Tensile strain rupture

One of the simplest criteria specific to the internal port cracking failure mode is based on the uniaxial strain capability in simple tension. Since the material properties are known to be strain rate- and temperature-dependent, tests are conducted under various conditions, and a failure strain boundary is generated. Strain at rupture is plotted against a variable such as reduced time, and any strain requirement which falls outside of the boundary will lead to rupture, and any condition inside will be considered safe. Ad hoc criteria have been proposed, such as that of Landel (55) in which the failure strain eL is defined as the ratio of the maximum true stress to the initial modulus, where the true stress is defined as the product of the extension ratio and the engineering stress —i.e., breaks down at low strain rates and higher temperatures. Milloway and Wiegand (68) suggested that motor strain should be less than half of the uniaxial tensile strain at failure at 0.74 min.-1. This criterion was based on 41 small motor tests. 

What this relationship, in effect, says is that every material will fail during creep when the strain in that material reaches a certain value independent of how slow or how fast that strain was reached. That the Monkman-Grant expression is valid for Si3N4 is shown in Fig. 12.14, where the range of data obtained for the vast majority of tensile stress rupture tests lies in the hatched area. On such a curve, Eq. (12.42) would appear as a straight line with a slope of 1, which appears to be the case. 

Tables 2-4 show the effect of the dry/cold. moderate, and humid/hot environments on the tensile properties of the adhesive FM 300K tested at the 10 "/s. lO /s. and lO Vs strain rates, respectively. The values of the yield strength, the yield strain, and the offset obtained with the SED method and the corresponding values from the 0.2 % offset method are shown. The tensile strength, rupture strain, and elastic modulus are provided for information. On average, the time to rupture of the specimens tested at the lO /s, lO /s, and lO Vs strain rates were 4 seconds. 6 minutes, and 15 hours, respectively. The data are listed in ascending order of yield strength. The tensile properties listed in parentheses at the bottom of each cell are averages for replicate specimens. For ease of comparison, these averages are summarized in Table 5.

When a thin bonded block is subjected to tensile loading, a state of approximately equal triaxial tension is set up in the central region of the block. The magnitude of the stress in each direction is given by the tensile stress, or negative pressure, <72 at r = 0 that is, Eea /h, from Eq. (1.32). Under this outwardly directed tension a small cavity in the central region of the block will expand indefinitely at a critical value of the tension, of about 5 /6. Thus, if cavities are present in the interior of a bonded block, they are predicted to expand indefinitely (i.e., rupture) at a critical tensile strain Cc, given approximately by... 

Breaking extension n. Elongation necessary to cause rupture of a test specimen the tensile strain at the moment of rupture. 

Although long-fiber composites typically fail at low tensile strains, they are generally not considered to be brittle, i.e., in the realm of glass or ceramics. The fibers do have strain to failure, and the failures can be predicted. A bundle of fibers bound together hy a matrix does not usually fail when the first fiber ruptures. Instead, the final failure is preceded by a period of progressive damage. 

The tensile straining of fibrous polymer ruptures a great many tie molecules, thus producing very unstable primary end-of-chain radicals. By chain transfer they are rapidly transformed into the more stable secondary center-of-chain radicals which are detectable by electron spin resonance (ESR). In nylon 6 and 66 the dependence of radical population on strain and time was... 

PVA fibres tend to rupture instead of pull-out of a cementitious matrix, due to the strong chemical bonding and the resulting slip-hardening response during pullout [133]. Li etal. [134] were able to produce composites with an ultimate tensile strain exceeding 4% and a tensile strength of 4.5 MPa, with a fibre volume of only... 

Figure 2.3 shows deformation curves plotted in tensile strain versus tensile stress coordinates. The endpoints on the curves conform to the time of sample rupture with respective stress and strain. The elasticity modulus of the samples was calculated by the tangent of the angle of slope of the initial segments of the deformation curves. The deformation curves of filled SAN are characteristic of plastics with brittle failure. Nonfilled SAN exhibits considerable deformations. As seen in Figure 2.3 and Table 2.4, addition of up to 10% diamond carbon to SAN... 

Creep Rupture. When a plastic is subjected to a constant tensile stress its strain increases until a point is reached where the material fractures. This is called creep rupture or, occasionally, static fatigue. It is important for designers... 

Even plastics with fairly linear stress-strain curves to failure, for example short-fiber reinforced TSs (RPs), usually display moduli of rupture values that are higher than the tensile strength obtained in uniaxial tests wood behaves much the same. Qualitatively, this can be explained from statistically considering flaws and fractures and the fracture energy available in flexural samples under a constant rate of deflection as compared to tensile samples under the same load conditions. These differences become less as the... 

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