Advanced Materials Research Vols. 634-638

Abstract: Pozzolanic reactivity of silica fume(SF) in silica fume-cement (SFC)pastes was studied by ²⁹Si MAS NMR combined with deconvoluton technique, respectively. The experimental results indicate that SF possess an high pozzolanic reactivity. About 41% of SF at 3d and about 96% at 120d have reacted in a paste with SF of 10% in mass. In the highly alkaline environment of the cement paste, monomers formed after the covalent bonds of Si-O-Si in SF were broken, which can connect C-S-H dimers to form highly polymerized C-S-H, and increase the ACL of C-S-H.

Abstract: A finite cylindrical cavity expansion model for metal targets was proposed in consideration of the lateral free boundary and strain-hardening effect. Analytical solutions of radial pressure on the cavity wall were obtained. An engineering model for the penetration of rigid sharp-nosed projectiles into thick cylindrical metal targets with finite radius was developed. The influence of the radius ratio of target to projectile on penetration depth was studied. The present engineering model has good agreement with ballistic experiments and numerical simulation. The influence of the lateral free boundary of target on penetration depth needs to be considered for radius ratio of target to projectile less than 20.

Abstract: Recently, the transformation method has been extended to control solid elastic waves in case of high frequency or small material gradient. An important device in practice, the approximate elastodynamic directional-cloak with isotropic homogeneous materials, can be designed based on this method. In this paper, this device’s design method is discussed in detail and its effect on cloaking arbitrary shaped obstacles is explored. It is also shown that this useful device cannot be designed based on the conventional transformation elastodynamics. Examples are conceived and validated by numerical simulations.

Abstract: Three gel-type vehicles were synthesised and their rheological behavior was investigated in this paper. The main differences of three samples are the concentraton of resin (R-1>> G-1> G-2) and gelata (R-1<< G-1< G-2). The results show that R-1 is more temperature sensitive which might not favorable for the high speed printing. G-2 and G-1, which contain higher amount of gelling agent, might have a enhanced net-structure due to the reaction between gelling agent and resin. And the results of dynamic strain sweep and frequency sweep indicate that the gelata can give a good viscoelastic to the vehicle while the higher amount of resin might benefit the stability of vehicle. Although the most suitable ratio of gel-vehicle desired further discovery, the rheological behavior could be a proper means as to optimize the formula of ink.

Abstract: This paper deals with the failure analysis of a carbon fibre reinforced plastic (CFRP) plate which is joined to a structure using a steel pin. The analysis was carried out experimentally and numerically using the finite element method (FEM) system MSC.Marc. The Puck´s failure criterion for 3D stress state was used after its implementation into the MSC.Marc system. Experimental specimens were symmetrical laminates with 8 layers. A special experimental device which allowed monitoring of all visible changes of the experimental specimens with cameras was designed. This device was installed into the testing machine Zwick/Roell Z050. Obtained images were evaluated using the digital image correlation technique. Moreover, the vibrations in the surroundings of the specimens were measured to detect acoustic emissions which occur during damage.

Abstract: Adopting an accurate micro-tensile method based on dynamic mechanical analyzer (DMA) instrument, the tensile strength of three kinds of copper-wire/solder/copper-wire sandwich structured microscale lead-free solder joints that underwent current stressing with a direct current density of 1.0×10⁴ A/cm² and loading time of 48 hours were investigated, and compared with those solder joints isothermal aged at 100 0C for 48 hours and as-reflowed condition. These three kinds of microscale columnar solder joints have different volumes, i.e., a same diameter of 300 μm but different heights of 100 μm, 200 μm and 300 μm. Experimental results show that both current stressing and isothermal aging degrades the tensile strength of microscale solder joints, and the solder joint with smaller volume obtains higher tensile strength under same test condition. In addition, current stressing induces obvious electromigration (EM) issue under high current density of 1.0×10⁴ A/cm², resulting in the decreasing of tensile strength and different fracture position, mode and surface morphology of microscale solder joints. The degree of strength degradation increases with the increasing of joint height when keep joint diameter constant, this is mainly due to that electromigration leads to voids form and grow at the interface of cathode, and solder joints with larger volume may contains more soldering defects as well.

Abstract: This paper dealt with the fracture failure of a GCr15 steel ball screw nut. Through testing and analysis of hardness, microstructure, scanning electron microscopy and energy dispersive spectrum meter, it was found that there are local carbide network, few oversized carbide particles and metallic inclusions. The analysis showed that carbide network was failed to be eliminated through spheroidizing annealing treatment, while the presence of non-uniform carbide particles and metallic inclusions easily induced the crack and consequently led to the fracture of the nut.

Abstract: Explored the influence of pore structure of foam metal material on mechanical behavior of fracture. Discuss fracture toughness of several different micro geometric structure of foam metal material with finite element method. The author's calculations showed, microstructure and loading mode has an important effect on the fracture toughness of the foam metal material. due to ignoring the effects of cell structure on the mechanical properties of materials, the classic fracture toughness criterion -crack tip opening displacement (COD) is incomplete, it would be more efficient to take opening displacement change rate of the crack-tip as the parameter to characteristic the metallic foam material fracture toughness.

Abstract: A constitutive model, adopting the modified Khan, Huang and Liang (KHL) viscoplastic model to describe plastic deformation of metallic materials with different grain sizes in the range of nanometers to micrometers at different strain rates, was presented to simulate the mechanical behavior of iron sample with nanocrystalline surface layer. Stress-strain curve and yield stress of the iron sample were calculated by means of this model. Influence of grain size distribution in the cross section was also investigated. The simulation results indicate that the yield stress can be increased after the formation of the nanocrystalline surface layer. And an increment of the fraction of the nanocrystalline layer can improve the yield stress further.

Abstract: According to the computation model of the stress, the strain, and the extend ratio in tension leveling, under the platform of mat lab, take the linear strengthening ball plastic model as the foundation, established the simulated program of the quantitative parameters enactment of tension leveling craft, this procedure consideration initial remaining stress of strip, namely random shape defects, assign tensile stress and the curving curvature, compute the strip’s stress and strain change and elongation ratio after tension leveling, given the stress and strain and the extension rate of the main process parameters from the simulation results of each roller, analysis of different process parameters set on impact of the simulation results, and the results conform to reality tension leveling production.