台阶爆破岩石破碎平均粒径预测的支持向量机方法(英文)

针对传统的岩石台阶爆破破碎评估问题,运用统计学理论,建立预测不同矿山岩石爆破破碎后的平均粒径(X50)的支持向量机(SVMs)回归模型。爆破参数包括爆破设计参数、炸药参数、弹性模量及现场块度大小。SVMs模型选用7个参量作为预测岩石爆破破碎的平均粒径X50输入自变量:台阶高度与钻孔荷载比(H/B),间距与荷载比(S/B),荷载与孔径比(B/D),炮泥与荷载比(T/B),粉因数(PF),弹性模量(E)和现场块度大小(XB)。利用世界各地不同矿山和岩层测量的90组数据来训练和测试SVMs模型,其他12组爆破数据来验证该模型的有效性,并将SVR的预测结果与人工神经网络(ANN)、多元回归分析(MVRA)、传统的Kuznetsov方法及X50实测值进行比较。该方法显现出很好的效果,其预测精度是可以接受的。     

An analysis of the size effect on void growth in single crystals using discrete dislocation dynamics

The effect of size on the mechanical behavior and the void growth rate in a voided single crystal was studied using two-dimensional discrete dislocation dynamics. The simulations were based on the methodology developed by Van der Giessen and Needleman [Van der Giessen E, Needleman A. Modell Simul Mater Sci Eng 1995;3:689], which was extended to non-convex domains through the use of finite elements with embedded discontinuities [Romero I, Segurado J, LLorca J. Modell Simul Mater Sci Eng 2008;16:035008]. Square crystals (in the range 0.5–2.5 μm) with an initial void volume fraction of 10% were deformed under plane strain conditions in uniaxial tension, uniaxial deformation and biaxial deformation. The results of the simulations show two size effects, one on the initial flow stress and strain-hardening rate of the voided crystal (“smaller is stronger”) and another on the void growth rate (“smaller is slower”). The magnitude of both size effects increased with triaxiality. The physical micromechanisms responsible for these size effects were elucidated from the simulation results.     

An investigation on quench cracking behavior of superalloy udimet 720LI using a fracture mechanics approach

Quench cracking can be a serious problem in the heat treatment of high strength superalloys. A new fracture mechanics approach, quench cracking toughness (K _Q ), was introduced to evaluate the on-cooling quench cracking resistance of superalloy Udimet 720LI. A fully automatic computer controlled data acquisition and processing system was set up to track the on-cooling quenching process and to simulate the quench cracking. The influences of grain size, cooling rate, solution temperature, and alloy processing routes on quench cracking resistance were investigated. Research results indicate that quench cracking revealed a typical brittle and intergranular failure at high temperatures, which causes a lower quench cracking toughness in comparison to fracture toughness at room temperature. Fine grain structures show the higher quench cracking resistance and lower failure temperatures than intermediate grain structures at the same cooling rates. Moreover, higher cooling rate results in lower cracking toughness under the same grain size structures. In comparison of processing routes, powder metallurgy (PM) alloys show higher cracking resistance than cast and wrought (CW) alloys for fine grain structures at the same cooling rates. However, for intermediate grain structure, there is no obvious difference of K _Q between the two processing routes in this study.     

Manifestation of external size reduction effects on the yield point of nanocrystalline rhodium using nanopillars approach

In this study, pure rhodium was fabricated and mechanically investigated at the nanoscale for the first time. The nanopillars approach was employed to study the effects of size on the yield point. Nanopillars with different diameters were fabricated using electroplating followed by uniaxial compression tests. Scanning electron microscopy (SEM) was used as a quality control technique by imaging the pillars before and after compression to ensure the absence of cracks, buckling, barrelling or any other problems. Transmission electron microscopy and SEM were used as microstructural characterization techniques. Due to substrate-induced effects, only the plastic region of the stress–strain curves were investigated, and it was revealed that the yield point increases with size reduction up to certain limit, then decreases with further reduction of the nanopillar size (diameter). The later weakening effect is consistent with the literature, which demonstrates the reversed size effect (the failure of the plasticity theory) in nanocrystalline metals, i.e. smaller is weaker. In this study, however, the effect of size reduction is not only weakening, but is strengthening-then-weakening, which the authors believe is the true behavior of nanocrystalline materials.     

标准热处理对采用BNi-9焊料的瞬时液相连接IN-738LC高温合金的影响

研究标准热处理对扩散焊IN-738LC高温合金显微组织和力学性能的影响。对连接样品进行全固溶退火、部分固溶退火和时效处理3个不同的热处理。结果表明,在1120℃下焊接5 min,会导致不完全等温凝固,在焊缝处形成富Ni、Cr的硼化物共晶相。当保温时间延长到45 min时,接头中发生完全等温凝固,形成镍的先共晶固溶体γ相。等温凝固和非等温凝固样品的标准热处理能完全消除扩散影响区的硼化物相,并在等温凝固区形成γ’析出相。然而,在非等温凝固样品的接头区观察到不连续的再凝固产物。等温凝固样品经标准热处理后,剪切强度最高(约801 MPa),为基材剪切强度的99%。     

Structural size effects of intermetallic compounds on the mechanical properties of Mo-Si-B alloy: An experimental investigation

In general, size, shape and dispersion of phases in alloys significantly affect mechanical properties. In this study, the mechanical properties of Mo-Si-B alloys were experimentally investigated with regards to the refinement of intermetallic compound. To confirm the size effect of the intermetallic compound phases on mechanical properties, two differently sized intermetallic compound powders consisting Mo₅SiB₂ and Mo₃Si were fabricated by mechano-chemical process and high-energy ball milling. A modified powder metallurgy method was used with core-shell intermetallic powders where the intermetallic compound particles were the core and nano-sized Mo particles which formed by the hydrogen reduction of Mo oxide were the shells, leading to the microstructures with uniformly distributed intermetallic compound phases within a continuous α-Mo matrix phase. Vickers hardness and fracture toughness were measured to examine the mechanical properties of sintered bodies. Vickers hardness was 472 Hv for the fine intermetallic compound powder and 415 Hv for the coarse intermetallic compound powder. The fracture toughness was 12.4 MPa·√m for the fine IMC powders and 13.5 MPa·√m for the coarse intermetallic compound powder.     

On plasticity and fracture of nanostructured Cu/X (X = Au,Cr) multilayers: The effects of length scale and interface/boundary

Plastic deformation and fracture behavior of two different types of Cu/X (X = Au, Cr) multilayers subjected to tensile stress were investigated via three-point bending experiments. It was found that the plastic deformation ability and fracture mode depended on layer thickness and interface/boundary. The Cu/Au multilayer showed significant features of plastic flow before fracture, and such plasticity was gradually suppressed by premature unstable shearing across the layer interface with decreasing layer thickness. In comparison, Cu/Cr multilayers were prone to a quasi-brittle normal fracture with decreasing layer thickness. Both experimental observations and theoretical analyses revealed differences in plasticity and fracture mode between the two types of metallic multilayers and the relevant physical mechanism transition due to length scale constraint and interface/boundary blocking of dislocation motion.