Glass flexural strength

The properties of SAN resins depend on their acrylonittile content. Both melt viscosity and hardness increase with increasing acrylonittile level. Unnotched impact and flexural strengths depict dramatic maxima at ca 87.5 mol % (78 wt %) acrylonitrile (8). With increasing acrylonitrile content, copolymers show continuous improvements in barrier properties and chemical and uv resistance, but thermal stabiUty deteriorates (9). The glass-transition... 

Glass-Based Grades. Grade G-3 is glass fabric with phenohc resin binder which shows high impact and flexural strength. It is used for thermal and mechanical apphcations and has good dimensional stabihty. 

Grade G-11, glass fabric with heat-resistant epoxy resin binder, has properties similar to those of Grade G-10 at room temperature and, in addition, has high retention of flexural strength at elevated temperatures. 

The properties of the laminate are dependent on the resin and type of glass cloth used, the method of arranging the plies, the resin content and the curing schedule. Figure 29.4 shows how the flexural strength may be affected by the nature of the resin and by the resin content. 

Figure 29.4. Influence of resin content on the flexural strength of glass-cloth laminates made with two silicone resins A and B. (After Gale " )...

Resin Melting or glass transition tensile temperature strength (X) (MPa) compressive strength (MPa) flexural strength (MPa) Izod impact, 1/8 in. (J/m)... 

Flexural strength and fracture toughness are clinically more significant than compressive strength. The flexural strength of a glass-ionomer cement can reach 39 MPa after 24 hours (Pearson Atkinson, 1991) which is a much higher value than that attained by any dental silicate cement. 

However, these values are less than those recorded for composite resins used in dentistry. Goldman (1985) reports values of 29 to 49 MPa for anterior composite resins and Lloyd Adamson (1987) values of 76 to 125 MPa for posterior composite resins. A typical amalgam has a flexural strength of 6 MPa (Lloyd Adamson, 1987) (Table 5.16). However, the flexural strengths of some glass-ionomer cements increase with time and values as high as 59 MPa (after 3 months) and 70 MPa (after 7 days) have been reported (Pearson Atkinson, 1991). 

These low values for flexural strength and fracture toughness compared with the values for composite resins and dental amalgams make the glass-ionomer cement less suitable than these materials in high-stress situations. 

Recently, Oldfield Ellis (1991) have examined the reinforcement of glass-ionomer cement with alumina (Safil) and carbon fibres. The introduction of only small amounts of carbon fibres (5% to 7-5% by volume) into cements based on MP4 and G-338 glasses was found to increase considerably both the elastic modulus and flexural strength. There was an increase in work of fracture attributable to fibre pull-out. A modulus as high as 12-5 GPa has been attained with the addition of 12% by voliune of fibre into MP4 glass (Bailey et al, 1991). Results using alumina fibre were less promising as there was no fibre pull-out because of the brittle nature of alumina fibres which fractured under load. 

Pearson, G. J. Atkinson, A. S. (1991). Long-term flexural strength of glass-ionomer cements. Biomaterials, 12, 658-60. 

Prosser, H. J., Powis, D. R. Wilson, A. D. (1986). Glass-ionomer cements of improved flexural strength. Journal of Dental Research, 65,... 

Little information is available on other tests of strength. Isolated measurements give a flexural strength of 24-5 MPa (0ilo, 1988) and a tensile strength of 13-6 MPa (Kent Wilson, 1971). These values lie within the range of those recorded for glass polyalkenoate cement. Translucency is easily achieved as values for the inverse property of opacity show (Table 6.10). 

ISO 3597-2 2003 Textile-glass-reinforced plastics - Determination of mechanical properties on rods made of roving-reinforced resin - Part 2 Determination of flexural strength ISO 5893 2002 Rubber and plastics test equipment - Tensile, flexural and compression types (constant rate of traverse) - Specification ISO 6721-3 1995 Plastics - Determination of dynamic mechanical properties - Part 3 Flexural vibration - Resonance-curve method... 

Figure 4.113 displays three examples of flexural strength retention versus temperature for neat, carbon fibre reinforced and glass fibre reinforced polyamide-imides. The three curves are not distinguishable note the steady decay up to 260°C. 

Improvement in flexural strength due to silane treatments in glass liber thermoplastic matrix composites"... 

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