Mechanical and thermal properties of toughened polypropylene composites

The mechanical, thermal, and structural properties of a new flexible composite containing polypropylene fiber (PP) in a random poly(propylene‐co‐ethylene) (PPE) matrix with ethylene–propylene elastomer (EP) was investigated with emphasis on the effect of EP elastomer concentration. The intrinsic composition of the composites, toughening of the matrix with EP and the fiber–matrix interface determined the properties of the composites. Through the incorporation of EP elastomer into the polypropylene–poly (propylene‐co‐ethylene) (all‐PP) composite, tensile and storage modulus (E′) decreased, flexural modulus and loss modulus (E″, damping) increased slightly to 0.15 EP and then decreased. There was an increase in impact resistance for the toughened composites, with about 100% increase in comparison with an untoughened all‐PP composite. The composition corresponding to 0.20 weight fraction EP gave optimum impact and mechanical properties. Creep resistance of the composite decreased with increasing EP content, but recovery showed an increase with increasing EP content up to 0.20. Fracture surfaces of composites after impact tests were studied with scanning electron microscopy. Moreover, the use and limitation of theoretical equations to predict the tensile and flexural modulus of the flexible PP composite is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

采用底部开缝立方体劈拉试件测定混凝土起裂断裂韧度

为了测定混凝土起裂断裂韧度,提出了一种采用底部开缝立方体劈拉试件的试验方法,并采用数值分析方法拟合了该加载条件下缝尖的应力强度因子计算公式,通过测量高度为１００ｍｍ、２００ｍｍ和３００ｍｍ,缝高比为０．２、０．３、０．５和０．７的立方体劈拉试件及三点弯曲梁试件的起裂荷载,进而计算起裂断裂韧度并研究其尺寸效应。结果表明,采用底部开缝立方体劈拉试件和三点弯曲梁试件测定的起裂韧度基本一致,计算结果皆无明显尺寸效应,说明提出的方法能够有效测定混凝土起裂断裂韧度。与传统的三点弯曲梁方法相比,该方法具有试件制备简单、试验操作方便等优点,为现有的混凝土断裂参数实验测定提供有效补充。     

MPS改性聚合物路面混凝土的若干路用力学性能的研究

针对普通路用混凝土抗折强度低、耐久性低和返修率高等特性,拟采用掺加不同含量甲基丙烯酸甲酯及酚醛树脂粉末的方法,利用聚合物改性混凝土的原理,增强普通路用混凝土的路用性能.试验效果表示随着聚合物掺入量的增加,主要路用性能会逐渐增强,在P=7.5%至10%之间效果最优.     

Structure-property relations for a phase-pure,nanograined tetragonal zirconia ceramic stabilized with minimum CaO doping

Dense (~97%) CaO-stabilized ZrO₂ ceramic was stabilized with minimum (3 mol%) doping (reported to date) and processed via conventional sintering at a low temperature (~1200°C); compositional analysis via X-ray florescence confirmed the CaO doping accuracy. Phase-pure tetragonal structure (characterized via both X-ray diffraction and Raman spectroscopy) along with uniform nanograins (90 nm) of the ceramic ensured the evolution of no monoclinic phase even after vigorous low-temperature degradation experiments (both thermal and hydrothermal aging for 80-100 h). The sintered ceramic recorded a high hardness (~15 GPa); the indentation toughness value was also comparable to a 3 mol% yttria-stabilized zirconia system. The remarkable structure–property correlations in the 3 mol% CaO-stabilized ZrO₂ ceramic suggests that the same may be worth examining for suitable future applications (e.g., in dental ceramics).     

Polystyrene and poly(methyl methacrylate) interfaces reinforced with diblock carbon nanotubes

An asymmetric double cantilever beam test was used to determine the ability of carbon nanotubes with varying chemistry along their lengths, that is, diblock nanotubes, to compatibilize the polystyrene/poly(methyl methacrylate) (PS/PMMA) interface. PS molecules were grafted primarily to one of the blocks to cause that block to migrate to the PS phase since otherwise both blocks would prefer to reside in PMMA. Fracture toughnesses increased monotonically with increasing diblock carbon nanotube concentration and maximum values were like those for block copolymer-reinforced interfaces while single-chemistry nanotubes showed no reinforcing effect. However, the abrupt increase in fracture toughness with added compatibilizer indicative of a transition to crazing was not found consistent with nanotubes suppressing crazing in homopolymers. Scanning electron microscopy images of the fractured surfaces show agglomerates of carbon nanotubes present which are likely limiting the efficacy of carbon nanotubes at toughening the interface.     

Indentation method for fracture resistance determination of metal/ceramic interfaces in thick TBCs

The indentation technique has been used to measure the adhesion of plasma- sprayed ceramic coatings on metals intended for thick thermal barrier coating ( TTBC) applications. This approach provides the adhesion value as the critical strain energy release rate,Gc, of the interface, which also takes into account any residual stresses. The theoretical background of the method is outlined, and specific examples are reported with respect to the effect of substrate temperature on the metal/ceramic adhesion of thick TBCs.     

高韧性自保护药芯焊丝

采用正交设计方法，研制出一种新氟钙钛渣系（ＣａＦ２－ＴｉＯ２－ＭｇＯ）的自保护药芯焊丝，其焊接工艺性能良好，烟雾少，并且熔敷金属组织均匀，细小，塑性和低温韧性高，是与５５０ＭＰａ级低合金高强钢相匹配的一种高效焊接材料，适于野外焊接重要结构。     

Structure/property relationships in sintered and thermally sprayed WC-Co

Thermally sprayed WC-Co is widely used as a wear-resistant coating for a variety of applications. Although it is well established that thermal spray processes significantly affect chemistry, microstructure, and the phase distribution of WC-Co coatings, little is known about how these changes influence wear resistance. In this study, the microstructure and wear behavior of sintered and thermally sprayed WC-Co materials are examined. Powders of WC-12 wt% Co and WC-17 wt% Co were pressed and sintered, as well as thermally sprayed by high-velocity oxy-fuel (HVOF), air plasma spray (APS), and vacuum plasma spray (VPS) techniques. Results indicated considerable differences in the resulting microstructures, mechanical properties, and wear resistance. The thermally sprayed coatings showed anisotropic fracture toughness, whereas the sintered materials did not. It was also shown that a combined mechanical property/microstructure parameter, based on considerations of indentation fracture mechanisms, can be used in most cases to describe abrasive and erosive wear resistance of thermally sprayed WC-Co materials as follows: Wear resistance a whereK _ic is the indentation fracture toughness,H is hardness, andV ^Co _f is the volume fraction of cobalt. This relationship provides a means for assessing wear resistance of WC-Co coatings intended for industrial applications requiring abrasion and/or erosion resistance.     

残余奥氏体对20Mn2SiVB钢的疲劳裂纹扩展的影响

研究了残余奥氏体对20Mn2SiVB钢疲劳裂纹扩展的影响。结果表明,在贝氏体铁索体中有残余奥氏体膜的存在,残余奥氏体膜可起到提高断裂韧性的作用;在应力强度因子较高的范围内,疲劳裂纹扩展速率受钢的断裂韧性影响,断裂韧性高,裂纹扩展速率低。