Heat deflection data

Figure 1.50 Heat deflection data on generic family of plastics.

Creep test data when plotted on log-log paper usually form a straight line and tend themselves to extrapolation. Tlie slope of the straight line, which indicates a decreasing modulus, depends on the nature of the material (principally its rigidity and temperature of heat deflection), the temperature of the environment in which the product is used, and the amount of stress in relation to tensile strength. 

Comparison with Asbestos and Glass. Tables III, IV, V, and VI catalog the properties obtained when the two polystyrenes were reinforced with asbestos and glass. Table VII compares the reinforcing effects of the several fibers studied at 30 wt %. The data show that particular fibers improve particular properties. The tensile modulus and tensile strength are most improved by glass the heat deflection is most improved by asbestos, and the impact strength is most improved by polyester. 

The onset of softening is usually measured as the temperature required for a particular polymer to deform a given amount under a specified load. These values are known as heat deflection temperatures. Such data do not have any direct connection with results of X-ray, thermal analysis, or other measurements of the melting of crystallites, but they are widely used in designing with plastics. 

Application areas for the new Co-PCs include electrical engineering/elec-tronics, domestic appliances, lighting, automotive engineering, and medical technology. In automotive engineering the headlamp lens will be offered by headlamp manufacturers as the plastics alternative to main headlamps and fog lamps. The best compromise on optical data, mechanical strength, and heat deflection resistance for their application is shown by PC. 

As a further comparison, the flexural modulus of glass-filled polyphenylene sulfide at 450° F is about 10 times that of unfilled polytetra-fiuoroethylene at room temperature. These data illustrate the outstanding retention of stiffness of this material at elevated temperatures. The heat-deflection temperature of polyphenylene sulfide containing 40% glass fibers is greater than 425°F, accounting for the excellent retention of mechanical properties at elevated temperatures. 

The data characterizing the changes of the properties of the crosslinked polymers during aging in air (Table 30) show that the increase in heat deflection temperature (TM) and hardness is accompanied by a decrease in flexural strength. It is noteworthy that the modification with ACECs results in an increase in hardness, whereas the flexural strength does not change. 

Figure 3.42. Concentration of poly(acrylonitrile-styrene-acrylate) in PVC blend vs. heat deflection temperature. [Data from Zerafati, S.,J. Vinyl Additive TechnoL, 4,1, 35-38,1998.]...

Define the temperature failure criteria for the material. The experimental formulas were blended and extruded. The extruded products were measured for heat deflection temperature using ASTM D 648 as a guideline. Multiple measurements at various heating rates were conducted. An appropriate engineering safety factor was applied to the data. A critical temperature failure criteria was defined as 70°C for these particular experimental formulas. 70°C was considered the maximum sustained temperature the extrusions could withstand and still provide acceptable engineering performance. 

Heat deflection temperature— ASTM D648. This data is dangerous in the respect that it often is the only temperature data provided on a resin data sheet, which leaves the impression that it is a reliable indicator of the limit to which the product can be used (see the section on Relative Temperature Index later in this chapter). It is really nothing more than the temperature at which a given load (66 or 264 Ib/in ) will deflect a specimen an arbitrary amoinit. Other temperature tests are also used, and some are described in the following sections. Results of those tests are usually available from the resin manufacturer. 

Heat deflection temperature data for composites containing HAR-160 mica is shown in Table 14.27. In composites containing untreated mica, annealed specimens with HAR-160 mica had heat deflection temperature increases of 20.9%, 20.3%, and 21.2% for 20, 30, and 40 wt% loadings, respectively, compared with unannealed specimens. 

Heat-deflection temperature does not correspond to the practical use temperature however, it has been widely used in the plastics industry to compare the physical response of materials to temperature at a single-load level. In Figure 5, HDT vs tensile strengths at two different loads are reported. Both groups of data roughly show a proportional trend that can be ascribed to the fact that in many cases the molecular structure of the chain influences, in the same sense, the mechanical and thermal properties. 

Additional data are shown in Figs. 2-19, -20, -21, -22, -23, -24, and -26 for flexural strength and heat-deflection temperatures of nylon 6/6, and Izod impact and heat deflection temperatures of polypropylene. See also par. 2-5.2 for discussion of critical fiber length. 

Abstract The vast majority of the short-term properties that appear in a material data sheet are measured at room temperature. The heat deflection tempoature (HDT) represents the only systematic attempt to characterize elevated temperature performance. The HDT test describes a particular response to temperature under a very spedfic set of conditions, however it is often used in the material selection process as a maximum continuous use temperature. As the trend toward the computerization of property data has progressed, the tendency to rank order properties for a large number of materials from different families has increased the separation between the property value and its significance to the design engineer. 

In the world of material selection, ideally we want to select a material before any parts are made. In this situation we will not have any measurement data, and the mathematical tools discussed above are not applicable. While there is published data on measured properties of materials— lots of published data— there are very few mathematical tools available to evaluate this data in a comprehensive manner. One can compare the tensile strength data of different materials, or the flexural modulus, or the heat deflection temperature (HDT) it is difficult to compare all of the available data on material candidates and be certain you are making an optimal selection. However, there are mathematical tools that can help guide this process. 

The part material used is 1.5 mm thick Lucite CP PMMA sheet. This material has a 1.8 MPa heat deflection temperature of 90 °C (manufacturer s data). The tool consists of a 100 mm diameter (100) silicon wafer. The wafer has been etched to a depth of 14 1 pm using a fluorine-based plasma by deep reactive ion etching. The tool is patterned with a set of test features including rectangles, squares, and other shapes. The features widths vary from 3 pm to more than 100 pm, and their spacings vary from 0.1 times to 10 times their widths. An example of e tool features is shown in Figure 2. 

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