Tensile rupture ratio

In order to describe the process of the rupture of tongue tip precisely, a technical term, tensile rupture ratio, is Introduced and defined as a ratio of the rupture length of the tongue tip to the original length of the tongue (Figure 2). Thus,... 

As seen from Equations (3), (5) and (6), the tensile rupture ratio can be roughly considered to be directly proportional to the frictional force and inversely proportional to the tensile strength ... 

There are two independent variables in the characteristic function of unsteady state, i.e., the number of revolutions and the tensile rupture ratio. The effect of the number of revolutions on unsteady-state rate of wear is obvious as seen by Figure 8 ( y. However, the influence of the tensile rupture ratio on wear rate is still not established. 

As seen in Figure 10, the larger the tensile rupture ratio, the larger the value of the characteristic function is, and, the earlier the steady state is reached (Figure 9). It is also supported by the experimental observation that the larger the frictional force, the earlier the ridges appeared. 

Besides, as shown in Figure 9, the slope of the curve is a steep rise along with an increase in the tensile rupture ratio. 

Hence, the fact that the unsteady-state rate of wear of unfilled NBF is much more sensitive to the number of revolutions than that of filled NBR would be ascribed to the difference in tensile strength or in tensile rupture ratio, i.e., the tensile strength of unfilled NBR is less than that of filled NBF, in other words, the tensile rupture ratio of unfilled NBR is much more than that of filled NBR. 

Evidently, the higher the tensile rupture ratio, the lower the value of the state criterion is. Thus, this state criterion can be applied to estimate the wear characteristics of different elastomers under similar running conditions. 

The characteristic function, f (N,6 ), is a characterizing factor of rubber abrasion in unsteady state. Its value increases with an increase in the number of revolutions and tensile rupture ratio. However, it approaches unity as a limit in the unsteady-state process of wear. Hence, a steady state is reached if once 1 (N,6j ) = 1. 

Figure 10. Characteristic function plotted against tensile rupture ratio (A) i = 20 rev (B) i = 40 rev (C) i = 60 rev.

The number of revolutions transformed the wear state from unsteady to steady can be regarded as a state criterion of rubber abrasion to estimate the wear characteristics of rubber under identical r jnning conditions. It was found to be proportional to a negative exponent of the tensile rupture ratio. 

Tough materials with sufficient high elongation at rupture - in the minimum 10 % - and with a good ratio between allowed yield strength and the tensile strength-ratio of approximately 0.85 and better should be chosen. The cooperation with a experienced steel manufacturer is an important link in the design process. 

Compression failure is the most desirable of the above failure modes. This failure mode is less abrupt than tension failure, and is similar to the failure of an over-reinforced section when using steel reinforcement. Tension failure is less desirable, since tensile rupture of FRP reinforcement will occur with less warning. Tension failure will occur when the reinforcement ratio is below the balanced reinforcement ratio for the section. This failure mode is permissible with certain safeguards. 

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. 

Elastic modulus Bulk modulus Poisson s ratio Tensile strength Compressive strength Modulus of rupture Fracture toughness Hardness Fatigue Creep... 

The ends of the microfibrils create about Itf m point vacancies in the microfibrillar superlattice (Fig. 11). Under applied tensile load they may fail first, eventually by microcrack formation so that the adjacent microfibrils have to carry a heavier load than the rest of the sample. Hence they are first candidates for rupture detectable by the rascals formed at the rupture of tie molecules in at least one amorphous layer of the microfibril affected. Depending on the ratio of axial strength to lateral adhesion of the microfibrils the microcracks will grow parallel (high ratio) or perpendicular (low ratio) to the fibre axis yielding a large number of broken, chains and radicals in the former and a small one in the latter case. Nylon is an example of the former and linear polyethylene of the latter type. 

Another fatigue-testing device is the (Monsanto) Fatigue to Failure Tester. This instrument measures the ultimate fatigue fife as cycles to failure. Tensile-like samples are stretched at 100 cycles per minute at a preselected extension ratio. Samples can be strained over a range of 10 to 120 percent. The fatigue performance of compounds can be measured (number of cycles to failure, i.e., rupture) and compared either at constant extension ratio (strain) or at constant strain energies (work input). 

Fiber Tenacity (g/den) Breaking extension (%) work factor Elastic recovery 2% elongation (%) Stiffness (g/tex) Toughness (g/tex) Work to rupture (mN/tex) biitial modulus (N/tex) Ratio tensile modulus over shear modulus Breaking twist angle (a°)... 

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