拉丝环境湿度对高强度光纤动态疲劳的影响

文章研究了高强度石英玻璃光纤的动态疲劳性能与拉丝环境相对湿度的函数关系。光纤是在采用石墨感应加热炉加热,并在控制温度、相对湿度和拉丝环境尘埃粒子数的条件下拉制的。所谓拉丝环境指的是从感应加热拉丝炉至涂覆点之间的空间。通常,人们采用两种不同的加载方式,即拉伸和两点弯曲来测量拉制的光纤的动态疲劳。业已发现,拉丝湿度对用张力法加载方式测得的光纤的动态疲劳起着决定性的影响。     

Small-world brain functional network altered by watching 2D/3DTV

With the development of display technology, the healthy problems caused by watching 2D/3DTV have received more and more attention. This paper utilized resting-state functional magnetic resonance imaging to study the changes of small-world brain network before and after one-hour 2D/3DTV watching, and explored the brain fatigue mechanism caused by watching 2D/3DTV. We conclude that one-hour watching of 2DTV will not increase the burden of brain. On the contrary, one-hour watching of 3DTV requires the brain to regulate the efficiency of brain areas, such as temporal lobe and occipital lobe, which may explain the fact that watching 3DTV can easier cause brain fatigue than watching 2DTV.     

Effect of thermal cycles on the mechanical strength of quad flat pack leads/Sn-3.5Ag-X (X=Bi and Cu) solder joints

Quad Flat Pack (QFP) Leads/Sn-3.5Ag-X (X=Bi and Cu) joint was thermally cycled between 243 K and 403 K or 273 K and 373 K, and both metallographic examination and mechanical pull test were performed to evaluate thermal fatigue damage of the joint. The addition of bismuth drastically degrades the thermal fatigue resistance of Sn-3.5Ag solder. On the other hand, the pull strength of Sn-3.5Ag-Cu solder joints slightly decreased with increasing number of thermal cycles, though it still remains higher in comparison to that for conventional Sn-37Pb or bismuth containing solder joint. The behavior observed here reflects the isothermal fatigue properties of bulk solder, because thermal fatigue crack initiates at the surface of solder fillet and propagates within the fillet in an early stage of fatigue damage. Furthermore, the lead phases lying at the interface between lead-frame and bismuth containing solder joint may promote the crack propagation at the interface, resulting in the extremely low thermal fatigue resistance of the joint.     

激光喷丸强化变形镁合金的疲劳寿命数值分析

以ABAQUS和MSC.fatigue软件为平台, 建立了激光喷丸强化前后试样疲劳寿命及薄弱位置预测的有限元分析模型。为研究材料强度对激光喷丸强化效果的影响, 以AZ31B和ZK60两种不同强度变形镁合金为对象, 对激光喷丸强化后的残余应力和塑性变形进行了分析, 并预测了喷丸前后的疲劳寿命, 两种材料的疲劳寿命增益分别为112.04%和181.2%。结果表明, 高强度材料激光喷丸强化效果优于低强度材料。     

Low-cycle fatigue prediction model for pb-free solder 96.5Sn-3.5Ag

Low-cycle fatigue (LCF) data of Sn-Ag eutectic solder (96.5Sn-3.5Ag) under various temperatures and frequencies has been described using three different prediction models, i.e., Coffin-Manson model, Smith-Watson-Topper (SWT) model, and Morrow energy model. The LCF behavior represented by the present prediction models showed temperature and frequency dependences, i.e., the fatigue ductility coefficient increased with increasing frequency and decreasing temperature. In order to better correlate the LCF data, a flow stress and/or frequency-dependent modifications were introduced to the Coffin-Manson and Morrow energy models. The frequency-modified Coffin-Manson model could not describe the influence of temperature on LCF behavior, while the flow stress-modified frequency-modified Morrow energy model, into which the metallurgical response (flow stress and frequency) was introduced to account for the effect of temperature and frequency on LCF behavior, gave reasonable predictions of LCF data under various temperatures and frequencies.     

工程机械用800 MPa低合金高强度钢焊接接头低周疲劳性能研究

针对大型工程机械用800 MPa低合金高强度钢及其焊接接头,进行低周疲劳性能研究。试验在常温下进行,对称三角波加载。试验结果表明,母材两个轧制方向的应变疲劳寿命没有明显差别,焊接接头的疲劳寿命偏低。焊接接头的局部软化是应变集中,导致应变疲劳寿命降低的主要原因。应变疲劳断口有明显的条纹特征,母材疲劳断口上伴有与条纹平行的二次裂纹,焊接接头的疲劳断口条纹清晰且宽度较细。试验确定的循环应力应变特性参数和应变疲劳寿命参数有明显的相关关系。     

Bi3.25La0.75Ti3O12薄膜的化学溶液淀积方法制备及表征

采用新颖的化学溶液淀积方法,配制出可长时间稳定的先体溶液,采用红外分析和热分析等手段,对成膜过程中发生的反应变化进行了分析,结果表明采用新的方法可以增加先体的稳定性,并且确定了薄膜的析晶温度.XRD测试表明薄膜在不到500℃即开始析晶,并且析晶情况与Bi含量有关.对薄膜的电学性能研究表明随着Bi含量的增加,薄膜的漏电性能和抗疲劳特性变差,矫顽场变大,而2Pr在Bi过量10%的情况下达到最大31.6 μ C/cm2.     

Thermomechanical fatigue behavior of Sn-Ag solder joints

Microstructural studies of thermomechanically fatigued actual electronic components consisting of metallized alumina substrate and tinned copper lead, soldered with Sn-Ag or 95.5Ag/4Ag/0.5Cu solder were carried out with an optical microscope and environmental scanning electron microscope (ESEM). Damage characterization was made on samples that underwent 250 and 1000 thermal shock cycles between −40°C and 125°C, with a 20 min hold time at each extreme. Surface roughening and grain boundary cracking were evident even in samples thermally cycled for 250 times. The cracks were found to originate on the free surface of the solder joint. With increased thermal cycles these cracks grew by grain boundary decohesion. The crack that will affect the integrity of the solder joint was found to originate from the free surface of the solder very near the alumina substrate and progress towards and continue along the solder region adjacent to the Ag₃Sn intermetallic layer formed with the metallized alumina substrate. Re-examination of these thermally fatigued samples that were stored at room temperature after ten months revealed the effects of significant residual stress due to such thermal cycles. Such observations include enhanced surface relief effects delineating the grain boundaries and crack growth in regions inside the joint.     

利用C630车床进行曲轴圆角滚压强化

介绍利用630车床对6V87Q-1005020曲轴进行圆角滚压强化的机理,并简要叙述了曲轴圆角滚压强化系统的设计方法及应用。     

镀铬对0Cr13Ni4Mo钢疲劳强度的影响

研究了镀铬对轴用0Cr13Ni4Mo钢疲劳强度的影响,发现镀铬可导致疲劳强度σ-1(107次)下降37.5%～41%.电镜观察发现,镀层中的微裂纹是引发速断的疲劳源.低温去氢无助于疲劳性能改善.