Flexural, and Tensile Strength

These LCT materials have very high tensile and flexural strength, and excellent mechanical and chemical resistance properties. Some commercial LCT are Vectra (Hoechst-Celanese) and Xydar (Amoco). Du Pont, ICI, GE, and Dow Chemical are also suppHers. Their appHcation in electronic embedding is stiU. in its infancy because of the high temperature processing requirement. Nevertheless, this class of thermoplastic polymers will play an important role in electronic embedding. 

The mechanical properties of the laminates are somewhat poorer than observed with phenolic and melamine laminates. Tensile and flexural strength figures are typically about 20% less than for the corresponding P-F and M-F materials and about 60% of values for epoxy laminates. 

High heat distortion, low water absorption, low elongation, good impact strength, good tensile and flexural strength... 

AB cements tend to be essentially brittle materials. This means that when subjected to mechanical loading, they tend to rupture suddenly with minimal deformation. There are a number of different types of strength which have been identified and have been determined for AB cements. These include compressive, tensile and flexural strengths. Which one is determined depends on the direction in which the fracturing force is applied. For full characterization, it is necessary to evaluate all of these parameters for a given material no one of them can be regarded as the sole criterion of strength. 

It can be concluded that water-reducing admixtures of the lignosulfonate and hydroxycarboxylic acid types will not alter the relationship between the compressive strength and the tensile and flexural strengths. 

Table 1.18 Relationship between the compressive strength and the tensile and flexural strengths...

The presence of the cement hydrate/polymer comatrix in LMM and LMC confers superior properties, such as high tensile and flexural strengths, excellent adhesion, high waterproofhess, high abrasion resistance and good chemical resistance, when compared to ordinary cement mortar and concrete. The degree of these improvements however depends on polymer type, polymer-cement ratio, water-cement ratio, air content and curing conditions. Some of the properties affected by these factors are discussed below [87, 88, 93-95]. 

Tensile and flexural strengths values are usually lower than what would be expected from compressive strength values. This probably reflects the effect of laminations and other defects in the shotcrete on tensile strength. Flexural strength values follow a similar relationship observed for regular concrete. 

Thus the effects of the rate of application of stress and the ambient temperature must be recognized when polymers are used as structural materials, and definite rates and temperatures must be specified for tests, such as those for tensile and flexural strengths cited in Chapter 3. A knowledge of the structure of polymers is essential for the understanding of these effects, which differ from the effects of stress and temperature on all other materials of construction. 

These copolymers are thermally stable, but they have slightly lower tensile strengths than the homopolymer The copolymer has a lower heat deflection temperature (110 C) and a low coefficient of friction and specific gravity. When reinforced by 25% fiberglass, the copolymer has a heat deflection temperature of 160 C, a coefficient of linear expansion of S.O X 10 cm/ cm C, a specific gravity of 1.61, and much higher tensile and flexural strengths than the unfilled copolymer. 

Dyes can also have an undesirable effect on properties. Because they dissolve in the matrix, they can sometimes have a plasticizing effect. This will reduce the material s tensile and flexural strength as well as the HDT (heat deflection temperature under load). The plasticizing effect of dyes can also influence the way they process... 

K. M. Prewo, Tensile and Flexural Strength of SiC Fiber-Reinforced Glass-Ceramic Composite , J. Mat. Sci., 21, 3590 (1986). 

An unusual application involves the use of carbon fiber to reinforce cement. This results in improved tensile and flexural strength, high impact strength, improved dimensional stability, etc. 

---