HYDROGEN BOND EFFECT IN THERMOPLASTIC POLYURETHANE ELASTOMERS

Hydrogen bond effects in thermoplastic polyurethane elastomers (TPU) with different chain extender structures and hard segment contents have been studied quantitatively by dynamic mechanical analysis. It has been found that the hydrogen bond effects in TPU decrease with the increase of temperature. The temperature dependence of hydrogen bonding in TPU's can be described by the Arrhenius equation, and the activation energy of hydrogen bonding as well as the physical cross-link density have been calculated.     

THE EFFECT OF THE CBN WHEEL DRESSING AND THE GRAIN HEIGHT PROTRUDING FROM THE BOND ON THE GRINDING PERFORMANCE

CBN (Cubic Boron Nitride) is a highly efficient abrasive and has unique properties (highhardness, high thermal stability and high chemical inertia). As early as 1969 CBN Wheels had al-ready been made and showed excellent performance for grainding high speed steels and othermaterials hard to be ground. So far, however, CBN Wheels are still not popularly utilized in theindustry, the writer considers the main reason being the inadequate study for practical applica-tions and especially the suitable dressing technique. The dressing of resinoid CBN Wheels discussed in the paper, is different from that ofconventional ones. It has to be divided into two operations, truing and sharpening, each of whichhas its specific and independent functions. A simple dressing method with a lot of informationsuitable for production is studied; finally, the grain height protruding from the bond is taken asan index for evaluating the dressing results, and the effect of grain height on the grinding per-formance is discussed. By selecting proper conditions according to the workpiece requirements, abetter technical and economical benifit can be obtained.     

ANALOGY BETWEEN TRANSFER MATRIX AND BOND GRAPH IN VIBRATION PROBLEMS

In this paper we have disucced the analogy between transfer matrix and bond graph, chiefly asfollows: ① Power or energy flow is their common characteristic, ② Lumped masses and elasticmembers in transfer matrix just correspond respectively to the inertia and the capacitance elementsin the bond graph, ③ Point transfer matrix and field transfer matrix behave respectively as 1-and0-junction in bond graph,     

A THEORETICAL APPROACH TO HYDROGEN BOND STRENGTH DISTRIBUTION IN POLYURETHANES

A new approach to the hydrogen bond strength distriubtion has been developed based on thehydrogen bond strength distribution model proposed by Coleman et al. By using the method ofequilibrium thermodynamics, a thermodynamic equation for describing the hydrogen bondstrength distribution has been derived for the first time. By means of the equation some IR thermalanalysis results can be explained theoretically. Furthermore, the formulas for calculating theenthalpy and entropy change of the hydrogen bond dissociation have been established.