Defects in laminated composite structures like voids and impact damages have a major influence on the fatigue behaviour. These defects may occur in the manufacturing process and during lifetime of composite parts and lead to matrix cracks within single layers and to delaminations between adjacent layers with different fibre orientations. We investigated the relationship between voids and impact damage and fatigue lifetime. Specimens made of a glass fibre non‐crimp fabric were produced by vacuum assisted resin infusion. Voids were introduced by air‐bypass simulating a leakage during the vacuum assisted resin infusion‐process. Impact damage was induced using a canon. Stringer‐panels with the basic dimensions of 1000 mm × 1200 mm and a radius of 1980 mm were tested under multiaxial load situations in a hexapod test rig and a tension/compression‐shear test rig.

Two alternative chlorofluorocarbons, CFC-123 and CFC-141b, have been proposed as substitute blowing agents for CFC-11 in rigid urethane foams. Both of these have similar boiling points to CFC-11 but substantially reduced ozone depletion potentials. Mobay Corporation has evaluated both of these in a variety of systems to determine their potential use as blowing agents for rigid urethane foams in appliance applications. Due to the different molecular weights compared to CFC-11, there is theoretically 11 weight percent more CFC and 15 weight percent less CFC-141b required in foam formulation to obtain equivalent gas volumes. Using the same gas volumes as CFC- 11, CFC-123 and CFC-141b gave poorer flowability resulting in higher foam densi ties. With CFC-123, depending on the formulation, the nature of the isocyanate, the chemical structure and on the technique of foam preparation, there was a remarkable difference in densities and physical properties. The highest densities and the poorest physical properties were found in PMDI polyurethane foams because of a plasticiz ing effect of the CFC-123 in the polymer. However, in TDI polyurethane foams, densities and properties were more comparable to foams with CFC-11. CFC-123 also showed good performance in rigid polyisocyanurate foams. In all systems, CFC- 141b was closer to CFC-11 m overall properties. Both alternatives produced as theoretically expected, higher k-factor foams than CFC-11. In corresponding foam systems, we measured up to 15 percent higher ther mal conductivities. The k-value retention of foams made with CFC-123 and CFC- 141b appeared to be similar to CFC-11. The formulations tested were developed originally for use with CFC-11. To improve the performance of the alternatives as blowing agents in rigid polyure thane appliance foams, adjustments and optimization of the formulations will be nec essary.

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