reported for injection molded nylons. A diffuse damage zone, several millimeters in size, was observed at the crack tip for the glass-filled RIM nylon 6. The zone was observed to pulsate with the applied oscillating load. The growth of the damage zone volume with increasing crack length (and thus increasing stress intensity factor range) followed the Paris law, as did the crack growth rate data. The damage mechanism is attributed to void formation and microcracking at the fiber–matrix interface. The results of this study show that, for milled glass-reinforced RIM nylon 6, the crack growth rates were much more rapid than observed for injection-molded nylon 6 containing chopped glass fibers. This difference is attributed to the greatly reduced glass fiber lengths for the milled glasses.     

Fatigue and Static Crack Propagation in Yttria-Stabilized Tetragonal Zirconia Polycrystals: Crack Growth Micromechanisms and Precracking Effects

The influence of precracking techniques in the crack growth behavior of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is investigated. Load-bridge and cyclic-compression precracking enhance subsequent tensile crack growth rates, in comparison to results that are found with precracks that are extended under four-point bending prior to testing. The actual influence of these precracking techniques in the near-threshold crack growth regime is remarkably different. Although load-bridge precracking produces a pattern of crack growth fluctuations for stress intensity factors, K , lower than the effective crack-growth threshold of the material, compression-fatigue precracks start to propagate under far-field tensile loads at very fast growth rates and for K values that are slightly higher than the effective threshold. Crack-tip shielding by tetragonal-to-monoclinic transformation develops gradually, influencing the crack growth behavior in Y-TZP. Proposed fatigue crack growth micromechanisms involve damage accumulation at the crack-tip region. For K _max > 3 MPa·m^1/2, fatigue crack growth rates are strongly affected by environmental interactions at the crack tip, and postulated fatigue micromechanisms include the cyclic degradation of crack-tip shielding.     

Fatigue Growth of Cohesive Defects in T-Peel Joints

This paper uses 2D and 3D finite element models to predict the stresses within bonded and weld-bonded T-peel joints. Epoxy adhesive is modelled as a homogeneous layer providing a perfect bond between aluminium adherends. Knowledge of the critical tensile stresses enables the likely region of fatigue crack initiation to be predicted. The long term reliability and durability of a joint depend directly on its fatigue strength. This research elucidates the region of cohesive crack initiation, the subsequent direction of crack propagation and the relative duration of the different stages of fatigue crack growth. The various stages of embedded, surface and through-width fatigue growth of cohesive defects within a T-peel joint are compared. This establishes fatigue life from crack initiation to final joint fracture for typical bonded and weld-bonded T-peel joints.