Temperature dependent mechanical properties of composite materials and uncertainties in experimental measurements.

摘要

A new method for efficient determination of multiple material property values and improved techniques for reduction in experimental uncertainty were developed for use on composite and lightweight materials that perform under extreme temperatures and sustained load. The method calls for use of tension specimens only in determining the material properties, using a specially designed chamber with both cryogenic and high temperature testing capabilities. Mechanical properties of fiber reinforced composite materials were determined, such as transverse modulus (E2) and shear modulus (G12). Specially designed double notch tension specimens and shear strain gages were used to determine the shear properties in composites in a unique and more efficient way. A robust set of data from cryogenic to elevated temperatures for the two material properties of fiber reinforced composite materials was obtained and reported.; The fracture behavior of single crystal metallic materials was also investigated at room temperature. The Brazilian Disk Specimen (BDS) was proposed to study mode I, mode II and mixed mode fracture of these materials. During the study, questions arose concerning the effect of load misalignment on the stress field at the crack tip and crack propagation. To isolate the loading effects from the crystallographic effects, a systematic experimental study was conducted on aluminum specimens to characterize the effect of load misalignment and specimen orientation in the linear range as well as in the plastic range.