Micromechanical characterisation of fibre/matrix interfaces

Theoretical analyses for the single fibre pull-out and push-out models under monotonic loading are given which are based on a shear-lag analysis in a fracture mechanics approach considering non-constant friction at the debonded interface as a result of fibre Poisson contraction (or expansion). The solutions allow the determination of typical fibre/matrix interfacial properties such as the interfacial fracture toughness, G_ic, the coefficient of friction, μ, and the residual clamping stress, q₀. Under cyclic loading the interfacial properties are expected to degrade as a result of repetitive abrasion, and a power law function is assumed between μ and the number of elapsed cycles, N. However, G_ic is assumed to be unaffected and a fracture mechanics based debond criterion is derived for the relationship between the external applied stress, the debond length and the reduced friction coefficient for both fibre pull-out and fibre push-out. In addition, the relative displacements between the free fibre end and the matrix top are obtained for cyclic fatigue when the fibre is loaded and unloaded. A relationship obtained for the protrusion (or intrusion) length in fibre pull-out (or push-out) experiments allows the severity of the interface frictional degradation to be evaluated and characterised. Similarities and differences in the frictional degradation behaviour between fibre pull-out and push-out are also identified.     

Pressure-pulsed chemical vapour infiltration of TiN to SiC particulate preforms

SiC particulate preforms were infiltrated by TiN matrix from a gas mixture of TiCl₄ (5%), nitrogen (30%) and hydrogen using a repeating pressure pulse between 760 and about 1 torr. SiC particle sizes of 5 and 20 m were used. For matrix packing into deep level, optimum temperature was determined between 800 and 850 °C, and the maximum packing ratio reached 67% after 4 × 10⁴ pulses at 850 °C. The increase of TiCl⁴ concentration to 10% resulted in higher deposition rate and packing ratio. The decrease of nitrogen concentration led to slower deposition, that is, a similar effect to temperature lowering. The maximum flexural strength measured was 140 MPa.     

The essential work of plane stress ductile fracture of a strain-aged steel

The paper reports the results of an experimental investigation on the essential work of fracture of a strain-aged low carbon (0.1% C) temper-rolled 16-gauge sheet steel which has been subjected to pre-strain levels of 2 to 12% and ageing temperatures of 80 and 100C. Deep edge-notched tension specimens were used to determine the specific essential work by extrapolating the straight-line relationship between the specific work of fracture (W _f) and ligament length (I) to zero ligament length. The strain-aged steels at 80 and 100 give approximately the same specific essential fracture work of 0.18 to 0.20 J mm^–2 which is independent of the amount of prestrain. Advancing crack opening displacements (C.O.D.) have also been analysed, which give 0.60 to 0.63 mm for the strain-aged steels. For comparison, the prestrained but unaged steels have a higher essential work of fracture of 0.275 J mm^–2 and a larger C.O.D. of 0.73 mm. It is concluded, therefore, that the causes of strain-ageing embrittlement are primarily due to the reduction of both the essential work of fracture and the advancing C.O.D. at the crack tip end region.     

激光三角法位移传感器测头设计

本文以直射式激光三角测头为例,导出了满足Scheimpfiag成象条件下的待测面位移与象位移间的准确关系,作为仪器结构参数设计的基础,并对提高测量精度和实用性的各项改进设计进行了分析。     

我国有机食品的现状及发展趋势

介绍了有机食品的特点及对人与自然和谐发展的作用,并概述了我国有机食品的发展现状及趋势.     

β-PP/PA 6合金的结晶与熔融行为

为了研究β-成核剂在合金中分散对聚丙烯（PP）成核效率的影响,采用2种方法制备了负载型β-成核剂成核PP（β-PP）／聚酰胺6（PA6）合金。用差示扫描量热仪和广角X射线衍射仪研究了不同制备方法及熔融温度对β-PP／PA6合金的结晶行为、熔融特性和β-PP含量的影响。结果表明：PP,PA6先熔融再降温至／90℃加入成核剂制备β-PP,PA6合金的β-PP含量高于先制备β-PP再与PA6混炼制备的合金。熔融温度高有利于β-PP／PA6合金中PP形成β-PP。