Fatigue resin types

The homopolymers are more rigid, stronger, and have greater resistance to fatigue. Both types of acetal resins are degraded by uv light. 

These data imply that the fatigue strength is dominated by fibre type, i.e. glass rather than resin type or fibre length (provided the fibres are longer than the minimum length to transfer the load). 

Figure 10.15 Tensile fatigue of different resin types and blends showing fibre and matrix dominated properties (Echtermeyer/SAMPE).

Stiffness, resistance to deformation under constant applied load (creep resistance), resistance to damage by cyclical loading (fatigue resistance), and excellent lubricity are mechanical properties for which acetal resins are perhaps best known and which have contributed significantly to their excellent commercial success. General-purpose acetal resins are substantially stiffer than general-purpose polyamides (nylon-6 or -6,6 types) when the latter have reached equilibrium water content. 

Fatigue strengths should, wherever possible, he determined on the basis of tests on samples of the FRP laminate made with similar resin and glass fibre reinforcement of similar type and proportions. The conditions of the test should be appropriate to the loading conditions of the component being designed, and to the environmental conditions. 

Varying the carbon fiber type in the same resin matrix has little effect upon the fatigue behavior (Figure 17.60), but efforts to improve resin toughness have resulted in improved static strength but poorer fatigue properties (Figure 17.61). 

A new polymer modification process has been developed to reduce the cost of the engineering resin. The modification process is blended polymers. A blended polymer is a mixture of at least two polymers or a copolymer. There are three types of blended polymers miscible, immiscible, and compatible polymers. On occasion, blended polymers have properties that exceed those of either of the constituents. For instance, blends of polycarbonates (PC) resin and polyethylene terephthalate (PET) polyester were originally created to improve the chemical resistance of the PC. This is because PC actually had a fatigue resistance and low-temperature impact resistance that was superior to either of the individual polymers. 

To characterize the cyclic crack growth resistance of both neat resins and laminates, fatigue crack propagation (FCP) experiments under Mode I conditions were performed in laboratory air (23 C/50%r.h.) using a computer controlled servohydraulic fatigue testing machine. In the case of neat resins, compact-type (CT) specimens with a width of 50 mm, a hight-to-width ratio of 0.6, and a nominal thickness of 4 mm were used. For composite laminates double cantilever beam specimens (125 x 20 x 8 inm ) were employed. FCP tests were conducted at 10 Hz. The applied waveform was sinusoidal with a constant load amplitude and a minimum-to-maximum load ratio, R, of 0.1. 

Figure 3-68. Fatigue curves for reinforced plastic composites using different types and amounts of fibers and resins (ICI-LNP).

Figure 1.38 The effect of fatigue type on fatigue resistance at 25°C for Mitsubishi Engineering Plastics Corporation lupilon /Novarex PC resin [18].

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