Typical Room-Temperature Strength

Heat resistance is an important characteristic of the bond. The strength of typical abrasive stmctures is tested at RT and at 300°C. Flexural strengths are between 24.1 and 34.4 MPa (3500—5000 psi). An unmodified phenoHc resin bond loses about one-third of its room temperature strength at 298°C. Novolak phenoHc resins are used almost exclusively because these offer heat resistance and because the moisture given off during the cure of resole resins results in undesirable porosity. Some novolaks modified with epoxy or poly(vinyl butyral) resin are used for softer grinding action. 

Table 11.8 presents a typical triethylenetetramine cured epoxy adhesive formulated with selected fillers. In this formulation the use of aluminum powder and alumina increases substantially the resistance of the adhesive to boiling water.7 This is also true when DETA is used as the curing agent.8 A typical room temperature cured aliphatic amine cured epoxy adhesive for general-purpose use is shown in Table 11.9. This shows the difference that is achieved in shear strength by curing at elevated temperatures versus room temperature.

The physical properties of a typical room temperature-cured polyester concrete is as follows Barcol hardness (50), tensile strength (500 kg cm 2), elongation (0.45%), compressive strength (1400 kg cm 2) flexural strength (1050 kg cm ) and heat deflection (41"C). The latter may be Increased by 30 by the use of fumaric acid Instead of maleic acid. 

In spite of these difficulties, these adhesives can exhibit excellent properties. For short-term apphcations, they can retain in excess of 50% room temperature strength at approximately 300 °C. Table 1 indicates typical joint strength values that can be achieved. 

A higher impact energy than the test can generate. These are typical room-temperature values of notched Izod impact strength. A material that does not break in the Izod test is given a value of 1.06 -t kj/m. N/R Not reported UV Ultraviolet Source Author s own files ... 

There are, however, certain limitations associated with polyurethane structural adhesives, the most significant being their elevated temperature performance. It is typical of such adhesives to lose 50%, or more, of their room temperature strength on aluminum or steel at 80-100°C as shown in Table I. Urethanes produce only moderate strength bonds to metals, and adhesives which contain free isocyanate groups suffer from limited shelf stability due to their moisture sensitivity. 

Typical room-temperature tensile properties are higher than the guaranteed minimums (see table), which vary with section size. Lower strengths occur in the annealed condition, or when STA material has been worked in the P phase field prior to heat treatment. 

The typical aged tensile strengths at elevated temperatm e are high percentages of the room-temperature strength, as shown in the table below. Thermal Stability. Ti-7Al-4Mo may be used... 

Thus, several important mechanical properties of metals may be determined from tensile stress-strain tests. Table 6.2 presents some typical room-temperature values of yield strength, tensile strength, and ductility for several common metals. These properties are sensitive to any prior deformation, the presence of impurities, and/or any heat treatment to which the metal has been subjected. The modulus of elasticity is one mechanical parameter that is insensitive to these treatments. As with modulus of elasticity, the magnitudes of both yield and tensile strengths decline with increasing temperature just the reverse holds for ductility —it usually increases with temperature. Figure 6.14 shows how the stress-strain behavior of iron varies with temperature. 

Table B.4 Typical Room-Temperature Yield Strength, Tensile Strength, and Ductility (Percent Elongation) Values for Various Engineering Materials...

Eor reinforcement, room temperature tensile strength and Young s modulus (stress—strain ratio) are both important. Typical values for refractory fibers are shown in Table 2. 

Because of the effects of impurity content and processing history, the mechanical properties of vanadium and vanadium alloys vary widely. The typical RT properties for pure vanadium and some of its alloys are hsted in Table 4. The effects of ahoy additions on the mechanical properties of vanadium have been studied and some ahoys that exhibit room-temperature tensile strengths of 1.2 GPa (175,000 psi) have strengths of up to ca 1000 MPa (145,000 psi) at 600°C. Beyond this temperature, most ahoys lose tensile strength rapidly. 

The above data relate to very pure iron samples with low dislocation densities. In real steels the trapping effects result in much lower apparent diffusivities, which are dependent on the metallurgical state of the steel, as well as its chemical composition. Typical values for the apparent diffusion coefficient of hydrogen in high-strength alloy steel at room temperature are in the region of 10" mVs. 

The mass fraction crystallinity of molded PHB samples is typically around 60%. As shown in Table 3, PHB resembles isotactic polypropylene (iPP) with respect to melting temperature (175-180°C), Young s modulus (3.5-4 GPa) and the tensile strength (40 MPa). In addition, the crystallinity of iPP is approximately 65% [18]. Accordingly, the fracture behavior of PHB may be anticipated to be tough at room temperature. Molded PHB samples do indeed show ductile behavior, but over a period of several days at ambient conditions, they slowly become more brittle [82, 85, 86]. Consequently, the elongation to break of the ultimate PHB (3-8%) is markedly lower than that of iPP (400%). 

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