Effects of Nd element addition on microstructure and mechanical properties of Ti-6Al-4V-2Cr alloy

本试验采用冷等静压法及粉末冶金法制备钛合金,消除了成分偏析对合金性能的影响。在Ti-6Al-4V-2Cr中加入稀土Nd元素并进行热处理,运用光学; 显微镜、XRD和TEM对其组织和性能进行观察和分析。通过观察发现合金的组织为均匀的alpha +; beta相。运用XRD和TEM观察发现,晶界和晶内均有Nd_2O_3析出物,Nd_2O_3的出现细化了晶粒,提高了形核率,降低了晶粒尺寸。运用精; 密万能试验机进行了力学性能测试,当Nd元素含量为1%时,合金的综合力学性能最好,合金的抗拉强度提高了10.7%,伸长率提高了49.1%。The Ti-6Al-4V-2Cr-xNd alloys were prepared by the cold isostatic; pressing method and powder metallurgy with addition of Nd element,the; effect of composition segregation on properties of the titanium alloy; was eliminated,and microstructure and the properties of the alloy after; heat treatment were studied by means of optical microscope,XRD and TEM.; The results show that the microstructure of the Ti-6Al-4V-2Cr-xNd is; composed of homogeneous alpha + beta phase. Nd_2O_3 precipitates are; observed in the grain boundaries and in the grains by XRD and TEM,and it; can refine the grains,increase the nucleation rate and decrease the; grain size. The optimal mechanical properties of the alloy are obtained; when the Nd content is 1%,and the tensile strength and elongation of the; alloy increase by 10.7% and 49.1%,respectively.军工863项目; 国防973支持项

Damage detection of sandwich panels with truss core based on time domain dynamic responses

A damage identification method, based on structural time domain dynamic responses and Teager energy operator, is presented for sandwich panels with truss core in the paper. The dimensionless structural dynamic responses, i.e., dimensionless velocity and displacement, are combined to construct damage index. Application of the method on sandwich panels in the cases of single damage and multiple damages with different extents are conducted. Effects of some factors on the method are discussed, including excitation location, excitation frequency, boundary condition, number of points N in Poincare maps. Numerical and experimental results show that the proposed method is effective in detecting both single damage and multiple damages with different extents. Excitation location plays a very important role in affecting the effectiveness of the method. Excitation frequency has little effect on the method, and there is a great selection space of excitation frequencies. Increasing the boundary condition constraint is beneficial for damage identification

Internal Damage Identification of Sandwich Panels With Truss Core Through Dynamic Properties and Deep Learning

For sandwich panels with truss core, the weakest part is the low-density core; therefore, some effective damage identification methods have been previously proposed for sandwich panels. However, these studies have mainly focused on damage location identification and only a few studies have discussed detection of the extent of the damage. In this study, a damage identification method integrating a deep learning technique with dynamic properties is proposed to identify both the location and extent of internal damage in sandwich panels with truss core. An analytical model verified by experiments based on a laser vibrometer is used to obtain raw data, which can generate various levels of damage inside the two face sheets. Instead of using surface photographs or raw data as the deep learning training dataset, the dataset is constructed using damage indices. By combining this with an analytical model, a dataset of specimens with various defects was collected and used as the input for the neural networks. The ability to identify the locations of damage and the extent of damage was used to evaluate the effectiveness of the proposed technique. The results show that the proposed method could be used to identify the location and extent of internal damage accurately

Damage identification of low-density material-filled sandwich panels with truss core based on vibration properties

A damage-identification method based on flexibility matrix and Teager energy operator is proposed for low-density material-filled sandwich panels with truss core. In the proposed damage index, weight coefficient r is introduced to consider the effect of damages on both high-order and low-order modes. Numerical simulations and experiments are conducted to assess the performance of the proposed method. Effects of Young's modulus of the filler material on the accuracy of the proposed method are also discussed. Results reveal that the method is reliable and effective for single-damage and multiple-damages identification of filled sandwich panels with truss core, and weight coefficient plays an important role, especially for cases with multiple damages or damages of small extent. Damage identification becomes more difficult as Young's modulus of the filler increases, and there is a critical value, after which the damage could not be identified by the proposed method

金雕巢期行为谱及时间分配/Ethogram and time budget of golden eagle during breeding season in Tianshan Mts.[J]

2010年7～9月、2011年4～9月、2012年7月,采用焦点动物取样法,累计对新疆西北部别珍套山和阿拉套山巢期的5对金雕(Aquila chrysaetos)及其雏鸟观测89d,行为记录911 h.制成金雕的行为谱,将各行为分为12类46种,并进行了相关描述.依据巢期的不同阶段(孵化期和育雏期)统计出各行为的时间分配:孵化期,亲鸟行为以孵卵为主(95.28％);育雏期,亲鸟的各行为时间分配依次为,离巢(77.81％)、护幼(18.5％)、喂食(2.64％)、警戒(1.05％),在育雏期的前(0～3周)、中(3～6周)、后(6-雏鸟离巢)阶段,护幼、喂食、离巢的时间分配差异极其显著(p＜0.01).雏鸟各行为时间分配依次为,休息(68.73％)、警戒(21.41％)、取食(5.56％)、运动(4.28％)、保养(1.02％).育雏期的前、中、后阶段,雏鸟的休息、警戒和运动行为的时间分配差异极其显著(p＜0.01).行为时间分配的差异,主要受不同阶段金雕能量需求、身体发育状况的影响