Localized heat generation during fracture of cyclically loaded steel

A theoretical model describing heat generation in the plastically deforming region near a crack tip under cyclic loading conditions has been developed. It predicts crack-tip temperature as a function of stress-intensity amplitude, cyclic loading frequency, time under load, and material parameters. Crack-tip temperatures are measured in AISI 4135 steel at a loading frequency of 20 Hz by employing a scanning infrared camera system. Measured temperatures compare reasonably well with values predicted by the theoretical model. Temperature changes are small under prevailing testing conditions.     

The influence of drawing temperature on mechanical properties and organization of melt spun polyethylene solid-state drawn in the pseudo-affine regime

Mechanical properties of high density polyethylene (HDPE) solid-state drawn with fixed draw ratio at different temperatures in a fiber/tape spin line were investigated. All drawing experiments were performed in the pseudo-affine regime, i.e. no effective relaxation of the molecules occurs during drawing. For such conditions, the Young's modulus is uniquely determined by the applied draw ratio. The general appearance of the stress-strain behavior of drawn HDPE, and in particular its yield strength, however, is strongly influenced by the stretching temperature applied. For a fixed draw ratio, a significant drop in yield stress can be observed with decreasing drawing temperature. Characterization of structure and organization of the solid-state drawn HDPE was performed using various analytical techniques, such as wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). It is proposed that solid-state drawing at temperatures above the α-relaxation temperature results in relative large crystals so that corresponding tapes show a high yield point. Drawing at low temperatures below the α-relaxation temperature of PE, however, causes formation of small or imperfect crystals that can be destructed at low stress (low yield point), which is a preferable start situation for a second solid-state drawing step in a multiple drawing process.     

饰面的原则

19和20世纪之交,维也纳建筑界为模仿之风所主导,饰面的原初目的与意义已然不在。针对这一状况.阿道夫·路斯基于森佩尔的"饰面的原则"进一步提出"饰面的律令",强调饰面的材料不能模仿被覆盖在其底下的材料以使建筑获得似乎高级的材料地位,而应该在材料和形式上都忠实于自己的特性。路斯还认为,真正的建筑师,其首要任务在于空间或者说"效果"的创造。正是因为这一原因,饰面成为建筑中最重要的部分,而后面起支撑作用的结构部分反倒退居其次。"律令"则成为这一"原则"在特定条件下的具体应用规范,也帮助人们重新回到这一原则。     

Time-dependent probabilistic capacity degradation assessment of prestressed concrete piles in marine environment

As coastal infrastructure systems are continuously exposed to deterioration, it is increasingly crucial to analyse their current and future serviceability performance. This paper investigates effects of chloride corrosion on the lateral force capacity and ductility of a wharf-supporting prestressed concrete marine pile and provides new insights into the state of marine structures. A probabilistically generated finite element modelling approach is developed for piles, which includes discrete concrete pile cross-sectional models connected to steel tendon non-linear elements via a series of non-linear springs that simulate bonding behaviour. Moreover, a prestressed material model is established that incorporates alternate failure modes including stress corrosion cracking and brittle failure to capture chloride-induced pitting corrosion in piles. It is shown that various failure modes cause an overall decrease in the maximum force capacity as piles age. Specifically, the alternate failure modes result in 31 and 56% reductions in the maximum capacity of the pile and associated top pile displacement, respectively, as the age of the pile increases from 25 years to 75 years. The presented methodology and results can greatly assist in decision-making for repair or replacement of wharves and aid in the design of new wharves considering their future performance.     

Exfoliated soluble graphite

Reduction of graphite by lithium in liquid ammonia yields graphite salts that can be reacted with dodecyl iodide to yield soluble dodecylated graphite. The height of the soluble graphite nanoplatelets was determined by scanning tunneling microscopy (STM) to be 3.5 nm, corresponding to approximately 10 layers of graphene. Solubility in organic solvents was determined to be 20 mg/L in chloroform and 70 mg/L in 1,2,4-trichlorobenzene.     

Viscosity–pressure–temperature behaviour of mineral and synthetic oils

A new high‐pressure viscometer that can measure viscosity at pressures up to 0.8 GPa has been developed in the authors' laboratory. The ‘modulus equation’ has been used to compare the behaviour of mineral and synthetic lubricants. Among the oils investigated there was one ester that biodegraded rapidly both before and after ageing in a long‐term test‐rig operation. To facilitate a comparison or application of the results to other oils, an analysis of the correlation between the viscosity—pressure coefficient and the kinematic viscosity measured at atmospheric pressure has been provided. A prediction of lubricant film thickness based on high‐pressure viscosity data is compared with film thickness measurements in a roller bearing.     

Resin transfer molding (RTM) with toughened cyanate ester resin systems

This investigation explored the feasibility of recently developed toughened cyanate ester networks as candidate materials for high performance composite matrix applications. The resin investigated was a bisphenol-A cyanate ester toughened with hydroxy functionalized phenolphthalein based amorphous poly(arylene ether sulfone). A series of four toughened cyanate ester resins were generated by varying the concentration and the molecular weight of the toughener. The thermoplastic modified toughened networks exhibited improvement in the fracture toughness over the base cyanate ester networks without significant reductions in mechanical properties or glass transition temperature. Carbon fabric composite panels were manufactured by liquid molding processes (resin transfer molding and resin film infusion) with the untoughened and toughened cyanate ester resin systems. The panels were subjected to physical, impact damage, and fracture toughness tests. The results of physical testing indicate consistently uniform quality, and the maximum void content was found to be less than 2%. The toughened cyanate ester composites exhibited significantly improved impact damage resistance and tolerance compared with hot-melt epoxy systems. A marked increase in the mode II composite fracture toughness was observed with an increase in the concentration and the molecular weight of the toughener.     

New developments in water-borne resins for industrial coatings

Conclusions  Several examples of water-borne resins for industrial coatings have been discussed. Water-borne two-pack systems for metal substrates as well as one-component systems for wood, showed interesting properties. These resins can be regarded as the first products of a new generation, where-in, good performance is combined with compliance with environmental legislation.     

In situ sensor monitoring and intelligent control of the resin transfer molding process

An intelligent closed-loop expert control system has been developed for automated control of the resin transfer molding process of a graphite fiber preform using an epoxy resin, E905L. The sensor model system has been developed to make intelligent decisions based on the achievement of landmarks in the cure process, such as full preform impregnation, the viscosity, and the degree of cure of the resin rather than time or temperature. In-situ frequency dependent electromagnetic sensor (FDEMS) and the Loos resin transfer model are used to monitor and control the processing properties of the epoxy resin during RTM impregnation and cure of an advanced fiber architecture stitched preform. Once correlated with viscosity (η) and degree of cure (α), the FDEMS sensor monitors and the RTM processing model predicts the reaction advancement of the resin, viscosity and the impregnation of the fabric. This provides a direct means for monitoring, evaluating, and controlling intelligently the progress of the RTM process in situ in the mold throughout the fabrication process and for verification of the quality of the composites.     

The effect of dispersants on the tensile properties of carbon nanotube/vinyl ester composites

The effects of eight different dispersants on the stability of multiwalled carbon nanotubes (MWCNTs) in vinyl ester (VE) resin systems have been systematically analyzed. Suspensions incorporating different amounts of dispersants relative to the concentration of MWCNTs in the VE have been prepared. The resistance to sedimentation of MWCNTs in the resin was investigated by using a centrifugation technique. One dispersing agent (B60H) was found to impart long‐term stability to suspensions of MWCNTs in VE. VE‐based composites reinforced with MWCNTs were prepared using different amounts of the dispersing agent. Tensile tests were performed to analyze the effect of different concentrations of MWCNTs and the use of the dispersing agent in the composites. Fracture surfaces of VE nanocomposites have been analyzed using scanning electron microscopy (SEM) to elucidate the reinforcing effect of the CNTs. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers