The variability and interdependence of spider drag line tensile properties

There is considerable interest in producing fibres that mimic the impressive tensile properties of spider drag line silk. It must, however, be recognised that these properties have been assessed largely on the basis of their average values; there can be significant variability about these averages. The natural variability can also serve as a useful indicator of the range of values over which particular properties of biomimetic silk may be tailored. Here we quantify several tensile properties of drag line from Argiope trifasciata spiders. We distinguish between two groups of properties on the basis of their statistical coefficient of variation. There is significantly greater scope for tailoring the viscoplastic hardening aspects of drag line, compared to the variability of the initial elastic response or the yield strength. We also consider whether elastic modulus, yield strength and viscoplastic hardening can be controlled independently of one another.     

机电排灌工程管理之我见

机电排灌工程是丘陵、滨湖地区的主要灌溉设施，必须建立适应市场经济的管理新机制，确保工程良性运行和巩固发展，满足不断发展的工农业生产需要。     

Creep of aromatic polyamide fibres

Creep of Kevlar 29, Kevlar 49 and PRD 49-III fibres was investigated. The fibres exhibited transient creep and the strain-time relationship was represented by a logarithmic time law. The creep strain recovered with time when the load was removed. Upon reloading to the same creep stress the strain-time relationship was again logarithmic but the creep rate was reduced. Modulus measurements were made during the creep test and these showed that the modulus increased with time. This result indicated a crystallite rotation mechanism which could account for the experimentally observed creep strain. Creep in PRD 49-III fibres exhibited a small temperature dependence over the temperature range 20°C to 150°C. The apparent creep activation energy was consistent with the range of values reported for hydrogen bonding. This suggests one possible creep mechanism in which the combined action of stress and thermal activation causes rearrangement of intercrystalline bonds in the crystallite boundaries resulting in boundary creep. Boundary creep allows crystallite rotation which produces the macroscopic creep strain. Boundary creep is discussed in terms of the fibre morphology and a model of delayed elasticity.     

深孔松动爆破提高瓦斯抽放率的应用研究

本文探讨了深孔松动爆破孔和瓦斯抽放孔的布置参数及工艺等 ,并设计了实施方案。在潘一矿的应用试验表明 ,用深孔松动爆破技术来提高低透气性煤层的瓦斯抽放效果 ,是一条很好的途径。     

回归分析法简化钻爆设计

以某工程钻爆参数为例,阐述了在地下工程掘进施工中,应用回归分析法建立钻爆参数的相关模型,并利用此模型帮助建立某断面钻爆方案.     

圩区排涝模数计算方法研究

合理确定圩区排涝模数对于降低涝灾损失有重要意义。圩区内土地利用性质的不同,会导致产汇流机制和排涝标准的不同,但排涝模数的计算方法基本一致。本文根据圩区下垫面条件进行产汇流计算,入河流量扣除滞蓄量得到排涝模数,充分考虑到圩内河道的调蓄作用。以常熟市为例,对城镇圩区、农业圩区排涝模数进行计算,并分析了两种圩区不同的排涝要求对排涝模数计算方法的影响。     

分子模拟技术对润滑脂滴点的初步预测

制备了不同类型的单皂和复皂润滑脂，测定了其理化性能。采用分子模拟技术对润滑脂滴点进行了初步预测，并计算了润滑脂中各种金属皂分子间氢键键长和分子体积模量。结果表明，复合钙皂和复合锂皂的分子体积模量分别大于钙皂和锂皂的分子体积模量。金属皂分子体积模量与其所形成的润滑脂的滴点呈对应关系，即分子体积模量大的，其形成的润滑脂滴点也高，反之则反。采用分子模拟技术可以从分子的层次指导润滑脂的研究。     

Application of the dynamical flexural resonance technique to industrial materials characterisation

The determination of the Young’s modulus and damping coefficient Q⁻¹ by means of non-destructive vibrating techniques has been applied to bulk and coated industrial materials. Extensions of a previous analytic model of composite beam allow to determine accurately the macroscopic modulus of each component of multilayered structural materials as coated superalloys or nitride-hardened steels. Furthermore, the study of glasses and polymers has been investigated. An attempt of normalisation of the modulus versus temperature curves allows to establish master curves depending on the specific structure, from metallic glasses to polymeric glasses. Finally a comparison of dynamical modulus and Q⁻¹ values measured between resonant (>1 kHz) and subresonant techniques (10⁻³ to 10 Hz) in relation to the loading frequencies applied in real conditions has been under folder. For metallic materials such as forged or rolled titanium alloys, the brittle-to-fragile transition occurs abruptly or smoothly with a shift of 300 K following the range of excitation frequencies.     

Implicit integration and consistent tangent modulus of a time‐dependent non‐unified constitutive model

This paper describes the implicit integration and consistent tangent modulus of an inelastic constitutive model with transient and steady strain rates, both of which are time‐ and temperature‐dependent; the transient rate is influenced by the evolution of back stress decomposed into parts, while the steady rate depends only on applied stress and temperature. Such a non‐unified model is useful for high‐temperature structural analysis and is practical owing to the ease in determining material constants. The implicit integration is shown to result in two scalar‐valued coupled equations, and the consistent tangent modulus is derived in a quite versatile form by introducing a set of fourth‐rank constitutive parameters into the discretized evolution rule of back stress. The constitutive model is, then, implemented in a finite element program and applied to a lead‐free solder joint analysis. It is demonstrated that the implicit integration is very accurate if the multilinear kinematic hardening model of Ohno and Wang is employed, and that the consistent tangent modulus certainly affords quadratic convergence to the Newton–Raphson iteration in solving nodal force equilibrium equations. Copyright © 2003 John Wiley & Sons, Ltd.