Polycarbonate stress-strain curves

Figure C2.1.17. Stress-strain curve measured from plane-strain compression of bisphenol-A polycarbonate at 25 ° C. The sample was loaded to a maximum strain and then rapidly unloaded. After unloading, most of the defonnation remains.

Fig. 2. Stress—strain curve for standard polycarbonate resin at 23°C where the points A, B, and C correspond to the proportional limit (27.6 MPa), the yield point (62 MPa), and the ultimate strength (65.5 MPa), respectively. To convert MPa to psi, multiply by 145.

Figure 1. Stress-strain curves of polycarbonate-polydimethyl-siloxane block copolymers (Crosshead Speeds 5 cm/min). (Reproduced from Refs. 15 18. Copyright 1980, 1984 American Chemical Society.)...

Mechanical Properties. The room temperature modulus and tensile strength are similar to those of other amorphous thermoplastics, but the impact strength and ductility are unusually high. Whereas most amorphous polymers arc glass-like and brittle below their glass-transition temperatures, polycarbonate remains ductile to about — 10°C. The stress-strain curve for polycarbonate typical of ductile materials, places it in an ideal position for use as a metal replacement. Weight savings as a metal replacement are substantial, because polycarbonate is only 44% as dense as aluminum and one-sixth as dense as steel. 

The mechanical properties of a craze were first investigated by Kambour who measured the stress-strain curves of crazes in polycarbonate (Lexan, M = 35000) which had first been grown across the whole cross-section of the specimen in a liquid environment and subsequently dried. Figure 25 gives examples of the stress-strain curves of the craze determined after the 1st and 5th tensile loading cycle and in comparison the tensile behavior of the normal polymer. The craze becomes more and more elastic in character with increasing load cycles and its behavior has been characterized as similar to that of an opencell polymer foam. When completely elastic behavior is observed the apparent craze modulus is 25 % that of the normal poly-... 

Fig. 25a and b. Stress-strain curves of a craze in polycarbonate grown across the total cross-section of the specimen... 

Figure 1.20 Stress-strain curves in extension for polycarbonate at various temperatures at a strain rate of 0.05 min-. (From Matsuoka 1992, reprinted with permission from Hanser Gardner Publications.)...

Figure 14.8 shows stress-strain curves for polycarbonate at 77 K obtained in tension and in uniaxial compression (12), where it can be seen that the yield stress differs in these two tests. In general, for polymers the compressive yield stress is higher than the tensile yield stress, as Figure 14.8 shows for polycarbonate. Also, yield stress increases significantly with hydrostatic pressure on polymers, though the Tresca and von Mises criteria predict that the yield stress measured in uniaxial tension is the same as that measured in compression. The differences observed between the behavior of polymers in uniaxial compression and in uniaxial tension are due to the fact that these materials are mostly van der Waals solids. Therefore it is not surprising that their mechanical properties are subject to hydrostatic pressure effects. It is possible to modify the yield criteria described in the previous section to take into account the pressure dependence. Thus, Xy in Eq. (14.10) can be expressed as a function of hydrostatic pressure P as... 

Figure 14.8 Stress-strain curves for polycarbonate at T = 11 K determined under tension and uniaxial compression. The nominal stress curves, cs , correspond to the dashed lines, and those for the true stress, o- correspond to solid lines. The material tested under tension fractures immediately after reaching yield, unlike the situation that occurs under compression. (From Ref. 12.)...

Figure 14.10 Tensile stress-strain curves for polycarbonate as a function of tem-...

Figure 14.11 Tensile stress-strain curves for polycarbonate as a function of strain at 25°C. The yield stress, Oy (maximum in the curve vs. e ), increases with increasing strain rate. (From Ref. 14.)...

As could be expected, the mechanical properties of a crazed polymer differ from those of the bulk polymer. A craze containing even 50% microcavities can still withstand loads because fibrils, which are oriented in the direction of the load, can bear stress. Some experiments with crazed polymers such as polycarbonate were carried out to get the stress-strain curves of the craze matter. To achieve this aim, the polymer samples were previously exposed to ethanol. The results are shown in Figure 14.24 where the cyclic stress-strain behavior of bulk polycarbonate is also illustrated (32). It can be seen that the modulus of the crazed polymer is similar to that of the bulk polymer, but yielding of the craze occurs at a relatively low stress and is followed by strain hardening. From the loading and unloading curves, larger hysteresis loops are obtained for the crazed polymer than for the bulk polymer. 

The stress-strain curves of ductile thermoplastics (including both glassy amorphous polymers such as bisphenol-A polycarbonate and semicrystalline polymers such as polyethylene at room temperature) have the general shapes shown in Figure 11.16(a), which can be compared with the shape of the stress-strain curve of a very brittle material shown in Figure 11.16(b). The stress-strain curves of polymers which are neither very ductile nor very brittle under the testing conditions being utilized have appearances which are intermediate between these. two extremes. 

Figure C2.1.17. Stress-strain curve measured from plane-strain compression of bisphenol-A polycarbonate at 25 °... 

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. 

Figure 13.17. Compressive stress-strain curves of PMMA, polycarbonate, poly[vinylchloride] PVC), and polyurea-crosslinked surfactant-templated silica aerogel (X-MP4-T310 MCF type material) at high strain rates.

Pig. 5. True stress-strain curves for a polycarbonate under tension and compression. After Boyce and Arruda (19) with permission. 

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...

Figure 3-47. An example of isochronous stress-strain curves for polycarbonates resulting from stress relaxation.

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