Yield stress variation, tensile

Figure 11.3. Variation of tensile yield stress with melt flow index (10 kg load at 190 C) and isotactic index. (After Crespi and Ranalli )...

The tensile yield stress variation as a function of W for a material which has a von Mises-type yield locus is illustrated schematically in Figure 5. This variation is caused by the fact that as the width of the specimen increases, the biaxiality also increases toward the asymptotic value at plane strain. If the material obeys the von Mises yield criterion exactly, the plane strain yield stress should be 15% higher than it would be for simple tension. On the other hand, if the material obeys the Tresca yield criterion, the plane strain yield stress should be identical... 

Variation of true tensile yield stress with true strain, fitted by Eq. (8.20), for various polymers. K is the slope of the lines in MPa (From G Sell C and Jonas, J.J. Mater. Sc/., 16, 1966, 1981, Chapman and Hall). 

Fig. 2. The variation of tensile yield stress with 0, the angle between the initial draw direction and the tensile axis. The material is oriented polyethylene terephthalate sheet, draw ratio 5 1. Equation (8) was used to construct the full-line and is a good fit to the available data (after Brown et...

Fig. 7.29. Experimentally determined variation of the effect of film thickness on the tensile yield stress of polycrystalline A1 thin films on Si substrates at 60 °C. The data are shown for three different grain sizes. Adapted from Venkatraman and Bravman (1992).

Fig. 9. Variation of tensile properties and grain stmcture with cold working and annealing A, elongation B, yield stress and C, ultimate tensile stress.

The variation in loop width (at a nominal stress of 10 MPa) for both the tension and compression side of an ABS sample, tested at a stress amplitude of 31 MPa, is shown in Fig. 43. In this case strain softening initiates early and develops rapidly within the first 100 cycles or so. It then continues to increase with increased cycling, at essentially a steady rate on both the tension and compression side of the hysteresis loops. As crazing becomes a significant mode of deformation, which here occurs at about 650 cycles, the loop width increases more rapidly on the tensile side. From this type of graph, we can estimate, for various stress amplitudes, the number of cycles required to initiate shear type softening, N, and the number of cycles required to initiate craze yielding, N. . 

Figure 4.22. Variation of hardness H with tensile Yt (solid symbols) and compressive Yc yield stresses (open symbols). O,, compression-moulded samples A, A, annealed samples at atmospheric pressure , , CEPE samples. (From Flores et al, 2000.)...

Figure 4.30 Stress transfer to a single fibre in a thermoset matrix, under tension in the x direction. The graph shows the variation of the fibre tensile stress and the interfacial shear stress, when the interface yields at both ends of the fibre.

Alpha-titanium alloys. These alloys range in yield tensile strength from 173 to 483 MPa. Variations are generally achieved by alloy selection and not heat treatment. They usually contain alpha stabilizers and have the lowest strengths. However, they are formable and weldable. Some contain beta stabilizers to improve strength. Alpha-titanium alloys are generally in the annealed or stress-relieved condition. They are considered fully annealed after... 

The stiffness of PP is a function of temperature. The variation of flexural modulus of different grades of PP as a function of temperature is shown in Figure 13. PP homopolymers are slightly stiffer than copolymers at room temperature. However, the difference between the two types is diminished as the temperature rises. The flexural modulus of elastomer-modified PP is significantly lower than the homopolymer or copolymer PP, and its service temperature is around 90 °C, much lower than that of homopolymer PP. PP becomes more ductile as the usage temperature inereases, shown by an increase in elongation at break and decrease in ultimate tensile strength and yield stress. 

Table 3 lists the average tensile properties of the 13 specimens, including standard deviation (STD) and coefficient of variation (COV) with symbols of E = modulus of elasticity, Oyo.2% and e o.2% = yi W stress and yield strain at 0.2% offset, a = tensile strength, and e = elongation at break. 

In a modification of the napkin ring shear test, the adherends are solid bars and the adhesive forms a penny-shaped slab similar to the butt joint tensile test. Such a test will give the relationship between torque and twist, but whereas in the napkin ring test it may be assumed that all the adhesive is at the same stress and strain, with a solid butt joint there is a radial variation of strain, but a non-linear variation of stress after yield. It is then necessary to use the Nadai correction (see Adams and Wake") to determine the true stress-strain curve of the adhesive. 

The stress-whitening of the neighboring material, that was produced when the crack was opened up, suggested that the material was not degraded. Mechanical testing of samples, machined from a number of seats, verified this. Tensile modulus was 340 ksi, yield sfress - 4800 psi, strain at break - 38%, and Notched Izod impact strength of 4.2 ft-lb/in (with some minor variations, depending on the color of the seat material - these values are for the compounded materials, not pure Noryl). 

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