Flexural strength, temperature effects

Figure 11. Effect of temperature of lOwt.% NaOH solution on retention of flexural strength of iso-UP.

Figure 5.49 Effect of porosity on the flexural strength of AI2O3 at room temperature. Reprinted, by permission, from W. Callister, Materials Science and Engineering An Introduction, 5th ed., p. 413. Copyright 2000 by John Wiley Sons, Inc.

Thus the effects of the rate of application of stress and the ambient temperature must be recognized when polymers are used as structural materials, and definite rates and temperatures must be specified for tests, such as those for tensile and flexural strengths cited in Chapter 3. A knowledge of the structure of polymers is essential for the understanding of these effects, which differ from the effects of stress and temperature on all other materials of construction. 

The work of Sterman and Marsden and Plueddeman was carried out with glasscloth polymer laminates (10, II, 14,15). In this way the effect of the silane could be optimized as to time and temperature of the molding cycle. Additionally, the glass was being used in its maximum strength form in that it was continuous. An additional factor is the absence of any shear forces. As an example, for a polystyrene laminate, the use of an epoxyfunctional silane increased the flexural strength 90% over the bare... 

Table 20.2 shows the effect on physical properties of a 2.5% letdown of a 70% Ti02 dispersion in liquid color. Tensile yield strength, Heat deflection temperature (HDT), and flexural strength and modulus are the only properties where there is some negative effect, essentially a plasticizing effect. Several properties in various resins are enhanced or unaffected. Consult this table before choosing a coloration system and decide what properties are important. 

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. 

Dyes can also have an undesirable effect on properties. Because they dissolve in the matrix, they can sometimes have a plasticizing effect. This will reduce the material s tensile and flexural strength as well as the HDT (heat deflection temperature under load). The plasticizing effect of dyes can also influence the way they process... 

In addition to the initial work in the alumina and mullite matrix systems previously mentioned, SiC whiskers have also been used to reinforce other ceramic matrices such as silicon nitride,9-13 glass,14 15 magnesia-alumina spinel,16 cordierite,17 zirconia,18 alumina/zirconia,18 19 mullite/zirconia,18-21 and boron carbide.22 A summary of the effect of SiC whisker additions on the mechanical properties of various ceramics is given in Table 2.1. As shown, the addition of whiskers increases the fracture toughness of the ceramics in all cases as compared to the same monolithic materials. In many instances, improvements in the flexural strengths were also observed. Also important is the fact that these improvements over the monolithic materials are retained at elevated temperatures in many cases. 

The effect of different whisker types from various manufacturers on the high temperature flexural strength is shown in Fig. 2.6. As before, the strengths remain relatively constant up to 1000°C and decrease at higher temperatures. The decrease is most dramatic for the composite with whiskers from American Matrix. This is related to the relatively high impurity content of... 

Effect of Temperature on Flexural Strength of Composite Materials... 

Effect of Temperature on Strength. Work by Rennie et al. indicates that the flexural strength of IVz in. X 1% in. X 10 in. sulfur prisms depends markedly on the temperature at which they are equilibrated before testing (2). Other investigators (3) have noted that sulfur specimens having a substantial volume/surface area ratio may undergo thermal shock, a durability problem in which a fluctuating temperature may... 

---