Test method deflection temperature under load

Two particular test methods have become very widely used. They are the Vicat softening point test (VSP test) and the heat deflection temperature under load test (HDT test) (which is also widely known by the earlier name of heat distortion temperature test). In the Vicat test a sample of the plastics material is heated at a specified rate of temperature increase and the temperature is noted at which a needle of specified dimensions indents into the material a specified distance under a specified load. In the most common method (method A) a load of ION is used, the needle indentor has a cross-sectional area of 1 mm, the specified penetration distance is 1 mm and the rate of temperature rise is 50°C per hour. For details see the relevant standards (ISO 306 BS 2782 method 120 ASTM D1525 and DIN 53460). (ISO 306 describes two methods, method A with a load of ION and method B with a load of SON, each with two possible rates of temperature rise, 50°C/h and 120°C/h. This results in ISO values quoted as A50, A120, B50 or B120. Many of the results quoted in this book predate the ISO standard and unless otherwise stated may be assumed to correspond to A50.)... 

The strength properties more often specified for plastics materials are (1) tensile strength and elongation, (2) flexural strength, (3) Izod and Gardner impact, and (4) heat deflection temperature under load. Our purpose here is not to describe each test in detail but to point out some of the known effects that colorants and other formulation ingredients can have on these properties. Table 22.1 lists the ISO and ASTM test methods for most of the physical properties, and ref. 1 (pp. 7-112) describes each of the methods in detail. Table 22.2 lists typical values of the above cite four properties for selected thermoplastics. 

Two particular test methods have become very widely used. These are the Vicat softening point test and the test widely known as the heat distortion temperature test (also called the deflection temperature under load test). In the Vicat softening point test a sample of polymer is heated at a specified rate temperature increase and the temperature is noted at which a needle of specified dimensions indents into the polymer a specified distance under a specified load. 

The deflection temperature under load (DTUL), also called the heat distortion temperature (HDT) of a plastic is a method to guide or assess its load-bearing capacity at an elevated temperature. Details on the method of testing are given in ASTM D648. Basically, a 1.27-cm (i-in.)-deep plastic test bar is mounted on supports 10.16 cm (4 in.) apart and loaded as a beam (see Fig. 2-21). A bending stress of either 66 psi or 264 psi (455 g Pa or 1,820 g Pa) is applied at the center of the span. The test is conducted in a bath of oil, with the temperature increased at a constant rate of 2 C per minute. The DTUL is the temperature at which the sample attains a deflection of 0.0254 cm (0.010 in.). 

An accepted criterion for describing high-temperature performance of a plastic is the deflection temperature under load (DTUL). This is based on a short-term test that identifies the temperature at which a polymer distorts beyond acceptable limits. It has the limitation of not being able to predict long-term behavior but is a convenient method by which to compare materials. 

ISO 75 An International Organization for Standardization (ISO) standard test method for determination of heat deflection temperature (HDT) and deflection temperature under load (DTUL). HDT is a relative measure of a materials ability to perform for a short time at elevated temperatures while supporting a load. The test measures the effect of temperature on stiffiiess a standard test specimen is given a defined surface stress and the temperature is raised at a uniform rate. Alternate test methods for HDT and DTUL are DIN 53461 and ASTM D648. 

ASTM D 648 describes a method for determining the heat deflection temperature (HDT) or deflection temperature under load (DTUL). With the trend toward globalization, this method is reflected in and refined by ISO 75. Both tests seek to define the temperature at which a given degree of bending is achieved in a sample placed under a fixed flexural stress. The apparatus used to conduct the test is shown (Figure 1). The working portion of the instrument is immersed in an oil-based fluid, which is used as the heat transfer medium. A specimen is placed in a 3-point bend fixture and the desired stress... 

FIGURE 3.80 Test for deflection temperature of plastics under flexural load. Heat distortion temperattue is the temperature at which a sample deflects by 0.1 in. (2.5 mm). Two measurements are made and quoted (a) with a stress of 66 Ibf/in. (4.6 kgf/cm ) and (b) with a stress of 264 Ibf/in." (I8.5 kgf/cm ). Standard test methods ASTM D648, BS 2782 method 102, ISO R75. 

ISO 75-1 2004 Plastics - Determination of temperature of deflection under load - Part 1 General test method... 

It has been shown that fracture is a very complex process and the fracture performance depends on both the initiation and the propagation of a defect [6-10] in the material. Under impact, most polymers break in very distinct manners. Several types of fracture have been identified depending on the amount of plastic deformation at the crack tip and the stability of crack propagation. For each type, an appropriate analysis has been developed to determine the impact fracture energy of the material. These methods have also been verified in various plastics [11,12]. The different fracture behaviors in most polymers are illustrated in Figure 27.1, which shows a schematic drawing of the load-deflection diagram of Charpy tests on HIPS [13] under an impact velocity of 2 m/s at various temperatures. 

Initial Deformation Temperature (IDT). IDT was determined as the temperature at which a standard test bar (1.27 cm wide x 0.635 cm deep), centrally loaded on a 100 mm span, deflected an additional 0.25 mm under a load that gave a maximum (outer-layer) stress of 1.82 MPa, while being heated at a rate of 2 C/min. The operating procedure followed ASTM Method D648-72 for "Deflection Temperature of Plastics Under Flexural Load"... 

A very popular test method for measuring the softening point of plastics is the temperature of deflection under load test, also known as the heat distortion or HDT test, standardized in ISO 75 [138]. The standard is now published in three parts. Part 1 covering general principles. Part 2 for plastics and ebonite, and Part 3 for reinforced plastics. Part 3 will not be considered further in this chapter. 

BS 2782. Method 121. General test method for determination of temperature of deflection under load of plastics, 1994. 

ASTM D638-95, Standard Test Method for Tensile Properties of Plastics (Philadelphia, 1996) ASTM D648-82, Deflection Temperature of Plastics Under Flexural Load (Philadelphia, 1988) ASTM D671-93, Flexural Fatigue of Plastics by Constant Amplitude of Force (Philadelphia, 1993)... 

Plastics—Determination of Water Absorption Plastics—Determination of Temperature of Deflection under Load—Part 1 General Test Method... 

The heat deflection temperature test is a method of comparing the relative ability of plastic materials to maintain dimensional integrity at elevated temperatures. It indicates the temperature at which a plastic material will no longer maintain its shape under an apphed load (in this... 

ASTM D648-04, Standard Test Method for Deflection Temperature of Plastics Under Flexural Load in the Edgewise Position, 2004. 

DIN EN ISO 75-1, Plastics - Determination of Temperature of Deflection Under Load - Part 1 General Test Method, 2005. 

ASTM D648, Standard test method for deflection temperature of plastics under flexural load in the edgewise position, 2007. 

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