Polypropylene stress-strain curves

The mechanical response of polypropylene foam was studied over a wide range of strain rates and the linear and non-linear viscoelastic behaviour was analysed. The material was tested in creep and dynamic mechanical experiments and a correlation between strain rate effects and viscoelastic properties of the foam was obtained using viscoelasticity theory and separating strain and time effects. A scheme for the prediction of the stress-strain curve at any strain rate was developed in which a strain rate-dependent scaling factor was introduced. An energy absorption diagram was constructed. 14 refs. 

A detailed atomistic approach was used to investigate the molecular segment kinematics of a glassy, atactic polypropylene system dilated by 30%. ° The microstructural stress—dilation response consists of smooth, reversible portions bounded by sudden, irreversible stress jumps. But compared to the micro-structural stress—strain curve of the shear simulation, the overall trend more closely resembles macroscopic stress—strain curves. The peak negative pressure was in the neighborhood of 12% dilatation, with a corresponding secondary maximum in the von Mises shear stress. The peak negative pressure was re-... 

The volume increase depends on the filler fraction and on the applied strain. This is confiimed in practice. Debonding correlates with loss of stiffness. The first part of the stress-strain curve (elastic stage) is related to the strains beyond which debonding occurs. In glass bead filled polypropylene, this strain was 0.7%. ... 

Figure 3. Stress-strain curve of polypropylene before and after 7 Mrad irradiation...

In spite of our reluctance to quote numerical values at this point, the effective modulus obtained from the initial portion of the tensile curve ranges from 1 to 5 X 10 dyn cm". Many individual PE crystals have moduli from 3 X 10 to 10 dyn cm" and fracture at forces of about 0.2 dyn. Orientation effects are expected to be present and are presently being investigated. There is no comparable experimental data with which we can directly relate these values. However, moduli are in the range found for bulk specimens but are considerably less than the value of 70 X 10 dyn cm reported by Perkins et al. (8) for ultra-drawn HDPE fibers. The x-ray measurements of the lattice moduli by Ito (9) using an x-ray technique for oriented sheet samples is perhaps the most relevant comparison. He found values of 240 X 10 dyn cm" in a direction parallel to the fiber axis and a value of 4 X 10 dyn cm for the perpendicular direction which would be the closest comparison with our orientation. We are not yet certain whether the initial portion of the stress-strain curve shows nonlinear viscoelastic effects such as found by Chen et al. (4) for springy polypropylene (PP) fibers. 

FIGURE 3.36 Stress-strain curves for polypropylene spun at various take-up velocities at 250°C. (From Shimizu, J. Toriumi, K. Imai, Y. Sen-i Gakkaishi, 1977, 33, T-255. With permission.)... 

It is also possible to obtain crimped fibres by the split-fibre technology in a different way. If a laminated film is produced by extruding the raw material or raw materials in such a way that the layers display during stretching stress-strain curves which do not coincide, then a spontaneous crimp can be obtained immediately after fibrillation without additional thermal treatments of the fibres. It is, of course, necessary that the layers adhere well to each other. If both layers consist of polypropylene or copolymers of propylene, this is no problem. However, if different polymers are used, the adhesion is usually insufficient. 

Fig. 8.5 The computer-simulated equivalent stress-strain curve of amorphous polypropylene in a cubic simulation cell, strained by static energy minimization at 235 K, showing a number of unit plastic events as the system stress drops (O) and as the system pressure drops (O). Arrows show directions of forward and reverse straining (from Mott et al. (1993) courtesy of Taylor and Francis).

Fig. 11.4 Typical stress-strain curves for polypropylene blended with ethylene-propylene rubber (EPDM) at different rubber concentrations. Strain rate 10 s , room temperature. The plot illustrates the relation of modulus and strain presented in Eq. 11.9 (From Gaymans (2000) reproduced with permission of Wiley)...

The melt-spun thermoplastic fibres, nylon, polyester, polypropylene, show a quite different form of breakage. In undrawn fibres, which are unoriented or partially oriented, rupture occurs at the end of a long period of plastic extension at slowly increasing tension. In oriented fibres, which have been drawn, the stress-strain curve terminates in a short yield region, the residual plastic extension, before rupture occurs. Break starts as a crack, usually from a flaw but otherwise self-generated by coalescence of voids. Fig. 3a. The... 

The stress-strain curve in Fig. 7.24b first of all exhibits elastic and preplastic behaviour. It then reaches a maximum whose sharpness depends on the polymer and also the deformation rate. Beyond this point, the stress remains almost constant over a certain region, before suddenly increasing to fracture. This is brittle fracture, perpendicular to the load. Many semi-crystalline polymers, such as polyethylene, polypropylene, polyamide 6 and polyamide 6,6 exhibit this type of behaviour at ambient temperature. However, among amorphous polymers in the glassy state, polycarbonate is one of the rare examples to behave in this way. 

Stress-strain curves of polypropylene, polycarbonate, and Mylar at 77 K before and after irradiation of 9 X 10 nvt with a y dose of 2.4 x lO R at 5 K. The stress-strain curves of polycarbonate and Mylar before irradiation are in the hatched region. 

Fig. 2. Typical stress-strain curves for oriented and nonoriented polypropylene films.

Argon and co-workers (95,96) have developed an atomistic mechanics model of polypropylene and related it to experiments performed at a temperature of 10°C below the glass-transition temperature. Stress-strain curves calculated after small strain increments showed a series of generally monotonically increasing... 

FIGURE 9.1 Stress-strain curves of semicrystalline polypropylenes allow a classification based on their mechanical properties. 

FIGURE 9.28 Stress-strain curves of melt-pressed polypropylene samples prepared with 9a/MAO show a transition from elastomeric to plastomeric deformation behavior when the tnmtnm content rises above 40%. 

Comparing the stress-strain curves obtained for the two series of polypropylenes A and B, similar Young s moduli were found for samples with similar mmmm contents. This can be explained by similar amounts of crystalline aggregates formed within the samples. Nevertheless, a closer look at the stress-strain curves reveals a clear difference in mechanical behavior for samples with similar mmmm contents, but showing different chain microstructures (e.g., A43, 43% mmmm. Figure 9.28... 

Figure 11.5 True stress-strain curves at room temperature for polycarbonate (a) and polypropylene (b). (Reproduced with permission from Amoedo and Lee, Polym. Eng. Sci., 32 1055...

Stress-strain curves of irradiated highly crystalline polypropylene exposed to gamma rays exhibit its ductile behavior with elongation values for the nonirradiated samples up to 80%. After irradiation, highly crystalline polypropylene becomes less ductile and tensile stress decreases as well. 

Figure 6.40 Tensile stress-strain curves of composite materials prepared using an internal mixing-compression molding method, (a) Pure polypropylene, (b) 10% whisker content. 

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