Wj Jan Coumans

A mathematical relation between volume strain, elongational strain and stress in homogeneous deformation

A model is presented for the volume strain of a two-phase blend which elongates homogeneously in a tensile test apparatus. In the case when only elastic deformation and crazing take place the volume strain against elongation curve can be constructed and calculated from the data of the stress-strain curve alone. When, as well as crazing and elastic deformation, shearing takes place, the data of the stress against elongation curve and the volume strain against elongation curve can be used to calculate the separate contributions of the three deformation mechanisms at any elongation. In principle, the model can be also used for any homogeneous system which deforms without necking and where one or more deformation mechanism is present.

Dilatometric investigation of deformation mechanisms in polystyrene-polyethylene block copolymer blends. Correlation between Poisson ratio and adhesion

Abstract To gain more insight into the deformation behaviour of blends containing polystyrene (PS), low density polyethylene(IdPE) and a PSPE block copolymer, tensile tests have been performed with simultaneous volume measurements. Assuming that shearing does not give rise to volume changes, it is shown that, after yielding, crazing is the only deformation mechanism of blends with a low PE and PSPE block copolymer content. Shearing becomes important at relatively high copolymer concentrations. This is explained by the formation of a semi-continuous low-modulus phase. The decrease of the Poisson ratio with PE content in PSPE blends, as opposed to an increase if some block copolymer has been added to these blends, shows that the Poisson ratio is very sensitive to adhesion between the components. Toughness of PSPE blends is discussed in terms of concentrations of craze nuclei. Too few craze nuclei give rise to brittle failure: the resulting low number of crazes cannot take over much of the deformation of the matrix. Too many craze nuclei cause brittle failure because chances are high that some of the high number of crazes formed will combine to produce a fatal crack. Therefore high toughness is only obtained at intermediate craze nuclei concentrations. The concentration of craze nuclei is shown to be dependent on the number of dispersed particles and the adhesion between these particles and the matrix.

Dilatometer for use in tensile tests

Abstract An accurate dilatometer system is presented, which permits a simultaneous and automatic recording of sample volume change during a tensile test on a commercial tensile tester. Liquid displacements in the dilatometer capillary, which correspond to volume changes of the sample, are detected by means of a conductivity meter; tensile load is obtained from the testing machine itself; sample elongation is measured by means of an inductive displacement meter. Some experimental curves are reproduced and briefly discussed.

Drying: a fascinating unit operation

This special issue contains a selection of papers presented at the 12th International Drying Symposium, held from 28 to 31 August 2000, in Noorwijkerhout, The Netherlands. Other selections are presented in special issues of Drying Technology [1,2]. The proceedings are published by Elsevier Science [3]. The final programme and some background information can be found at website http://www.ids2000.tue.nl. In this journal, it might be worthwhile to make a few statements about drying in the context of chemical engineering. In 1972, Keey [4] wrote in the preface to his first book: “Drying is a commonly practised art, but a neglected science, at least by workers whose mother-tongue is English.” And in Chapter 1 of his book: “The reasons for drying are almost as diverse as the materials that are dried.” And one more statement: “The diversity of purpose is matched by the diversity of methods.” Now, three decades later, the diversity has not decreased; but what about the art and science? For extending drying as a science, the development of a “drying community” was very important. The following initiatives in the past have been invaluable: organising of the International Drying Symposia by Arun Mujumdar, start of the journal Drying Technology, and the publication of a series of handbooks and monographs. As a result of the founding of national working parties on drying in a number of countries, the EFChE has incorporated a Working Party on Drying. All these initiatives have roused great interest, enthusiastic participation and cooperation from workers in the field, all coming from a very diverse world. Meanwhile, the International Drying Symposium has found a firm basis in the International Advisory Panel. In many respects, drying remains still an art, but its character is changing from alchemy and craftsmanship to inspired virtuosity. The science of drying is no longer neglected; it is flowering. However, both in the world of drying itself and in that of chemical engineering, appreciation and application still have considerable room for improvement. For this reason, we will touch upon a few aspects of drying in general,

Some impressions from IDS '96

• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publishers website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers.