Dimensional changes measurement

The dimensional changes measured by the strain gauge are typically very small, on the order of perhaps 10-100 millionths of an inch per inch (microstrain), but measurable physical deflections nonetheless. As the tooling deflects when a part is formed, the in-die force sensor which has the strain gauges attached also deflects, typically in compression. When this occurs, a resistance change takes... 

DSC measures heat flow versus temperature rather than the dimensional changes measured by TMA. The heat absorbed or given off will also change as the temperature increases through theTg of the resin system.Tg measured by DSC is often somewhat higher than measurements by TMA. 

Dimensional Stability. Plastics, ia general, are subject to dimensional change at elevated temperature. One important change is the expansion of plastics with increa sing temperature, a process that is also reversible. However, the coefficient of thermal expansion (GTE), measured according to ASTM E831, frequendy is not linear with temperature and may vary depending on the direction in which the sample is tested, that is, samples may not be isotropic (Eig. 7). 

Eig. 7. GTE of a 40% glass-filled PPS as functions of both temperature and direction. GTE values are measured in micrometers of dimensional change per... 

The strain resulting from a particular stress is formally quantified by a dimensional change, often in the length of the material under stress. Strain may be readily converted into a measure of the reduction of plant productivity, a more generally applicable strain for agriculture and ecology. 

An additional consideration under mechanical properties is the characterization of formulation performance by measuring solvent resistance. This parameter is defined as the ability of an elastomeric closure to retain original mechanical and physical properties without undue dimensional change, decomposition or... 

Thermoanalytical methods comprise a series of techniques in which a property is determined at different temperatures or as the temperature changes continuously. The property measured may include the mass of the sample (TGA), the heat flow to the sample (DSC), the magnetic character of the sample (TMA), or some other property such as dimensional changes. Each of these types of measurements gives information on some change undergone by the sample, and if the change is followed over time, it is possible to derive kinetic information about the transformation. 

Angersbach, A., Heinz, V., and Knorr, D. 2002. Evaluation of process induced dimensional changes in the membrane structure of biological cells using impedance measurement. Biotechnol. Progr. 18, 597-603. 

Hill, C.A.S. and Ormondroyd, G.A. (2004). Dimensional changes in Corsican pine (Pinus nigra Arnold) modified with acetic anhydride measured using a helium pycnometer. Hol forschung, 58(5), 544-547. 

Generally, vulcanised rubber is dimensionally very stable (unless it is strained), which probably explains the lack of standard test methods for this property. In this context, thermal expansion and swelling in liquids are properties considered in their own right and not normally thought of as being measures of dimensional stability. This is a different situation to that which exists with plastics where a number of dimensional stability tests are in existence. If a measure of dimensional change is required, the appropriate dimensions of a suitable sized test piece can be measured by any of the methods mentioned in this chapter before and after an ageing treatment. 

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