Elongation at yield

Tensile stress at yield Elongation at yield Elongation at break Elasticity modulus... 

E = elastic modulus or = maximal strength [Pg.630]

A E s TENSILE STRENGTH AT BREAK ELONGATION AT BREAK B = TENSILE STRENGTH ATYIELD ELONGATION AT YIELD C = TENSILE STRESS AT BREAK ELONGATION AT BREAK D = TENSILE STRESS AT YIELD... 

Generic Material Type Modulus, MPa Yield Stress, MPa Elongation at Yield, % Elongation at Break, %... 

From this line can be estimated the time at which the strain will be such as to cause tolerance problems in product performance. Or by using the elongation at yield as the point at which the material has attained the limit of its useful life, we can estimate the time at which this limit will be reached. 

The elongation at yield for this particular ABS is 0.0275, which could be considered the end of the useful strength of the material. The apparent modulus corresponding to this strain at 1,000 psi and 23°C is ... 

Polymer [molecular weight]0 Glass Transition Tg CC) Decomposition onset peak CC) (V) Tensile strength (kg/cm2) Tensile modulus (kg cm ) Elongation at yield break (%) (%) Solubility... 

The maximum in the curve denotes the stress at yield av and the elongation at yield v. The end of the curve denotes the failure of the material, which is characterized by the tensile strength a and the ultimate strain or elon gation to break. These values are determined from a stress-strain curve while the actual experimental values are generally reported as load-deformation curves. Thus (he experimental curves require a transformation of scales to obtain the desired stress-strain curves. This is accomplished by the following definitions. For tensile tests ... 

Polyethylene and VAE or EBA copolymers such as LED PE geomembrane pond liners, HD PE alloy geomembrane liners, lightweight tarps and containment liners. Beware of low elongations at yield and the stress cracking sensitivity of certain polyethylenes. 

The E. I. DuPont Co. presented empirical equations for the tensile strength, elongation at yield, and tensile modulus as a function of cation type, water content, and equivalent weight in the range 1000 < EW < 1400 and at temperatures in the range 0 < T < 85 These equations were shown in early... 

FIGURE 14.8 Typical stress-strain curves for plastics where (right) A is the elongation at yield point, B is the yield stress, C is the elongation at break, and the area under the curve is the ultimate strength. 

The elongation is generally understood to be the extension with respect to the original length. The elongation at yield is accordingly the extension, Al = I-... 

When the strain reaches a value called the elongation at yield, the curve becomes very non-linear. The stress at this point, the yield stress is sufficiently high to move the crystallites around in their very viscous surroundings, and to cause them to melt and then recrystallize in new orientations that partly relieve the stress. 

One can consider that at a given temperature T, yielding occurs when the polymer reaches a critical state, at which it becomes suddenly rubbery. Then, the above relationship allows us to determine the elongation at yield,... 

Polymer Tensile strength at yield Elongation at yield (%) Tensile strength at break Elongation at break (%) Tensile modulus Flexural strength Flexural modulus Compressi strength... 

Table 20.2 Tensile tests on compression molded sPS/HDPE and sPS/HDPE/SEBS blends Young s modulus (E) strength (ab), elongation (et,) and energy at break (Eb) elongation at yield (ey). Reprinted from Ref. 33 by permission of Wiley-VCH...

Composites of polypyrrole and poly(vinyl chloride) have been prepared by several groups (64-67). Polythiophene-poly(vinyl chloride) composites have also been prepared (68). The electropolymerization of pyrrole on poly(vinyl chloride)-coated electrodes yielded composites with mechanical properties (tensile strength, percent elongation at break, percent elongation at yield) similar to poly(vinyl chloride) (65) but with a conductivity of 5-50 S/cm, which is only slightly inferior to polypyrrole (30-60 S/cm) prepared under similar conditions. In addition, the environmental stability was enhanced. Morphological studies (69) showed that the polypyrrole was not uniformly distributed in the film and had polypyrrole-rich layers next to the electrode. Similarly, poly(vinyl alcohol) (70) poly[(vinylidine chloride)-co-(trifluoroethylene)] (69) and brominated poly(vinyl carbazole) (71) have been used as the matrix polymers. The chemical polymerization of pyrrole in a poly(vinyl alcohol) matrix by ferric chloride and potassium ferricyanide also yielded conducting composites with conductivities of 10 S/cm (72-74). 

Precision of flexnral modulus measurements is usually fair. ASTM D 638-03 lists examples for several different plastics, including polypropylene, tested by eight laboratories nsing the Type I specimen, of nominal 0.125-in. thickness. Each test result was based on five individual determinations. Each laboratory obtained two test results for each material. For polyethylene, tensile modnlns of elasticity was 210,000+8900 psi for within-laboratory tests and 210,000+71,000 psi for between-laboratory tests. Tensile strength at yield for polypropylene was 3630+22 psi for within-laboratory tests and 3630+161 psi for between-laboratory tests. Elongation at yield was 8.79+0.45 and 8.8+5.9% for within- and between-laboratory tests, respectively. 

ASTM procedure recommends employing of tensile strength and elongation at yield as more reproducible tests, related in most cases to the practical usefulness. 

Later, these workers investigated the effect of irradiation on the tensile properties of the LDPE/PP blends. For the non-irradiated blends, the mechanical behavior gradually changed with composition. The elongation at yield gradually increased from PP to LDPE, whereas the elongation at break showed a minimum at 75 wt% PP [Spadaro et al, 1984]. The results are shown in Table 11.14. 

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