Showing papers on "Micromechanics published in 1977"
TL;DR: In this paper, the micromechanics of crack initiation and early growth in 4340 steel are studied using the SEM, and it is found that growth is discontinuous and transgranular, with the distance between growth steps corresponding to the prior austenite grain size spread.
85 citations
TL;DR: In this paper, the Jones-Nelson strain energy based nonlinear mechanical property model is extended to treat all nonlinearities of fiber-reinfor ced composites, and the predicted strains are also close to strains predicted by Hahn and Tsai, who use a material model with a single nonlinearity.
Abstract: Fiber-reinforced composite materials generally exhibit nonlinear stress-strain behavior in at least one of the principal material directions. For example, boron/epoxy and graphite/epoxy have highly nonlinear shear behavior. Moreover, boron/aluminum has nonlinear behavior transverse to the fibers as well as a shear nonlinearity, and carbon/carbon has nonlinearities in all principal material directions. The Jones-Nelson strain energy based nonlinear mechanical property model is extended to treat all nonlinearities of fiber-reinfor ced composites. The basic model will converge only up to a specific strain energy value. That limitation is eased by using new extrapolations of the stress-strain curve and mechanical property - energy curve for strain energies above available stress-strain data. These extrapolations are necessary because the strain energies of biaxial loading exceed the strain energies of uniaxial loading under which the properties are defined and because the maximum strain energies under uniaxial loading are different in the various principal directions due to orthotropy. Strains predicted with the new material model correlate well with strains measured by Cole and Pipes in uniaxial off-axis loading of boron/epoxy and graphite/epoxy. The predicted strains are also close to strains predicted by Hahn and Tsai, who use a material model with a single (shear) nonlinearity. Our model can be used for the several nonlinearities of boron/aluminu m and carbon/carbon; therefore, it is more widely applicable than the Hahn and Tsai model.
66 citations
TL;DR: In this article, the vibration characteristics of a composite fan blade for high-tip speed applications were determined theoretically and the results compared with measured data using a computerized capability consisting of NASTRAN coupled with composite mechanics by way of pre- and postprocessors.
Abstract: The vibration characteristics of a composite fan blade for high-tip-speed applications were determined theoretically and the results compared with measured data. The theoretical results were obtained using a computerized capability consisting of NASTRAN coupled with composite mechanics by way of pre- and postprocessors. The predicted vibration frequencies and mode shapes were in reasonable agreement with the measured data. Theoretical results showed that different laminate configurations from the same composite system had only small effects on the blade frequency. However, the use of adhesively bonded titanium/beryllium laminar composites may improve considerably the blade vibration characteristics.
18 citations
01 Jan 1977
TL;DR: In this article, an integrated theory is developed for predicting the hydrothermomechanical (HDTM) response of fiber composite components based on a combined theoretical and experimental investigation, which is structured to assess the combined hydrothermal effects on the mechanical properties of unidirectional composites loaded along the material axis and off-axis.
Abstract: An integrated theory is developed for predicting the hydrothermomechanical (HDTM) response of fiber composite components. The integrated theory is based on a combined theoretical and experimental investigation. In addition to predicting the HDTM response of components, the theory is structured to assess the combined hydrothermal effects on the mechanical properties of unidirectional composites loaded along the material axis and off-axis, and those of angleplied laminates. The theory developed predicts values which are in good agreement with measured data at the micromechanics, macromechanics, laminate analysis and structural analysis levels.
5 citations
TL;DR: In this paper, an analytical system was developed for prediction of the onset and progress of plastic flow of oriented fiber composite materials in which both externally applied complex stress states and stress raisers were present.
Abstract: An analytical system was developed for prediction of the onset and progress of plastic flow of oriented fiber composite materials in which both externally applied complex stress states and stress raisers were present. The predictive system was a unique combination of two numerical systems, the “SAAS II” finite element analysis system and a micromechanics finite element program. The SAAS II system was used to generate the three-dimensional stress distributions, which were used as the input into the finite element micromechanics program. Appropriate yielding criteria were then applied to this latter program. The accuracy of the analytical system was demonstrated by the agreement between the analytically predicted and the experimentally measured flow values of externally notched tungsten wire reinforced copper oriented fiber composites, in which the fiber fraction was 50 vol pct.