DMA instrumentation, commercial

Commercial DMA instruments vary in their design. One commercial instrument is shown in Fig. 16.36, set up for a three-point bend test under dynamic load. A different commercial instrument schematic. Fig. 16.37 shows a sample clamped between two arms that are free to move about the pivot points [Fig. 16.37(a)] the electromagnetic drive and arm/ sample assembly are shown in Fig. 16.37(b). The electromagnetic motor oscillates the arm/sample system and drives the arm/sample system to a preselected amplitude (strain). The sample undergoes a flexural deformation as seen in Fig. 16.37(a). An LVDT on the driver arm measures the sample s response to the applied stress, calculates the modulus (stiffness) and the damping properties (energy dissipation) of the material. 

Obviously, the autotension mode will influence the DMA curve, since it may lead to different levels of shrinkage, creep, and change in orientation. Almost all presently available commercial DMA instruments have special fiber and film fixtures sometimes the same fixture can be used for both types of measurements. 

Dynamic testing DMTA, DMA, torsional braid analysis (Enns and Gillham, 1983) is first used as a thermal analysis method to detect the transitions, using dissipation peaks. Certain commercial DMTA instruments have a relatively low accuracy in measuring forces and/or strains. In contrast, they give relatively accurate values of the damping factor tan 5, so that dissipation spectra tan 8 = f (oo, T), are very useful analytical tools. 

The main changes in this edition are as follows (1) Numerous new applications of thermal analysis techniques have been added to the chapters on TG, DTA, DSC, EGD/EGA, and others. (2) Other techniques, not used as often, are described in greater detail, such as EGD/EGA, TMA, DMA. thermoptometry, thermoelectrometry, thermosonimetry, and others. (3) The chapter on EGD/EGA has been rewritten, as has the chapter on miscellaneous techniques. (4) The determination of purity by DSC has been rewritten. (5) Commercially available instruments have been briefly described for each technique, including the application of microcomputers to many of these instruments. 

Spain has become home to two mobility groups during the past decade. The Sociedad Europea de AnaUsis Diferencial de Movilidad SL (SEADM) in Boecillo was founded in February 2005 to develop DMAs based on the work of its technical consultant and cofounder Professor Juan Fernandez de la Mora of Yale University. Efforts are largely directed to DMA/MS methods. In contrast, stand-alone DMA instruments are produced by RAMEM, SA, in Madrid. A stand-alone mobility analyzer is commercially available with multivariate analysis software a default library includes standards and one of several nonradioactive ionization sources, including photoionization, corona discharge, and ESI. 

Dynamic mechanical analyzers can be divided into resonant and defined frequency instruments. The torsion pendulum just described is, for example, a resonant instrument. The schematic of a defined-frequency instrument is shown in Fig. 4.155. The basic elements are the force generator and the strain meter. Signals of both are collected by the module CPU, the central processing unit, and transmitted to the computer for data evaluation. The diagram is drawn after a commercial DMA which was produced by Seiko. At the bottom of Fig. 4.155, a typical sample behavior for a DMA experiment is sketched. An applied sinusoidal stress, o, is followed with a phase lag, 6, by the strain, e. The analysis of such data in terms of the dynamic moduli (stress-strain ratios, see Fig. 4.143) at different frequencies and temperature is the subject of DMA. 

The major practical difficulty in running photocures in the DMA is the current lack of a commercially available photocuring accessory, comparable to the photocalorimeters on the market. One normally has to adapt a commercial DMA to run these experiments. The PerkinElmer DMA-7e has been successfully adapted [95] to use quartz fixtures and a commercial UV source from EPOS, triggered from the DMA s software. This is a fairly easy process, and other instruments such as the RheoSci DMTA Mark 5 have also been adapted. 

One of the stated goals of the NOSH Consortium is to evaluate commercial aerosol instrumentation with the purpose to report on the instrument specifications, ease of use, applicability to different operating conditions, and types or form of data generated to the membership, and to discuss these results with particular emphasis in communicating issues or sensitivities that are relevant to occupational safety and health issues. Major focus areas were in comparing commercial classification and detection instmmentation (1) nano-DMA and long-DMA, (2) ELPI and DMA, and (3) CNC and AE. 

Frequency Dependencies in Transition Studies. The choice of a testing frequency or its effect on the resulting data must be addressed. A short discussion of how frequencies are chosen and how they affect the measurement of transitions is in order. Considering that higher frequencies induce more elasticlike behavior, there is some concern that a material will act stiffer than it really is if the test frequency is chosen to be too high. Frequencies for testing are normally chosen by one of three methods. The most scientific method would be to use the frequency of the stress or strain that the material is exposed to in the real world. However, this is often outside of the range of the available instrumentation. In some cases, the test method or the industry standard sets a certain frequency and this frequency is used. Ideally a standard method like this is chosen so that the data collected on various commercial instruments can be shown to be compatible. Some of the ASTM methods for TMA (thermomechanical analysis) and DMA are listed in Table 1. Many industries have their own standards so it is important to... 

A number of conunercial instruments are made that apply a harmonic stress or strain to a sample and measnre the response [2,3]. In a dynamic mechanical (thermal) analyzer, often abbreviated as DMA or DMTA, modulus and loss can be measured as a function of controlled freqnency, amplitude, and temperature. Commercial machines may inclnde provisions for testing materials in tension, bending, or... 

The instrument is a commercially available DMA called the VTM (Dynisco Company). Figure 3 shows the parallel plate die system with the grooves on the die to prevent slippage of samples. Note that the sample is contained in a sealed and pressurized sample chamber during a test. The outer edge of the sample cavity contains two seal plates and two seals, which completely seal the sample cavity. The sample is placed onto the lower die and then the upper die is... 

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