Bibliography: pages 92-98. / In this thesis a simplified analysis procedure is developed, in which creep laws are decoupled from damage laws, for the purposb of constructing methods of use in the early stages of high temperature design. The procedure is based on the creep and damage laws proposed by Kachanov and Rabotnov. The creep laws are normalised. with respect to a convenient normalising stress. As a consequence of this normalisation, the dependence of the creep law on the stress constant, the time and temperature functions, and the actual load level is removed. In addition, if the reference stress of the component is chosen as the normalising stress, the creep law becomes insensitive to the stress exponent. The non-dimensional creep laws are then implemented in a standard finite element scheme, from which the results of a stationary state creep analysis are then in non-dimensional form. In order to estimate rupture times, the maximum stationary stresses in a component are used together with the damage laws. Conservative failure criteria are derived from the creep and damage laws to extend the method to residual life assessment and damage monitoring. The procedure is illustrated and tested against simple examples and case studies.

The main source of the time-dependent behavior of fiber-reinforced composites is their polymeric matrix, which causes concerns about their long term durability. Although for composites where organic fibers such as Graphite are used, the fibers are also a contributing factor. A composite material may exhibit an appreciable amount of creep, depending on the state of stress and temperature. Viscoelastic flow in the matrix and internal flaw formation and growth are the main sources of this creep. Thus a study was made on the viscoelastic behavior of GI/BMI fiber reinforced composite. An experimental method for testing a large number of composite materials in compression was developed. The samples were tested according to the test matrix consisting of combinations of static and cyclic loads and temperatures. The fixtures were calibrated to check the validity of measurements and reproducibility of results. Stress gradients were caused by frictional effects between the fixture and samples. The modulus change of samples over a period of time were studied. Bending parameters in samples were measured and analyzed for different stresses, clamping forces, temperatures and time. Mechanical models were used to explain the basic principles behind creep of a viscoelastic material followed by a theoretical explanation and study of creep. The linear and non-linear viscoelastic constants were studied and a methodology to analyze these results was presented. The linear and non-linear constants were used in a prediction model and predictions of a composite creep strain with time were made. Creep data obtained tor [45/0/-45/90]������ for a period of three months were compared to the prediction model. / Graduation date: 1994