Statistical evaluation of the variation in laminated composite properties resulting from ply misalignment

Production tolerances must allow for deviations in ply angles in composite laminates. A Monte Carlo simulation of these deviations has been used to evaluate the distribution of properties for two symmetric laminates formed from P7SS/930 (graphite/epoxy) uniaxial composite plies. Although the nominal laminate mechanical properties are essentially identical for the two cases considered, the consistency of these properties varies with the layup. This analysis was used to select the laminate which provides the greatest consistency in Critical properties. Techniques used in this evaluation may be applied to any general laminate. This type of analysis is particularly useful in laminate evaluation whenever mechathcal properties must be tightly controlled, as typically required for optical support structures. For any given ply angle alignment tolerance and mechanical property variation, the reject rate can be estimated. Two types of ply misalignment are considered. In the first case, the alignment error of each layer is considered to be random. In the second case, systematic errors such as those which might be caused by imperfections in the cutting template that would affect all plies at a specified angle are considered. Graphs are used to present a statistical summary of the results. A program for IBM-PC1 computers using a commercially available matrix manipulation program has been developed to perform the analysis.