Irradiation tensile modulus

Typical tension stress-strain curves of baseline and irradiated unidirectional T300/934 composites tested in [0] and [90] orientations at three different temperatures (121 are shown in Figures 11 and 12. Irradiation had essentially no effect on the fiber-dominated tensile modulus of the [0] specimen and caused only a small (10-15%) reduction in strength at the low and elevated temperatures. For the matrix-dominated [90] laminates, irradiation caused a very substantial decrease in strength at three test temperatures (-38% at -157°C, -26% R.T., -13% 121°C). Irradiation increased the modulus at -157°C and R.T. (10 - 15%), but lowered it at 121°C (-15%). These results are consistent with results obtained on the neat resin specimens discussed above. 

Figure 17. Thermal cycling and irradiation effects on composite tensile modulus. (Reproduced from reference 9.)...

It has been demonstrated that molecular orientation can be achieved starting with a low molecular weight species which is oriented in an elongational flow and subsequently cured under UV-irradiation. The orientation of the monomer is frozen-in by the ultra-fast process of polymerization and crosslinking. Both extrusion and stretching can be carried out at relatively low temperatures and pressures. Polymer filaments produced in this way are definitely anisotropic as is evidenced by their birefringence and by a strong increase of the tensile modulus and a decrease of the thermal expansion coefficient in the axial direction. 

Figure 3.104 Effect of UV irradiation in a QUV Weather-o-meter on the tensile properties of PVF, PVDF and ETFE (a) tensile modulus b) tensile strength (c) break elongationJ i...

The gel fraction and melt viscosities of the irradiated samples indicated that in the blends LLDPE was crosslinked (Table 11.20). The tensile modulus of the LLDPE-rich blends was found to be improved by irradiation. In contrast, the PA-6 underwent predominantiy chain branching. As a result, impact strength of the PA-6-rich blends was found to be ameliorated [Valenza et al, 1994] (Table 11.20). For the neat LLDPE, the gel fraction varied from 84% at 50 kGy to 95% at 400 kGy. The gel fraction of the LLDPE decreased only marginally as the LLDPE component was reduced in the blends, e.g., from 95% at 100% LLDPE to 92% at 25% LLDPE at 400 kGy. However, at 10% LLDPE the gel fraction dropped sharply to 19%, indicating that at very low concentrations the radiation-induced crosslinking may be affected by partial solubilization of the LLDPE in PA-6 [Spadaro et al., 1993]. 

Polycarbonates, although they tend to strongly discolor for unstabilized grades, are relatively resistant to irradiation showing retention of elongation at yield and tensile modulus after irradiation up to 1,000 kGy [198]. 

Irradiation dose before foaming (kGy) Average cell diameter (gm) Foam density (g/cm ) Tensile strength (MPa) Tensile modulus (MPa) Elongation at break (%)... 

Clay hllers were surface modihed with TMPTA or triethoxyvinyl silane (TEVS) followed by EB irradiation by Ray and Bhowmick [394]. Both the untreated and treated fillers were incorporated in an ethylene-octene copolymer. Mechanical, dynamic mechanical, and rheological properties of the EB-cured unfilled and filled composites were studied and a significant improvement in tensile strength, elongation at break, modulus, and tear strength was observed in the case of surface-treated clay-filled vulcanizates. Dynamic mechanical studies conducted on these systems support the above findings. 

FIGURE 31.13 (a) Plot showing the stress-strain behavior of various irradiated rubbers, (b) Plot showing the variation of tensile strength and modulus of rubbers irradiated with different doses, (c) Plot showing the variation of hysteresis loss, set, and elongation at break of irradiated fluorocarbon rubbers. (From Banik, I. and Bhowmick, A.K., Radial. Phys. Chem., 54, 135, 1999. With permission.)... 

Figure 14.17. Young s modulus and tensile strength of SWNT membrane as a function of irradiation dose.

In the case of PSSZ a more extensive study was carried out. In particular, it was shown that the nitrogen content of the ceramic is in good correlation with the value of x when x < 0.75. For X > 0.5 Si-Si-Si sequences were hardly detected. A PSSZ prepared with equimolar amounts of Me2SiCl2 and (ClHMeSi)2NH was converted into PCSZ upon thermolysis (temperature of the bath 425 °C, 8h), cross-linked by y-irradiation, then pyrolyzed to afford SiCN-based material containing a very small amount of oxygen [4a]. In a preliminary study carried out at the Laboratoire des Composites Thermostructuraux, F-33600 Pessac, France (Prof R. Naslain), SiCN fibers were obtained (tensile strength 2 400 MPa Young s modulus 235 GPa). 

The mechanical properties of most polymers are modified by irradiation. They usually deteriorate in polymers undergoing predominant chain scission. In crosslinked polymers, the mechanical properties strongly depend on the temperature at which the measurements are performed and improvements are often obtained, especially above the melting point. Crosslinked polyethylene, for instance, is a rubbery solid above its crystalline melting point instead of being a viscous liquid if not irradiated. At room temperature, the elastic modulus and tensile strength are often increased by irradiation. Results on individual polymers will be discussed in section 5. 

Elongation of PVC as a function of dose and temperature has been performed by Chapiro [432]. Minor changes are observed after irradiation in vacuo (Fig. 46). After a 41 Mrad dose, however, the polymer does not flow even at 250°C since a three-dimensional network was formed. Irradiation in air reduces the temperature of breaking even at low doses. A stress—strain curve for PVC is reported by Busch [433]. An important reduction in tensile strength is observed. Neutron-irradiated PVC, vinyl chloride—vinylidene chloride copolymers and vinyl acetate—vinyl chloride copolymers were compared. Reduction in tensile strength and elastic modulus was observed for the first copolymer whereas the second showed considerable increase in the elongation at break [434]. 

Reactor exposure causes decrease in elongation at break and increase in the modulus of elasticity due to crosslink formation [434]. High doses are, however, required to produce appreciable change. 7-Irradiation gives decreased tensile strength and elongation at break for nylon 6 and nylon 6, 6 [433] (Fig. 47). The dynamic mechanical properties of nylon 6, 6 were studied by Sauer et al. [436] after neutron irradiation. Rubber-like behaviour was observed for temperatures above the main softening temperature. 

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