The influence of composition and thermomechanical condition on mechanical properties of TaC and TaB strengthened chromium
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Filippi, A. M.↗
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Thermomechanical coupling in fatigue fracture of viscoelastic materials
Subcritical crack growth in a linear viscoelastic material subjected to cyclic loading is investigated starting with the thermodynamic power balance. Physically, it is supposed that the subcritical slow crack growth is due to local weakening of the material in the neighborhood of the crack tip. Under fatigue loading it is assumed that all energy dissipation goes into heat and that this heat build-up is the dominant irreversible process governing crack growth. The cycle averaged temperature distribution around the crack tip is obtained from local application of the first law of thermodynamics (i.e., conservation of energy). The analysis leads to the solution of a nonlinear integro-differential equation for crack length as a function of time which is coupled with the local energy equation. A regular perturbation technique is used to obtain an analytical solution which compares very well with experimental results.
Hufferd, W. L.↗
Effects of thermomechanical processing on strength and toughness of Fe-12Ni reactive metal alloys at 77K
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Stephens, J. R.↗
Thermomechanical response of Gr/Pi composites
The effects of temperature changes upon the stresses and strains in composite laminates having carbon fibers in a polyimide matrix were evaluated. Composites having laminae in which there were nonlinear stress-strain relations for stresses transverse to the fibers and for axial shear stresses were treated. Material properties were considered to be temperature dependent. Separately, the effects of laminae viscoelastic response were also treated. The results suggest that, for this material, nonlinearities due either to stress or time dependent effects do not appear to be of major practical importance for conventional high temperature composite structures.
Rosen, B. W.↗
Influence of thermomechanical processing on elevated temperature slow plastic flow properties of B2 aluminide Fe-39.8at.% Al
A study of the elevated temperature slow plastic flow properties of the B2 aluminide Fe-39.8at.% Al was undertaken. Polycrystalline materials possessing several different microstructures were produced by the hot extrusion of prealloyed powder and, in some cases, postextrusion heat treatments. Compression tests were conducted in air at 1200, 1300 and 1400 K. Such testing revealed that the extrusion temperature affected the active deformation mechanisms where material extruded at 1505 K had a stress exponent about twice that of the intermetallic extruded at 1200 K. Grain size refinement to about 10 microns was found to strengthen the Fe-39.8at.% Al material; unfortunately, the effectiveness of such strengthening is limited to a homologous temperature of about 0.75 for strain rates of commercial interest (less than 10 to the -7th/sec).
Whittenberger, J. D.↗
A thermomechanical model for energy propagation in a solid-fluid-solid system with one boundary in relative motion
A model is developed to predict the behavior of a thin fluid film in the wake of a tool in relative motion with respect to the table. Computational procedures are developed and limitations of the model are discussed. In general the fluid-interface temperature is controlled by conduction into the table. From the numerical results four regimes are identified: convective cooling, partial evaporation of the fluid film, extended evaporation due to a limiting evaporative heat flux, and surface dryout due to total evaporation of the fluid layer. These regimes are qualitatively illustrated in terms of the parameters film thickness, viscosity, and relative velocity.
Braun, M. J.↗
On thermomechanical testing in support of constitutive equation development for high temperature alloys
Three major categories of testing are identified that are necessary to provide support for the development of constitutive equations for high temperature alloys. These are exploratory, charactrization and verification tests. Each category is addressed and specific examples of each are given. An extensive, but not exhaustive, set of references is provided concerning pertinent experimental results and their relationships to theoretical development. This guide to formulating a meaningful testing effort in support of consitutive equation development can also aid in defining the necessary testing equipment and instrumentation for the establishment of a deformation and structures testing laboratory.
Robinson, D. N.↗
Thermomechanical evolution of oceanic fracture zones
To explain the topographic and gravitational signals of fracture zones (FZs), a realistic model is developed and compared with Seasat altimeter data across three major FZs. The model is based on the thermal, subsidence, and mechanical models of the oceanic lithosphere. The model is used to calculate the FZ topography and the evolution of the geoid signature across a FZ. When lithospheric flexure is included, the model explains the persistence of sharp FZ geoid steps on old seafloor as well as the asymmetry of the geoid steps across major FZs. The model does not explain the disappearance of the thermal part of the FZ geoid signature. The model profiles are used to access the various techniques for estimating the overall geoid offsets across FZs. It is shown that steps may be underestimated by as much as 50 percent. These predictions, if correct, will force reinterpretation of published geoid height versus age data derived from altimeter profiles across FZs.
Sandwell, D. T.↗
Thermomechanical design criteria for ceramic-coated surfaces
Some early history of ceramic applications is presented. Finite element modeling of components to determine service and fabrication loads found inelastic behavior and residual stresses to be significant to component life. Inelastic behavior mitigates peak strains but enhances residual strains. Results of furnace, Mach 0.3 burner, and engine tests are discussed and categorized into design criteria (loading, geometry, fabrication, materials, analysis, and testing). These design rules and finite element analyses are brought to bear on two test cases: turboshaft engine seals, and rocket thrust chambers.
Mullen, R. L.↗
Thermomechanical modeling of the Colorado Plateau-Basin and range transition zone
The Colorado Plateau (CP) basin and range (B & R) boundary is marked by a transition zone on the order of 75 to 150 km in width. As one moves westward across this transition from the CP interior to the B & R there is a variation in the surface topography, surface heat flow, Bouguer gravity, seismicity, and crustal structure. This transition extends eastward into the western CP from the Wastach-Hurricane fault line and is largely coincident with the high plateaus of Utah and the Wasatch Mountains. It has been suggested that this transition zone marks a thermal and tectonic encroachment of the CP by the B & R. A simple two dimensional numerical model of the thermal regime for the transition zone was constructed to test the hypothesis that the observed geophysical signatures across the transition are due to lateral heat conduction from steady state uniform extension within the B & R lithosphere. Surface heat flow, uplift due to flexure from thermal buoyant loading, and regional Bouguer gravity are computed for various extension rates, crustal structures, and compensation depths.
Londe, M. D.↗
Thermomechanical Properties Indicate Degree of Epoxy Cure
Glass-transition temperature and density increase as reaction proceeds. Cured epoxy resin found to be related to extent of cure. In addition to providing insight into chemical reactions of curing, relationships show potential for process monitoring and control in fabrication of strong, lightweight composite parts.
Cizmecioglu, Muzaffer↗
Thermomechanical effects in high-speed seal rubs
The analytical effort was aimed at development of numerical model of thermal and mechanical phenomena which occur during seal rub. Finite element programs were develped for studying the temperatures that result from frictional heating during rubs, and the plastic deformation which is caused by rub forces. The experiment phase was originally intended to aid in verification of the results of the analytical model. Experimental techniques were developed for measuring surface temperatures and deformations during single pass rubs. Modifications were made to the device to permit testing at both high and cryogenic temperatures. The results from the experiments are discussed.
Kennedy, Francis E., Jr.↗
Thermomechanical force application
The present work conducted in Summer 1987 continues investigations on Thermal Components for 1.8 K Space Cryogenics (Grant NAG 1-412 of 1986). The topics addressed are plug characterization efforts in a small pore size regime of sintered metal plugs, characterization in the nonlinear regime, temperature profiles in a heat supply unit for a fountain effect pump and modeling efforts.
Frederking, T. H. K.↗
Use of inelastic strain as a basis for analyzing thermomechanical test data
It was shown that the proposed data analysis method, based on inelastic strain-time response, can be used effectively to represent cyclic response at elevated temperatures for Hastelloy-X. A high level of confidence in this method was built by making comparisons of the experimental and fitted data in two forms. Because of this level of confidence, the analysis was taken one step further and inelastic strain rates were calculated from the derivatives of the fit equations.
Bartolotta, P. A.↗
Total strain version of strainrange partitioning for thermomechanical fatigue at low strains
A new method is proposed for characterizing and predicting the thermal fatigue behavior of materials. The method is based on three innovations in characterizing high temperature material behavior: (1) the bithermal concept of fatigue testing; (2) advanced, nonlinear, cyclic constitutive models; and (3) the total strain version of traditional strainrange partitioning.
Halford, G. R.↗
Nonlinear response of composite tubes under combined thermomechanical loading
An analytical investigation was conducted to study the effect of material nonlinearities on the response of graphite/epoxy composite tubes subjected to combined axial and torsional loading. The endochronic theory of Valanis (1971) was employed to model the nonlinear response of the individual graphite/epoxy layers. Thermal loading was included in the analysis in order to incorporate the effect of residual stresses on subsequent mechanical response. The predictions of the analytical model are compared with the response of P75/934 graphite/epoxy tubes with a stacking sequence of (15/0/+/- 10/0/-15)s. Good qualitative correlation between analysis and experiment is obtained when microstructural details of the tube's cross-section, residual stresses and nonlinear effects are taken into account.
Derstine, M. S.↗
A simple test for thermomechanical evaluation of ceramic fibers
A simple bend stress relaxation (BSR) test was developed to measure the creep related properties of ceramic fibers and whiskers. The test was applied to a variety of commercial and developmental Si based fibers to demonstrate capabilities and to evaluate the relative creep resistance of the fibers at 1200 to 1400 C. The implications of these results and the advantages of the BSR test over typical tensile creep tests are discussed.
Morscher, Gregory N.↗
Plasticity analysis of fibrous composite laminates under thermomechanical loads
Elastic-plastic behavior of fibrous composite laminates is analyzed for coupled in-plane mechanical loads and uniform thermal changes. Constitutive equations of the individual fibrous layers are derived from a vanishing fiber diameter model that represents the essential axial constraint between the phases. This permits derivation of closed form equations for the overall yield condition, stress concentration factors, and instantaneous compliance. Thermoelastic properties of the phases and yield stress of the matrix phase are functions of temperature. The effect of the model assumptions on the predicted behavior of composite laminates is examined by comparing the calculated response under cyclic thermal changes to available theoretical results and experimental measurements.
Bahei-El-din, Yehia A.↗