Resistance-foil strain-gage technology as applied to composite materials
A general review of existing strain-gage technologies as applied to orthotropic-composite materials is given. The specific topics addressed are gage-bonding procedures, transverse-sensitivity effects, errors due to gage misalignment, and temperature-compensation methods. The discussion is supplemented by numerical examples where appropriate. It is shown that the orthotropic behavior of composites can result in experimental error which would not be expected based on practical experience with isotropic materials. In certain cases, the transverse sensitivity of strain gages and/or slight gage misalignment can result in strain-measurement errors exceeding 50 percent.
Damage Quantification in Metal Matrix Composites
An experimental procedure is presented to quantify damage in terms of microcrack density. This is accomplished by experimentally evaluating the components of a second-order damage tensor for a metal matrix composite material. The procedure involves the use of a scanning electron microscope and image analyzing software to quantify physical damage features found on a representative volume element. These features are quantified in terms of crack density, which is used in developing the second-order damage tensor. This procedure is applied to a titanium aluminide SiC-reinforced laminate. Laminates of the following staking sequences, (0/90)s and (±45)s, are tested under uniaxial tensile loadings. Damage evolution is obtained by loading the specimens over a range of load intensities from rupture load down to 70% rupture load. A proposed formulation for a coupled anisotropic damage model for the inelastic response of composite materials is presented in this work.
Joint application of time — Temperature and time — Stress analogies to constructing unified curves
The possibility of constructing unified curves by joint application of time—temperature and time—stress analogies has been examined. It has been shown that by using this method the time scale can be expanded in constructing the unified curves that serve as models of long-time creep of material on the basis of short-time tests. The dependence of the influencing factorsaT andaσ on stress and temperature has been studied.