Simulation of the Long Term Behavior of Polymers on the Basis of Short Term Data

The mechanical long term behavior of polymers is usually determined by long term creep experiments up to 10.000 h which are very time and cost consuming. Therefore these data are often not available for the engineer. But even if long term data is available FEA-tools used in industrial practice usually can not sufficiently represent the nonlinear time, temperature and load-dependency of the mechanical long term behaviour. Hence the dimensioning of polymer parts is still a rather difficult engineering task. As a consequence of this, additional time consuming and expensive component tests in combination with several iterations are often necessary to design a polymer part for long term behaviour. This paper develops a method for the modeling of the load and temperature-dependent mechanical behaviour of polymers over a wide time, load and temperature range by means of finite element analysis. The method includes a material model as well as the determination of material parameters to calibrate the model. As a special feature of this method the model is calibrated by using creep data generated from short term experiments. The procedure improves the simulation of the long term behaviour of plastic-components and reduces the experimental effort significantly. The simulation results are finally validated by creep experiments performed on an example part

Exploring the North Atlantic Ocean on floppy disks

Data from four floppy disks found in the zip fileA selection of hydrographic station data in the Atlantic between 8°S and 70°N is packed on four 5 1/4" floppy disks. Sample utility programs for reading and plotting the data are also on the disks. We present this computer atlas in preliminary form for use by students and professionals, in the belief that easy access to this valuable historical data will be educational and stimulating.Funding was provided by the Office of Naval Research under contract Number N00014-84-C-0134, and the National Science Foundation through grant Number OCE86-13810

On the nature of estuarine circulation : part I (chapters 3 and 4)

The reader will quickly see that the subject matter of Chapter 3 is confined to the hydraulics of sharply stratified media, whereas real estuaries are always more or less diffusely stratified. What is more, no discussion is made of the order of magnitude of the friction terms. In ordinary single layer flow (such as in rivers) engineers already have crude approximations of the friction terms (Chezy and Manning formulas), but we do not have even these approximations for two layer flow. For this reason the differential equations of gradually varied flow of two layers are for the most part left unintegrated and all that is demonstrated is the qualitative aspects of the flow. In the case of entrainment of water from one layer into another we can only perform integrations of the equations when the amount of entrainment is known, whereas in real estuaries we do not have a priori knowledge of this amount. The reader will see, therefore, that the subject matter of Chapter 3 is really very incomplete, leaving undetermined all the constants which depend upon turbulent mixing, upon the frictional stresses on the bottom, and the free surface and the walls, and upon the amount of entrainment. The contents of Chapter 4 are somewhat different. First of all, they contain summaries of several of these papers have proceeded on the basis of hypotheses already published papers on the mixing in estuaries. Most about the nature of the mixing process. The applicability of these hypotheses appears to be restricted to only certain estuaries, and it must be admitted that more work has been done that involves guessing what the mixing processes in an estuary might be, than has been done in trying to find out what the mixing processes in an estuary actually are. As incomplete as the subject matter of Chapter 4 is, it is hoped that it will suggest which of the possible mixing processes in estuaries may be important in any particular one which is the subject of study, and that it will also suggest the type of observations which will be most desirable in studying a particular estuary. For example: in an unstratified estuary it seems that a more or less uniform spacing of stations up and down the estuary is desirable; but in an estuary which appears to be subject to the constraint of overmixing (Section 4.51) the location of stations should be largely confined to control sections.Office of Naval Research under Contract No. N6onr-27701 (NR-083-004)

Origin of the Mediterranean outflow

Toe origin of the Mediterranean outflow is one of oceanography\u27s oldest problems. In this work, the flow of western Mediterranean deep water up and over the sill at Gibraltar is investigated from hydrographic observations and current measurements. The deep water is found to flow westward along the Moroccan continental slope in the western Mediterranean or Alboran Sea and to rise as it approaches the Strait of Gibraltar...

The electrical field induced by ocean currents and waves, with applications to the method of towed electrodes

The purpose of this paper is to discuss the nature of the electrical field induced in the ocean by particular types of velocity distribution. It is believed that these examples will be helpful in the interpretation of measurements by towed electrodes in the sea. The electrical field induced by waves and tidal streams, originally predicted by Faraday (1832), was first measured experimentally by Young, Gerrard and Jevons (1920), who used both moored and towed electrodes in their observations. Recently, the technique of towed electrodes has been developed by von Arx (1950, 1951) and others into a useful means of detecting water movements in the deep ocean. While the method has been increasingly used, the problem of interpreting the measurements in terms of water movements has become of great importance. Two of the present authors have made theoretical studies (Longuet-Higgins 1949, Stommel 1948) dealing with certain cases of velocity fields, and Malkus and Stern (1952) have proved some important integral theorems. There seems, however, to be a need for a more extended discussion of the principles underlying the method, and for the computation of additional illustrative examples. This is all the more desirable since some of the theoretical discussions published previously have been misleading

Experimental multi-scale approach to determine the local mechanical properties of foam base material in polyisocyanurate metal panels

Polyisocyanurate (PIR) foams were examined regarding their local chemical composition using ATR-IR spectroscopy. As a special parameter the PIR: Amide III intensity ratio is to be mentioned, which represents the quantity of the formed PIR groups. Based on the local PIR: Amide III intensity ratio, the mechanical properties (Young's modulus) of the foam base material were analyzed at defined positions by AFM and Nanoindentation. It turned out that the AFM method is only suitable for qualitative analysis, because the values differ strongly from macroscopic measurements. For the measurements using nanoindentation, a new embedding method was developed, which achieves significantly more realistic and reproducible results compared to the embedding method used in the literature and shows a very good agreement with the macroscopic values. In general, it has been shown that a higher PIR: Amide III intensity ratio tends to lead to a higher Young's modulus. Nevertheless, there are other, currently unknown characteristic values which also influence the Young's modulus

A Contribution to Predict the Structural Dynamics of Mounted Short Glass Fiber Reinforced Thermoplastic Components

At the state of art, current simulative methods modelling joint properties as fixed interaction between components or concentrate on the characterization of the joint stiffness and damping of coupled metallic structures. In the current work, the developed thin layer interaction (TLI) method was applied to study the influence of the joint stiffness and damping of plastic components coupled with metallic structures. The joint stiffness and damping of different coupled metallic-plastic joint structures was characterized experimentally and was used to fill the reduced transverse shear stiffness and damping tensors of the numerical TLI model. The TLI model was used to determine the structural dynamics behavior of a short glass fiber reinforced plastic engine bracket mounted to a steel block. The comparison of experimental and simulative results shows a better correlation under the usage of the TLI model compared to a fixed modeled joint behavior. As result, the TLI model allows a better prediction of the structural dynamics of coupled plastic components. Further researches focus on the accurate experimental estimation of the boundary conditions regarding excitation and mounting of the plastic components. Thus, a more realistic modelling of the numerical joint boundary conditions is possible for an improved simulation of the structural dynamics of plastic components

Vertical distribution of temperature and humidity over the Caribbean Sea

The observations presented and discussed in this paper were obtained as part of a research project conducted under contract NObs-2083 with the Bureau of Ships of the U. S. Navy by the Woods Hole Oceanographic Institution. The observations and their original reduction were carried out under the direction of Jeffries Wyman. The airplane soundings were undertaken by Kenneth McCasland and Alfred Woodcock. The sea surface temperature was measured on the surface ships by David F. Barnes and Roger Patterson. The necessary airplane (PBY-SA) and surface boats (PC's) were made available by the U. S. Navy. All observations were made during the spring of 1946 at about 19.5°N latitude, 66°W longitude, north of San Juan, Puerto Rico, and at about lO°N latitude, 79.5°W longitude, north of Coco Solo, Panama. An extensive preliminary report on the results of the expedition with a limited circulation was prepared by Wyman and his collaborators during the summer of 1946. The present paper deals with certain phases of the work in a more detailed fashion. Special attention is given to the temperature and humidity distributions in the vertical and to their interpretation in the light of meteorological principles. A discussion of atmospheric turbulence based on airplane measurements has already been published elsewhere (Langwell, 1948), and an application of the airplane soundings to the theory of cumulus clouds has been studied by Stommel (1947). The second and third chapters of this publication deal with the description of observational techniques used by the expedition, with the methods of reduction and present the data on which the later discussion is based. It has been thought desirable to publish these data in extenso because they may be of interest to other meteorologists in view of the sparsity of upper-air observations in this region. The actual preparation of Chapters II and III is largely the work of Bunker and Stommel. In order to show how the observations made off Puerto Rico fit into the general pattern of climatic and weather conditions in the Caribbean area Chapter iv presents a survey of the climate of this region and of the weather conditions during the time when the observations were taken. This Chapter was contributed by Joanne Malkus. It is pertinent to include in this general introduction the conclusion drawn in Chapter IV namely that the weather situations encountered represented, in general, a relatively undisturbed trade-wind regime of early spring. The homogeneous layer of nearly dry-adiabatic lapse-rate of temperature and almost constant mixing ratio is one of the most characteristic phenomena in the lowest atmosphere of this region. It is also of utmost importance for the energy budget of the hydrosphere and the atmosphere. Therefore, a special discussion of this layer by Bunker is given in Chapter V. Because of the nearly dry-adiabatic lapse-rate in the homogeneous layer most of the heat transfer between water and air in the trade-wind zone must be in the form of latent heat of vaporization, a conclusion whose thermodynamic implications were discussed thoroughly by Ficker (1936). For this reason the distribution of water vapor deserves special attention, and Chapter VI deals with this variable as a problem in turbulent mass exchange. The analysis presented in this chapter is due to Haurwitz and Stommel