Mechanical properties of nanostructured Mg–5 wt%Al–x wt%AlN composite synthesized from Mg chips

In the present investigation, Mg chips are recycled to produce nanostructured Mg–5wt%Al reinforced with 1, 2 and 5 wt% nanosized AlN particulates by mechanical milling (MM). Each batch of composite mixture was milled for different milling durations to produce different degrees of grain refinement. The mechanical properties such as tensile strength, ductility and hardness with respect to the effect of grain refinement, in other words, milling duration were studied. It was found that grain size played an important role in controlling ductility of the composites.     

Quantitative characterization of nanoprecipitates in irradiated low-alloy steels: advances in the application of FEG-STEM quantitative microanalysis to real materials

The characterization of the solute-enriched features (clusters or nanoprecipitates in irradiated low-alloy steels) requires extremely high spatial and elemental resolution, previously necessitating analysis using atom probe field-ion microscopy. In this investigation, field-emission gun-scanning transmission electron microscope (FEG-STEM) quantitative energy dispersive X-ray (EDX) microanalysis (spectrum imaging) has been applied to the characterization of the irradiation-induced nanoprecipitates in a low-alloy forging steel. Refinements in the EDX data have been possible via the application of multivariate statistical analysis (MSA) to the spectrum images, resulting in significantly reduced noise in the images. Most importantly, MSA permitted the clear identification of other elements in these Ni-enriched nanoprecipitates—including Mn and Cu. The processed X-ray spectrum images also provided direct evidence of the preferential formation of these irradiation-induced features along pre-existing dislocations within the steel, as well as the formation of intragranular nanoprecipitates. This research has provided the first direct X-ray spectrum images of irradiation-induced nanoprecipitates in high Ni A508 Gr4N forging steel, and has demonstrated the significant improvements attainable though the application of MSA techniques to the spectrum images. These results independently confirmed the analyses of the Ni-enriched nanoprecipitates previously conducted by 3D-APFIM, with the performance of the FEG-STEM/EDX technique shown to be comparable to that of the 3D-APFIM technique.     

A weight function-critical plane approach for low-cycle fatigue under variable amplitude multiaxial loading

Low‐cycle fatigue data of type 304 stainless steel obtained under axial‐torsional loading of variable amplitudes are analyzed using four multiaxial fatigue parameters: SWT, KBM, FS and LKN. Rainflow cycle counting and Morrow's plastic work interaction rule are used to calculate fatigue damage. The performance of a fatigue model is dependent on the fatigue parameter, the critical plane and the damage accumulation rule employed in the model. The conservatism and non‐conservatism of predicted lives are examined for some combinations of these variables. A new critical plane called the weight function‐critical plane is introduced for variable amplitude loading. This approach is found to improve the KBM‐based life predictions.     

Residual strength prediction of multiple cracked stiffened panels

Prediction of the coalescence of adjacent cracks is critical for residual strength estimation of structures under multiple site damage conditions. A methodology successfully developed for the case of crack link‐up prediction of un‐stiffened plates, is extended for the case of typical cracked stiffened aircraft panels. The proposed link‐up criterion is based on the change in the magnitudes of elastic and plastic strain energies of the stiffened panel, before and after the cracks coalesce. The strain energy magnitudes of interest are calculated using non‐linear elastic–plastic finite‐element analysis. For the application and verification of the method, experimental results from the open literature are used. Residual strength values calculated by the proposed methodology are in good agreement with the experimental results. The present criterion provides superior results when compared to the existing and commonly applied link‐up criteria.     

Nanocrystalline diamond growth on different substrates

Nanocomposite films consisting of diamond nanoparticles of 3-5 nm diameter embedded in an amorphous carbon matrix have been deposited by means of microwave plasma chemical vapour deposition (MWCVD) from CH₄/N₂ gas mixtures. Si wafers, Si coated with TiN, polycrystalline diamond (PCD) and cubic boron nitride films, and Ti-6Al-4V alloy have been used as substrates. Some of the substrates have been pretreated ultrasonically with diamond powder in order to enhance the nucleation density n_nuc. It turned out that n_nuc depends critically on the chemical nature of the substrate, its smoothness and the pretreatment applied. No differences to the nucleation behaviour of CVD PCD films were observed. On the other hand, the growth process seems to be not affected by the substrate material. The crystallinity (studied by X-ray diffraction) and the bonding environment (investigated by Raman spectroscopy) show no significant differences for the various substrates. The mechanical and tribological properties, finally, reflect again the influence of the substrate material: on TiN, a lower hardness was measured as compared to Si, PCD and c-BN, whereas the adhesion of c-BN/nanocrystalline diamond (NCD) system was determined by that of the c-BN film on the underlying Si substrate.     

Thermomechanical behavior of Ti-Ni shape memory alloy films deposited by DC magnetron sputtering

In this study, thermomechanical properties of titanium-nickel (Ti-Ni) shape memory alloy (SMA) films are investigated in order to derive constitutive relations. Ti-Ni SMA films, deposited by DC magnetron sputtering under controlled film composition, are characterized by uniaxial tensile tests. At room temperature (R.T.), Ti-Ni films having Ti contents less than 50 at% exhibit superelastic behavior, and those having Ti contents greater than 50 at% exhibit shape memory behavior. However, the Ni—53.2 at% Ti film fractured at a tensile strain of 0.8% because of an increase in brittleness with increasing Ti content. At elevated temperatures, Ti-Ni films having Ti contents of 50.2 to 52.6 at% undergo phase change from martensite to austenite. The Young's modulus of the Ti-Ni films depends on temperature at each phase, regardless of film composition. Film composition does, however, affect the measured material constants b_A, b_M, c_A, and c_M. Stress-strain curves calculated from the constructed constitutive equation closely agree with those obtained from tensile tests, for both the martensite and austenite phases. The constitutive equations are expected to find great utility in the design of Ti-Ni film-actuated microelectromechanical systems (MEMS).     

钻孔爆破断裂控制技术研究

提出了一种新型的断裂控制爆破方法——在炮孔内同时利用不同的偶合介质(水和空气)爆破法。利用空气和水不同的物理特性和传能性质,控制爆炸能量的释放过程及作用方向,从而达到控制断裂方向,以起到崩落一侧而保护另一侧的目的。分析了水和空气不偶合装药爆破对周围介质的作用,通过模拟试验,对爆破后水介质所在方向和空气介质所在方向的应变和损伤分别进行了对比,反映出了介质中的受力和变形情况。实验表明,能够有效地控制裂缝的产生和发展,是一种行之有效的断裂控制爆破方法。     

基于残余应变的多侧压下混凝土受拉疲劳损伤研究

在侧压分别为0.25fc和0.50fc及其组合条件下,进行了混凝土在多侧压下的受拉等幅与变幅疲劳试验,得到了疲劳累积极限应变和残余极限应变,建立了残余应变与疲劳次数关系方程,并给出了残余应变与循环次数关系曲线。根据残余应变的稳定性,也即不受加载历程的影响,主要与侧应力水平和相对疲劳次数有关,以残余应变与相应应力水平下的残余极限应变之比作为损伤变量,建立了损伤变量与疲劳次数关系的统一方程,并给出了损伤变量与疲劳次数关系曲线。同时,对单轴、单、双侧压下的混凝土受拉疲劳的累积极限应变和残余极限应变与相应应力条件下的静态峰值应变进行了比较,其结果是随着侧应力水平的增加,相应的极限应变增加,再次说明了侧应力水平的影响。静态峰值应变与相应条件下的疲劳累积极限应变接近,残余极限应变与静态峰值应变及疲劳累积极限应变的比值较为稳定,其变化区间在0.22~0.28之间,且两种比值之间相差0.0~0.2。最后,对Miner准则进行了改进,并根据所建立的损伤模型与改进的Miner准则,对变幅疲劳寿命进行了预测,其结果是较为合理的。     

铝-钢爆炸焊接试验与分析

介绍了一种铝-钢复合板爆炸焊接工艺，包括所采用的炸药、复合板的性能和爆炸焊接材料的准备等。采用了金相技术、电子探钳和电子显微镜物相鉴定手段以及力学性能分析．结果显示．该复合板的结合区存在着金属强烈的塑性变形、熔化和原子间的相互扩散等冶金过程；铝-钢复合板是一种具有特殊使用性能的新型结构材料．具有很高的经济效益和广泛的应用前景。     

大型预焙电解槽侧部碳块破损的原因及补救措施

分析了电解槽侧部碳块破损的现象及原因,并提出了一些破损补救方法,以期对大型电解槽生产管理工作有一定帮助.