Substituent Effects on EI-MS Fragmentation Patterns of 5-Allyloxy-1-aryl-tetrazoles and 4-Allyl-1-aryl-tetrazole-5-ones; Correlation with UV-Induced Fragmentation Channels

1,4- and 1,5-disubstituted tetrazoles possess enriched structures and versatile chemistry, representing a challenge for chemists. In the present work, we unravel the fragmentation patterns of a chemically diverse range of 5-allyloxy-1-aryl-tetrazoles and 4-allyl-1-aryl-tetrazolole-5-ones when subjected to electron impact mass spectrometry (EI-MS) and investigate the correlation with the UV-induced fragmentation channels of the matrix-isolated tetrazole derivatives. Our results indicate that the fragmentation pathways of the selected tetrazoles in EI-MS are highly influenced by the electronic effects induced by substitution. Multiple pathways can be envisaged to explain the mechanisms of fragmentation, frequently awarding common final species, namely arylisocyanate, arylazide, arylnitrene, isocyanic acid and hydrogen azide radical cations, as well as allyl/aryl cations. The identified fragments are consistent with those found in previous investigations concerning the photochemical stability of the same class of molecules. This parallelism showcases a similarity in the behaviour of tetrazoles under EI-MS and UV-irradiation in the inert environment of cryogenic matrices of noble gases, providing efficient tools for reactivity predictions, whether for analytical ends or more in-depth studies. Theoretical calculations provide complementary information to articulate predictions of resulting products.     

Ballistic and numerical simulation of impacting goods on conveyor belt rubber

Impact loading is an important process in the transport industry as it causes wear and failure of critical components. Conveyor belts are of particular importance as they are used in practically every industry where large quantities of goods are moved over short (<10 m) or long distances (>1 km). To investigate stress levels inside the material during impact loading, a gas gun was utilized to shoot 9 mm spherical steel balls onto the surface of a rubber conveyor belt. A high speed video recording system was employed in order to determine penetration depth and dissipated energy of the steel ball. Maximal penetration depths of up to 3.9 mm and maximal dissipated energies of up to 86.8 % were measured. Additionally, a numerical simulation using smooth particle applied mechanics was conducted and compared to the experimental results obtained with the gas gun. The calculated von Mises stresses affected the conveyor belts up to a maximum depth of 8.8 mm with at least 20 MPa. Maximum von Mises stresses were calculated to reach 60 MPa.     

Improving the impact property and heat‐resistance of PLA/PC blends through coupling molecular chains at the interface

The influences of both the molecular structure and the melt viscosity differences between Poly(lactic acid) (PLA) and polycarbonate (PC) on the interpenetration of molecular chains at the interface were investigated by comparing the dynamic mechanical properties and morphologies of the as‐prepared PLA/PC solution‐casting blends with those of their corresponding annealed (180°C, 8 h) samples or PLA/PC melt blends. Additionally, two chain extenders containing epoxy groups (ADR and TGDDM) were used to improve the interfacial strength. Subsequently, the interpenetration of PLA and PC molecular chains at the interface was also surveyed. Finally, the effects of the morphology formed by after adding ADR or TGDDM on the impact property, and heat resistance were discussed. The results showed that there was no interpenetration of molecular chains at the interface in PLA/PC melt blends because of the serious hindrance of the molecular structure and the melt viscosity differences. Although the interfacial strength achieved significant increase after adding ADR or TGDDM, the increase of the interfacial strength should be caused by the connection of ADR or TGDDM molecules with PLA and PC molecules at the interface through chemical bonds rather than the entanglements of PLA and PC molecular chains because of no interpenetration of PLA and PC molecular chains at the interface. Thus, the morphology formed after adding ADR or TGDDM is still the type of complete phase separation, which may be the most suitable morphology for achieving high impact and heat resistance PLA/PC blends because these two properties strongly depend on the crystallinity of PLA phase. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of polyethylene glycol on the crystallization and impact properties of polylactide‐based blends

Polylactide (PLA) was plasticized by polyethylene glycols (PEGs) with five different molecular weights (M_w = 200–20,000 g/mol). The effects of content and molecular weight of PEG on the crystallization and impact properties of PLA were studied by wide‐angle X‐ray diffraction, differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, and V‐notched impact tests, respectively. The results revealed that PEG‐10,000 could significantly improve the crystallization capacity and impact toughness of PLA. When the PEG‐10,000 content ranged from 0 to 20 wt%, the increases in both V‐notched Izod and Charpy impact strengths of PLA/PEG‐10,000 blends were 206.10% and 137.25%, respectively. Meanwhile, the crystallinity of PLA/PEG‐10,000 blends increased from 3.95% to 43.42%. For 10 wt% PEG content, the crystallization and impact properties of PLA/PEG blends mainly depended upon PEG molecular weight. With increasing the M_w of PEG, the crystallinity and impact strength of PLA/PEG blends first decreased and then increased. The introduction of PEG reduced the intermolecular force and enhanced the mobility of PLA chains, thus improving the crystallization capacity and flexibility of PLA. Copyright © 2015 John Wiley & Sons, Ltd.     

冲击消振器的概周期碰振运动分析

建立了冲击消振器对称周期运动的Poincar啨映射方程 ,讨论了对称周期运动的稳定性与局部分岔。通过数值仿真研究了冲击消振器在非共振、弱共振和强共振条件下的概周期碰振运动及其向混沌的转迁过程。     

Plane Collision Problem for Two Identical Elastic Parabolic Bodies—Direct Central Impact

A direct central collision of two identical infinite cylindrical bodies is studied. A nonstationary plane elastic problem is solved. The variable boundary of the contact area is determined. A mixed boundary problem is formulated. Its solution is represented by Fourier series. An infinite system of Volterra equations of the second kind for the unknown expansion coefficients is derived by satisfying boundary conditions. The basic characteristics of the collision process are determined numerically depending on the curvature of the frontal surface of the bodies     

Dynamic shearing resistance of molten metal films under high pressures and extremely high shearing rates

In the present study plate-impact pressureshear experiments have been conducted to study the dynamic shearing resistance of molten metal films at shearing rates of approximately 10⁷ s⁻¹. These molten films are generated by pressure-shear impact of relatively low melt-point metals such as 7075-T6 Al alloy with high hardness and high flow-strength tool-steel plates. By employing high impact speeds and relatively smooth impacting surfaces, normal interfacial pressures ranging from 1–3 GPa and slip speeds of over 100 m/s are generated during the pressure-shear loading. The resulting friction stress (∼100 to 400 MPa) combined with the high slip speeds generate conditions conductive to interfacial temperatures approaching the fully melt temperature regime of the lower melt-point metal (7075-T6 aluminum alloy) comprising the tribo-pair. During pressure-shear loading, laser interferometry is employed to measure normal and transverse motion at the rear surface of the target plate. The normal component of the particle velocity provides the interfacial normal traction while the transverse component provides the shearing resistance of the interface as it passes through melt. In order to extract the critical interfacial parameters, such as the interfacial slip-speed and interfacial temperatures, a Lagrangian finiteelement code is developed. The computational procedure accounts for dynamic effects, heat conduction, contact with friction, and full thermo-mechanical coupling. At temperatures below melt the flyer and target materials are described as an isotropic thermally softening elastic-viscoplastic solid. For material elements with temperatures in excess of the melt point, a purely Newtonian fluid constitutive model is employed. The results of this hybrid experimental-computational study provide insights into the dynamic shearing resistance of molten metal films at high pressures and extremely high shearing rates.     

The indenter tip radius effect in micro- and nanoindentation hardness experiments.

Nix and Gao established an important relation between the microindentation hardness and indentation depth. Such a relation has been verified by many microindentation experiments (indentation depths in the micrometer range), but it does not always hold in nanoindentation experiments (indentation depths approaching the nanometer range). Indenter tip radius effect has been proposed by Qu et al. and others as possibly the main factor that causes the deviation from Nix and Gao's relationship. We have developed an indentation model for micro- and nanoindentation, which accounts for two indenter shapes, a sharp, conical indenter and a conical indenter with a spherical tip. The analysis is based on the conventional theory of mechanism-based strain gradient plasticity established from the Taylor dislocation model to account for the effect of geometrically necessary dislocations. The comparison between numerical result and Feng and Nix's experimental data shows that the indenter tip radius effect indeed causes the deviation from Nix-Gao relation, but it seems not be the main factor. The project supported by the National Natural Science Foundation of China (10121202) and the Ministry of Education of China (20020003023)     

柱形聚碳酸酯弹丸撞击刚性靶的实验研究

用Ф22×64mm的聚碳酸酯(PC)圆柱形弹丸,以172m/s~234m/s的速度撞击刚性靶板,用幅频为4.05×104幅/秒的高速数字相机记录了PC弹丸撞击时的变形过程,用PVDF测力薄膜测定了弹丸头部与刚性靶表面碰靶过程的应力-时间曲线,获得了可供建立分析模型参考的实验数据。采用Syomds-Cowper过应力模型对PC材料应变率敏感性进行了初步分析,根据经典的Taylor理论计算了PC的名义应变率和相应的动态流动应力,其结果与实验数据基本一致。     

Mechanism of wave formation at the interface in explosive welding

Some of the main progress on the investigation of the mechanism of the wave formation in explosive welding at the Institute of Mechanics is summarized and others' previous works are reviewed. Our systematic experiments and analysis do not substantiate the theory of wave formation based on Karman vortex-street analogy or Helmholtz instability. On the contrary, they show that material strength insensitive to strain rate plays an important role. A simple hydro-plastic model is presented to explain the main features regarding the interfacial wave formation and to estimate the magnitude of wave length. The result is in broad agreement with experiment.