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Sample records for creep buckling behavior

  1. Non-isothermal buckling behavior of viscoplastic shell structures

    NASA Technical Reports Server (NTRS)

    Riff, Richard; Simitses, G. J.

    1988-01-01

    Described are the mathematical model and solution methodologies for analyzing the structural response of thin, metallic elasto-viscoplastic shell structures under large thermomechanical loads and their non-isothermal buckling behavior. Among the system responses associated with these loads and conditions are snap-through, buckling, thermal buckling, and creep buckling. This geometric and material nonlinearities (of high order) can be anticipated and are considered in the model and the numerical treatment.

  2. Effects of state recovery on creep buckling under variable loading

    NASA Technical Reports Server (NTRS)

    Robinson, D. N.; Arnold, S. M.

    1986-01-01

    Structural alloys embody internal mechanisms that allow recovery of state with varying stress and elevated temperature, i.e., they can return to a softer state following periods of hardening. Such material behavior is known to strongly influence structural response under some important thermomechanical loadings, for example, that involving thermal ratchetting. The influence of dynamic and thermal recovery on the creep buckling of a column under variable loading is investigated. The column is taken as the idealized (Shanley) sandwich column. The constitutive model, unlike the commonly employed Norton creep model, incorporates a representation of both dynamic and thermal (state) recovery. The material parameters of the constitutive model are chosen to characterize Narloy Z, a representative copper alloy used in thrust nozzle liners of reusable rocket engines. Variable loading histories include rapid cyclic unloading/reloading sequences and intermittent reductions of load for extended periods of time; these are superimposed on a constant load. The calculated results show that state recovery significantly affects creep buckling under variable loading. Structural alloys embody internal mechanisms that allow recovery of state with varying stress and time.

  3. Non-isothermal elastoviscoplastic snap-through and creep buckling of shallow arches

    NASA Technical Reports Server (NTRS)

    Simitses, G. J.; Riff, R.

    1987-01-01

    The problem of buckling of shallow arches under transient thermomechanical loads is investigated. The analysis is based on nonlinear geometric and constitutive relations, and is expressed in a rate form. The material constitutive equations are capable of reproducing all non-isothermal, elasto-viscoplastic characteristics. The solution scheme is capable of predicting response which includes pre and postbuckling with creep and plastic effects. The solution procedure is demonstrated through several examples which include both creep and snap-through behavior.

  4. Stochastic behavior of nanoscale dielectric wall buckling

    NASA Astrophysics Data System (ADS)

    Friedman, Lawrence H.; Levin, Igor; Cook, Robert F.

    2016-03-01

    The random buckling patterns of nanoscale dielectric walls are analyzed using a nonlinear multi-scale stochastic method that combines experimental measurements with simulations. The dielectric walls, approximately 200 nm tall and 20 nm wide, consist of compliant, low dielectric constant (low-k) fins capped with stiff, compressively stressed TiN lines that provide the driving force for buckling. The deflections of the buckled lines exhibit sinusoidal pseudoperiodicity with amplitude fluctuation and phase decorrelation arising from stochastic variations in wall geometry, properties, and stress state at length scales shorter than the characteristic deflection wavelength of about 1000 nm. The buckling patterns are analyzed and modeled at two length scales: a longer scale (up to 5000 nm) that treats randomness as a longer-scale measurable quantity, and a shorter-scale (down to 20 nm) that treats buckling as a deterministic phenomenon. Statistical simulation is used to join the two length scales. Through this approach, the buckling model is validated and material properties and stress states are inferred. In particular, the stress state of TiN lines in three different systems is determined, along with the elastic moduli of low-k fins and the amplitudes of the small-scale random fluctuations in wall properties—all in the as-processed state. The important case of stochastic effects giving rise to buckling in a deterministically sub-critical buckling state is demonstrated. The nonlinear multiscale stochastic analysis provides guidance for design of low-k structures with acceptable buckling behavior and serves as a template for how randomness that is common to nanoscale phenomena might be measured and analyzed in other contexts.

  5. Stochastic behavior of nanoscale dielectric wall buckling

    PubMed Central

    Friedman, Lawrence H.; Levin, Igor; Cook, Robert F.

    2016-01-01

    The random buckling patterns of nanoscale dielectric walls are analyzed using a nonlinear multi-scale stochastic method that combines experimental measurements with simulations. The dielectric walls, approximately 200 nm tall and 20 nm wide, consist of compliant, low dielectric constant (low-k) fins capped with stiff, compressively stressed TiN lines that provide the driving force for buckling. The deflections of the buckled lines exhibit sinusoidal pseudoperiodicity with amplitude fluctuation and phase decorrelation arising from stochastic variations in wall geometry, properties, and stress state at length scales shorter than the characteristic deflection wavelength of about 1000 nm. The buckling patterns are analyzed and modeled at two length scales: a longer scale (up to 5000 nm) that treats randomness as a longer-scale measurable quantity, and a shorter-scale (down to 20 nm) that treats buckling as a deterministic phenomenon. Statistical simulation is used to join the two length scales. Through this approach, the buckling model is validated and material properties and stress states are inferred. In particular, the stress state of TiN lines in three different systems is determined, along with the elastic moduli of low-k fins and the amplitudes of the small-scale random fluctuations in wall properties—all in the as-processed state. The important case of stochastic effects giving rise to buckling in a deterministically sub-critical buckling state is demonstrated. The nonlinear multiscale stochastic analysis provides guidance for design of low-k structures with acceptable buckling behavior and serves as a template for how randomness that is common to nanoscale phenomena might be measured and analyzed in other contexts. PMID:27330220

  6. Buckling Behavior of Individual and Bundled Microtubules

    PubMed Central

    Soheilypour, Mohammad; Peyro, Mohaddeseh; Peter, Stephen J.; Mofrad, Mohammad R.K.

    2015-01-01

    As the major structural constituent of the cytoskeleton, microtubules (MTs) serve a variety of biological functions that range from facilitating organelle transport to maintaining the mechanical integrity of the cell. Neuronal MTs exhibit a distinct configuration, hexagonally packed bundles of MT filaments, interconnected by MT-associated protein (MAP) tau. Building on our previous work on mechanical response of axonal MT bundles under uniaxial tension, this study is focused on exploring the compression scenarios. Intracellular MTs carry a large fraction of the compressive loads sensed by the cell and therefore, like any other column-like structure, are prone to substantial bending and buckling. Various biological activities, e.g., actomyosin contractility and many pathological conditions are driven or followed by bending, looping, and buckling of MT filaments. The coarse-grained model previously developed in our lab has been used to study the mechanical behavior of individual and bundled in vivo MT filaments under uniaxial compression. Both configurations show tip-localized, decaying, and short-wavelength buckling. This behavior highlights the role of the surrounding cytoplasm and MAP tau on MT buckling behavior, which allows MT filaments to bear much larger compressive forces. It is observed that MAP tau interconnections improve this effect by a factor of two. The enhanced ability of MT bundles to damp buckling waves relative to individual MT filaments, may be interpreted as a self-defense mechanism because it helps axonal MTs to endure harsher environments while maintaining their function. The results indicate that MT filaments in a bundle do not buckle simultaneously implying that the applied stress is not equally shared among the MT filaments, that is a consequence of the nonuniform distribution of MAP tau proteins along the bundle length. Furthermore, from a pathological perspective, it is observed that axonal MT bundles are more vulnerable to failure in

  7. Creep and creep-rupture behavior of Alloy 718

    SciTech Connect

    Brinkman, C.R.; Booker, M.K.; Ding, J.L.

    1991-01-01

    Data obtained from creep and creep-rupture tests conducted on 18 heats of Alloy 718 were used to formulate models for predicting high temperature time dependent behavior of this alloy. Creep tests were conducted on specimens taken from a number of commercial product forms including plate, bar, and forgoing material that had been procured and heat treated in accordance with ASTM specifications B-670 or B-637. Data were obtained over the temperature range of 427 to 760{degree}C ad at test times to about 87,000 h. Comparisons are given between experimental data and the analytical models. The analytical models for creep-rupture included one based on lot-centering regression analysis and two based on the Minimum Commitment Method. A master'' curve approach was used to develop and equation for estimating creep deformation up to the onset of tertiary creep. 11 refs., 13 figs.

  8. Dynamic buckling behavior of thin metal film lines from substrate

    NASA Astrophysics Data System (ADS)

    Wu, Dan; Xie, Huimin; Wang, Heling; Zhang, Jie; Li, Chuanwei

    2014-10-01

    The dynamic buckling behavior of thin films from substrate is studied in this work. The experimental results show that the buckling morphology of the constantan film lines from the polymer substrate is inconsistent and non-sinusoidal, which is different from the sinusoidal form of the buckling morphology under static loads. The plastic deformation of the film lines results in the non-sinusoidal buckling morphology and residual deformation when unloaded. Finite element modeling results with regard to the plastic dissipation of the constantan film lines reveal that the plastic dissipation suppresses the buckling-driven delaminating under impact loads. This study will give some new perspectives on the buckling behavior of thin film from substrate.

  9. Creep and relaxation behavior of Inconel-617

    SciTech Connect

    Osthoff, W.; Ennis, P.J.; Nickel, H.; Schuster, H.

    1984-08-01

    The static and dynamic creep behavior of Inconel alloy 617 has been determined in constant load creep tests, relaxation tests, and stress reduction tests in the temperature range 1023 to 1273 K. The results have been interpreted using the internal stress concept: The dependence of the internal stress on the applied stress and test temperature was determined. In a few experiments, the influence of cold deformation prior to the creep test on the magnitude of the internal stress was also investigated. It was found that the experimentally observed relaxation behavior could be more satisfactorily described using the Norton creep equation modified by incorporation of the internal stress than by the conventional Norton creep equation.

  10. Creep behavior of niobium alloy PWC-11

    NASA Technical Reports Server (NTRS)

    Titran, R. H.; Moore, T. J.; Grobstein, T. L.

    1987-01-01

    The high vacuum creep and creep-rupture behavior of a Nb-1Zr-.1C alloy (PWC 11) was investigated at 1350 and 1400 K with an applied stress of 40 MPa. The material was tested in the following four conditions: annealed (1 hr 1755 K/2 hr 1475 K); annealed plus EB welded; annealed plus aged for 1000 hr at 1350 or 1400 K; and annealed, welded, and aged. It was found that the material in the annealed state was the most creep-resistant condition tested, and that aging the alloy for 1000 hr without an applied stress greatly reduced that strength; however, it was still approximately three times as creep resistant as Nb-1Zr. Additionally, the EB weld region was stronger than the base metal in each condition tested, and phase extraction of the dispersed precipitate revealed the presence of a 70%ZrC-30%NbC cubic monocarbide phase.

  11. Investigation of Buckling Behavior of Composite Shell Structures with Cutouts

    NASA Astrophysics Data System (ADS)

    Arbelo, Mariano A.; Herrmann, Annemarie; Castro, Saullo G. P.; Khakimova, Regina; Zimmermann, Rolf; Degenhardt, Richard

    2015-12-01

    Thin-walled cylindrical composite shell structures can be applied in space applications, looking for lighter and cheaper launcher transport system. These structures are prone to buckling under axial compression and may exhibit sensitivity to geometrical imperfections. Today the design of such structures is based on NASA guidelines from the 1960's using a conservative lower bound curve generated from a database of experimental results. In this guideline the structural behavior of composite materials may not be appropriately considered since the imperfection sensitivity and the buckling load of shells made of such materials depend on the lay-up design. It is clear that with the evolution of the composite materials and fabrication processes this guideline must be updated and / or new design guidelines investigated. This need becomes even more relevant when cutouts are introduced to the structure, which are commonly necessary to account for access points and to provide clearance and attachment points for hydraulic and electric systems. Therefore, it is necessary to understand how a cutout with different dimensions affects the buckling load of a thin-walled cylindrical shell structure in combination with other initial geometric imperfections. In this context, this paper present some observations regarding the buckling load behavior vs. cutout size and radius over thickness ratio, of laminated composite curved panels and cylindrical shells, that could be applied in further recommendations, to allow identifying when the buckling of the structure is dominated by the presence of the cutout or by other initial imperfections.

  12. The dynamic aspects of thermo-elasto-viscoplastic snap-through and creep buckling phenomena

    NASA Technical Reports Server (NTRS)

    Riff, R.; Simitses, G. J.

    1987-01-01

    Use of a mathematical model and solution methodology, to examine dynamic buckling and dynamic postbuckling behavior of shallow arches and spherical caps made of a realistic material and undergoing non-isothermal, elasto-viscoplastic deformation was examined. Thus, geometric as well as material type nonlinearities of higher order are included in this analysis. The dynamic stability problem is studied under impulsive loading and suddenly applied loading with loads of constant magnitude and infinite duration. A finite element model was derived directly from the incrementally formulated nonlinear shell equations, by using a tensor-oriented procedure. As an example of the results, the time history of the midspan displacement of a damped shallow circular arch is presented.

  13. Buckling behavior of long anisotropic plates subjected to combined loads

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1995-01-01

    A parametric study is presented of the buckling behavior of infinitely long symmetrically laminated anisotropic plates subjected to combined loads. The study focuses on the interaction of a subcritical (stable) secondary loading state of constant magnitude and a primary destabilizing load that is increased in magnitude until buckling occurs. The loads, considered in this report are uniform axial compression, pure in-plane bending, transverse tension and compression, and shear. Results are presented that were obtained by using a special purpose nondimensional analysis that is well suited for parametric studies of clamped and simply supported plates. In particular, results are presented for a +/- 45(sub S) graphite-epoxy laminate that is highly anisotropic and representative of a laminate used for spacecraft applications. In addition, generic buckling-design charts are presented for a wide range of nondimensional parameters that are applicable to a broad class of laminate constructions. These results show the general behavioral trends of specially orthotropic plates and the effects of flexural anisotropy on plates subjected to various combined loading conditions. An important finding of the present study is that the effects of flexural anisotropy on the buckling resistance of a plate can be significantly more important for plates subjected to combined loads than for plates subjected to single-component loads.

  14. Creep behavior of uranium carbide-based alloys

    NASA Technical Reports Server (NTRS)

    Seltzer, M. S.; Wright, T. R.; Moak, D. P.

    1975-01-01

    The present work gives the results of experiments on the influence of zirconium carbide and tungsten on the creep properties of uranium carbide. The creep behavior of high-density UC samples follows the classical time-dependence pattern of (1) an instantaneous deformation, (2) a primary creep region, and (3) a period of steady-state creep. Creep rates for unalloyed UC-1.01 and UC-1.05 are several orders of magnitude greater than those measured for carbide alloys containing a Zr-C and/or W dispersoid. The difference in creep strength between alloyed and unalloyed materials varies with temperature and applied stress.

  15. Torque-induced buckling behavior in stretched intertwined DNAs

    NASA Astrophysics Data System (ADS)

    Brahmachari, Sumitabha; Marko, John F.

    Two intertwined DNA molecules (a DNA 'braid') is a common occurrence in the cell and is a relevant substrate for the study of topoisomerase and recombination enzymes. Single molecule experiments have observed the signature of a buckling transition in braids under tensile and torsional stress. We present a free energy model for braided DNA to investigate the mechanical properties of these structures. Our model is based on the semi-flexible polymer model for double helix DNA and is in quantitative accord with the experiments. We identify coexistence of a force-extended state with a plectonemically buckled state, which is reminiscent of single supercoiled DNA behavior. However, the absence of an intrinsic twist modulus in braided DNA results in unique mechanical properties such as non-linear torque in the extended state. At the buckling transition, we predict a jump in the braid extension due to the plectoneme end loop which acts as a nucleation barrier. We investigate the effect of salt concentration on the mechanical response of braids, e.g. we find that buckling starts at a lower linking number for lower salt concentration, the opposite of what is seen for single supercoiled DNAs. Also, concentrations less than 20 mM monovalent salt favor formation of multiple plectoneme domains. NSF Grant: DMR-9734178.

  16. Buckling Behavior of Long Anisotropic Plates Subjected to Combined Loads

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1995-01-01

    A parametric study of the buckling behavior of infinitely long symmetrically laminated anisotropic plates subjected to combined loads is presented. The study focuses on the interaction of a stable subcritical secondary loading state of constant magnitude and a primary destabilizing load that is increased in magnitude until buckling occurs. The loads considered are uniform axial compression, pure inplane bending, transverse tension and compression, and shear. Results obtained using a special purpose plates with a significant potential for reducing structural nondimensional analysis that is well suited for parametric studies are presented for clamped and simply supported plates. In particular, results are presented for a (+/- 45)(sub s) graphite-epoxy laminate, and generic buckling design charts are presented for a wide range of non-dimensional parameters that are applicable to a broad class of laminate constructions. These results show the effects of flexural orthotropy and flexural anisotropy on plates subjected to various combined loading conditions. An important finding of the present study is that the effect of flexural anisotropy herein as flexural anisotropy on the buckling resistance of a plate can be increased significantly for certain types of combined loads.

  17. Long-Term Creep and Creep Rupture Behavior of Woven Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Haque, A.; Rahman, M.; Mach, A.; Jeelani, S.; Verrilli, Michael J. (Technical Monitor)

    2001-01-01

    Tensile creep behavior of SiC/SiNC ceramic matrix composites at elevated temperatures and at various stress levels have been investigated for turbine engine applications. The objective of this research is to present creep behavior of SiC/SiCN composites at stress levels above and below the monotonic proportional limit strength and predict the life at creep rupture conditions. Tensile creep-rupture tests were performed on an Instron 8502 servohydraulic testing machine at constant load conditions up to a temperature limit of 1000 C. Individual creep curves indicate three stages such as primary, secondary, and tertiary. The creep rate increased linearly at an early stage and then gradually became exponential at higher strains. The stress exponent and activation energy were also obtained at 700 and 1000 C. The specimen lifetime was observed to be 55 hrs at 121 MPa and at 700 C. The life span reduced to 35 hrs at 143 MPa and at 1000 C. Scanning electron microscopy observations revealed significant changes in the crystalline phases and creep damage development. Creep failures were accompanied by extensive fiber pullout, matrix cracking, and debonding along with fiber fracture. The creep data was applied to Time-Temperature-Stress superposition model and the Manson-Haferd parametric model for long-time life prediction.

  18. Creep behavior of Utah oil shale subject to uniaxial loading

    SciTech Connect

    Chong, K.P.; Dana, G.F.; Chen, J.L.

    1982-06-01

    This paper presents results of a study on the creep behavior of Utah oil shale. A Conbel Model 355 pneumatic driven testing machine is used. The set of duplicate test specimens required for creep testing were cut from a single oil shale layer using a wire saw to avoid any surface damage. A rheological model was developed for creep behavior of oil shale as a function of stress level and organic content. Data from creep testing and Fischer assay analyses were used to demonstrate correlation between various stress levels and organic contents for samples taken from the Mahogany Zone of the Parachute Creek Member in Utah's Cowboy Canyon.

  19. Creep contributes to the fatigue behavior of bovine trabecular bone.

    PubMed

    Bowman, S M; Guo, X E; Cheng, D W; Keaveny, T M; Gibson, L J; Hayes, W C; McMahon, T A

    1998-10-01

    Repetitive, low-intensity loading from normal daily activities can generate fatigue damage in trabecular bone, a potential cause of spontaneous fractures of the hip and spine. Finite element models of trabecular bone (Guo et al., 1994) suggest that both creep and slow crack growth contribute to fatigue failure. In an effort to characterize these damage mechanisms experimentally, we conducted fatigue and creep tests on 85 waisted specimens of trabecular bone obtained from 76 bovine proximal tibiae. All applied stresses were normalized by the previously measured specimen modulus. Fatigue tests were conducted at room temperature; creep tests were conducted at 4, 15, 25, 37, 45, and 53 degrees C in a custom-designed apparatus. The fatigue behavior was characterized by decreasing modulus and increasing hysteresis prior to failure. The hysteresis loops progressively displaced along the strain axis, indicating that creep was also involved in the fatigue process. The creep behavior was characterized by the three classical stages of decreasing, constant, and increasing creep rates. Strong and highly significant power-law relationships were found between cycles-to-failure, time-to-failure, steady-state creep rate, and the applied loads. Creep analyses of the fatigue hysteresis loops also generated strong and highly significant power law relationships for time-to-failure and steady-state creep rate. Lastly, the products of creep rate and time-to-failure were constant for both the fatigue and creep tests and were equal to the measured failure strains, suggesting that creep plays a fundamental role in the fatigue behavior of trabecular bone. Additional analysis of the fatigue strain data suggests that creep and slow crack growth are not separate processes that dominate at high and low loads, respectively, but are present throughout all stages of fatigue.

  20. Tensile creep behavior of polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.

    1993-01-01

    Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

  1. Tensile creep and creep-recovery behavior of a SiC-fiber-Si3N4-matrix composite

    NASA Technical Reports Server (NTRS)

    Holmes, John W.; Park, Yong H.; Jones, J. W.

    1993-01-01

    The tensile creep and creep-recovery behavior of a hot-pressed unidirectional SiC-fiber/Si3N4-matrix composite was investigated at 1200 C in air, in order to determine how various sustained and cyclic creep loading histories would influence the creep rate, accumulated creep strain, and the amount of strain recovered upon specimen unloading. The data accumulated indicate that the fundamental damage mode for sustained tensile creep at stresses of 200 and 250 MPa was periodic fiber fracture and that the creep life and the failure mode at 250 MPa were strongly influenced by the rate at which the initial creep stress was applied. Cyclic loading significantly lowered the duration of primary creep and the overall creep-strain accumulation. The implications of the results for microstructural and component design are discussed.

  2. Buckling of structures; Proceedings of the Symposium, Harvard University, Cambridge, Mass., June 17-21, 1974

    NASA Technical Reports Server (NTRS)

    Budiansky, B.

    1976-01-01

    The papers deal with such topics as the buckling and post-buckling behavior of plates and shells; methods of calculating critical buckling and collapse loads; finite element representations for thin-shell instability analysis; theory and experiment in the creep buckling of plates and shells; creep instability of thick shell structures; analytical and numerical studies of the influence of initial imperfections on the elastic buckling of columns; mode interaction in stiffened panels under compression; imperfection-sensitivity in the interactive buckling of stiffened plates; buckling of stochastically imperfect structures; and the Liapunov stability of elastic dynamic systems. A special chapter is devoted to design problems, including the design of a Mars entry 'aeroshell', and buckling design in vehicle structures. Individual items are announced in this issue.

  3. Computer program for predicting creep behavior of bodies of revolution

    NASA Technical Reports Server (NTRS)

    Adams, R.; Greenbaum, G.

    1971-01-01

    Computer program, CRAB, uses finite-element method to calculate creep behavior and predict steady-state stresses in an arbitrary body of revolution subjected to a time-dependent axisymmetric load. Creep strains follow a time hardening law and a Prandtl-Reuss stress-strain relationship.

  4. Bending and buckling behavior analysis of foamed metal circular plate.

    PubMed

    Fan, Jian Ling; Ma, Lian Sheng; Zhang, Lu; De Su, Hou

    2016-01-01

    This paper establishes a density gradient model along the thickness direction of a circular plate made of foamed material. Based on the first shear deformation plate theory, the result is deduced that the foamed metal circular plate with graded density along thickness direction yields axisymmetric bending problem under the action of uniformly distributed load, and the analytical solution is obtained by solving the governing equation directly. The analyses on two constraint conditions of edge radial clamping and simply supported show that the density gradient index and external load may affect the axisymmetric bending behavior of the plate. Then, based on the classical plate theory, the paper analyzes the behavior of axisymmetric buckling under radial pressure applied on the circular plate. Shooting method is used to obtain the critical load, and the effects of gradient nature of material properties and boundary conditions on the critical load of the plate are analyzed. PMID:27339281

  5. Mechanical behavior of low porosity carbonate rock: from brittle creep to ductile creep

    NASA Astrophysics Data System (ADS)

    Nicolas, A.; Fortin, J.; Gueguen, Y.

    2013-12-01

    Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this experimental study, we focus on the mechanical behavior of a low porosity (9%) white Tavel (France) carbonate rock (>98% calcite) at P-Q conditions beyond the elastic domain. It has been shown that in sandstones composed of quartz, cracks are developing under these conditions. However, in carbonates, calcite minerals can meanwhile also exhibit microplasticity. The samples were deformed in the triaxial cell of the Ecole Normale Superieure de Paris at effective confining pressures ranging from 35 MPa to 85 MPa and room temperature. Experiments were carried on dry and water saturated samples to explore the role played by the pore fluids. Time dependency was investigated by a creep steps methodology: at each step, differential stress was increased rapidly and kept constant for at least 24h. During these steps elastic wave velocities (P and S) and permeability were measured continuously. Our results show two different creep behaviors: (1) brittle creep is observed at low confining pressures, whereas (2) ductile creep is observed at higher confining pressures. These two creep behaviors have a different signature in term of elastic wave velocities and permeability changes. Indeed, in the brittle domain, the primary creep is associated with a decrease of elastic wave velocities and an increase of permeability, and no secondary creep is observed. In the ductile domain, the primary creep

  6. Accelerated characterization for long-term creep behavior of polymer

    NASA Astrophysics Data System (ADS)

    Zhao, Rongguo; Chen, Chaozhong; Li, Qifu; Luo, Xiyan

    2008-11-01

    Based on the observation that high stress results in increasing creep rate of polymeric material, which is analogous to the time-temperature equivalence, where high temperature accelerates the process of creep or relaxation of polymer, the time-stress equivalence is investigated. The changes of intrinsic time in polymer induced by temperature and stress are studied using the free volume theory, and a clock model based on the time-temperature and time-stress equivalence is constructed to predict the long-term creep behavior of polymer. Polypropylene is used for this work. The specimens with shape of dumbbell are formed via injection molding. The short-term creep tests under various stress levels are carried out at ambient temperature. The creep strains of specimens are modeled according to the concept of time-stress equivalence, and the corresponding stress shift factors are calculated. A master creep curve is built by the clock model. The result indicates that the time-stress superposition principle provides an accelerated characterization method in the laboratory. Finally, the time-dependent axial elongations at sustained stress levels, whose values are close to the tensile strength of polypropylene, are measured. The three phases of creep, i.e., the transient, steady state and accelerated creep phases, are studied, and the application and limitation of the time-stress superposition principle are discussed.

  7. Creep behavior of abaca fibre reinforced composite material

    SciTech Connect

    Tobias, B.C.; Lieng, V.T.

    1996-12-31

    This study investigates the creep behavior of abaca fibre reinforced composite lamina. The optimum proportions of constituents and loading conditions, temperature and stresses, are investigated in terms of creep properties. Lamina with abaca fibre volume fractions of 60, 70 and 80 percent, embedded in polyester resin were fabricated. Creep tests in tension at three temperature levels 20{degrees}C, 100{degrees}C and 120{degrees}C and three constant stress levels of 0. 1 MPa, 0. 13 Mpa and 0. 198 MPa using a Dynamic Mechanical Analyzer (DMA) were performed. The creep curves show standard regions of an ideal creep curve such as primary and secondary creep stage. The results also show that the minimum creep rate of abaca fibre reinforced composite increases with the increase of temperature and applied stress. Plotting the minimum creep rate against stress, depicts the variations of stress exponents which vary from 1.6194 at 20{degrees}C to 0.4576 at 120{degrees}C.

  8. Creep and Environmental Effects on High Temperature Creep-Fatigue Behavior of Alloy 617

    SciTech Connect

    L. J. Carroll; C. Cabet; R. Madland; R. Wright

    2011-06-01

    Alloy 617 is the leading candidate material for Intermediate Heat Exchanger (IHX) of a Very High Temperature Reactor (VHTR), expected to have an outlet temperature as high as 950 C. System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior in both air and impure helium, representative of the VHTR primary coolant. Strain controlled LCF tests including hold times at maximum tensile strain were conducted at total strain range of 0.3% in air at 950 C. Creep-fatigue testing was also performed in a simulated VHTR impure helium coolant for selected experimental conditions. The fatigue resistance decreased when a hold time was added at peak tensile stress, consistent with the observed change in fracture mode from transgranular to intergranular with introduction of a tensile hold. Increases in the tensile hold time, beyond 180 sec, was not detrimental to the creep-fatigue resistance. Grain boundary damage in the form of grain boundary cracking was present in the bulk of the creep-fatigue specimens. This bulk cracking was quantified and found to be similar for hold times of up to 1800 sec consistent with the saturation in failure lives and rapid stress relaxation observed during the creep portion of the creep-fatigue cycle.

  9. Thermal Behavior of Cylindrical Buckling Restrained Braces at Elevated Temperatures

    PubMed Central

    Talebi, Elnaz; Tahir, Mahmood Md.; Yasreen, Airil

    2014-01-01

    The primary focus of this investigation was to analyze sequentially coupled nonlinear thermal stress, using a three-dimensional model. It was meant to shed light on the behavior of Buckling Restraint Brace (BRB) elements with circular cross section, at elevated temperature. Such bracing systems were comprised of a cylindrical steel core encased in a strong concrete-filled steel hollow casing. A debonding agent was rubbed on the core's surface to avoid shear stress transition to the restraining system. The numerical model was verified by the analytical solutions developed by the other researchers. Performance of BRB system under seismic loading at ambient temperature has been well documented. However, its performance in case of fire has yet to be explored. This study showed that the failure of brace may be attributed to material strength reduction and high compressive forces, both due to temperature rise. Furthermore, limiting temperatures in the linear behavior of steel casing and concrete in BRB element for both numerical and analytical simulations were about 196°C and 225°C, respectively. Finally it is concluded that the performance of BRB at elevated temperatures was the same as that seen at room temperature; that is, the steel core yields prior to the restraining system. PMID:24526915

  10. Buckling and postbuckling behavior of compression-loaded isotropic plates with cutouts

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1990-01-01

    An experimental study of the buckling and postbuckling behavior of square and rectangular compression loaded aluminum plates with centrally located circular, square, and elliptical cutouts is presented. Experimental results indicate that the plates exhibit overall trends of increasing buckling strain and decreasing initial postbuckling stiffness with increasing cutout width. Corresponding plates with circular and square cutouts of the same width buckle at approximately the same strain level, and exhibit approximately the same initial postbuckling stiffness. Results show that the reduction in initial postbuckling stiffness due to a cutout generally decreases as the plate aspect ratio increases. Other results presented indicate that square plates with elliptical cutouts having a large cutout-width-to-plate-width ratio generally lose prebuckling and initial postbuckling stiffness as the cutout height increases. However, the plates buckle at essentially the same strain level. Results also indicate that postbuckling stiffness is more sensitive to changes in elliptical cutout height than are prebuckling stiffness and buckling strain.

  11. Creep behavior of tungsten fiber reinforced niobium metal matrix composites

    NASA Technical Reports Server (NTRS)

    Grobstein, T. L.

    1989-01-01

    Tungsten fiber reinforced niobium metal matrix composites were evaluated for use in space nuclear power conversion systems. The composite panels were fabricated using the arc-spray monotape technique at the NASA Lewis Research Center. The creep behavior of W/Nb composite material was determined at 1400 and 1500 K in vacuum over a wide range of applied loads. The time to reach 1 percent strain, the time to rupture, and the minimum creep rate were measured. The W/Nb composites exceeded the properties of monolithic niobium alloys significantly even when compared on a strength to density basis. The effect of fiber orientation on the creep strength also was evaluated. Kirkendall void formation was observed at the fiber/matrix interface; the void distribution differed depending on the fiber orientation relative to the stress axis. A relationship was found between the fiber orientation and the creep strength.

  12. Creep behavior of tungsten fiber reinforced niobium metal matrix composites

    NASA Technical Reports Server (NTRS)

    Grobstein, Toni L.

    1992-01-01

    Tungsten fiber reinforced niobium metal matrix composites were evaluated for use in space nuclear power conversion systems. The composite panels were fabricated using the arc-spray monotape technique at the NASA Lewis Research Center. The creep behavior of W/Nb composite material was determined at 1400 and 1500 K in vacuum over a wide range of applied loads. The time to reach 1 percent strain, the time to rupture, and the minimum creep rate were measured. The W/Nb composites exceeded the properties of monolithic niobium alloys significantly even when compared creep strength also was evaluated. Kirkendall void formation was observed at the fiber/matrix interface; the void distribution differed depending the fiber orientation relative to the stress axis. A relationship was found between the fiber orientation and the creep strength.

  13. Tensile creep and creep rupture behavior of monolithic and SiC-whisker-reinforced silicon nitride ceramics

    SciTech Connect

    Ohji, Tatsuki; Yamauchi, Yukihiko )

    1993-12-01

    The tensile creep and creep rupture behavior of silicon nitride was investigated at 1,200 to 1,350 C using hot-pressed materials with and without SiC whiskers. Stable steady-state creep was observed under low applied stresses at 1,200 C. Accelerated creep regimes, which were absent below 1,300 C, were identified above that temperature. The appearance of accelerated creep at the higher temperatures attributable to formation of microcracks throughout a specimen. The whisker-reinforced material exhibited better creep resistance than the monolith at 1,200 C. Considerably high values 3 to 5, were obtained for the creep exponent in the overall temperature range. The exponent tended to decrease with decreasing applied stress at 1,200 C. The primary creep mechanism was considered cavitation-enhanced creep. Specimen lifetimes followed the Monkman-Grant relationship except for fractures with large accelerated creep regimes. The creep rupture behavior is discussed in association with cavity formation and crack adolescence.

  14. Threshold Stress Creep Behavior of Alloy 617 at Intermediate Temperatures

    SciTech Connect

    J.K. Benz; L.J. Carroll; J.K. Wright; R.N. Wright; T. Lillo

    2014-06-01

    Creep of Alloy 617, a solid solution Ni-Cr-Mo alloy, was studied in the temperature range of 1023 K to 1273 K (750 °C to 1000 °C). Typical power-law creep behavior with a stress exponent of approximately 5 is observed at temperatures from 1073 K to 1273 K (800 °C to 1000 °C). Creep at 1023 K (750 °C), however, exhibits threshold stress behavior coinciding with the temperature at which a low volume fraction of ordered coherent y' precipitates forms. The threshold stress is determined experimentally to be around 70 MPa at 1023 K (750 °C) and is verified to be near zero at 1173 K (900 °C)—temperatures directly correlating to the formation and dissolution of y' precipitates, respectively. The y' precipitates provide an obstacle to continued dislocation motion and result in the presence of a threshold stress. TEM analysis of specimens crept at 1023 K (750 °C) to various strains, and modeling of stresses necessary for y' precipitate dislocation bypass, suggests that the climb of dislocations around the y' precipitates is the controlling factor for continued deformation at the end of primary creep and into the tertiary creep regime. As creep deformation proceeds at an applied stress of 121 MPa and the precipitates coarsen, the stress required for Orowan bowing is reached and this mechanism becomes active. At the minimum creep rate at an applied stress of 145 MPa, the finer precipitate size results in higher Orowan bowing stresses and the creep deformation is dominated by the climb of dislocations around the y' precipitates.

  15. Creep rupture behavior of Stirling engine materials

    NASA Technical Reports Server (NTRS)

    Titran, R. H.; Scheuerman, C. M.; Stephens, J. R.

    1985-01-01

    The automotive Stirling engine, being investigated jointly by the Department of Energy and NASA Lewis as an alternate to the internal combustion engine, uses high-pressure hydrogen as the working fluid. The long-term effects of hydrogen on the high temperature strength properties of materials is relatively unknown. This is especially true for the newly developed low-cost iron base alloy NASAUT 4G-A1. This iron-base alloy when tested in air has creep-rupture strengths in the directionally solidified condition comparable to the cobalt base alloy HS-31. The equiaxed (investment cast) NASAUT 4G-A1 has superior creep-rupture to the equiaxed iron-base alloy XF-818 both in air and 15 MPa hydrogen.

  16. Mechanical behavior of carbon nanotubes in the rippled and buckled phase

    NASA Astrophysics Data System (ADS)

    Jackman, H.; Krakhmalev, P.; Svensson, K.

    2015-02-01

    We have studied the mechanical behavior of multi-walled carbon nanotubes for bending strains beyond the onset for rippling and buckling. We found a characteristic drop in the bending stiffness at the rippling and buckling onset and the relative retained stiffness was dependent on the nanotube dimensions and crystallinity. Thin tubes are more prone to buckle, where some lose all of their bending stiffness, while thicker tubes are more prone to ripple and on average retain about 20% of their bending stiffness. In defect rich tubes, the bending stiffness is very low prior to rippling, but these tubes retain up to 70% of their initial bending stiffness.

  17. Effect of misalignment on mechanical behavior of metals in creep. [computer programs

    NASA Technical Reports Server (NTRS)

    Wu, H. C.

    1979-01-01

    Application of the endochronic theory of viscoplasticity to creep, creep recovery, and stress relaxation at the small strain and short time range produced the following results: (1) The governing constitutive equations for constant-strain-rate stress-strain behavior, creep, creep recovery, and stress relaxation were derived by imposing appropriate constraints on the general constitutive equation of the endochronic theory. (2) A set of material constants was found which correlate strain-hardening, creep, creep recovery, and stress relaxation. (3) The theory predicts with reasonable accuracy the creep and creep recovery behaviors at short time. (4) The initial strain history prior to the creep stage affects the subsequent creep significantly. (5) A critical stress was established for creep recovery. A computer program, written for the misalignment problem is reported.

  18. Transient creep and semibrittle behavior of crystalline rocks

    USGS Publications Warehouse

    Carter, N.L.; Kirby, S.H.

    1978-01-01

    We review transient creep and semibrittle behavior of crystalline solids. The results are expected to be pertinent to crystalline rocks undergoing deformation in the depth range 5 to 20 km, corresponding to depths of focus of many major earthquakes. Transient creep data for crystalline rocks at elevated temperatures are analyzed but are poorly understood because of lack of information on the deformation processes which, at low to moderate pressure, are likely to be semibrittle in nature. Activation energies for transient creep at high effective confining pressure are much higher than those found for atmospheric pressure tests in which thermally-activated microfracturing probably dominates the creep rate. Empirical transient creep equations are extrapolated at 200?? to 600??C, stresses from 0.1 to 1.0 kbar, to times ranging from 3.17??102 to 3.17??108 years. At the higher temperatures, appreciable transient creep strains may take place but the physical significance of the results is in question because the flow mechanisms have not been determined. The purpose of this paper is to stimulate careful research on this important topic. ?? 1978 Birkha??user Verlag.

  19. The high temperature creep behavior of oxides and oxide fibers

    NASA Technical Reports Server (NTRS)

    Jones, Linda E.; Tressler, Richard E.

    1991-01-01

    A thorough review of the literature was conducted on the high-temperature creep behavior of single and polycrystalline oxides which potentially could serve as fiber reinforcements in ceramics or metal matrix applications. Sapphire when oriented with the basal plane perpendicular to the fiber axis (c-axis oriented) is highly creep resistant at temperatures in excess of 1600 C and applied loads of 100 MPa and higher. Pyramidal slip is preferentially activated in sapphire under these conditions and steady-state creep rates in the range of 10(exp -7) to 10 (exp -8)/s were reported. Data on the creep resistance of polycrystalline beryllia suggest that C-axiz oriented single crystal beryllia may be a viable candidate as a fiber reinforcement material; however, the issure of fabricability and moisture sensitivity must be addressed for this material. Yttrium aluminum garnet (YAG) also appears to be a fiber candidate material having a high resistance to creep which is due to it's complex crystal structure and high Peierl resistance. The high creep resistance of garnet suggests that there may be other complex ternary oxides such as single crystal mullite which may also be candidate materials for fiber reinforcements. Finally, CVD and single crystal SiC, although not oxides, do possess a high resistance to creep in the temperature range between 1550 and 1850 C and under stresses of 110 to 220 MPa. From a review of the literature, it appears that for high creep resistant applications sapphire, silicon carbide, yttrium aluminum garnet, mullite, and beryllia are desirable candidate materials which require further investigation.

  20. Creep and recovery behavior analysis of space mesh structures

    NASA Astrophysics Data System (ADS)

    Tang, Yaqiong; Li, Tuanjie; Ma, Xiaofei

    2016-11-01

    The Schapery's nonlinear viscoelastic theory and nonlinear force-density method have been investigated to analyze the creep and recovery behaviors of space deployable mesh reflectors in this paper. Based on Schapery's nonlinear viscoelastic theory, we establish the creep and recovery constitutive model for cables whose pretensions were applied stepwise in time. This constitutive model has been further used for adjustment of cables' elongation rigidity. In addition, the time-dependent tangent stiffness matrix is calculated by the partial differentiation of the corresponding load vector with respect to the nodal coordinate vector obtained by the nonlinear force-density method. An incremental-iterative solution based on the Newton-Raphson method is adopted for solving the time-dependent nonlinear statics equations. Finally, a hoop truss reflector antenna is presented as a numerical example to illustrate the efficiency of the proposed method for the creep and recovery behavior analysis of space deployable mesh structures.

  1. Buckling behavior of composite cylinders subjected to compressive loading

    NASA Technical Reports Server (NTRS)

    Carri, R. L.

    1973-01-01

    Room temperature compressive buckling strengths of eight cylinders, four boron-epoxy and four boron-epoxy reinforced-titanium, with diameter to thickness ratios ranging between 40 and 67 are determined experimentally and compared with analytical predictions. Numerical buckling strengths are presented for Donnell's, Flugge's and Sanders' shell theories for anisotropic and orthotropic material cases. Comparison of analytical predictions with experimental results indicates good agreement and the recommended correlation factor suggested in the literature is applicable for design. For the cylinders tested, the correlation between experiment and theory ranged from 0.73 to 0.97.

  2. Creep Behavior and Durability of Cracked CMC

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Fox, Dennis; Smith, Craig

    2015-01-01

    To understand failure mechanisms and durability of cracked Ceramic matrix composites (CMCs), Melt Infiltration (MI) SiCSiC composites with Sylramic-iBN fibers and full Chemical vapour infiltration SiCSiC composites with Sylramic-ion bombarded BN (iBN) and Hi-Nicalon -S fibers were pre-cracked between 150 to 200 megapascal and then creep and Sustained Peak Low Cycle Fatigue (SPLCF) tested at 13150 C at stress levels from 35 to 103 megapascal for up to 200 hours under furnace and burner rig conditions. In addition creep testing was also conducted on pre-cracked full Chemical vapour infiltration SiCSiC composites at 14500 C between 35 and 103 megapascal for up to 200 hours under furnace conditions. If the specimens survived the 200 hour durability tests, then they were tensile tested at room temperature to determine their residual tensile properties. The failed specimens were examined by Scanning electron microscope (SEM) to determine the failure modes and mechanisms. The influence of crack healing matrix, fiber types, crack density, testing modes and interface oxidation on durability of cracked Ceramic matrix composites (CMCs) will be discussed.

  3. Algorithms for elasto-plastic-creep postbuckling

    NASA Technical Reports Server (NTRS)

    Padovan, J.; Tovichakchaikul, S.

    1984-01-01

    This paper considers the development of an improved constrained time stepping scheme which can efficiently and stably handle the pre-post-buckling behavior of general structure subject to high temperature environments. Due to the generality of the scheme, the combined influence of elastic-plastic behavior can be handled in addition to time dependent creep effects. This includes structural problems exhibiting indefinite tangent properties. To illustrate the capability of the procedure, several benchmark problems employing finite element analyses are presented. These demonstrate the numerical efficiency and stability of the scheme. Additionally, the potential influence of complex creep histories on the buckling characteristics is considered.

  4. Creep and creep-rupture behavior of a continuous strand, swirl mat reinforced polymer composite in automotive environments

    SciTech Connect

    Ren, W.; Brinkman, C.R.

    1998-12-31

    Creep and creep-rupture behavior of an isocyanurate based polyurethane matrix with a continuous strand, swirl mat E-glass reinforcement was investigated for automotive applications. The material under stress was exposed to various automobile service environments. Results show that environment has substantial effects on its creep and creep-rupture properties. Proposed design guide lines and stress reduction factors were developed for various automotive environments. These composites are considered candidate structural materials for light weight and fuel efficient automobiles of the future.

  5. Mechanical Behavior of Low Porosity Carbonate Rock: From Brittle Creep to Ductile Creep.

    NASA Astrophysics Data System (ADS)

    Nicolas, A.; Fortin, J.; Gueguen, Y.

    2014-12-01

    Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this study, we focus on the mechanical behavior of a 14.7% porosity white Tavel (France) carbonate rock (>98% calcite). The samples were deformed in a triaxial cell at effective confining pressures ranging from 0 MPa to 85 MPa at room temperature and 70°C. Experiments were carried under dry and water saturated conditions in order to explore the role played by the pore fluids. Two types of experiments have been carried out: (1) a first series in order to investigate the rupture envelopes, and (2) a second series with creep experiments. During the experiments, elastic wave velocities (P and S) were measured to infer crack density evolution. Permeability was also measured during creep experiments. Our results show two different mechanical behaviors: (1) brittle behavior is observed at low confining pressures, whereas (2) ductile behavior is observed at higher confining pressures. During creep experiments, these two behaviors have a different signature in term of elastic wave velocities and permeability changes, due to two different mechanisms: development of micro-cracks at low confining pressures and competition between cracks and microplasticity at high confining pressure. The attached figure is a summary of 20 triaxial experiments performed on Tavel limestone under different conditions. Stress states C',C* and C*' and brittle strength are shown in the P-Q space: (a) 20°C and dry

  6. Assessment of Tungsten Content on Tertiary Creep Deformation Behavior of Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Vanaja, J.; Laha, Kinkar

    2015-10-01

    Tertiary creep deformation behavior of reduced activation ferritic-martensitic (RAFM) steels having different tungsten contents has been assessed. Creep tests were carried out at 823 K (550 °C) over a stress range of 180 to 260 MPa on three heats of the RAFM steel (9Cr-W-0.06Ta-0.22V) with tungsten content of 1, 1.4, and 2.0 wt pct. With creep exposure, the steels exhibited minimum in creep rate followed by progressive increase in creep rate until fracture. The minimum creep rate decreased, rupture life increased, and the onset of tertiary stage of creep deformation delayed with the increase in tungsten content. The tertiary creep behavior has been assessed based on the relationship, , considering minimum creep rate () instead of steady-state creep rate. The increase in tungsten content was found to decrease the rate of acceleration of tertiary parameter ` p.' The relationships between (1) tertiary parameter `p' with minimum creep rate and time spent in tertiary creep deformation and (2) the final creep rate with minimum creep rate revealed that the same first-order reaction rate theory prevailed in the minimum creep rate as well as throughout the tertiary creep deformation behavior of the steel. A master tertiary creep curve of the steels has been developed. Scanning electron microscopic investigation revealed enhanced coarsening resistance of carbides in the steel on creep exposure with increase in tungsten content. The decrease in tertiary parameter ` p' with tungsten content with the consequent decrease in minimum creep rate and increase in rupture life has been attributed to the enhanced microstructural stability of the steel.

  7. Magnetic field effects on buckling behavior of smart size-dependent graded nanoscale beams

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Farzad; Reza Barati, Mohammad

    2016-07-01

    In this article, buckling behavior of nonlocal magneto-electro-elastic functionally graded (MEE-FG) beams is investigated based on a higher-order beam model. Material properties of smart nanobeam are supposed to change continuously throughout the thickness based on the power-law model. Eringen's nonlocal elasticity theory is adopted to capture the small size effects. Nonlocal governing equations of MEE-FG nanobeam are obtained employing Hamilton's principle and they are solved using the Navier solution. Numerical results are presented to indicate the effects of magnetic potential, electric voltage, nonlocal parameter and material composition on buckling behavior of MEE-FG nanobeams. Therefore, the present study makes the first attempt in analyzing the buckling responses of higher-order shear deformable (HOSD) MEE-FG nanobeams.

  8. Buckling and Postbuckling Behavior of Laminated Composite Plates With a Cutout

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1996-01-01

    This paper addresses the effects of a cutout on the buckling and postbuckling behavior of rectangular plates made of advanced composite materials. An overview of past research is presented, and several key findings and behavioral characteristics are discussed. These findings include the effects of cutout size, shape, eccentricity, and orientation; plate aspect and slenderness ratios; loading and boundary conditions; and plate orthotropy and anisotropy. Some overall important findings of these studies are that plates that have a cutout can buckle at loads higher than the buckling loads for corresponding plates without a cutout and can exhibit substantial postbuckling load-carrying capability. In addition, laminate construction, coupled with cutout geometry, offers a viable means for tailoring structural response.

  9. Buckling behavior of long symmetrically laminated plates subjected to combined loadings

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1992-01-01

    A parametric study is presented of the buckling behavior of infinitely long, symmetrically laminated anisotropic plates subjected to combined loadings. The loading conditions considered are axial tension and compression transverse tension and compression, and shear. Results obtained using a special-purpose analysis, well-suited for parametric studies, are presented for clamped and simply supported plates. Moreover, results are presented for some common laminate constructions, and generic buckling design charts are presented for a wide range of parameters. The generic design charts are presented in terms of useful nondimensional parameters, and the dependence of the nondimensional parameters on laminate fiber orientation, stacking sequence, and material properties is discussed. An important finding of the study is that the effects of anisotropy are much more pronounced in shear-loaded plates than in compression-loaded plates. In addition, the effects of anisotropy on plates subjected to combined loadings are generally manifested as a phase shift of self-similar buckling interaction curves. A practical application of this phase shift is that the buckling resistance of long plates can be improved by applying a shear loading with a specific orientation. In all cases considered in the study, the buckling coefficients of infinitely long plates are found to be independent of the bending stiffness ratio (D sub 11/D sub 22)(1/4).

  10. Buckling Behavior of Long Anisotropic Plates Subjected to Fully Restrained Thermal Expansion

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    2003-01-01

    An approach for synthesizing buckling results and behavior for thin, balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and which are fully-restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters are derived and used to determine critical temperature changes in terms of physically intuitive mechanical buckling coefficients. The effects of membrane orthotropy and anisotropy are included. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of the generic buckling design curves that are presented in the paper. Several generic buckling design curves are presented that provide physical insight into buckling response and provide useful design data. Examples are presented that demonstrate the use of generic design curves. The analysis approach and generic results indicate the effects and characteristics of laminate thermal expansion, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general, unifying manner.

  11. Buckling Behavior of Long Anisotropic Plates Subjected to Fully Restrained Thermal Expansion

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    2001-01-01

    An approach for synthesizing buckling results and behavior for thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and fully restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters are derived that are used to determine critical temperatures in terms of physically intuitive mechanical buckling coefficients, and the effects of membrane orthotropy and membrane anisotropy are included. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of the generic buckling design curves that are presented in the paper. Several generic buckling design curves are presented that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of the generic design curves. The analysis approach and generic results indicate the effects and characteristics of laminate thermal expansion, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general and unifying manner.

  12. Buckling behavior of long symmetrically laminated plates subjected to combined loads

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1992-01-01

    A parametric study of the buckling behavior of infinitely long symmetrically laminated anisotropic plates subjected to combined loadings is presented. The loading conditions considered are axial tension and compression, transverse tension and compression, and shear. Results obtained using a special purpose analysis, well suited for parametric studies are presented for clamped and simply supported plates. Moreover, results are presented for some common laminate constructions, and generic buckling design charts are presented for a wide range of parameters. The generic design charts are presented in terms of useful nondimensional parameters, and dependence of the nondimensional parameters on laminate fiber orientation, stacking sequence, and material properties is discussed. An important finding of the study is that the effects of anisotropy are much more pronounced in shear-loaded plates than in compression loaded plates. In addition, the effects of anisotropy on plates subjected to combined loadings are generally manifested as a phase shift of self-similar buckling interaction curves. A practical application of this phase shift is the buckling resistance of long plates can be improved by applying a shear loading with a specific orientation. In all cases considered, it is found that the buckling coefficients of infinitely long plates are independent of the bending stiffness ratio (D sub 11/D sub 22) sup 1/4.

  13. On the buckling behavior of connected carbon nanotubes with parallel longitudinal axes

    NASA Astrophysics Data System (ADS)

    Imani Yengejeh, Sadegh; Akbar Zadeh, Mojtaba; Öchsner, Andreas

    2014-06-01

    The application of hetero-junction carbon nanotubes (CNTs) is increasing continuously due to their outstanding properties in nano-mechanical systems. Several investigations have been conducted to study the behavior of CNTs. In this paper, straight hetero-junctions and their constituent CNTs (armchair and zigzag) were simulated by a commercial finite element package. Then, the buckling behavior of CNTs was evaluated by comparing the critical buckling load of each straight hetero-junction and its constituent CNTs. Both obtained, i.e. analytical calculations and computational, results were compared. The investigations showed that, first, the behavior of homogeneous CNTs under cantilevered boundary conditions follows the assumption of the classical Euler equation. Second, the analytical solutions are in good agreement with the finite element simulation results. In addition, it was shown that the first critical buckling load of hetero-junctions lies within the value of the fundamental homogeneous CNT range. It was also concluded that the buckling load of straight hetero-junctions and their fundamental CNTs increases by increasing the chiral number of both armchair and zigzag CNTs. The current study provides a better insight towards the prediction of straight hetero-junction CNTs behavior.

  14. The creep behavior of acrylic denture base resins.

    PubMed

    Sadiku, E R; Biotidara, F O

    1996-01-01

    The creep behavior of acrylic dental base resins, at room temperature and at different loading conditions, has been examined. The behaviors of these resins are similar to that of "commercial perspex" at room temperature over a period of 1000 seconds. The pseudo-elastic moduli of the blends of PMMA VC show a significant increase compared with PMMA alone. The addition of the PVC powder to the heat-cured acrylic resin increased the time-dependent elastic modulus. This increase in elastic modulus is advantageous in the production of denture based resins of improv mechanical properties.

  15. Creep behavior of tungsten/niobium and tungsten/niobium-1 percent zirconium composites

    NASA Technical Reports Server (NTRS)

    Petrasek, Donald W.; Titran, Robert H.

    1988-01-01

    The creep behavior and microstructural stability of tungsten fiber reinforced niobium and niobium 1 percent zirconium was determined at 1400 and 1500 K in order to assess the potential of this material for use in advanced space power systems. The creep behavior of the composite materials could be described by a power law creep equation. A linear relationship was found to exist between the minimum creep rate of the composite and the inverse of the composite creep rupture life. The composite materials had an order of magnitude increase in stress to achieve 1 percent creep strain and in rupture strength at test temperatures of 1400 and 1500 K compared to unreinforced material. The composite materials were also stronger than the unreinforced materials by an order of magnitude when density was taken into consideration. Results obtained on the creep behavior and microstructural stability of the composites show significant potential improvement in high temperature properties and mass reduction for space power system components.

  16. Microstructural development and creep behavior in A286 superalloy

    SciTech Connect

    De Cicco, H.; Luppo, M.I.; Gribaudo, L.M.; Ovejero-Garcia, J

    2004-05-15

    The precipitation-hardened alloy A286 has been characterized as a function of ageing treatment, and the creep behavior has been studied in the temperature range of 600-700 deg. C and at 230-740 MPa. Microhardness tests of samples aged at different temperatures have been performed, and it was observed that the fastest precipitation kinetics of the metastable {gamma}' occurred during ageing at 730 deg. C. Further exposure at this temperature degraded the good mechanical properties of the material because the {gamma}' dissolved, and the stable {eta} phase formed. Optical and scanning and transmission electron microscopy (SEM and TEM, respectively) characterization of samples in as-received state and after ageing were performed to study the microstructural development. In all creep tests, the damage observed was intergranular. The correlation between secondary strain rate and time to failure was shown to be a modified Monkman-Grant, including the elongation to rupture and an exponent different of 1 for the strain rate to obtain a better correlation. The Larson-Miller parameter has been used to correlate creep stress, temperature and rupture time for the aged material.

  17. Creep and Stress-strain Behavior After Creep from Sic Fiber Reinforced, Melt-infiltrated Sic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Pujar, Vijay

    2004-01-01

    Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated Si were subjected to creep at 1315 C for a number of different stress conditions, This study is aimed at understanding the time-dependent creep behavior of CMCs for desired use-conditions, and also more importantly, how the stress-strain response changes as a result of the time-temperature-stress history of the crept material. For the specimens that did not rupture, fast fracture experiments were performed at 1315 C or at room temperature immediately following tensile creep. In many cases, the stress-strain response and the resulting matrix cracking stress of the composite change due to stress-redistribution between composite constituents during tensile creep. The paper will discuss these results and its implications on applications of these materials for turbine engine components.

  18. Creep-rupture behavior of candidate Stirling engine iron supperalloys in high-pressure hydrogen. Volume 2: Hydrogen creep-rupture behavior

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, S.; Peterman, W.; Hales, C.

    1984-01-01

    The creep rupture behavior of nine iron base and one cobalt base candidate Stirling engine alloys is evaluated. Rupture life, minimum creep rate, and time to 1% strain data are analyzed. The 3500 h rupture life stress and stress to obtain 1% strain in 3500 h are also estimated.

  19. Buckling Behavior of Long Anisotropic Plates Subjected to Elastically Restrained Thermal Expansion

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    2002-01-01

    An approach for synthesizing buckling results for, and behavior of, thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and elastically restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters and compliance coefficients are derived that are used to determine critical temperatures in terms of physically intuitive mechanical-buckling coefficients. The effects of membrane orthotropy and membrane anisotropy are included in the general formulation. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of generic buckling design curves. Several curves that illustrate the fundamental parameters used in the analysis are presented, for nine contemporary material systems, that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of generic design curves. The analysis approach and generic results indicate the effects and characteristics of elastically restrained laminate thermal expansion or contraction, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general and unifying manner.

  20. Creep of Refractory Fibers and Modeling of Metal and Ceramic Matrix Composite Creep Behavior

    NASA Technical Reports Server (NTRS)

    Tewari, S.N.

    1995-01-01

    Our concentration during this research was on the following subprograms. (1) Ultra high vacuum creep tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires, temperature range from 1100 K to 1500 K, creep time of 1 to 500 hours. (2) High temperature vacuum tensile tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires. (3) Air and vacuum tensile creep tests on polycrystalline and single crystal alumina fibers, such as alumina-mullite Nextel fiber, yttrium aluminum ganet (YAG) and Saphikon, temperature range from 1150 K to 1470 K, creep time of 2 to 200 hours. (4) Microstructural evaluation of crept fibers, TEM study on the crept metal wires, SEM study on the fracture surface of ceramic fibers. (5) Metal Matrix Composite creep models, based on the fiber creep properties and fiber-matrix interface zone formation.

  1. Impression Creep Behavior of 316LN Stainless Steel

    NASA Astrophysics Data System (ADS)

    Mathew, M. D.; Naveena; Vijayanand, D.

    2013-02-01

    Impression creep tests have been carried out at 923 K on 316LN SS containing 0.07, 0.14, and 0.22 wt.% nitrogen, under different applied stress levels. It was observed that the impression creep depth versus time curves were similar to the creep curves obtained from conventional uniaxial creep tests. The impression creep curves were characterized by a loading strain and primary and secondary creep stages similar to uniaxial creep curves. The tertiary stage observed in uniaxial creep curves was absent. The steady-state impression velocity was found to increase with increasing applied stress. The equivalent steady-state creep rates calculated from impression velocities were found to be in good agreement with the steady-state creep rates obtained from conventional uniaxial creep tests. Equivalence between applied stress and steady-state impression velocity with uniaxial creep stress and steady-state creep rate, respectively, has been established based on the laws of mechanics for time-dependent plasticity. It was found that impression velocity was sensitive to the variation in nitrogen content in the steel; impression velocity decreased with increasing nitrogen content, and the results obtained in this study were in agreement with those obtained from uniaxial creep tests.

  2. The vibrational and buckling behaviors of piezoelectric nanobeams with surface effects.

    PubMed

    Yan, Z; Jiang, L Y

    2011-06-17

    In this work, the influence of surface effects, including residual surface stress, surface elasticity and surface piezoelectricity, on the vibrational and buckling behaviors of piezoelectric nanobeams is investigated by using the Euler-Bernoulli beam theory. The surface effects are incorporated by applying the surface piezoelectricity model and the generalized Young-Laplace equations. The results demonstrate that surface effects play a significant role in predicting these behaviors. It is found that the influence of the residual surface stress and the surface piezoelectricity on the resonant frequencies and the critical electric potential for buckling is more prominent than the surface elasticity. The nanobeam boundary conditions are also found to influence the surface effects on these parameters. This study also shows that the resonant frequencies can be tuned by adjusting the applied electrical load. The present study is envisaged to provide useful insights for the design and applications of piezoelectric-beam-based nanodevices.

  3. Creep Behavior of Organic-Rich Shales - Evidences of Microscale Strain Partitioning

    NASA Astrophysics Data System (ADS)

    Sone, H.; Morales, L. F. G.; Dresen, G. H.

    2015-12-01

    Laboratory creep experiments conducted using organic-rich shales show that these rocks exhibit some ductility under sustained loading conditions although they may appear to be elastic and brittle (Young's modulus 15-80 GPa) at shorter time scales. At room-temperature and in-situ pressure conditions, creep strain observed after 3 hours of sustained loading reach strains on the order of 10-5per megapascal of applied differential stress. The creep behavior is highly anisotropic such that creep occurs more in the direction perpendicular to the bedding plane than in the direction parallel to the bedding plane. In general, we find that the creep behavior is largely controlled by the amount of clay mineral and organic content. This is also supported by evidences of elastic stiffening and sample volume reduction during creep which imply that the creep is accommodated by localized compaction occurring within clay-aggregates and/or organic materials, the relatively porous members in the rock. We also find that the tendency to creep has a unique relation with the Young's modulus regardless of the loading direction or the mineral composition. Sone and Zoback (2013) explained this correlation by appealing to the stress partitioning behavior that occurs between the relatively stiff and soft components of the rock, and also by assuming that creep only occurs within the soft components, namely the clay and organic contents, with a specific local 3-hour creep compliance value of 10-4 MPa-1. In order to confirm that such strain-partitioning occurs during creep deformation, we also performed creep experiments under a scanning electron microscope using a deformation stage setup. Such experiments allow us to directly observe the deformation and quantify the strain-partitioning occurring between the different mineral constituents with the aid of digital image correlation analysis. Results suggest that strain-partitioning do occur during creep deformation and inferred creep properties of

  4. Seismic effects and buckling behavior of pipelines in the central and eastern United States

    SciTech Connect

    Beavers, J.E.; Nyman, D.J.; Hammond, C.R.

    1992-04-01

    The status of knowledge on the seismic effects and buckling behavior of pipelines in the central and eastern United States is reviewed. Types of ground response to earthquake motions that result in pipeline failure and pipeline response to such motions are discussed. The primary focus is on oil and gas transmission lines constructed of welded steel pipe. Results of vulnerability studies, the need for better determination of the potential for existing pipeline failures, and design procedures for new pipelines are presented.

  5. Creep and recovery behaviors of magnetorheological elastomer based on polyurethane/epoxy resin IPNs matrix

    NASA Astrophysics Data System (ADS)

    Qi, S.; Yu, M.; Fu, J.; Li, P. D.; Zhu, M.

    2016-01-01

    This paper mainly investigated the creep and recovery behaviors of magnetorheological elastomers (MRE) based on polyurethane/epoxy resin (EP) graft interpenetrating polymer networks (IPNs). The influences of constant stress level, content of EP, particle distribution, magnetic field and temperature on the creep and recovery behaviors were systematically investigated. As expected, results suggested that the presence of IPNs leads to a significant improvement of creep resistance of MRE, and creep and recovery behaviors of MRE were highly dependent on magnetic field and temperature. To further understand its deformation mechanism, several models (i.e., Findley’s power law model, Burgers model, and Weibull distribution equation) were used to fit the measured creep and recovery data. Results showed that the modeling of creep and recovery of samples was satisfactorily conducted by using these models. The influences of content of EP and magnetic field on fitting parameters were discussed, and relevant physical mechanism was proposed to explain it qualitatively.

  6. Semi-analytical solution of time-dependent thermomechanical creep behavior of FGM hollow spheres

    NASA Astrophysics Data System (ADS)

    Jafari Fesharaki, J.; Loghman, A.; Yazdipoor, M.; Golabi, S.

    2014-02-01

    By using a method of successive elastic solution, the time-dependent creep behavior of a functionally graded hollow sphere under thermomechanical loads has been investigated. Based on volume percentage, the mechanical and thermal properties of material, except for the Poisson's ratio, are assumed to be radially dependent. Total strains are assumed to be the sum of elastic, thermal and creep strains. Creep strains are temperature-, stress- and time-dependent. Using the Prandtl-Reuss relations and Sherby's law, histories of stresses and strains are presented from their initial elastic values at zero time up to 30 years after loading. The results show that the creep stresses and strains change with time and material inhomogeneity has influence on thermomechanical creep behavior. The aim of this work was to understand the effect of creep behavior on a functionally graded hollow sphere subjected to thermomechanical load.

  7. Modeling the buckling behavior of carbon nanotubes under simultaneous combination of compressive and torsional loads

    NASA Astrophysics Data System (ADS)

    Motevalli, B.; Montazeri, A.; Tavakoli-Darestani, R.; Rafii-Tabar, H.

    2012-09-01

    A number of studies have been performed on the mechanical and deformational properties of carbon nanotubes under different loading conditions, such as compression, tension, torsion, bending, and hydrostatic pressure. However, in practical applications, such as in nanotube-reinforced nanocomposites, these different loading conditions are present simultaneously. We employ molecular dynamics simulation to compute the behavior and deformation properties of carbon nanotubes under combined application of compression and torsion. The buckling properties and the corresponding mode shapes are investigated, for the first time, for different rotational and axial displacement rates. It is found that the critical loads and the buckling deformations strongly depend upon the ratio of these displacement rates. Finally, a relationship between the shear and normal stresses is established, which can be used for determining the stress limits when designing practical carbon nanotube-based systems in which combined loads may be applied.

  8. Estimation of long-term creep behavior of salt

    SciTech Connect

    Chun, R.C.

    1980-08-01

    A computer routine for both primary and secondary creep laws has been developed using a modified strain hardening law. The computations reveal that results from Heard's steady-state creep law and Lomenick and Bradshaw's primary creep law can differ from each other by a factor of thirty after about 6 hours of creep deformation, but the difference diminishes as time becomes large. The belief that these two creep laws may yield long-term results that are orders of magnitude apart is shown to be unfounded.

  9. Nonlinear and Buckling Behavior of Curved Panels Subjected to Combined Loads

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Nemeth, Michael P.; Starnes, James H., Jr.

    2001-01-01

    The results of an analytical study of the nonlinear and buckling response characteristics of curved panels subjected to combined loads are presented. Aluminum and laminated composite panels are considered in the study and a flat and shallow curved panel configurations are considered as well. The panels are subjected to combined axial compression and transverse tension or compression loads or combined axial compression and inplane shear loads. Results illustrating the effects of various combined load states on the buckling response of the panels are presented. In addition, results illustrating the effects of laminate orthotropy and anisotropy and panel curvature on the panel response are presented. The results indicate that panel curvature can have a significant effect on the nonlinear and buckling behavior of the panels subjected to combined loads. Results are included that show that geometrically perfect panels do not exhibit bifurcation points for some combined loads. Results are also presented that show the effects of laminate orthotropy and anisotropy on the interaction of combined loads.

  10. On the nonlinear axisymmetric dynamic buckling behavior of clamped functionally graded spherical caps

    NASA Astrophysics Data System (ADS)

    Prakash, T.; Sundararajan, N.; Ganapathi, M.

    2007-01-01

    Here, the dynamic thermal buckling behavior of functionally graded spherical caps is studied considering geometric nonlinearity based on von Karman's assumptions. The formulation is based on first-order shear deformation theory and it includes the in-plane and rotary inertia effects. The material properties are graded in the thickness direction according to the power-law distribution in terms of volume fractions of the material constituents. The effective material properties are evaluated using homogenization method. The governing equations obtained using finite element approach are solved employing the Newmark's integration technique coupled with a modified Newton-Raphson iteration scheme. The pressure load corresponding to a sudden jump in the maximum average displacement in the time history of the shell structure is taken as the dynamic buckling load. The present model is validated against the available isotropic case. A detailed numerical study is carried out to highlight the influences of shell geometries, power law index of functional graded material and boundary conditions on the dynamic buckling load of shallow spherical shells.

  11. Determination of Creep Behavior of Thermal Barrier Coatings Under Laser Imposed High Thermal and Stress Gradient Conditions

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Miller, Robert A.

    1999-01-01

    A laser sintering/creep technique has been established to determine the creep behavior of thermal barrier coatings under steady-state high heat flux conditions. For a plasma sprayed zirconia-8 wt. % yttria coating, a significant primary creep strain and a low apparent creep activation energy were observed. Possible creep mechanisms involved include stress induced mechanical sliding and temperature and stress enhanced cation diffusion through the splat and grain boundaries. The elastic modulus evolution, stress response, and total accumulated creep strain variation across the ceramic coating are simulated using a finite difference approach. The modeled creep response is consistent with experimental observations.

  12. Mechanisms Governing the Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems

    SciTech Connect

    Vasudevan, Vijay; Carroll, Laura; Sham, Sam

    2015-04-06

    This research project, which includes collaborators from INL and ORNL, focuses on the study of alloy 617 and alloy 800H that are candidates for applications as intermediate heat exchangers in GEN IV nuclear reactors, with an emphasis on the effects of grain size, grain boundaries and second phases on the creep properties; the mechanisms of dislocation creep, diffusional creep and cavitation; the onset of tertiary creep; and theoretical modeling for long-term predictions of materials behavior and for high temperature alloy design.

  13. Heterogeneous microstructures and macroscopic creep behavior of polycrystalline ice (Invited)

    NASA Astrophysics Data System (ADS)

    Lebensohn, R.

    2009-12-01

    We present results of two complementary formulations, a full-field approach based on fast Fourier transforms (FFT) [1] and a mean-field approach based on rigorous nonlinear homogenization [2] to study the influence of different microstructural features on the macroscopic behavior of polycrystalline ice. The FFT-based model is used for the prediction of local fields in columnar ice polycrystals deforming in compression by dislocation creep [3]. The predicted intragranular mechanical fields are in qualitative good agreement with experimental observations, in particular those involving the formation of shear and kink bands. These localization bands are associated with the large internal stresses that develop during creep in such anisotropic material, and their location, intensity, morphology and extension are found to depend strongly on the crystallographic orientation of the grains and on their interaction with neighbor crystals. In turn, this numerically-intensive full-field formulation is used to validate the predictions of different, more efficient homogenization approaches. We show that a recent second-order formulation, which explicitly uses information on average intragranular field fluctuations, implemented within the widely used ViscoPlastic Self-Consistent (VPSC) code [4], yields the most accurate results. References: [1] H. Moulinec and P. Suquet, Comput. Methods Appl. Mech. Eng. 157, 69 (1998). [2] P. Ponte Castañeda, J. Mech. Phys. Solids 50, 737 (2002). [3] R.A. Lebensohn, M. Montagnat, P. Mansuy et al. Acta Mater. 57, 1405, (2009). [4] R.A. Lebensohn, C.N. Tomé and P. Ponte Castañeda. Phil. Mag. 87, 4287 (2007).

  14. Evaluation of the strength and creep-fatigue behavior of hot isostatically pressed silicon nitride

    SciTech Connect

    Ferber, M.K.; Jenkins, M.G. )

    1992-09-01

    This paper reports that the strength of a commerically available hot isostatically pressed silicon nitride was measured as a function of temperature. To evaluate long-term mechanical reliability of this material, the tensile creep and fatigue behavior was measured at 1150[degrees], 1260[degrees], and 1370[degrees]C. The stress and temperature sensitivities of the secondary (or minimum) creep strain rate were used to estimate the stress exponent and activation energy associated with the dominant creep mechanism. The fatigue characteristics were evaluated by allowing individual creep tests to continue until specimen failure. The applicability of the four-point load geometry to the study of strength and creep behavior was also determined by conducting a limited number of flexural creep tests. The tensile fatigue data revealed two distinct failure mechanisms. At 1150[degrees]C, failure was controlled by a slow crack growth mechanism. At 1260[degrees] and 1370[degrees]C, the accumulation of creep damage in the form of grain boundary cavities and cracks dominated the fatigue behavior. In this temperature regime, the fatigue life was controlled by the secondary (or minimum) creep strain rate in accordance with the Monkman-Grant relation.

  15. High-Temperature Creep Behavior Of Fiber-Reinforced Niobium

    NASA Technical Reports Server (NTRS)

    Petrasek, Donald W.; Titran, Robert H.

    1990-01-01

    Study conducted to determine feasibility of using composite materials in advanced space power systems, described in 22-page report. Tungsten fibers reduce creep and mass in advanced power systems. Reinforcing niobium alloys with tungsten fibers increases their resistances to creep by factors of as much as 10.

  16. Out-of-pile creep behavior of uranium carbide

    NASA Technical Reports Server (NTRS)

    Wright, T. R.; Seltzer, M. S.

    1974-01-01

    Compression creep tests were investigated on various UC-based fuel materials having a variation in both density and composition. Specimens were prepared by casting and by hot pressing. Steady-state creep rates were measured under vacuum at 1400 to 1800 C in the stress range 500-4000 psi.

  17. Long-time creep behavior of the niobium alloy C-103

    NASA Technical Reports Server (NTRS)

    Titran, R. H.; Klopp, W. D.

    1980-01-01

    The creep behavior of C-103 was studied as a function of stress, temperature, and grain size for test times to 19000 hr. Over the temperature range 827 to 1204 C and the stress range 6.89 to 138 MPa, only tertiary (accelerating) creep was observed. The creep strain epsilon can be related to time t by an exponential relation epsilon = epsilon(0) + K e raised to power (st) - 1), where epsilon (0) is initial creep strain, K is the tertiary creep strain parameter, and s is the tertiary creep rate parameter. The observed stress exponent 2.87 is similar to the three power law generally observed for secondary (linear) creep of Class I solid solutions. The apparent activation energy 374 kj/g mol is close to that observed for self diffusion of pure niobium. The initial tertiary creep rate was slightly faster for fine grained than for coarse-grained material. The strain parameter K can be expressed as a combination of power functions of stress and grain size and an exponential function of temperature. Strain time curves generated by using calculated values for K and s showed reasonable agreement with observed curves to strains of at least 4 percent. The time to 1 percent strain was related to stress, temperature, and grain size in a similar manner as the initial tertiary creep rate.

  18. The post-buckling behavior of a beam constrained by springy walls

    NASA Astrophysics Data System (ADS)

    Katz, Shmuel; Givli, Sefi

    2015-05-01

    The post-buckling behavior of a beam subjected to lateral constraints is of practical importance in a variety of applications, such as stent procedures, filopodia growth in living cells, endoscopic examination of internal organs, and deep drilling. Even though in reality the constraining surfaces are often deformable, the literature has focused mainly on rigid and fixed constraints. In this paper, we make a first step to bridge this gap through a theoretical and experimental examination of the post-buckling behavior of a beam constrained by a fixed wall and a springy wall, i.e. one that moves laterally against a spring. The response exhibited by the proposed system is much richer compared to that of the fixed-wall system, and can be tuned by choosing the spring stiffness. Based on small-deformation analysis, we obtained closed-form analytical solutions and quantitative insights. The accuracy of these results was examined by comparison to large-deformation analysis. We concluded that the closed-form solution of the small-deformation analysis provides an excellent approximation, except in the highest attainable mode. There, the system exhibits non-intuitive behavior and non-monotonous force-displacement relations that can only be captured by large-deformation theories. Although closed-form solutions cannot be derived for the large-deformation analysis, we were able to reveal general properties of the solution. In the last part of the paper, we present experimental results that demonstrate various features obtained from the theoretical analysis.

  19. Estimation of creep and recovery behavior of a shape memory polymer

    NASA Astrophysics Data System (ADS)

    Sakai, Takenobu; Tao, Takayuki; Somiya, Satoshi

    2015-11-01

    The shape recovery and shape fixity properties of shape memory polymers (SMPs), advanced functional materials, were investigated in this study. Although the shape recovery behavior of these polymers has been examined from a viscoelastic point of view, questions remain with regard to quantifying the recovery behavior of SMPs. SMPs can recover their shape after the molding process; this recovery occurs via creep recovery and/or shape recovery; an estimation of SMP recovery requires a good understanding of both processes. In this study, the time-temperature superposition principle was applied to the creep and shape recovery behavior of SMPs. The creep behavior was estimated using an experimentally obtained master curve and time-temperature shift factors. Our estimated results were in good agreement with the experimental data. However, the estimation of the creep recovery with changing temperature below or above the glass transition temperature was not successful due to the lack of consideration of the shape recovery behavior. The time and temperature dependency of the shape recovery were confirmed for creep behavior, using the master curve for the recovery ratio and the corresponding shift factors for shape recovery. The values of the shape recovery shift factors differed from those for the time-temperature shift factors obtained for creep behavior. Therefore, these shape recovery shift factors were used in the estimation of creep and shape recovery behavior using the master curve for the creep tests. The estimated results were closer to the results obtained experimentally. Moreover, our results indicated that the recovery behavior above Tg was dominated by shape recovery as a result of polymer viscoelasticity.

  20. Creep-rupture behavior of 6 candidate stirling engine iron-base superalloys in high pressure hydrogen. Volume 1: Air creep-rupture behavior

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, S.

    1982-01-01

    Four wrought alloys (A-286, IN 800H, N-155, and 19-9DL) and two cast alloys (CRM-6D and XF-818) were tested to determine their creep-rupture behavior. The wrought alloys were used in the form of sheets of 0.89 mm (0.035 in.) average thickness. The cast alloy specimens were investment cast and machined to 6.35 mm (0.250 in.) gage diameter. All specimens were tested to rupture in air at different times up to 3000 h over the temperature range of 650 C to 925 C (1200 F to 1700 F). Rupture life, minimum creep rate, and time to 1% creep strain were statistically analyzed as a function of stress at different temperatures. Temperature-compensated analysis was also performed to obtain the activation energies for rupture life, time to 1% creep strain, and the minimum creep rate. Microstructural and fracture analyses were also performed. Based on statistical analyses, estimates were made for stress levels at different temperatures to obtain 3500 h rupture life and time to 1% creep strain. Test results are to be compared with similar data being obtained for these alloys under 15 MPa (2175 psi) hydrogen.

  1. Creep behavior of pack cementation aluminide coatings on Grade 91 ferritic martensitic alloy

    SciTech Connect

    Bates, Brian; Zhang, Ying; Dryepondt, Sebastien N; Pint, Bruce A

    2014-01-01

    The creep behavior of various pack cementation aluminide coatings on Grade 91 ferritic-martensitic steel was investigated at 650 C in laboratory air. The coatings were fabricated in two temperature regimes, i.e., 650 or 700 C (low temperature) and 1050 C(high temperature), and consisted of a range of Al levels and thicknesses. For comparison, uncoated specimens heat-treated at 1050 C to simulate the high temperature coating cycle also were included in the creep test. All coated specimens showed a reduction in creep resistance, with 16 51% decrease in rupture life compared to the as-received bare substrate alloy. However, the specimens heat-treated at 1050 C exhibited the lowest creep resistance among all tested samples, with a surprisingly short rupture time of < 25 h, much shorter than the specimen coated at 1050 C. Factors responsible for the reduction in creep resistance of both coated and heat-treated specimens were discussed.

  2. The effect of high frequencies on the cyclic creep behavior of an ODS superalloy

    SciTech Connect

    Stefani, J.A.; Nardone, V.C.; Tien, J.K.

    1987-01-01

    The anelastic strain controlled model is capable of explaining the behavior of the cyclic creep rate as a function of frequency for the ODS superalloy MA 6000, especially the sharp drop in cyclic creep rate that occurs at a frequency of about 0.2 cycles/h. The success of the anelastic strain model depends upon the plausibility of assuming that anelastic strain storage completely delays nonrecoverable strain, i.e., that anelastic and nonrecoverable strain storage are a series process. This is an important point since, as seen in the comparison of the predicted and obtained cyclic creep results, there is the excellent fit of the data in the region where there is a sharp drop in the cyclic creep rate but a poorer fit in the higher frequency region. In the higher frequency regime, there is an observed positive cyclic creep rate when the refined anelastic model predicts a zero strain rate.

  3. Creep behavior of commercial FeCrAl foils: beneficial and detrimental effect of oxidation

    SciTech Connect

    Dryepondt, Sebastien N; Pint, Bruce A; Lara-Curzio, Edgar

    2012-01-01

    Creep tests were performed at 875 and 1050 C on commercially available FeCrAl foils (~50 m, 2 mil thickness) over a wide range of stress and duration to characterize their creep behavior. The oxide scales formed on the creep specimens were analyzed and compared to those that formed on unstressed specimens to assess the effect of stress and strain on oxide growth mechanisms. Below a specific stress threshold, creep rate and lifetime become independent of the applied load and rupture occurs due to the onset of breakaway oxidation. A creep rate model based on the strengthening of the FeCrAl foils due to load-bearing by the thermally-grown alumina scale was observed to be in good agreement with the experimental results.

  4. Creep Behavior of a New Cast Austenitic Alloy

    SciTech Connect

    Shingledecker, John P; Maziasz, Philip J; Evans, Neal D; Pollard, Michael J

    2007-01-01

    A new cast austenitic alloy, CF8C-Plus, has been developed by Oak Ridge National Laboratory (ORNL) and Caterpillar for a wide range of high temperature applications including diesel exhaust components and turbine casings. The creep strength of the CF8C-Plus steel is much greater than that of the standard cast CF8C stainless steel and is comparable to the highest strength wrought commercial austenitic stainless steels and alloys, such as NF709. The creep properties of CF8C-Plus are discussed in terms of the alloy design methodology and the evaluation of some long-term creep tested specimens (over 20,000 hours). Microcharacterization shows that the excellent creep strength is due mainly to the precipitation of very fine nano-scale and stable MC carbides, without the formation of deleterious intermetallic phases.

  5. Creep behavior of 6 micrometer linear low density polyethylene film

    NASA Technical Reports Server (NTRS)

    Simpson, J. M.; Schur, W. W.

    1993-01-01

    Creep tests were performed to provide material characteristics for a 6.4-micron polyethylene film used to construct high altitude balloons. Results suggest simple power law relationships are adequate for stresses below about 4.83 MPa.

  6. Elastic properties and buckling behavior of single-walled carbon nanotubes functionalized with diethyltoluenediamines using molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Ansari, R.; Ajori, S.; Rouhi, S.

    2015-01-01

    Carbon nanotube (CNT) modification processes are of great importance for good dispersion of CNTs and load transfer issues in nanocomposites. Among these processes, polymer covalent functionalization is found to be an effective way to alter the mechanical properties and behavior of pristine CNTs. Therefore, the mechanical properties and buckling behavior of diethyltoluenediamines (DETDA) functionalized CNTs are investigated employing molecular dynamics (MD) simulations. The results demonstrate that as the polymer weight percentage increases, Young's modulus and critical buckling load increase almost linearly for both regular and random polymer distributions, whereas critical strain decreases with different trends depending on the type of polymer distribution. Finally, the buckling mode shapes of the presented models are illustrated and it was revealed that there are some differences between the mode shapes of functionalized CNTs and those of pristine CNTs.

  7. Creep behavior for advanced polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

    1997-08-01

    A bend stress relaxation (BSR) test is planned to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Baseline 1 hr and 100 hr BSR thermal creep {open_quotes}m{close_quotes} curves have been obtained for five selected advanced SiC fiber types and for standard Nicalon CG fiber. The transition temperature, that temperature where the S-shaped m-curve has a value 0.5, is a measure of fiber creep resistance. In order of decreasing thermal creep resistance, with the 100 hr BSR transition temperature given in parenthesis, the fibers ranked: Sylramic (1261{degrees}C), Nicalon S (1256{degrees}C), annealed Hi Nicalon (1215{degrees}C), Hi Nicalon (1078{degrees}C), Nicalon CG (1003{degrees}C) and Tyranno E (932{degrees}C). The thermal creep for Sylramic, Nicalon S, Hi Nicalon and Nicalon CG fibers in a 5000 hr irradiation creep BSR test is projected from the temperature dependence of the m-curves determined during 1 and 100 hr BSR control tests.

  8. Creep and precipitation behaviors of AL6XN austenitic steel at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Meng, L. J.; Sun, J.; Xing, H.

    2012-08-01

    Creep behaviors of the solution-treated AL6XN austenitic stainless steel have been investigated at 873-1023 K and 120-260 MPa. The results showed that the creep stress exponent and activation energy of the AL6XN steel are 5 and 395.4 kJ/mol, respectively in the power-law breakdown regime. TEM observations revealed that dislocations distributed homogenously in grains. The creep deformation mechanism is mainly attributed to viscous dislocation glide. Precipitates in the steel after creep deformation were additionally analyzed by TEM, and the results showed that there are four different types of precipitates, such as M23C6, M6C, σ phase and Laves phase. The M23C6 carbides were observed at grain boundaries in the steel after creep at 873 K. The M6C, σ phase and Laves phase precipitates were found when the creep temperature increases to 923-1023 K. Although the AL6XN steel exhibited low steady state creep rates, a high volume fraction of brittle precipitates of σ and Laves phases reduced the creep lifetime of the steel at elevated temperatures.

  9. Creep deformation behavior in eutectic Sn-Ag solder joints using a novel mapping technique

    SciTech Connect

    Lucas, J.P.; Guo, F.; McDougall, J.; Bieler, T.R.; Subramanian, K.N.; Park, J.K.

    1999-11-01

    Creep deformation behavior was measured for 60--100 {micro}m thick solder joints. The solder joints investigated consisted of: (1) non-composite solder joints made with eutectic Sn-Ag solder, and (2) composite solder joints with eutectic Sn-Ag solder containing 20 vol.%, 5 {micro}m diameter in-situ Cu{sub 6}Sn{sub 5} intermetallic reinforcements. All creep testing in this study was carried out at room temperature. Qualitative and quantitative assessment of creep deformation was characterized on the solder joints. Creep deformation was analyzed using a novel mapping technique where a geometrical-regular line pattern was etched over the entire solder joint using excimer laser ablation. During creep, the laser-ablation (LA) pattern becomes distorted due to deformation in the solder joint. By imaging the distortion of laser-ablation patterns using the SEM, actual deformation mapping for the entire solder joint is revealed. The technique involves sequential optical/digital imaging of the deformation versus time history during creep. By tracing and recording the deformation of the LA patterns on the solder over intervals of time, local creep data are obtained in many locations in the joint. This analysis enables global and localized creep shear strains and strain rate to be determined.

  10. Tensile and compressive creep behavior of extruded Mg–10Gd–3Y–0.5Zr (wt.%) alloy

    SciTech Connect

    Wang, H.; Wang, Q.D.; Boehlert, C.J.; Yin, D.D.; Yuan, J.

    2015-01-15

    The tensile and compressive creep behavior of an extruded Mg–10Gd–3Y–0.5Zr (wt.%) alloy was investigated at temperatures ranging from 200 °C to 300 °C and under stresses ranging from 30 MPa to 120 MPa. There existed an asymmetry in the tensile and compressive creep properties. The minimum creep rate of the alloy was slightly greater in tension than in compression. The measured values of the transient strain and initial creep rate in compression were greater than those in tension. The creep stress exponent was approximately 2.5 at low temperatures (T < 250 °C) and 3.4 at higher temperatures both in tension and in compression. The compression creep activation energy at low temperatures and high temperatures was 83.4 and 184.3 kJ/mol respectively, while one activation energy (184 kJ/mol) represented the tensile–creep behavior over the temperature range examined. Dislocation creep was suggested to be the main mechanism in tensile creep and in the high-temperature regime in compressive creep, while grain boundary sliding was suggested to dominate in the low-temperature regime in compressive creep. Precipitate free zones were observed near grain boundaries perpendicular to the loading direction in tension and parallel to the loading direction in compression. Electron backscattered diffraction analysis revealed that the texture changed slightly during creep. Non-basal slip was suggested to contribute to the deformation after basal slip was introduced. In the tensile–creep ruptured specimens, intergranular cracks were mainly observed at general high-angle boundaries. - Highlights: • Creep behavior of an extruded Mg–RE alloy was characterized by EBSD. • T5 aging treatment enhanced the tension–compression creep asymmetry. • The grains grew slightly during tensile creep, but not for compressive creep. • Precipitate free zones (PFZs) were observed at specific grain boundaries. • Intergranular fracture was dominant and cracks mainly originated at

  11. Buckling and postbuckling behavior of square compression-loaded graphite-epoxy plates with circular cutouts

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    1990-01-01

    An experimental study of the postbuckling behavior of square compression-loaded graphite-epoxy plates and isotropic plates with a central circular cutout is presented. Results are presented for unidirectional (0 sub 10)s and (90 sub 10)s plates, (0/90 sub 5)s plates, and for aluminum plates. Results are also presented for (+ or - O sub 6)s angle-ply plates for values of O = 30, 46, and 60 degrees. The experimental results indicate that the change in axial stiffness of a plate at buckling is strongly dependent upon cutout size and plate orthotropy. The presence of a cutout gives rise to an internal load distribution that changes, sometimes dramtically, as a function of cutout size coupled with the plate orthotropy. In the buckled state, the role of orthotropy becomes more significant since bending in addition to membrane orthotropy is present. Most of the plates with cutouts exhibited less postbuckling stiffness than the corresponding plate without a cutout, and the postbuckling stiffness decreased with increasing cutout size. However, some of the highly orthotropic plates with cutouts exhibited more postbuckling stiffness than the corresponding plate without a cutout.

  12. Creep behavior of tungsten/niobium and tungsten/niobium-1 percent zirconium composites

    NASA Technical Reports Server (NTRS)

    Petrasek, D. W.; Titran, R. H.

    1988-01-01

    A study was conducted to determine the feasibility of using tungsten fiber reinforced niobium or niobium-1 percent zirconium matrix composites to meet the anticipated increased temperature and creep resistance requirements imposed by advanced space power systems. The results obtained on the short time tensile properties indicated that W/Nb composites showed significant improvements in high temperature strength and offer significant mass reductions for high temperature space power systems. The prime material requirement for space power systems applications is long time creep resistance. A study was conducted to determine the effect of high temperature exposure on the properties of these composites, with emphasis upon their creep behavior at elevated temperatures.

  13. The development of methods for the prediction of primary creep behavior in metals

    NASA Technical Reports Server (NTRS)

    Zerwekh, R. P.

    1978-01-01

    The applicability of a thermodynamic constitutive theory of deformation to the prediction of primary creep and creep strain relaxation behavior in metals is examined. Constitutive equations derived from the theory are subjected to a parametric analysis in order to determine the influence of several parameters on the curve forms generated by the equations. A computer program is developed which enables the solution of a generalized constitutive equation using experimental data as input. Several metals were tested to form a data base of primary creep and relaxation behavior. The extent to which these materials conformed to the constitutive equation showed wide variability, with the alloy Ti-6Al-4V exhibiting the most consistent results. Accordingly, most of the analysis is concentrated upon data from that alloy, although creep and relaxation data from all the materials tested are presented. Experimental methods are outlined as well as some variations in methods of analysis. Various theoretical and practical implications of the work are discussed.

  14. On the Through-the-Width Multiple Delamination, and Buckling and Postbuckling Behaviors of Symmetric and Unsymmetric Composite Laminates

    NASA Astrophysics Data System (ADS)

    Liu, P. F.; Zheng, J. Y.

    2013-12-01

    Multiple delamination causes severe degradation of the stiffness and strength of composites. Interactions between multiple delamination, and buckling and postbuckling under compressive loads add the complexity of mechanical properties of composites. In this paper, the buckling, postbuckling and through-the-width multiple delamination of symmetric and unsymmetric composite laminates are studied using 3D FEA, and the virtual crack closure technique with two delamination failure criteria: B-K law and power law is used to predict the delamination growth and to calculate the mixed-mode energy release rate. The compressive load-strain curves, load-central deflection curves and multiple delamination process for eight composite specimens with different initial delamination sizes and their distributions as well as two angle-ply configurations 04//(± θ)6//04 ( θ = 0° and 45°, and "//" denotes the delaminated interface) are comparatively studied. From numerical results, the unsymmetry decreases the local buckling load and initial delamination load, but does not affect the global buckling load compared with the symmetric laminates. Besides, the unsymmetry affects the unstable delamination and buckling behaviors of composite laminates largely when the initial multiple delamination sizes are relatively small.

  15. Creep behavior for advanced polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

    1997-04-01

    A bend stress relaxation (BSR) test has been utilized to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Qualitative, S-shaped 1hr BSR curves were compared for three selected advanced SiC fiber types and standard Nicalon CG fiber. The temperature corresponding to the middle of the S-curve (where the BSR parameter m = 0.5) is a measure of a fiber`s thermal stability as well as it creep resistance. In order of decreasing thermal creep resistance, the measured transition temperatures were Nicalon S (1450{degrees}C), Sylramic (1420{degrees}C), Hi-Nicalon (1230{degrees}C) and Nicalon CG (1110{degrees}C).

  16. Creep behavior of epoxy resin during irradiation at cryogenic temperature

    NASA Astrophysics Data System (ADS)

    Nishiura, Tetsuya; Nishijima, Shigehiro; Okada, Toichi

    1999-11-01

    Creep tests of an epoxy resin during bending and irradiation have been carried out to investigate the synergistic effects of radiation and stress on mechanical properties of the resin. Simultaneous application of stress and irradiation on the epoxy resin enhanced creep rates in comparison with the application of stress on an irradiated sample. In order to clarify the mechanism of the radiation-induced creep, measurements of solvent swelling of specimens have been performed. The swelling increased with the dose and the increase of the swelling corresponds to the increase of the chain scission. The mechanism of increased deformation of the resin during irradiation is proposed to be caused by increased chain scission following the release of the local strain energy.

  17. Non-Classical Creep Behavior of Fusion-Cast Alumina Refractories

    SciTech Connect

    Hemrick, James Gordon; Wereszczak, Andrew A

    2009-01-01

    The compressive creep behavior of a typical 50% -/50% -alumina fusion-cast refractory block was examined as a function of temperature. Test temperatures (1450-1650oC) were chosen to correspond to those typical of service conditions, while relatively high compressive test stresses (0.6 and 1.0 MPa compared to 0.2-0.4 MPa which is typical of service) were chosen to promote exaggerated deformation and to more accurately measure the resulting creep strain. It was found that the measured creep strain responses in this alumina were a sum of (contracting) compressive creep strain and expansion strain due to time and temperature dependent microcracking. Long term, isothtermal expansion tests were also conducted, and their results allowed for the deconvolution of the compressive creep and expansion strains present in the measured creep strain test data. The analysis shows that despite complications associated with conflicting expansion and contraction effects, classical creep analysis may be used with this alumina refractory after the strains associated with the non-steady-state mechanism are considered and accounted for.

  18. Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems

    NASA Astrophysics Data System (ADS)

    Wen, Xingshuo

    The Very High Temperature Reactor (VHTR) is one of the leading concepts of the Generation IV nuclear reactor development, which is the core component of Next Generation Nuclear Plant (NGNP). The major challenge in the research and development of NGNP is the performance and reliability of structure materials at high temperature. Alloy 617, with an exceptional combination of high temperature strength and oxidation resistance, has been selected as a primary candidate material for structural use, particularly in Intermediate Heat Exchanger (IHX) which has an outlet temperature in the range of 850 to 950°C and an inner pressure from 5 to 20MPa. In order to qualify the material to be used at the operation condition for a designed service life of 60 years, a comprehensive scientific understanding of creep behavior at high temperature and low stress regime is necessary. In addition, the creep mechanism and the impact factors such as precipitates, grain size, and grain boundary characters need to be evaluated for the purpose of alloy design and development. In this study, thermomechanically processed specimens of alloy 617 with different grain sizes were fabricated, and creep tests with a systematic test matrix covering the temperatures of 850 to 1050°C and stress levels from 5 to 100MPa were conducted. Creep data was analyzed, and the creep curves were found to be unconventional without a well-defined steady-state creep. Very good linear relationships were determined for minimum creep rate versus stress levels with the stress exponents determined around 3-5 depending on the grain size and test condition. Activation energies were also calculated for different stress levels, and the values are close to 400kJ/mol, which is higher than that for self-diffusion in nickel. Power law dislocation climb-glide mechanism was proposed as the dominant creep mechanism in the test condition regime. Dynamic recrystallization happening at high strain range enhanced dislocation climb and

  19. Tension/compression asymmetry in creep behavior of a Ni-based superalloy

    SciTech Connect

    Kakehi, K.

    1999-08-06

    Orientation and temperature dependence of yield stress or CRSS (Critical Resolved Shear Stress) and tension/compression anisotropy of the yield stress of CRSS have been shown by Shah and Duhl, Heredia and Pope, and Miner et al. Tension/compression asymmetry in the yield strength of Ni-based superalloys has been explained in terms of the core width effect. Shah and Duhl observed the tension/compression asymmetry in creep deformation, which is similar to that observed in the yield strength, and indicated that it can be attributed to cross slip and dislocation core-constriction mechanisms associated with octahedral slip. However, little is known about the mechanism of tension/compression asymmetry in creep. In the present study, single crystals of a Ni-base superalloy were subjected to tensile and compressive creep tests. Tension/compression asymmetry in creep behavior was examined in detail for each orientation.

  20. A Modified Theta Projection Model for Creep Behavior of Metals and Alloys

    NASA Astrophysics Data System (ADS)

    Kumar, Manish; Singh, I. V.; Mishra, B. K.; Ahmad, S.; Venugopal Rao, A.; Kumar, Vikas

    2016-09-01

    In this work, a modified theta projection model is proposed for the constitutive modeling of creep behavior of metals and alloys. In the conventional theta projection model, strain hardening exponent is a function of time and theta, whereas in the modified theta projection model, the exponent is taken as a function of time, theta, and applied stress. The results obtained by the modified theta projection model for Al 2124 T851 alloy at constant uniaxial tensile stress are compared with the experimental results and with the predictions of the conventional theta projection method. The creep behavior of Al 7075 T651 alloy is also predicted using modified and conventional theta projection model and compared with the available experimental data. It is observed that the modified theta projection model captures the creep behavior more accurately as compared to the conventional theta projection model. The modified theta projection model can be used to predict the creep strain of pure metals and class M alloys (similar creep behavior to pure metals) for intermediate range of stress and temperature.

  1. Bending creep behavior of pressureless sintered MoSi{sub 2}

    SciTech Connect

    Dusza, J.; Hvizdos, P.; Steinkellner, W.; Kromp, K.

    1997-08-15

    Creep behavior in bending of the hot pressed MoSi{sub 2} was studied in the temperature and stress intervals from 1,100 C--1,200 C and from 20 to 100 MPa, respectively. In spite of the fact that the MoSi{sub 2} was not reinforced with a second particle/whisker phase the creep resistance of the material was comparably high because of the clean character of the MoSi{sub 2}/MoSi{sub 2} grain boundaries. The resulting data, the creep exponent from n = 1.3 to 2.4 and the apparent activation energy from Q = 159 to 634 kJ mol{sup {minus}1} are comparable with the data achieved in compressive creep tests for similar materials and together with TEM results they prove that the principal creep mechanism at 1,200 C is probably dislocation climbing. The bending creep test seems to be a good technique for the characterization of the high temperature mechanical properties of MoSi{sub 2} based materials, but similarly as in the case of structural ceramics it is limited to the low-deformation regimes.

  2. Time-Dependent Behaviors of Granite: Loading-Rate Dependence, Creep, and Relaxation

    NASA Astrophysics Data System (ADS)

    Hashiba, K.; Fukui, K.

    2016-07-01

    To assess the long-term stability of underground structures, it is important to understand the time-dependent behaviors of rocks, such as their loading-rate dependence, creep, and relaxation. However, there have been fewer studies on crystalline rocks than on tuff, mudstone, and rock salt, because the high strength of crystalline rocks makes the detection of their time-dependent behaviors much more difficult. Moreover, studies on the relaxation, temporal change of stress and strain (TCSS) conditions, and relations between various time-dependent behaviors are scarce for not only granites, but also other rocks. In this study, previous reports on the time-dependent behaviors of granites were reviewed and various laboratory tests were conducted using Toki granite. These tests included an alternating-loading-rate test, creep test, relaxation test, and TCSS test. The results showed that the degree of time dependence of Toki granite is similar to other granites, and that the TCSS resembles the stress-relaxation curve and creep-strain curve. A viscoelastic constitutive model, proposed in a previous study, was modified to investigate the relations between the time-dependent behaviors in the pre- and post-peak regions. The modified model reproduced the stress-strain curve, creep, relaxation, and the results of the TCSS test. Based on a comparison of the results of the laboratory tests and numerical simulations, close relations between the time-dependent behaviors were revealed quantitatively.

  3. Phase Transformation and Creep Behavior in Ti50Pd30Ni20 High Temperature Shape Memory Alloy in Compression

    NASA Technical Reports Server (NTRS)

    Kumar, Parikshith K.; Desai, Uri; Monroe, James; Lagoudas, Dimitris C.; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glenn

    2010-01-01

    The creep behavior and the phase transformation of Ti50Pd30Ni20 High Temperature Shape Memory Alloy (HTSMA) is investigated by standard creep tests and thermomechanical tests. Ingots of the alloy are induction melted, extruded at high temperature, from which cylindrical specimens are cut and surface polished. A custom high temperature test setup is assembled to conduct the thermomechanical tests. Following preliminary monotonic tests, standard creep tests and thermally induced phase transformation tests are conducted on the specimen. The creep test results suggest that over the operating temperatures and stresses of this alloy, the microstructural mechanisms responsible for creep change. At lower stresses and temperatures, the primary creep mechanism is a mixture of dislocation glide and dislocation creep. As the stress and temperature increase, the mechanism shifts to predominantly dislocation creep. If the operational stress or temperature is raised even further, the mechanism shifts to diffusion creep. The thermally induced phase transformation tests show that actuator performance can be affected by rate independent irrecoverable strain (transformation induced plasticity + retained martensite) as well as creep. The rate of heating and cooling can adversely impact the actuators performance. While the rate independent irrecoverable strain is readily apparent early in the actuators life, viscoplastic strain continues to accumulate over the lifespan of the HTSMA. Thus, in order to get full actuation out of the HTSMA, the heating and cooling rates must be sufficiently high enough to avoid creep.

  4. Effects of multiple delaminations on compressive buckling behaviors of composite panels

    NASA Astrophysics Data System (ADS)

    Suemasu, Hiroshi

    1993-01-01

    Compressive buckling stability of composite panels with through-width, equally spaced multiple delaminations are investigated analytically and experimentally. An analytical method is formulated on the basis of Rayleigh-Ritz approximation technique. Timoshenko type shear effects are included. An experiment and a finite element analysis are also conducted on the present model. The analytical results agree very well with the experimental and finite element results. The buckling load, which is the compressive strength of the panel in the case of the present model, reduces significantly due to the existence of multiple delaminations. The mechanism causing the significant loss of the compressive buckling load due to the delaminations is well explained.

  5. Effect of anisotropy on creep behavior in a functionally graded material disc of variable thickness

    NASA Astrophysics Data System (ADS)

    Gupta, Vandana; Singh, S. B.

    2014-09-01

    In this paper, an effort has been made to study the effect of anisotropy on the steady state creep behavior in the functionally graded material disc with hyperbolic thickness made of Al-SiC (particle). The content of silicon carbide particles in the disc is assumed to decrease linearly from the inner to the outer radius of the disc. The creep behavior of the disc under stresses developing due to rotation at 15,000 rpm has been determined by Sherby's law. The creep parameters of the FGM disc vary along the radial distance due to varying composition and this variation has been estimated by regression fit of the available experimental data. The creep response of rotating disc is expressed by a threshold stress with value of stress exponent as 8. The study reveals that the anisotropy has a significant effect on the steady state creep response of rotating FGM disc. Thus, the care to introduce anisotropy should be taken for the safe design of the rotating FGM disc with hyperbolic thickness.

  6. Buckling Behavior of Long Anisotropic Plates Subjected to Elastically Restrained Thermal Expansion and Contraction

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    2004-01-01

    An approach for synthesizing buckling results for thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and elastically restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexural anisotropic plates that are subjected to combined mechanical loads. In addition, stiffness-weighted laminate thermal-expansion parameters and compliance coefficients are derived that are used to determine critical temperatures in terms of physically intuitive mechanical-buckling coefficients. Many results are presented for some common laminates that are intended to facilitate a structural designer s transition to the use of the generic buckling design curves. Several curves that illustrate the fundamental parameters used in the analysis are presented, for nine contemporary material systems, that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of the generic design curves.

  7. Representative volume element to estimate buckling behavior of graphene/polymer nanocomposite

    PubMed Central

    2012-01-01

    The aim of the research article is to develop a representative volume element using finite elements to study the buckling stability of graphene/polymer nanocomposites. Research work exploring the full potential of graphene as filler for nanocomposites is limited in part due to the complex processes associated with the mixing of graphene in polymer. To overcome some of these issues, a multiscale modeling technique has been proposed in this numerical work. Graphene was herein modeled in the atomistic scale, whereas the polymer deformation was analyzed as a continuum. Separate representative volume element models were developed for investigating buckling in neat polymer and graphene/polymer nanocomposites. Significant improvements in buckling strength were observed under applied compressive loading when compared with the buckling stability of neat polymer. PMID:22994951

  8. Behavior of Repeating Earthquake Sequences in Central California and the Implications for Subsurface Fault Creep

    SciTech Connect

    Templeton, D C; Nadeau, R; Burgmann, R

    2007-07-09

    Repeating earthquakes (REs) are sequences of events that have nearly identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth. We investigate the occurrence of these REs along faults in central California to determine which faults exhibit creep and the spatio-temporal distribution of this creep. At the juncture of the San Andreas and southern Calaveras-Paicines faults, both faults as well as a smaller secondary fault, the Quien Sabe fault, are observed to produce REs over the observation period of March 1984-May 2005. REs in this area reflect a heterogeneous creep distribution along the fault plane with significant variations in time. Cumulative slip over the observation period at individual sequence locations is determined to range from 5.5-58.2 cm on the San Andreas fault, 4.8-14.1 cm on the southern Calaveras-Paicines fault, and 4.9-24.8 cm on the Quien Sabe fault. Creep at depth appears to mimic the behaviors seen of creep on the surface in that evidence of steady slip, triggered slip, and episodic slip phenomena are also observed in the RE sequences. For comparison, we investigate the occurrence of REs west of the San Andreas fault within the southern Coast Range. Events within these RE sequences only occurred minutes to weeks apart from each other and then did not repeat again over the observation period, suggesting that REs in this area are not produced by steady aseismic creep of the surrounding fault surface.

  9. Low Cycle Fatigue and Creep-Fatigue Behavior of Alloy 617 at High Temperature

    SciTech Connect

    Cabet, Celine; Carroll, Laura; Wright, Richard

    2013-10-01

    Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) application of the Very High Temperature Nuclear Reactor (VHTR), expected to have an outlet temperature as high as 950 degrees C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Initial creep-fatigue work on Alloy 617 suggests a more dominant role of environment with increasing temperature and/or hold times evidenced through changes in creep-fatigue crack growth mechanism/s and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 degrees C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens, although evidence of grain boundary cavitation was not observed. Despite the absence of grain boundary cavitation to accelerate crack propagation, the addition of a hold time at peak tensile strain was detrimental to cycle life. This suggests that creepfatigue interaction may occur by a different mechanism or that the environment may be partially responsible for accelerating failure.

  10. Tensile and Creep Behavior of Extruded AA6063/SiC{sub p} Al MMCs

    SciTech Connect

    Khalifa, Tarek A.; Mahmoud, Tamer S.

    2010-03-01

    Composites of AA6063 Al alloy reinforced with SiC particles (SiC{sub p}) were prepared by the vortex method. Hot extrusion was carried out for the as cast composites with a reduction in area of 25%. Tensile and creep behavior of as-cast and extruded composites were studied at elevated temperatures. Tensile tests carried out at room temperature showed that for the as-cast composites, the addition of SiC{sub p} up to 10% by weight improves the strength but reduces ductility. Further addition of SiC{sub p} reduces the strength and ductility of the composites. At 150 and 300 deg. C the matrix alloy exhibits higher strength than the composites. Extrusion generally raised the strength of the composites at both room and elevated temperatures. Time rupture creep tests carried out at 300 deg. C showed that the composites exhibit higher creep resistance as compared to the matrix alloy except at relatively low stresses where the matrix has a better creep resistance. Extrusion improved the resistance of composites to creep rupture.

  11. 1300 K Creep Behavior of [001] Oriented Ni-49Al-1Hf (at.%) Single Crystals

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel; Locci, I. E.; Darolia, Ram; Bowman, R.

    1999-01-01

    A study of the 1300 K compressive and tensile creep properties of [001]-oriented NiAl-1Hf (D209) single crystals has been undertaken. Neither post homogenization cooling treatment, minor chemical variations within an ingot or from ingot-to-ingot, nor testing procedure had a significant effect on mechanical behavior; however a heat treatment which dissolved the initial G-phase precipitates and promoted formation of Heusler particles led to a strength reduction. Little primary creep was found utilizing direct measurement of strain, and a misorientation of 18 deg from the [001] did not reduce the creep strength. The effects of heat treatments on properties and a comparison of the flow stress-strain rate data to those predicted by the Jaswon-Cottrell solid solution hardening model indicate that the 1300 K strength in NiAl-1Hf single crystals is mainly due to precipitation hardening mechanisms.

  12. Investigation of Asphalt Mixture Creep Behavior Using Thin Beam Specimens

    NASA Astrophysics Data System (ADS)

    Zofka, Adam; Marasteanu, Mihai; Turos, Mugur

    2008-02-01

    The asphalt pavement layer consists of two or more lifts of compacted asphalt mixture; the top of the layer is also exposed to aging, a factor that significantly affects the mixture properties. The current testing specifications use rather thick specimens that cannot be used to investigate the gradual change in properties with pavement depth. This paper investigates the feasibility of using the 3-point bending test with thin asphalt mixture beams (127×12.7×6.35 mm) to determine the low-temperature creep compliance of the mixtures. Several theoretical and semi-empirical models, from the theory of composites, are reviewed and evaluated using numerical and experimental data. Preliminary results show that this method can be used for low-temperature mixture characterization but several crucial factors need further inspection and interpretation.

  13. Investigation of Asphalt Mixture Creep Behavior Using Thin Beam Specimens

    SciTech Connect

    Zofka, Adam; Marasteanu, Mihai; Turos, Mugur

    2008-02-15

    The asphalt pavement layer consists of two or more lifts of compacted asphalt mixture; the top of the layer is also exposed to aging, a factor that significantly affects the mixture properties. The current testing specifications use rather thick specimens that cannot be used to investigate the gradual change in properties with pavement depth. This paper investigates the feasibility of using the 3-point bending test with thin asphalt mixture beams (127x12.7x6.35 mm) to determine the low-temperature creep compliance of the mixtures. Several theoretical and semi-empirical models, from the theory of composites, are reviewed and evaluated using numerical and experimental data. Preliminary results show that this method can be used for low-temperature mixture characterization but several crucial factors need further inspection and interpretation.

  14. Buckling Behavior of Compression-Loaded Composite Cylindrical Shells with Reinforced Cutouts

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Starnes, James H., Jr.

    2002-01-01

    Results from a numerical study of the response of thin-wall compression-loaded quasi-isotropic laminated composite cylindrical shells with reinforced and unreinforced square cutouts are presented. The effects of cutout reinforcement orthotropy, size, and thickness on the nonlinear response of the shells are described. A high-fidelity nonlinear analysis procedure has been used to predict the nonlinear response of the shells. The analysis procedure includes a nonlinear static analysis that predicts stable response characteristics of the shells and a nonlinear transient analysis that predicts unstable dynamic buckling response characteristics. The results illustrate how a compression-loaded shell with an unreinforced cutout can exhibit a complex nonlinear response. In particular, a local buckling response occurs in the shell near the cutout and is caused by a complex nonlinear coupling between local shell-wall deformations and in-plane destabilizing compression stresses near the cutout. In general, the addition of reinforcement around a cutout in a compression-loaded shell can retard or eliminate the local buckling response near the cutout and increase the buckling load of the shell, as expected. However, results are presented that show how certain reinforcement configurations can actually cause an unexpected increase in the magnitude of local deformations and stresses in the shell and cause a reduction in the buckling load. Specific cases are presented that suggest that the orthotropy, thickness, and size of a cutout reinforcement in a shell can be tailored to achieve improved response characteristics.

  15. Buckling Behavior of Compression-Loaded Composite Cylindrical Shells With Reinforced Cutouts

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Sarnes, James H., Jr.

    2004-01-01

    Results from a numerical study of the response of thin-walled compression-loaded quasi-isotropic laminated composite cylindrical shells with unreinforced and reinforced square cutouts are presented. The effects of cutout reinforcement orthotropy, size, and thickness on the nonlinear response of the shells are described. A nonlinear analysis procedure has been used to predict the nonlinear response of the shells. The results indicate that a local buckling response occurs in the shell near the cutout when subjected to load and is caused by a nonlinear coupling between local shell-wall deformations and in-plane destabilizing compression stresses near the cutout. In general, reinforcement around a cutout in a compression-loaded shell is shown to retard or eliminate the local buckling response near the cutout and increase the buckling load of the shell. However, some results show that certain reinforcement configurations can cause an unexpected increase in the magnitude of local deformations and stresses in the shell and cause a reduction in the buckling load. Specific cases are presented that suggest that the orthotropy, thickness, and size of a cutout reinforcement in a shell can be tailored to achieve improved buckling response characteristics.

  16. Tensile and creep rupture behavior of P/M processed Nb-base alloy, WC-3009

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G.; Titran, Robert H.

    1988-01-01

    Due to its high strength at temperatures up to 1600 K, fabrication of niobium base alloy WC-3009 (Nb30Hf9W) by traditional methods is difficult. Powder metallurgy (P/M) processing offers an attractive fabrication alternative for this high strength alloy. Spherical powders of WC-3009 produced by electron beam atomizing (EBA) process were successfully consolidated into a one inch diameter rod by vacuum hot pressing and swaging techniques. Tensile strength of the fully dense P/M material at 300-1590 K were similar to the arc-melted material. Creep rupture tests in vacuum indicated that WC-3009 exhibits a class 1 solid solution (glide controlled) creep behavior in the 1480 to 1590 K temperature range and stress range of 14 to 70 MPa. The creep behavior was correlated with temperature and stress using a power law relationship. The calculated stress exponent n, was about 3.2 and the apparent activation energy, Q, was about 270 kJ/mol. The large creep ductility exhibited by WC-3009 was attributed to its high strain rate sensitivity.

  17. The effect of sheet processing on the microstructure, tensile, and creep behavior of INCONEL alloy 718

    NASA Astrophysics Data System (ADS)

    Boehlert, C. J.; Dickmann, D. S.; Eisinger, Ny. N. C.

    2006-01-01

    The grain size, grain boundary character distribution (GBCD), creep, and tensile behavior of INCONEL alloy 718 (IN 718) were characterized to identify processing-microstructure-property relationships. The alloy was sequentially cold rolled (CR) to 0, 10, 20, 30, 40, 60, and 80 pct followed by annealing at temperatures between 954 °C and 1050 °C and the traditional aging schedule used for this alloy. In addition, this alloy can be superplastically formed (IN 718SPF) to a significantly finer grain size and the corresponding microstructure and mechanical behavior were evaluated. The creep behavior was evaluated in the applied stress (σ a ) range of 300 to 758 MPa and the temperature range of 638 °C to 670 °C. Constant-load tensile creep experiments were used to measure the values of the steady-state creep rate and the consecutive load reduction method was used to determine the values of backstress (σ0). The values for the effective stress exponent and activation energy suggested that the transition between the rate-controlling creep mechanisms was dependent on effective stresses (σ e =σ a σ0) and the transition occurred at σ e ≅ 135 MPa. The 10 to 40 pct CR samples exhibited the greatest 650 °C strength, while IN 718SPF exhibited the greatest room-temperature (RT) tensile strength (>1550 MPa) and ductility (ɛ f >16 pct). After the 954 °C annealing treatment, the 20 pct CR and 30 pct CR microstructures exhibited the most attractive combination of elevated-temperature tensile and creep strength, while the most severely cold-rolled materials exhibited the poorest elevated-temperature properties. After the 1050 °C annealing treatment, the IN 718SPF material exhibited the greatest backstress and best creep resistance. Electron backscattered diffraction was performed to identify the GBCD as a function of CR and annealing. The data indicated that annealing above 1010 °C increased the grain size and resulted in a greater fraction of twin boundaries, which in

  18. Creep Deformation and Rupture Behavior of Single- and Dual-Pass 316LN Stainless-Steel-Activated TIG Weld Joints

    NASA Astrophysics Data System (ADS)

    Vijayanand, V. D.; Vasudevan, M.; Ganesan, V.; Parameswaran, P.; Laha, K.; Bhaduri, A. K.

    2016-06-01

    Creep deformation and rupture behavior of single-pass and dual-pass 316LN stainless steel (SS) weld joints fabricated by an autogenous activated tungsten inert gas welding process have been assessed by performing metallography, hardness, and conventional and impression creep tests. The fusion zone of the single-pass joint consisted of columnar zones adjacent to base metals with a central equiaxed zone, which have been modified extensively by the thermal cycle of the second pass in the dual-pass joint. The equiaxed zone in the single-pass joint, as well as in the second pass of the dual-pass joint, displayed the lowest hardness in the joints. In the dual-pass joint, the equiaxed zone of the first pass had hardness comparable to the columnar zone. The hardness variations in the joints influenced the creep deformation. The equiaxed and columnar zone in the first pass of the dual-pass joint was more creep resistant than that of the second pass. Both joints possessed lower creep rupture life than the base metal. However, the creep rupture life of the dual-pass joint was about twofolds more than that of the single-pass joint. Creep failure in the single-pass joint occurred in the central equiaxed fusion zone, whereas creep cavitation that originated in the second pass was blocked at the weld pass interface. The additional interface and strength variation between two passes in the dual-pass joint provides more restraint to creep deformation and crack propagation in the fusion zone, resulting in an increase in the creep rupture life of the dual-pass joint over the single-pass joint. Furthermore, the differences in content, morphology, and distribution of delta ferrite in the fusion zone of the joints favors more creep cavitation resistance in the dual-pass joint over the single-pass joint with the enhancement of creep rupture life.

  19. Prediction and Monitoring Systems of Creep-Fracture Behavior of 9Cr-1Mo Steels for Teactor Pressure Vessels

    SciTech Connect

    Potirniche, Gabriel; Barlow, Fred D.; Charit, Indrajit; Rink, Karl

    2013-11-26

    A recent workshop on next-generation nuclear plant (NGNP) topics underscored the need for research studies on the creep fracture behavior of two materials under consideration for reactor pressure vessel (RPV) applications: 9Cr-1Mo and SA-5XX steels. This research project will provide a fundamental understanding of creep fracture behavior of modified 9Cr-1Mo steel welds for through modeling and experimentation and will recommend a design for an RPV structural health monitoring system. Following are the specific objectives of this research project: Characterize metallurgical degradation in welded modified 9Cr-1Mo steel resulting from aging processes and creep service conditions; Perform creep tests and characterize the mechanisms of creep fracture process; Quantify how the microstructure degradation controls the creep strength of welded steel specimens; Perform finite element (FE) simulations using polycrystal plasticity to understand how grain texture affects the creep fracture properties of welds; Develop a microstructure-based creep fracture model to estimate RPVs service life; Manufacture small, prototypic, cylindrical pressure vessels, subject them to degradation by aging, and measure their leak rates; Simulate damage evolution in creep specimens by FE analyses; Develop a model that correlates gas leak rates from welded pressure vessels with the amount of microstructural damage; Perform large-scale FE simulations with a realistic microstructure to evaluate RPV performance at elevated temperatures and creep strength; Develop a fracture model for the structural integrity of RPVs subjected to creep loads; and Develop a plan for a non-destructive structural health monitoring technique and damage detection device for RPVs.

  20. A Comparison of Tension and Compression Creep in a Polymeric Composite and the Effects of Physical Aging on Creep Behavior

    NASA Technical Reports Server (NTRS)

    Gates, Thomas S.; Veazie, David R.; Brinson, L. Catherine

    1996-01-01

    Experimental and analytical methods were used to investigate the similarities and differences of the effects of physical aging on creep compliance of IM7/K3B composite loaded in tension and compression. Two matrix dominated loading modes, shear and transverse, were investigated for two load cases, tension and compression. The tests, run over a range of sub-glass transition temperatures, provided material constants, material master curves and aging related parameters. Comparing results from the short-term data indicated that although trends in the data with respect to aging time and aging temperature are similar, differences exist due to load direction and mode. The analytical model used for predicting long-term behavior using short-term data as input worked equally as well for the tension or compression loaded cases. Comparison of the loading modes indicated that the predictive model provided more accurate long term predictions for the shear mode as compared to the transverse mode. Parametric studies showed the usefulness of the predictive model as a tool for investigating long-term performance and compliance acceleration due to temperature.

  1. Nonlocal and surface effects on the buckling behavior of functionally graded nanoplates: An isogeometric analysis

    NASA Astrophysics Data System (ADS)

    Ansari, R.; Norouzzadeh, A.

    2016-10-01

    The size-dependent static buckling responses of circular, elliptical and skew nanoplates made of functionally graded materials (FGMs) are investigated in this article based on an isogeometric model. The Eringen nonlocal continuum theory is implemented to capture nonlocal effects. According to the Gurtin-Murdoch surface elasticity theory, surface energy influences are also taken into account by the consideration of two thin surface layers at the top and bottom of nanoplate. The material properties vary in the thickness direction and are evaluated using the Mori-Tanaka homogenization scheme. The governing equations of buckled nanoplate are achieved by the minimum total potential energy principle. To perform the isogeometric analysis as a solution methodology, a novel matrix-vector form of formulation is presented. Numerical examples are given to study the effects of surface stress as well as other important parameters on the critical buckling loads of functionally graded nanoplates. It is found that the buckling configuration of nanoplates at small scales is significantly affected by the surface free energy.

  2. Creep behavior of a rabbit model of ligament laxity after electrothermal shrinkage in vivo.

    PubMed

    Wallace, Andrew L; Hollinshead, Robert M; Frank, Cyril B

    2002-01-01

    Deformation of capsular tissue under constant load (creep) may lead to recurrent laxity after thermal shrinkage for shoulder instability. We investigated the effects of thermal shrinkage in a rabbit model in which the tibial insertion of the medial collateral ligament was elevated and shifted toward the joint line to create abnormal laxity. On the right side, radiofrequency electrothermal energy was applied to the shifted ligament, while the left side served as a control. Length, laxity, mass, cross-sectional area, water content, and creep behavior of the ligament were assessed at 0 (N = 8), 3 (N = 7), and 12 (N = 6) weeks postoperatively. Laxity was reduced with thermal treatment (0.65 +/- 0.31 compared with 3.33 +/- 0.25 mm). After 3 weeks, ligament mass, area, and water content were significantly increased in the thermally treated group compared with the untreated controls. At 12 weeks, cyclic creep strain remained greater than that in controls (1.25% +/- 0.65% compared with 0.93% +/- 0.22%). Although thermal shrinkage reduced laxity, there was increased potential to creep and failure at low physiologic stresses. These findings suggest that loading of thermally treated tissues should be carefully controlled during the early phase of rehabilitation after surgery. PMID:11799003

  3. Tensile creep and stress-rupture behavior of polymer derived SiC fibers

    SciTech Connect

    Yun, H.M.; Goldsby, J.C.; Dicarlo, J.A.

    1994-08-01

    Tensile creep and stress-rupture studies were conducted on polymer derived Nicalon, Hi-Nicalon, and SiC/BN-coated Nicalon SiC fibers. Test conditions were temperatures from 1200 to 1400 C, stresses from 100 to 1600 MPa, stress application times up to 200 hours, and air, argon, and vacuum test environments. For all fibers, creep occurred predominantly in the primary stage. Hi-Nicalon had much higher 0.2 and 1 percent creep strengths than as-produced as well as-coated Nicalon fibers. The stress-rupture strength of Hi-Nicalon up to 100 hours was also higher than that of the coated and as-produced Nicalon fibers. SiC/BN coating on Nicalon increased only the short-term low-temperature rupture strength. Limited testing in argon and vacuum suggests that for all fiber types, creep and rupture resistances are reduced in comparison to the results in air. Possible mechanisms for the observed behavior are discussed.

  4. Tensile creep and stress-rupture behavior of polymer derived SiC fibers

    SciTech Connect

    Yun, H.M.; Goldsby, J.C.; DiCarlo, J.A.

    1994-12-31

    Tensile creep and stress-rupture studies were conducted on polymer derived Nicalon, Hi-Nicalon, and SiC/BN-coated Nicalon SiC fibers. Test conditions were temperatures from 1200 to 1400{degrees}C, stresses from 100 to 1600 MPa, stress application times up to 200 hours, and air, argon, and vacuum test environments. For all fibers, creep occurred predominantly in the primary stage. Hi-Nicalon had much higher 0.2 and 1% creep strengths than as-produced as well as coated Nicalon fibers. The stress-rupture strength of Hi-Nicalon up to 100 hours was also higher than that of the coated and as-produced Nicalon fibers. SiC/BN coating on Nicalon increased only the short-term low-temperature rupture strength. Limited testing in argon and vacuum suggests that for all fiber types, creep and rupture resistances are reduced in comparison to the results in air. Possible mechanisms for the observed behavior are discussed.

  5. Endochronic theory of transient creep and creep recovery

    NASA Technical Reports Server (NTRS)

    Wu, H. C.; Chen, L.

    1979-01-01

    Short time creep and creep recovery were investigated by means of the endochronic theory of viscoplasticity. It is shown that the constitutive equations for constant-strain-rate stress-strain behavior, creep, creep recovery, and stress relaxation can all ber derived from the general constitutive equation by imposing appropriate constraints. In this unified approach, the effect of strain-hardening is naturally accounted for when describing creep and creep recovery. The theory predicts with reasonable accuracy the creep and creep recovery behaviors for Aluminum 1100-0 at 150 C. It was found that the strain-rate history at prestraining stage affects the subsequent creep. A critical stress was also established for creep recovery. The theory predicts a forward creep for creep recovery stress greater than the critical stress. For creep recovery stress less than the critical stress, the theory then predicts a normal strain recovery.

  6. Buckling of spherical capsules.

    PubMed

    Knoche, Sebastian; Kierfeld, Jan

    2011-10-01

    We investigate buckling of soft elastic capsules under negative pressure or for reduced capsule volume. Based on nonlinear shell theory and the assumption of a hyperelastic capsule membrane, shape equations for axisymmetric and initially spherical capsules are derived and solved numerically. A rich bifurcation behavior is found, which is presented in terms of bifurcation diagrams. The energetically preferred stable configuration is deduced from a least-energy principle both for prescribed volume and prescribed pressure. We find that buckled shapes are energetically favorable already at smaller negative pressures and larger critical volumes than predicted by the classical buckling instability. By preventing self-intersection for strongly reduced volume, we obtain a complete picture of the buckling process and can follow the shape from the initial undeformed state through the buckling instability into the fully collapsed state. Interestingly, the sequences of bifurcations and stable capsule shapes differ for prescribed volume and prescribed pressure. In the buckled state, we find a relation between curvatures at the indentation rim and the bending modulus, which can be used to determine elastic moduli from experimental shape analysis. PMID:22181297

  7. Creep Behavior of Glass/Ceramic Sealant and its Effect on Long-term Performance of Solid Oxide Fuel Cells

    SciTech Connect

    Liu, Wenning N.; Sun, Xin; Koeppel, Brian J.; Stephens, Elizabeth V.; Khaleel, Mohammad A.

    2009-10-14

    The creep behavior of glass or glass-ceramic sealant materials used in solid oxide fuel cells (SOFCs) becomes relevant under SOFC operating temperatures. In this paper, the creep of glass-ceramic sealants was experimentally examined, and a standard linear solid model was applied to capture the creep behavior of glass ceramic sealant materials developed for planar SOFCs at high temperatures. The parameters of this model were determined based on the creep test results. Furthermore, the creep model was incorporated into finite-element software programs SOFC-MP and Mentat-FC developed at Pacific Northwest National Laboratory for multi-physics simulation of SOFCs. The effect of creep of glass ceramic sealant materials on the long-term performance of SOFC stacks was investigated by studying the stability of the flow channels and the stress redistribution in the glass seal and on the various interfaces of the glass seal with other layers. Finite element analyses were performed to quantify the stresses in various parts. The stresses in glass seals were released because of creep behavior during operations.

  8. Creep-rupture behavior of iron superalloys in high pressure hydrogen

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, S.

    1981-01-01

    Two cast alloys (CRM-6D and XF-818) and four sheet alloys (A-26, Incoloy 800H, N-155, and 19-9DL) in the thickness range of 0.79 to 0.99 mm were evaluated for use in the Stirling engine. The creep rupture behavior of these iron base high temperature alloys is being determined in air for 10 hr to 3,00 hr, and in 20.7 MPa (3,000 psi) H2 for 10 to 300 hr at temperatures of 650 deg to 925 deg. Material procurement, preparation and air creep rupture testing are described and existing data is analyzed. Systems for the high pressure hydrogen testing are discussed. Statistical analysis of temperature-compensated rupture data for each alloy is included.

  9. Creep-Fatigue Behavior of Alloy 617 at 850 and 950°C, Revision 2

    SciTech Connect

    Carroll, L.; Carroll, M.

    2015-05-01

    Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests including hold times up to 9000 s at maximum tensile strain were conducted at 850 and 950 degrees C. At both temperatures, the fatigue resistance decreased when a hold time was added at peak tensile strain. The magnitude of this effect depended on the specific mechanisms and whether they resulted in a change in fracture mode from transgranular in pure fatigue to intergranular in creep-fatigue for a particular temperature and strain range combination. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep-fatigue resistance at 950 degrees C but did continue to degrade the lifetimes at 850 degrees C.

  10. Creep deformation and rupture behavior of CLAM steel at 823 K and 873 K

    NASA Astrophysics Data System (ADS)

    Zhong, Boyu; Huang, Bo; Li, Chunjing; Liu, Shaojun; Xu, Gang; Zhao, Yanyun; Huang, Qunying

    2014-12-01

    China Low Activation Martensitic (CLAM) steel is selected as the candidate structural material in Fusion Design Study (FDS) series fusion reactor conceptual designs. The creep property of CLAM steel has been studied in this paper. Creep tests have been carried out at 823 K and 873 K over a stress range of 150-230 MPa. The creep curves showed three creep regimes, primary creep, steady-state creep and tertiary creep. The relationship between minimum creep rate (ε˙min) and the applied stress (σ) could be described by Norton power law, and the stress exponent n was decreased with the increase of the creep temperature. The creep mechanism was analyzed with the fractographes of the rupture specimens which were examined by scanning electron microscopy (SEM). The coarsening of precipitates observed with transmission electron microscope (TEM) indicated the microstructural degradation after creep test.

  11. Creep deformation behavior of Sn-3.5Ag solder/Cu couple at small length scales

    SciTech Connect

    Kerr, M.; Chawla, N

    2004-09-06

    In order to adequately characterize the behavior of solder balls in electronic devices, the mechanical behavior of solder joints needs to be studied at small length scales. The creep behavior of single solder ball Sn-Ag/Cu solder joints was studied in shear, at 25, 60, 95, and 130 deg. C, using a microforce testing system. A change in the creep stress exponent with increasing stress was observed and explained in terms of a threshold stress for bypass of Ag{sub 3}Sn particles by dislocations. The stress exponent was also temperature dependent, exhibiting an increase in exponent of two from lower to higher temperature. The activation energy for creep was found to be temperature dependant, correlating with self-diffusion of pure Sn at high temperatures, and dislocation core diffusion of pure Sn at lower temperatures. Normalizing the creep rate for activation energy and the temperature-dependence of shear modulus allowed for unification of the creep data. Microstructure characterization, including preliminary TEM analysis, and fractographic analysis were conducted in order to fully describe the creep behavior of the material.

  12. Elevated temperature tension, compression and creep-rupture behavior of (001)-oriented single crystal superalloy PWA 1480

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G.; Miner, Robert V.

    1987-01-01

    Tensile and compressive flow behavior at various temperatures and strain rates, and tensile creep rupture behavior at 850 and 1050 C and various stresses were studied for (001)-oriented single crystals of the Ni-base superalloy PWA 1480. At temperatures up to 760 C, the flow stress is insensitive to strain rate and of greater magnitude in tension than in compression. At temperatures of 800 C and above, the flow stress decreases continuously with decreasing strain rate and the tension/compression anisotropy diminishes. The second stage creep rate and rupture time exhibited power law relationships with the applied stress for both 850 and 1050 C, however with different stress dependencies. The stress exponent for the steady state creep rate was about 7 at 1050 C, but much higher at 850 C, about 12. Directional coarsening of the gamma' phase occurred during creep at 1050 C, but not at 850 C.

  13. Effect of minor carbon additions on the high-temperature creep behavior of a single-crystal nickel-based superalloy

    SciTech Connect

    Wang, L. Wang, D.; Liu, T.; Li, X.W.; Jiang, W.G.; Zhang, G.; Lou, L.H.

    2015-06-15

    Different amounts of carbon were added to a single-crystal nickel-based superalloy. The microstructural evolution of these alloys before and after high-temperature creep tests was investigated by employing scanning electron microscopy and transmission electron microscopy. Upon increasing the carbon contents, the volume fraction and diameter of the carbides increased gradually: however, the creep lives of the alloys increased slightly at first and subsequently decreased. The formation of second-phase particles, such as the nano-sized M{sub 23}C{sub 6}, blocky and needle-shaped μ phase, was observed in the creep samples, which was closely related to the high-temperature creep behaviors. - Highlights: • Creep behaviors of alloys with different amounts of carbon were investigated. • The creep rupture lives increased and later decreased with more carbon. • Second-phase particles were responsible for the different creep behaviors.

  14. Influence of Hold Time on Creep-Fatigue Behavior of an Advanced Austenitic Alloy

    SciTech Connect

    Mark Carroll; Laura Carroll

    2011-09-01

    An advanced austenitic alloy, HT-UPS (high temperature-ultrafine precipitate strengthened), is a candidate material for the structural components of fast reactors and energy-conversion systems. HT-UPS provides improved creep resistance through a composition based on 316 stainless steel (SS) with additions of Ti and Nb to form nano-scale MC precipitates in the austenitic matrix. The low cycle fatigue and creep-fatigue behavior of a HT-UPS alloy has been investigated at 650 C, 1.0% total strain, and an R ratio of -1 with hold times as long as 9000 sec at peak tensile strain. The cyclic deformation response of HT-UPS is compared to that of 316 SS. The cycles to failure are similar, despite differences in peak stress profiles and the deformed microstructures. Cracking in both alloys is transgranular (initiation and propagation) in the case of continuous cycle fatigue, while the primary cracks also propagate transgranularly during creep-fatigue cycling. Internal grain boundary damage as a result of the tensile hold is present in the form of fine cracks for hold times of 3600 sec and longer and substantially more internal cracks are visible in 316 SS than HT-UPS. The dislocation substructures observed in the deformed material are different. An equiaxed cellular structure is observed in 316 SS, whereas tangles of dislocations are present at the nanoscale MC precipitates in HT-UPS and no cellular substructure is observed.

  15. Impression creep behavior of atmospheric plasma sprayed and hot pressed MoSi{sub 2}/Si{sub 3}N{sub 4}

    SciTech Connect

    Hollis, K.J.; Butt, D.P.; Castro, R.G.

    1997-09-01

    The use of MoSi{sub 2} as a high temperature oxidation resistant structural material is hindered by its poor elevated temperature creep resistance. The addition of second phase Si{sub 3}N{sub 4} holds promise for improving the creep properties of MoSi{sub 2} without decreasing oxidation resistance. The high temperature impression creep behavior of atmospheric plasma sprayed (APS) and hot pressed (HP) MoSi{sub 2}/Si{sub 3}N{sub 4} composites was investigated. Values for steady state creep rates, creep activation energies, and creep stress exponents were measured. Grain boundary sliding and splat sliding were found to be the dominant creep mechanisms for the APS samples while grain boundary sliding and plastic deformation were found to be the dominant creep mechanisms for the HP samples.

  16. Propagating episodic creep and the aseismic slip behavior of the Calaveras fault north of Hollister, California

    SciTech Connect

    Evans, K.F.; Burford, R.O.; King, G.C.P.

    1981-05-10

    A detailed kinematic study of fault slip occurring from the surface to a depth of about 7 km on the Calaveras fault north of Hollister was conducted during the summer of 1977. The observations coincided with a period of propagating episodic fault creep activity sensed along the fault trace. Data used in the investigation consist of creepmeter records, near-field strainmeter observations, and high-resolution geodetic measurements, all collected contemporaneously over a period of 4 months. Detailed descriptions and analyses of the creepmeter and geodetic data have been presented elsewhere. The near-field strain measurements are here reported in detail, and their analysis draws upon the previous two data sets for support. The strainmeter observations are most sensitive to slip occurring in the upper 2 km; hence the emphasis of the paper is placed upon the role of propagating episode creep in the broad-scale behavior of the fault. The results suggest that propagating episodic fault creep as sensed along the fault trace is confined to the upper kilometer or so of the crust and represents the response of the surface layers to a longer-term form of episode aseismic slip occurring below. The mean form of the advancing rupture front within the upper kilometer is ostensibly the same as that indicated by records from the surface creepmeters. Evidence is presented, however, which suggests that propagating creep events may not always break the surface and may propagate at velocities much slower and at amplitudes significantly larger than those generally observed at the surface.

  17. PROCESSING, MICROSTRUCTURE AND CREEP BEHAVIOR OF Mo-Si-B-BASED INTERMETALLIC ALLOYS FOR VERY HIGH TEMPERATURE STRUCTURAL APPLICATIONS

    SciTech Connect

    Vijay K. Vasudevan

    2005-12-21

    This research project is concerned with developing a fundamental understanding of the effects of processing and microstructure on the creep behavior of refractory intermetallic alloys based on the Mo-Si-B system. During this year, the compressive creep behavior of a Mo-3Si-1B (in wt.%) alloy at 1100 and 1200 C were studied and related to the deformation mechanisms through electron microscopy observations of microstructural changes and deformation structures. The microstructure of this alloy was three-phase, being composed of {alpha}-Mo, Mo{sub 3}Si and T2-Mo{sub 5}SiB{sub 2} phases. Results of compressive creep tests at 1200 and 1100 C showed that the creep rates were quite high at stress levels between 250 and 500 MPa, Two minima in the creep strain rate versus strain data were noted, one at small strain values and the second at much larger strains. A stress exponent of 4.26 was obtained upon plotting the strain rate corresponding to the first minima versus stress, which suggests that dislocation climb and glide dominate the creep process in the early stages. On the other hand, the large strain, minimum creep rate versus stress data gave a stress exponent of {approx}1.18, which indicates diffusional mechanisms and recrystallization dominate the later stages of the creep process. At 1100 C, a stress exponent of 2.26 was obtained, which suggests that both diffusional and dislocation mechanisms contribute to the creep strain. Based on the minimum creep rate data at 1100 C and 1200 C, the activation energy for creep was determined to be 525 kJ/mole, which is somewhat higher than that reported for self diffusion in {alpha}-Mo. Microstructural observations of post-crept samples indicated the presence of many voids in the {alpha}-Mo grains and few cracks in the intermetallic particles and along their interfaces with the {alpha}-Mo matrix. In addition, TEM observations revealed the presence of recrystallized grains and sub-grain boundaries composed of dislocation arrays

  18. On the bending and buckling behaviors of Mindlin nanoplates considering surface energies

    NASA Astrophysics Data System (ADS)

    Ansari, R.; Shahabodini, A.; Faghih Shojaei, M.; Mohammadi, V.; Gholami, R.

    2014-03-01

    Due to the high surface to volume ratio of the nanoscale domain, the surface stress effect is a major concern in the analysis of mechanical response of the nanomaterials and nanostructures. This paper is concerned with the applicability of a continuum model including the surface properties for describing the bending and buckling configuration of the nanoscale plates. The Gurtin-Murdoch surface theory of elasticity is first incorporated into Mindlin’s plate theory. Then, the principle of virtual work is applied to derive the size-dependent governing equations along with various boundary conditions. To solve the governing equations, the generalized differential quadrature (GDQ) method is employed. The critical uniaxial and biaxial buckling loads and the maximum deflection of the nanoplate due to a uniform transverse load are calculated in the presence and absence of the surface effects for various edge conditions. It is found that the significance of the surface effects on the response of the nanoplate relies on its size, type of edge support and selected surface constants.

  19. On the behavior of dissipative systems in contact with a heat bath: Application to Andrade creep

    NASA Astrophysics Data System (ADS)

    Sullivan, T.; Koslowski, M.; Theil, F.; Ortiz, M.

    2009-07-01

    We develop a theory of statistical mechanics for dissipative systems governed by equations of evolution that assigns probabilities to individual trajectories of the system. The theory is made mathematically rigorous and leads to precise predictions regarding the behavior of dissipative systems at finite temperature. Such predictions include the effect of temperature on yield phenomena and rheological time exponents. The particular case of an ensemble of dislocations moving in a slip plane through a random array of obstacles is studied numerically in detail. The numerical results bear out the analytical predictions regarding the mean response of the system, which exhibits Andrade creep.

  20. Compressive creep behavior of alloys based on B2 FeAl

    NASA Technical Reports Server (NTRS)

    Mantravadi, N.; Vedula, K.; Gaydosh, D.; Titran, R. H.

    1986-01-01

    Alloys based on FeAl are attractive alternate materials for environmental resistance at intermediate temperatures. Addition of small amounts of Nb, Hf, Ta, Mo, Zr, and B were shown to improve the compressive creep of this alloy at 1100 K. Boron, in particular, was found to have a synergistic effect along with Zr in providing properties substantially better than the binary alloy. This improvement seems to be related to the higher activation energy found for this alloy, suggesting a modification in the diffusion behavior due to the alloying additions.

  1. Compressive creep behavior of alloys based on B2 FeAl

    NASA Technical Reports Server (NTRS)

    Mantravadi, N.; Vedula, K.; Gaydosh, D.; Titran, R. H.

    1987-01-01

    Alloys based on FeAl are attractive alternative materials for environmental resistance at intermediate temperatures. Addition of small amounts of Nb, Hf, Ta, Mo, Zr, and B were shown to improve the compressive creep of this alloy at 1100 K. Boron, in particular, was found to have a synergistic effect along with Zr in providing properties substantially better than the binary alloy. This improvement seems to be related to the higher activation energy found for this alloy, suggesting a modification in the diffusion behavior due to the alloying additions.

  2. A molecular dynamics investigation into the size-dependent buckling behavior of a novel three-dimensional metallic carbon nanostructure (T6)

    NASA Astrophysics Data System (ADS)

    Ansari, R.; Ajori, S.; Hassani, R.

    2016-09-01

    The buckling behavior of a novel three-dimensional metallic carbon nanostructure known as T6 is investigated herein employing the molecular dynamics (MD) simulations. The models are prepared on the basis of two beam- and plate-like structures to study the effects of size and geometry on the critical buckling force and critical strain. It is observed that the range of critical force for the beam-like and plate-like T6 with different geometrical parameters is approximately identical. Moreover, it is demonstrated that the critical buckling force decreases and increases by increasing the length and the width of T6, respectively. Moreover, it is shown that critical strain of beam-like T6 decreases by increasing the length, whereas, in the case of plate-like T6, the critical strain only fluctuates around 2% by increasing the width. It is further found that the buckling parameters of T6 are not comparable with those of single-walled carbon nanotubes (SWCNTs) and graphene with a relatively similar dimension. The critical buckling force and critical strain of T6 are considerably smaller than those of SWCNT and larger than those of graphene.

  3. Creep behavior of tantalum alloy T-222 at 1365 to 1700 K

    NASA Technical Reports Server (NTRS)

    Titran, R. H.

    1974-01-01

    High vacuum creep tests on the tantalum T-222 alloy at 0.42 to 0.52 T sub m show that the major portion of the creep curves, up to at least 1 percent strain, can be best described by an increasing creep rate, with strain varying linearly with time. Correlation and extrapolation of the creep curves on the basis of increasing creep rates results in more accurate engineering design data than would use of approximated linear rates. Based on increasing creep rates, the stress for 1 percent strain in 10,000 hours for T-222 is about four times greater than for the Ta-10W alloy. Increasing the grain size results in increased creep strength. Thermal aging prior to testing caused precipitation of the hexagonal close packed (Hf,Ta) sub 2 C, which initially increased creep strength. However, this dimetal carbide was converted during creep testing to face-centered cubic (Hf,Ta)C.

  4. Osmotic buckling of spherical capsules.

    PubMed

    Knoche, Sebastian; Kierfeld, Jan

    2014-11-01

    We study the buckling of elastic spherical shells under osmotic pressure with the osmolyte concentration of the exterior solution as a control parameter. We compare our results for the bifurcation behavior with results for buckling under mechanical pressure control, that is, with an empty capsule interior. We find striking differences for the buckling states between osmotic and mechanical buckling. Mechanical pressure control always leads to fully collapsed states with opposite sides in contact, whereas uncollapsed states with a single finite dimple are generic for osmotic pressure control. For sufficiently large interior osmolyte concentrations, osmotic pressure control is qualitatively similar to buckling under volume control with the volume prescribed by the osmolyte concentrations inside and outside the shell. We present a quantitative theory which also captures the influence of shell elasticity on the relationship between osmotic pressure and volume. These findings are relevant for the control of buckled shapes in applications. We show how the osmolyte concentration can be used to control the volume of buckled shells. An accurate analytical formula is derived for the relationship between the osmotic pressure, the elastic moduli and the volume of buckled capsules. This also allows use of elastic capsules as osmotic pressure sensors or deduction of elastic properties and the internal osmolyte concentration from shape changes in response to osmotic pressure changes. We apply our findings to published experimental data on polyelectrolyte capsules. PMID:25209240

  5. Effects of Thermal Treatment on Tensile Creep and Stress-Rupture Behavior of Hi-Nicalon SiC Fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.; Dicarlo, J. A.

    1995-01-01

    Tensile creep and stress-rupture studies were conducted on Hi-Nicalon SiC fibers at 1200 and 1400 C in argon and air. Examined were as-received fibers as well as fibers annealed from 1400 to 1800 C for 1 hour in argon before testing. The creep and rupture results for these annealed fibers were compared to those of the as-received fibers to determine the effects of annealing temperature, test temperature, and test environment. Argon anneals up to 1500 C degrade room temperature strength of Hi-Nicalon fibers, but improve fiber creep resistance in argon or air by as much as 100% with no significant degradation in rupture strength. Argon anneals above 1500 C continue to improve fiber creep resistance when tested in argon, but significantly degrade creep resistance and rupture strength when tested in air. Decrease in creep resistance in air is greater at 1200 C than at 1400 C. Mechanisms are suggested for the observed behavior.

  6. An experimental and theoretical investigation of the low temperature creep deformation behavior of single phase titanium alloys

    NASA Astrophysics Data System (ADS)

    Oberson, P. Gregory

    Titanium alloys are used for many applications due to their desirable properties, including its high strength-to-weight ratio, corrosion resistance, and biocompatibility. Titanium alloys are used extensively for aerospace, chemical, nuclear, industrial, biomedical, and consumer applications. In many applications, titanium components may be subject to stresses for extended periods of time. It has long been known that single-phase hexagonally close-packed (HCP) alpha and body-centered cubic (BCC) beta titanium alloys deform over time, or creep, at low temperatures (<0.25*Tm). As such, creep is an important factor to consider when assessing the structural reliability of titanium components. However, the factors that affect creep behavior such as grain size and alloy chemistry and the deformation mechanisms associated with creep such as slip and twinning are not well understood. The aim of this investigation is to experimentally and theoretically study the creep deformation behavior of single-phase alpha and beta titanium alloys. The first part of the investigation concerns alpha-Ti alloys. The low temperature creep behavior was studied experimentally, using alpha-Ti-1.6wt.%V as the model alloy. Creep testing was performed at a range of temperatures and slip and twinning were identified as creep deformation mechanisms by optical, SEM and TEM microscopy. The activation energy for creep was measured for the first time for an alpha-Ti than deforms by twinning. The activation energy was found to increase as a function of creep strain, suggesting that there is a change in the predominant deformation mechanism from slip at low strain to twinning at high strain. The reason for this change is explained by a model for twin nucleation caused by dislocation pileups. The theoretical aspect of the study of alpha-Ti, concerns the phenomenon of slow twin growth (time-dependent twinning) during low temperature creep. This phenomenon is unusual and poorly understood as twins in bulk

  7. Creep behavior of thin laminates of iron-cobalt alloys for use in switched reluctance motors and generators

    NASA Astrophysics Data System (ADS)

    Fingers, Richard Todd

    The United States Air Force is in the process of developing magnetic bearings as well as an aircraft Integrated Power Unit and an Internal Starter/Generator for main propulsion engines. These developments are the driving force behind a new emphasis on high temperature, high strength magnetic materials for power applications. Analytical work, utilizing elasticity theory, in conjunction with design requirements, indicates a need for magnetic materials to have strengths in excess of 80 ksi up to about 1000sp°F. It is this combination of desired material characteristics that is the motivation for this effort to measure, model, and predict the creep behavior of such advanced magnetic materials. Hipercosp°ler Alloy 50HS, manufactured by Carpenter Technology Corporation, is one of the leading candidates for application and is studied in this effort by subjecting mechanical test specimens to a battery of tensile and creep tests. The tensile tests provide stress versus strain behaviors that clearly indicate: a yield point, a heterogeneous deformation described as Luders elongation, the Portevin-LeChatelier effect at elevated temperatures, and, most often, a section of homogeneous deformation that concluded with necking and fracture. Creep testing indicated two distinct types of behavior. The first was a traditional response with primary, secondary and tertiary stages, while the second type could be characterized by an abrupt increase in strain rate that acted as a transition from one steady state behavior to another. This second linear region was then followed by the tertiary stage. The relationship between the tensile response and the creep responses is discussed. Analyses of the mechanical behavior includes double linear regression of empirically modeled data, scanning electron microscopy for microstructural investigations, isochronous stress-strain relations, and constant strain rate testing to relate the tensile and creep test parameters. Also, elastic and creep

  8. PROCESSING, MICROSTRUCTURE AND CREEP BEHAVIOR OF MO-SI-B-BASED INTERMETALLIC ALLOYS FOR VERY HIGH TEMPERATURE STRUCTURAL APPLICATIONS

    SciTech Connect

    Vijay K. Vasudevan

    2005-02-08

    This research project is concerned with developing a fundamental understanding of the effects of processing and microstructure on the creep behavior of refractory intermetallic alloys based on the Mo-Si-B system. During this year, the microstructure, bend strength and compressive creep behavior of a Mo-3Si-1B (in wt.%) alloy were studied. The microstructure of this alloy was three-phase, being composed of {alpha}-Mo, Mo{sub 3}Si and T2-Mo{sub 5}SiB{sub 2} phases. The elastic limit strength of the alloy remained quite high until 1200 C with a value of 800MPa, but dropped rapidly thereafter to a value of 220 MPa at 1400 C. Results of compressive creep tests at 1200 C showed that the creep rates were quite high and varied nearly linearly with stress between 250 and 500 MPa, which suggests that diffusional mechanisms dominate the creep process. Microstructural observations of post-crept samples indicated the presence of many voids in the {alpha}-Mo grains and few cracks in the intermetallic particles and along their interfaces with the {alpha}-Mo matrix. These results and presented and discussed.

  9. In Situ Observation of Creep and Fatigue Failure Behavior for Plasma-Sprayed Thermal Barrier Coating Systems

    NASA Astrophysics Data System (ADS)

    Takahashi, Satoru; Harada, Yoshio

    In order to investigate crack initiation sites and the crack propagation behavior in connection with the microstructure of thermal barrier coating (TBC) systems under creep and fatigue loadings, the failure behavior was observed in situ for plasma-sprayed TBC systems by optical microscopy, as a first step for elucidating the thermo-mechanical failure mechanism. Two types of TBC systems with differing top-coat (TC) microstructures were prepared by changing the processing conditions. The mechanical failure behavior of TBC system was found to depend strongly on the loading conditions. Under static creep loading, many segmentation cracks in the TC widened with increasing creep strain in the substrate. However, the propagation of these cracks into the bond-coat (BC) and alloy substrate was prevented due to the stress relief induced by plastic flow in the BC layer at elevated temperatures. As a result, the TBC system exhibited typical creep rupture behavior with nucleation and coalescence of microcracks in the alloy substrate interior regardless of the TC microstructure. Under dynamic fatigue loading, on the other hand, many fatigue cracks initiated not only from the tips of segmentation cracks in the TC layer but also from the TC/BC interface. Furthermore, it was found that the fatigue cracks propagated into the BC and alloy substrate even at elevated temperatures above the ductile-brittle transition temperature of the BC; the fatigue failure behavior under dynamic fatigue loading was dependent on the TC microstructure and the properties of the TC/BC interface.

  10. Creep-Fatigue Behavior of Alloy 617 at 850°C

    SciTech Connect

    Carroll, Laura

    2015-05-01

    Creep-fatigue deformation is expected to be a significant contributor to the potential factors that limit the useful life of the Intermediate Heat Exchanger (IHX) in the Very High Temperature Reactor (VHTR) nuclear system.[1] The IHX of a high temperature gas reactor will be subjected to a limited number of transient cycles due to start-up and shut-down operations imparting high local stresses on the component. This cycling introduces a creep-fatigue type of interaction as dwell times occur intermittently. The leading candidate alloy for the IHX is a nickel-base solid solution strengthened alloy, Alloy 617, which must safely operate near the expected reactor outlet temperature of up to 950 °C.[1] This solid solution strengthened nickel-base alloy provides an interesting creep-fatigue deformation case study because it has characteristics of two different alloy systems for which the cyclic behavior has been extensively investigated. Compositionally, it resembles nickel-base superalloys, such as Waspalloy, IN100, and IN718, with the exception of its lower levels of Al. At temperatures above 800 °C, the microstructure of Alloy 617, however, does not contain the ordered ?’ or ?’’ phases. Thus microstructurally, it is more similar to an austenitic stainless steel, such as 316 or 304, or Alloy 800H comprised of a predominantly solid solution strengthened matrix phase with a dispersion of inter- and intragranular carbides. Previous studies of the creep-fatigue behavior of Alloy 617 at 950 °C indicate that the fatigue life is reduced when a constant strain dwell is added at peak tensile strain.[2-5] This results from the combination of faster crack initiation occurring at surface-connected grain boundaries due to oxidation from the air environment along with faster, and intergranular, crack propagation resulting from the linking of extensive interior grain boundary cracking.[3] Saturation, defined as the point at which further increases in the strain

  11. Creep to inertia dominated stick-slip behavior in sliding friction modulated by tilted non-uniform loading.

    PubMed

    Tian, Pengyi; Tao, Dashuai; Yin, Wei; Zhang, Xiangjun; Meng, Yonggang; Tian, Yu

    2016-01-01

    Comprehension of stick-slip motion is very important for understanding tribological principles. The transition from creep-dominated to inertia-dominated stick-slip as the increase of sliding velocity has been described by researchers. However, the associated micro-contact behavior during this transition has not been fully disclosed yet. In this study, we investigated the stick-slip behaviors of two polymethyl methacrylate blocks actively modulated from the creep-dominated to inertia-dominated dynamics through a non-uniform loading along the interface by slightly tilting the angle of the two blocks. Increasing the tilt angle increases the critical transition velocity from creep-dominated to inertia-dominated stick-slip behaviors. Results from finite element simulation disclosed that a positive tilt angle led to a higher normal stress and a higher temperature on blocks at the opposite side of the crack initiating edge, which enhanced the creep of asperities during sliding friction. Acoustic emission (AE) during the stick-slip has also been measured, which is closely related to the different rupture modes regulated by the distribution of the ratio of shear to normal stress along the sliding interface. This study provided a more comprehensive understanding of the effect of tilted non-uniform loading on the local stress ratio, the local temperature, and the stick-slip behaviors.

  12. Creep to inertia dominated stick-slip behavior in sliding friction modulated by tilted non-uniform loading

    PubMed Central

    Tian, Pengyi; Tao, Dashuai; Yin, Wei; Zhang, Xiangjun; Meng, Yonggang; Tian, Yu

    2016-01-01

    Comprehension of stick-slip motion is very important for understanding tribological principles. The transition from creep-dominated to inertia-dominated stick-slip as the increase of sliding velocity has been described by researchers. However, the associated micro-contact behavior during this transition has not been fully disclosed yet. In this study, we investigated the stick-slip behaviors of two polymethyl methacrylate blocks actively modulated from the creep-dominated to inertia-dominated dynamics through a non-uniform loading along the interface by slightly tilting the angle of the two blocks. Increasing the tilt angle increases the critical transition velocity from creep-dominated to inertia-dominated stick-slip behaviors. Results from finite element simulation disclosed that a positive tilt angle led to a higher normal stress and a higher temperature on blocks at the opposite side of the crack initiating edge, which enhanced the creep of asperities during sliding friction. Acoustic emission (AE) during the stick-slip has also been measured, which is closely related to the different rupture modes regulated by the distribution of the ratio of shear to normal stress along the sliding interface. This study provided a more comprehensive understanding of the effect of tilted non-uniform loading on the local stress ratio, the local temperature, and the stick-slip behaviors. PMID:27641908

  13. Creep to inertia dominated stick-slip behavior in sliding friction modulated by tilted non-uniform loading.

    PubMed

    Tian, Pengyi; Tao, Dashuai; Yin, Wei; Zhang, Xiangjun; Meng, Yonggang; Tian, Yu

    2016-01-01

    Comprehension of stick-slip motion is very important for understanding tribological principles. The transition from creep-dominated to inertia-dominated stick-slip as the increase of sliding velocity has been described by researchers. However, the associated micro-contact behavior during this transition has not been fully disclosed yet. In this study, we investigated the stick-slip behaviors of two polymethyl methacrylate blocks actively modulated from the creep-dominated to inertia-dominated dynamics through a non-uniform loading along the interface by slightly tilting the angle of the two blocks. Increasing the tilt angle increases the critical transition velocity from creep-dominated to inertia-dominated stick-slip behaviors. Results from finite element simulation disclosed that a positive tilt angle led to a higher normal stress and a higher temperature on blocks at the opposite side of the crack initiating edge, which enhanced the creep of asperities during sliding friction. Acoustic emission (AE) during the stick-slip has also been measured, which is closely related to the different rupture modes regulated by the distribution of the ratio of shear to normal stress along the sliding interface. This study provided a more comprehensive understanding of the effect of tilted non-uniform loading on the local stress ratio, the local temperature, and the stick-slip behaviors. PMID:27641908

  14. Creep to inertia dominated stick-slip behavior in sliding friction modulated by tilted non-uniform loading

    NASA Astrophysics Data System (ADS)

    Tian, Pengyi; Tao, Dashuai; Yin, Wei; Zhang, Xiangjun; Meng, Yonggang; Tian, Yu

    2016-09-01

    Comprehension of stick-slip motion is very important for understanding tribological principles. The transition from creep-dominated to inertia-dominated stick-slip as the increase of sliding velocity has been described by researchers. However, the associated micro-contact behavior during this transition has not been fully disclosed yet. In this study, we investigated the stick-slip behaviors of two polymethyl methacrylate blocks actively modulated from the creep-dominated to inertia-dominated dynamics through a non-uniform loading along the interface by slightly tilting the angle of the two blocks. Increasing the tilt angle increases the critical transition velocity from creep-dominated to inertia-dominated stick-slip behaviors. Results from finite element simulation disclosed that a positive tilt angle led to a higher normal stress and a higher temperature on blocks at the opposite side of the crack initiating edge, which enhanced the creep of asperities during sliding friction. Acoustic emission (AE) during the stick-slip has also been measured, which is closely related to the different rupture modes regulated by the distribution of the ratio of shear to normal stress along the sliding interface. This study provided a more comprehensive understanding of the effect of tilted non-uniform loading on the local stress ratio, the local temperature, and the stick-slip behaviors.

  15. Redesigning of a Canard Control Surface of an Advanced Fighter Aircraft: Effect on Buckling and Aerodynamic Behavior

    NASA Astrophysics Data System (ADS)

    Shrivastava, Sachin; Mohite, P. M.

    2015-01-01

    A redesign of canard control-surface of an advanced all-metallic fighter aircraft was carried out by using carbon fibre composite (CFC) for ribs and panels. In this study ply-orientations of CFC structure are optimized using a Genetic-Algorithm (GA) with an objective function to have minimum failure index (FI) according to Tsai-Wu failure criterion. The redesigned CFC structure was sufficiently strong to withstand aerodynamic loads from stress and deflection points of view. Now, in the present work CFC canard structure has been studied for its buckling strength in comparison to existing metallic design. In this study, the existing metallic design was found to be weak in buckling. Upon a detailed investigation, it was revealed that there are reported failures in the vicinity of zones where initial buckling modes are excited as predicted by the finite element based buckling analysis. In view of buckling failures, the redesigned CFC structure is sufficiently reinforced with stringers at specific locations. After providing reinforcements against buckling, the twist and the camber variations of the airfoil are checked and compared with existing structure data. Finally, the modal analysis has been carried out to compare the variation in excitation frequency due to material change. The CFC structure thus redesigned is safe from buckling and aerodynamic aspects as well.

  16. Creep/Rupture Behavior of Melt-Infiltrated SiC/SiC Composites Being Investigated

    NASA Technical Reports Server (NTRS)

    Hurst, Janet B.

    2001-01-01

    The failure behavior of melt-infiltrated SiC/SiC ceramic matrix composites is under investigation at the NASA Glenn Research Center as part of NASA's Ultra-Efficient Engine Technology Program. This material was originally developed under the High Speed Research Office's Enabling Propulsion Materials Program. Creep and rupture data provide accelerated testing information to predict material behavior under engine use situations (1500 to 2400 F). This information gives insights into various material development paths to improve composites as well as improve understanding of failure mechanisms. The left figure shows the fracture surface of a CMC material following over 200 hr of testing at 2400 F. This surface demonstrates the kind of fibrous pullout desirable for maximum crack deflection, hence non-brittle failure. Microscopy suggests that creep and rupture of these materials can best be considered as a probabilistic property, rather than a material property. Fiber failure occurs first in isolated regions, while stronger adjacent fibers remain intact. The right figure shows a region where oxide deposits blur and round the fiber images. Because the oxidation kinetics of SiC are well understood, this oxide scale can be used as a measure of the length of time various regions of the composites have been exposed to the environment, hence providing vital information regarding the sequence of failure. The oxide scale in the right figure indicates an early failure of this tow of fibers, whereas adjacent tows remain oxide free, suggesting failure much later in time. The path of various cracks can be followed throughout the composite in this manner, suggesting failure mechanisms.

  17. High-Temperature Creep Deformation and Fracture Behavior of a Directionally Solidified Ni-Base Superalloy DZ951

    NASA Astrophysics Data System (ADS)

    Chu, Zhaokuang; Yu, Jinjiang; Sun, Xiaofeng; Guan, Hengrong; Hu, Zhuangqi

    2009-12-01

    The high-temperature creep deformation and fracture behavior of a directionally solidified Ni-base superalloy DZ951 have been investigated over a wide stress range of 110 to 880 MPa at high temperatures (700 °C to 1000 °C). In this article, the detailed creep deformation and fracture mechanism have been studied. The results show that the creep curves exhibit strong temperature dependence. From transmission election microscopy (TEM) observations, it is suggested that the deformation mechanism is temperature dependent and mainly consists of three dislocation-controlling mechanisms: stacking faults and dislocation-pair shearing, dislocation bowing, and dislocation climbing. It is found that the fracture mode of DZ951 alloy changes from cleavagelike fracture at low temperature to ductile fracture at high temperature. At 700 °C, the creep cracks mainly initiate at the surface and propagate along the cleavagelike facets. With increasing temperature, cracks can initiate at the surface, carbide/matrix interface, and cast pore. The growth of microcrack has a direction perpendicular to the stress direction. The creep-rupture data follow the Monkman-Grant relationship in different temperature regions.

  18. Type IV Creep Damage Behavior in Gr.91 Steel Welded Joints

    NASA Astrophysics Data System (ADS)

    Hongo, Hiromichi; Tabuchi, Masaaki; Watanabe, Takashi

    2012-04-01

    Modified 9Cr-1Mo steel (ASME Grade 91 steel) is used as a key structural material for boiler components in ultra-supercritical (USC) thermal power plants at approximately 873 K (600 °C). The creep strength of welded joints of this steel decreases as a result of Type IV creep cracking that forms in the heat-affected zone (HAZ) under long-term use at high temperatures. The current article aims to elucidate the damage processes and microstructural degradations that take place in the HAZ of these welded joints. Long-term creep tests for base metal, simulated HAZ, and welded joints were conducted at 823 K, 873 K, and 923 K (550 °C, 600 °C, and 650 °C). Furthermore, creep tests of thick welded joint specimens were interrupted at several time steps at 873 K (600 °C) and 90 MPa, after which the distribution and evolution of creep damage inside the plates were measured quantitatively. It was found that creep voids are initiated in the early stages (0.2 of life) of creep rupture life, which coalesce to form a crack at a later stage (0.8 of life). In a fine-grained HAZ, creep damage is concentrated chiefly in an area approximately 20 pct below the surface of the plate. The experimental creep damage distributions coincide closely with the computed results obtained by damage mechanics analysis using the creep properties of a simulated fine-grained HAZ. Both the concentration of creep strain and the high multiaxial stress conditions in the fine-grained HAZ influence the distribution of Type IV creep damage.

  19. Cyclic creep-rupture behavior of three high-temperature alloys.

    NASA Technical Reports Server (NTRS)

    Halford, G. R.

    1972-01-01

    Study of some important characteristics of the cyclic creep-rupture curves for the titanium alloy 6Al-2Sn-4Zr-2Mo at 900 and 1100 F (755 and 865 K), the cobalt-base alloy L-605 at 1180 F (910 K), and for two hardness levels of 316 stainless steel at 1300 F (980 K). The cyclic creep-rupture curve relates tensile stress and tensile time-to-rupture for strain-limited cyclic loading and has been found to be independent of the total strain range and the level of compressive stress employed in the cyclic creep-rupture tests. The cyclic creep-rupture curve was always found to be above and to the right of the conventional (constant load) monotonic creep-rupture curve by factors ranging from 2 to 10 in time-to-rupture. This factor tends to be greatest when the creep ductility is large. Cyclic creep acceleration was observed in every cyclic creep-rupture test conducted. The phenomenon was most pronounced at the highest stress levels and when the tensile and compressive stresses were completely reversed. In general, creep rates were found to be lower in compression than in tension for equal true stresses. The differences, however, were strongly material-dependent.

  20. Creep deformation and fracture behavior of types 316 and 316L(N) stainless steels and their weld metals

    NASA Astrophysics Data System (ADS)

    Sasikala, G.; Mannan, S. L.; Mathew, M. D.; Rao, K. Bhanu

    2000-04-01

    The creep properties of a nuclear-grade type 316(L) stainless steel (SS) alloyed with nitrogen (316L(N) SS) and its weld metal were studied at 873 and 923 K in the range of applied stresses from 100 to 335 MPa. The results were compared with those obtained on a nuclear-grade type 316 SS, which is lean in nitrogen. The creep rupture lives of the weld metals were found to be lower than those of the respective base metals by a factor of 5 to 10. Both the base and weld metals of 316L(N) SS exhibited better resistance to creep deformation compared to their 316 SS counterparts at identical test conditions. A power-law relationship between the minimum creep rate and applied stress was found to be obeyed for both the base and weld metals. Both the weld metals generally exhibited lower rupture elongation than the respective base metals; however, at 873 K, the 316 SS base and weld metals had similar rupture elongation at identical applied stresses. Comparison of the rupture lives of the two steels to the ASME curves for the expected minimum stress to rupture for 316 SS base and weld metals showed that, for 316L(N) SS, the specifications for maximum allowable stresses based on data for 316 SS could prove overconservative. The influence of nitrogen on the creep deformation and fracture behavior, especially in terms of its modifying the precipitation kinetics, is discussed in light of the microstructural observations. In welds containing δ ferrite, the kinetics of its transformation and the nature of the transformation products control the deformation and fracture behavior. The influence of nitrogen on the δ ferrite transformation behavior and coarsening kinetics is also discussed, on the basis of extensive characterization by metallographic techniques.

  1. The effects of molecular weight on the single lap shear creep and constant strain rate behavior of thermoplastic polyimidesulfone adhesive

    NASA Technical Reports Server (NTRS)

    Dembosky, Stanley K.; Sancaktar, Erol

    1985-01-01

    The bonded shear creep and constant strain rate behaviors of zero, one, and three percent endcapped thermoplastic polyimidesulfone adhesive were examined at room and elevated temperatures. Endcapping was accomplished by the addition of phthalic anhydrides. The primary objective was to determine the effects of molecular weight on the mechanical properties of the adhesive. Viscoelastic and nonlinear elastic constitutive equations were utilized to model the adhesive. Ludwik's and Crochet's relations were used to describe the experimental failure data. The effects of molecular weight changes on the above mentioned mechanical behavior were assessed. The viscoelastic Chase-Goldsmith and elastic nonlinear relations gave a good fit to the experimental stress strain behavior. Crochet's relations based on Maxwell and Chase-Goldsmith models were fit to delayed failure data. Ludwik's equations revealed negligible rate dependence. Ultimate stress levels and the safe levels for creep stresses were found to decrease as molecular weight was reduced.

  2. Development of constitutive models for cyclic plasticity and creep behavior of super alloys at high temperature

    NASA Technical Reports Server (NTRS)

    Haisler, W. E.

    1983-01-01

    An uncoupled constitutive model for predicting the transient response of thermal and rate dependent, inelastic material behavior was developed. The uncoupled model assumes that there is a temperature below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this temperature, the rate dependent inelastic strain (creep) dominates. The rate insensitive inelastic strain component is modelled in an incremental form with a yield function, blow rule and hardening law. Revisions to the hardening rule permit the model to predict temperature-dependent kinematic-isotropic hardening behavior, cyclic saturation, asymmetric stress-strain response upon stress reversal, and variable Bauschinger effect. The rate dependent inelastic strain component is modelled using a rate equation in terms of back stress, drag stress and exponent n as functions of temperature and strain. A sequence of hysteresis loops and relaxation tests are utilized to define the rate dependent inelastic strain rate. Evaluation of the model has been performed by comparison with experiments involving various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy X.

  3. Intervertebral disc creep behavior assessment through an open source finite element solver.

    PubMed

    Castro, A P G; Wilson, W; Huyghe, J M; Ito, K; Alves, J L

    2014-01-01

    Degenerative Disc Disease (DDD) is one of the largest health problems faced worldwide, based on lost working time and associated costs. By means of this motivation, this work aims to evaluate a biomimetic Finite Element (FE) model of the Intervertebral Disc (IVD). Recent studies have emphasized the importance of an accurate biomechanical modeling of the IVD, as it is a highly complex multiphasic medium. Poroelastic models of the disc are mostly implemented in commercial finite element packages with limited access to the algorithms. Therefore, a novel poroelastic formulation implemented on a home-developed open source FE solver is briefly addressed throughout this paper. The combination of this formulation with biphasic osmotic swelling behavior is also taken into account. Numerical simulations were devoted to the analysis of the non-degenerated human lumbar IVD time-dependent behavior. The results of the tests performed for creep assessment were inside the scope of the experimental data, with a remarkable improvement of the numerical accuracy when compared with previously published results obtained with ABAQUS(®). In brief, this in-development open-source FE solver was validated with literature experimental data and aims to be a valuable tool to study the IVD biomechanics and DDD mechanisms. PMID:24210477

  4. Effects of Microstructure and Processing Methods on Creep Behavior of AZ91 Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Shahbeigi Roodposhti, Peiman; Sarkar, Apu; Murty, Korukonda L.; Scattergood, Ronald O.

    2016-09-01

    This review sheds light on the creep properties of AZ91 magnesium alloys with a major emphasis on the influence of microstructure on the creep resistance and underlying creep deformation mechanism based on stress exponent and activation energy. Effects of processing routes such as steel mold casting, die casting, and thixoforming are considered. Roles of a wide range of additional alloying elements such as Si, Sb, Bi, Ca, Sn, REs, and combined addition of them on the microstructure modification were investigated. The reaction between these elements and the Mg or Al in the matrix develops some thermally stable intermetallic phases which improves the creep resistance at elevated temperatures, however does not influence the creep mechanism.

  5. Creep Behavior of Near-Stoichiometric Polycrystalline Binary NiAl

    NASA Technical Reports Server (NTRS)

    Raj, S. V.

    2002-01-01

    New and published constant load creep and constant engineering strain rate data on near-stoichiometric binary NiAl in the intermediate temperature range 700 to 1300 K are reviewed. Both normal and inverse primary creep curves are observed depending on stress and temperature. Other characteristics relating to creep of NiAl involving grain size, stress and temperature dependence are critically examined and discussed. At stresses below 25 MPa and temperatures above 1000 K, a new grain boundary sliding mechanism was observed with n approx. 2, Qc approx. 100 kJ/ mol and a grain size exponent of about 2. It is demonstrated that Coble creep and accommodated grain boundary sliding models fail to predict the experimental creep rates by several orders of magnitude.

  6. Creep Behavior and Degradation of Subgrain Structures Pinned by Nanoscale Precipitates in Strength-Enhanced 5 to 12 Pct Cr Ferritic Steels

    NASA Astrophysics Data System (ADS)

    Ghassemi Armaki, Hassan; Chen, Ruiping; Maruyama, Kouichi; Igarashi, Masaaki

    2011-10-01

    Creep behavior and degradation of subgrain structures and precipitates of Gr. 122 type xCr-2W-0.4Mo-1Cu-VNb ( x = 5, 7, 9, 10.5, and 12 pct) steels were evaluated during short-term and long-term static aging and creep with regard to the Cr content of steel. Creep rupture life increased from 5 to 12 pct Cr in the short-term creep region, whereas in the long-term creep region, it increased up to 9 pct Cr and then decreased with the addition of Cr from 9 to 12 pct. Behavior of creep rupture life was attributed to the size of elongated subgrains. In the short-term creep region, subgrain size decreased from 5 to 12 pct Cr, corresponding to the longer creep strength. However, in the long-term creep region after 104 hours, subgrain size increased up to 9 pct Cr and then decreased from 9 to 12 pct, corresponding to the behavior of creep rupture life. M23C6 and MX precipitates had the highest number fraction among all of the precipitates present in the studied steels. Cr concentration dependence of spacing of M23C6 and MX precipitates exhibited a V-like shape during short-term as well as long-term aging at 923 K (650 °C), and the minimum spacing of precipitates belonged to 9 pct Cr steel, corresponding to the lowest recovery speed of subgrain structures. In the short-term creep region, subgrain coarsening during creep was controlled by strain and proceeded slower with the addition of Cr, whereas in long-term creep region, subgrain coarsening was controlled by the stability of precipitates rather than due to the creep plastic deformation and took place faster from 9 to 12 pct and 9 to 5 pct Cr. However, M23C6 precipitates played a more important role than MX precipitates in the control of subgrain coarsening, and there was a closer correlation between spacing of M23C6 precipitates and subgrain size during static aging and long-term creep region.

  7. Prediction and verification of creep behavior in metallic materials and components, for the space shuttle thermal protection system. Volume 1, phase 1: Cyclic materials creep predictions

    NASA Technical Reports Server (NTRS)

    Davis, J. W.; Cramer, B. A.

    1974-01-01

    Cyclic creep response was investigated and design methods applicable to thermal protection system structures were developed. The steady-state (constant temperature and load) and cyclic creep response characteristics of four alloys were studied. Steady-state creep data were gathered through a literature survey to establish reference data bases. These data bases were used to develop empirical equations describing creep as a function of time, temperature, and stress and as a basis of comparison for test data. Steady-state creep tests and tensile cyclic tests were conducted. The following factors were investigated: material thickness and rolling direction; material cyclic creep response under varying loads and temperatures; constant stress and temperature cycles representing flight conditions; changing stresses present in a creeping beam as a result of stress redistribution; and complex stress and temperature profiles representative of space shuttle orbiter trajectories. A computer program was written, applying creep hardening theories and empirical equations for creep, to aid in analysis of test data. Results are considered applicable to a variety of structures which are cyclicly exposed to creep producing thermal environments.

  8. Effect of fiber-matrix adhesion on the creep behavior of CF/PPS composites: temperature and physical aging characterization

    NASA Astrophysics Data System (ADS)

    Motta Dias, M. H.; Jansen, K. M. B.; Luinge, J. W.; Bersee, H. E. N.; Benedictus, R.

    2016-06-01

    The influence of fiber-matrix adhesion on the linear viscoelastic creep behavior of `as received' and `surface modified' carbon fibers (AR-CF and SM-CF, respectively) reinforced polyphenylene sulfide (PPS) composite materials was investigated. Short-term tensile creep tests were performed on ±45° specimens under six different isothermal conditions, 40, 50, 60, 65, 70 and 75 °C. Physical aging effects were evaluated on both systems using the short-term test method established by Struik. The results showed that the shapes of the curves were affected neither by physical aging nor by the test temperature, allowing then superposition to be made. A unified model was proposed with a single physical aging and temperature-dependent shift factor, a_{T,te}. It was suggested that the surface treatment carried out in SM-CF/PPS had two major effects on the creep response of CF/PPS composites at a reference temperature of 40 °C: a lowering of the initial compliance of about 25 % and a slowing down of the creep response of about 1.1 decade.

  9. Creep Behavior of Hafnia and Ytterbium Silicate Environmental Barrier Coating Systems on SiC/SiC Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Fox, Dennis S.; Ghosn, Louis J.; Harder, Bryan

    2011-01-01

    Environmental barrier coatings will play a crucial role in future advanced gas turbine engines because of their ability to significantly extend the temperature capability and stability of SiC/SiC ceramic matrix composite (CMC) engine components, thus improving the engine performance. In order to develop high performance, robust coating systems for engine components, appropriate test approaches simulating operating temperature gradient and stress environments for evaluating the critical coating properties must be established. In this paper, thermal gradient mechanical testing approaches for evaluating creep and fatigue behavior of environmental barrier coated SiC/SiC CMC systems will be described. The creep and fatigue behavior of Hafnia and ytterbium silicate environmental barrier coatings on SiC/SiC CMC systems will be reported in simulated environmental exposure conditions. The coating failure mechanisms will also be discussed under the heat flux and stress conditions.

  10. Stick-slip and creep behavior in lubricated granular material: Insights into the brittle-ductile transition

    NASA Astrophysics Data System (ADS)

    Reber, Jacqueline E.; Hayman, Nicholas W.; Lavier, Luc L.

    2014-05-01

    Crustal deformation can occur via stick-slip events, viscous creep, or strain transients at variable rates. Here we explore such strain transients with physical experiments comprising a quasi-two-dimensional shear zone with elastic, acrylic discs and interstitial viscous silicone. Experiments of solely elastic discs produce stick-slip events and an overall (constant volume) strengthening. The addition of the viscous silicone enhances localization but does not greatly change the overall pattern of strengthening. It does, however, damp the stick-slip events, leading to transient, creep-like behavior that approaches the behavior of a Maxwell body. There is no gradual transition from frictional to viscous deformation with increasing amounts of silicone, suggesting that the mixed rheology is in effect as soon as an interstitial fluid is present. Our experiments support the hypothesis that a possible cause for strain transients in nature is an interstitial viscous phase in shear zones.

  11. Microstructural Evolution and Creep-Rupture Behavior of Fusion Welds Involving Alloys for Advanced Ultrasupercritical Power Generation

    NASA Astrophysics Data System (ADS)

    Bechetti, Daniel H., Jr.

    Projections for large increases in the global demand for electric power produced by the burning of fossil fuels, in combination with growing environmental concerns surrounding these fuel sources, have sparked initiatives in the United States, Europe, and Asia aimed at developing a new generation of coal fired power plant, termed Advanced Ultrasupercritical (A-USC). These plants are slated to operate at higher steam temperatures and pressures than current generation plants, and in so doing will offer increased process cycle efficiency and reduced greenhouse gas emissions. Several gamma' precipitation strengthened Ni-based superalloys have been identified as candidates for the hottest sections of these plants, but the microstructural instability and poor creep behavior (compared to wrought products) of fusion welds involving these alloys present significant hurdles to their implementation and a gap in knowledge that must be addressed. In this work, creep testing and in-depth microstructural characterization have been used to provide insight into the long-term performance of these alloys. First, an investigation of the weld metal microstructural evolution as it relates to creep strength reductions in A-USC alloys INCONELRTM 740, NIMONICRTM 263 (INCONEL and NIMONIC are registered trademarks of Special Metals Corporation), and HaynesRTM 282RTM (Haynes and 282 are registered trademarks of Haynes International) was performed. gamma'-precipitate free zones were identified in two of these three alloys, and their development was linked to the evolution of phases that precipitate at the expense of gamma'. Alloy 282 was shown to avoid precipitate free zone formation because the precipitates that form during long term aging in this alloy are poor in the gamma'-forming elements. Next, the microstructural evolution of INCONELRTM 740H (a compositional variant of alloy 740) during creep was investigated. Gleeble-based interrupted creep and creep-rupture testing was used to

  12. Creep-rupture behavior of iron superalloys in high-pressure hydrogen

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, S.; Peterman, W.

    1984-01-01

    The creep-rupture properties of five iron-base and one cobalt-base high temperature alloys were investigated to assess the feasibility of using the alloys as construction materials in a Stirling engine. The alloys were heat treated and hardness measurements were taken. Typical microstructures of the alloys are shown. The creep-rupture properties of the alloys were determined at 760 and 815 C in 15.0 MPa H2 for 200 to 1000 hours. Plots of rupture life versus stress for the six superalloys are presented along with creep strain-time plots.

  13. Effect of Double Aging Heat Treatment on the Short-Term Creep Behavior of the Inconel 718

    NASA Astrophysics Data System (ADS)

    Caliari, Felipe Rocha; Candioto, Kátia Cristiane Gandolpho; Couto, Antônio Augusto; Nunes, Carlos Ângelo; Reis, Danieli Aparecida Pereira

    2016-06-01

    This research studies the effect of double aging heat treatment on the short-term creep behavior of the superalloy Inconel 718. The superalloy, received in the solution treated state, was subjected to an aging treatment which comprises a solid solution at 1095 °C for 1 h, a first aging step of 955 °C for 1 h, then aged at 720 and 620 °C, 8 h each step. Creep tests at constant load mode, under temperatures of 650, 675, 700 °C and stress of 510, 625 and 700 MPa, were performed before and after heat treatment. The results indicate that after the double aging heat treatment creep resistance is increased, influenced by the presence of precipitates γ' and γ″ and its interaction with the dislocations, by grain size growth (from 8.20 to 7.23 ASTM) and the increase of hardness by approximately 98%. Creep parameters of primary and secondary stages have been determined. There is a breakdown relationship between dot{\\upvarepsilon }_{{s}} and stress at 650 °C of Inconel 718 as received, around 600 MPa. By considering the internal stress values, effective stress exponent, effective activation energy, and TEM images of Inconel 718 double aged, it is suggested that the creep mechanism is controlled by the interaction of dislocations with precipitates. The fracture mechanism of Inconel 718 as received is transgranular (coalescence of dimples) and mixed (transgranular-intergranular), whereas the Inconel 718 double aged condition crept surfaces evidenced the intergranular fracture mechanism.

  14. The Microstructure, Creep, and Tensile Behavior for Ti-5Al-45Nb (Atomic Percent) Fully- β Alloy

    NASA Astrophysics Data System (ADS)

    Cowen, C. J.; Boehlert, C. J.

    2007-11-01

    The microstructure, tensile, and creep behavior of a Ti-5Al-45Nb (at. pct) alloy was evaluated. The main objective of processing and characterizing this alloy was to obtain the constituent properties of a fully- β Ti-Al-Nb alloy to aid in modeling the tensile and creep properties of two-phase orthorhombic + body-centered-cubic (O + bcc) alloys. A second objective was to compare the tensile and creep behavior of this fully- β alloy to that for two-phase O + bcc alloys. This alloy exhibited a single-phase microstructure, containing the disordered bcc phase ( β), after all the processing and heat treatments performed. This alloy was easily fabricated and workable; however, its creep resistance was significantly worse than that for fully-O and two-phase O + bcc alloys. The alloy exhibited little strain hardening along with a room-temperature yield strength (YS) of 545 MPa, an ultimate tensile stress (UTS) of 559 MPa, a Young’s modulus (E) of 86 GPa, and a tensile elongation to failure of 25 pct. Extensive surface slip was evident on the deformed material. Its room-temperature tensile properties were quite similar to those for a fully- β Ti-12Al-38Nb microstructure (YS = 553 MPa, UTS = 566 MPa, E = 84, and ɛ f > 27 pct). Thus, the room-temperature tensile properties and behavior of fully- β Ti-Al-Nb microstructures containing 50 at. pct Ti are not sensitive to compositional variations between 5 to 12 at. pct Al and 38 to 45 at. pct Nb.

  15. Mechanisms of high-temperature, solid-state flow in minerals and ceramics and their bearing on the creep behavior of the mantle

    USGS Publications Warehouse

    Kirby, S.H.; Raleigh, C.B.

    1973-01-01

    The problem of applying laboratory silicate-flow data to the mantle, where conditions can be vastly different, is approached through a critical review of high-temperature flow mechanisms in ceramics and their relation to empirical flow laws. The intimate association of solid-state diffusion and high-temperature creep in pure metals is found to apply to ceramics as well. It is shown that in ceramics of moderate grain size, compared on the basis of self-diffusivity and elastic modulus, normalized creep rates compare remarkably well. This comparison is paralleled by the near universal occurrence of similar creep-induced structures, and it is thought that the derived empirical flow laws can be associated with dislocation creep. Creep data in fine-grained ceramics, on the other hand, are found to compare poorly with theories involving the stress-directed diffusion of point defects and have not been successfully correlated by self-diffusion rates. We conclude that these fine-grained materials creep primarily by a quasi-viscous grain-boundary sliding mechanism which is unlikely to predominate in the earth's deep interior. Creep predictions for the mantle reveal that under most conditions the empirical dislocation creep behavior predominates over the mechanisms involving the stress-directed diffusion of point defects. The probable role of polymorphic transformations in the transition zone is also discussed. ?? 1973.

  16. Prediction and verification of creep behavior in metallic materials and components for the space shuttle thermal protection system. Volume 2: Phase 2 subsize panel cyclic creep predictions

    NASA Technical Reports Server (NTRS)

    Cramer, B. A.; Davis, J. W.

    1975-01-01

    A method for predicting permanent cyclic creep deflections in stiffened panel structures was developed. The resulting computer program may be applied to either the time-hardening or strain-hardening theories of creep accumulation. Iterative techniques were used to determine structural rotations, creep strains, and stresses as a function of time. Deflections were determined by numerical integration of structural rotations along the panel length. The analytical approach was developed for analyzing thin-gage entry vehicle metallic-thermal-protection system panels subjected to cyclic bending loads at high temperatures, but may be applied to any panel subjected to bending loads. Predicted panel creep deflections were compared with results from cyclic tests of subsize corrugation and rib-stiffened panels. Empirical equations were developed for each material based on correlation with tensile cyclic creep data and both the subsize panels and tensile specimens were fabricated from the same sheet material. For Vol. 1, see N75-21431.

  17. A novel on chip test method to characterize the creep behavior of metallic layers under heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Lapouge, P.; Onimus, F.; Vayrette, R.; Raskin, J.-P.; Pardoen, T.; Bréchet, Y.

    2016-08-01

    An on chip test method has been developed to characterize the irradiation creep behavior of thin freestanding films under uniaxial tension. The method is based on the use of a long beam involving large internal stress protected from the irradiation flux that imposes a spring like deformation to a specimen beam. These elementary freestanding structures fabricated using a combination of deposition, lithography and release steps are multiplied with different dimensions in order to test different levels of stress and of initial plastic deformation. The method has been validated on 200 and 500 nm thick copper films under heavy copper ions irradiation. The irradiation creep rate is shown to be at least one order of magnitude larger than in the absence of irradiation.

  18. The Effect of Thermomechanical Processing on the Tensile, Fatigue, and Creep Behavior of Magnesium Alloy AM60

    SciTech Connect

    Chen, Zhe; Huang, J; Decker, R; Lebeau, S; Walker, Larry R; Cavin, Odis Burl; Watkins, Thomas R; Boehlert, C. J.

    2011-01-01

    Tensile, fatigue, fracture toughness, and creep experiments were performed on a commercially available magnesium-aluminum alloy (AM60) after three processing treatments: (1) as-THIXOMOLDED (as-molded), (2) THIXOMOLDED then thermomechanically processed (TTMP), and (3) THIXOMOLDED then TTMP then annealed (annealed). The TTMP procedure resulted in a significantly reduced grain size and a tensile yield strength greater than twice that of the as-molded material without a debit in elongation to failure ({epsilon}{sub f}). The as-molded material exhibited the lowest strength, while the annealed material exhibited an intermediate strength but the highest {epsilon}{sub f} (>1 pct). The TTMP and annealed materials exhibited fracture toughness values almost twice that of the as-molded material. The as-molded material exhibited the lowest fatigue threshold values and the lowest fatigue resistance. The annealed material exhibited the greatest fatigue resistance, and this was suggested to be related to its balance of tensile strength and ductility. The fatigue lives of each material were similar at both room temperature (RT) and 423 K (150 C). The tensile-creep behavior was evaluated for applied stresses ranging between 20 and 75 MPa and temperatures between 373 and 473 K (100 and 200 C). During both the fatigue and creep experiments, cracking preferentially occurred at grain boundaries. Overall, the results indicate that thermomechanical processing of AM60 dramatically improves the tensile, fracture toughness, and fatigue behavior, making this alloy attractive for structural applications. The reduced creep resistance after thermomechanical processing offers an opportunity for further research and development.

  19. Effects of cold rolling deformation on microstructure, hardness, and creep behavior of high nitrogen austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Sun, Shi-Cheng; Sun, Gui-Xun; Jiang, Zhong-Hao; Ji, Chang-Tao; Liu, Jia-An; Lian, Jian-She

    2014-02-01

    Effects of cold rolling deformation on the microstructure, hardness, and creep behavior of high nitrogen austenitic stainless steel (HNASS) are investigated. Microstructure characterization shows that 70% cold rolling deformation results in significant refinement of the microstructure of this steel, with its average twin thickness reducing from 6.4 μm to 14 nm. Nanoindentation tests at different strain rates demonstrate that the hardness of the steel with nano-scale twins (nt-HNASS) is about 2 times as high as that of steel with micro-scale twins (mt-HNASS). The hardness of nt-HNASS exhibits a pronounced strain rate dependence with a strain rate sensitivity (m value) of 0.0319, which is far higher than that of mt-HNASS (m = 0.0029). nt-HNASS shows more significant load plateaus and a higher creep rate than mt-HNASS. Analysis reveals that higher hardness and larger m value of nt-HNASS arise from stronger strain hardening role, which is caused by the higher storage rate of dislocations and the interactions between dislocations and high density twins. The more significant load plateaus and higher creep rates of nt-HNASS are due to the rapid relaxation of the dislocation structures generated during loading.

  20. The creep behavior of gamma alloy Ti-46.5Al-3Nb-2Cr-0.2W (alloy K5) in two microstructural conditions

    SciTech Connect

    Schwenker, S.W.; Kim, Y.W.

    1995-12-31

    The creep behavior of a wrought gamma alloy Ti-46.5Al-3Nb-2Cr-0.2W (Alloy K5) has been investigated in both a fine-grained duplex ({approximately}10 {micro}m grain size) and a refined fully-lamellar (RFL) microstructural condition (average lamellar grain size of {approximately} 300 {micro}m). Creep tests were conducted in laboratory air under constant tensile load at temperatures between 676 and 870 C and stresses between 69 and 242 MPa. The results show that the RFL condition exhibits creep resistance significantly improved over the duplex microstructure. At 800 C and 138 MPa the RFL material exhibited a secondary or minimum creep rate of 3.8 {times} 10{sup {minus}5} h{sup {minus}1} which is nearly two orders of magnitude slower than for the fine duplex. Activation energies and stress exponents for power law creep were measured and found to be similar for the two microstructures over the range of conditions investigated. Microstructural studies conducted on crept RFL specimens showed evidence of bulk deformation within the lamellar grains which lead to break up or spheroidization of the {alpha}{sub 2} laths at high creep strains. Creep failure occurred by intergranular cracking and cavity formation along grain boundaries in the material.

  1. Deterministic Multiaxial Creep and Creep Rupture Enhancements for CARES/Creep Integrated Design Code

    NASA Technical Reports Server (NTRS)

    Jadaan, Osama M.

    1998-01-01

    High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep rupture criterion. However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of sum, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of Ns methodology and the

  2. Microstructural Evolution and Creep-Rupture Behavior of A-USC Alloy Fusion Welds

    NASA Astrophysics Data System (ADS)

    Bechetti, Daniel H.; DuPont, John N.; Siefert, John A.; Shingledecker, John P.

    2016-09-01

    Characterization of the microstructural evolution of fusion welds in alloys slated for use in advanced ultrasupercritical (A-USC) boilers during creep has been performed. Creep-rupture specimens involving INCONEL® 740, NIMONIC® 263 (INCONEL and NIMONIC are registered trademarks of Special Metals Corporation), and Haynes® 282® (Haynes and 282 are registered trademarks of Haynes International) have been analyzed via light optical microscopy, scanning electron microscopy, X-ray diffraction, and thermodynamic and kinetic modeling. Focus has been given to the microstructures that develop along the grain boundaries in these alloys during creep at temperatures relevant to the A-USC process cycle, and particular attention has been paid to any evidence of the formation of local γ'-denuded or γ'-free zones. This work has been performed in an effort to understand the microstructural changes that lead to a weld strength reduction factor (WSRF) in these alloys as compared to solution annealed and aged alloy 740 base metal. γ' precipitate-free zones have been identified in alloy 740 base metal, solution annealed alloy 740 weld metal, and alloy 263 weld metal after creep. Their development during long-term thermal exposure is correlated with the stabilization of phases that are rich in γ'-forming elements ( e.g., η and G) and is suppressed by precipitation of phases that do not contain the γ' formers ( e.g., M23C6 and μ). The location of failure and creep performance in terms of rupture life and WSRF for each welded joint is presented and discussed.

  3. Creep Behavior at 1273 K (1000 °C) in Nb-Bearing Austenitic Heat-Resistant Cast Steels Developed for Exhaust Component Applications

    NASA Astrophysics Data System (ADS)

    Zhang, Yinhui; Li, Mei; Godlewski, Larry A.; Zindel, Jacob W.; Feng, Qiang

    2016-07-01

    A series of Nb-bearing austenitic heat-resistant cast steels with variations of N/C ratios were investigated, and the morphological change of Nb(C,N) from faceted blocks, mixed flake-blocks to "Chinese-script" was observed as N/C ratios decreased. The creep behavior of these alloys was studied at 1273 K (1000 °C), and the longest creep life and lowest creep rate occurred in model alloys with script Nb(C,N). Residual δ-ferrites and (Cr,Fe)23C6 were adverse to creep properties. This work indicates that the control of N/C ratio is required for the as-cast microstructural strengthening.

  4. Stress rupture and creep behavior of a low pressure plasma-sprayed NiCoCrAlY coating alloy in air and vacuum

    NASA Technical Reports Server (NTRS)

    Hebsur, M. G.; Miner, R. V.

    1987-01-01

    The creep behavior of a NiCoCrAlY coating alloy in air and vacuum at 660 and 850 C is studied. The microstructure of the coating alloy is described. Analysis of the creep curves reveal that the secondary creep rates, the transition from secondary to tertiary creep, and the strain-to-failure are affected by the environment, preexposure, stress, and temperature. It is observed that the rupture lives of the NiCoCrAlY alloy at 660 and 850 C are greater in air than in vacuum. Several mechanisms that may explain the lack of crack growth from surface-connected pores during tests in air are proposed.

  5. Processing, Microstructure and Creep Behavior of Mo-Si-B-Based Intermetallic Alloys for Very High Temperature Structural Applications

    SciTech Connect

    Vijay Vasudevan

    2008-03-31

    This research project is concerned with developing a fundamental understanding of the effects of processing and microstructure on the creep behavior of refractory intermetallic alloys based on the Mo-Si-B system. In the first part of this project, the compression creep behavior of a Mo-8.9Si-7.71B (in at.%) alloy, at 1100 and 1200 C was studied, whereas in the second part of the project, the constant strain rate compression behavior at 1200, 1300 and 1400 C of a nominally Mo-20Si-10B (in at.%) alloy, processed such as to yield five different {alpha}-Mo volume fractions ranging from 5 to 46%, was studied. In order to determine the deformation and damage mechanisms and rationalize the creep/high temperature deformation data and parameters, the microstructure of both undeformed and deformed samples was characterized in detail using x-ray diffraction, scanning electron microscopy (SEM) with back scattered electron imaging (BSE) and energy dispersive x-ray spectroscopy (EDS), electron back scattered diffraction (EBSD)/orientation electron microscopy in the SEM and transmission electron microscopy (TEM). The microstructure of both alloys was three-phase, being composed of {alpha}-Mo, Mo{sub 3}Si and T2-Mo{sub 5}SiB{sub 2} phases. The values of stress exponents and activation energies, and their dependence on microstructure were determined. The data suggested the operation of both dislocation as well as diffusional mechanisms, depending on alloy, test temperature, stress level and microstructure. Microstructural observations of post-crept/deformed samples indicated the presence of many voids in the {alpha}-Mo grains and few cracks in the intermetallic particles and along their interfaces with the {alpha}-Mo matrix. TEM observations revealed the presence of recrystallized {alpha}-Mo grains and sub-grain boundaries composed of dislocation arrays within the grains (in Mo-8.9Si-7.71B) or fine sub-grains with a high density of b = 1/2<111> dislocations (in Mo-20Si-10B), which

  6. A New Local Debonding Model with Application to the Transverse Tensile and Creep Behavior of Continuously Reinforced Titanium Composites

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Arnold, Steven M.

    2000-01-01

    A new, widely applicable model for local interfacial debonding in composite materials is presented. Unlike its direct predecessors, the new model allows debonding to progress via unloading of interfacial stresses even as global loading of the composite continues. Previous debonding models employed for analysis of titanium matrix composites are surpassed by the accuracy, simplicity, and efficiency demonstrated by the new model. The new model was designed to operate seamlessly within NASA Glenn's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC), which was employed to simulate the time- and rate-dependent (viscoplastic) transverse tensile and creep behavior of SiC/Ti composites. MAC/GMC's ability to simulate the transverse behavior of titanium matrix composites has been significantly improved by the new debonding model. Further, results indicate the need for a more accurate constitutive representation of the titanium matrix behavior in order to enable predictions of the composite transverse response, without resorting to recalibration of the debonding model parameters.

  7. Irradiation Creep in Graphite

    SciTech Connect

    Ubic, Rick; Butt, Darryl; Windes, William

    2014-03-13

    An understanding of the underlying mechanisms of irradiation creep in graphite material is required to correctly interpret experimental data, explain micromechanical modeling results, and predict whole-core behavior. This project will focus on experimental microscopic data to demonstrate the mechanism of irradiation creep. High-resolution transmission electron microscopy should be able to image both the dislocations in graphite and the irradiation-induced interstitial clusters that pin those dislocations. The team will first prepare and characterize nanoscale samples of virgin nuclear graphite in a transmission electron microscope. Additional samples will be irradiated to varying degrees at the Advanced Test Reactor (ATR) facility and similarly characterized. Researchers will record microstructures and crystal defects and suggest a mechanism for irradiation creep based on the results. In addition, the purchase of a tensile holder for a transmission electron microscope will allow, for the first time, in situ observation of creep behavior on the microstructure and crystallographic defects.

  8. Precipitate Evolution and Creep Behavior of a W-Free Co-based Superalloy

    NASA Astrophysics Data System (ADS)

    Liu, Qinyuan; Coakley, James; Seidman, David N.; Dunand, David C.

    2016-09-01

    The morphological and temporal evolution of γ ^' } (L1_2 )-precipitates is studied in a polycrystalline Co-based superalloy (Co-30Ni-9.9Al-5.1Mo-1.9Nb at. pct) free of tungsten, aged at 1173 K (900 °C). Over a 1000 {{{hours}}} heat-treatment, the γ ^' } morphology evolves due to precipitate coalescence. The particles grow in size and the volume fraction decreases, while there is no significant change in the microhardness value. Compressional creep tests at 1123 K (850 °C) on a specimen aged at 1173 K (900 °C) demonstrate that the creep resistance is comparable to the original, W-containing, higher-density Co-based superalloy (Co-9Al-9.8W at. pct). This represents the first creep study of the Co-Al-Mo-Nb-based superalloy system. The W-free alloy exhibits directional coarsening of the γ ^' } precipitates in the direction perpendicular to the applied compressive stress, which indicates a positive misfit. This is consistent with neutron diffraction results.

  9. Numerical modeling on tertiary creep behavior of extreme rainfall-induced landslides with TRMM application for landslide early warning

    NASA Astrophysics Data System (ADS)

    Dok, A.; Fukuoka, H.; Katsumi, T.; Inui, T.

    2012-12-01

    In help issue warning of extreme rainfall-induced landslide in tropical soils of Southeast Asian countries, it requires the study of landslide mechanism induced by generated excess pore water pressure at the sliding surface due to groundwater table rise under rainfall storm, and examination of empirical relationship between rainfall characteristics and past landslide occurrence (precipitation analysis). To investigate the tertiary creep behavior in soils found by Fukuzono, 1985 (d2x/dt2=A(dx/dt)α, where x is surface displacement, t is time, and A and α are constant), a series of pore-pressure-controlled tests on saturated sands were undertaken in the ring shear apparatus. The tests were conducted under combined condition of predefined normal stress and shear stress with pore water pressure changes to simulate the potential sliding surface condition in heavy rainfall. Sand, its mixture with clay material, and soil samples taken at actual landslide sliding surface were used for specimen. Repeated shear test for a specimen was also additionally conducted to produce reactivated motion landslides. Numerical model simulating the Tertiary creep behavior (or progressive failure) is constructed to develop a most appropriate method for landslide early warning combined with TRMM satellite rainfall data. TRMM data were selected to apply to the Japanese Soil Water Index (SWI) in distributing threshold of highly nonlinear rainfall patterns for estimating the landslide occurrence in developing regions: Southeast Asian countries, where very limited number of rain gauges is available, and there is no implemented methodology for issuing effective warming of landslides yet. It is through the plot of total water of 3 serial tank models and daily precipitation with case example of landslide disasters took place in Beichuan city, (located on the 2008 Chinese Wenchuan earthquake fault) and Hofu city, Japan which were hit by heavy rainfall attacked in 2009. Consequently, it is

  10. Development of an accurate molecular mechanics model for buckling behavior of multi-walled carbon nanotubes under axial compression.

    PubMed

    Safaei, B; Naseradinmousavi, P; Rahmani, A

    2016-04-01

    In the present paper, an analytical solution based on a molecular mechanics model is developed to evaluate the elastic critical axial buckling strain of chiral multi-walled carbon nanotubes (MWCNTs). To this end, the total potential energy of the system is calculated with the consideration of the both bond stretching and bond angular variations. Density functional theory (DFT) in the form of generalized gradient approximation (GGA) is implemented to evaluate force constants used in the molecular mechanics model. After that, based on the principle of molecular mechanics, explicit expressions are proposed to obtain elastic surface Young's modulus and Poisson's ratio of the single-walled carbon nanotubes corresponding to different types of chirality. Selected numerical results are presented to indicate the influence of the type of chirality, tube diameter, and number of tube walls in detailed. An excellent agreement is found between the present numerical results and those found in the literature which confirms the validity as well as the accuracy of the present closed-form solution. It is found that the value of critical axial buckling strain exhibit significant dependency on the type of chirality and number of tube walls.

  11. Creep and Oxidation Behavior of Modified CF8C-Plus with W, Cu, Ni, and Cr

    NASA Astrophysics Data System (ADS)

    Unocic, Kinga A.; Dryepondt, Sebastien; Yamamoto, Yukinori; Maziasz, Philip J.

    2016-04-01

    The microstructures of modified CF8C-Plus (Fe-19Cr-12Ni-0.4W-3.8Mn-0.2Mo-0.6Nb-0.5Si-0.9C) with W and Cu (CF8CPWCu) and CF8CPWCu enhanced with 21Cr + 15Ni or 22Cr + 17.5Ni were characterized in the as-cast condition and after creep testing. When imaged at lower magnifications, the as-cast microstructure was similar among all three alloys as they all contained a Nb-rich interdendritic phase and Mn-based inclusions. Transmission electron microscopy (TEM) analysis showed the presence of nanoscale Cu-rich nanoprecipitates distributed uniformly throughout the matrix of CF8CPWCu, whereas in CF8CPWCu22/17, Cu precipitates were found primarily at the grain boundaries. The presence of these nanoscale Cu-rich particles, in addition to W-rich Cr23C6, nanoscale Nb carbides, and Z-phase (Nb2Cr2N2), improved the creep strength of the CF8CPWCu steel. Modification of CF8CPWCu with Cr and Ni contents slightly decreased the creep strength but significantly improved the oxidation behavior at 1073 K (800 °C). In particular, the addition of 22Cr and 17.5Ni strongly enhanced the oxidation resistance of the stainless steel resulting in a 100 degrees or greater temperature improvement, and this composition provided the best balance between improving both mechanical properties and oxidation resistance.

  12. Creep and oxidation behavior of modified CF8C-plus with W, Cu, Ni, and Cr

    DOE PAGES

    Unocic, Kinga A.; Dryepondt, Sebastien N.; Yamamoto, Yukinori; Maziasz, Philip J.

    2016-02-01

    Here, the microstructures of modified CF8C-Plus (Fe-19Cr-12Ni-0.4W-3.8Mn-0.2Mo-0.6Nb-0.5Si-0.9C) with W and Cu (CF8CPWCu) and CF8CPWCu enhanced with 21Cr + 15Ni or 22Cr + 17.5Ni were characterized in the as-cast condition and after creep testing. When imaged at lower magnifications, the as-cast microstructure was similar among all three alloys as they all contained a Nb-rich interdendritic phase and Mn-based inclusions. Transmission electron microscopy (TEM) analysis showed the presence of nanoscale Cu-rich nanoprecipitates distributed uniformly throughout the matrix of CF8CPWCu, whereas in CF8CPWCu22/17, Cu precipitates were found primarily at the grain boundaries. The presence of these nanoscale Cu-rich particles, in addition to W-richmore » Cr23C6, nanoscale Nb carbides, and Z-phase (Nb2Cr2N2), improved the creep strength of the CF8CPWCu steel. Modification of CF8CPWCu with Cr and Ni contents slightly decreased the creep strength but significantly improved the oxidation behavior at 1073 K (800 °C). In particular, the addition of 22Cr and 17.5Ni strongly enhanced the oxidation resistance of the stainless steel resulting in a 100 degrees or greater temperature improvement, and this composition provided the best balance between improving both mechanical properties and oxidation resistance.« less

  13. Crack growth behavior under creep-fatigue conditions using compact and double edge notch tension-compression specimens

    NASA Astrophysics Data System (ADS)

    Narasimha Chary, Santosh Balaji

    inspection of fatigue surfaces, it has been found that that better alignment control procedures are needed to ensure symmetric crack fronts for the DEN(T-C) specimen. Creep-fatigue crack growth tests were conducted on 9Cr-1Mo (P91) steels at 625°C with various hold times. These tests were conducted using C(T) specimens under constant load amplitude conditions (tension-tension) and DEN(T-C) specimens under displacement like conditions (tension-compression). Crack growth data generated under creep-fatigue conditions using standard C(T) specimens correlated well with crack growth data generated using DEN(T-C) specimens. The crack growth rates per cycle increased significantly with increase in hold time when crack growth data were plotted with the cyclic stress intensity parameter, Delta-K. A transient behavior in the initial portion of da/dN versus Delta-K plots were observed for the hold time tests, as reported previously by several other researchers. It is shown for the C(T) specimens that the creep-fatigue interactions during crack growth for various hold times are represented better by the (Ct)avg parameter implying that the P91 steel behaves in a creep-ductile manner. Significant differences (factors of 2 to 5) were observed between the calculated values of (Ct)avg and those based on measured values of force-line deflection. It is also shown that there is a high risk of obtaining invalid data in longer hold time tests under force-control conditions. The usefulness of DEN(T-C) specimens for crack growth studies under displacement controlled conditions to combat ratcheting problems in tests conducted under load conditions is established. The tests conditions for the round-robin program on creep-fatigue crack growth testing in support of ASTM E-2760 are finalized. Further developments needed in creep-fatigue crack growth testing are also presented.

  14. Effect of Notches on Creep-Fatigue Behavior of a P/M Nickel-Based Superalloy

    NASA Technical Reports Server (NTRS)

    Telesman, Jack; Gabb, Timothy P.; Ghosn, Louis J.; Gayda, John, Jr.

    2015-01-01

    A study was performed to determine and model the effect of high temperature dwells on notched low cycle fatigue (NLCF) and notch stress rupture behavior of a fine grain LSHR powder metallurgy (PM) nickel-based superalloy. It was shown that a 90 second dwell applied at the minimum stress (min dwell) was considerably more detrimental to the NLCF lives than similar dwell applied at the maximum stress (max dwell). The short min dwell NLCF lives were shown to be caused by growth of small oxide blisters which caused preferential cracking when coupled with high concentrated notch root stresses. The cyclic max dwell notch tests failed mostly by a creep accumulation, not by fatigue, with the crack origin shifting internally to a substantial distance away from the notch root. The classical von Mises plastic flow model was unable to match the experimental results while the hydrostatic stress profile generated using the Drucker-Prager plasticity flow model was consistent with the experimental findings. The max dwell NLCF and notch stress rupture tests exhibited substantial creep notch strengthening. The triaxial Bridgman effective stress parameter was able to account for the notch strengthening by collapsing the notched and uniform gage geometry test data into a singular grouping.

  15. Effect of particle size and temperature on rheology and creep behavior of barley β-d-glucan concentrate dough.

    PubMed

    Ahmed, Jasim

    2014-10-13

    Concentrated β-D-glucan has been added in the formulation of food products development that attributing human health. The purpose of this study is to assess the role of particle size (74, 105, 149, 297 and 595 μm) of barley β-D-glucan concentrate (BGC) on two fundamental rheological properties namely oscillatory rheology and creep in a dough system (sample to water = 1:2). The water holding capacity, sediment volume fraction and protein content increased with an increase in particle size from 74 μm to 595 μm, which directly influences the mechanical strength and visco-elasticity of the dough. The dough exhibited predominating solid-like behavior (elastic modulus, G'>viscous modulus, G"). The G' decreased systematically with increasing temperature from 25 to 85 °C at the frequency range of 0.1-10 Hz except for the dough having particle size of 105 μm, which could be associated with increase in protein content in the fraction. A discrete retardation spectrum is employed to the creep data to obtain retardation time and compliance parameters which varied significantly with particle size and the process temperature. All those information could be helpful to identify the particle size range of BGC that could be useful to produce a β-D-glucan enriched designed food.

  16. Biaxial Creep Specimen Fabrication

    SciTech Connect

    JL Bump; RF Luther

    2006-02-09

    This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Naval Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments.

  17. Prediction and verification of creep behavior in metallic materials and components for the space shuttle thermal protection system

    NASA Technical Reports Server (NTRS)

    Davis, J. W.; Cramer, B. A.

    1976-01-01

    A method of analysis was developed for predicting permanent cyclic creep deflections in stiffened panel structures. This method uses creep equations based on cyclic tensile creep tests and a computer program to predict panel deflections as a function of mission cycle. Four materials were investigated - a titanium alloy (Ti-6Al-4V), a cobalt alloy (L605), and two nickel alloys (Rene'41 and TDNiCr). Steady-state and cyclic creep response data were obtained by testing tensile specimens fabricated from thin gage sheet (0.025 and 0.63 cm nominal). Steady-state and cyclic creep equations were developed which describe creep as a function of time, temperature and load. Tests were also performed on subsize (6.35 x 30.5 cm) rib and corrugation stiffened panels. These tests were used to correlate creep responses between elemental specimens and panels. The panel response was analyzed by use of a specially written computer program.

  18. Sintering and Creep Behavior of Plasma-Sprayed Zirconia and Hafnia Based Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Miller, Robert A.

    1998-01-01

    The sintering and creep of plasma-sprayed ceramic thermal barrier coatings under high temperature conditions are complex phenomena. Changes in thermomechanical and thermophysical properties and in the stress response of these coating systems as a result of the sintering and creep processes are detrimental to coating thermal fatigue resistance and performance. In this paper, the sintering characteristics of ZrO2-8wt%y2O3, ZrO2-25wt%CeO2-2.5wt%Y2O3, ZrO2-6w%NiO- 9wt%Y2O3, ZrO2-6wt%Sc2O3-2wt%y2O3 and HfO2-27wt%y2O3 coating materials were investigated using dilatometry. It was found that the HfO2-Y2O3 and baseline ZrO2-Y2O3 exhibited the best sintering resistance, while the NiO-doped ZrO2-Y2O3 showed the highest shrinkage strain rates during the tests. Higher shrinkage strain rates of the coating materials were also observed when the specimens were tested in Ar+5%H2 as compared to in air. This phenomenon was attributed to an enhanced metal cation interstitial diffusion mechanism under the reducing conditions. It is proposed that increased chemical stability of coating materials will improve the material sintering resistance.

  19. Creep deformation and rupture behavior of 2.25Cr-1Mo steel weldments and its constituents (base metal, weld metal and simulated heat affected zones)

    SciTech Connect

    Laha, K.; Chandravathi, K.S.; Rao, K.B.S.; Mannan, S.L.

    1995-12-31

    Microstructure across a weldment base metal through transformed heat-affected zone (HAZ) to cast weld metal. HAZ of 2.25Cr-1Mo weldment consists of coarse-grain bainite, fine-grain bainite and intercritical region. These HAZ microstructures were simulated by isothermal heat-treatments. Creep tests were carried out on base metal, weld metal, weldment and the simulated HAZ structures. Creep deformation and fracture behavior of 2.25Cr-1Mo weldments has been assessed based on the properties of its constituents. Coarse-grain bainite with low ductility and intercritical structure with low strength are the critical components of HAZ determining performance of the weldments.

  20. Creep-rupture behavior of candidate Stirling engine alloys after long-term aging at 760 deg C in low-pressure hydrogen

    NASA Technical Reports Server (NTRS)

    Titran, R. H.

    1984-01-01

    Nine candidate Stirling automotive engine alloys were aged at 760 C for 3500 hr in low pressure hydrogen or argon to determine the resulting effects on mechanical behavior. Candidate heater head tube alloys were CG-27, W545, 12RN72, INCONEL-718, and HS-188 while candidate cast cylinder-regenerator housing alloys were SA-F11, CRM-6D, XF-818, and HS-31. Aging per se is detrimental to the creep rupture and tensile strengths of the iron base alloys. The presence of hydrogen does not significantly contribute to strength degradation. Based percent highway driving cycle; CG-27 has adequate 3500 hr - 870 C creep rupture strength and SA-Fll, CRM-6D, and XF-818 have adequate 3500 hr - 775 C creep rupture strength.

  1. Micro-buckling in the nanocomposite structure of biological materials

    NASA Astrophysics Data System (ADS)

    Su, Yewang; Ji, Baohua; Hwang, Keh-Chih; Huang, Yonggang

    2012-10-01

    Nanocomposite structure, consisting of hard mineral and soft protein, is the elementary building block of biological materials, where the mineral crystals are arranged in a staggered manner in protein matrix. This special alignment of mineral is supposed to be crucial to the structural stability of the biological materials under compressive load, but the underlying mechanism is not yet clear. In this study, we performed analytical analysis on the buckling strength of the nanocomposite structure by explicitly considering the staggered alignment of the mineral crystals, as well as the coordination among the minerals during the buckling deformation. Two local buckling modes of the nanostructure were identified, i.e., the symmetric mode and anti-symmetric mode. We showed that the symmetric mode often happens at large aspect ratio and large volume fraction of mineral, while the anti-symmetric happens at small aspect ratio and small volume fraction. In addition, we showed that because of the coordination of minerals with the help of their staggered alignment, the buckling strength of these two modes approached to that of the ideally continuous fiber reinforced composites at large aspect ratio given by Rosen's model, insensitive to the existing "gap"-like flaws between mineral tips. Furthermore, we identified a mechanism of buckling mode transition from local to global buckling with increase of aspect ratio, which was attributed to the biphasic dependence of the buckling strength on the aspect ratio. That is, for small aspect ratio, the local buckling strength is smaller than that of global buckling so that it dominates the buckling behavior of the nanocomposite; for comparatively larger aspect ratio, the local buckling strength is higher than that of global buckling so that the global buckling dominates the buckling behavior. We also found that the hierarchical structure can effectively enhance the buckling strength, particularly, this structural design enables

  2. Numerical analysis of the creeping behavior of the S. Andrea di Perarolo secondary landslide (Italian Eastern Alps)

    NASA Astrophysics Data System (ADS)

    Cioli, C.; Genevois, R.; Iafelice, M.; Zorzi, L.

    2012-04-01

    The S. Andrea landslide is a complex secondary phenomenon characterized by continuous movements causing a very high hazard condition for the near Perarolo di Cadore village (Italian Eastern Alps). A significant amount of geological and geotechnical investigations has been carried out in the past allowing the detection of the basal sliding surface. In specific, the sliding surface coincides with the contact between the bedrock and the overlying mass of an old landslides, involving a volume of about 180.000 cubic meters. A numerical approach has been adopted to analyze the stability of slope. This method is able to simulate the formation and development of shear zones as areas of strain localization in the model. Indeed, the S. Andrea landslide has been, then, investigated using FLAC, a two-dimensional explicit finite difference program, particularly useful in case of slopes with complex geometry. In order to build up a suitable model, variation of geological, hydrogeological and geotechnical parameters have been identified from the interpretation of all available data. In a preliminary stage, a Mohr-Coulomb plasticity model has been adopted except for the bedrock, which was characterized by an isotropic elastic model. Groundwater flow condition has been performed evaluating the change in pore pressure coupled to the mechanical deformation calculation. Numerical results show that this model cannot simulate real displacement behavior of the slope mainly due to both the complex material behavior and lithological heterogeneity, and due to geotechnical spatial complexity of different soils and mechanical parameters. It has been assumed that it was necessary to improve the model in the light of a time dependent behavior of existing soils. An elastic-viscoplastic model has been then used to reproduce the observed creeping behavior, and only in viscoplastic region time effects have been considered. Discussion of results points out on: i) the evolution of the ``mechanical

  3. Buckling instability in arteries.

    PubMed

    Vandiver, Rebecca M

    2015-04-21

    Arteries can become tortuous in response to abnormal growth stimuli, genetic defects and aging. It is suggested that a buckling instability is a mechanism that might lead to artery tortuosity. Here, the buckling instability in arteries is studied by examining asymmetric modes of bifurcation of two-layer cylindrical structures that are residually stressed. These structures are loaded by an axial force, internal pressure and have nonlinear, anisotropic, hyperelastic responses to stresses. Strain-softening and reduced opening angle are shown to lower the critical internal pressure leading to buckling. In addition, the ratio of the media thickness to the adventitia thickness is shown to have a dramatic impact on arterial instability.

  4. Model for transient creep of southeastern New Mexico rock salt

    SciTech Connect

    Herrmann, W; Wawersik, W R; Lauson, H S

    1980-11-01

    In a previous analysis, existing experimental data pertaining to creep tests on rock salt from the Salado formation of S.E. New Mexico were fitted to an exponential transient creep law. While very early time portions of creep strain histories were not fitted very well for tests at low temperatures and stresses, initial creep rates in particular generally being underestimated, the exponential creep law has the property that the transient creep strain approaches a finite limit with time, and is therefore desirable from a creep modelling point of view. In this report, an analysis of transient creep is made. It is found that exponential transient creep can be related to steady-state creep through a universal creep curve. The resultant description is convenient for creep analyses where very early time behavior is not important.

  5. Oxidation and creep behavior of Mo*5*Si*3* based materials

    SciTech Connect

    Meyer, M.

    1995-06-19

    Mo{sub 5}Si{sub 3} shows promise as a high temperature creep resistant material. The high temperature oxidation resistance of Mo{sub 5}Si{sub 3} has been found to be poor, however, limiting its use in oxidizing atmospheres. Undoped Mo{sub 5}Si{sub 3} exhibits mass loss in the temperature range 800{degrees}-1200{degrees}C due to volatilization of molybdenum oxide, indicating that the silica scale does not provide a passivating layer. The addition of boron results in protective scale formation and parabolic oxidation kinetics in the temperature range of 1050{degrees}-1300{degrees}C. The oxidation rate of Mo{sub 5}Si{sub 3} was decreased by 5 orders of magnitude at 1200{degrees}C by doping with less than two weight percent boron. Boron doping eliminates catastrophic {open_quote}pest{close_quote} oxidation at 800{degrees}C. The mechanism for improved oxidation resistance of boron doped Mo{sub 5}Si{sub 3} is due to scale modification by boron.

  6. Electrothermal shrinkage reduces laxity but alters creep behavior in a lapine ligament model.

    PubMed

    Wallace, A L; Hollinshead, R M; Frank, C B

    2001-01-01

    Thermal denaturation of collagen in ligament tissue has the potential to enhance arthroscopic shoulder stabilization. Previous studies have shown that laser energy produces significant capsular shortening without alteration of viscoelastic properties, but little information is available on the effects of radio frequency electrothermal energy. We assessed the acute effects of radio frequency shrinkage with use of the lapine medial collateral ligament model, in which the tibial insertion was shifted proximally to produce abnormal laxity. Thermal treatment resulted in restoration of laxity from 3.33 +/- 0.25 mm to 0.66 +/- 0.31 mm, which was not significantly different from medial collateral ligaments replaced anatomically (0.50 +/- 0.34 mm). When tested at 4.1 megapascals, cyclic and static creep strains were increased twofold to threefold in thermally-treated ligaments (P <.01), and partial failure occurred in 2 of 8 cases. We conclude that radio frequency electrothermal shrinkage is effective at reducing laxity but significantly alters viscoelastic properties, posing a risk of recurrent stretching-out at "physiological" loads. PMID:11182728

  7. Creep rupture behavior of polypropylene suture material and its applications as a time-release mechanism

    SciTech Connect

    Kusy, R.P.; Whitley, J.Q.

    1983-05-01

    The controlled failure of polypropylene (PP) sutures is studied via creep rupture tests. From plots of log time (tB) vs. stress (sigma), linear relationships are generated over the failure times of 1-1000 h. Results show that as a function of stress, the time dependence varies with irradiation dose (15, 20, 25, and 50 Mrad), irradiation atmosphere (air and vacuum), suture diameter (7-0, 6-0, 5-0, and 4-0), and test temperature (26 and 37 degrees C). For a given stress, the time to failure is least for the greatest dose in the presence of air and at the highest temperature. When suture loops are wrapped around a small wire sheave, however, failure occurs in the largest suture as much as two decades sooner than the smallest suture studied. Within the limitations stated herein, they are independent of test method, loop diameter, aging, and humidity. Consequently, after irradiation in vacuum and postirradiation heat treatment, the processed material may be stored at room temperature for at least 1 month. Such materials are advocated when the time release of a dental or medical device is required, for example, in the self-activating cleft palate appliance.

  8. Effect of Tungsten on Primary Creep Deformation and Minimum Creep Rate of Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Vanaja, J.; Laha, Kinkar; Mathew, M. D.

    2014-10-01

    Effect of tungsten on transient creep deformation and minimum creep rate of reduced activation ferritic-martensitic (RAFM) steel has been assessed. Tungsten content in the 9Cr-RAFM steel has been varied between 1 and 2 wt pct, and creep tests were carried out over the stress range of 180 and 260 MPa at 823 K (550 °C). The tempered martensitic steel exhibited primary creep followed by tertiary stage of creep deformation with a minimum in creep deformation rate. The primary creep behavior has been assessed based on the Garofalo relationship, , considering minimum creep rate instead of steady-state creep rate . The relationships between (i) rate of exhaustion of transient creep r' with minimum creep rate, (ii) rate of exhaustion of transient creep r' with time to reach minimum creep rate, and (iii) initial creep rate with minimum creep rate revealed that the first-order reaction-rate theory has prevailed throughout the transient region of the RAFM steel having different tungsten contents. The rate of exhaustion of transient creep r' and minimum creep rate decreased, whereas the transient strain ɛ T increased with increase in tungsten content. A master transient creep curve of the steels has been developed considering the variation of with . The effect of tungsten on the variation of minimum creep rate with applied stress has been rationalized by invoking the back-stress concept.

  9. Deterministic and Probabilistic Creep and Creep Rupture Enhancement to CARES/Creep: Multiaxial Creep Life Prediction of Ceramic Structures Using Continuum Damage Mechanics and the Finite Element Method

    NASA Technical Reports Server (NTRS)

    Jadaan, Osama M.; Powers, Lynn M.; Gyekenyesi, John P.

    1998-01-01

    High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep ripture criterion However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of stress, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of this methodology and

  10. Oscillatory rheology and creep behavior of barley β-D-glucan concentrate dough: effect of particle size, temperature, and water content.

    PubMed

    Ahmed, Jasim; Thomas, Linu; Al-Attar, Hasan

    2015-01-01

    Small amplitude oscillatory rheology and creep behavior of β-glucan concentrate (BGC) dough were studied as function of particle size (74, 105, 149, 297, and 595 μm), BGC particle-to-water ratio (1:4, 1:5, and 1:6), and temperature (25, 40, 55, 70, and 85 °C). The color intensity and protein content increased with decreasing particle size by creating more surface areas. The water holding capacity (WHC) and sediment volume fraction increased with increasing particle size from 74 to 595 μm, which directly influences the mechanical rigidity and viscoelasticity of the dough. The dough exhibited predominating solid-like behavior (elastic modulus, G' > viscous modulus, G″). A discrete retardation spectrum is employed to the creep data to obtain retardation time and compliance parameters, which varied significantly with particle size and the process temperature. Creep tests exhibited more pronounced effect on dough behavior compared to oscillatory measurement. The protein denaturation temperature was insignificantly increased with particle fractions from 107 to 110 °C. All those information could be helpful to identify the particle size range and WHC of BGC that could be useful to produce a β-d-glucan enriched designed food.

  11. Effect of Zn and Sb Additions on the Impression Creep Behavior of Lead-Free Sn-3.5Ag Solder Alloy

    NASA Astrophysics Data System (ADS)

    Pourmajidian, M.; Mahmudi, R.; Geranmayeh, A. R.; Hashemizadeh, S.; Gorgannejad, S.

    2016-01-01

    The effect of separate additions of 1.5 wt.% Zn and 1.5 wt.% Sb on the creep behavior of Sn-3.5 wt.% Ag lead-free solder alloy was investigated by impression testing. The tests were carried out under constant punching stresses in the range of 60-120 MPa and at temperatures in the range of 298-370 K. Both of the ternary alloys showed creep resistances higher than that of the eutectic binary Sn-3.5Ag alloy. The superior creep resistance of the ternary Sn-3.5Ag-1.5Sb alloy is attributed to the strong solid solutioning effect of antimony in the tin matrix, while the formation of AgZn particles and refinement of the Ag3Sn precipitates account for the higher creep resistance of the Sn-3.5Ag-1.5Zn alloy. The average stress exponents of 8.2, 8.5, and 8.6 and activation energies of 47.4 kJ mol-1, 45.3 kJ mol-1, , and 43.3 kJ mol-1 were obtained for Sn-3.5Ag, Sn-3.5Ag-1.5Zn, and Sn-3.5Ag-1.5Sb, respectively. These activation energies are close to 46 kJ mol-1 for dislocation pipe diffusion of tin. This, together with the stress exponents of 8.2-8.6, suggests that dislocation climb controlled by dislocation pipe diffusion is the predominant creep mechanism in these alloys.

  12. Size and thickness effect on creep behavior in conventional and vitamin E-diffused highly crosslinked polyethylene for total hip arthroplasty.

    PubMed

    Takahashi, Yasuhito; Tateiwa, Toshiyuki; Shishido, Takaaki; Masaoka, Toshinori; Kubo, Kosuke; Yamamoto, Kengo

    2016-09-01

    Since the early 2000s, the use of large femoral heads is becoming increasingly popular in total hip arthroplasty (THA), which provides an improved range of motion and joint stability. Large femoral heads commonly necessitate to be coupled with thinner acetabular liners than the conventionally used because of the limited sizes of outer shells (especially for patients with small pelvic size). However, the influence of the liner thinning on the mechanical performance is still not clearly understood. The objective of this study was to experimentally clarify the size and thickness effect on the rates of compressive creep strain in conventional (virgin low-crosslinked) and vitamin E-diffused highly crosslinked, ultra-high molecular weight polyethylene (UHMWPE) acetabular liners. We applied uniaxial compression to these liners of various internal diameters (28, 32 and 36mm) and thicknesses (4.8, 6.8 and 8.9mm) up to 4320min under the constant load of 3000N. Vitamin E-diffused highly crosslinked UHMWPE components showed significantly greater creep resistance than the conventional ones. In the both types of UHMWPE, the rates of creep strain significantly decreased by increasing the internal diameter and thickness. Varying the component thickness contributed more largely to the creep behavior rather than the internal diameter. Our results suggest the positive mechanical advantage of using large femoral heads, but at the same time, a considerable liner thinning is not recommended for minimizing creep strain. Therefore, the further in-vitro as well as in-vivo research are necessary to conclude the optimal balance of head diameter and liner thickness within the limited sizes of outer shells. PMID:27261923

  13. Nanogranular origin of concrete creep.

    PubMed

    Vandamme, Matthieu; Ulm, Franz-Josef

    2009-06-30

    Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calcium-silicate-hydrates (C-S-H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C-S-H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C-S-H forms: low density, high density, ultra-high density. We demonstrate that the creep rate ( approximately 1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years.

  14. Nanogranular origin of concrete creep

    PubMed Central

    Vandamme, Matthieu; Ulm, Franz-Josef

    2009-01-01

    Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calcium–silicate–hydrates (C–S–H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C–S–H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C–S–H forms: low density, high density, ultra-high density. We demonstrate that the creep rate (≈1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years. PMID:19541652

  15. Buckling and vibration of flexoelectric nanofilms subjected to mechanical loads

    NASA Astrophysics Data System (ADS)

    Liang, Xu; Yang, Wenjun; Hu, Shuling; Shen, Shengping

    2016-03-01

    Piezoelectric nanofilms (PNFs) are widely used in microelectromechanical systems, buckling commonly occurs when subjected to compressive mechanical loads in their applications. In this paper we comprehensively study the flexoelectric effect on the buckling and vibrational behaviors of PNFs. The results from the analytical solutions indicate the significance of the flexoelectricity. The critical buckling loads and natural frequency are enhanced by the flexoelectricity. Analytical results indicate that the critical buckling load is not only influenced by the thickness of the PNFs, but also by the in-plane aspect ratio. When the thickness of the PNFs is several micrometers, the critical buckling load predicted by the present model is much higher than the prediction by the classical piezoelectric plate model. And the natural frequency calculated by the current model is much higher than that obtained by the classical piezoelectricity plate theory when the thickness is several tens of nanometers.

  16. Creep Deformation of Allvac 718Plus

    SciTech Connect

    Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam

    2014-11-11

    The creep deformation behavior of Allvac 718Plus was studied over the temperature range 650° to 732°C at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature stress regime this alloy exhibits Class M type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys this gamma prime strengthened superalloy does not exhibit steady state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics are common amongst the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non Nb bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.

  17. Creep Deformation of Allvac 718Plus

    DOE PAGES

    Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam

    2014-11-11

    The creep deformation behavior of Allvac 718Plus was studied over the temperature range 650° to 732°C at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature stress regime this alloy exhibits Class M type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys this gamma prime strengthened superalloy does not exhibit steady state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics aremore » common amongst the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non Nb bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.« less

  18. Creep-fatigue behavior of NiCoCrAlY coated PWA 1480 superalloy single crystals

    NASA Technical Reports Server (NTRS)

    Miner, R. V.; Gayda, J.; Hebsur, M. G.

    1985-01-01

    Single crystal specimens of a Ni base superalloy, PWA 1480, with a low pressure plasma sprayed NiCoCrAlY coating were tested in various 0.1 Hz fatigue and creep fatigue cycles both at 1015 and 1050 C. Creep fatigue tests of the cp, pc, and cc types were conducted with various constant total strain ranges employing creep dwells at various constant stresses. Considerable cyclic softening occurred as was evidenced particularly by rapidly increasing creep rates in the creep fatigue tests. The cycle time in the creep fatigue tests typically decreased by more than 80 percent at 0.5 N sub f. Though cyclic life did correlate with delta epsilon sub in a better correlation existed with sub f for both the fatigue and creep fatigue tests, and poor correlations were observed with either sigma sub max or the average cycle time. A model containing both delta sigma and delta sigma (sub in), N sub f = alpha delta sigma (sub in) beta delta sigma gamma, with best fit values of sigma for each cycle type, but the same values of beta and gamam, was found to provide good correlations. Life lines were not greatly different among the cycle types, differing only by a factor of about three. The cp cycle life line was lowest for both test temperatures, however among the other three cycle types there was no consistent ranking. For all test types failure occurred predominately by multiple internal cracking originating at pores. The strong correlation of life with delta sigma may reflect a significant crack growth period in the life of the specimens.

  19. Long-Term Creep Behavior of the Intervertebral Disk: Comparison between Bioreactor Data and Numerical Results

    PubMed Central

    Castro, A. P. G.; Paul, C. P. L.; Detiger, S. E. L.; Smit, T. H.; van Royen, B. J.; Pimenta Claro, J. C.; Mullender, M. G.; Alves, J. L.

    2014-01-01

    The loaded disk culture system is an intervertebral disk (IVD)-oriented bioreactor developed by the VU Medical Center (VUmc, Amsterdam, The Netherlands), which has the capacity of maintaining up to 12 IVDs in culture, for approximately 3 weeks after extraction. Using this system, eight goat IVDs were provided with the essential nutrients and submitted to compression tests without losing their biomechanical and physiological properties, for 22 days. Based on previous reports (Paul et al., 2012, 2013; Detiger et al., 2013), four of these IVDs were kept in physiological condition (control) and the other four were previously injected with chondroitinase ABC (CABC), in order to promote degenerative disk disease (DDD). The loading profile intercalated 16 h of activity loading with 8 h of loading recovery to express the standard circadian variations. The displacement behavior of these eight IVDs along the first 2 days of the experiment was numerically reproduced, using an IVD osmo-poro-hyper-viscoelastic and fiber-reinforced finite element (FE) model. The simulations were run on a custom FE solver (Castro et al., 2014). The analysis of the experimental results allowed concluding that the effect of the CABC injection was only significant in two of the four IVDs. The four control IVDs showed no signs of degeneration, as expected. In what concerns to the numerical simulations, the IVD FE model was able to reproduce the generic behavior of the two groups of goat IVDs (control and injected). However, some discrepancies were still noticed on the comparison between the injected IVDs and the numerical simulations, namely on the recovery periods. This may be justified by the complexity of the pathways for DDD, associated with the multiplicity of physiological responses to each direct or indirect stimulus. Nevertheless, one could conclude that ligaments, muscles, and IVD covering membranes could be added to the FE model, in order to improve its accuracy and properly

  20. Long-Term Creep Behavior of the Intervertebral Disk: Comparison between Bioreactor Data and Numerical Results.

    PubMed

    Castro, A P G; Paul, C P L; Detiger, S E L; Smit, T H; van Royen, B J; Pimenta Claro, J C; Mullender, M G; Alves, J L

    2014-01-01

    The loaded disk culture system is an intervertebral disk (IVD)-oriented bioreactor developed by the VU Medical Center (VUmc, Amsterdam, The Netherlands), which has the capacity of maintaining up to 12 IVDs in culture, for approximately 3 weeks after extraction. Using this system, eight goat IVDs were provided with the essential nutrients and submitted to compression tests without losing their biomechanical and physiological properties, for 22 days. Based on previous reports (Paul et al., 2012, 2013; Detiger et al., 2013), four of these IVDs were kept in physiological condition (control) and the other four were previously injected with chondroitinase ABC (CABC), in order to promote degenerative disk disease (DDD). The loading profile intercalated 16 h of activity loading with 8 h of loading recovery to express the standard circadian variations. The displacement behavior of these eight IVDs along the first 2 days of the experiment was numerically reproduced, using an IVD osmo-poro-hyper-viscoelastic and fiber-reinforced finite element (FE) model. The simulations were run on a custom FE solver (Castro et al., 2014). The analysis of the experimental results allowed concluding that the effect of the CABC injection was only significant in two of the four IVDs. The four control IVDs showed no signs of degeneration, as expected. In what concerns to the numerical simulations, the IVD FE model was able to reproduce the generic behavior of the two groups of goat IVDs (control and injected). However, some discrepancies were still noticed on the comparison between the injected IVDs and the numerical simulations, namely on the recovery periods. This may be justified by the complexity of the pathways for DDD, associated with the multiplicity of physiological responses to each direct or indirect stimulus. Nevertheless, one could conclude that ligaments, muscles, and IVD covering membranes could be added to the FE model, in order to improve its accuracy and properly

  1. Low cycle fatigue and creep-fatigue behavior of Ni-based alloy 230 at 850 C

    SciTech Connect

    Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A; ERDMAN III, DONALD L; Mo, Kun; Stubbins, James

    2013-01-01

    Strain-controlled low cycle fatigue (LCF) and creep-fatigue testing of Ni-based alloy 230 were carried out at 850 C. The material creep-fatigue life decreased compared with its low cycle fatigue life at the same total strain range. Longer hold time at peak tensile strain further reduced the material creep-fatigue life. Based on the electron backscatter diffraction, a novel material deformation characterization method was applied, which revealed that in low cycle fatigue testing as the total strain range increased, the deformation was segregated to grain boundaries since the test temperature was higher than the material equicohesive temperature and grain boundaries became weaker regions compared with grains. Creep-fatigue tests enhanced the localized deformation, resulting in material interior intergranular cracking, and accelerated material damage. Precipitation in alloy 230 helped slip dispersion, favorable for fatigue property, but grain boundary cellular precipitates formed after material exposure to the elevated temperature had a deleterious effect on the material low cycle fatigue and creep-fatigue property.

  2. Scleral Buckling with Chandelier Illumination

    PubMed Central

    Seider, Michael I.; Nomides, Riikka E. K.; Hahn, Paul; Mruthyunjaya, Prithvi; Mahmoud, Tamer H.

    2016-01-01

    Scleral buckling is a highly successful technique for the repair of rhegmatogenous retinal detachment that requires intra-operative examination of the retina and treatment of retinal breaks via indirect ophthalmoscopy. Data suggest that scleral buckling likely results in improved outcomes for many patients but is declining in popularity, perhaps because of significant advances in vitrectomy instrumentation and visualization systems. Emerging data suggest that chandelier-assisted scleral buckling is safe and has many potential advantages over traditional buckling techniques. By combining traditional scleral buckling with contemporary vitreoretinal visualization techniques, chandelier-assistance may increase the popularity of scleral buckling to treat primary rhegmatogenous retinal detachment for surgeons of the next generation, maintaining buckling as an option for appropriate patients in the future. PMID:27621789

  3. Effects of thermomechanical processing on tensile and long-time creep behavior of Nb-1 percent Zr-0.1 percent C sheet

    NASA Technical Reports Server (NTRS)

    Titran, Robert H.; Uz, Mehmet

    1994-01-01

    Effects of thermomechanical processing on the mechanical properties of Nb-1 wt. percent Zr-0.1 wt. percent C, a candidate alloy for use in advanced space power systems, were investigated. Sheet bars were cold rolled into 1-mm thick sheets following single, double, or triple extrusion operations at 1900 K. All the creep and tensile specimens were given a two-step heat treatment 1 hr at 1755 K + 2 hr 1475 K prior to testing. Tensile properties were determined at 300 as well as at 1350 K. Microhardness measurements were made on cold rolled, heat treated, and crept samples. Creep tests were carried out at 1350 K and 34.5 MPa for times of about 10,000 to 19,000 hr. The results show that the number of extrusions had some effects on both the microhardness and tensile properties. However, the long-time creep behavior of the samples were comparable, and all were found to have adequate properties to meet the design requirements of advanced power systems regardless of thermomechanical history. The results are discussed in correlation with processing and microstructure, and further compared to the results obtained from the testing of Nb-1 wt. percent Zr and Nb-1 wt. percent Zr-0.06 wt. percent C alloys.

  4. Buckling of Microtubules on a 2D Elastic Medium

    PubMed Central

    Kabir, Arif Md. Rashedul; Inoue, Daisuke; Afrin, Tanjina; Mayama, Hiroyuki; Sada, Kazuki; Kakugo, Akira

    2015-01-01

    We have demonstrated compression stress induced mechanical deformation of microtubules (MTs) on a two-dimensional elastic medium and investigated the role of compression strain, strain rate, and a MT-associated protein in the deformation of MTs. We show that MTs, supported on a two-dimensional substrate by a MT-associated protein kinesin, undergo buckling when they are subjected to compression stress. Compression strain strongly affects the extent of buckling, although compression rate has no substantial effect on the buckling of MTs. Most importantly, the density of kinesin is found to play the key role in determining the buckling mode of MTs. We have made a comparison between our experimental results and the ‘elastic foundation model’ that theoretically predicts the buckling behavior of MTs and its connection to MT-associated proteins. Taking into consideration the role of kinesin in altering the mechanical property of MTs, we are able to explain the buckling behavior of MTs by the elastic foundation model. This work will help understand the buckling mechanism of MTs and its connection to MT-associated proteins or surrounding medium, and consequently will aid in obtaining a meticulous scenario of the compression stress induced deformation of MTs in cells. PMID:26596905

  5. Creep-rupture behavior of a developmental cast-iron-base alloy for use up to 800 deg C

    NASA Technical Reports Server (NTRS)

    Titran, Robert H.; Scheuermann, Coulson M.

    1987-01-01

    A promising iron-base cast alloy is being developed as part of the DOE/NASA Stirling Engine Systems Project under contract DEN 3-282 with the United Technologies Research Center. This report presents the results of a study at the Lewis Research Center of the alloy's creep-rupture properties. The alloy was tested under a variety of conditions and was found to exhibit the normal 3-stage creep response. The alloy compared favorably with others being used or under consideration for the automotive Stirling engine cylinder/regenerator housing.

  6. Simultaneous observations of reaction kinetics, creep behavior, and AE activities during syndeformational antigorite dehydration at high pressures

    NASA Astrophysics Data System (ADS)

    Kubo, T.; Iwasato, T.; Higo, Y.; Kato, T.; Kaneshima, S.; Uehara, S.; Koizumi, S.; Imamura, M.; Tange, Y.

    2015-12-01

    Intermediate-depth earthquakes are seismic activities in Wadati-Benioff zone at depths from 60 km to 300 km, where subducting plates deform plastically rather than brittle failure. Although it has been reported that unstable faulting occurred during antigorite dehydration even at higher pressures than ~2 GPa (e.g., Jung et al., 2009), the recent study by Chernak and Hirth (2011) revealed that the syndefromational antigorite dehydration does not produces stick-slip instabilities but stable fault slip. In the present study, we newly developed an AE monitoring system for high-pressure reaction-deformation processes combined with D-DIA and synchrotron monochromatic X-ray to observe reaction kinetics, creep behaviors, and AE activities simultaneously. We applied this technique to investigate shear instability during syndeformational antigorite dehydration. High-pressure deformation experiments were conducted up to ~8 GPa, ~1050 K, and strain rates of 3.4-9.2 x 10-5 s-1 in compression using a D-DIA type apparatus installed at BL-04B1, SPring-8. 50 keV mono X-ray were used to measure reaction kinetics and stress-strain data. To monitor shear instabilities by detecting AEs, six piezoelectric devices were positioned between first and second stage anvils of MA 6-6 type system. We used three kinds of starting materials of polycrystalline antigorite, fine-grained forsterite polycrystal, and two-phase mixtures of antigorite and San Carlos olivine (10%, 30%, and 50%atg). Clear contrasts were observed in AE activities between forsterite and antigorite samples. AE activities detected within the forsterite polycrystal suggested (semi) brittle behaviors at low pressures during the cold compression stage.
Almost no AEs were detected within the antigorite samples during any stages of cold compression, ramping, deformation, and syndeformational dehydration although localized deformation textures were observed in recovered samples. Instead, we detected some AEs outside the sample

  7. Critical buckling pressure in mouse carotid arteries with altered elastic fibers.

    PubMed

    Luetkemeyer, Callan M; James, Rhys H; Devarakonda, Siva Teja; Le, Victoria P; Liu, Qin; Han, Hai-Chao; Wagenseil, Jessica E

    2015-06-01

    Arteries can buckle axially under applied critical buckling pressure due to a mechanical instability. Buckling can cause arterial tortuosity leading to flow irregularities and stroke. Genetic mutations in elastic fiber proteins are associated with arterial tortuosity in humans and mice, and may be the result of alterations in critical buckling pressure. Hence, the objective of this study is to investigate how genetic defects in elastic fibers affect buckling pressure. We use mouse models of human disease with reduced amounts of elastin (Eln+/-) and with defects in elastic fiber assembly due to the absence of fibulin-5 (Fbln5-/-). We find that Eln+/- arteries have reduced buckling pressure compared to their wild-type controls. Fbln5-/- arteries have similar buckling pressure to wild-type at low axial stretch, but increased buckling pressure at high stretch. We fit material parameters to mechanical test data for Eln+/-, Fbln5-/- and wild-type arteries using Fung and four-fiber strain energy functions. Fitted parameters are used to predict theoretical buckling pressure based on equilibrium of an inflated, buckled, thick-walled cylinder. In general, the theoretical predictions underestimate the buckling pressure at low axial stretch and overestimate the buckling pressure at high stretch. The theoretical predictions with both models replicate the increased buckling pressure at high stretch for Fbln5-/- arteries, but the four-fiber model predictions best match the experimental trends in buckling pressure changes with axial stretch. This study provides experimental and theoretical methods for further investigating the influence of genetic mutations in elastic fibers on buckling behavior and the development of arterial tortuosity.

  8. Oxidation resistance and compressive creep behavior of boron doped Mo{sub 5}Si{sub 3}

    SciTech Connect

    Meyer, M.K.; Akinc, M. |; Kramer, M.J.

    1995-10-01

    Use of Mo{sub 5}Si{sub 3} in high temperature applications is limited by oxidation induced catastrophic failure above 800 C. Oxidation resistance of Mo{sub 5}Si{sub 3} is substantially improved from 800--1,300 C by the addition of boron. The oxidation rate at 1,200 C was decreased by five orders of magnitude with less than 2 weight percent boron addition. The improvement in oxidation resistance of B doped Mo{sub 5}Si{sub 3} is due to formation of a protective scale layer due to viscous flow. The compressive creep rate of B doped Mo{sub 5}Si{sub 3} was measured at various temperature/stress levels and found to be similar to that of the undoped material. The creep rate of B doped Mo{sub 5}Si{sub 3} was measured as 1.8 {times} 10{sup {minus}7} s{sup {minus}1} at 1,242 C and 138 MPa. Creep tests were conducted at 140--180 MPa and 1,220--1,320 C. Average creep activation energy and stress exponent in this range were found to be E{sub a} {approx} 400 kJ/mol and n = 4.3 respectively.

  9. Pseudo-nonlinear dynamic analysis of buckled pipes

    NASA Astrophysics Data System (ADS)

    Gültekin Sınır, B.

    2013-02-01

    In this study, the post-divergence behavior of fluid-conveying pipes supported at both ends is investigated using the nonlinear equations of motion. The governing equation exhibits a cubic nonlinearity arising from mid-plane stretching. Exact solutions for post-buckling configurations of pipes with fixed-fixed, fixed-hinged, and hinged-hinged boundary conditions are investigated. The pipe is stable at its original static equilibrium position until the flow velocity becomes high enough to cause a supercritical pitchfork bifurcation, and the pipe loses stability by static divergence. In the supercritical fluid velocity regime, the equilibrium configuration becomes unstable and bifurcates into multiple equilibrium positions. To investigate the vibrations that occur in the vicinity of a buckled equilibrium position, the pseudo-nonlinear vibration problem around the first buckled configuration is solved precisely using a new solution procedure. By solving the resulting eigenvalue problem, the natural frequencies and the associated mode shapes of the pipe are calculated. The dynamic stability of the post-buckling configurations obtained in this manner is investigated. The first buckled shape is a stable equilibrium position for all boundary conditions. The buckled configurations beyond the first buckling mode are unstable equilibrium positions. The natural frequencies of the lowest vibration modes around each of the first two buckled configurations are presented. Effects of the system parameters on pipe behavior as well as the possibility of a subcritical pitchfork bifurcation are also investigated. The results show that many internal resonances might be activated among the vibration modes around the same or different buckled configurations.

  10. Creep of posterior dental composites.

    PubMed

    Papadogianis, Y; Boyer, D B; Lakes, R S

    1985-01-01

    The creep of microspecimens of posterior dental composites was studied using a torsional creep apparatus. Shear stresses were maintained for 3 h and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50 degrees C and four torque levels. The effect of conditioning the specimens in water up to 8 weeks was studied. The posterior composites exhibited linear viscoelastic behavior at low deformations. They had higher shear moduli and greater resistance to creep than conventional and microfilled composites. In aging experiments, maximum shear moduli occurred when specimens were 48 h to 1 week old. Subsequent softening was attributed to water absorption. Residual strain was highest when the composites were stressed within 24 h of initiating polymerization. Residual strain was very low in specimens 48 h to 8 weeks of age.

  11. Buckling and failure characteristics of graphite-polyimide shear panels

    NASA Technical Reports Server (NTRS)

    Shuart, M. J.; Hagaman, J. A.

    1983-01-01

    The buckling and failure characteristics of unstiffened, blade stiffened, and hat stiffened graphite-polyimide shear panels are described. The picture frame shear test is used to obtain shear stress-strain data at room temperature and at 316 deg C. The experimental results are compared with a linear buckling analysis, and the specimen failure modes are described. The effect of the 316 deg C test temperature on panel behavior are discussed.

  12. Buckling of a holey column.

    PubMed

    Pihler-Puzović, D; Hazel, A L; Mullin, T

    2016-09-14

    We report the results from a combined experimental and numerical investigation of buckling in a novel variant of an elastic column under axial load. We find that including a regular line of centred holes in the column can prevent conventional, global, lateral buckling. Instead, the local microstructure introduced by the holes allows the column to buckle in an entirely different, internal, mode in which the holes are compressed in alternate directions, but the column maintains the lateral reflection symmetry about its centreline. The internal buckling mode can be accommodated within a smaller external space than the global one; and it is the preferred buckling mode over an intermediate range of column lengths for sufficiently large holes. For very short or sufficiently long columns a modification of the classical, global, lateral buckling is dominant. PMID:27501288

  13. Buckling of dislocation in graphene

    NASA Astrophysics Data System (ADS)

    Yao, Yin; Wang, Shaofeng; Bai, Jianhui; Wang, Rui

    2016-10-01

    The buckling of dislocation in graphene is discussed through the lattice theory of dislocation and elastic theory. The approximate solution of the buckling is obtained based on the inner stress distribution caused by different structure of dislocations and is proved to be suitable by the simulation. The position of the highest buckling is predicted to be at the vertex of the pentagon far away from the heptagon. The buckling is strongly influenced by the internal stress and the distance between the extrusive area and stretching area, as well as the critical stress σc. The SW defect is proved to be unbuckled due to its strong interaction between extrusion and stretching.

  14. Buckling-induced retraction of spherical shells: A study on the shape of aperture

    NASA Astrophysics Data System (ADS)

    Lin, Sen; Xie, Yi Min; Li, Qing; Huang, Xiaodong; Zhou, Shiwei

    2015-06-01

    Buckling of soft matter is ubiquitous in nature and has attracted increasing interest recently. This paper studies the retractile behaviors of a spherical shell perforated by sophisticated apertures, attributed to the buckling-induced large deformation. The buckling patterns observed in experiments were reproduced in computational modeling by imposing velocity-controlled loads and eigenmode-affine geometric imperfection. It was found that the buckling behaviors were topologically sensitive with respect to the shape of dimple (aperture). The shell with rounded-square apertures had the maximal volume retraction ratio as well as the lowest energy consumption. An effective experimental procedure was established and the simulation results were validated in this study.

  15. Creep Deformation of B2 Alumindes

    NASA Technical Reports Server (NTRS)

    Nathal, M. V.

    1991-01-01

    The creep resistance and elevated temperature deformation mechanisms in CoAl, FeAl, and NiAl are reviewed. The stress and temperature dependencies of the steady state creep rate, the primary creep behavior, the dislocation substructure, and the response during transient tests are used as the main indicators of the deformation processes. In single phase intermetallics, the influence of grain size, stoichiometry, and solid solution hardening have been examined. In addition, the effect of adding dispersoids, precipitates, and other types of reinforcements to improve creep strength are compared.

  16. Scaling behaviors and novel creep motion of ac-driven flux lines in type II superconductor with random point pins

    NASA Astrophysics Data System (ADS)

    Cao, Wei-Ping; Luo, Meng-Bo; Hu, Xiao

    2012-01-01

    We performed Langevin dynamics simulations for the ac-driven flux lines in a type II superconductor with random point-like pinning centers. Scaling properties of flux-line velocity with respect to an instantaneous driving force of small frequency and around the critical dc depinning force are revealed successfully, which provides precise estimates on dynamic critical exponents. From the scaling function, we derive a creep law associated with activation by regular shaking. The effective energy barrier vanishes at the critical dc depinning point in a square-root way when the instantaneous driving force increases. The frequency plays a similar role to temperature in conventional creep motions, but in a nontrivial way governed by the critical exponents. We have also performed systematic finite-size scaling analysis for flux-line velocity in transient processes with dc driving, which provide estimates on critical exponents in good agreement with those derived with ac driving. The scaling law is checked successfully.

  17. Room temperature creep in metals and alloys

    SciTech Connect

    Deibler, Lisa Anne

    2014-09-01

    Time dependent deformation in the form of creep and stress relaxation is not often considered a factor when designing structural alloy parts for use at room temperature. However, creep and stress relaxation do occur at room temperature (0.09-0.21 Tm for alloys in this report) in structural alloys. This report will summarize the available literature on room temperature creep, present creep data collected on various structural alloys, and finally compare the acquired data to equations used in the literature to model creep behavior. Based on evidence from the literature and fitting of various equations, the mechanism which causes room temperature creep is found to include dislocation generation as well as exhaustion.

  18. Empirical law for fault-creep events

    USGS Publications Warehouse

    Crough, S.T.; Burford, R.O.

    1977-01-01

    Fault-creep events measured on the San Andreas and related faults near Hollister, California, can be described by a rheological model consisting of a spring, power-law dashpotand sliding block connected in series. An empirical creep-event law, derived from many creep-event records analyzed within the constraints of the model, provides a remarkably simple and accurate representation of creep-event behavior. The empirical creep law is expressed by the equation: D(t)= Df [1-1/{ct(n-1)Dfn-1+1}/(n-1)] where D is the value of displacement at time t following the onset of an event, Df is the final equilibrium value of the event displacementand C is a proportionality constant. This discovery should help determine whether the time-displacement character of creep events is controlled by the material properties of fault gouge, or by other parameters. ?? 1977.

  19. Material behavior under complex loading

    SciTech Connect

    Breuer, H.J.; Raule, G.; Rodig, M.

    1984-09-01

    Studies of material behavior under complex loading form a bridge between standard material testing methods and the stress analysis calculations for reactor components at high temperatures. The aim of these studies is to determine the influence of typical load change sequences on material properties, to derive the equations required for stress analyses, to carry out tests under multiaxial conditions, and to investigate the structural deformation mechanisms of creep buckling and ratcheting. The present state of the investigations within the high-temperature gas-cooled reactor materials program is described, with emphasis on the experimental apparatus, the scope of the program, and the initial results obtained.

  20. Buckle Driven Delamination in Thin Hard Film Compliant Substrate Systems

    NASA Astrophysics Data System (ADS)

    Moody, N. R.; Reedy, E. D.; Corona, E.; Adams, D. P.; Kennedy, M. S.; Cordill, M. J.; Bahr, D. F.

    2010-06-01

    Deformation and fracture of thin films on compliant substrates are key factors constraining the performance of emerging flexible substrate devices. [1-3] These systems often contain layers of thin polymer, ceramic and metallic films and stretchable interconnects where differing properties induce high normal and shear stresses. [4] As long as the films remain bonded to the substrates, they may deform far beyond their freestanding form. Once debonded, substrate constraint disappears leading to film failure. [3] Experimentally it is very difficult to measure properties in these systems at sub-micron and nanoscales. Theoretically it is very difficult to determine the contributions from the films, interfaces, and substrates. As a result our understanding of deformation and fracture behavior in compliant substrate systems is limited. This motivated a study of buckle driven delamination of thin hard tungsten films on pure PMMA substrates. The films were sputter deposited to thicknesses of 100 nm, 200 nm, and 400 nm with a residual compressive stress of 1.7 GPa. An aluminum oxide interlayer was added on several samples to alter interfacial composition. Buckles formed spontaneously on the PMMA substrates following film deposition. On films without the aluminum oxide interlayer, an extensive network of small telephone cord buckles formed following deposition, interspersed with regions of larger telephone cord buckles. (Figure 1) On films with an aluminum oxide interlayer, telephone cord buckles formed creating a uniform widely spaced pattern. Through-substrate optical observations revealed matching buckle patterns along the film-substrate interface indicating that delamination occurred for large and small buckles with and without an interlayer. The coexistence of large and small buckles on the same substrate led to two distinct behaviors as shown in Figure 2 where normalized buckle heights are plotted against normalized film stress. The behaviors deviate significantly from

  1. The secondary buckling transition: wrinkling of buckled spherical shells.

    PubMed

    Knoche, Sebastian; Kierfeld, Jan

    2014-07-01

    We theoretically explain the complete sequence of shapes of deflated spherical shells. Decreasing the volume, the shell remains spherical initially, then undergoes the classical buckling instability, where an axisymmetric dimple appears, and, finally, loses its axisymmetry by wrinkles developing in the vicinity of the dimple edge in a secondary buckling transition. We describe the first axisymmetric buckling transition by numerical integration of the complete set of shape equations and an approximate analytic model due to Pogorelov. In the buckled shape, both approaches exhibit a locally compressive hoop stress in a region where experiments and simulations show the development of polygonal wrinkles, along the dimple edge. In a simplified model based on the stability equations of shallow shells, a critical value for the compressive hoop stress is derived, for which the compressed circumferential fibres will buckle out of their circular shape in order to release the compression. By applying this wrinkling criterion to the solutions of the axisymmetric models, we can calculate the critical volume for the secondary buckling transition. Using the Pogorelov approach, we also obtain an analytical expression for the critical volume at the secondary buckling transition: The critical volume difference scales linearly with the bending stiffness, whereas the critical volume reduction at the classical axisymmetric buckling transition scales with the square root of the bending stiffness. These results are confirmed by another stability analysis in the framework of Donnel, Mushtari and Vlasov (DMV) shell theory, and by numerical simulations available in the literature. PMID:25039007

  2. Buckling of offshore structures

    SciTech Connect

    Walker, A.C.; Ellinas, C.P.; Supple, W.J.

    1984-01-01

    This new handbook gives detailed design guidance for a wide range of structural components and types of loading related to the buckling of offshore structures. It presents many hundreds of test results that have been examined and collated to give a common base of comparison, and its surveys all the relevant national and international design codes, comparing the relative accuracy of their predictions against the available test results. Contents are: unstiffened cord and bracing elements; ring-stiffened cylinders; stringer-stiffened and orthogonally-stiffened cylinders; flat panels; and end-closures and transition shells.

  3. Buckle up for Interesting Times

    ERIC Educational Resources Information Center

    Myers, Miles

    2011-01-01

    Those who are involved in the current Common Core Standards should buckle up for a rocky ride. Some of the same issues that churned within the National Council of Teachers of English (NCTE) during the standards movement of the 1990s (1989-1997) are here once again. The author's buckle is pulled tight, having already had his standards report…

  4. Buckling of polymerized monomolecular films

    NASA Astrophysics Data System (ADS)

    Bourdieu, L.; Daillant, J.; Chatenay, D.; Braslau, A.; Colson, D.

    1994-03-01

    The buckling of a two-dimensional polymer network at the air-water interface has been evidenced by grazing incidence x-ray scattering. A comprehensive description of the inhomogeneous octadecyltrichlorosilane polymerized film was obtained by atomic force microscopy and x-ray scattering measurements. The buckling occurs with a characteristic wavelength ~=10 μm.

  5. Creep of laminated aluminum composites

    NASA Astrophysics Data System (ADS)

    Moore, W.; Davies, T. J.

    1980-08-01

    The creep behavior of a laminate system consisting of alternate layers of pure aluminum and SAP (sintered aluminum powder) sheet has been examined in the temperature range 323 to 473 K and in the stress range 35 to 68 MN m-2. It was observed that secondary creep strain in the laminates was greater than in elemental SAP; the secondary creep strain rate in laminates was lower than that in pure aluminum and the creep rate decreased with increasing fracture of SAP. A stress exponent ( n) value of ˜20 was observed for most of the laminates and was reasonably constant for 3, 5, 7, and 9 ply laminates and volume fractions V f ) in the range 0.3 < V f < 0.65. For higher volume fractions of SAP the mechanical behavior of the laminates was similar to that of SAP. The experimental activation energy for creep of 30.5 ± 5 Kcal mol-1 correlates well with that for self-diffusion in aluminum. Laminating induced appreciable ductility to the SAP.

  6. Buckling failures in insect exoskeletons.

    PubMed

    Parle, Eoin; Herbaj, Simona; Sheils, Fiona; Larmon, Hannah; Taylor, David

    2016-02-01

    Thin walled tubes are often used for load-bearing structures, in nature and in engineering, because they offer good resistance to bending and torsion at relatively low weight. However, when loaded in bending they are prone to failure by buckling. It is difficult to predict the loading conditions which cause buckling, especially for tubes whose cross sections are not simple shapes. Insights into buckling prevention might be gained by studying this phenomenon in the exoskeletons of insects and other arthropods. We investigated the leg segments (tibiae) of five different insects: the locust (Schistocerca gergaria), American cockroach (Periplaneta americana), death's head cockroach (Blaberus discoidalis), stick insect (Parapachymorpha zomproi) and bumblebee (Bombus terrestris audax). These were tested to failure in cantilever bending and modelled using finite element analysis (FEA). The tibiae of the locust and the cockroaches were found to be approximately circular in shape. Their buckling loads were well predicted by linear elastic FEA, and also by one of the analytical solutions available in the literature for elastic buckling. The legs of the stick insect are also circular in cross section but have several prominent longitudinal ridges. We hypothesised that these ridges might protect the legs against buckling but we found that this was not the case: the loads necessary for elastic buckling were not reached in practice because yield occurred in the material, causing plastic buckling. The legs of bees have a non-circular cross section due to a pollen-carrying feature (the corbicula). We found that this did not significantly affect their resistance to buckling. Our results imply that buckling is the dominant failure mode in the tibia of insects; it likely to be a significant consideration for other arthropods and any organisms with stiff exoskeletons. The interactions displayed here between material properties and cross sectional geometry may provide insights for the

  7. Creep Measurement Video Extensometer

    NASA Technical Reports Server (NTRS)

    Jaster, Mark; Vickerman, Mary; Padula, Santo, II; Juhas, John

    2011-01-01

    Understanding material behavior under load is critical to the efficient and accurate design of advanced aircraft and spacecraft. Technologies such as the one disclosed here allow accurate creep measurements to be taken automatically, reducing error. The goal was to develop a non-contact, automated system capable of capturing images that could subsequently be processed to obtain the strain characteristics of these materials during deformation, while maintaining adequate resolution to capture the true deformation response of the material. The measurement system comprises a high-resolution digital camera, computer, and software that work collectively to interpret the image.

  8. Major along-strike variations in stick-slip to aseismic creep at the Hikurangi subduction interface, New Zealand: implications for controls on subduction megathrust slip behavior (Invited)

    NASA Astrophysics Data System (ADS)

    Wallace, L. M.; Williams, C. A.; Ellis, S. M.

    2013-12-01

    Campaign and continuous GPS measurements in the North Island of New Zealand show marked along-strike variations in slip behavior of the Hikurangi subduction thrust. The southern Hikurangi interface undergoes deep interseismic coupling (down to approximately 30 km depth), while most of the interface at the northern and central Hikurangi margin is dominated by aseismic creep and episodic slow slip events (SSEs). The character of SSEs at Hikurangi also undergoes strong along-strike variations. At southern Hikurangi, deep (30-50 km), long-duration (1 year), infrequent (5 year recurrence), large (Mw 7.0) SSEs occur along the down-dip transition from interseismic coupling to aseismic creep. Plate boundary slip on the shallow interface (<15 km depth) at northern Hikurangi is dominated by frequent (1-2 year recurrence), short (1-3 weeks), moderate to large (Mw 6.3-6.8) SSEs, with steady, aseismic creep below 15 km depth. In contrast, at central Hikurangi, the majority of the megathrust between <10-50 km depth undergoes SSE slip, indicating that the physical conditions conducive to SSE slip may be inherently broad. At central Hikurangi, we observe a full spectrum of SSE durations, magnitudes and recurrence characteristics that appear to vary with depth, including short, shallow (<15 km) SSEs beneath Hawke Bay, long-duration, deep (30-50 km) large SSEs in the Manawatu region, and newly observed moderate duration (~3 months) SSEs at 30-40 km depth, directly down-dip of the shallow Hawke Bay SSEs. Along-strike changes in megathrust behavior at Hikurangi are also accompanied by along-strike variations in convergence rate, sediment thickness on the incoming plate, degree of accretion vs. subduction erosion, upper plate stress regime (i.e., a shift from back-arc extension to transpression in the upper plate), geochemical signature of fluids emerging within the forearc, seismic attributes of the plate interface and upper plate, among other characteristics. These features make the

  9. Buckling of Cracked Laminated Composite Cylindrical Shells Subjected to Combined Loading

    NASA Astrophysics Data System (ADS)

    Allahbakhsh, Hamidreza; Shariati, Mahmoud

    2013-10-01

    A series of finite element analysis on the cracked composite cylindrical shells under combined loading is carried out to study the effect of loading condition, crack size and orientation on the buckling behavior of laminated composite cylindrical shells. The interaction buckling curves of cracked laminated composite cylinders subject to different combinations of axial compression, bending, internal pressure and external pressure are obtained, using the finite element method. Results show that the internal pressure increases the critical buckling load of the CFRP cylindrical shells and bending and external pressure decrease it. Numerical analysis show that axial crack has the most detrimental effect on the buckling load of a cylindrical shell and results show that for lower values of the axial compressive load and higher values of the external pressure, the buckling is usually in the global mode and for higher values of axial compressive load and lower levels of external pressure the buckling mode is mostly in the local mode.

  10. The Effect of Stabilization Heat Treatments on the Tensile and Creep Behavior of an Advanced Nickel-Based Disk Alloy

    NASA Technical Reports Server (NTRS)

    Gayda, John

    2003-01-01

    As part of NASA s Advanced Subsonic Technology Program, a study of stabilization heat treatment options for an advanced nickel-base disk alloy, ME 209, was performed. Using a simple, physically based approach, the effect of stabilization heat treatments on tensile and creep properties was analyzed in this paper. Solutions temperature, solution cooling rate, and stabilization temperature/time were found to have a significant impact on tensile and creep properties. These effects were readily quantified using the following methodology. First, the effect of solution cooling rate was assessed to determine its impact on a given property. The as-cooled property was then modified by using two multiplicative factors which assess the impact of solution temperature and stabilization parameters. Comparison of experimental data with predicted values showed this physically based analysis produced good results that rivaled the statistical analysis employed, which required numerous changes in the form of the regression equation depending on the property and temperature in question. As this physically based analysis uses the data for input, it should be noted that predictions which attempt to extrapolate beyond the bounds of the data must be viewed with skepticism. Future work aimed at expanding the range of the stabilization/aging parameters explored in this study would be highly desirable, especially at the higher solution cooling rates.

  11. A Phenomenological Description of Primary Creep in Class M Materials

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Freed, A. D.

    1999-01-01

    Observations of creep microstructures in the primary creep region in class M materials show a remarkable similarity with those formed in the exponential creep regime. As a result, it is proposed that the constitutive creep law for normal primary creep is similar to that for the exponential creep regime. A phenomenological description is discussed to rationalize these microstructural observations in terms of a normalized strain rate vs. stress plot. The implications of this plot in describing different testing procedures, steady-state flow, and on the observed deviations from the universal creep law are discussed. The plot is also extended to explain the observed similarities in the transient creep behavior in pre-strained materials and in stress change experiments.

  12. Creep, Fatigue and Fracture Behavior of Environmental Barrier Coating and SiC-SiC Ceramic Matrix Composite Systems: The Role of Environment Effects

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Ghosn, Louis J.

    2015-01-01

    Advanced environmental barrier coating (EBC) systems for low emission SiCSiC CMC combustors and turbine airfoils have been developed to meet next generation engine emission and performance goals. This presentation will highlight the developments of NASAs current EBC system technologies for SiC-SiC ceramic matrix composite combustors and turbine airfoils, their performance evaluation and modeling progress towards improving the engine SiCSiC component temperature capability and long-term durability. Our emphasis has also been placed on the fundamental aspects of the EBC-CMC creep and fatigue behaviors, and their interactions with turbine engine oxidizing and moisture environments. The EBC-CMC environmental degradation and failure modes, under various simulated engine testing environments, in particular involving high heat flux, high pressure, high velocity combustion conditions, will be discussed aiming at quantifying the protective coating functions, performance and durability, and in conjunction with damage mechanics and fracture mechanics approaches.

  13. Plastic buckling of cylinders under biaxial loading

    NASA Astrophysics Data System (ADS)

    Giezen, Jurgen J.

    An experimental investigation is carried out to study the effects of nonproportional loading in the plastic range on a buckling load. The discrepancy between experimental and theoretical results points to some principal shortcoming in the analysis. The problem has been simplified by applying axial tensile load and external press to simple cylindrical shell specimen and observing the buckling load for various nonproportional load-paths. Results are compared to numerical predictions (BOSOR5) using classical type plasticity models such as [...] deformation and [...] incremental theory. Significant discrepancy was found an attributed to inadequate modeling of the nonlinear material behavior. The effects of geometrical imperfections and large deflections were found to insignificant, thereby leading to an idea [...] of the discrepancy between test and theory is due to a use of inadequate plastic model. The introduction of the Southwell plot into elastic shell buckling problem reduced the already minor effects of geometric imperfections.The Christoffersen-Hutchinson corner theory model was introduced into BOSAR5 in its simplest form as presented by Poh-Sang Lam. Results obtained with this model, which allows corners to form on an initially smooth yield surface, displayed better agreement with experimental data. However, increased computational time and problems related to abrupt changes in load-path at the corner are a major concern at this present time.

  14. Analytical and experimental vibration and buckling characteristics of a pretensioned stayed column

    NASA Technical Reports Server (NTRS)

    Belvin, W. K.

    1982-01-01

    Modal vibration tests to determine lateral modes of vibration of a stayed column and static axial compression tests to determine the column's buckling and postbuckling behavior have been performed. Effects of stay tension levels and vibration-load interaction are presented. Two finite element models are used to analyze the column, a three-dimensional frame using NASTRAN and an equivalent two-dimensional frame using an exact dynamic stiffness matrix. Both analyses correlated well with the linear vibration and buckling experimental data. Results indicate premature buckling of the column due to vibration-load interaction and nonlinear oscillations due to stay slackening. Postbuckling behavior of the column is unusual because of stay slackening and results in a postbuckling restoring force of less than the bifurcation buckling load. Guidelines for design of pretensioned structures are presented which consider buckling, postbuckling and vibration behavior.

  15. Chemical controls on fault behavior: weakening of serpentinite sheared against quartz-bearing rocks and its significance for fault creep in the San Andreas system

    USGS Publications Warehouse

    Moore, Diane E.; Lockner, David A.

    2013-01-01

    The serpentinized ultramafic rocks found in many plate-tectonic settings commonly are juxtaposed against crustal rocks along faults, and the chemical contrast between the rock types potentially could influence the mechanical behavior of such faults. To investigate this possibility, we conducted triaxial experiments under hydrothermal conditions (200-350°C), shearing serpentinite gouge between forcing blocks of granite or quartzite. In an ultramafic chemical environment, the coefficient of friction, µ, of lizardite and antigorite serpentinite is 0.5-0.6, and µ increases with increasing temperature over the tested range. However, when either lizardite or antigorite serpentinite is sheared against granite or quartzite, strength is reduced to µ ~ 0.3, with the greatest strength reductions at the highest temperatures (temperature weakening) and slowest shearing rates (velocity strengthening). The weakening is attributed to a solution-transfer process that is promoted by the enhanced solubility of serpentine in pore fluids whose chemistry has been modified by interaction with the quartzose wall rocks. The operation of this process will promote aseismic slip (creep) along serpentinite-bearing crustal faults at otherwise seismogenic depths. During short-term experiments serpentine minerals reprecipitate in low-stress areas, whereas in longer experiments new Mg-rich phyllosilicates crystallize in response to metasomatic exchanges across the serpentinite-crustal rock contact. Long-term shear of serpentinite against crustal rocks will cause the metasomatic mineral assemblages, which may include extremely weak minerals such as saponite or talc, to play an increasingly important role in the mechanical behavior of the fault. Our results may explain the distribution of creep on faults in the San Andreas system.

  16. Creep substructure formation in sodium chloride single crystals in the power law and exponential creep regimes

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Pharr, G. M.

    1989-01-01

    Creep tests conducted on NaCl single crystals in the temperature range from 373 to 1023 K show that true steady state creep is obtained only above 873 K when the ratio of the applied stress to the shear modulus is less than or equal to 0.0001. Under other stress and temperature conditions, corresponding to both power law and exponential creep, the creep rate decreases monotonically with increasing strain. The transition from power law to exponential creep is shown to be associated with increases in the dislocation density, the cell boundary width, and the aspect ratio of the subgrains along the primary slip planes. The relation between dislocation structure and creep behavior is also assessed.

  17. Buckling analysis of laminated thin shells in a hot environment

    NASA Technical Reports Server (NTRS)

    Gotsis, Pascal K.; Guptil, James D.

    1993-01-01

    Results are presented of parametric studies to assess the effects of various parameters on the buckling behavior of angle-ply, laminated thin shells in a hot environment. These results were obtained by using a three-dimensional finite element analysis. An angle-ply, laminated thin shell with fiber orientation of (theta/-theta)(sub 2) was subjected to compressive mechanical loads. The laminated thin shell had a cylindrical geometry. The laminate contained T300 graphite fibers embedded in an intermediate-modulus, high-strength (IMHS) matrix. The fiber volume fraction was 55 percent and the moisture content was 2 percent. The residual stresses induced into the laminate structure during the curing were taken into account. Parametric studies were performed to examine the effect on the critical buckling load of the following parameters: cylinder length and thickness, internal hydrostatic pressure, different ply thicknesses, different temperature profiles through the thickness of the structure, and different lay up configurations and fiber volume fractions. In conjunction with these parameters the ply orientation was varied from 0 deg to 90 deg. Seven ply angles were examined: 0 deg, 15 deg, 30 deg, 45 deg, 60 deg, 75 deg, and 90 deg. The results show that the ply angle theta and the laminate thickness had significant effects on the critical buckling load. The fiber volume fraction, the fiber orientations, and the internal hydrostatic pressure had important effects on the critical buckling load. The cylinder length had a moderate influence on the buckling load. The thin shell with (theta/-theta)(sub 2) or (theta/-theta)(sub s) angle-ply laminate had better buckling-load performance than the thin shell with (theta)(sub 4) angle-ply laminate. The temperature profiles through the laminate thickness and various laminates with the different ply thicknesses has insignificant effects on the buckling behavior of the thin shells.

  18. Creep and Creep-Fatigue of Alloy 617 Weldments

    SciTech Connect

    Wright, Jill K.; Carroll, Laura J.; Wright, Richard N.

    2014-08-01

    Alloy 617 is the primary candidate material for the heat exchanger of a very high temperature gas cooled reactor intended to operate up to 950°C. While this alloy is currently qualified in the ASME Boiler and Pressure Vessel Code for non-nuclear construction, it is not currently allowed for use in nuclear designs. A draft Code Case to qualify Alloy 617 for nuclear pressure boundary applications was submitted in 1992, but was withdrawn prior to approval. Prior to withdrawal of the draft, comments were received indicating that there was insufficient knowledge of the creep and creep-fatigue behavior of Alloy 617 welds. In this report the results of recent experiments and analysis of the creep-rupture behavior of Alloy 617 welds prepared using the gas tungsten arc process with Alloy 617 filler wire. Low cycle fatigue and creep-fatigue properties of weldments are also discussed. The experiments cover a range of temperatures from 750 to 1000°C to support development of a new Code Case to qualify the material for elevated temperature nuclear design. Properties of the welded material are compared to results of extensive characterization of solution annealed plate base metal.

  19. Detyrosinated microtubules buckle and bear load in contracting cardiomyocytes.

    PubMed

    Robison, Patrick; Caporizzo, Matthew A; Ahmadzadeh, Hossein; Bogush, Alexey I; Chen, Christina Yingxian; Margulies, Kenneth B; Shenoy, Vivek B; Prosser, Benjamin L

    2016-04-22

    The microtubule (MT) cytoskeleton can transmit mechanical signals and resist compression in contracting cardiomyocytes. How MTs perform these roles remains unclear because of difficulties in observing MTs during the rapid contractile cycle. Here, we used high spatial and temporal resolution imaging to characterize MT behavior in beating mouse myocytes. MTs deformed under contractile load into sinusoidal buckles, a behavior dependent on posttranslational "detyrosination" of α-tubulin. Detyrosinated MTs associated with desmin at force-generating sarcomeres. When detyrosination was reduced, MTs uncoupled from sarcomeres and buckled less during contraction, which allowed sarcomeres to shorten and stretch with less resistance. Conversely, increased detyrosination promoted MT buckling, stiffened the myocyte, and correlated with impaired function in cardiomyopathy. Thus, detyrosinated MTs represent tunable, compression-resistant elements that may impair cardiac function in disease. PMID:27102488

  20. Thermo-mechanical buckling analysis of FGM plate using generalized plate theory

    NASA Astrophysics Data System (ADS)

    Sharma, Kanishk; Kumar, Dinesh; Gite, Anil

    2016-05-01

    This paper investigates the thermo-mechanical buckling behavior of simply-supported FGM plate under the framework of generalized plate theory (GPT), which includes classical plate theory (CPT), first order shear deformation theory (FSDT) and higher order shear deformation theory (HSDT) as special cases. The governing equations for FGM plate under thermal and mechanical loading conditions are derived from the principle of virtual displacements and Navier-type solution is assumed for simply supported boundary condition. The efficiency and applicability of presented methodology is illustrated by considering various examples of thermal and mechanical buckling of FGM plates. The closed form solutions in the form of critical thermal and mechanical buckling loads, predicted by CPT, FSDT and HSDT are compared for different side-to-thickness of FGM plate. Subsequently, the effect of material gradation profile on critical buckling parameters is examined by evaluating the buckling response for a range of power law indexes. The effect of geometrical parameters on mechanical buckling of FGM plate under uni-axial and bi-axial loading conditions are also illustrated by calculating the critical load for various values of slenderness ratios. Furthermore a comparative analysis of critical thermal buckling loads of FGM plate for different temperature profiles is also presented. It is identified that all plate theories predicted approximately same critical buckling loads and critical buckling temperatures for thin FGM plate, however for thick FGM plates, CPT overestimates the critical buckling parameters. Moreover the critical buckling loads and critical buckling temperatures of FGM plate are found to be significantly lower than the corresponding homogenous isotropic ceramic plate (n=0).

  1. Investigations into the coupled fluid flow and mechanical creep closure behavior of waste disposal rooms in bedded salt

    SciTech Connect

    Mendenhall, F.T.; Butcher, B.M.; Davies, P.B.

    1991-01-01

    This paper presents the results of numerical simulations of a Waste Isolation Pilot Plant (WIPP) disposal room. In particular the results show: (1) that an initially empty disposal room will consolidate in 195 years to less than 10% of is initial volume, (2) that if waste, backfill, and gas generation are allowed to generate backstress, room consolidation ceases at about 9--10 MPa backstress and room expansion can occur with backstress slightly higher than 9--10 MPa, (3) that reducing the gas generation potentials and rates by a factor of five, drops the maximum room pressure from about 22 MPa to about 18 MPa and decreases the minimum room porosity from about 0.30 to 0.09, (4) that for two-phase fluid flow, brine and gas are driven out of the disposal room into the nonhalite interbeds and that pressures build in these interbeds near the disposal room, and (5) that the interbed pressurization shown in the two-phase flow can exceed lithostatic pressure of 14.8 MPa, which has the potential of opening preexisting fractures between disposal rooms in about 270 years. This work demonstrates the complex interdependent interactions of creep closure affecting void volume, gas pressurization, brine flow, gas generation, and interbed fracture dilation. Finally, work aiming at achieving greater coupling in the simulations of WIPP disposal rooms is discussed.

  2. Interfacial Control of Creep Deformation in Ultrafine Lamellar TiAl

    SciTech Connect

    Hsiung, L M

    2002-11-26

    Solute effect on the creep resistance of two-phase lamellar TiAl with an ultrafine microstructure creep-deformed in a low-stress (LS) creep regime [where a linear creep behavior was observed] has been investigated. The resulted deformation substructure and in-situ TEM experiment revealed that interface sliding by the motion of pre-existing interfacial dislocations is the predominant deformation mechanism in LS creep regime. Solute segregation at lamellar interfaces and interfacial precipitation caused by the solute segregation result in a beneficial effect on the creep resistance of ultrafine lamellar TiAl in LS creep regime.

  3. Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part I; Isothermal Creep

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Noebe, R. D.

    2013-01-01

    This two-part paper is the first published report on the long term, low temperature creep of hot-extruded near-stoichiometric NiTi. Constant load tensile creep tests were conducted on hot-extruded near-stoichiometric NiTi at 300, 373 and 473 K under initial applied stresses varying between 200 and 350 MPa as long as 15 months. These temperatures corresponded to the martensitic, two-phase and austenitic phase regions, respectively. Normal primary creep lasting several months was observed under all conditions indicating dislocation activity. Although steady-state creep was not observed under these conditions, the estimated creep rates varied between 10(exp -10) and 10(exp -9)/s. The creep behavior of the two phases showed significant differences. The martensitic phase exhibited a large strain on loading followed by a primary creep region accumulating a small amount of strain over a period of several months. The loading strain was attributed to the detwinning of the martensitic phase whereas the subsequent strain accumulation was attributed to dislocation glide-controlled creep. An "incubation period" was observed before the occurrence of detwinning. In contrast, the austenitic phase exhibited a relatively smaller loading strain followed by a primary creep region, where the creep strain continued to increase over several months. It is concluded that the creep of the austenitic phase occurs by a dislocation glide-controlled creep mechanism as well as by the nucleation and growth of deformation twins.

  4. Anomalous Buckling Characteristics of Laminated Metal-Matrix Composite Plates with Central Square Holes

    NASA Technical Reports Server (NTRS)

    Ko, William L.

    1998-01-01

    Compressive buckling analysis was performed on metal-matrix composite (MMC) plates with central square holes. The MMC plates have varying aspect ratios and hole sizes and are supported under different boundary conditions. The finite-element structural analysis method was used to study the effects of plate boundary conditions, plate aspect ratio, hole size, and the composite stacking sequence on the compressive buckling strengths of the perforated MMC plates. Studies show that by increasing the hole sizes, compressive buckling strengths of the perforated MMC plates could be considerably increased under certain boundary conditions and aspect ratios ("anomalous" buckling behavior); and that the plate buckling mode could be symmetrical or antisymmetrical, depending on the plate boundary conditions, aspect ratio, and the hole size. For same-sized plates with same-sized holes, the compressive buckling strengths of the perforated MMC plates with [90/0/0/90]2 lamination could be as much as 10 percent higher or lower than those of the [45/- 45/- 45/45]2 laminations, depending on the plate boundary conditions, plate aspect ratios, and the hole size. Clamping the plate edges induces far stronger "anomalous" buckling behavior (enhancing compressive buckling strengths at increasing hole sizes) of the perforated MMC plates than simply supporting the plate edges.

  5. Molecular dynamics analysis on buckling of defective carbon nanotubes.

    PubMed

    Kulathunga, D D T K; Ang, K K; Reddy, J N

    2010-09-01

    Owing to their remarkable mechanical properties, carbon nanotubes have been employed in many diverse areas of applications. However, similar to any of the many man-made materials used today, carbon nanotubes (CNTs) are also susceptible to various kinds of defects. Understanding the effect of defects on the mechanical properties and behavior of CNTs is essential in the design of nanotube-based devices and composites. It has been found in various past studies that these defects can considerably affect the tensile strength and fracture of CNTs. Comprehensive studies on the effect of defects on the buckling and vibration of nanotubes is however lacking in the literature. In this paper, the effects of various configurations of atomic vacancy defects, on axial buckling of single-walled carbon nanotubes (SWCNTs), in different thermal environments, is investigated using molecular dynamics simulations (MDS), based on a COMPASS force field. Our findings revealed that even a single missing atom can cause a significant reduction in the critical buckling strain and load of SWCNTs. In general, increasing the number of missing atoms, asymmetry of vacancy configurations and asymmetric distribution of vacancy clusters seemed to lead to higher deterioration in buckling properties. Further, SWCNTs with a single vacancy cluster, compared to SWCNTs with two or more vacancy clusters having the same number of missing atoms, appeared to cause higher deterioration of buckling properties. However, exceptions from the above mentioned trends could be expected due to chemical instabilities of defects. Temperature appeared to have less effect on defective CNTs compared to pristine CNTs.

  6. Suprachoroidal Buckling: Technique and Indications

    PubMed Central

    El Rayes, Ehab N; Elborgy, Ebrahim

    2013-01-01

    The authors herein report the feasibility of suprachoroidal buckling (SCB) procedure as a new approach for treating different forms of retinal detachment (RD) by creating suprachoroidal indentation (buckling effect). With this technique, specially designed devices, i.e. a catheter or cannula, are guided in the suprachoroidal space to reach the target area. Then, a suprachoroidal filler (long lasting hyaluronic acid) is injected to indent the choroid creating SCB, thereby closing retinal tears and supporting the overlying retina. This procedure was performed to treat both myopic tractional maculopathy (MTM), including myopic macular holes, as well as peripheral retinal breaks. SCB may be used alone or in conjunction with vitrectomy. In myopic patients, restoration of retinal layers was achieved in all eyes with myopic foveoschisis. Most eyes with macular hole detachments demonstrated closure of the holes. All peripheral retinal breaks were adequately buckled and closed in a single procedure. The buckling effect was long enough in duration to seal the tears and promote adequate chorioretinal scarring. The procedure was safe and relatively simple in terms of reaching the treatment area and injecting the filler. SCB adds to our surgical options for treating selected cases of peripheral retinal tears and rhegmatogenous RD, and avoids potential problems of episcleral buckles. Moreover it may avoid vitrectomy in selected cases of rhegmatogenous RD. PMID:24653830

  7. Compressive buckling analysis of hat-stiffened panel

    NASA Technical Reports Server (NTRS)

    Ko, William L.; Jackson, Raymond H.

    1991-01-01

    Buckling analysis was performed on a hat-stiffened panel subjected to uniaxial compression. Both local buckling and global buckling were analyzed. It was found that the global buckling load was several times higher than the buckling load. The predicted local buckling loads compared favorably with both experimental data and finite-element analysis.

  8. Creep deformation at crack tips in elastic-viscoplastic solids

    NASA Astrophysics Data System (ADS)

    Riedel, H.

    1981-02-01

    THE EVALUATION of crack growth tests under creep conditions must be based on the stress analysis of a cracked body taking into account elastic, plastic and creep deformation. In addition to the well-known analysis of a cracked body creeping in secondary (steady-state) creep, the stress field at the tip of a stationary crack is calculated for primary (strain-hardening) or tertiary (strain-softening) creep of the whole specimen. For the special hardening creep-law considered, a path-independent integral C∗h, can be defined which correlates the near-tip field to the applied load. It is also shown how, after sudden load application, creep strains develop in the initially elastic or, for a higher load level, plastic body. Characteristic times are derived to distinguish between short times when the creep-zones, in which creep strains are concentrated, are still small, and long times when the whole specimen creeps extensively in primary and finally in secondary and tertiary creep. Comparing the creep-zone sizes with the specimen dimensions or comparing the characteristic times with the test duration, one can decide which deformation mechanism prevails in the bulk of the specimen and which load parameter enters into the near-tip stress field and determines crack growth behavior. The governing load parameter is the stress intensity factor K 1 if the bulk of the specimen is predominantly elastic and it is the J-integral in a fully-plastic situation when large creep strains are still confined to a small zone. The C∗h-integral applies if the bulk of the specimen deforms in primary or tertiary creep, and C∗ is the relevant load parameter for predominantly secondary creep of the whole specimen.

  9. Effect of unloading time on interrupted creep in copper

    SciTech Connect

    Chandler, H.D. . School of Mechanical Engineering)

    1994-06-01

    The effect of unloading time on the interrupted creep behavior of polycrystalline copper specimens was investigated over the temperature range 298--773 K. Up to 553 K, cyclic creep acceleration could be explained in terms of deformation and hardening using a dislocation glide model with recovery during unloading being due to dislocation climb. At higher temperatures, recrystallization effects probably influence behavior.

  10. Irradiation creep behavior of V-4Cr-4Ti alloys irradiated in a liquid sodium environment at the JOYO fast reactor

    NASA Astrophysics Data System (ADS)

    Fukumoto, Ken-ichi; Matsui, Hideki; Narui, Minoru; Yamazaki, Masanori

    2013-06-01

    Irradiation experiments on V-4Cr-4Ti alloys with sodium-enclosed irradiation capsules in the JOYO fast reactor were conducted using pressurized creep tubes (PCTs). The irradiation creep strain was significantly larger than the thermal creep strain below 686 °C, but there was no swelling of the neutron-irradiated V-4Cr-4Ti alloys. At temperatures below 500 °C, the irradiation creep was found to be proportional to the square root of the neutron dose and linear with the stress level. Above 500 °C, it was expected to be proportional to the stress level to a power greater than unity, because the irradiation creep mechanism could change from the stress-induced preferred absorption mechanism (SIPA) to the preferred absorption glide mechanism (PGA). By comparing annealed PCT specimens with cold-worked specimens, the cold-worked V-4Cr-4Ti alloys exhibited a larger irradiation creep strain compared with the annealed alloys. The irradiation creep compliance of the V-4Cr-4Ti alloys were ˜10 × 10-6 MPa-1 dpa-1 below 500 °C and 50-200 × 10-6 MPa-1 dpa-1 above 500 °C, a value greater than that of commercial V-4Cr-4Ti alloys, austenitic steels and ferritic steels.

  11. Long-term Creep Behavior (1928-2002) of the Hayward Fault at Depth in the Claremont Water Tunnel, Berkeley, CA

    NASA Astrophysics Data System (ADS)

    Cain, W. J.; Hampton, J. L.

    2003-12-01

    The Claremont Tunnel, a nine foot horseshoe shaped water tunnel conveying up to 175 million gallons per day (mgd) of treated drinking water to 800,000 residents on the east side of San Francisco Bay, crosses the Hayward Fault approximately 850 feet from the west portal of the tunnel. Creep along the fault has offset the tunnel at a depth of about 130 feet below the ground surface. Completed in 1928, the tunnel has undergone two inspections (1966 and 2002) in which detailed survey measurements have been made of the creep movements of the fault. There have been few opportunities to secure creep measurements below the ground surface. This paper will present the results of the two surveys showing the creep that has occurred at a depth of 130 feet and give time-based creep rates based on survey measurements. It will compare these measured creep rates with the tectonic creep model developed by NOAA. Due to the large time interval between the two surveys, surveying technology has dramatically changed. A discussion of the techniques used in each survey will be presented with discussions of how current technology compares with historical methods and what impact this has on the results.

  12. Tensile creep and creep fracture of a fiber-reinforced SiC/SiC composite

    SciTech Connect

    Wilshire, B.; Carreno, F.; Percival, M.J.L.

    1998-08-11

    Several studies have been completed on silicon carbide fiber-reinforced silicon carbide (SiC{sub f}/SiC) composites produced with carbon-coated fibres having a 0/90{degree} architecture. Yet, while mechanical property measurements have been made at temperatures up to 1,473K in air and argon high-temperature creep tests have been carried out only under protective atmospheres. To clarify the creep behavior patterns displayed by continuous-fiber-reinforced CMCs, while simultaneously providing information relevant to aeroengine turbine design, the tensile creep and creep fracture properties of a 0/90{degree} SiC{sub f}/SiC composite have been determined over a stress range giving creep rupture lives up to approximately 2,000 hours in air at 1,573K.

  13. Artery Buckling: New Phenotypes, Models, and Applications

    PubMed Central

    Han, Hai-Chao; Chesnutt, Jennifer K. W.; Garcia, Justin R.; Liu, Qin; Wen, Qi

    2012-01-01

    Arteries are under significant mechanical loads from blood pressure, flow, tissue tethering, and body movement. It is critical that arteries remain patent and stable under these loads. This review summarizes the common forms of buckling that occur in blood vessels including cross-sectional collapse, longitudinal twist buckling, and bent buckling. The phenomena, model analyses, experimental measurements, effects on blood flow, and clinical relevance are discussed. It is concluded that mechanical buckling is an important issue for vasculature, in addition to wall stiffness and strength, and requires further studies to address the challenges. Studies of vessel buckling not only enrich vascular biomechanics but also have important clinical applications. PMID:23192265

  14. Buckling and Delamination Growth Analysis of Composite Laminates Containing Embedded Delaminations

    NASA Astrophysics Data System (ADS)

    Hosseini-Toudeshky, H.; Hosseini, S.; Mohammadi, B.

    2010-04-01

    The objective of this work is to study the post buckling behavior of composite laminates, containing embedded delamination, under uniaxial compression loading. For this purpose, delamination initiation and propagation is modeled using the softening behavior of interface elements. The full layer-wise plate theory is also employed for approximating the displacement field of laminates and the interface elements are considered as a numerical layer between any two adjacent layers which delamination is expected to propagate. A finite element program was developed and the geometric non-linearity in the von karman sense is incorporated to the strain/displacement relations, to obtain the buckling behavior. It will be shown that, the buckling load, delamination growth process and buckling mode of the composite plates depends on the size of delamination and stacking sequence of the laminates.

  15. Buckling modes in pantographic lattices

    NASA Astrophysics Data System (ADS)

    Giorgio, Ivan; Della Corte, Alessandro; dell'Isola, Francesco; Steigmann, David J.

    2016-07-01

    We study buckling patterns in pantographic sheets, regarded as two-dimensional continua consisting of lattices of continuously distributed fibers. The fibers are modeled as beams endowed with elastic resistance to stretching, shearing, bending and twist. Included in the theory is a non-standard elasticity due to geodesic bending of the fibers relative to the lattice surface. xml:lang="fr"

  16. Optimal stabilization of indefinite plate buckling problems

    NASA Astrophysics Data System (ADS)

    Chase, J. Geoffrey; Bhashyam, Srinivas

    2001-08-01

    Indefinite plate buckling problems arise when the applied load case results in buckling loads which are not all of the same sign. Examples include the important cases of shear buckling and general combinations of tensile and compressive in-plane edge loads. Optimal controllers which actively stabilize these general, indefinite plate buckling problems, by transforming them into a system of definite plate buckling problems, are presented. Important features of this approach include the ability to select the designed closed loop critical buckling load, and to pre-determine what load cases a given controller will stabilize when the exact load combination varies or is unknown. This last result enables the control designer to know exactly, by design, what load combinations will be stabilized. A numerical example is presented where the controllers developed are employed to stabilize multiple, definite and indefinite buckling modes for laminated composite plates similar to aircraft wing skins.

  17. Unified creep-plasticity model for halite

    SciTech Connect

    Krieg, R. D.

    1980-11-01

    There are two national energy programs which are considering caverns in geological salt (NaCl) as a storage repository. One is the disposal of nuclear wastes and the other is the storage of oil. Both short-time and long-time structural deformations and stresses must be predictable for these applications. At 300K, the nominal initial temperature for both applications, the salt is at 0.28 of the melting temperature and exhibits a significant time dependent behavior. A constitutive model has been developed which describes the behavior observed in an extensive set of triaxial creep tests. Analysis of these tests showed that a single deformation mechanism seems to be operative over the stress and temperature range of interest so that the secondary creep data can be represented by a power of the stress over the entire test range. This simple behavior allowed a new unified creep-plasticity model to be applied with some confidence. The resulting model recognizes no inherent difference between plastic and creep strains yet models the total inelastic strain reasonably well including primary and secondary creep and reverse loadings. A multiaxial formulation is applied with a back stress. A Bauschinger effect is exhibited as a consequence and is present regardless of the time scale over which the loading is applied. The model would be interpreted as kinematic hardening in the sense of classical plasticity. Comparisons are made between test data and model behavior.

  18. Buckling and Failure of Compression-Loaded Composite Laminated Shells With Cutouts

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.

    2007-01-01

    Results from a numerical and experimental study that illustrate the effects of laminate orthotropy on the buckling and failure response of compression-loaded composite cylindrical shells with a cutout are presented. The effects of orthotropy on the overall response of compression-loaded shells is described. In general, preliminary numerical results appear to accurately predict the buckling and failure characteristics of the shell considered herein. In particular, some of the shells exhibit stable post-local-buckling behavior accompanied by interlaminar material failures near the free edges of the cutout. In contrast another shell with a different laminate stacking sequence appears to exhibit catastrophic interlaminar material failure at the onset of local buckling near the cutout and this behavior correlates well with corresponding experimental results.

  19. Buckling-induced retraction of spherical shells: A study on the shape of aperture

    PubMed Central

    Lin, Sen; Xie, Yi Min; Li, Qing; Huang, Xiaodong; Zhou, Shiwei

    2015-01-01

    Buckling of soft matter is ubiquitous in nature and has attracted increasing interest recently. This paper studies the retractile behaviors of a spherical shell perforated by sophisticated apertures, attributed to the buckling-induced large deformation. The buckling patterns observed in experiments were reproduced in computational modeling by imposing velocity-controlled loads and eigenmode-affine geometric imperfection. It was found that the buckling behaviors were topologically sensitive with respect to the shape of dimple (aperture). The shell with rounded-square apertures had the maximal volume retraction ratio as well as the lowest energy consumption. An effective experimental procedure was established and the simulation results were validated in this study. PMID:26096171

  20. Thermal and Mechanical Buckling Analysis of Hypersonic Aircraft Hat-Stiffened Panels With Varying Face Sheet Geometry and Fiber Orientation

    NASA Technical Reports Server (NTRS)

    Ko, William L.

    1996-01-01

    Mechanical and thermal buckling behavior of monolithic and metal-matrix composite hat-stiffened panels were investigated. The panels have three types of face-sheet geometry: Flat face sheet, microdented face sheet, and microbulged face sheet. The metal-matrix composite panels have three types of face-sheet layups, each of which is combined with various types of hat composite layups. Finite-element method was used in the eigenvalue extractions for both mechanical and thermal buckling. The thermal buckling analysis required both eigenvalue and material property iterations. Graphical methods of the dual iterations are shown. The mechanical and thermal buckling strengths of the hat-stiffened panels with different face-sheet geometry are compared. It was found that by just microdenting or microbulging of the face sheet, the axial, shear, and thermal buckling strengths of both types of hat-stiffened panels could be enhanced considerably. This effect is more conspicuous for the monolithic panels. For the metal-matrix composite panels, the effect of fiber orientations on the panel buckling strengths was investigated in great detail, and various composite layup combinations offering, high panel buckling strengths are presented. The axial buckling strength of the metal-matrix panel was sensitive to the change of hat fiber orientation. However, the lateral, shear, and thermal buckling strengths were insensitive to the change of hat fiber orientation.

  1. Compression creep of filamentary composites

    NASA Technical Reports Server (NTRS)

    Graesser, D. L.; Tuttle, M. E.

    1988-01-01

    Axial and transverse strain fields induced in composite laminates subjected to compressive creep loading were compared for several types of laminate layups. Unidirectional graphite/epoxy as well as multi-directional graphite/epoxy and graphite/PEEK layups were studied. Specimens with and without holes were tested. The specimens were subjected to compressive creep loading for a 10-hour period. In-plane displacements were measured using moire interferometry. A computer based data reduction scheme was developed which reduces the whole-field displacement fields obtained using moire to whole-field strain contour maps. Only slight viscoelastic response was observed in matrix-dominated laminates, except for one test in which catastrophic specimen failure occurred after a 16-hour period. In this case the specimen response was a complex combination of both viscoelastic and fracture mechanisms. No viscoelastic effects were observed for fiber-dominated laminates over the 10-hour creep time used. The experimental results for specimens with holes were compared with results obtained using a finite-element analysis. The comparison between experiment and theory was generally good. Overall strain distributions were very well predicted. The finite element analysis typically predicted slightly higher strain values at the edge of the hole, and slightly lower strain values at positions removed from the hole, than were observed experimentally. It is hypothesized that these discrepancies are due to nonlinear material behavior at the hole edge, which were not accounted for during the finite-element analysis.

  2. Compressive buckling of rectangular composite plates with a free-edge delamination

    NASA Astrophysics Data System (ADS)

    Suemasu, Hiroshi; Gozu, Katsuhisa; Hayashi, Kunio; Ishikawa, Takashi

    1995-02-01

    An experimental and analytical investigation is conducted on the compressive buckling behavior of orthotropic plates with a delamination. The plates, which have three simply supported edges and one free edge, are a simplified model of stiffener plates of a stiffened panel. A uniform width delamination is located at their free edges over the whole length. In the analysis, the Rayleigh-Ritz approximation method is adopted. A constrained point is introduced to allow the contact between the two delaminated surfaces. Imaginary springs about relative displacement and two relative slopes are introduced at the constrained point. With the constraint, buckling loads of physically admissible buckling modes can be obtained by ordinary buckling analysis. The global buckling load reduction is found to be significant and almost proportional to the delamination width. Local delamination buckling is found to occur when the delamination is located near the surface and its size is relatively large compared with that of the plate. The local buckling mode is different from the global one, and more wave number in loading direction and constrained points are necessary to obtain physically admissible solutions. The analytical results agree well with the experimental ones.

  3. Primary and secondary creep in aluminum alloys as a solid state transformation

    NASA Astrophysics Data System (ADS)

    Fernández, R.; Bruno, G.; González-Doncel, G.

    2016-08-01

    Despite the massive literature and the efforts devoted to understand the creep behavior of aluminum alloys, a full description of this phenomenon on the basis of microstructural parameters and experimental conditions is, at present, still missing. The analysis of creep is typically carried out in terms of the so-called steady or secondary creep regime. The present work offers an alternative view of the creep behavior based on the Orowan dislocation dynamics. Our approach considers primary and secondary creep together as solid state isothermal transformations, similar to recrystallization or precipitation phenomena. In this frame, it is shown that the Johnson-Mehl-Avrami-Kolmogorov equation, typically used to analyze these transformations, can also be employed to explain creep deformation. The description is fully compatible with present (empirical) models of steady state creep. We used creep curves of commercially pure Al and ingot AA6061 alloy at different temperatures and stresses to validate the proposed model.

  4. Creep-Rupture Behavior and Recrystallization in HR6W and Haynes Alloy 230 Cold-Bent Boiler Tubing for Ultrasupercritical (USC) Steam Boiler Applications

    SciTech Connect

    Shingledecker, John P

    2007-01-01

    Creep-rupture experiments were conducted on HR6W and Haynes 230, candidate Ultrasupercritical (USC) alloys, tubes to evaluate the effects of cold-work and recrystallization during high-temperature service. These creep tests were performed by internally pressurizing cold-bent boiler tubes at 775 C for times up to 8000 hours. The bends were fabricated with cold-work levels beyond the current ASME Boiler and Pressure Vessel (ASME B&PV) Code Section I limits for austenitic stainless steels. Destructive metallographic evaluation of the crept tube bends was used to determine the effects of cold-work and the degree of recrystallization. The metallographic analysis combined with an evaluation of the creep and rupture data suggest that solid-solution strengthened nickel-based alloys can be fabricated for high-temperature service at USC conditions utilizing levels of cold-work higher than the current allowed levels for austenitic stainless steels.

  5. Deformation Microstructures and Creep Mechanisms in Advanced ZR-Based Cladding Under Biazal Loading

    SciTech Connect

    K. Linga Murty

    2008-08-11

    Investigate creep behavior of Zr-based cladding tubes with attention to basic creep mechanisms and transitions in them at low stresses and/or temperatures and study the dislocation microstructures of deformed samples for correlation with the underlying micromechanism of creep

  6. Improved Creep Behavior of a High Nitrogen Nb-Stabilized 15Cr-15Ni Austenitic Stainless Steel Strengthened by Multiple Nanoprecipitates

    NASA Astrophysics Data System (ADS)

    Ha, Vu The; Jung, Woo Sang; Suh, Jin Yoo

    2011-11-01

    Austenitic stainless steels are expected to be a major material for boiler tubes and steam turbines in future ultra-supercritical (USC) fossil power plants. It is of great interest to maximize the creep strength of the materials without increasing the cost. Precipitation strengthening was found to be the best and cheapest way for increasing the creep strength of such steels. This study is concerned with improving creep properties of a high nitrogen Nb-stabilized 15Cr-15Ni austenitic alloy through introducing a high number of nanosized particles into the austenitic matrix. The addition of around 4 wt pct Mn and 0.236 wt pct N into the 15Cr-15Ni-0.46Si-0.7Nb-1.25Mo-3Cu-Al-B-C matrix in combination with a special multicycled aging-quenching heat treatment resulted in the fine dispersion of abundant quantities of thermally stable (Nb,Cr,Fe)(C,N) precipitates with sizes of 10 to 20 nm. Apart from the carbonitrides, it was found that a high number of coherent copper precipitates with size 40 to 60 nm exist in the microstructure. Results of creep tests at 973 K and 1023 K (700 °C and 750 °C) showed that the creep properties of the investigated steel are superior compared to that of the commercial NF709 alloy. The improved creep properties are attributed to the improved morphology and thermal stability of the carbonitrides as well as to the presence of the coherent copper precipitates inside the austenitic matrix.

  7. The Effects of Boundary Conditions and Friction on the Helical Buckling of Coiled Tubing in an Inclined Wellbore.

    PubMed

    Gong, Yinchun; Ai, Zhijiu; Sun, Xu; Fu, Biwei

    2016-01-01

    Analytical buckling models are important for down-hole operations to ensure the structural integrity of the drill string. A literature survey shows that most published analytical buckling models do not address the effects of inclination angle, boundary conditions or friction. The objective of this paper is to study the effects of boundary conditions, friction and angular inclination on the helical buckling of coiled tubing in an inclined wellbore. In this paper, a new theoretical model is established to describe the buckling behavior of coiled tubing. The buckling equations are derived by applying the principles of virtual work and minimum potential energy. The proper solution for the post-buckling configuration is determined based on geometric and natural boundary conditions. The effects of angular inclination and boundary conditions on the helical buckling of coiled tubing are considered. Many significant conclusions are obtained from this study. When the dimensionless length of the coiled tubing is greater than 40, the effects of the boundary conditions can be ignored. The critical load required for helical buckling increases as the angle of inclination and the friction coefficient increase. The post-buckling behavior of coiled tubing in different configurations and for different axial loads is determined using the proposed analytical method. Practical examples are provided that illustrate the influence of the angular inclination on the axial force. The rate of change of the axial force decreases with increasing angular inclination. Moreover, the total axial friction also decreases with an increasing inclination angle. These results will help researchers to better understand helical buckling in coiled tubing. Using this knowledge, measures can be taken to prevent buckling in coiled tubing during down-hole operations. PMID:27649535

  8. The Effects of Boundary Conditions and Friction on the Helical Buckling of Coiled Tubing in an Inclined Wellbore

    PubMed Central

    Ai, Zhijiu; Sun, Xu; Fu, Biwei

    2016-01-01

    Analytical buckling models are important for down-hole operations to ensure the structural integrity of the drill string. A literature survey shows that most published analytical buckling models do not address the effects of inclination angle, boundary conditions or friction. The objective of this paper is to study the effects of boundary conditions, friction and angular inclination on the helical buckling of coiled tubing in an inclined wellbore. In this paper, a new theoretical model is established to describe the buckling behavior of coiled tubing. The buckling equations are derived by applying the principles of virtual work and minimum potential energy. The proper solution for the post-buckling configuration is determined based on geometric and natural boundary conditions. The effects of angular inclination and boundary conditions on the helical buckling of coiled tubing are considered. Many significant conclusions are obtained from this study. When the dimensionless length of the coiled tubing is greater than 40, the effects of the boundary conditions can be ignored. The critical load required for helical buckling increases as the angle of inclination and the friction coefficient increase. The post-buckling behavior of coiled tubing in different configurations and for different axial loads is determined using the proposed analytical method. Practical examples are provided that illustrate the influence of the angular inclination on the axial force. The rate of change of the axial force decreases with increasing angular inclination. Moreover, the total axial friction also decreases with an increasing inclination angle. These results will help researchers to better understand helical buckling in coiled tubing. Using this knowledge, measures can be taken to prevent buckling in coiled tubing during down-hole operations. PMID:27649535

  9. Limit Load and Buckling Analysis for Assessing Hanford Single-Shell Tank Dome Structural Integrity - 12278

    SciTech Connect

    Johnson, Ken I.; Deibler, John E.; Karri, Naveen K.; Pilli, Siva P.; Julyk, Larry J.

    2012-07-01

    dome, so the penetration does reduce the concentrated limit load somewhat. However, the safety factors comparing the limit loads to the maximum allowable applied loads remain well above the required value of 3.0. The buckling analysis method accounts for the geometric imperfections, concrete creep, cracking and reinforcements, and concrete plasticity in determining the allowable buckling load limits. The method was demonstrated in this paper for the evaluation of a tank before and after a penetration is added in the dome center. Finite element buckling models were used to accurately calculate the linear critical buckling loads. The models showed that adding the penetration reduces the linear critical buckling load by only 2.5%. Bounding cases also showed that the possible range of soil support on the walls does not significantly affect the dome buckling loads. Buckling models of the full 360 deg. dome also showed that the dome is more resistant to buckling when the load is offset than when it is positioned over the center. These limit load and buckling analysis methods are being used at the Hanford site to assess the tank loads that can be safely applied during future waste retrieval activities. (authors)

  10. Dynamic Delamination Buckling In Composite Laminates

    NASA Technical Reports Server (NTRS)

    Grady, Joseph E.; Chamis, Christos C.; Aiello, Robert A.

    1989-01-01

    Procedure for mathematical modeling of dynamic delamination buckling and propagation of delamination, with plate bending elements and multipoint constraints, developed and incorporated into finite-element computer program. Predicts time at which delamination buckling occurs, shape of dynamic-buckling mode, and strain-energy-release rate due to extension of delamination crack. Method extended to handle such other defects as transply and edge cracks.

  11. Thermal-structural panel buckling tests

    NASA Technical Reports Server (NTRS)

    Thompson, Randolph C.; Richards, W. Lance

    1991-01-01

    The buckling characteristics of a titanium matrix composite hat-stiffened panel were experimentally examined for various combinations of thermal and mechanical loads. Panel failure was prevented by maintaining the applied loads below real-time critical buckling predictions. The test techniques used to apply the loads, minimize boundary were shown to compare well with a finite-element buckling analysis for previous panels. Comparisons between test predictions and analysis for this panel are ongoing.

  12. Irradiation creep of nano-powder sintered silicon carbide at low neutron fluences

    SciTech Connect

    Koyanagi, Takaaki; Shimoda, Kazuya; Kondo, Sosuke; Hinoki, Tatsuya; Ozawa, Kazumi; Katoh, Yutai

    2014-12-01

    The irradiation creep behavior of nano-powder sintered silicon carbide was investigated using the bend stress relaxation method under neutron irradiation up to 1.9 dpa. The creep deformation was observed at all temperatures ranging from 380 to 1180 °C mainly from the irradiation creep but with the increasing contributions from the thermal creep at higher temperatures. Microstructural observation and data analysis were performed.

  13. And the Variscan Orogen Buckled

    NASA Astrophysics Data System (ADS)

    Pastor-Galán, D.; Groenewegen, T.; Gutiérrez-Alonso, G.; Langereis, C. G.

    2013-12-01

    Oroclines are the largest scale folds in nature, and as folds can be produced by bending or by buckling. The most commonly invoked bending mechanisms are indentation (the Himalayan syntaxes) and slab roll-back (The Calabria Arc) whereas buckling usually are commonly related with collision of the apex of ribbon continents along strike (Alaskan oroclines). In Western Europe the tectonostratigraphic zonation of Variscan orogen shows a complex 'S' shape pattern recently interpreted as a double orocline consisting of a northern and southern arc. The northern arc, known as Cantabria-Asturias Arc or Cantabrian Orocline, was developed after closure of the Rheic Ocean and the building and collapse of the Variscan orogenic edifice and, therefore, is considered post-Variscan in age. On the other hand, neither the geometry nor the kinematics of the so-called Central Iberian orocline, situated at the south of the Iberian peninsula are properly known. However, it seems reasonable to think that both oroclines developed at the same time as other coupled oroclines, such as the New England oroclines or the Carpathian oroclines. The particular paleogeography of the Variscan belt in Pangea and the kinematics of the oroclinal formation make impossible the mechanisms of indentation or buckling of a ribbon continent. The occurrence of an intense syn- and slightly post-Cantabrian orocline magmatic event (310-290 Ma) has been linked to the development of the orocline(s) due to the particular spatial-temporal distribution of these post-tectonic granitoids and its isotopic signature which would imply that the oroclines (if synchronous) are thick-skinned. This magmatic pulse has also been interpreted as due to slab roll-back. We present widespread evidences of buckling around the whole orocline at different lithospheric levels and new insights of the particular geometry of the southern orocline which is difficult to reconcile with a roll-back related origin. Therefore, a major change in the

  14. Irradiation Induced Creep of Graphite

    SciTech Connect

    Burchell, Timothy D; Murty, Prof K.L.; Eapen, Dr. Jacob

    2010-01-01

    The current status of graphite irradiation induced creep strain prediction is reviewed and the major creep models are described. The ability of the models to quantitatively predict the irradiation induced creep strain of graphite is reported. Potential mechanisms of in-crystal creep are reviewed as are mechanisms of pore generation under stress. The case for further experimental work is made and the need for improved creep models across multi-scales is highlighted.

  15. Elastic buckling of tapered circular plates

    NASA Astrophysics Data System (ADS)

    Wang, C. M.; Hong, G. M.; Tan, T. J.

    1995-06-01

    This paper is concerned with the elastic buckling of tapered circular plates. The study is prompted by the fact that results hitherto available are restricted to a narrow range of taper parameters and are somewhat different from each other. For the buckling analysis, a simple and yet accurate numerical method is presented. It is based on the shooting method and the Rayleigh-Ritz approach. Comprehensive generic buckling results of circular plates with linearly and parabolically varying thicknesses are generated. Comparison studies of the buckling results showed that some of the existing results were erroneous. Optimal values of taper parameters for such tapered plates are also given.

  16. Simplified dynamic buckling assessment of steel containments

    SciTech Connect

    Farrar, C.R.; Duffey, T.A.; Renick, D.H.

    1993-02-01

    A simplified, three-degree-of-freedom analytical procedure for performing a response spectrum buckling analysis of a thin containment shell is developed. Two numerical examples with R/t values which bound many existing steel containments are used to illustrate the procedure. The role of damping on incipient buckling acceleration level is evaluated for a regulatory seismic spectrum using the two numerical examples. The zero-period acceleration level that causes incipient buckling in either of the two containments increases 31% when damping is increased from 1% to 4% of critical. Comparisons with finite element results on incipient buckling levels are favorable.

  17. Controlled localized buckling responses of orthodontic arch wires.

    PubMed

    Nikolai, R J; Chung, A Y

    1999-09-01

    The orthodontic arch wire is often activated locally, in transverse bending and/or longitudinal torsion, to engage an individual malaligned tooth. Arch wires with substantial flexibilities and elastic ranges in bending are available. Several clinical reports of distal displacements of molars with appliances activated by locally buckling the arch wire have appeared in the recent published literature. This article contains an explanation of buckling or "column" action and the postbuckling response of a wire, and a report of the results of a controlled, in-vitro study of a sample of 256 wire segments subjected to activation-deactivation, buckling-postbuckling-unbuckling cycles. Continuous force-displacement diagrams were obtained from mechanical tests run at oral temperature. Four orthodontics-relevant, mechanical characteristics were quantified from each diagram, and each specimen was subjected to posttest evaluation for inelastic behavior. Although the deformation of the buckled wire is, in fact, bending, the force-displacement diagrams obtained differed substantially from their familiar counterparts generated in transverse bending. Judging from the force magnitudes induced as the deactivation half-cycles commenced as well as the deactivation rates, not all of the 8 wires seem to be clinically suitable for activation initiated by buckling. Magnitudes of springback were substantial from activations as large as 6 mm, and only 2 of the 8 wires exhibited full deactivations less than 80% of their activating displacements. This relatively new mode of arch wire activation that enables delivery to the dentition of mesiodistal pushing forces has substantial potential for clinical application from several biomechanical standpoints. PMID:10474103

  18. Creep Resistant Zinc Alloy

    SciTech Connect

    Frank E. Goodwin

    2002-12-31

    This report covers the development of Hot Chamber Die Castable Zinc Alloys with High Creep Strengths. This project commenced in 2000, with the primary objective of developing a hot chamber zinc die-casting alloy, capable of satisfactory service at 140 C. The core objectives of the development program were to: (1) fill in missing alloy data areas and develop a more complete empirical model of the influence of alloy composition on creep strength and other selected properties, and (2) based on the results from this model, examine promising alloy composition areas, for further development and for meeting the property combination targets, with the view to designing an optimized alloy composition. The target properties identified by ILZRO for an improved creep resistant zinc die-casting alloy were identified as follows: (1) temperature capability of 1470 C; (2) creep stress of 31 MPa (4500 psi); (3) exposure time of 1000 hours; and (4) maximum creep elongation under these conditions of 1%. The project was broadly divided into three tasks: (1) Task 1--General and Modeling, covering Experimental design of a first batch of alloys, alloy preparation and characterization. (2) Task 2--Refinement and Optimization, covering Experimental design of a second batch of alloys. (3) Task 3--Creep Testing and Technology transfer, covering the finalization of testing and the transfer of technology to the Zinc industry should have at least one improved alloy result from this work.

  19. Compression Buckling Behavior of Large-Scale Friction Stir Welded and Riveted 2090-T83 Al-Li Alloy Skin-Stiffener Panels

    NASA Technical Reports Server (NTRS)

    Hoffman, Eric K.; Hafley, Robert A.; Wagner, John A.; Jegley, Dawn C.; Pecquet, Robert W.; Blum, Celia M.; Arbegast, William J.

    2002-01-01

    To evaluate the potential of friction stir welding (FSW) as a replacement for traditional rivet fastening for launch vehicle dry bay construction, a large-scale friction stir welded 2090-T83 aluminum-lithium (Al-Li) alloy skin-stiffener panel was designed and fabricated by Lockheed-Martin Space Systems Company - Michoud Operations (LMSS) as part of NASA Space Act Agreement (SAA) 446. The friction stir welded panel and a conventional riveted panel were tested to failure in compression at the NASA Langley Research Center (LaRC). The present paper describes the compression test results, stress analysis, and associated failure behavior of these panels. The test results provide useful data to support future optimization of FSW processes and structural design configurations for launch vehicle dry bay structures.

  20. Shear buckling analysis of a hat-stiffened panel

    NASA Technical Reports Server (NTRS)

    Ko, William L.; Jackson, Raymond H.

    1994-01-01

    A buckling analysis was performed on a hat-stiffened panel subjected to shear loading. Both local buckling and global buckling were analyzed. The global shear buckling load was found to be several times higher than the local shear buckling load. The classical shear buckling theory for a flat plate was found to be useful in predicting the local shear buckling load of the hat-stiffened panel, and the predicted local shear buckling loads thus obtained compare favorably with the results of finite element analysis.

  1. The role of cobalt on the creep of Waspaloy

    NASA Technical Reports Server (NTRS)

    Jarrett, R. N.; Chin, L.; Tien, J. K.

    1984-01-01

    Cobalt was systematically replaced with nickel in Waspaloy (which normally contains 13% Co) to determine the effects of cobalt on the creep behavior of this alloy. Effects of cobalt were found to be minimal on tensile strengths and microstructure. The creep resistance and the stress rupture resistance determined in the range from 704 to 760 C (1300 to 1400 C) were found to decrease as cobalt was removed from the standard alloy at all stresses and temperatures. Roughly a ten-fold drop in rupture life and a corresponding increase in minimum creep rate were found under all test conditions. Both the apparent creep activation energy and the matrix contribution to creep resistance were found to increase with cobalt. These creep effects are attributed to cobalt lowering the stacking fault energy of the alloy matrix. The creep resistance loss due to the removal of cobalt is shown to be restored by slightly increasing the gamma' volume fraction. Results are compared to a previous study on Udimet 700, a higher strength, higher gamma' volume fraction alloy with similar phase chemistry, in which cobalt did not affect creep resistance. An explanation for this difference in behavior based on interparticle spacing and cross-slip is presented.

  2. Buckle propagation in tubular structures

    SciTech Connect

    Nogueira, A.C.; Tassoulas, J.L.

    1995-12-01

    A novel method for the analysis of buckle propagation in tubes such as tendons of tension leg platforms and pipelines for deep-water applications is presented. Results are reported for the propagation pressure and state deformation in tubes of various materials (SS-304, CS-1010 and X-52 steel tubes) with a wide range of values of the diameter-to-thickness ratio (D/t). Not only the method overcomes the prohibitive computational demands of earlier procedures, but also it is in excellent agreement with experimental data for all values of D/t investigated (from D/t = 78 to as low as D/t = 12.8).

  3. Probabilistic Dynamic Buckling of Smart Composite Shells

    NASA Technical Reports Server (NTRS)

    Abumeri, Galib H.; Chamis, Christos C.

    2003-01-01

    A computational simulation method is presented to evaluate the deterministic and nondeterministic dynamic buckling of smart composite shells. The combined use of composite mechanics, finite element computer codes, and probabilistic analysis enable the effective assessment of the dynamic buckling load of smart composite shells. A universal plot is generated to estimate the dynamic buckling load of composite shells at various load rates and probabilities. The shell structure is also evaluated with smart fibers embedded in the plies right below the outer plies. The results show that, on the average, the use of smart fibers improved the shell buckling resistance by about 10 percent at different probabilities and delayed the buckling occurrence time. The probabilistic sensitivities results indicate that uncertainties in the fiber volume ratio and ply thickness have major effects on the buckling load while uncertainties in the electric field strength and smart material volume fraction have moderate effects. For the specific shell considered in this evaluation, the use of smart composite material is not recommended because the shell buckling resistance can be improved by simply re-arranging the orientation of the outer plies, as shown in the dynamic buckling analysis results presented in this report.

  4. Probabilistic Dynamic Buckling of Smart Composite Shells

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.; Abumeri, Galib H.

    2007-01-01

    A computational simulation method is presented to evaluate the deterministic and nondeterministic dynamic buckling of smart composite shells. The combined use of intraply hybrid composite mechanics, finite element computer codes, and probabilistic analysis enable the effective assessment of the dynamic buckling load of smart composite shells. A universal plot is generated to estimate the dynamic buckling load of composite shells at various load rates and probabilities. The shell structure is also evaluated with smart fibers embedded in the plies right next to the outer plies. The results show that, on the average, the use of smart fibers improved the shell buckling resistance by about 10% at different probabilities and delayed the buckling occurrence time. The probabilistic sensitivities results indicate that uncertainties in the fiber volume ratio and ply thickness have major effects on the buckling load while uncertainties in the electric field strength and smart material volume fraction have moderate effects. For the specific shell considered in this evaluation, the use of smart composite material is not recommended because the shell buckling resistance can be improved by simply re-arranging the orientation of the outer plies, as shown in the dynamic buckling analysis results presented in this report.

  5. A Unified View of Engineering Creep Parameters

    SciTech Connect

    Eno, Daniel R.; Young, George A.; Sham, Sam

    2008-01-01

    Creep data are often analyzed using derived engineering parameters to correlate creep life (either time to rupture, or time to a specified strain) to applied stress and temperature. Commonly used formulations include Larson-Miller, Orr-Sherby-Dorn, Manson-Haferd, and Manson-Succop parameterizations. In this paper, it is shown that these parameterizations are all special cases of a common general framework based on a linear statistical model. Recognition of this fact allows for statistically efficient estimation of material model parameters and quantitative statistical comparisons among the various parameterizations in terms of their ability to fit a material database, including assessment of a stress-temperature interaction in creep behavior. This provides a rational basis for choosing the best parameterization to describe a particular material. Furthermore, using the technique of maximum likelihood estimation to estimate model parameters allows for a statistically proper treatment of runouts in a test database via censored data analysis methods, and for construction of probabilistically interpretable upper and lower bounds on creep rate. A generalized Larson-Miller formulation is developed, which is comparable in complexity to the Manson-Haferd parameter, but utilizes a reciprocal temperature dependence. The general framework for analysis of creep data is illustrated with analysis of Alloy 617 and Alloy 230 test data.

  6. Fluctuations and Scaling in Creep Deformation

    NASA Astrophysics Data System (ADS)

    Rosti, Jari; Koivisto, Juha; Laurson, Lasse; Alava, Mikko J.

    2010-09-01

    The spatial fluctuations of deformation are studied in the creep in Andrade’s power law and the logarithmic phases, using paper samples. Measurements by the digital image correlation technique show that the relative strength of the strain rate fluctuations increases with time, in both creep regimes. In the Andrade creep phase characterized by a power-law decay of the strain rate γt˜t-θ, with θ≈0.7, the fluctuations obey Δγt˜t-γ, with γ≈0.5. The local deformation follows a data collapse appropriate for a phase transition. Similar behavior is found in a crystal plasticity model, with a jamming or yielding transition.

  7. Tensile creep of dental amalgam.

    PubMed

    Greener, E H; Szurgot, K; Lautenschlager, E P

    1982-04-01

    Rather than the usual compressive dental creep, various types of one week old dental amalgams were continuously monitored in tensile creep. Testing was done at 37, 45 and 50 degrees C, in a specially designed apparatus capable of 0 to 60 degrees C while maintaining a constant true tensile stress of 17 MPa. For the first time, the classical four stages of creep were observed at elevated temperatures in the low Cu amalgams, including creep rupture. The high Cu systems displayed only transient creep up to 50 degrees C and no rupture. Approximately one half the stress was needed in tension to provide the equivalent creep in compression. PMID:7082735

  8. Study on Buckling of Stiff Thin Films on Soft Substrates as Functional Materials

    NASA Astrophysics Data System (ADS)

    Ma, Teng

    In engineering, buckling is mechanical instability of walls or columns under compression and usually is a problem that engineers try to prevent. In everyday life buckles (wrinkles) on different substrates are ubiquitous -- from human skin to a rotten apple they are a commonly observed phenomenon. It seems that buckles with macroscopic wavelengths are not technologically useful; over the past decade or so, however, thanks to the widespread availability of soft polymers and silicone materials micro-buckles with wavelengths in submicron to micron scale have received increasing attention because it is useful for generating well-ordered periodic microstructures spontaneously without conventional lithographic techniques. This thesis investigates the buckling behavior of thin stiff films on soft polymeric substrates and explores a variety of applications, ranging from optical gratings, optical masks, energy harvest to energy storage. A laser scanning technique is proposed to detect micro-strain induced by thermomechanical loads and a periodic buckling microstructure is employed as a diffraction grating with broad wavelength tunability, which is spontaneously generated from a metallic thin film on polymer substrates. A mechanical strategy is also presented for quantitatively buckling nanoribbons of piezoelectric material on polymer substrates involving the combined use of lithographically patterning surface adhesion sites and transfer printing technique. The precisely engineered buckling configurations provide a route to energy harvesters with extremely high levels of stretchability. This stiff-thin-film/polymer hybrid structure is further employed into electrochemical field to circumvent the electrochemically-driven stress issue in silicon-anode-based lithium ion batteries. It shows that the initial flat silicon-nanoribbon-anode on a polymer substrate tends to buckle to mitigate the lithiation-induced stress so as to avoid the pulverization of silicon anode. Spontaneously

  9. Sequential buckling of an elastic wall

    NASA Astrophysics Data System (ADS)

    Bico, Jose; Bense, Hadrien; Keiser, Ludovic; Roman, Benoit; Melo, Francisco; Abkarian, Manouk

    A beam under quasistatic compression classically buckles beyond a critical threshold. In the case of a free beam, the lowest buckling mode is selected. We investigate the case of a long ``wall'' grounded of a compliant base and compressed in the axial compression. In the case of a wall of slender rectangular cross section, the selected buckling mode adopts a nearly fixed wavelength proportional to the height of the wall. Higher compressive loads only increase the amplitude of the buckle. However if the cross section has a sharp shape (such as an Eiffel tower profile), we observe successive buckling modes of increasing wavelength. We interpret this unusual evolution in terms of scaling arguments. At small scales, this variable periodicity might be used to develop tunable optical devices. We thank ECOS C12E07, CNRS-CONICYT, and Fondecyt Grant No. N1130922 for partially funding this work.

  10. Effects of Elastic Edge Restraints and Initial Prestress on the Buckling Response of Compression-Loaded Composite Panels

    NASA Technical Reports Server (NTRS)

    Hilburger, Mark W.; Nemeth, Michael P.; Riddick, Jaret C.; Thornburgh, Robert P.

    2004-01-01

    A parametric study of the effects of test-fixture-induced initial prestress and elastic edge restraints on the prebuckling and buckling responses of a compression-loaded, quasi-isotropic curved panel is presented. The numerical results were obtained by using a geometrically nonlinear finite element analysis code with high-fidelity models. The results presented show that a wide range of prebuckling and buckling behavior can be obtained by varying parameters that represent circumferential loaded-edge restraint and rotational unloaded-edge restraint provided by a test fixture and that represent the mismatch in specimen and test-fixture radii of curvature. For a certain range of parameters, the panels exhibit substantial nonlinear prebuckling deformations that yield buckling loads nearly twice the corresponding buckling load predicted by a traditional linear bifurcation buckling analysis for shallow curved panels. In contrast, the results show another range of parameters exist for which the nonlinear prebuckling deformations either do not exist or are relatively benign, and the panels exhibit buckling loads that are nearly equal to the corresponding linear bifurcation buckling load. Overall, the results should also be of particular interest to scientists, engineers, and designers involved in simulating flight-hardware boundary conditions in structural verification and certification tests, involved in validating structural analysis tools, and interested in tailoring buckling performance.

  11. Circular Functions Based Comprehensive Analysis of Plastic Creep Deformations in the Fiber Reinforced Composites

    NASA Astrophysics Data System (ADS)

    Monfared, Vahid

    2016-06-01

    Analytically based model is presented for behavioral analysis of the plastic deformations in the reinforced materials using the circular (trigonometric) functions. The analytical method is proposed to predict creep behavior of the fibrous composites based on basic and constitutive equations under a tensile axial stress. New insight of the work is to predict some important behaviors of the creeping matrix. In the present model, the prediction of the behaviors is simpler than the available methods. Principal creep strain rate behaviors are very noteworthy for designing the fibrous composites in the creeping composites. Analysis of the mentioned parameter behavior in the reinforced materials is necessary to analyze failure, fracture, and fatigue studies in the creep of the short fiber composites. Shuttles, spaceships, turbine blades and discs, and nozzle guide vanes are commonly subjected to the creep effects. Also, predicting the creep behavior is significant to design the optoelectronic and photonic advanced composites with optical fibers. As a result, the uniform behavior with constant gradient is seen in the principal creep strain rate behavior, and also creep rupture may happen at the fiber end. Finally, good agreements are found through comparing the obtained analytical and FEM results.

  12. ORNL irradiation creep facility

    SciTech Connect

    Reiley, T.C.; Auble, R.L.; Beckers, R.M.; Bloom, E.E.; Duncan, M.G.; Saltmarsh, M.J.; Shannon, R.H.

    1980-09-01

    A machine was developed at ORNL to measure the rates of elongation observed under irradiation in stressed materials. The source of radiation is a beam of 60 MeV alpha particles from the Oak Ridge Isochronous Cyclotron (ORIC). This choice allows experiments to be performed which simulate the effects of fast neutrons. A brief review of irradiation creep and experimental constraints associated with each measurement technique is given. Factors are presented which lead to the experimental choices made for the Irradiation Creep Facility (ICF). The ICF consists of a helium-filled chamber which houses a high-precision mechanical testing device. The specimen to be tested must be thermally stabilized with respect to the temperature fluctuations imposed by the particle beam which passes through the specimen. Electrical resistance of the specimen is the temperature control parameter chosen. Very high precision in length measurement and temperature control are required to detect the small elongation rates relevant to irradiation creep in the test periods available (approx. 1 day). The apparatus components and features required for the above are presented in some detail, along with the experimental procedures. The damage processes associated with light ions are discussed and displacement rates are calculated. Recent irradiation creep results are given, demonstrating the suitability of the apparatus for high resolution experiments. Also discussed is the suitability of the ICF for making high precision thermal creep measurements.

  13. Bounds on Flexural Properties and Buckling Response for Symmetrically Laminated Plates

    NASA Technical Reports Server (NTRS)

    Weaver, Paul M.; Nemeth, Michael P.

    2007-01-01

    Nondimensional parameters and equations governing the buckling behavior of rectangular symmetrically laminated plates are presented that can be used to represent the buckling resistance, for plates made of all known structural materials, in a very general, insightful, and encompassing manner. In addition, these parameters can be used to assess the degree of plate orthotropy, to assess the importance of anisotropy that couples bending and twisting deformations, and to characterize quasi-isotropic laminates quantitatively. Bounds for these nondimensional parameters are also presented that are based on thermodynamics and practical laminate construction considerations. These bounds provides insight into potential gains in buckling resistance through laminate tailoring and composite-material development. As an illustration of this point, upper bounds on the buckling resistance of long rectangular orthotropic plates with simply supported or clamped edges and subjected to uniform axial compression, uniform shear, or pure inplane bending loads are presented. The results indicate that the maximum gain in buckling resistance for tailored orthotropic laminates, with respect to the corresponding isotropic plate, is in the range of 26-36% for plates with simply supported edges, irrespective of the loading conditions. For the plates with clamped edges, the corresponding gains in buckling resistance are in the range of 9-12% for plates subjected to compression or pure inplane bending loads and potentially up to 30% for plates subjected to shear loads.

  14. A multilevel approach for minimum weight structural design including local and system buckling constraints

    NASA Technical Reports Server (NTRS)

    Schmit, L. A., Jr.; Ramanathan, R. K.

    1977-01-01

    A rational multilevel approach for minimum weight structural design of truss and wing structures including local and system buckling constraints is presented. Overall proportioning of the structure is achieved at the system level subject to strength, displacement and system buckling constraints, while the detailed component designs are carried out separately at the component level satisfying local buckling constraints. Total structural weight is taken to be the objective function at the system level while employing the change in the equivalent system stiffness of the component as the component level objective function. Finite element analysis is used to predict static response while system buckling behavior is handled by incorporating a geometric stiffness matrix capability. Buckling load factors and the corresponding mode shapes are obtained by solving the eigenvalue problem associated with the assembled elastic stiffness and geometric stiffness matrices for the structural system. At the component level various local buckling failure modes are guarded against using semi-empirical formulas. Mathematical programming techniques are employed at both the system and component level.

  15. An Approximate Solution and Master Curves for Buckling of Symmetrically Laminated Composite Cylinders

    NASA Technical Reports Server (NTRS)

    Nemeth, Michael P.

    2013-01-01

    Nondimensional linear-bifurcation buckling equations for balanced, symmetrically laminated cylinders with negligible shell-wall anisotropies and subjected to uniform axial compression loads are presented. These equations are solved exactly for the practical case of simply supported ends. Nondimensional quantities are used to characterize the buckling behavior that consist of a stiffness-weighted length-to-radius parameter, a stiffness-weighted shell-thinness parameter, a shell-wall nonhomogeneity parameter, two orthotropy parameters, and a nondimensional buckling load. Ranges for the nondimensional parameters are established that encompass a wide range of laminated-wall constructions and numerous generic plots of nondimensional buckling load versus a stiffness-weighted length-to-radius ratio are presented for various combinations of the other parameters. These plots are expected to include many practical cases of interest to designers. Additionally, these plots show how the parameter values affect the distribution and size of the festoons forming each response curve and how they affect the attenuation of each response curve to the corresponding solution for an infinitely long cylinder. To aid in preliminary design studies, approximate formulas for the nondimensional buckling load are derived, and validated against the corresponding exact solution, that give the attenuated buckling response of an infinitely long cylinder in terms of the nondimensional parameters presented herein. A relatively small number of "master curves" are identified that give a nondimensional measure of the buckling load of an infinitely long cylinder as a function of the orthotropy and wall inhomogeneity parameters. These curves reduce greatly the complexity of the design-variable space as compared to representations that use dimensional quantities as design variables. As a result of their inherent simplicity, these master curves are anticipated to be useful in the ongoing development of

  16. Flux Creep and Giant Flux Creep in High Tc Hg,Pb-based Superconductors

    NASA Astrophysics Data System (ADS)

    Kirven, Douglas; Owens, Frank; Iqbal, Z.; Bleiweiss, M.; Lungu, A.; Datta, T.

    1996-03-01

    Dynamic behavior of the trapped flux in fields of up to 17.5 T was studied in a set of Hg-Pb based superconductors with a Tc in excess of 130 K. Depending on the experimental conditions, both creep and giant flux creep dynamics were observed. Results were analyzed using to standard models such as Anderson-Kim and giant-flux creep models (GFC). The plots of relaxation rate of remnant magnetization versus temperature show a peak below Tc. These results were compared with other Cu-O compounds. A distribution of activation energies was found from the magnetization rate. The activation energy distribution shows a peak around 50 K. The peak determines the temperature where the flux flow rate is a maximum. A universal relation of the resistive behavior was also found as a function of temperature and field. The zero-field/field-cooled results gave a reversibility curve that also obeyed a universal power relation.

  17. Material Parameters for Creep Rupture of Austenitic Stainless Steel Foils

    NASA Astrophysics Data System (ADS)

    Osman, H.; Borhana, A.; Tamin, M. N.

    2014-08-01

    Creep rupture properties of austenitic stainless steel foil, 347SS, used in compact recuperators have been evaluated at 700 °C in the stress range of 54-221 MPa to establish the baseline behavior for its extended use. Creep curves of the foil show that the primary creep stage is brief and creep life is dominated by tertiary creep deformation with rupture lives in the range of 10-2000 h. Results are compared with properties of bulk specimens tested at 98 and 162 MPa. Thin foil 347SS specimens were found to have higher creep rates and higher rupture ductility than their bulk specimen counterparts. Power law relationship was obtained between the minimum creep rate and the applied stress with stress exponent value, n = 5.7. The value of the stress exponent is indicative of the rate-controlling deformation mechanism associated with dislocation creep. Nucleation of voids mainly occurred at second-phase particles (chromium-rich M23C6 carbides) that are present in the metal matrix by decohesion of the particle-matrix interface. The improvement in strength is attributed to the precipitation of fine niobium carbides in the matrix that act as obstacles to the movement of dislocations.

  18. Experimental pressure solution creep of polymineralic aggregates

    NASA Astrophysics Data System (ADS)

    Zoubtsov, S.; Renard, F.; Gratier, J.-P.; Guiguet, R.; Dysthe, D. K.; Traskine, V.

    2003-04-01

    Unexpected creep behavior is obtained when experimentally compacting an aggregate containing two different minerals. Sieved mixtures of calcite and halite grains are experimentally compacted in pressure cells in the presence of a saturated aqueous solution. The individual halite grains deform easily by pressure solution creep whereas calcite grains act as hard objects and resist compaction. The fastest rate of compaction of the mixed aggregates is not obtained for a 100% halite aggregate but for a content of halite grains between 45% and 75%. This unusual creep behavior reflects the competition between two mechanisms at the grain scale: intergranular pressure solution at grain contacts and grain boundary healing between halite grains that prevent further compaction. Our experimental data can be used to estimate the relative rates of pressure solution and contact healing on halite crystals. Moreover, we can describe this effect with a single unknown parameter that represents surface effects of pressure solution at various contacts. This behaviour has fundamental implications for the rheological properties of rocks of the earth's crust which can be monomineralic or which can be the result of a mixing of different minerals, as in the case of a fault gouge for example. Key words: compaction, diagenesis, pressure solution, creep

  19. Macro stress mapping on thin film buckling

    SciTech Connect

    Goudeau, P.; Villain, P.; Renault, P.-O.; Tamura, N.; Celestre, R.S.; Padmore, H.A.

    2002-11-06

    Thin films deposited by Physical Vapour Deposition techniques on substrates generally exhibit large residual stresses which may be responsible of thin film buckling in the case of compressive stresses. Since the 80's, a lot of theoretical work has been done to develop mechanical models but only a few experimental work has been done on this subject to support these theoretical approaches and nothing concerning local stress measurement mainly because of the small dimension of the buckling (few 10th mm). This paper deals with the application of micro beam X-ray diffraction available on synchrotron radiation sources for stress mapping analysis of gold thin film buckling.

  20. Vibration and buckling of super elliptical plates

    NASA Astrophysics Data System (ADS)

    Wang, C. M.; Wang, L.; Liew, K. M.

    1994-03-01

    This paper is concerned with the vibration and buckling of a new class of plates, the periphery shape of which is defined by a super elliptical function. Such a plate shape has practical applications, as the advantageous curved corners help to diffuse stress concentrations. The loading considered for the buckling problem is that of in-plane uniform pressure along the periphery. Accurate frequency and buckling factors are tabulated for such plates with either simply supported or clamped edges. The solutions are obtained using the pb - 2 Rayleigh-Ritz method.

  1. Buckling of a beam extruded into highly viscous fluid

    NASA Astrophysics Data System (ADS)

    Gosselin, F. P.; Neetzow, P.; Paak, M.

    2014-11-01

    Inspired by microscopic Paramecia which use trichocyst extrusion to propel themselves away from thermal aggression, we propose a macroscopic experiment to study the stability of a slender beam extruded in a highly viscous fluid. Piano wires were extruded axially at constant speed in a tank filled with corn syrup. The force necessary to extrude the wire was measured to increase linearly at first until the compressive viscous force causes the wire to buckle. A numerical model, coupling a lengthening elastica formulation with resistive-force theory, predicts a similar behavior. The model is used to study the dynamics at large time when the beam is highly deformed. It is found that at large time, a large deformation regime exists in which the force necessary to extrude the beam at constant speed becomes constant and length independent. With a proper dimensional analysis, the beam can be shown to buckle at a critical length based on the extrusion speed, the bending rigidity, and the dynamic viscosity of the fluid. Hypothesizing that the trichocysts of Paramecia must be sized to maximize their thrust per unit volume as well as avoid buckling instabilities, we predict that their bending rigidity must be about 3 ×10-9N μ m2 . The verification of this prediction is left for future work.

  2. Nanoindentation of Si Nanostructures: Buckling and Friction at Nanoscales

    NASA Astrophysics Data System (ADS)

    Huang, Huai; Li, Bin; Zhao, Qiu; Luo, Zhiquan; Im, Jay; Kang, Min K.; Allen, Richard A.; Cresswell, Michael W.; Huang, Rui; Ho, Paul S.

    2009-06-01

    A nanoindentation system was employed to characterize mechanical properties of silicon nanolines (SiNLs), which were fabricated by an anisotropic wet etching (AWE) process. The SiNLs had the linewidth ranging from 24 nm to 90 nm, having smooth and vertical sidewalls and the aspect ratio (height/linewidth) from 7 to 18. During indentation, a buckling instability was observed at a critical load, followed by a displacement burst without a load increase, men a full recovery of displacement upon unloading. This phenomenon was explained by two bucking modes. It was also found that the difference in friction at the contact between the indenter and SiNLs directly affected buckling response of these nanolines. The friction coefficient was estimated to be in a range of 0.02 to 0.05. For experiments with large indentation displacements, irrecoverable indentation displacements were observed due to fracture of Si nanolines, with the strain to failure estimated to be from 3.8% to 9.7%. These observations indicated that the buckling behavior of SiNLs depended on the combined effects of load, line geometry, and the friction at contact. This study demonstrated a valuable approach to fabrication of well-defined Si nanoline structures and the application of the nanoindentation method for investigation of their mechanical properties at the nanoscale.

  3. Carnivorous Utricularia: the buckling scenario.

    PubMed

    Vincent, Olivier; Marmottant, Philippe

    2011-11-01

    We review recent results about the functioning of aquatic carnivorous traps from the genus Utricularia. The use of high speed cameras has helped to elucidate the mechanism at the origin of the ultra fast capture process of Utricularia, at a millisecond time scale. As water is pumped out of the trap, pressure decreases inside the trap and elastic energy is stored due to the change of shape of the trap body. This energy is suddenly released when the trap is fired: the trap door undergoes an elastical instability--buckling--which allows its fast and passive opening and closure. This mechanism is used by Utricularia both to catch preys touching its trigger hairs and to fire spontaneously at regular time intervals. The results leading to this interpretation are reviewed and discussed and suggestions for further work are briefly presented.

  4. Bend stress relaxation and tensile primary creep of a polycrystalline alpha-SiC fiber

    NASA Technical Reports Server (NTRS)

    Hee Man, Yun; Goldsby, Jon C.; Morscher, Gregory N.

    1995-01-01

    Understanding the thermomechanical behavior (creep and stress relaxation) of ceramic fibers is of both practical and basic interest. On the practical level, ceramic fibers are the reinforcement for ceramic matrix composites which are being developed for use in high temperature applications. It is important to understand and model the total creep of fibers at low strain levels where creep is predominantly in the primary stage. In addition, there are many applications where the component will only be subjected to thermal strains. Therefore, the stress relaxation of composite consituents in such circumstances will be an important factor in composite design and performance. The objective of this paper is to compare and analyze bend stress relaxation and tensile creep data for alpha-SiC fibers produced by the Carborundum Co. (Niagara Falls, NY). This fiber is of current technical interest and is similar in composition to bulk alpha-SiC which has been studied under compressive creep conditions. The temperature, time, and stress dependences will be discussed for the stress relaxation and creep results. In addition, some creep and relaxation recovery experiments were performed in order to understand the complete viscoelastic behavior, i.e. both recoverable and nonrecoverable creep components of these materials. The data will be presented in order to model the deformation behavior and compare relaxation and/or creep behavior for relatively low deformation strain conditions of practical concern. Where applicable, the tensile creep results will be compared to bend stress relaxation data.

  5. Creep deformation mechanisms in modified 9Cr-1Mo steel

    NASA Astrophysics Data System (ADS)

    Shrestha, Triratna; Basirat, Mehdi; Charit, Indrajit; Potirniche, Gabriel P.; Rink, Karl K.; Sahaym, Uttara

    2012-04-01

    Modified 9Cr-1Mo (Grade 91) steel is currently considered as a candidate material for reactor pressure vessels (RPVs) and reactor internals for the Very High Temperature Reactor (VHTR). The tensile creep behavior of modified 9Cr-1Mo steel (Grade 91) was studied in the temperature range of 873-1023 K and stresses between 35 MPa and 350 MPa. Analysis of creep results yielded stress exponents of ∼9-11 in the higher stress regime and ∼1 in the lower stress regime. The high stress exponent in the power-law creep regime was rationalized by invoking the concept of threshold stress, which represents the lattice diffusion controlled dislocation climb process. Without threshold stress compensation, the activation energy was 510 ± 51 kJ/mol, while after correcting for the threshold stress, the activation energy decreased to 225 ± 24 kJ/mol. This value is close to the activation energy for lattice self-diffusion in α-Fe. Threshold stress calculations were performed for the high stress regime at all test temperatures. The calculated threshold stress showed a strong dependence on temperature. The creep behavior of Grade 91 steel was described by the modified Bird-Mukherjee-Dorn relation. The rate controlling creep deformation mechanism in the high stress regime was identified as the edge dislocation climb with a stress exponent of n = 5. On the other hand, the deformation mechanism in the Newtonian viscous creep regime (n = 1) was identified as the Nabarro-Herring creep.

  6. Avoiding Project Creep.

    ERIC Educational Resources Information Center

    Kennerknecht, Norbert J.; Scarnati, James T.

    1998-01-01

    Discusses how to keep school district capital-improvement projects within budget. Examines areas where runaway costs creep into a project and ways of cutting or lessening these costs, such as using standard agreements, controlling architect's expense reimbursements, developing a quality-control process, and reducing document duplication. (GR)

  7. Creep-rupture behavior of seven iron-base alloys after long term aging at 760 deg in low pressure hydrogen

    NASA Technical Reports Server (NTRS)

    Witzke, W. R.; Stephens, J. R.

    1980-01-01

    Seven candidate iron-base alloys for heater tube application in the Stirling automotive engine were aged for 3500 hours at 760 C in argon and hydrogen. Aging degraded the tensile and creep-rupture properties. The presence of hydrogen during aging caused additional degradiation of the rupture strength in fine grain alloys. Based on current design criteria for the Mod 1 Stirling engine, N-155 and 19-9DL are considered the only alloys in this study with strengths adequate for heater tube service at 760 C.

  8. Strain rate sensitivity of nanoindentation creep in an AlCoCrFeNi high-entropy alloy

    NASA Astrophysics Data System (ADS)

    Jiao, Z. M.; Wang, Z. H.; Wu, R. F.; Qiao, J. W.

    2016-09-01

    Creep behaviors of an AlCoCrFeNi high-entropy alloy with the body-centered cubic structure were investigated by nanoindentation. The enhanced strain gradient induced by higher strain rate leads to decreased strain rate sensitivity during creep process. The present alloy exhibits excellent creep resistance, mainly due to its large entropy of mixing and highly distorted lattice structure.

  9. Buckling optimisation of sandwich cylindrical panels

    NASA Astrophysics Data System (ADS)

    Abouhamzeh, M.; Sadighi, M.

    2016-06-01

    In this paper, the buckling load optimisation is performed on sandwich cylindrical panels. A finite element program is developed in MATLAB to solve the governing differential equations of the global buckling of the structure. In order to find the optimal solution, the genetic algorithm Toolbox in MATLAB is implemented. Verifications are made for both the buckling finite element code and also the results from the genetic algorithm by comparisons to the results available in literature. Sandwich cylindrical panels are optimised for the buckling strength with isotropic or orthotropic cores with different boundary conditions. Results are presented in terms of stacking sequence of fibers in the face sheets and core to face sheet thickness ratio.

  10. Use of quadratic components for buckling calculations

    SciTech Connect

    Dohrmann, C.R.; Segalman, D.J.

    1996-12-31

    A buckling calculation procedure based on the method of quadratic components is presented. Recently developed for simulating the motion of rotating flexible structures, the method of quadratic components is shown to be applicable to buckling problems with either conservative or nonconservative loads. For conservative loads, stability follows from the positive definiteness of the system`s stiffness matrix. For nonconservative loads, stability is determined by solving a nonsymmetric eigenvalue problem, which depends on both the stiffness and mass distribution of the system. Buckling calculations presented for a cantilevered beam are shown to compare favorably with classical results. Although the example problem is fairly simple and well-understood, the procedure can be used in conjunction with a general-purpose finite element code for buckling calculations of more complex systems.

  11. Thermal-structural panel buckling tests

    NASA Astrophysics Data System (ADS)

    Thompson, Randolph C.; Richards, W. L.

    A titanium-matrix-composite (TMC) hat-stiffened panel of 61 cm sq area and 3.175 cm thick was nondestructively tested to 649 C to examine its buckling characteristics. Compressive loads were applied to the panel in a 978.6 kN uniaxial load frame system. High-temperature testing was performed using quartz lamp heating. A single-strain-age force/stiffness buckling prediction technique was developed to predict panel buckling loads. For the monolithic panel, these test predictions correlated within 10 percent with a finite-element buckling analyses performed elsewhere. Comparisons between force/stiffness predictions and analyses for the TMC panel are in progress.

  12. Thermal-structural panel buckling tests

    NASA Technical Reports Server (NTRS)

    Thompson, Randolph C.; Richards, W. L.

    1991-01-01

    A titanium-matrix-composite (TMC) hat-stiffened panel of 61 cm sq area and 3.175 cm thick was nondestructively tested to 649 C to examine its buckling characteristics. Compressive loads were applied to the panel in a 978.6 kN uniaxial load frame system. High-temperature testing was performed using quartz lamp heating. A single-strain-age force/stiffness buckling prediction technique was developed to predict panel buckling loads. For the monolithic panel, these test predictions correlated within 10 percent with a finite-element buckling analyses performed elsewhere. Comparisons between force/stiffness predictions and analyses for the TMC panel are in progress.

  13. Finite Element Analysis of Plastic Deformation During Impression Creep

    NASA Astrophysics Data System (ADS)

    Naveena; Ganesh Kumar, J.; Mathew, M. D.

    2015-04-01

    Finite element (FE) analysis of plastic deformation associated with impression creep deformation of 316LN stainless steel was carried out. An axisymmetric FE model of 10 × 10 × 10 mm specimen with 1-mm-diameter rigid cylindrical flat punch was developed. FE simulation of impression creep deformation was performed by assuming elastic-plastic-power-law creep deformation behavior. Evolution of the stress with time under the punch during elastic, plastic, and creep processes was analyzed. The onset of plastic deformation was found to occur at a nominal stress about 1.12 times the yield stress of the material. The size of the developed plastic zone was predicted to be about three times the radius of the punch. The material flow behavior and the pile-up on specimen surface have been modeled.

  14. Creep behaviour and creep mechanisms of normal and healing ligaments

    NASA Astrophysics Data System (ADS)

    Thornton, Gail Marilyn

    Patients with knee ligament injuries often undergo ligament reconstructions to restore joint stability and, potentially, abate osteoarthritis. Careful literature review suggests that in 10% to 40% of these patients the graft tissue "stretches out". Some graft elongation is likely due to creep (increased elongation of tissue under repeated or sustained load). Quantifying creep behaviour and identifying creep mechanisms in both normal and healing ligaments is important for finding clinically relevant means to prevent creep. Ligament creep was accurately predicted using a novel yet simple structural model that incorporated both collagen fibre recruitment and fibre creep. Using the inverse stress relaxation function to model fibre creep in conjunction with fibre recruitment produced a superior prediction of ligament creep than that obtained from the inverse stress relaxation function alone. This implied mechanistic role of fibre recruitment during creep was supported using a new approach to quantify crimp patterns at stresses in the toe region (increasing stiffness) and linear region (constant stiffness) of the stress-strain curve. Ligament creep was relatively insensitive to increases in stress in the toe region; however, creep strain increased significantly when tested at the linear region stress. Concomitantly, fibre recruitment was evident at the toe region stresses; however, recruitment was limited at the linear region stress. Elevating the water content of normal ligament using phosphate buffered saline increased the creep response. Therefore, both water content and fibre recruitment are important mechanistic factors involved in creep of normal ligaments. Ligament scars had inferior creep behaviour compared to normal ligaments even after 14 weeks. In addition to inferior collagen properties affecting fibre recruitment and increased water content, increased glycosaminoglycan content and flaws in scar tissue were implicated as potential mechanisms of scar creep

  15. Buckling in serpentine microstructures and applications in elastomer-supported ultra-stretchable electronics with high areal coverage

    PubMed Central

    Zhang, Yihui; Xu, Sheng; Fu, Haoran; Lee, Juhwan; Su, Jessica; Hwang, Keh-Chih; Rogers, John A.; Huang, Yonggang

    2014-01-01

    Lithographically defined electrical interconnects with thin, filamentary serpentine layouts have been widely explored for use in stretchable electronics supported by elastomeric substrates. We present a systematic and thorough study of buckling physics in such stretchable serpentine microstructures, and a strategic design of serpentine layout for ultra-stretchable electrode, via analytical models, finite element method (FEM) computations, and quantitative experiments. Both the onset of buckling and the postbuckling behaviors are examined, to determine scaling laws for the critical buckling strain and the limits of elastic behavior. Two buckling modes, namely the symmetric and anti-symmetric modes, are identified and analyzed, with experimental images and numerical results that show remarkable levels of agreement for the associated postbuckling processes. Based on these studies and an optimization in design layout, we demonstrate routes for application of serpentine interconnects in an ultra-stretchable electrode that offer, simultaneously, an areal coverage as high as 81%, and a biaxial stretchability as large as ~170%. PMID:25309616

  16. Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson's Ratio.

    PubMed

    Dai, Zhaohe; Weng, Chuanxin; Liu, Luqi; Hou, Yuan; Zhao, Xuanliang; Kuang, Jun; Shi, Jidong; Wei, Yueguang; Lou, Jun; Zhang, Zhong

    2016-01-01

    In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson's ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on. PMID:27608928

  17. Post-Buckling and Ultimate Strength Analysis of Stiffened Composite Panel Base on Progressive Damage

    NASA Astrophysics Data System (ADS)

    Zhang, Guofan; Sun, Xiasheng; Sun, Zhonglei

    Stiffened composite panel is the typical thin wall structure applied in aerospace industry, and its main failure mode is buckling subjected to compressive loading. In this paper, the development of an analysis approach using Finite Element Method on post-buckling behavior of stiffened composite structures under compression was presented. Then, the numerical results of stiffened panel are obtained by FE simulations. A thorough comparison were accomplished by comparing the load carrying capacity and key position strains of the specimen with test. The comparison indicates that the FEM results which adopted developed methodology could meet the demand of engineering application in predicting the post-buckling behavior of intact stiffened structures in aircraft design stage.

  18. Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson’s Ratio

    PubMed Central

    Dai, Zhaohe; Weng, Chuanxin; Liu, Luqi; Hou, Yuan; Zhao, Xuanliang; Kuang, Jun; Shi, Jidong; Wei, Yueguang; Lou, Jun; Zhang, Zhong

    2016-01-01

    In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on. PMID:27608928

  19. Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson's Ratio.

    PubMed

    Dai, Zhaohe; Weng, Chuanxin; Liu, Luqi; Hou, Yuan; Zhao, Xuanliang; Kuang, Jun; Shi, Jidong; Wei, Yueguang; Lou, Jun; Zhang, Zhong

    2016-09-09

    In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson's ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on.

  20. Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson’s Ratio

    NASA Astrophysics Data System (ADS)

    Dai, Zhaohe; Weng, Chuanxin; Liu, Luqi; Hou, Yuan; Zhao, Xuanliang; Kuang, Jun; Shi, Jidong; Wei, Yueguang; Lou, Jun; Zhang, Zhong

    2016-09-01

    In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on.

  1. Calculating Buckling And Vibrations Of Lattice Structures

    NASA Technical Reports Server (NTRS)

    Anderson, M. S.; Durling, B. J.; Herstrom, C. L.; Williams, F. W.; Banerjee, J. R.; Kennedy, D.; Warnaar, D. B.

    1989-01-01

    BUNVIS-RG computer program designed to calculate vibration frequencies or buckling loads of prestressed lattice structures used in outer space. For buckling and vibration problems, BUNVIS-RG calculates deadload axial forces caused in members by any combination of externally-applied static point forces and moments at nodes, axial preload or prestrain in members, and such acceleration loads as those due to gravity. BUNVIS-RG is FORTRAN 77 computer program implemented on CDC CYBER and VAX computer.

  2. A creep model for metallic composites based on matrix testing: Application to Kanthal composites

    NASA Technical Reports Server (NTRS)

    Binienda, W. K.; Robinson, D. N.; Arnold, S. M.; Bartolotta, Paul A.

    1990-01-01

    An anisotropic creep model is formulated for metallic composites with strong fibers and low to moderate fiber volume percent (less than 40 percent). The idealization admits no creep in the local fiber direction and assumes equal creep strength in longitudinal and transverse shear. Identification of the matrix behavior with that of the isotropic limit of the theory permits characterization of the composite through uniaxial creep tests on the matrix material. Constant and step-wise creep tests are required as a data base. The model provides an upper bound on the transverse creep strength of a composite having strong fibers embedded in a particular matrix material. Comparison of the measured transverse strength with the upper bound gives an assessment of the integrity of the composite. Application is made to a Kanthal composite, a model high-temperature composite system. Predictions are made of the creep response of fiber reinforced Kanthal tubes under interior pressure.

  3. Buckling instability in ordered bacterial colonies

    NASA Astrophysics Data System (ADS)

    Boyer, Denis; Mather, William; Mondragón-Palomino, Octavio; Orozco-Fuentes, Sirio; Danino, Tal; Hasty, Jeff; Tsimring, Lev S.

    2011-04-01

    Bacterial colonies often exhibit complex spatio-temporal organization. This collective behavior is affected by a multitude of factors ranging from the properties of individual cells (shape, motility, membrane structure) to chemotaxis and other means of cell-cell communication. One of the important but often overlooked mechanisms of spatio-temporal organization is direct mechanical contact among cells in dense colonies such as biofilms. While in natural habitats all these different mechanisms and factors act in concert, one can use laboratory cell cultures to study certain mechanisms in isolation. Recent work demonstrated that growth and ensuing expansion flow of rod-like bacteria Escherichia coli in confined environments leads to orientation of cells along the flow direction and thus to ordering of cells. However, the cell orientational ordering remained imperfect. In this paper we study one mechanism responsible for the persistence of disorder in growing cell populations. We demonstrate experimentally that a growing colony of nematically ordered cells is prone to the buckling instability. Our theoretical analysis and discrete-element simulations suggest that the nature of this instability is related to the anisotropy of the stress tensor in the ordered cell colony.

  4. Post buckling behaviour of stiffened composite panels loaded in cyclic compression and shear

    NASA Astrophysics Data System (ADS)

    Segal, A.; Frostig, Y.; Shalev, D.; Weller, T.; Sheinman, Y.

    1993-02-01

    This paper presents the summary of a multiphase experimental - analytical study of the post-buckling mechanical behavior of a graphite/epoxy integrally stiffened panel. The first phase of the study included cyclic compression tests in the post-buckling regime of flat panels stiffened by either 'I' or 'J' shaped stiffeners. Static residual strength of the panels after 250,000 cycles was greater than the reference strength; however, some stiffness loss was observed. A series of tests of individual stiffeners, identical to those in the panels, was also carried out and the results showed the same trends as had been observed in the panels. There were no cases of early failure during the cyclic tests. The second phase included an experimental study of the post-buckling behavior of cylindrical panels integrally stiffened in the axial and transverse directions. Panels were tested in cyclic compression, cyclic torsion, and in combinations of both. The panels were stressed through 40,000 cycles, damage was inflicted, and an additional 40,000 cycles were imposed. No damage development was observed. The third phase of the study included an analytical effort for the development of a computer code, PBCOMP, for the buckling and post-buckling analysis of stiffened laminated flat and curved panels. The results of this study clearly show a great potential for the safe use of stiffened graphite/epoxy panels in aircraft structures.

  5. Mathematical modeling and full-scale shaking table tests for multi-curve buckling restrained braces

    NASA Astrophysics Data System (ADS)

    Tsai, C. S.; Lin, Yungchang; Chen, Wenshin; Su, H. C.

    2009-09-01

    Buckling restrained braces (BRBs) have been widely applied in seismic mitigation since they were introduced in the 1970s. However, traditional BRBs have several disadvantages caused by using a steel tube to envelope the mortar to prevent the core plate from buckling, such as: complex interfaces between the materials used, uncertain precision, and time consumption during the manufacturing processes. In this study, a new device called the multi-curve buckling restrained brace (MC-BRB) is proposed to overcome these disadvantages. The new device consists of a core plate with multiple neck portions assembled to form multiple energy dissipation segments, and the enlarged segment, lateral support elements and constraining elements to prevent the BRB from buckling. The enlarged segment located in the middle of the core plate can be welded to the lateral support and constraining elements to increase buckling resistance and to prevent them from sliding during earthquakes. Component tests and a series of shaking table tests on a full-scale steel structure equipped with MC-BRBs were carried out to investigate the behavior and capability of this new BRB design for seismic mitigation. The experimental results illustrate that the MC-BRB possesses a stable mechanical behavior under cyclic loadings and provides good protection to structures during earthquakes. Also, a mathematical model has been developed to simulate the mechanical characteristics of BRBs.

  6. Modeling the Role of Dislocation Substructure During Class M and Exponential Creep. Revised

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Iskovitz, Ilana Seiden; Freed, A. D.

    1995-01-01

    The different substructures that form in the power-law and exponential creep regimes for single phase crystalline materials under various conditions of stress, temperature and strain are reviewed. The microstructure is correlated both qualitatively and quantitatively with power-law and exponential creep as well as with steady state and non-steady state deformation behavior. These observations suggest that creep is influenced by a complex interaction between several elements of the microstructure, such as dislocations, cells and subgrains. The stability of the creep substructure is examined in both of these creep regimes during stress and temperature change experiments. These observations are rationalized on the basis of a phenomenological model, where normal primary creep is interpreted as a series of constant structure exponential creep rate-stress relationships. The implications of this viewpoint on the magnitude of the stress exponent and steady state behavior are discussed. A theory is developed to predict the macroscopic creep behavior of a single phase material using quantitative microstructural data. In this technique the thermally activated deformation mechanisms proposed by dislocation physics are interlinked with a previously developed multiphase, three-dimensional. dislocation substructure creep model. This procedure leads to several coupled differential equations interrelating macroscopic creep plasticity with microstructural evolution.

  7. Buckling transition in long α-helices

    SciTech Connect

    Palenčár, Peter; Bleha, Tomáš

    2014-11-07

    The treatment of bending and buckling of stiff biopolymer filaments by the popular worm-like chain model does not provide adequate understanding of these processes at the microscopic level. Thus, we have used the atomistic molecular-dynamic simulations and the Amber03 force field to examine the compression buckling of α-helix (AH) filaments at room temperature. It was found that the buckling instability occurs in AHs at the critical force f{sub c} in the range of tens of pN depending on the AH length. The decrease of the force f{sub c} with the contour length follows the prediction of the classic thin rod theory. At the force f{sub c} the helical filament undergoes the swift and irreversible transition from the smoothly bent structure to the buckled one. A sharp kink in the AH contour arises at the transition, accompanied by the disruption of the hydrogen bonds in its vicinity. The kink defect brings in an effective softening of the AH molecule at buckling. Nonbonded interactions between helical branches drive the rearrangement of a kinked AH into the ultimate buckled structure of a compact helical hairpin described earlier in the literature.

  8. Analyses of Transient and Tertiary Small Punch Creep Deformation of 316LN Stainless Steel

    NASA Astrophysics Data System (ADS)

    Ganesh Kumar, J.; Ganesan, V.; Laha, K.

    2016-09-01

    Creep deformation behavior of 316LN stainless steel (SS) under small punch creep (SPC) and uniaxial creep test has been assessed and compared at 923 K (650 °C). The transient and tertiary creep deformation behaviors have been analyzed according to the equation proposed for SPC deflection, δ = δ0 + δ_{{T}} \\cdot (1 - {{e}}^{ - κ \\cdot t} ) + dot{δ }_{{s}} t + δ3 {{e}}^{{[ {φ ( {t - t_{{r}} } )} ]}} on the basis of Dobes and Cadek equation for uniaxial creep strain. Trends in the variations of (i) rate of exhaustion of transient creep ( κ) with steady-state deflection rate ( dot{δ }_{{s}} ) (ii) ` κ' with time to attain steady-state deflection rate, and (iii) initial creep deflection rate with steady-state deflection rate implied that transient SPC deformation obeyed first-order reaction rate theory. The rate of exhaustion of transient creep ( r') values that were determined from uniaxial creep tests were correlated with those obtained from SPC tests. Master curves representing transient creep deformation in both SPC and uniaxial creep tests have been derived and their near coincidence brings unique equivalence between both the test techniques. The relationships between (i) rate of acceleration of tertiary creep ( φ) and steady-state deflection rate, (ii) ` φ' and time spent in tertiary stage, and (iii) final creep deflection rate and steady-state deflection rate revealed that first-order reaction rate theory governed SPC deformation throughout the tertiary region also. Interrelationship between the transient, secondary, and tertiary creep parameters indicated that the same mechanism prevailed throughout the SPC deformation.

  9. Creep properties of Pb-free solder joints

    SciTech Connect

    Song, H.G.; Morris Jr., J.W.; Hua, F.

    2002-04-01

    Describes the creep behavior of three Sn-rich solders that have become candidates for use in Pb-free solder joints: Sn-3.5Ag, Sn-3Ag-0.5Cu and Sn-0.7Cu. The three solders show the same general behavior when tested in thin joints between Cu and Ni/Au metallized pads at temperatures between 60 and 130 C. Their steady-state creep rates are separated into two regimes with different stress exponents(n). The low-stress exponents range from {approx}3-6, while the high-stress exponents are anomalously high (7-12). Strikingly, the high-stress exponent has a strong temperature dependence near room temperature, increasing significantly as the temperature drops from 95 to 60 C. The anomalous creep behavior of the solders appears to be due to the dominant Sn constituent. Joints of pure Sn have stress exponents, n, that change with stress and temperature almost exactly like those of the Sn-rich solder joints. Research on creep in bulk samples of pure Sn suggests that the anomalous temperature dependence of the stress exponent may show a change in the dominant mechanism of creep. Whatever its source, it has the consequence that conventional constitutive relations for steady-state creep must be used with caution in treating Sn-rich solder joints, and qualification tests that are intended to verify performance should be carefully designed.

  10. Buckling condensation in constrained growth

    NASA Astrophysics Data System (ADS)

    Dervaux, Julien; Ben Amar, Martine

    2011-03-01

    The multiple complexities inherent to living objects have motivated the search for abiotic substitutes, able to mimic some of their relevant physical properties. Hydrogels provide a highly monitorable counterpart and have thus found many applications in medicine and bioengineering. Recently, it has been recognized that their ability to swell could be used to unravel some of the universal physical processes at work during biological growth. However, it is yet unknown how the microscopic distinctions between swelling and biological growth affect macroscopic changes (shape, stresses) induced by volume variations. To answer this question, we focus on a clinically motivated example of growth. Some solid tumors such as melanoma or glioblastoma undergo a shape transition during their evolution. This bifurcation appears when growth is confined at the periphery of the tumor and is concomitant with the transition from the avascular to the vascular stage of the tumor evolution. To model this phenomenon, we consider in this paper the deformation of an elastic ring enclosing a core of different stiffness. When the volume of the outer ring increases, the system develops a periodic instability. We consider two possible descriptions of the volume variation process: either by imposing a homogeneous volumetric strain (biological growth) or through migration of solvent molecules inside a solid network (swelling). For thin rings, both theories are in qualitative agreement. When the interior is soft, we predict the emergence of a large wavelength buckling. Upon increasing the stiffness of the inner disc, the wavelength of the instability decreases until a condensation of the buckles occurs at the free boundary. This short wavelength pattern is independent of the stiffness of the disc and is only limited by the presence of surface tension. For thicker rings, two scenarios emerge. When a volumetric strain is prescribed, compressive stresses accumulate in the vicinity of the core and the

  11. Elevated temperature tensile and creep behavior of a SiC fiber-reinforced titanium metal matrix composite. Final Report, 22 Dec. 1994 M.S. Thesis, 7 May 1993

    NASA Technical Reports Server (NTRS)

    Thurston, Rita J.

    1995-01-01

    In this research program, the tensile properties and creep behavior in air of (0)(sub 4), (0/90)(sub s) and (90)(sub 4) SCS-9/Beta 21S composite layups with 0.24 volume fraction fiber were evaluated. Monotonic tensile tests at 23, 482, 650 and 815 C yielded the temperature dependence of the elastic modulus, proportional limit, ultimate tensile strength and total strain at failure. At 650 C, the UTS of the (0)(sub 4) and (0/90)(sub s) layups decreases by almost 50 percent from the room temperature values, indicating that operating temperatures should be less than 650 C to take advantage of the specific tensile properties of these composites.

  12. Proton irradiation creep of FM steel T91

    NASA Astrophysics Data System (ADS)

    Xu, Cheng; Was, Gary S.

    2015-04-01

    Ferritic-martensitic (FM) steel T91 was subjected to irradiation with 3 MeV protons while under load at stresses of 100-200 MPa, temperatures between 400 °C and 500 °C, and dose rates between 1.4 × 10-6 dpa/s and 5 × 10-6 dpa/s to a total dose of less than 1 dpa. Creep behavior was analyzed for parametric dependencies. The temperature dependence was found to be negligible between 400 °C and 500 °C, and the dose rate dependence was observed to be linear. Creep rate was proportional to stress at low stress values and varied with stress to the power 14 above 160 MPa. The large stress exponent of the proton irradiation creep experiments under high stress suggested that dislocation glide was driving both thermal and irradiation creep. Microstructure observations of anisotropic dislocation loops also contributed to the total creep strain. After subtracting the power law creep and anisotropic dislocation loop contributions, the remaining creep strain was accounted for by dislocation climb enabled by stress induced preferential absorption (SIPA) and preferential dislocation glide (PAG).

  13. A creep apparatus to explore the quenching and ageing phenomena of PVC films

    NASA Technical Reports Server (NTRS)

    Lee, H. H. D.; Mcgarry, F. J.

    1991-01-01

    A creep apparatus has been constructed for an in situ determination of length and length change. Using this apparatus, the creep behavior of PVC thin films associated with quenching and aging was studied. The more severe the quench through the glass transition temperature, the greater is the instantaneous elastic deformation and the subsequent creep behavior. As aging proceeds, the quenched films gradually lose the ductility incurred by quenching. These results agree well with the well-known phenomena of physical aging. Thus, the changes reflecting molecular mobilities due to quenching and aging can be properly monitored by such a creep apparatus.

  14. Irradiation creep of the US Heat 832665 of V-4Cr-4Ti

    SciTech Connect

    Li, Meimei; Hoelzer, D. T.; Grossbeck, Martin L.; Rowcliffe, A. F.; Zinkle, Steven J.; Kurtz, Richard J.

    2009-04-30

    The paper presents irradiation creep data for V-4Cr-4Ti irradiated to 3.7 dpa at 425 and 600 _C in the HFIR-17J experiment. Creep deformation was characterized by measuring diametral changes of pressur-ized creep tubes before and after irradiation. It was found that the creep strain rate of the US Heat 832665 of V-4Cr-4Ti exhibited a linear relationship with stress up to _180 MPa at 425 _C with a creep coefficient of 2.50 _10_6 MPa_1 dpa_1. A linear relationship between creep rate and applied stress was observed below _110 MPa at 600 _C with a creep coefficient of 5.41 _10_6 MPa_1 dpa_1; non-linear creep behavior was observed above _110 MPa, and it may not be fully accounted by invoking thermal creep. The bilinear creep behavior observed in the same alloy irradiated in BR-10 was not observed in this study.

  15. Creep-fatigue response of structural ceramics: 1, Comparison of flexure, tension, and compression testing

    SciTech Connect

    Ferber, M.K.; Jenkins, M.G.; Nolan, T.A.; Yeckley, R.

    1990-12-31

    The stress sensitivities of the creep rates of commercially available Al{sub 2}O{sub 3} and Si{sub 3}N{sub 4} ceramics were measured at elevated temperatures using tension, compression, and flexure specimens. Pronounced differences in creep deformation behavior in compression and tension were observed for both ceramics. These differences were attributed to the generation of a creep-induced damage zone under tensile loading which accelerated the creep rate. The evolution of this damage zone was confirmed by (1) fractographic studies of failed tensile samples and (2) the observed stress-dependence of the creep failure strain. The creep rate-stress data generated fromn the flexure creep testing were found to be in fair agreement with results predicted from a creep deformation model. Differences between experimental and predicted creep behavior were attributed to the failure of the model to account for primary creep. This model was also capable of describing differences in the fatigue-life characteristics of a silicon nitride measured in flexure and tension.

  16. Creep-fatigue response of structural ceramics: 1, Comparison of flexure, tension, and compression testing

    SciTech Connect

    Ferber, M.K.; Jenkins, M.G.; Nolan, T.A. ); Yeckley, R. )

    1990-01-01

    The stress sensitivities of the creep rates of commercially available Al{sub 2}O{sub 3} and Si{sub 3}N{sub 4} ceramics were measured at elevated temperatures using tension, compression, and flexure specimens. Pronounced differences in creep deformation behavior in compression and tension were observed for both ceramics. These differences were attributed to the generation of a creep-induced damage zone under tensile loading which accelerated the creep rate. The evolution of this damage zone was confirmed by (1) fractographic studies of failed tensile samples and (2) the observed stress-dependence of the creep failure strain. The creep rate-stress data generated fromn the flexure creep testing were found to be in fair agreement with results predicted from a creep deformation model. Differences between experimental and predicted creep behavior were attributed to the failure of the model to account for primary creep. This model was also capable of describing differences in the fatigue-life characteristics of a silicon nitride measured in flexure and tension.

  17. Investigation of the rate-controlling mechanism(s) for high temperature creep and the relationship between creep and melting by use of high pressure as a variable

    SciTech Connect

    Not Available

    1991-01-01

    Using high pressure as a variable, the rate-controlling mechanism for high temperature creep and the relationship between creep and melting is investigated for silicon and nickel. An apparatus is used in which the samples are heated to melting point and subjected to 1 to 3 GigaPascal pressure. The stress behavior of the materials are then studied.

  18. Creep of Mg-PSZ at room temperature

    SciTech Connect

    Finlayson, T.R. . Dept. of Physics); Gross, A.K. . Dept. of Materials Engineering); Griffiths, J.R. . Div. of Manufacturing Technology); Kisi, E.H. . Faculty of Science and Technology)

    1994-03-01

    Transient [beta], or Andrade, creep occurs when magnesia-partially-stabilized zirconia is loaded in tension at room temperature. The equation relating the longitudinal or tensile creep strain [var epsilon][sub l][sup c] to the tensile stress, [sigma], and to the time, t, has been determined to be [var epsilon][sub l][sup c] = A[sigma][sup m]t[sup n] in which the constants A, m, and n depend on the phase content of the zirconia. Observations are reported of the tetragonal-to-monoclinic and tetragonal-to-orthorhombic phase transformations which occur during creep: there is also a progressive development of microcracking. It is shown that a combination of these phenomena can account for the observed creep behavior.

  19. Creep-fatigue analysis by strain-range partitioning.

    NASA Technical Reports Server (NTRS)

    Manson, S. S.; Halford, G. R.; Hirschberg, M. H.

    1971-01-01

    The framework of a new method is outlined for treating creep-fatigue behavior of metals. Inelastic strain-ranges are partitioned into the components of (1) completely reversed plasticity, (2) tensile plasticity reversed by compressive creep, or tensile creep reversed by compressive plasticity, and (3) completely reversed creep. Each of these components is shown to be related to cyclic life by a Manson-Coffin type power-law equation. A linear life fraction rule is used to combine the damaging effects of the individual components enabling the prediction of life. Test results are presented for a 2.25 Cr-1 Mo steel as well as limited information for a Type 316 stainless steel.

  20. Short-wavelength buckling and shear failures for compression-loaded composite laminates. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Shuart, M. J.

    1985-01-01

    The short-wavelength buckling (or the microbuckling) and the interlaminar and inplane shear failures of multi-directional composite laminates loaded in uniaxial compression are investigated. A laminate model is presented that idealizes each lamina. The fibers in the lamina are modeled as a plate, and the matrix in the lamina is modeled as an elastic foundation. The out-of-plane w displacement for each plate is expressed as a trigonometric series in the half-wavelength of the mode shape for laminate short-wavelength buckling. Nonlinear strain-displacement relations are used. The model is applied to symmetric laminates having linear material behavior. The laminates are loaded in uniform end shortening and are simply supported. A linear analysis is used to determine the laminate stress, strain, and mode shape when short-wavelength buckling occurs. The equations for the laminate compressive stress at short-wavelength buckling are dominated by matrix contributions.

  1. Column buckling of doubly parallel slender nanowires carrying electric current acted upon by a magnetic field

    NASA Astrophysics Data System (ADS)

    Kiani, Keivan

    2016-08-01

    Axial buckling of current-carrying double-nanowire-systems immersed in a longitudinal magnetic field is aimed to be explored. Each nanowire is affected by the magnetic forces resulted from the externally exerted magnetic field plus the magnetic field resulted from the passage of electric current through the adjacent nanowire. To study the problem, these forces are appropriately evaluated in terms of transverse displacements. Subsequently, the governing equations of the nanosystem are constructed using Euler-Bernoulli beam theory in conjunction with the surface elasticity theory of Gurtin and Murdoch. Using a meshless technique and assumed mode method, the critical compressive buckling load of the nanosystem is determined. In a special case, the obtained results by these two numerical methods are successfully checked. The roles of the slenderness ratio, electric current, magnetic field strength, and interwire distance on the axial buckling load and stability behavior of the nanosystem are displayed and discussed in some detail.

  2. Prediction and verification of creep behavior in metallic materials and components for the space shuttle thermal protection system. Volume 3, phase 3: Full size heat shield data correlation and design criteria. [reentry

    NASA Technical Reports Server (NTRS)

    Cramer, B. A.; Davis, J. W.

    1975-01-01

    Analysis methods for predicting cyclic creep deflection in stiffened metal panel structures, were applied to full size panels. Results were compared with measured deflections from cyclic tests of thin gage L605, Rene' 41, and TDNiCr full size corrugation stiffened panels. A design criteria was then formulated for metallic thermal protection panels subjected to creep. A computer program was developed to calculate creep deflections.

  3. Tissue morphogenesis: a surface buckling mechanism.

    PubMed

    Volokh, Konstantin Y

    2006-01-01

    Surface patterns can emerge during growth of anisotropic tissues because of surface buckling. This morphogenetic scenario is examined in the present paper based on a simple phenomenological theory of tissue growth. In particular, we show that constrained growth can lead to tissue compression, which in turn may result in surface buckling of the tissue. The latter means the appearance of wavy patterns on the surface. These patterns decay away from the surface. It is interesting that the critical magnitude of the parameter of mass supply, which corresponds to surface buckling, is independent of the pattern wavelength and various patterns can generally be generated in growth. Results of theoretical analysis show that the surface buckling scenario is realistic if the growing tissue matches the following two conditions. First, compression should appear during tissue growth. Second, the tissue should exhibit strong anisotropy. The former condition does not necessarily mean geometric constraints: inhomogeneous growth or material inhomogeneity and anisotropy can lead to the appearance of compressive stresses. The latter condition is typical of some tissues with fiber reinforcement in planes parallel to the surface. In the latter case, the tissue material is much softer in the out-of-plane direction than in plane. The creation of patterns by restraining tissue growth and forcing the surface to buckle represents a challenging experimental problem.

  4. A Biomechanical Model of Artery Buckling

    PubMed Central

    Han, Hai-Chao

    2010-01-01

    The stability of arteries under blood pressure load is essential to the maintenance of normal arterial function and the loss of stability can lead to tortuosity and kinking that are associated with significant clinical complications. However, mechanical analysis of arterial bent buckling is lacking. To address this issue, this paper presents a biomechanical model of arterial buckling. Using a linear elastic cylindrical arterial model, the mechanical equations for arterial buckling were developed and the critical buckling pressure was found to be a function of the wall stiffness (Young’s modulus), arterial radius, length, wall thickness, and the axial strain. Both the model equations and experimental results demonstrated that the critical pressure is related to the axial strain. Arteries may buckle and become tortuous due to reduced (sub-physiological) axial strain, hypertensive pressure, and a weakened wall. These results are in accordance with, and provide a possible explanation to the clinical observations that these changes are the risk factors for arterial tortuosity and kinking. The current model is also applicable to veins and ureters. PMID:17689541

  5. Buckled diamond-like carbon nanomechanical resonators

    NASA Astrophysics Data System (ADS)

    Tomi, Matti; Isacsson, Andreas; Oksanen, Mika; Lyashenko, Dmitry; Kaikkonen, Jukka-Pekka; Tervakangas, Sanna; Kolehmainen, Jukka; Hakonen, Pertti J.

    2015-08-01

    We have developed capacitively-transduced nanomechanical resonators using sp2-rich diamond-like carbon (DLC) thin films as conducting membranes. The electrically conducting DLC films were grown by physical vapor deposition at a temperature of 500 °C. Characterizing the resonant response, we find a larger than expected frequency tuning that we attribute to the membrane being buckled upwards, away from the bottom electrode. The possibility of using buckled resonators to increase frequency tuning can be of advantage in rf applications such as tunable GHz filters and voltage-controlled oscillators.We have developed capacitively-transduced nanomechanical resonators using sp2-rich diamond-like carbon (DLC) thin films as conducting membranes. The electrically conducting DLC films were grown by physical vapor deposition at a temperature of 500 °C. Characterizing the resonant response, we find a larger than expected frequency tuning that we attribute to the membrane being buckled upwards, away from the bottom electrode. The possibility of using buckled resonators to increase frequency tuning can be of advantage in rf applications such as tunable GHz filters and voltage-controlled oscillators. Electronic supplementary information (ESI) available: Detailed transmission measurements, discussion about mechanical contacts and surface roughness, derivation of the equations describing the eigenspectrum of a buckled beam under electrostatic load. See DOI: 10.1039/c5nr02820e

  6. Active control of buckling of flexible beams

    NASA Technical Reports Server (NTRS)

    Baz, A.; Tampe, L.

    1989-01-01

    The feasibility of using the rapidly growing technology of the shape memory alloys actuators in actively controlling the buckling of large flexible structures is investigated. The need for such buckling control systems is becoming inevitable as the design trends of large space structures have resulted in the use of structural members that are long, slender, and very flexible. In addition, as these truss members are subjected mainly to longitudinal loading they become susceptible to structural instabilities due to buckling. Proper control of such instabilities is essential to the effective performance of the structures as stable platforms for communication and observation. Mathematical models are presented that simulate the dynamic characteristics of the shape memory actuator, the compressive structural members, and the associated active control system. A closed-loop computer-controlled system is designed, based on the developed mathematical models, and implemented to control the buckling of simple beams. The performance of the computer-controlled system is evaluated experimentally and compared with the theoretical predictions to validate the developed models. The obtained results emphasize the importance of buckling control and suggest the potential of the shape memory actuators as attractive means for controlling structural deformation in a simple and reliable way.

  7. Creep and fracture of dispersion-strengthened materials

    NASA Technical Reports Server (NTRS)

    Raj, Sai V.

    1991-01-01

    The creep and fracture of dispersion strengthened materials is reviewed. A compilation of creep data on several alloys showed that the reported values of the stress exponent for creep varied between 3.5 and 100. The activation energy for creep exceeded that for lattice self diffusion in the matrix in the case of some materials and a threshold stress behavior was generally reported in these instances. The threshold stress is shown to be dependent on the interparticle spacing and it is significantly affected by the initial microstructure. The effect of particle size and the nature of the dispersoid on the threshold stress is not well understood at the present time. In general, most studies indicate that the microstructure after creep is similar to that before testing and very few dislocations are usually observed. It is shown that the stress acting on a dispersoid due to a rapidly moving dislocation can exceed the particle yield strength of the G sub p/1000, where G sub p is the shear modulus of the dispersoid. The case when the particle deforms is examined and it is suggested that the dislocation creep threshold stress of the alloy is equal to the yield strength of the dispersoid under these conditions. These results indicate that the possibility that the dispersoid creep threshold stress is determined by either the particle yield strength or the stress required to detach a dislocation from the dispersoid matrix interface. The conditions under which the threshold stress is influenced by one or the other mechanism are discussed and it is shown that the particle yield strength is important until the extent of dislocation core relaxation at the dispersoid matrix interface exceeds about 25 pct. depending on the nature of the particle matrix combination. Finally, the effect of grain boundaries and grain morphology on the creep and fracture behavior of dispersoid strengthened alloys is examined.

  8. Influence of cold work level on the irradiation creep and creep rupture of titanium-modified austenitic stainless steels

    SciTech Connect

    Garner, F.A.; Hamilton, M.L. ); Eiholzer, C.R. ); Toloczko, M.B. ); Kumar, A.S. )

    1992-06-01

    A titanium-modified austenitic type stainless steel was tested at three cold work levels to determine its creep and creep rupture properties under both thermal aging and neutron irradiation conditions. Both the thermal and irradiation creep behavior exhibit a complex non-monotonic relationship with cold work level that reflects the competition between a number of stress-sensitive and temperature-dependent microstructural processes. Increasing the degree of cold work to 30% form the conventional 20% level was detrimental to its performance, especially for applications above 550{degrees}C. The 20% cold work level is preferable to the 10% level, in terms of both in- reactor creep rapture response and initial strength.

  9. Irradiation creep and creep rupture of titanium-modified austenitic stainless steels and their dependence on cold work level

    SciTech Connect

    Garner, F.A.; Hamilton, M.L.; Eiholzer, C.R.; Toloczko, M.B.; Kumar, A.S.

    1991-11-01

    A titanium-modified austenitic type stainless steel was tested at three cold work levels to determine its creep and creep rupture properties under both thermal aging and neutron irradiation conditions. Both the thermal and irradiation creep behavior exhibit a complex non-monotonic relationship with cold work level that reflects the competition between a number of stress-sensitive and temperature-dependent microstructural processes. Increasing the degree of cold work to 30% from the conventional 20% level was detrimental to its performance, especially for applications above 550{degrees}c. The 20% cold work level is preferable to the 10% level, in terms of both in-reactor creep rupture response and initial strength.

  10. Creep, compressibility differences emerging in geothermal studies

    SciTech Connect

    Not Available

    1983-11-01

    This article discusses geopressured formations situated at depths of 12,000 to 15,000 feet and below. The trapped formations, in which enormous pressure and heat have built up, consist mainly of sandstones containing salty water and dissolved methane gas. Studies of geopressured rocks have revealed nonlinear variations in compressibility, creep, permeability, resistivity, and other factors related to flow rates and reservoir characterization. Compressibility and creep are tested by placing salt water and a sample of sandstone in a pressure vessel that simulates geopressured conditions. Rock compaction studies are being conducted at elevated temperatures (385/sup 0/F) in order to determine how compressibility and other rock behavior are affected by geopressured temperature. It is suggested that the geopressuredgeothermal formations that lie along the curve of the US Gulf Coast could provide a new source of energy.

  11. Euler buckling of geothermal well casing

    SciTech Connect

    Rechard, R.P.; Schuler, K.W.

    1983-02-01

    Geothermal well operators have expressed concern over the vulnerability of unsupported casing to buckling from thermal elongation. Preliminary numerical and theoretical calculations are presented, which indicate the buckling phenomenon should not be serious in N-80 casing if the string is tension preloaded. Buckling would be detrimental for K-55 casing. The effect of wall contact was found to be beneficial for closely confined pipe strings and of no detriment when hole gaps are large. The weakness of API screw joints in bending appears to be the structural limitation. The analysis assumed stresses above yield constituted failure, that thermal expansion was strain controlled, and that the casing was continuous. Excessive internal pressure instability was ignored. The temperature variation considered was between cementing conditions of 100 to 200/sup 0/F (40 to 95/sup 0/C) and shut-in conditions of 425 to 450/sup 0/F (220 to 230/sup 0/C).

  12. Buckling instability in amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Zhu, X. D.; Narumi, K.; Naramoto, H.

    2007-06-01

    In this paper, we report the buckling instability in amorphous carbon films on mirror-polished sapphire (0001) wafers deposited by ion beam assisted deposition at various growth temperatures. For the films deposited at 150 °C, many interesting stress relief patterns are found, which include networks, blisters, sinusoidal patterns with π-shape, and highly ordered sinusoidal waves on a large scale. Starting at irregular buckling in the centre, the latter propagate towards the outer buckling region. The maximum length of these ordered patterns reaches 396 µm with a height of ~500 nm and a wavelength of ~8.2 µm. However, the length decreases dramatically to 70 µm as the deposition temperature is increased to 550 °C. The delamination of the film appears instead of sinusoidal waves with a further increase of the deposition temperature. This experimental observation is correlated with the theoretic work of Crosby (1999 Phys. Rev. E 59 R2542).

  13. The Buckling of Curved Tension-field Girders

    NASA Technical Reports Server (NTRS)

    Limpert, G

    1938-01-01

    The present paper reports on experiments made to determine the buckling load under shear of circular curved tension-field webs. The buckling load of the webs may be expressed with reference to the buckling load of the stiffeners. It is found that within the explored range the buckling load is approximately twice as great as that of the identically stiffened flat wall of equal web depth.

  14. Nonlinear buckling analyses of a small-radius carbon nanotube

    NASA Astrophysics Data System (ADS)

    Liu, Ning; Wang, Yong-Gang; Li, Min; Jia, Jiao

    2014-04-01

    Carbon nanotube (CNT) was first discovered by Sumio Iijima. It has aroused extensive attentions of scholars from all over the world. Over the past two decades, we have acquired a lot of methods to synthesize carbon nanotubes and learn their many incredible mechanical properties such as experimental methods, theoretical analyses, and computer simulations. However, the studies of experiments need lots of financial, material, and labor resources. The calculations will become difficult and time-consuming, and the calculations may be even beyond the realm of possibility when the scale of simulations is large, as for computer simulations. Therefore, it is necessary for us to explore a reasonable continuum model, which can be applied into nano-scale. This paper attempts to develop a mathematical model of a small-radius carbon nanotube based on continuum theory. An Isotropic circular cross-section, Timoshenko beam model is used as a simplified mechanical model for the small-radius carbon nanotube. Theoretical part is mainly based on modified couple stress theory to obtain the numerical solutions of buckling deformation. Meanwhile, the buckling behavior of the small radius carbon nanotube is simulated by Molecular Dynamics method. By comparing with the numerical results based on modified couple stress theory, the dependence of the small-radius carbon nanotube mechanical behaviors on its elasticity constants, small-size effect, geometric nonlinearity, and shear effect is further studied, and an estimation of the small-scale parameter of a CNT (5, 5) is obtained.

  15. Flutter of buckled shape memory alloy reinforced laminates

    NASA Astrophysics Data System (ADS)

    Kuo, Shih-Yao; Shiau, Le-Chung; Lai, Chin-Hsin

    2012-03-01

    The effect of shape memory alloys (SMA) on the linear and nonlinear flutter behaviors of buckled cross-ply and angle-ply laminates was investigated in the frequency and time domains using the finite element method. In particular, this study takes the first move toward examining the effect of varying the SMA fiber spacing. Von Karman large deformation assumptions and quasi-steady aerodynamic theory were employed. The flutter boundary, stability boundary, time history response, and phase plane plots of SMA reinforced cross-ply and angle-ply laminates are presented. The numerical results show that increase in the SMA fiber volume fraction and prestrain may generate more recovery stress, and increase the stiffness of the SMA reinforced laminates. Therefore, the flutter boundary and critical load of the plate may be increased significantly. All five types of panel behavior, namely flat, buckled, limit-cycle, periodic, and chaotic motion, are clearly displayed and successively identified. This study sheds light on improving the flutter boundary efficiently by increasing the SMA fiber volume fraction to reinforce the center of the plate.

  16. Nonlinear buckling analyses of a small-radius carbon nanotube

    SciTech Connect

    Liu, Ning Li, Min; Jia, Jiao; Wang, Yong-Gang

    2014-04-21

    Carbon nanotube (CNT) was first discovered by Sumio Iijima. It has aroused extensive attentions of scholars from all over the world. Over the past two decades, we have acquired a lot of methods to synthesize carbon nanotubes and learn their many incredible mechanical properties such as experimental methods, theoretical analyses, and computer simulations. However, the studies of experiments need lots of financial, material, and labor resources. The calculations will become difficult and time-consuming, and the calculations may be even beyond the realm of possibility when the scale of simulations is large, as for computer simulations. Therefore, it is necessary for us to explore a reasonable continuum model, which can be applied into nano-scale. This paper attempts to develop a mathematical model of a small-radius carbon nanotube based on continuum theory. An Isotropic circular cross-section, Timoshenko beam model is used as a simplified mechanical model for the small-radius carbon nanotube. Theoretical part is mainly based on modified couple stress theory to obtain the numerical solutions of buckling deformation. Meanwhile, the buckling behavior of the small radius carbon nanotube is simulated by Molecular Dynamics method. By comparing with the numerical results based on modified couple stress theory, the dependence of the small-radius carbon nanotube mechanical behaviors on its elasticity constants, small-size effect, geometric nonlinearity, and shear effect is further studied, and an estimation of the small-scale parameter of a CNT (5, 5) is obtained.

  17. Handbook of Structural Stability Part I: Buckling of Flat Plates

    NASA Technical Reports Server (NTRS)

    Gerard, George; Becker, Herbert

    1957-01-01

    The various factors governing buckling of flat plates are critically reviewed and the results are summarized in a comprehensive series of charts and tables. Numerical values are presented for buckling coefficients of flat plates with various boundary conditions and applied loadings. The effects of plasticity are incorporated in non dimensional buckling charts utilizing the three-parameter description of stress-strain curves.

  18. Repeated buckling of composite shear panels

    NASA Technical Reports Server (NTRS)

    Singer, Josef; Weller, Tanchum

    1990-01-01

    Failures in service of aerospace structures and research at the Technion Aircraft Structures Laboratory have revealed that repeatedly buckled stiffened shear panels might be susceptible to premature fatigue failures. Extensive experimental and analytical studies have been performed at Technion on repeated buckling, far in excess of initial buckling, for both metal and composite shear panels with focus on the influence of the surrounding structure. The core of the experimental investigation consisted of repeated buckling and postbuckling tests on Wagner beams in a three-point loading system under realistic test conditions. The effects of varying sizes of stiffeners, of the magnitude of initial buckling loads, of the panel aspect ratio and of the cyclic shearing force, V sub cyc, were studied. The cyclic to critical shear buckling ratios, (V sub cyc/V sub cr) were on the high side, as needed for efficient panel design, yet all within possible flight envelopes. The experiments were supplemented by analytical and numerical analyses. For the metal shear panels the test and numerical results were synthesized into prediction formulas, which relate the life of the metal shear panels to two cyclic load parameters. The composite shear panels studied were hybrid beams with graphite/epoxy webs bonded to aluminum alloy frames. The test results demonstrated that composite panels were less fatigue sensitive than comparable metal ones, and that repeated buckling, even when causing extensive damage, did not reduce the residual strength by more than 20 percent. All the composite panels sustained the specified fatigue life of 250,000 cycles. The effect of local unstiffened holes on the durability of repeatedly buckled shear panels was studied for one series of the metal panels. Tests on 2024 T3 aluminum panels with relatively small unstiffened holes in the center of the panels demonstrated premature fatigue failure, compared to panels without holes. Preliminary tests on two graphite

  19. Creep-Fatigue Interaction Testing

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.

    2001-01-01

    Fatigue fives in metals are nominally time independent below 0.5 T(sub Melt). At higher temperatures, fatigue lives are altered due to time-dependent, thermally activated creep. Conversely, creep rates are altered by super. imposed fatigue loading. Creep and fatigue generally interact synergistically to reduce material lifetime. Their interaction, therefore, is of importance to structural durability of high-temperature structures such as nuclear reactors, reusable rocket engines, gas turbine engines, terrestrial steam turbines, pressure vessel and piping components, casting dies, molds for plastics, and pollution control devices. Safety and lifecycle costs force designers to quantify these interactions. Analytical and experimental approaches to creep-fatigue began in the era following World War II. In this article experimental and life prediction approaches are reviewed for assessing creep-fatigue interactions of metallic materials. Mechanistic models are also discussed briefly.

  20. A constitutive model for representing coupled creep, fracture, and healing in rock salt

    SciTech Connect

    Chan, K.S.; Bodner, S.R.; Munson, D.E.; Fossum, A.F.

    1996-03-01

    The development of a constitutive model for representing inelastic flow due to coupled creep, damage, and healing in rock salt is present in this paper. This model, referred to as Multimechanism Deformation Coupled Fracture model, has been formulated by considering individual mechanisms that include dislocation creep, shear damage, tensile damage, and damage healing. Applications of the model to representing the inelastic flow and fracture behavior of WIPP salt subjected to creep, quasi-static loading, and damage healing conditions are illustrated with comparisons of model calculations against experimental creep curves, stress-strain curves, strain recovery curves, time-to-rupture data, and fracture mechanism maps.

  1. Review of data on irradiation creep of monolithic SiC

    SciTech Connect

    Garner, F.A.; Youngblood, G.E.; Hamilton, M.L.

    1996-04-01

    An effort is now underway to design an irradiation creep experiment involving SiC composites to SiC fibers. In order to successfully design such an experiment, it is necessary to review and assess the available data for monolithic SiC to establish the possible bounds of creep behavior for the composite. The data available show that monolithic SiC will indeed creep at a higher rate under irradiation compared to that of thermal creep, and surprisingly, it will do so in a temperature-dependant manner that is typical of metals.

  2. Investigation of creep by use of closed loop servo-hydraulic test system

    NASA Technical Reports Server (NTRS)

    Wu, H. C.; Yao, J. C.

    1981-01-01

    Creep tests were conducted by means of a closed loop servo-controlled materials test system. These tests are different from the conventional creep tests in that the strain history prior to creep may be carefully monitored. Tests were performed for aluminum alloy 6061-0 at 150 C and monitored by a PDP 11/04 minicomputer at a preset constant plastic-strain rate prehistory. The results show that the plastic-strain rate prior to creep plays a significant role in creep behavior. The endochronic theory of viscoplasticity was applied to describe the observed creep curves. The concepts of intrinsic time and strain rate sensitivity function are employed and modified according to the present observation.

  3. Cumulative creep fatigue damage in 316 stainless steel

    NASA Technical Reports Server (NTRS)

    Mcgaw, Michael A.

    1989-01-01

    The cumulative creep-fatigue damage behavior of 316 stainless steel at 1500 F was experimentally established for the two-level loading cases of fatigue followed by fatigue, creep fatigue followed by fatigue, and fatigue followed by creep fatigue. The two-level loadings were conducted such that the lower life (high strain) cycling was applied first for a controlled number of cycles and the higher life (low strain) cycling was conducted as the second level to failure. The target life levels in this study were 100 cycles to failure for both the fatigue and creep-fatigue lowlife loading, 5000 cycles to failure for the higher life fatigue loading and 10,000 cycles to failure for the higher life creep-fatigue loading. The failed specimens are being examined both fractographically and metallographically to ascertain the nature of the damaging mechanisms that produced failure. Models of creep-fatigue damage accumulation are being evaluated and knowledge of the various damaging mechanisms is necessary to ensure that predictive capability is instilled in the final failure model.

  4. The activation energy for creep of columbium /niobium/.

    NASA Technical Reports Server (NTRS)

    Klein, M. J.; Gulden, M. E.

    1973-01-01

    The activation energy for creep of nominally pure columbium (niobium) was determined in the temperature range from 0.4 to 0.75 T sub M by measuring strain rate changes induced by temperature shifts at constant stress. A peak in the activation energy vs temperature curve was found with a maximum value of 160 kcal/mole. A pretest heat treatment of 3000 F for 30 min resulted in even higher values of activation energy (greater than 600 kcal/mole) in this temperature range. The activation energy for the heat-treated columbium (Nb) could not be determined near 0.5 T sub M because of unusual creep curves involving negligible steady-state creep rates and failure at less than 5% creep strain. It is suggested that the anomalous activation energy values and the unusual creep behavior in this temperature range are caused by dynamic strain aging involving substitutional atom impurities and that this type of strain aging may be in part responsible for the scatter in previously reported values of activation energy for creep of columbium (Nb) near 0.5 T sub M.

  5. Creep strength of niobium alloys, Nb-1%Zr and PWC-11

    SciTech Connect

    Titran, R.H.

    1990-01-01

    A study is being conducted at NASA Lewis Research Center to determine the feasibility of using a carbide particle strengthened Nb-1% Zr base alloy to meet the anticipated temperature and creep resistance requirements of proposed near term space power systems. In order to provide information to aid in the determination of the suitability of the PWC-11 alloy as an alternative to Nb-1% Zr in space power systems this study investigated (1) the long-time high-vacuum creep behavior of the PWC-11 material and the Nb-1% Zr alloy, (2) the effect of prior stress-free thermal aging on this creep behavior, (3) the effect of electron beam (EB) welding on this creep behavior, and (4) the stability of creep strengthening carbide particles. 14 refs., 5 figs., 2 tabs.

  6. Investigation of the effect of aggregates' morphology on concrete creep properties by numerical simulations

    SciTech Connect

    Lavergne, F.; Sab, K.; Sanahuja, J.; Bornert, M.; Toulemonde, C.

    2015-05-15

    Prestress losses due to creep of concrete is a matter of interest for long-term operations of nuclear power plants containment buildings. Experimental studies by Granger (1995) have shown that concretes with similar formulations have different creep behaviors. The aim of this paper is to numerically investigate the effect of size distribution and shape of elastic inclusions on the long-term creep of concrete. Several microstructures with prescribed size distribution and spherical or polyhedral shape of inclusions are generated. By using the 3D numerical homogenization procedure for viscoelastic microstructures proposed by Šmilauer and Bažant (2010), it is shown that the size distribution and shape of inclusions have no measurable influence on the overall creep behavior. Moreover, a mean-field estimate provides close predictions. An Interfacial Transition Zone was introduced according to the model of Nadeau (2003). It is shown that this feature of concrete's microstructure can explain differences between creep behaviors.

  7. Creep strength of niobium alloys, Nb-1%Zr and PWC-11

    NASA Technical Reports Server (NTRS)

    Titran, Robert H.

    1989-01-01

    A study is being conducted at NASA Lewis Research Center to determine the feasibility of using a carbide particle strengthened Nb-1 percent Zr base alloy to meet the anticipated temperature and creep resistance requirements of proposed near term space power systems. In order to provide information to aid in the determination of the suitability of the PWC-11 alloy as an alternative to Nb-1 percent Zr in space power systems this study investigated: (1) the long-time high-vacuum creep behavior of the PWC-11 material and the Nb-1 percent Zr alloy, (2) the effect of prior stress-free thermal aging on this creep behavior, (3) the effect of electron beam (EB) welding on this creep behavior, and (4) the stability of creep strengthening carbide particles.

  8. Variations in creep rate along the Hayward Fault, California, interpreted as changes in depth of creep

    USGS Publications Warehouse

    Simpson, R.W.; Lienkaemper, J.J.; Galehouse, J.S.

    2001-01-01

    Variations ill surface creep rate along the Hayward fault are modeled as changes in locking depth using 3D boundary elements. Model creep is driven by screw dislocations at 12 km depth under the Hayward and other regional faults. Inferred depth to locking varies along strike from 4-12 km. (12 km implies no locking.) Our models require locked patches under the central Hayward fault, consistent with a M6.8 earthquake in 1868, but the geometry and extent of locking under the north and south ends depend critically on assumptions regarding continuity and creep behavior of the fault at its ends. For the northern onshore part of the fault, our models contain 1.4-1.7 times more stored moment than the model of Bu??rgmann et al. [2000]; 45-57% of this stored moment resides in creeping areas. It is important for seismic hazard estimation to know how much of this moment is released coseismically or as aseismic afterslip.

  9. Correlation of creep rate with microstructural changes during high temperature creep

    NASA Technical Reports Server (NTRS)

    Young, C. T.; Sommers, B. R.; Lytton, J. L.

    1977-01-01

    Creep tests were conducted on Haynes 188 cobalt-base alloy and alpha titanium. The tests on Haynes 188 were conducted at 1600 F and 1800 F for stresses from 3 to 20 ksi, and the as-received, mill-annealed results were compared to specimens given 5%, 10%, and 15% room temperature prestrains and then annealed one hour at 1800 F. The tests on alpha titanium were performed at 7,250 and 10,000 psi at 500 C. One creep test was done at 527 C and 10,000 psi to provide information on kinetics. Results for annealed titanium were compared to specimens given 10% and 20% room temperature prestrains followed by 100 hours recovery at 550 C. Electron microscopy was used to relate dislocation and precipitate structure to the creep behavior of the two materials. The results on Haynes 188 alloy reveal that the time to reach 0.5% creep strain at 1600 F increases with increasing prestrain for exposure times less than 1,000 hours, the increase at 15% prestrain being more than a factor of ten.

  10. Further Developments in Modeling Creep Effects Within Structural SiC/SiC Components

    NASA Technical Reports Server (NTRS)

    Lang, Jerry; DiCarlo, James A.

    2008-01-01

    Anticipating the implementation of advanced SiC/SiC composites into turbine section components of future aero-propulsion engines, the primary objective of this on-going study is to develop physics-based analytical and finite-element modeling tools to predict the effects of constituent creep on SiC/SiC component service life. A second objective is to understand how to possibly manipulate constituent materials and processes in order to minimize these effects. Focusing on SiC/SiC components experiencing through-thickness stress gradients (e.g., airfoil leading edge), prior NASA creep modeling studies showed that detrimental residual stress effects can develop globally within the component walls which can increase the risk of matrix cracking. These studies assumed that the SiC/SiC composites behaved as isotropic viscoelastic continuum materials with creep behavior that was linear and symmetric with stress and that the creep parameters could be obtained from creep data as experimentally measured in-plane in the fiber direction of advanced thin-walled 2D SiC/SiC panels. The present study expands on those prior efforts by including constituent behavior with non-linear stress dependencies in order to predict such key creep-related SiC/SiC properties as time-dependent matrix stress, constituent creep and content effects on composite creep rates and rupture times, and stresses on fiber and matrix during and after creep.

  11. Rationalization of Creep Data of Creep-Resistant Steels on the Basis of the New Power Law Creep Equation

    NASA Astrophysics Data System (ADS)

    Wang, Q.; Yang, M.; Song, X. L.; Jia, J.; Xiang, Z. D.

    2016-07-01

    The conventional power law creep equation (Norton equation) relating the minimum creep rate to creep stress and temperature cannot be used to predict the long-term creep strengths of creep-resistant steels if its parameters are determined only from short-term measurements. This is because the stress exponent and activation energy of creep determined on the basis of this equation depend on creep temperature and stress and these dependences cannot be predicted using this equation. In this work, it is shown that these problems associated with the conventional power law creep equation can be resolved if the new power law equation is used to rationalize the creep data. The new power law creep equation takes a form similar to the conventional power law creep equation but has a radically different capability not only in rationalizing creep data but also in predicting the long-term creep strengths from short-term test data. These capabilities of the new power law creep equation are demonstrated using the tensile strength and creep test data measured for both pipe and tube grades of the creep-resistant steel 9Cr-1.8W-0.5Mo-V-Nb-B (P92 and T92).

  12. Generation of long time creep data on refractory alloys at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Sheffler, K. D.; Ebert, R. R.

    1973-01-01

    Four separate studies of various aspects of the vacuum creep behavior of two tantalum alloys (T-111 and ASTAR 811C) and of pure CVD tungsten are reported. The first part of the program involved a study of the influence of high temperature pre-exposure to vacuum or to liquid lithium on the subsequent creep behavior T-111 alloy. Results of this study revealed significant effects of pre-exposure on the 1% creep life of T-111, with life reductions of about 3 orders of magnitude being observed in extreme cases. The second part of this study involved an investigation of the creep behavior of T-111 under conditions of continuously increasing stress and decreasing temperature which simulated the conditions anticipated in radioisotope capsule service. Results of this study showed that such test conditions produced a creep curve having a very unusual shape, and led to the identification of a new creep design parameter for this type of service. The third area of investigation was a study of the influence of heat treatment on the microstructure and creep behavior of ASTAR 811C. The fourth part of the program was directed toward a preliminary characterization of the 1% creep life of CVD tungsten as obtained from two different sources.

  13. Buckling instability of self-assembled colloidal columns.

    PubMed

    Swan, James W; Vasquez, Paula A; Furst, Eric M

    2014-09-26

    Suspended, slender self-assembled domains of magnetically responsive colloids are observed to buckle in microgravity. Upon cessation of the magnetic field that drives their assembly, these columns expand axially and buckle laterally. This phenomenon resembles the buckling of long beams due to thermal expansion; however, linear stability analysis predicts that the colloidal columns are inherently susceptible to buckling because they are freely suspended in a Newtonian fluid. The dominant buckling wavelength increases linearly with column thickness and is quantitatively described using an elastohydrodynamic model and the suspension thermodynamic equation of state. PMID:25302919

  14. Buckling Instability of Self-Assembled Colloidal Columns

    NASA Astrophysics Data System (ADS)

    Swan, James W.; Vasquez, Paula A.; Furst, Eric M.

    2014-09-01

    Suspended, slender self-assembled domains of magnetically responsive colloids are observed to buckle in microgravity. Upon cessation of the magnetic field that drives their assembly, these columns expand axially and buckle laterally. This phenomenon resembles the buckling of long beams due to thermal expansion; however, linear stability analysis predicts that the colloidal columns are inherently susceptible to buckling because they are freely suspended in a Newtonian fluid. The dominant buckling wavelength increases linearly with column thickness and is quantitatively described using an elastohydrodynamic model and the suspension thermodynamic equation of state.

  15. Buckling modes of elastic thin films on elastic substrates

    NASA Astrophysics Data System (ADS)

    Mei, Haixia; Huang, Rui; Chung, Jun Young; Stafford, Christopher M.; Yu, Hong-Hui

    2007-04-01

    Two buckling modes have been observed in thin films: buckle delamination and wrinkling. This letter identifies the conditions for selecting the favored buckling modes for elastic films on elastic substrates. Transition from one buckling mode to another is predicted as the stiffness ratio between the substrate and the film or is predicted for variation of the stiffness ratio between the substrate and the film or variation of theinterfacial defect size. The theoretical results are demonstrated experimentally by observing the coexistence of both buckling modes and mode transition in one film-substrate system.

  16. Buckling analysis of spent fuel basket

    SciTech Connect

    Lee, A.S.; Bumpas, S.E.

    1995-05-01

    The basket for a spent fuel shipping cask is subjected to compressive stresses that may cause global instability of the basket assemblies or local buckling of the individual members. Adopting the common buckling design practice in which the stability capacity of the entire structure is based on the performance of the individual members of the assemblies, the typical spent fuel basket, which is composed of plates and tubular structural members, can be idealized as an assemblage of columns, beam-columns and plates. This report presents the flexural buckling formulas for five load cases that are common in the basket buckling analysis: column under axial loads, column under axial and bending loads, plate under uniaxial loads, plate under biaxial loadings, and plate under biaxial loads and lateral pressure. The acceptance criteria from the ASME Boiler and Pressure Vessel Code are used to determine the adequacy of the basket components. Special acceptance criteria are proposed to address the unique material characteristics of austenitic stainless steel, a material which is frequently used in the basket assemblies.

  17. Unilateral buckling of elastically restrained rectangular mild steel plates

    NASA Astrophysics Data System (ADS)

    Smith, S. T.; Bradford, M. A.; Oehlers, D. J.

    This paper considers the elastic unilateral buckling of rectangular mild steel plates that are restrained elastically and subjected to bending and axial actions. A variational formulation of the Ritz method using linear combinations of harmonic functions for the buckling deformations is used to establish an eigenproblem to determine the plate local buckling coefficients. The motivation for the study is the retrofit of reinforced concrete beams by gluing and then bolting steel plates to the sides of the beam. Such plates, when acting compositely with the concrete beam, are subjected to predominantly bending and axial actions which may cause unilateral local buckling. Whereas the bolts provide complete restraint against buckling at discrete points, the glue may also inhibit local buckling between these nodal points since it acts as a continuous elastic restraint. The influence of the glue stiffness, support conditions and plate proportions on the unilateral buckling of such plates are assessed.

  18. Lattice continuum and diffusional creep

    NASA Astrophysics Data System (ADS)

    Mesarovic, Sinisa Dj.

    2016-04-01

    Diffusional creep is characterized by growth/disappearance of lattice planes at the crystal boundaries that serve as sources/sinks of vacancies, and by diffusion of vacancies. The lattice continuum theory developed here represents a natural and intuitive framework for the analysis of diffusion in crystals and lattice growth/loss at the boundaries. The formulation includes the definition of the Lagrangian reference configuration for the newly created lattice, the transport theorem and the definition of the creep rate tensor for a polycrystal as a piecewise uniform, discontinuous field. The values associated with each crystalline grain are related to the normal diffusional flux at grain boundaries. The governing equations for Nabarro-Herring creep are derived with coupled diffusion and elasticity with compositional eigenstrain. Both, bulk diffusional dissipation and boundary dissipation accompanying vacancy nucleation and absorption, are considered, but the latter is found to be negligible. For periodic arrangements of grains, diffusion formally decouples from elasticity but at the cost of a complicated boundary condition. The equilibrium of deviatorically stressed polycrystals is impossible without inclusion of interface energies. The secondary creep rate estimates correspond to the standard Nabarro-Herring model, and the volumetric creep is small. The initial (primary) creep rate is estimated to be much larger than the secondary creep rate.

  19. Robust simulation of buckled structures using reduced order modeling

    NASA Astrophysics Data System (ADS)

    Wiebe, R.; Perez, R. A.; Spottswood, S. M.

    2016-09-01

    Lightweight metallic structures are a mainstay in aerospace engineering. For these structures, stability, rather than strength, is often the critical limit state in design. For example, buckling of panels and stiffeners may occur during emergency high-g maneuvers, while in supersonic and hypersonic aircraft, it may be induced by thermal stresses. The longstanding solution to such challenges was to increase the sizing of the structural members, which is counter to the ever present need to minimize weight for reasons of efficiency and performance. In this work we present some recent results in the area of reduced order modeling of post- buckled thin beams. A thorough parametric study of the response of a beam to changing harmonic loading parameters, which is useful in exposing complex phenomena and exercising numerical models, is presented. Two error metrics that use but require no time stepping of a (computationally expensive) truth model are also introduced. The error metrics are applied to several interesting forcing parameter cases identified from the parametric study and are shown to yield useful information about the quality of a candidate reduced order model. Parametric studies, especially when considering forcing and structural geometry parameters, coupled environments, and uncertainties would be computationally intractable with finite element models. The goal is to make rapid simulation of complex nonlinear dynamic behavior possible for distributed systems via fast and accurate reduced order models. This ability is crucial in allowing designers to rigorously probe the robustness of their designs to account for variations in loading, structural imperfections, and other uncertainties.

  20. Creep Burst Testing of a Woven Inflatable Module

    NASA Technical Reports Server (NTRS)

    Selig, Molly M.; Valle, Gerard D.; James, George H.; Oliveras, Ovidio M.; Jones, Thomas C.; Doggett, William R.

    2015-01-01

    A woven Vectran inflatable module 88 inches in diameter and 10 feet long was tested at the NASA Johnson Space Center until failure from creep. The module was pressurized pneumatically to an internal pressure of 145 psig, and was held at pressure until burst. The external environment remained at standard atmospheric temperature and pressure. The module burst occurred after 49 minutes at the target pressure. The test article pressure and temperature were monitored, and video footage of the burst was captured at 60 FPS. Photogrammetry was used to obtain strain measurements of some of the webbing. Accelerometers on the test article measured the dynamic response. This paper discusses the test article, test setup, predictions, observations, photogrammetry technique and strain results, structural dynamics methods and quick-look results, and a comparison of the module level creep behavior to the strap level creep behavior.

  1. Creep in electronic ceramics

    SciTech Connect

    Routbort, J. L.; Goretta, K. C.; Arellano-Lopez, A. R.

    2000-04-27

    High-temperature creep measurements combined with microstructural investigations can be used to elucidate deformation mechanisms that can be related to the diffusion kinetics and defect chemistry of the minority species. This paper will review the theoretical basis for this correlation and illustrate it with examples from some important electronic ceramics having a perovskite structure. Recent results on BaTiO{sub 3}, (La{sub 1{minus}x}Sr){sub 1{minus}y}MnO{sub 3+{delta}}, YBa{sub 2}Cu{sub 3}O{sub x}, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x}, (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} and Sr(Fe,Co){sub 1.5}O{sub x} will be presented.

  2. Microstructure Evolution of Alloy 625 Foil and Sheet During Creep at 750oC

    SciTech Connect

    Evans, Neal D; Maziasz, Philip J; Shingledecker, John P; Yamamoto, Yukinori

    2008-12-01

    Creep-rupture tests in air of foils and sheets of the nickel-based superalloy 625 at 750oC and 100 MPa have been conducted, and indicate the additional processing required to achieve foil form reduces creep life compared to thicker-section wrought product forms. Both scanning and transmission electron microscopy were employed to examine as-processed and creep-tested specimens to correlate observed microstructures and creep behavior. Prior to creep testing, the morphology consists of gamma phase with M6C precipitates. This morphology changes during creep to one consisting of orthorhombic delta phase extending across gamma grains, and grain boundaries dominated by the presence of rhombohedral mu phase, delta phase, and a diamond-cubic eta phase. Additionally, temperature ranges of equilibrium phase field stability were calculated using JMatPro. The phases predicted and their compositions generally agree with those observed within the superalloy after creep testing.

  3. Evolved Colloidosomes Undergoing Cell-like Autonomous Shape Oscillations with Buckling.

    PubMed

    Tamate, Ryota; Ueki, Takeshi; Yoshida, Ryo

    2016-04-18

    In living systems, there are many autonomous and oscillatory phenomena to sustain life, such as heart contractions and breathing. At the microscopic level, oscillatory shape deformations of cells are often observed in dynamic behaviors during cell migration and morphogenesis. In many cases, oscillatory behaviors of cells are not simplistic but complex with diverse deformations. So far, we have succeeded in developing self-oscillating polymers and gels, but complex oscillatory behaviors mimicking those of living cells have yet to be reproduced. Herein, we report a cell-like hollow sphere composed of self-oscillating microgels, that is, a colloidosome, that exhibits drastic shape oscillation in addition to swelling/deswelling oscillations driven by an oscillatory reaction. The resulting oscillatory profile waveform becomes markedly more complex than a conventional one. Especially for larger colloidosomes, multiple buckling and moving buckling points are observed to be analogous to cells. PMID:26960167

  4. Generation of long time creep data on refractory alloys at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Sheffler, K. D.

    1970-01-01

    Creep tests were conducted on two tantalum alloys (ASTAR 811C and T-111 alloy), on a molybdenum alloy (TZM), and on CVD tungsten. The T-111 alloy 1% creep life data have been subjected to Manson's station function analysis, and the progress on this analysis is described. In another test program, the behavior of T-111 alloy with continuously varying temperatures and stresses has been studied. The results indicated that the previously described analysis predicts the observed creep behavior with reasonable accuracy. In addition to the T-111 test program, conventional 1% creep life data have been obtained for ASTAR 811C alloy. Previously observed effects of heat treatment on the creep strength of this material have been discussed and a model involving carbide strengthening primarily at the grain boundaries, rather than in a classical dispersion hardening mechanism, has been proposed to explain the observed results.

  5. Solid-phase creep during the expression of palm-oil filter cakes

    SciTech Connect

    Kamst, G.F.; Bruinsma, O.S.L.; Graauw, J. de

    1997-03-01

    For an adequate model of the processes of compressible cake filtration and mechanical expression, permeability and compressibility data are required. Experimental and modeling results of the creep behavior of palm-oil filter cakes at constant and time-dependent pressures are presented. Creep curves of palm-oil cakes at constant pressures cannot be modeled with linear viscoelastic models. Modeling with a modified form of the empirical equation of Nutting gives satisfactory results. This modification does not lead to unrealistic values of the porosity at extreme conditions, contrary to the original form of the equation of Nutting. Creep curves at time-dependent pressures were modeled with two nonlinear viscoelastic models, which describe the time-dependent creep behavior as a function of the pressure history and creep curves at constant pressures. Modeling with the strain-hardening model provides the best porosity predictions.

  6. Creep of sound paths in consolidated granular material detected through coda wave interferometry.

    PubMed

    Espíndola, David; Galaz, Belfor; Melo, Francisco

    2016-07-01

    The time evolution of the contact force structure of a consolidated granular material subjected to a constant stress is monitored using the coda wave interferometry method. In addition, the nature of the aging and rejuvenation processes are investigated. These processes are interpreted in terms of affine and nonaffine structural path deformations. During the later stages of creep, the rearrangements of subgrains are so small that they only produce affine deformations in the contact paths, without any significant changes in the structural configuration. As a result, the strain path distribution follows the macroscopic strain. Conversely, in the presence of ultrasonic perturbations, the nonaffine grain buckling mechanism dominates, producing relatively drastic changes in the structural configuration accompanied by path deformations of the order of the grain size. This plastic mechanism induces material rejuvenation that is observed macroscopically as an ultrasonically accelerated creep. PMID:27575200

  7. Creep of sound paths in consolidated granular material detected through coda wave interferometry

    NASA Astrophysics Data System (ADS)

    Espíndola, David; Galaz, Belfor; Melo, Francisco

    2016-07-01

    The time evolution of the contact force structure of a consolidated granular material subjected to a constant stress is monitored using the coda wave interferometry method. In addition, the nature of the aging and rejuvenation processes are investigated. These processes are interpreted in terms of affine and nonaffine structural path deformations. During the later stages of creep, the rearrangements of subgrains are so small that they only produce affine deformations in the contact paths, without any significant changes in the structural configuration. As a result, the strain path distribution follows the macroscopic strain. Conversely, in the presence of ultrasonic perturbations, the nonaffine grain buckling mechanism dominates, producing relatively drastic changes in the structural configuration accompanied by path deformations of the order of the grain size. This plastic mechanism induces material rejuvenation that is observed macroscopically as an ultrasonically accelerated creep.

  8. Creep of sound paths in consolidated granular material detected through coda wave interferometry.

    PubMed

    Espíndola, David; Galaz, Belfor; Melo, Francisco

    2016-07-01

    The time evolution of the contact force structure of a consolidated granular material subjected to a constant stress is monitored using the coda wave interferometry method. In addition, the nature of the aging and rejuvenation processes are investigated. These processes are interpreted in terms of affine and nonaffine structural path deformations. During the later stages of creep, the rearrangements of subgrains are so small that they only produce affine deformations in the contact paths, without any significant changes in the structural configuration. As a result, the strain path distribution follows the macroscopic strain. Conversely, in the presence of ultrasonic perturbations, the nonaffine grain buckling mechanism dominates, producing relatively drastic changes in the structural configuration accompanied by path deformations of the order of the grain size. This plastic mechanism induces material rejuvenation that is observed macroscopically as an ultrasonically accelerated creep.

  9. Study of irradiation creep of vanadium alloys

    SciTech Connect

    Tsai, H.; Strain, R.V.; Smith, D.L.

    1997-08-01

    Thin-wall tubing was produced from the 832665 (500 kg) heat of V-4 wt.% Cr-4 wt.% Ti to study its irradiation creep behavior. The specimens, in the form of pressurized capsules, were irradiated in Advanced Test Reactor and High Flux Isotope Reactor experiments (ATR-A1 and HFIR RB-12J, respectively). The ATR-A1 irradiation has been completed and specimens from it will soon be available for postirradiation examination. The RB-12J irradiation is not yet complete.

  10. Phenomenology and control of buckling dynamics in multicomponent colloidal droplets

    NASA Astrophysics Data System (ADS)

    Pathak, Binita; Basu, Saptarshi

    2015-06-01

    Self-assembly of nano sized particles during natural drying causes agglomeration and shell formation at the surface of micron sized droplets. The shell undergoes sol-gel transition leading to buckling at the weakest point on the surface and produces different types of structures. Manipulation of the buckling rate with inclusion of surfactant (sodium dodecyl sulphate, SDS) and salt (anilinium hydrochloride, AHC) to the nano-sized particle dispersion (nanosilica) is reported here in an acoustically levitated single droplet. Buckling in levitated droplets is a cumulative, complicated function of acoustic streaming, chemistry, agglomeration rate, porosity, radius of curvature, and elastic energy of shell. We put forward our hypothesis on how buckling occurs and can be suppressed during natural drying of the droplets. Global precipitation of aggregates due to slow drying of surfactant-added droplets (no added salts) enhances the rigidity of the shell formed and hence reduces the buckling probability of the shell. On the contrary, adsorption of SDS aggregates on salt ions facilitates the buckling phenomenon with an addition of minute concentration of the aniline salt to the dispersion. Variation in the concentration of the added particles (SDS/AHC) also leads to starkly different morphologies and transient behaviour of buckling (buckling modes like paraboloid, ellipsoid, and buckling rates). Tuning of the buckling rate causes a transition in the final morphology from ring and bowl shapes to cocoon type of structure.

  11. Comprehensive Creep and Thermophysical Performance of Refractory Materials

    SciTech Connect

    Ferber, M.K.; Wereszczak, A.; Hemrick, J.A.

    2006-06-29

    Furnace designers and refractory engineers recognize that optimized furnace superstructure design and refractory selection are needed as glass production furnaces are continually striving toward greater output and efficiencies. Harsher operating conditions test refractories to the limit, while changing production technology (such as the conversion to oxy-fuel from traditional air-fuel firing) can alter the way the materials perform [1-3]. Refractories for both oxy- and air-fuel fired furnace superstructures (see Fig. 1) are subjected to high temperatures that may cause them to creep excessively or subside during service if the refractory material is not creep resistant, or if it is subjected to high stress, or both. Furnace designers can ensure that superstructure structural integrity is maintained if the creep behavior of the refractory material is well understood and well represented by appropriate engineering creep models. Several issues limit the abilities of furnace designers to (1) choose the optimum refractory for their applications, (2) optimize the engineering design, or (3) predict the service mechanical integrity of their furnace superstructures. Published engineering creep data are essentially nonexistent for almost all commercially available refractories used for glass furnace superstructures. The limited data that do exist are supplied by the various refractory suppliers. Unfortunately, the suppliers generally have different ways of conducting their mechanical testing, and they interpret and report their data differently. This inconsistency makes it hard for furnace designers to draw fair comparisons between competing grades of candidate refractories. Furthermore, the refractory suppliers' data are often not available in a form that can be readily used for furnace design or for the prediction and design of long-term structural integrity of furnace superstructures. As a consequence, the U.S. Department of Energy (DOE) Industrial Technology Program (ITP

  12. Hierarchical macroscopic fibrillar adhesives: in situ study of buckling and adhesion mechanisms on wavy substrates.

    PubMed

    Bauer, Christina T; Kroner, Elmar; Fleck, Norman A; Arzt, Eduard

    2015-10-23

    Nature uses hierarchical fibrillar structures to mediate temporary adhesion to arbitrary substrates. Such structures provide high compliance such that the flat fibril tips can be better positioned with respect to asperities of a wavy rough substrate. We investigated the buckling and adhesion of hierarchically structured adhesives in contact with flat smooth, flat rough and wavy rough substrates. A macroscopic model for the structural adhesive was fabricated by molding polydimethylsiloxane into pillars of diameter in the range of 0.3-4.8 mm, with up to three different hierarchy levels. Both flat-ended and mushroom-shaped hierarchical samples buckled at preloads one quarter that of the single level structures. We explain this behavior by a change in the buckling mode; buckling leads to a loss of contact and diminishes adhesion. Our results indicate that hierarchical structures can have a strong influence on the degree of adhesion on both flat and wavy substrates. Strategies are discussed that achieve highly compliant substrates which adhere to rough substrates.

  13. Selective buckling via states of self-stress in topological metamaterials.

    PubMed

    Paulose, Jayson; Meeussen, Anne S; Vitelli, Vincenzo

    2015-06-23

    States of self-stress--tensions and compressions of structural elements that result in zero net forces--play an important role in determining the load-bearing ability of structures ranging from bridges to metamaterials with tunable mechanical properties. We exploit a class of recently introduced states of self-stress analogous to topological quantum states to sculpt localized buckling regions in the interior of periodic cellular metamaterials. Although the topological states of self-stress arise in the linear response of an idealized mechanical frame of harmonic springs connected by freely hinged joints, they leave a distinct signature in the nonlinear buckling behavior of a cellular material built out of elastic beams with rigid joints. The salient feature of these localized buckling regions is that they are indistinguishable from their surroundings as far as material parameters or connectivity of their constituent elements are concerned. Furthermore, they are robust against a wide range of structural perturbations. We demonstrate the effectiveness of this topological design through analytical and numerical calculations as well as buckling experiments performed on two- and three-dimensional metamaterials built out of stacked kagome lattices.

  14. Nonlinear analysis of hydraulic buckling instability of ANS involute fuel plates

    SciTech Connect

    Sartory, W.K.

    1993-03-01

    The hydraulic buckling instability of the involute fuel plates and hydraulic coolant channels in the Advanced Neutron Source (ANS) uranium fission reactor is analyzed nonlinearly using the commercial ABAQUS finite element computer program for the fuel plates in conjunction with a user-written element for the two-dimensional fluid flow in the coolant channels. This methodology has been used for several purposes, including determination of the effect of the aluminum-clad plate plastic behavior and the effect of three-dimensional plate temperature distributions on hydraulic buckling. The present report concentrates on a study of the effect of hydraulic channel imperfections on buckling. The specific form of imperfection considered is an error in fluid channel thickness that is uniform within any one channel but that varies from one channel to the next. The calculated bifurcation (linear buckling) coolant velocity is about 45 m/s, whereas the present design coolant velocity is 25 m/s. At the design velocity, the calculated fluid-induced plate deflection due to the imperfection is somewhat less in magnitude and opposite in direction from the imperfection itself.

  15. Rigorous buckling analysis of size-dependent functionally graded cylindrical nanoshells

    NASA Astrophysics Data System (ADS)

    Sun, Jiabin; Lim, C. W.; Zhou, Zhenhuan; Xu, Xinsheng; Sun, Wei

    2016-06-01

    This paper presents new analytical solutions for buckling of carbon nanotubes (CNTs) and functionally graded (FG) cylindrical nanoshells subjected to compressive and thermal loads. The model applies Eringen's nonlocal differential constitutive relation to describe the size-dependence of nanoshells. Based on Reddy's higher-order shear deformation theory, governing equations are established and solved by separating the variables. The analysis first re-examines the classical buckling of single-walled CNTs. Accurate solutions are established, and it is found that the buckling stress decreases drastically when the nonlocal parameter reaches a certain value. For CNTs with constant wall-thickness, the buckling stress eventually decreases with enhanced size effect. By comparing with CNTs molecular dynamic simulations, the obtained nonlocal parameters are much smaller than those proposed previously. Subsequently, FG cylindrical nanoshells are analyzed, and it is concluded that similar behavior that has been observed for CNTs is also valid for FG cylindrical nanoshells. The paper further discusses in detail the effects of different geometric parameters, material distribution, and temperature field.

  16. Critical length for upheaval buckling of straight pipelines buried in ice rich soils

    SciTech Connect

    Quimby, T.B.

    1996-12-01

    Upheaval buckling, a phenomena receiving attention in offshore pipelines, has also been found to be a problem for onshore arctic pipelines buried in ice rich soils. While anticipated in overbend situations, it is also being found in pipelines designed to be straight. Understanding the mechanics and parameters affecting this behavior are essential to properly designing a buried arctic pipeline. This paper introduces the parameters that have led to upheaval buckling in at least one pipeline and describes the operation of a program that computes the critical buckling loads at various pipe lengths for the inception of upheaval buckling in a buried pipeline. The method uses finite elements to solve the eigenvalue problem for the axial stability of a column with flexible lateral restraints. This program can be used to predict critical lengths for straight pipelines that lose some or all of the lateral restraint of soil through erosion or thermal degradation. The results are used to make decisions concerning backfill and restrain design. The effects of soils stiffness are considered. Additional research needs are also discussed.

  17. Selective buckling via states of self-stress in topological metamaterials

    PubMed Central

    Paulose, Jayson; Meeussen, Anne S.; Vitelli, Vincenzo

    2015-01-01

    States of self-stress—tensions and compressions of structural elements that result in zero net forces—play an important role in determining the load-bearing ability of structures ranging from bridges to metamaterials with tunable mechanical properties. We exploit a class of recently introduced states of self-stress analogous to topological quantum states to sculpt localized buckling regions in the interior of periodic cellular metamaterials. Although the topological states of self-stress arise in the linear response of an idealized mechanical frame of harmonic springs connected by freely hinged joints, they leave a distinct signature in the nonlinear buckling behavior of a cellular material built out of elastic beams with rigid joints. The salient feature of these localized buckling regions is that they are indistinguishable from their surroundings as far as material parameters or connectivity of their constituent elements are concerned. Furthermore, they are robust against a wide range of structural perturbations. We demonstrate the effectiveness of this topological design through analytical and numerical calculations as well as buckling experiments performed on two- and three-dimensional metamaterials built out of stacked kagome lattices. PMID:26056303

  18. Buckled silicene formation on Ir(111).

    PubMed

    Meng, Lei; Wang, Yeliang; Zhang, Lizhi; Du, Shixuan; Wu, Rongting; Li, Linfei; Zhang, Yi; Li, Geng; Zhou, Haitao; Hofer, Werner A; Gao, Hong-Jun

    2013-02-13

    Silicene, a two-dimensional (2D) honeycomb structure similar to graphene, has been successfully fabricated on an Ir(111) substrate. It is characterized as a (√7×√7) superstructure with respect to the substrate lattice, as revealed by low energy electron diffraction and scanning tunneling microscopy. Such a superstructure coincides with the (√3×√3) superlattice of silicene. First-principles calculations confirm that this is a (√3×√3)silicene/(√7×√7)Ir(111) configuration and that it has a buckled conformation. Importantly, the calculated electron localization function shows that the silicon adlayer on the Ir(111) substrate has 2D continuity. This work provides a method to fabricate high-quality silicene and an explanation for the formation of the buckled silicene sheet.

  19. Postcrack creep of polymeric fiber-reinforced concrete in flexure

    SciTech Connect

    Kurtz, S.; Balaguru, P.

    2000-02-01

    Results of an experimental investigation of the creep-time behavior of polypropylene and nylon fiber-reinforced concrete (FRC) are presented. Gravity loads were applied in flexure to precracked low volume fraction (0.1%) polypropylene and nylon FRC beams. Beams were tested at a range of stress levels to produce three outcomes: load sustained indefinitely (low stress), creep failure (intermediate stress), and rapid failure (high stress). Emphasis was placed on determining the maximum flexural stress that is sustainable indefinitely. The results indicate that polypropylene FRC has higher initial strength but nylon FRC can sustain a higher stress level. For both groups the sustainable stress is much lower than the postcrack strength.

  20. Torsion and buckling of open sections

    NASA Technical Reports Server (NTRS)

    Wagner, Herbert

    1936-01-01

    In this paper is a discussion of the general principles for open sections of any shape. In what follows the torsion will be computed and on the basis of the results it will be possible to obtain a proper design of section in each case. The torsion of buckling members for the case where they are centrally loaded, leads to a problem in pure stability and is similar to that of stressed beams.

  1. Mechanical response of ceramics to creep loading

    SciTech Connect

    Blumenthal, W.R.

    1983-08-01

    The mechanical response of small, semi-elliptical, identification-induced surface cracks in fine-grain alumina was studied. The deformation behavior of the crack tip region was monitored using crack opening and surface displacements. Results indicate values of the secondary creep exponent, n, between 1.5 and 2 with a temperature dependence consistent with secondary creep data from the same material. Crack growth was measured at 1300 and 1400/sup 0/C and a narrow power-law growth regime was revealed. Again the power-law exponent and activation energy were very close to creep values. Asymptotic behavior was exhibited near both K/sub Ic/ and K/sub th/, the crack growth threshold. The threshold occurred near 0.4 K/sub Ic/, independent of temperature. Crack tip damage in the form of grain boundary cavities growing by diffusion was responsible for crack extension. The damage also exerts a strong influence on the displacement field as predicted by recent theories. The crack growth threshold is preceded by a transition in the size and distribution of damage. At K/sub I/ near K/sub Ic/ the damage is restricted to a few facets directly ahead of the crack tip. Near K/sub th/ damage concentrates in side-lobes far ahead of the crack tip and at angles between 20/sup 0/ to 60/sup 0/ from the plane of the crack. The transition between frontal and side-lobe damage is anticipated to be moderately dependent on grain size. 34 figures.

  2. Buckling mode localization in randomly disordered multispan continuous beams

    NASA Astrophysics Data System (ADS)

    Xie, Wei-Chau

    1995-06-01

    Buckling mode localization in large randomly disordered multispan continuous beams is studied. When the cross-sections of each span are uniform, an exact formulation is employed to establish the equations of equilibrium in terms of the angles of rotations at the supports. When the cross-sections of each span are not uniform, a finite element method is applied to set up the governing equations. Two approaches are applied to determine the localization factors, which characterize the average exponential rates of growth or decay of amplitudes of deformation. The first method applies a transfer matrix formulation and Furstenberg's theorem on the asymptotic behavior of products of random matrices. The second method uses a Green's function formulation for a linear eigenvalue problem of a block tridiagonal form.

  3. (Irradiation creep of graphite)

    SciTech Connect

    Kennedy, C.R.

    1990-12-21

    The traveler attended the Conference, International Symposium on Carbon, to present an invited paper, Irradiation Creep of Graphite,'' and chair one of the technical sessions. There were many papers of particular interest to ORNL and HTGR technology presented by the Japanese since they do not have a particular technology embargo and are quite open in describing their work and results. In particular, a paper describing the failure of Minor's law to predict the fatigue life of graphite was presented. Although the conference had an international flavor, it was dominated by the Japanese. This was primarily a result of geography; however, the work presented by the Japanese illustrated an internal program that is very comprehensive. This conference, a result of this program, was better than all other carbon conferences attended by the traveler. This conference emphasizes the need for US participation in international conferences in order to stay abreast of the rapidly expanding HTGR and graphite technology throughout the world. The United States is no longer a leader in some emerging technologies. The traveler was surprised by the Japanese position in their HTGR development. Their reactor is licensed and the major problem in their graphite program is how to eliminate it with the least perturbation now that most of the work has been done.

  4. Buckled graphene for efficient energy harvest, storage and conversion

    NASA Astrophysics Data System (ADS)

    Jiang, Jin-Wu

    2016-10-01

    Buckling is one of the most common phenomena in atom-thick layered structures like graphene. While the buckling phenomenon usually causes disaster for most nanodevices, we illustrate one positive application of buckled graphene for energy harvest, storage and conversion. More specifically, we perform molecular dynamical simulations to show that buckled graphene can be used to collect wasted mechanical energy and store the energy in the form of internal knotting potential. Through strain engineering, the knotting potential can be converted into useful kinetic (thermal) energy that is highly concentrated at the free edges of buckled graphene. The present study demonstrates potential applications of buckled graphene for converting dispersed wasted mechanical energy into concentrated useful kinetic (thermal) energy.

  5. Thin film buckling : a relation between adhesion and morphology

    NASA Astrophysics Data System (ADS)

    Barthel, Etienne; Faou, Jean-Yvon; Grachev, Sergey; Parry, Guillaume

    2013-03-01

    When thin films with low adhesion are compressively stressed, they may buckle. These buckles exhibit interesting morphologies such as the well known telephone cord. However our understanding of this form of buckling is limited because it couples the large displacement nonlinearities of plates with the subtleties of mixed-mode adhesion. Here we investigate the morphology of the thin film buckles as a function of mode mixity by a combination of experiments and simulations. We first exhibit a linear relation between the period of the telephone cord buckles and a characteristic parameter of the mixed mode adhesion. Furthermore we evidence a rich set of new buckle morphologies through experiments, and demonstrate that these morphologies can be reproduced in the simulations. We also show that we can rationalize the transitions between morphologies through a phase diagram. This excellent agreement between experimental results and numerical predictions further validates the simulation method we have developped recently.

  6. Buckled graphene for efficient energy harvest, storage and conversion.

    PubMed

    Jiang, Jin-Wu

    2016-10-01

    Buckling is one of the most common phenomena in atom-thick layered structures like graphene. While the buckling phenomenon usually causes disaster for most nanodevices, we illustrate one positive application of buckled graphene for energy harvest, storage and conversion. More specifically, we perform molecular dynamical simulations to show that buckled graphene can be used to collect wasted mechanical energy and store the energy in the form of internal knotting potential. Through strain engineering, the knotting potential can be converted into useful kinetic (thermal) energy that is highly concentrated at the free edges of buckled graphene. The present study demonstrates potential applications of buckled graphene for converting dispersed wasted mechanical energy into concentrated useful kinetic (thermal) energy. PMID:27581194

  7. Buckled graphene for efficient energy harvest, storage and conversion.

    PubMed

    Jiang, Jin-Wu

    2016-10-01

    Buckling is one of the most common phenomena in atom-thick layered structures like graphene. While the buckling phenomenon usually causes disaster for most nanodevices, we illustrate one positive application of buckled graphene for energy harvest, storage and conversion. More specifically, we perform molecular dynamical simulations to show that buckled graphene can be used to collect wasted mechanical energy and store the energy in the form of internal knotting potential. Through strain engineering, the knotting potential can be converted into useful kinetic (thermal) energy that is highly concentrated at the free edges of buckled graphene. The present study demonstrates potential applications of buckled graphene for converting dispersed wasted mechanical energy into concentrated useful kinetic (thermal) energy.

  8. Experimental investigations of creep in gold RF-MEMS microstructures

    NASA Astrophysics Data System (ADS)

    Somà, Aurelio; De Pasquale, Giorgio; Saleem, Muhammad Mubasher

    2015-05-01

    Lifetime prediction and reliability evaluation of micro-electro-mechanical systems (MEMS) are influenced by permanent deformations caused by plastic strain induced by creep. Creep in microstructures becomes critical in those applications where permanent loads persist for long times and thermal heating induces temperature increasing respect to the ambient. Main goal of this paper is to investigate the creep mechanism in RF-MEMS microstructures by means of experiments. This is done firstly through the detection of permanent deformation of specimens and, then, by measuring the variation of electro-mechanical parameters (resonance frequency, pull-in voltage) that provide indirect evaluation of mechanical stiffness alteration from creep. To prevent the errors caused be cumulative heating of samples and dimensional tolerances, three specimens with the same nominal geometry have been tested per each combination of actuation voltage and temperature. Results demonstrated the presence of plastic deformation due to creep, combined with a component of reversible strain linked to the viscoelastic behavior of the material.

  9. Power-law creep and residual stresses in carbopol microgels

    NASA Astrophysics Data System (ADS)

    Lidon, Pierre; Manneville, Sebastien

    We report on the interplay between creep and residual stresses in carbopol microgels. When a constant shear stress σ is applied below the yield stress σc, the strain is shown to increase as a power law of time, γ (t) =γ0 +(t / τ) α , with and exponent α ~= 0 . 38 that is strongly reminiscent of Andrade creep in hard solids. For applied shear stresses lower than some characteristic value of about σc / 10 , the microgels experience a more complex creep behavior that we link to the existence of residual stresses and to weak aging of the system after preshear. The influence of the preshear protocol, of boundary conditions and of microgel concentration on residual stresses is investigated. We discuss our results in light of previous works on colloidal glasses and other soft glassy systems.

  10. Creep-Rupture Data Analysis - Engineering Application of Regression Techniques. Ph.D. Thesis - North Carolina State Univ.

    NASA Technical Reports Server (NTRS)

    Rummler, D. R.

    1976-01-01

    The results are presented of investigations to apply regression techniques to the development of methodology for creep-rupture data analysis. Regression analysis techniques are applied to the explicit description of the creep behavior of materials for space shuttle thermal protection systems. A regression analysis technique is compared with five parametric methods for analyzing three simulated and twenty real data sets, and a computer program for the evaluation of creep-rupture data is presented.

  11. Creep-Rupture Strength of a Ni-Base Superalloy at 1400 K

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Nathal, Michael V.; Book, Patricia O.

    1993-01-01

    While NASAIR 100 is not the strongest of elevated-temperature single-crystal alloys, its higher-temperature properties are indicative of this technology's behavior. Attention is presently given to test results for this alloy which illuminate its 1400 K creep failure properties in air, and furnish a benchmark for the comparison of advanced materials to existing technology. The creep rupture behavior resembles that found after 1273 K testing, and is indicative of gamma-prime strengthening.

  12. Compressive Creep Response of T1000G/RS-14 Graphite/Polycyanate Composite Materials

    SciTech Connect

    Starbuck, J.M.

    1998-01-01

    The response of a T1000G/RS-14 graphite/polycyanate composite material system to transverse compressive loads is quantified via experimentation. The primary objective of the work was to quantify the effects of process environment and test environment on the T1000G/RS-14 compressive creep response. Tests were conducted on both the neat resin and the composite material system. In addition to the creep tests, static compressive strength tests were conducted to define the stress-strain response. The creep behavior for the RS-14 resin was quantified by conducting a series of tests to study the effects of different process environments (air and nitrogen), different cure temperatures, and different test environments (air and vacuum). The combined effect on the RS-14 resin compressive creep of processing in nitrogen and testing under vacuum versus processing in air and testing in air was a 47% decrease in the creep strain after 2177 hr. The test environment appeared to have a greater effect on the resin creep than the process environment. Following the conclusion of the resin creep tests, composite transverse compressive creep tests were conducted. The composite creep test cylinder was post-cured in a nitrogen environment prior to machining test specimens and all tests were conducted in a vacuum environment. The series of tests investigated the effects of initial stress level and test temperature on the creep behavior. At the end of the 2000-hr tests at 275{degrees}F on specimens stressed at 10,000 psi, the nitrogen-processed and vacuum-tested conditions reduced the composite transverse compressive creep strain by 19% compared to processing in air and testing in air. The effects of process and test environment on the creep behavior are not as great for the composite system as they were for the neat resin, primarily because of the low resin content in the composite material system. At the 275{degrees}F test temperature there was a significant increase in the composite

  13. Buckling analysis of planar compression micro-springs

    SciTech Connect

    Zhang, Jing; Sui, Li; Shi, Gengchen

    2015-04-15

    Large compression deformation causes micro-springs buckling and loss of load capacity. We analyzed the impact of structural parameters and boundary conditions for planar micro-springs, and obtained the change rules for the two factors that affect buckling. A formula for critical buckling deformation of micro-springs under compressive load was derived based on elastic thin plate theory. Results from this formula were compared with finite element analysis results but these did not always correlate. Therefore, finite element analysis is necessary for micro-spring buckling analysis. We studied the variation of micro-spring critical buckling deformation caused by four structural parameters using ANSYS software under two constraint conditions. The simulation results show that when an x-direction constraint is added, the critical buckling deformation increases by 32.3-297.9%. The critical buckling deformation decreases with increase in micro-spring arc radius or section width and increases with increase in micro-spring thickness or straight beam width. We conducted experiments to confirm the simulation results, and the experimental and simulation trends were found to agree. Buckling analysis of the micro-spring establishes a theoretical foundation for optimizing micro-spring structural parameters and constraint conditions to maximize the critical buckling load.

  14. Creep rupture testing of carbon fiber-reinforced epoxy composites

    NASA Astrophysics Data System (ADS)

    Burton, Kathryn Anne

    Carbon fiber is becoming more prevalent in everyday life. As such, it is necessary to have a thorough understanding of, not solely general mechanical properties, but of long-term material behavior. Creep rupture testing of carbon fiber is very difficult due to high strength and low strain to rupture properties. Past efforts have included testing upon strands, single tows and overwrapped pressure vessels. In this study, 1 inch wide, [0°/90°]s laminated composite specimens were constructed from fabric supplied by T.D. Williamson Inc. Specimen fabrication methods and gripping techniques were investigated and a method was developed to collect long term creep rupture behavior data. An Instron 1321 servo-hydraulic material testing machine was used to execute static strength and short term creep rupture tests. A hanging dead-weight apparatus was designed to perform long-term creep rupture testing. The testing apparatus, specimens, and specimen grips functioned well. Collected data exhibited a power law distribution and therefore, a linear trend upon a log strength-log time plot. Statistical analysis indicated the material exhibited slow degradation behavior, similar to previous studies, and could maintain a 50 year carrying capacity at 62% of static strength, approximately 45.7 ksi.

  15. GBT pre-buckling and buckling analyses of thin-walled members under axial and transverse loads

    NASA Astrophysics Data System (ADS)

    Taig, Gerard; Ranzi, Gianluca; Luongo, Angelo

    2016-03-01

    This paper presents an analytical approach for pre-buckling and buckling analyses of thin-walled members implemented within the framework of the Generalised Beam Theory (GBT). With the proposed GBT cross-sectional analysis, the set of deformation modes used in the analysis is represented by the dynamic modes obtained for an unrestrained frame representing the cross-section. In this manner, it is possible to account for the deformability of the cross-section in both pre-buckling and buckling analyses. Different loading conditions, including both axial and transverse arrangements, are considered in the applications to highlight under which circumstances the use of the GBT deformation modes is required for an adequate representation of the pre-buckling and buckling response. The numerical results have been validated against those determined using a shell element model developed in the finite element software ABAQUS.

  16. Remaining Creep Life Assessment Techniques Based on Creep Cavitation Modeling

    NASA Astrophysics Data System (ADS)

    Ankit, Kumar

    2009-05-01

    The boiler and its components are built with assumed nominal design and reasonable life of operation about two to three decades (one or two hundred thousand hours). These units are generally replaced or life is extended at the end of this period. Under normal operating conditions, after the initial period of teething troubles, the reliability of these units remains fairly constant up to about two decades of normal operation. The failure rate then increases as a result of their time-dependent material damage. Further running of these units may become uneconomical and dangerous in some cases. In the following article, step-by-step methodology to quantify creep cavitation based on statistical probability analysis and continuum damage mechanics has been described. The concepts of creep cavity nucleation have also been discussed with a special emphasis on the need for development of a model based on creep cavity growth kinetics.

  17. On the interaction of thermal buckling and debonding of patched structures

    NASA Astrophysics Data System (ADS)

    Carabetta, Pamela Marie

    unstable equilibrium configurations. In addition, examination of the energy release rate against the bond size reveals a variety of possible behaviors, dependent on flaw size, temperature difference, and bond strength. It is observed how and when separation leads to thermal buckling, and vice versa. Through this analysis, the onset, extent, and stability of debonding, as well as the relationship with buckling, are diagnosed and characterized.

  18. Creep of plasma sprayed zirconia

    NASA Technical Reports Server (NTRS)

    Firestone, R. F.; Logan, W. R.; Adams, J. W.

    1982-01-01

    Specimens of plasma-sprayed zirconia thermal barrier coatings with three different porosities and different initial particle sizes were deformed in compression at initial loads of 1000, 2000, and 3500 psi and temperatures of 1100 C, 1250 C, and 1400 C. The coatings were stabilized with lime, magnesia, and two different concentrations of yttria. Creep began as soon as the load was applied and continued at a constantly decreasing rate until the load was removed. Temperature and stabilization had a pronounced effect on creep rate. The creep rate for 20% Y2O3-80% ZrO2 was 1/3 to 1/2 that of 8% Y2O3-92% ZrO2. Both magnesia and calcia stabilized ZrO2 crept at a rate 5 to 10 times that of the 20% Y2O3 material. A near proportionality between creep rate and applied stress was observed. The rate controlling process appeared to be thermally activated, with an activation energy of approximately 100 cal/gm mole K. Creep deformation was due to cracking and particle sliding.

  19. Brittle creep and subcritical crack propagation in glass submitted to triaxial conditions

    NASA Astrophysics Data System (ADS)

    Mallet, Céline; Fortin, Jérôme; Guéguen, Yves; Bouyer, Frédéric

    2015-02-01

    An experimental work is presented that aimed at improving our understanding of the mechanical evolution of cracks under brittle creep conditions. Brittle creep may be an important slow deformation process in the Earth's crust. Synthetic glass samples have been used to observe and document brittle creep due to slow crack-propagation. A crack density of 0.05 was introduced in intact synthetic glass samples by thermal shock. Creep tests were performed at constant confining pressure (15 MPa) for water saturated conditions. Data were obtained by maintaining the differential-stress constant in steps of 24 h duration. A set of sensors allowed us to record strains and acoustic emissions during creep. The effect of temperature on creep was investigated from ambient temperature to 70°C. The activation energy for crack growth was found to be 32 kJ/mol. In secondary creep, a large dilatancy was observed that did not occur in constant strain rate tests. This is correlated to acoustic emission activity associated with crack growth. As a consequence, slow crack growth has been evidenced in glass. Beyond secondary creep, failure in tertiary creep was found to be a progressive process. The data are interpreted through a previously developed micromechanical damage model that describes crack propagation. This model allows one to predict the secondary brittle creep phase and also to give an analytical expression for the time to rupture. Comparison between glass and crystalline rock indicates that the brittle creep behavior is probably controlled by the same process even if stress sensitivity for glass is lower than for rocks.

  20. Specimen Size Effect on the Creep of Si3N4

    SciTech Connect

    Barnes, A.S.; Ferber, M.K.; Kirkland, T.P.; Wereszczak, A.A.

    1999-01-25

    The effect of specimen size on the measured tensile creep behavior of a commercially available gas pressure sintered Si3N4 was examined. Button-head tensile test specimens were used for the testing, and were machined to a variety of different gage section diameters (ranging from 2.5 to 6.35 mm) or different surface-area-to-volume ratios. The specimens were then creep tested at 1350 Degrees C and 200 MPa with tensile creep strain continuously measured as a function of time. The steady-state creep rate increased and the lifetime decreased with an increase in diameter (or decrease in the ratio of gage section surface area to volume). The time and specimen size dependence of transformation of a secondary phase correlated with the observed creep rate and lifetime dependence.

  1. Creep rupture strength of activated-TIG welded 316L(N) stainless steel

    NASA Astrophysics Data System (ADS)

    Sakthivel, T.; Vasudevan, M.; Laha, K.; Parameswaran, P.; Chandravathi, K. S.; Mathew, M. D.; Bhaduri, A. K.

    2011-06-01

    316L(N) stainless steel plates were joined using activated-tungsten inert gas (A-TIG) welding and conventional TIG welding process. Creep rupture behavior of 316L(N) base metal, and weld joints made by A-TIG and conventional TIG welding process were investigated at 923 K over a stress range of 160-280 MPa. Creep test results showed that the enhancement in creep rupture strength of weld joint fabricated by A-TIG welding process over conventional TIG welding process. Both the weld joints fractured in the weld metal. Microstructural observation showed lower δ-ferrite content, alignment of columnar grain with δ-ferrite along applied stress direction and less strength disparity between columnar and equiaxed grains of weld metal in A-TIG joint than in MP-TIG joint. These had been attributed to initiate less creep cavitation in weld metal of A-TIG joint leading to improvement in creep rupture strength.

  2. Temperature dependence of creep compliance of highly cross-linked epoxy: A molecular simulation study

    SciTech Connect

    Khabaz, Fardin Khare, Ketan S. Khare, Rajesh

    2014-05-15

    We have used molecular dynamics (MD) simulations to study the effect of temperature on the creep compliance of neat cross-linked epoxy. Experimental studies of mechanical behavior of cross-linked epoxy in literature commonly report creep compliance values, whereas molecular simulations of these systems have primarily focused on the Young’s modulus. In this work, in order to obtain a more direct comparison between experiments and simulations, atomistically detailed models of the cross-linked epoxy are used to study their creep compliance as a function of temperature using MD simulations. The creep tests are performed by applying a constant tensile stress and monitoring the resulting strain in the system. Our results show that simulated values of creep compliance increase with an increase in both time and temperature. We believe that such calculations of the creep compliance, along with the use of time temperature superposition, hold great promise in connecting the molecular insight obtained from molecular simulation at small length- and time-scales with the experimental behavior of such materials. To the best of our knowledge, this work is the first reported effort that investigates the creep compliance behavior of cross-linked epoxy using MD simulations.

  3. Axially compressed buckling of an embedded boron nitride nanotube subjected to thermo-electro-mechanical loadings

    NASA Astrophysics Data System (ADS)

    Salehi-Khojin, Amin; Jalili, Nader

    2007-04-01

    Unlike widely-used carbon nanotubes, boron nitride nanotubes (BNNTs) have shown to possess stable semiconducting behavior and strong piezoelectricity. Such properties along with their outstanding mechanical properties and thermal conductivity, make BNNTs promising candidate reinforcement materials for a verity of applications especially nanoelectronic and nanophotonic devices. Motivated by these abilities, we aim to study the buckling behavior of BNNT-reinforced piezoelectric polymeric composites when subjected to combined electro-thermo-mechanical loadings. For this, the multi-walled structure of BNNT is considered as elastic media and a set of concentric cylindrical shell with van der Waals interaction between them. Using three-dimensional equilibrium equations, Donnell shell theory is utilized to show that the axially compressive resistance of BNNT varies with applying thermal and electrical loads. The effect of BNNT piezoelectric property on the buckling behavior of the composites is demonstrated. More specifically, it is shown that applying direct and reverse voltages to BNNT changes the buckling loads for any axial and circumferential wavenumbers. Such capability could be uniquely utilized when designing BNNT-reinforced composites.

  4. Modeling Creep Effects within SiC/SiC Turbine Components

    NASA Technical Reports Server (NTRS)

    DiCarlo, J. A.; Lang, J.

    2008-01-01

    Anticipating the implementation of advanced SiC/SiC ceramic composites into the hot section components of future gas turbine engines, the primary objective of this on-going study is to develop physics-based analytical and finite-element modeling tools to predict the effects of constituent creep on SiC/SiC component service life. A second objective is to understand how to possibly select and manipulate constituent materials, processes, and geometries in order to minimize these effects. In initial studies aimed at SiC/SiC components experiencing through-thickness stress gradients, creep models were developed that allowed an understanding of detrimental residual stress effects that can develop globally within the component walls. It was assumed that the SiC/SiC composites behaved as isotropic visco-elastic materials with temperature-dependent creep behavior as experimentally measured in-plane in the fiber direction of advanced thin-walled 2D SiC/SiC panels. The creep models and their key results are discussed assuming state-of-the-art SiC/SiC materials within a simple cylindrical thin-walled tubular structure, which is currently being employed to model creep-related effects for turbine airfoil leading edges subjected to through-thickness thermal stress gradients. Improvements in the creep models are also presented which focus on constituent behavior with more realistic non-linear stress dependencies in order to predict such key creep-related SiC/SiC properties as time-dependent matrix stress, constituent creep and content effects on composite creep rates and rupture times, and stresses on fiber and matrix during and after creep.

  5. Dynamic Modeling of Coseismic Rupture on Partially-Creeping Strike-Slip Faults

    NASA Astrophysics Data System (ADS)

    Lozos, J.; Funning, G.; Oglesby, D. D.

    2013-12-01

    Partially creeping faults exhibit complex behavior in terms of which parts of the fault slip seismically versus aseismically; this complexity is both temporal and spatial. Several faults in California exhibit creep that is rapid enough to be detected geodetically using InSAR, GPS and near-field methods, such as theodolite measurements of alignment arrays. Such studies of the Hayward Fault in the San Francisco Bay Area suggest that it has a complex pattern of creeping and locked patches along strike and down dip. The spatial pattern of creeping versus locked zones may have as much of an effect on throughgoing rupture as the more general presence of creep does. We use the 3D finite element modeling code FaultMod to conduct single-cycle models of dynamic rupture on partially creeping strike slip faults, in order to determine whether coseismic rupture can propagate into creeping regions, and how the presence and distribution of creep affects the ability of rupture to propagate along strike. We implement a rate-state friction criterion, in which locked zones of the fault are represented by rate-weakening behavior, and creeping zones of the fault are assigned rate-strengthening properties. We model two simplified partial creep geometries: a locked patch at the base of a largely creeping fault (similar to what is inferred for the Hayward Fault), and a creeping patch at the surface of a predominantly locked fault (similar to what is inferred for the Rodgers Creek Fault). We find that, in the case of a locked patch within a creeping fault, rupture does not propagate more than a kilometer past the edges of the locked patch, regardless of the patch radius. The case of a creeping patch within a locked fault is more complicated. We find that the width of the locked areas around the creeping patch determine whether or not rupture is able to propagate around the creeping patch and along the full strike of the fault; if the width of locked zone between the edge of the creeping

  6. Study on effects of solar radiation and rain on shrinkage, shrinkage cracking and creep of concrete

    SciTech Connect

    Asamoto, Shingo; Ohtsuka, Ayumu; Kuwahara, Yuta; Miura, Chikako

    2011-06-15

    In this paper, the effects of actual environmental actions on shrinkage, creep and shrinkage cracking of concrete are studied comprehensively. Prismatic specimens of plain concrete were exposed to three sets of artificial outdoor conditions with or without solar radiation and rain to examine the shrinkage. For the purpose of studying shrinkage cracking behavior, prismatic concrete specimens with reinforcing steel were also subjected to the above conditions at the same time. The shrinkage behavior is described focusing on the effects of solar radiation and rain based on the moisture loss. The significant environment actions to induce shrinkage cracks are investigated from viewpoints of the amount of the shrinkage and the tensile strength. Finally, specific compressive creep behavior according to solar radiation and rainfall is discussed. It is found that rain can greatly inhibit the progresses of concrete shrinkage and creep while solar radiation is likely to promote shrinkage cracking and creep.

  7. Irradiation creep of nano-powder sintered silicon carbide at low neutron fluences

    NASA Astrophysics Data System (ADS)

    Koyanagi, T.; Shimoda, K.; Kondo, S.; Hinoki, T.; Ozawa, K.; Katoh, Y.

    2014-12-01

    The irradiation creep behavior of nano-powder sintered silicon carbide was investigated using the bend stress relaxation method under neutron irradiation up to 1.9 dpa. The creep deformation was observed at all temperatures ranging from 380 to 1180 °C mainly from the irradiation creep but with the increasing contributions from the thermal creep at higher temperatures. The apparent stress exponent of the irradiation creep slightly exceeded unity, and instantaneous creep coefficient at 380-790 °C was estimated to be ∼1 × 10-5 [MPa-1 dpa-1] at ∼0.1 dpa and 1 × 10-7 to 1 × 10-6 [MPa-1 dpa-1] at ∼1 dpa. The irradiation creep strain appeared greater than that for the high purity SiC. Microstructural observation and data analysis indicated that the grain-boundary sliding associated with the secondary phases contributes to the irradiation creep at 380-790 °C to 0.01-0.11 dpa.

  8. Interactions between creep, fatigue and strain aging in two refractory alloys

    NASA Technical Reports Server (NTRS)

    Sheffler, K. D.

    1972-01-01

    The application of low-amplitude, high-frequency fatigue vibrations during creep testing of two strain-aging refractory alloys (molybdenum-base TZC and tantalum-base T-111) significantly reduced the creep strength of these materials. This strength reduction caused dramatic increases in both the first stage creep strain and the second stage creep rate. The magnitude of the creep rate acceleration varied directly with both frequency and A ratio (ratio of alternating to mean stress), and also varied with temperature, being greatest in the range where the strain-aging phenomenon was most prominent. It was concluded that the creep rate acceleration resulted from a negative strain rate sensitivity which is associated with the strain aging phenomenon in these materials. (A negative rate sensitivity causes flow stress to decrease with increasing strain rate, instead of increasing as in normal materials). By combining two analytical expressions which are normally used to describe creep and strain aging behavior, an expression was developed which correctly described the influence of temperature, frequency, and A ratio on the TZC creep rate acceleration.

  9. Irradiation Creep of Chemically Vapor Deposited Silicon Carbide as Estimated by Bend Stress Relaxation Method

    SciTech Connect

    Katoh, Yutai; Snead, Lance Lewis; Hinoki, Tatsuya; Kondo, Sosuke; Kohyama, Akira

    2007-01-01

    The bend stress relaxation technique was applied for an irradiation creep study of high purity, chemically vapor-deposited beta-phase silicon carbide (CVD SiC) ceramic. A constant bend strain was applied to thin strip samples during neutron irradiation to fluences 0.2-4.2 dpa at various temperatures in the range {approx}400 to {approx}1080 C. Irradiation creep strain at <0.7 dpa exhibited only a weak dependence on irradiation temperature. However, the creep strain dependence on fluence was non-linear due to the early domination of the initial transient creep, and a transition in creep behavior was found between 950 and 1080 C. Steady-state irradiation creep compliances of polycrystalline CVD SiC at doses >0.7 dpa were estimated to be 2.7({+-}2.6) x 10{sup -7} and 1.5({+-}0.8) x 10{sup -6} (MPa dpa){sup -1} at {approx}600 to {approx}950 C and {approx}1080 C, respectively, whereas linear-averaged creep compliances of 1-2 x 10{sup -6} (MPa dpa){sup -1} were obtained for doses of 0.6-0.7 dpa at all temperatures. Monocrystalline 3C SiC samples exhibited significantly smaller transient creep strain and greater subsequent deformation when loaded along <0 1 1> direction.

  10. Fluid Creep and Over-resuscitation.

    PubMed

    Saffle, Jeffrey R

    2016-10-01

    Fluid creep is the term applied to a burn resuscitation, which requires more fluid than predicted by standard formulas. Fluid creep is common today and is linked to several serious edema-related complications. Increased fluid requirements may accompany the appropriate resuscitation of massive injuries but dangerous fluid creep is also caused by overly permissive fluid infusion and the lack of colloid supplementation. Several strategies for recognizing and treating fluid creep are presented. PMID:27600130

  11. Torsional Buckling Tests of a Simulated Solar Array

    NASA Technical Reports Server (NTRS)

    Thornton, E. A.

    1996-01-01

    Spacecraft solar arrays are typically large structures supported by long, thin deployable booms. As such, they may be particularly susceptible to abnormal structural behavior induced by mechanical and thermal loading. One example is the Hubble Space Telescope solar arrays which consist of two split tubes fit one inside the other called BiSTEMs. The original solar arrays on the Hubble Space Telescope were found to be severely twisted following deployment and later telemetry data showed the arrays were vibrating during daylight to night and night to daylight transition. The solar array twist however can force the BiSTEM booms to change in cross-section and cause tile solar arrays to react unpredictably to future loading. The solar arrays were redesigned to correct for tile vibration, however, upon redeployment they again twisted. To assess the influence of boom cross-sectional configuration, experiments were conducted on two types of booms, (1)booms with closed cross-sections, and (2) booms with open cross-sections. Both models were subjected to compressive loading and imposed tip deflections. An existing analytical model by Chung and Thornton was used to define the individual load ranges for each model solar array configuration. The load range for the model solar array using closed cross-section booms was 0-120 Newtons and 0-160 Newtons for the model solar array using open cross-section booms. The results indicate the model solar array with closed cross-section booms buckled only in flexure. However, the results of the experiment with open cross-section booms indicate the model solar array buckled only in torsion and with imposed tip deflections the cross section can degrade by rotation of the inner relative to the outer STEM. For tile Hubble Space Telescope solar arrays the results of these experiments indicate the twisting resulted from the initial mechanical loading of the open cross-section booms.

  12. Influence of precipitate morphology on intermediate temperature creep properties of a nickel-base superalloy single crystal

    NASA Technical Reports Server (NTRS)

    Nathal, M. V.; Mackay, R. A.; Miner, R. V.

    1989-01-01

    The relative creep behavior of cuboidal (as-heat treated) and rafted (precrept at 1000 C) gamma-prime microstructures in the single-crystal Ni-based superalloy NASAIR 100 at 760 C was investigated using SEM and TEM examinations of materials at various stages of creep. It was found that, at high applied stresses, the crystals with cuboidal gamma-prime structure had both lower minimum creep rates and longer rupture lives than the crystals with lamellar gamma-prime. At lower stress levels, the initially cuboidal gamma-prime microstructure maintained a lower creep rate, but exhibited a similar rupture life compared to the prerafted crystals.

  13. Investigation of the rate-controlling mechanism(s) for high temperature creep and the relationship between creep and melting by use of high pressure as a variable. Progress report

    SciTech Connect

    Not Available

    1991-12-31

    Using high pressure as a variable, the rate-controlling mechanism for high temperature creep and the relationship between creep and melting is investigated for silicon and nickel. An apparatus is used in which the samples are heated to melting point and subjected to 1 to 3 GigaPascal pressure. The stress behavior of the materials are then studied.

  14. Creep anomaly in electrospun fibers made of globular proteins

    NASA Astrophysics Data System (ADS)

    Regev, Omri; Arinstein, Arkadii; Zussman, Eyal

    2013-12-01

    The anomalous responses of electrospun nanofibers and film fabricated of unfolded bovine serum albumin (BSA) under constant stress (creep) is observed. In contrast to typical creep behavior of viscoelastic materials demonstrating (after immediate elastic response) a time-dependent elongation, in case of low applied stresses (<1 MPa) the immediate elastic response of BSA samples is followed by gradual contraction up to 2%. Under higher stresses (2-6 MPa) the contraction phase changes into elongation; and in case of stresses above 7 MPa only elongation was observed, with no initial contraction. The anomalous creep behavior was not observed when the BSA samples were subjected to additional creep cycles independently on the stress level. The above anomaly, which was not observed before either for viscoelastic solids or for polymers, is related to specific protein features, namely, to the ability to fold. We hypothesize that the phenomenon is caused by folding of BSA macromolecules into dry molten globule states, feasible after cross-linked bonds break up, resulting from the applied external force.

  15. Creep anomaly in electrospun fibers made of globular proteins.

    PubMed

    Regev, Omri; Arinstein, Arkadii; Zussman, Eyal

    2013-12-01

    The anomalous responses of electrospun nanofibers and film fabricated of unfolded bovine serum albumin (BSA) under constant stress (creep) is observed. In contrast to typical creep behavior of viscoelastic materials demonstrating (after immediate elastic response) a time-dependent elongation, in case of low applied stresses (<1 MPa) the immediate elastic response of BSA samples is followed by gradual contraction up to 2%. Under higher stresses (2-6 MPa) the contraction phase changes into elongation; and in case of stresses above 7 MPa only elongation was observed, with no initial contraction. The anomalous creep behavior was not observed when the BSA samples were subjected to additional creep cycles independently on the stress level. The above anomaly, which was not observed before either for viscoelastic solids or for polymers, is related to specific protein features, namely, to the ability to fold. We hypothesize that the phenomenon is caused by folding of BSA macromolecules into dry molten globule states, feasible after cross-linked bonds break up, resulting from the applied external force. PMID:24483479

  16. Bending and buckling of wet paper

    NASA Astrophysics Data System (ADS)

    Lee, Minhee; Kim, Seungho; Kim, Ho-Young; Mahadevan, L.

    2016-04-01

    Flat paper stained with water buckles and wrinkles as it swells and deforms out of the original plane. Here we quantify the geometry and mechanics of a strip of paper that swells when it imbibes water from a narrow capillary. Characterizing the hygroexpansive nature of paper shows that thickness-wise swelling is much faster than in-plane water imbibition, leading to a simple picture for the process by which the strip of paper bends out of the plane. We model the out-of-plane deformation using a quasi-static theory and show that our results are consistent with quantitative experiments.

  17. 49 CFR 179.400-6 - Bursting and buckling pressure.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 2 2010-10-01 2010-10-01 false Bursting and buckling pressure. 179.400-6 Section 179.400-6 Transportation Other Regulations Relating to Transportation PIPELINE AND HAZARDOUS MATERIALS... and 107A) § 179.400-6 Bursting and buckling pressure. (a) (b) The outer jacket of the...

  18. 49 CFR 179.400-6 - Bursting and buckling pressure.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Bursting and buckling pressure. 179.400-6 Section 179.400-6 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND... 107A) § 179.400-6 Bursting and buckling pressure. (a) (b) The outer jacket of the required...

  19. 49 CFR 179.400-6 - Bursting and buckling pressure.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Bursting and buckling pressure. 179.400-6 Section 179.400-6 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND... 107A) § 179.400-6 Bursting and buckling pressure. (a) (b) The outer jacket of the required...

  20. 49 CFR 179.400-6 - Bursting and buckling pressure.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Bursting and buckling pressure. 179.400-6 Section 179.400-6 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND... 107A) § 179.400-6 Bursting and buckling pressure. (a) (b) The outer jacket of the required...

  1. Dynamic buckling of stiffened plates subjected to explosion impact loads

    NASA Astrophysics Data System (ADS)

    Wang, J.; Guo, J.; Yao, X. L.; Zhang, A. M.

    2016-03-01

    The dynamic buckling characteristics and criteria of a ship's structural stiffened plate subjected to underwater explosion impact loads are investigated in this study. Using the structural deformations observed in the experiments of underwater explosions against a plated grillage model, the mode shapes of the dynamic buckling were obtained. Through the construction of a computational model of stiffened plates subjected to an underwater explosion shock wave, the impact load was theoretically calculated and transformed into a rectangular pulse. According to the different response patterns of stiffened plates under different impact loads, a dynamic buckling criterion for the stiffened plates subjected to an explosion shock wave was proposed. Additionally, the static buckling phenomenon in the stiffened plates was analysed based on the minimum excess principle. In combination with the dynamic buckling criterion, the effects of various stiffening configurations on the dynamic and static buckling loads are discussed. The calculation results show that when the equivalent rectangular pulse is 2-3 times that of the static buckling load, the responses of the stiffened plates under the original shock load and the equivalent rectangular pulse are virtually identical. The impact load amplitude is the primary influencing factor in the dynamic buckling of stiffened plates subjected to underwater explosive impact loads. The stiffened plate aspect ratio has a substantial influence on the dynamic load factor. The analytical method and results are presented, which can be used to design stiffened optimum hull structures to enhance the dynamic load carrying capacity to withstand underwater shock damage.

  2. Electromechanical interaction on the deformation behavior of metallic materials

    NASA Astrophysics Data System (ADS)

    Zhao, Guangfeng

    Metallic materials play important roles in providing electrical, thermal, and mechanical functions in electronic devices and systems. The understanding of the electrical-thermal-mechanical interaction caused by the passage of electric current with high density is important to improve the performance and reliability of electronic assembly and packaging. The electromechanical interaction on the deformation behavior of copper and tin is studied in this work. The electromechanical response of Cu strips was studied by passing a DC electric current. The electric resistance linearly increased with time before the occurrence of electric fusing. The electrothermal interaction led to the buckling of the Cu strips with the maximum deflection increasing with the increase of the electric current density. The total strain was found to be proportional to the square of the electric current density. A power law relation was used to describe the dependence of the time-to-fusing on the electric current density. Using the nanoindentation technique, the effect of electric current on the indentation deformation of copper and tin was studied. The reduced contact modulus of copper and tin decreased with increasing the electric current density. With the passage of a DC electric current, the indentation hardness of copper increased slightly with increasing electric current density. With the passage of an AC electric current, the indentation hardness of copper decreased with increasing the indentation deformation. With the passage of a DC electric current, the indentation hardness of tin decreased with increasing the indentation load, showing the normal indentation size effect. Both the limit of infinite depth and the characteristic length were dependent on the electric current density. Using the tensile creep technique, the creep deformation of pure tin was studied with the passage of a DC electric current. The steady state creep rate increased with the increase in temperature, tensile

  3. Investigation of Macroscopic Brittle Creep Failure Caused by Microcrack Growth Under Step Loading and Unloading in Rocks

    NASA Astrophysics Data System (ADS)

    Li, Xiaozhao; Shao, Zhushan

    2016-07-01

    The growth of subcritical cracks plays an important role in the creep of brittle rock. The stress path has a great influence on creep properties. A micromechanics-based model is presented to study the effect of the stress path on creep properties. The microcrack model of Ashby and Sammis, Charles' Law, and a new micro-macro relation are employed in our model. This new micro-macro relation is proposed by using the correlation between the micromechanical and macroscopic definition of damage. A stress path function is also introduced by the relationship between stress and time. Theoretical expressions of the stress-strain relationship and creep behavior are derived. The effects of confining pressure on the stress-strain relationship are studied. Crack initiation stress and peak stress are achieved under different confining pressures. The applied constant stress that could cause creep behavior is predicted. Creep properties are studied under the step loading of axial stress or the unloading of confining pressure. Rationality of the micromechanics-based model is verified by the experimental results of Jinping marble. Furthermore, the effects of model parameters and the unloading rate of confining pressure on creep behavior are analyzed. The coupling effect of step axial stress and confining pressure on creep failure is also discussed. The results provide implications on the deformation behavior and time-delayed rockburst mechanism caused by microcrack growth on surrounding rocks during deep underground excavations.

  4. Electrical characterization of a buckling thermal energy harvester

    NASA Astrophysics Data System (ADS)

    Trioux, E.; Rufer, L.; Monfray, S.; Skotnicki, T.; Muralt, P.; Basrour, S.

    2015-12-01

    This paper presents the electrical characterizations of a novel concept for thermal energy harvesting at micro scale. The devices presented here are based on a two-step transduction combining thermo-mechanical and piezoelectric conversion. The piezoelectric layer is directly integrated into a buckling bilayer plate made of aluminium and aluminium nitride. For the first time, we have characterized the structures electrically and we have investigated their output power during the buckling. Firstly, we have used an insulating tip to make the plate buckle in order to have an estimation of the output power due to piezoelectric contribution only, and to eliminate any pyroelectric contribution that might be present during the thermal actuation. Then, we heated up the structure and we collected the output signal with an instrumentation amplifier in order to measure the voltage generated during the buckling. The output power during the mechanical and the thermal buckling is compared in the paper.

  5. Novel Experiments to Characterize Creep-Fatigue Degradation in VHTR Alloys

    SciTech Connect

    J. K. Wright; J. A. Simpson; L. J. Carroll; R. N. Wright; T.-L. Sham

    2013-10-01

    It is well known in energy systems that the creep lifetime of high temperature alloys is significantly degraded when a cyclic load is superimposed on components operating in the creep regime. A test method has been developed in an attempt to characterize creep-fatigue behavior of alloys at high temperature. The test imposes a hold time during the tensile phase of a fully reversed strain-controlled low cycle fatigue test. Stress relaxation occurs during the strain-controlled hold period. This type of fatigue stress relaxation test tends to emphasize the fatigue portion of the total damage and does not necessarily represent the behavior of a component in-service well. Several different approaches to laboratory testing of creep-fatigue at 950°C have been investigated for Alloy 617, the primary candidate for application in VHTR heat exchangers. The potential for mode switching in a cyclic test from strain control to load control, to allow specimen extension by creep, has been investigated to further emphasize the creep damage. In addition, tests with a lower strain rate during loading have been conducted to examine the influence of creep damage occurring during loading. Very short constant strain hold time tests have also been conducted to examine the influence of the rapid stress relaxation that occurs at the beginning of strain holds.

  6. Parameter correlation of high-temperature creep constitutive equation for RPV metallic materials

    NASA Astrophysics Data System (ADS)

    Xie, Lin-Jun; Ren, Xin; Shen, Ming-Xue; Tu, Li-Qun

    2015-10-01

    Constant-temperature and constant-load creep tests of SA-508 stainless steel were performed at six temperatures, and the creep behavior and properties of this material were determined. Constitutive models were established based on an isothermal creep method to describe the high-temperature creep behavior of SA-508. Material parameter k, stress exponent nσ, and temperature exponent nt of the established constitutive models were determined through experimental data via numerical optimization techniques. The relationship of k, nσ, and nt was evaluated, and a new coefficient model of k-T, nσ-T, nt-T, and nt-nσ was formulated through the parameters of the isothermal creep equation. Moreover, the isothermal creep equation for this material at every temperature point from 450 °C to 1000 °C was obtained from the models. This method can serve as a reference for isothermal creep analysis and provide a way for the safety assessment of components of reactor pressure vessels.

  7. Buckling tests of structural elements applicable to large erectable space trusses

    NASA Technical Reports Server (NTRS)

    Heard, W. L., Jr.; Bush, H. G.; Agranoff, N.

    1978-01-01

    Detailed data on columns and center a joint for completeness is presented. Buckling data for a tripod arrangement of these columns using a cluster joint is also presented. The objectives of these test are: (1) to gain insight into joint requirements for truss structure; (2) to assess the structural qualities of the column and center joint designs; (3) to investigate the restraint provided by octetruss core members (tripod) to the cluster joints; (4) to provide insight into the level of analysis required to predict buckling behavior of Gr/E nestable columns both as simple columns and in a tripod arrangement; and (5) to provide a data base for Gr/E nestable columns.

  8. Life at Mission Creep U

    ERIC Educational Resources Information Center

    Dubrow, Greg; Moseley, Bryan; Dustin, Daniel

    2006-01-01

    The term "mission creep" was originally coined nearly a hundred years ago to describe the gradual process by which a military mission's stated methods and goals change, and recently the term has been applied to incremental organizational changes. In this article, the term is used to describe what happens when a teaching-oriented college or…

  9. Characterization of starch films containing starch nanoparticles. Part 2: viscoelasticity and creep properties.

    PubMed

    Shi, Ai-Min; Wang, Li-Jun; Li, Dong; Adhikari, Benu

    2013-07-25

    Starch films were successfully produced by incorporating spray dried and vacuum-freeze dried starch nanoparticles. The frequency sweep, creep-recovery behavior and time-temperature superposition (TTS) on these films were studied. All these films exhibited dominant elastic behavior (than viscous behavior) over the entire frequency range (0.1-100 rad/s). The incorporation of both types of starch nanoparticles increased the storage and loss modulus, tanδ, creep strain, creep compliance and creep rate at long time frame and reduced the recovery rate of films while the effect of different kinds of starch nanoparticles on these parameters was similar both in magnitude and trend. TTS method was successfully used to predict long time (over 20 days) creep behavior through the master curves. The addition of these nanoparticles could increase the activation energy parameter used in TTS master curves. Power law and Burger's models were capable of fitting storage and loss modulus (R(2)>0.79) and creep data (R(2)>0.96), respectively.

  10. Creep avalanches on the Central San Andreas Fault: Clues and Causes

    NASA Astrophysics Data System (ADS)

    Khoshmanesh, M.; Shirzaei, M.; Nadeau, R. M.

    2015-12-01

    The Central segment of San Andreas Fault (CSAF) is characterized by a nearly continuous right-lateral aseismic slip. However, observations of the creep rate obtained using Characteristically Repeating Earthquakes (CREs) show a quasi-periodic temporal variation, which is recently confirmed using both InSAR surface deformation time series and geodetic-based time-dependent kinematic model of creep along the CSAF. Here, we show that the statistical analysis of creep fronts along the CSAF indicates a sporadic behavior, signature of a burst-like creep dynamics. Moreover, the probability of creep velocities follows a Gumbel distribution characterized by longer tail toward the extreme positive rates. Fourier analysis of the time series of surface creep rate indicates a self-affine regime with Hurst exponent altering between 0.6 and 0.9 during the observation period of 2003-2011. The variable Hurst component is an indicator for temporal variation in the roughness of the fault zone. To explain the causes of creep avalanches, two possible mechanisms are considered, including temporal variation in: 1) fault geometry, and 2) Ambient normal stress. We find that the overall statistical dependence between the pattern of surface creep rate and the fault geometry is insignificant. To investigate the effect of ambient normal stress, primarily due to variation in pore pressure, we implement a rate and state friction law to link the time-dependent kinematic creep model to the spatiotemporal variations of the normal stress on the velocity-strengthening fault zones. These observations and models help to understand the driving mechanisms that govern the creep rate variations at short spatial length and low velocities. Under these circumstances, the other mechanisms such as thermal pressurization are not feasible.

  11. Dislocation Creep in Magnesium Calcite

    NASA Astrophysics Data System (ADS)

    Xu, L.; Xiao, X.; Evans, B. J.

    2003-12-01

    To investigate the effect of dissolved Mg on plastic deformation of calcite, we performed triaxial deformation experiments on synthetic calcite with varying amount of Mg content. Mixtures of powders of calcite and dolomite were isostatically hot pressed (HIP) at 850° C and 300 MPa confining pressure for different intervals (2 to 20hrs) resulting in homogeneous aggregates of high-magnesium calcite; Mg content varied from 0.07 to 0.17 mol%. Creep tests were performed at differential stresses from 20 to 160 MPa at 700 to 800° C. Grain sizes before and after deformation were determined from the images obtained from scanning electron microscope (SEM) and optical microscope. Grain sizes are in the range of 5 to 20 microns depending on the HIP time, and decrease with increasing magnesium content. Both BSE images and chemical analysis suggest that all dolomite are dissolved and the Mg distribution is homogeneous through the sample, after 2 hrs HIP. At stresses below 40 MPa, the samples deformed in diffusion region (Coble creep), as described previously by Herwegh. The strength decreases with increasing magnesium content, owing to the difference of grain size. At stresses above 80 MPa, the stress exponent is greater than 3, indicating an increased contribution of dislocation creep. The transition between diffusion to dislocation creep occurs at higher stresses for the samples with higher magnesium content and smaller grain size. Preliminary data suggests a slight increase in strength with increasing magnesium content, but more tests are needed to verify this effect. In a few samples, some strain weakening may have been evident. The activation energy in the transition region (at 80 MPa) is ˜200 KJ/mol with no dependence on magnesium content, agreeing with previous measurements of diffusion creep in natural and synthetic marbles.

  12. Deformation Mechanism and Microstructure Evolution of T92/S30432 Dissimilar Welded Joint During Creep

    NASA Astrophysics Data System (ADS)

    Xu, Lianyong; Wang, Yongfa; Jing, Hongyang; Zhao, Lei; Han, Yongdian

    2016-09-01

    The cross dissimilar welds between T92 martensitic steel and S30432 austenitic steel were crept at 625 °C with different applied stresses, and the creep deformation and microstructure behaviors were characterized. The results revealed that the creep deformation behavior of dissimilar weld joint was controlled by its martensitic T92 part due to the Ni-based filler metal employed. The fracture positions of crept dissimilar welded joints were located in base metal of T92 steel as the applied stress over than 140 MPa. The fracture type was mainly caused by plastic deformation and characterized by dimples and surface necking. In contrast, as applied stress was <140 MPa, fractured location was transferred into the fine-grained heat-affected zone of T92 part identified to be the intergranular brittle fracture. This phenomenon was controlled by creep deformation and related to undissolved carbides, fine grain size and constraint effect induced by creep deformation inconsistent in this zone.

  13. MOLECULAR DYNAMICS STUDY OF DIFFUSIONAL CREEP IN NANOCRYSTALLINE UO2

    SciTech Connect

    Tapan G. Desai; Paul C. Millett; Dieter Wolf

    2008-09-01

    We present the results of molecular dynamics (MD) simulations to study hightemperature deformation of nanocrystalline UO2. In qualitative agreement with experimental observations, the oxygen sub-lattice undergoes a structural transition at a temperature of about 2200 K (i.e., well below the melting point of 3450 K of our model system), whereas the uranium sub-lattice remains unchanged all the way up to melting. At temperatures well above this structural transition, columnar nanocrystalline model microstructures with a uniform grain size and grain shape were subjected to constantstress loading at levels low enough to avoid microcracking and dislocation nucleation from the GBs. Our simulations reveal that in the absence of grain growth, the material deforms via GB diffusion creep (also known as Coble creep). Analysis of the underlying self-diffusion behavior in undeformed nanocrystalline UO2 reveals that, on our MD time scale, the uranium ions diffuse only via the grain boundaries (GBs) whereas the much faster moving oxygen ions diffuse through both the lattice and the GBs. As expected for the Coble-creep mechanism, the creep activation energy agrees well with that for GB diffusion of the slowest moving species, i.e., of the uranium ions.

  14. Physical simulations of cavity closure in a creeping material

    SciTech Connect

    Sutherland, H.J.; Preece, D.S.

    1985-09-01

    The finite element method has been used extensively to predict the creep closure of underground petroleum storage cavities in rock salt. Even though the numerical modeling requires many simplifying assumptions, the predictions have generally correlated with field data from instrumented wellheads, however, the field data are rather limited. To gain an insight into the behavior of three-dimensional arrays of cavities and to obtain a larger data base for the verification of analytical simulations of creep closure, a series of six centrifuge simulation experiments were performed using a cylindrical block of modeling clay, a creeping material. Three of the simulations were conducted with single, centerline cavities, and three were conducted with a symmetric array of three cavities surrounding a central cavity. The models were subjected to body force loading using a centrifuge. For the single cavity experiments, the models were tested at accelerations of 100, 125 and 150 g's for 2 hours. For the multi-cavity experiments, the simulations were conducted at 100 g's for 3.25 hours. The results are analyzed using dimensional analyses. The analyses illustrate that the centrifuge simulations yield self-consistent simulations of the creep closure of fluid-filled cavities and that the interaction of three-dimensional cavity layouts can be investigated using this technique.

  15. CREEP MODELING FOR INJECTION-MOLDED LONG-FIBER THERMOPLASTICS

    SciTech Connect

    Nguyen, Ba Nghiep; Kunc, Vlastimil; Bapanapalli, Satish K.

    2008-06-30

    This paper proposes a model to predict the creep response of injection-molded long-fiber thermoplastics (LFTs). The model accounts for elastic fibers embedded in a thermoplastic resin that exhibits the nonlinear viscoelastic behavior described by the Schapery’s model. It also accounts for fiber length and orientation distributions in the composite formed by the injection-molding process. Fiber length and orientation distributions were measured and used in the analysis that applies the Eshelby’s equivalent inclusion method, the Mori-Tanaka assumption (termed as the Eshelby-Mori-Tanaka approach) and the fiber orientation averaging technique to compute the overall strain increment resulting from an overall constant applied stress during a given time increment. The creep model for LFTs has been implemented in the ABAQUS finite element code via user-subroutines and has been validated against the experimental creep data obtained for long-glass-fiber/polypropylene specimens. The effects of fiber orientation and length distributions on the composite creep response are determined and discussed.

  16. Energy harvesting from localized dynamic transitions in post-buckled elastic beams under quasi-static loading

    NASA Astrophysics Data System (ADS)

    Borchani, Wassim

    The deployability of structural health monitoring self-powered sensors relies on their capability to harvest energy from signals being monitored. Many of the signals required to assess the structure condition are quasi-static events which limits the levels of power that can be extracted. Several vibration-based techniques have been proposed to increase the transferred level of power and broaden the harvester operating bandwidth. However, these techniques require vibration input excitations at frequencies higher than dominant structural response frequencies which makes them inefficient and not suitable for ambient quasi-static excitations. This research proposes a novel sensing and energy harvesting technique at low frequencies using mechanical energy concentrators and triggers. These mechanisms consist of axially-loaded bilaterally-constrained beams with attached piezoelectric energy harvesters. When the quasi-static axial load reaches a certain mechanical threshold, a sudden snap-through mode-switching occurs. These transitions excite the attached piezoelectric scavengers with high-rate input accelerations, generating then electric power. The main objectives are to understand and model the post-buckling behavior of bilaterally-constrained beams, control it by tailoring geometry and material properties of the buckled elements or stacking them into system assemblies, and finally characterize the energy harvesting and sensing capability of the system under quasi-static excitations. The fundamental principle relies on the following concept. Under axial load, a straight slender beam buckles in the first buckling mode. The increased transverse deformations from a buckled shape lead to contact interaction with the lateral boundaries. The contact interaction generates transverse forces that induce the development of higher order buckling configurations. Transitions between the buckled configurations occur not only during loading, but also unloading. In this work, the post-buckling

  17. The effects of physical aging at elevated temperatures on the viscoelastic creep on IM7/K3B

    NASA Technical Reports Server (NTRS)

    Gates, Thomas S.; Feldman, Mark

    1994-01-01

    Physical aging at elevated temperature of the advanced composite IM7/K3B was investigated through the use of creep compliance tests. Testing consisted of short term isothermal, creep/recovery with the creep segments performed at constant load. The matrix dominated transverse tensile and in-plane shear behavior were measured at temperatures ranging from 200 to 230 C. Through the use of time based shifting procedures, the aging shift factors, shift rates and momentary master curve parameters were found at each temperature. These material parameters were used as input to a predictive methodology, which was based upon effective time theory and linear viscoelasticity combined with classical lamination theory. Long term creep compliance test data was compared to predictions to verify the method. The model was then used to predict the long term creep behavior for several general laminates.

  18. Cap buckling as a potential mechanism of atherosclerotic plaque vulnerability.

    PubMed

    Abdelali, Maria; Reiter, Steven; Mongrain, Rosaire; Bertrand, Michel; L'Allier, Philippe L; Kritikou, Ekaterini A; Tardif, Jean-Claude

    2014-04-01

    Plaque rupture in atherosclerosis is the primary cause of potentially deadly coronary events, yet about 40% of ruptures occur away from the plaque cap shoulders and cannot be fully explained with the current biomechanical theories. Here, cap buckling is considered as a potential destabilizing factor which increases the propensity of the atherosclerotic plaque to rupture and which may also explain plaque failure away from the cap shoulders. To investigate this phenomenon, quasistatic 2D finite element simulations are performed, considering the salient geometrical and nonlinear material properties of diverse atherosclerotic plaques over the range of physiological loads. The numerical results indicate that buckling may displace the location of the peak von Mises stresses in the deflected caps. Plaque buckling, together with its deleterious effects is further observed experimentally in plaque caps using a physical model of deformable mock coronary arteries with fibroatheroma. Moreover, an analytical approach combining quasistatic equilibrium equations with the Navier-Bresse formulas is used to demonstrate the buckling potential of a simplified arched slender cap under intraluminal pressure and supported by foundations. This analysis shows that plaque caps - calcified, fibrotic or cellular - may buckle in specific undulated shapes once submitted to critical loads. Finally, a preliminary analysis of intravascular ultrasonography recordings of patients with atherosclerotic coronary arteries corroborates the numerical, experimental and theoretical findings and shows that various plaque caps buckle in vivo. By displacing the sites of high stresses in the plaque cap, buckling may explain the atherosclerotic plaque cap rupture at various locations, including cap shoulders.

  19. Creep lifetime prediction of oxide-dispersion-strengthened nickel-base superalloys: A micromechanically based approach

    NASA Astrophysics Data System (ADS)

    Heilmaier, M.; Reppich, B.

    1996-12-01

    The high-temperature creep behavior of the oxide-dispersion-strengthened (ODS) nickel-base superalloys MA 754 and MA 6000 has been investigated at temperatures up to 1273 K and lifetimes of approximately 4000 hours using monotonic creep tests at constant true stress σ, as well as true constant extension rate tests (CERTs) atdot \\varepsilon . The derivation of creep rupture-lifetime diagrams is usually performed with conventional engineering parametric methods, according to Sherby and Dorn or Larson and Miller. In contrast, an alternative method is presented that is based on a more microstructural approach. In order to describe creep, the effective stress model takes into account the hardening contribution σ p caused by the presence of second-phase particles, as well as the classical Taylor back-stress σ p caused by dislocations. The modeled strain rate-stress dependence can be transferred directly into creep-rupture stress-lifetime diagrams using a modified Monkman-Grant (MG) relationship, which adequately describes the interrelation betweendot \\varepsilon representing dislocation motion, and lifetime t f representing creep failure. The comparison with measured creep-rupture data proves the validity of the proposed micromechanical concept.

  20. Creep rupture of materials: Insights from a fiber bundle model with relaxation

    NASA Astrophysics Data System (ADS)

    Jagla, E. A.

    2011-04-01

    I adapted a model recently introduced in the context of seismic phenomena to study creep rupture of materials. It consists of linear elastic fibers that interact in an equal load sharing scheme, complemented with a local viscoelastic relaxation mechanism. The model correctly describes the three stages of the creep process; namely, an initial Andrade regime of creep relaxation, an intermediate regime of rather constant creep rate, and a tertiary regime of accelerated creep toward final failure of the sample. In the tertiary regime, creep rate follows the experimentally observed creep rate over time-to-failure dependence. The time of minimum strain rate is systematically observed to be about 60%-65 % of the time to failure, in accordance with experimental observations. In addition, burst size statistics of breaking events display a -3/2 power law for events close to the time of failure and a steeper decay for the all-time distribution. Statistics of interevent times shows a tendency of the events to cluster temporarily. This behavior should be observable in acoustic emission experiments.

  1. Buckling Analysis of Debonded Sandwich Panel Under Compression

    NASA Technical Reports Server (NTRS)

    Sleight, David W.; Wang, John T.

    1995-01-01

    A sandwich panel with initial through-the-width debonds is analyzed to study the buckling of its faceskin when subject to an in-plane compressive load. The debonded faceskin is modeled as a beam on a Winkler elastic foundation in which the springs of the elastic foundation represent the sandwich foam. The Rayleigh-Ritz and finite-difference methods are used to predict the critical buckling load for various debond lengths and stiffnesses of the sandwich foam. The accuracy of the methods is assessed with a plane-strain finite-element analysis. Results indicate that the elastic foundation approach underpredicts buckling loads for sandwich panels with isotropic foam cores.

  2. Passive control of buckling deformation via Anderson Localization Phenomenon

    NASA Technical Reports Server (NTRS)

    Elishakoff, Isaac; Li, Y. W.; Starnes, J. H., Jr.

    1998-01-01

    Buckling problems of two types of multi-span elastic plates with transverse stiffeners are considered using a method based on the finite difference calculus. The discreteness of the stiffeners is accounted for. It is found that the torsional rigidity of the stiffener plays an important role in the buckling mode pattern. When the torsional rigidity is properly adjusted, the stiffener can act as an isolator of deformation for the structure at buckling so that the deflection is only limited to a small area.

  3. Finite-temperature buckling of an extensible rod

    NASA Astrophysics Data System (ADS)

    Bedi, Deshpreet Singh; Mao, Xiaoming

    2015-12-01

    Thermal fluctuations can play an important role in the buckling of elastic objects at small scales, such as polymers or nanotubes. In this paper, we study the finite-temperature buckling transition of an extensible rod by analyzing fluctuation corrections to the elasticity of the rod. We find that, in both two and three dimensions, thermal fluctuations delay the buckling transition, and near the transition, there is a critical regime in which fluctuations are prominent and make a contribution to the effective force that is of order √{T }. We verify our theoretical prediction of the phase diagram with Monte Carlo simulations.

  4. Buckled cantilevers for out-of-plane platforms

    NASA Astrophysics Data System (ADS)

    Johnstone, R. W.; Ma, A. H.; Sameoto, D.; Parameswaran, M.; Leung, A. M.

    2008-04-01

    In this paper, we show how surface-micromachined buckled cantilevers can be used to construct out-of-plane structures. We include the relevant theory necessary to predict the height and angle of plates attached to buckled cantilevers, as well as the mechanical stresses involved in assembly. These platforms can be assembled to any angle between 0° and 90° with respect to the substrate by changing the attachment point and the amount of deflection. Example devices were fabricated using PolyMUMPs™ and assembled. Using these devices, the deflection of the buckled cantilevers was verified, as well as the placement for raised platforms.

  5. Vibration and buckling of rotating, pretwisted, preconed beams including Cooriolis effects

    NASA Technical Reports Server (NTRS)

    Subrahmanyam, K. B.; Kaza, K. R. V.

    1985-01-01

    The effects of pretwist, precone, setting angle and Coriolis forces on the vibration and buckling behavior of rotating, torsionally rigid, cantilevered beams were studied. The beam is considered to be clamped on the axis of rotation in one case, and off the axis of rotation in the other. Two methods are employed for the solution of the vibration problem: (1) one based upon a finite-difference approach using second order central differences for solution of the equations of motion, and (2) based upon the minimum of the total potential energy functional with a Ritz type of solution procedure making use of complex forms of shape functions for the dependent variables. The individual and collective effects of pretwist, precone, setting angle, thickness ratio and Coriolis forces on the natural frequencies and the buckling boundaries are presented. It is shown that the inclusion of Coriolis effects is necessary for blades of moderate to large thickness ratios while these effects are not so important for small thickness ratio blades. The possibility of buckling due to centrifugal softening terms for large values of precone and rotation is shown.

  6. Vibration and buckling of rotating, pretwisted, preconed beams including Coriolis effects

    NASA Technical Reports Server (NTRS)

    Subrahmanyam, K. B.; Kaza, K. R. V.

    1985-01-01

    The effects of pretwist, precone, setting angle and Coriolis forces on the vibration and buckling behavior of rotating, torsionally rigid, cantilevered beams were studied. The beam is considered to be clamped on the axis of rotation in one case, and off the axis of rotation in the other. Two methods are employed for the solution of the vibration problem: (1) one based upon a finite-difference approach using second order central differences for solution of the equations of motion, and (2) based upon the minimum of the total potential energy functional with a Ritz type of solution procedure making use of complex forms of shape functions for the dependent variables. The individual and collective effects of pretwist, precone, setting angle, thickness ratio and Coriolis forces on the natural frequencies and the buckling boundaries are presented. It is shown that the inclusion of Coriolis effects is necessary for blades of moderate to large thickness ratios while these effects are not so important for small thickness ratio blades. The possibility of buckling due to centrifugal softening terms for large values of precone and rotation is shown.

  7. Dynamic Snap-Through of Thermally Buckled Structures by a Reduced Order Method

    NASA Technical Reports Server (NTRS)

    Przekop, Adam; Rizzi, Stephen A.

    2007-01-01

    The goal of this investigation is to further develop nonlinear modal numerical simulation methods for application to geometrically nonlinear response of structures exposed to combined high intensity random pressure fluctuations and thermal loadings. The study is conducted on a flat aluminum beam, which permits a comparison of results obtained by a reduced-order analysis with those obtained from a numerically intensive simulation in physical degrees-of-freedom. A uniformly distributed thermal loading is first applied to investigate the dynamic instability associated with thermal buckling. A uniformly distributed random loading is added to investigate the combined thermal-acoustic response. In the latter case, three types of response characteristics are considered, namely: (i) small amplitude vibration around one of the two stable buckling equilibrium positions, (ii) intermittent snap-through response between the two equilibrium positions, and (iii) persistent snap-through response between the two equilibrium positions. For the reduced-order analysis, four categories of modal basis functions are identified including those having symmetric transverse, anti-symmetric transverse, symmetric in-plane, and anti-symmetric in-plane displacements. The effect of basis selection on the quality of results is investigated for the dynamic thermal buckling and combined thermal-acoustic response. It is found that despite symmetric geometry, loading, and boundary conditions, the anti-symmetric transverse and symmetric in-plane modes must be included in the basis as they participate in the snap-through behavior.

  8. Shock-Sensitivity in Shell-Like Structures: With Simulations of Spherical Shell Buckling

    NASA Astrophysics Data System (ADS)

    Thompson, J. Michael T.; Sieber, Jan

    Under increasing compression, an unbuckled shell is in a metastable state which becomes increasingly precarious as the buckling load is approached. So to induce premature buckling, a lateral disturbance will have to overcome a decreasing energy barrier which reaches zero at buckling. Two archetypal problems that exhibit a severe form of this behavior are the axially-compressed cylindrical shell and the externally pressurized spherical shell. Focusing on the cylinder, a nondestructive technique was recently proposed to estimate the “shock-sensitivity” of a laboratory specimen using a lateral probe to measure the nonlinear load-deflection characteristic. If a symmetry-breaking bifurcation is encountered on the path, computer simulations showed how this can be suppressed by a controlled secondary probe. Here, we extend our understanding by assessing in general terms how a single control can capture remote saddle solutions: in particular, how a symmetric probe could locate an asymmetric solution. Then, more specifically, we analyze the spherical shell with point and ring probes, to test the procedure under challenging conditions to assess its range of applicability. Rather than a bifurcation, the spherical shell offers the challenge of a destabilizing fold (limit point) under the rigid control of the probe.

  9. Boundaries determine the formation energies of lattice defects in two-dimensional buckled materials

    NASA Astrophysics Data System (ADS)

    Jain, Sandeep K.; Juričić, Vladimir; Barkema, Gerard T.

    2016-07-01

    Lattice defects are inevitably present in two-dimensional materials, with direct implications on their physical and chemical properties. We show that the formation energy of a lattice defect in buckled two-dimensional crystals is not uniquely defined as it takes different values for different boundary conditions even in the thermodynamic limit, as opposed to their perfectly planar counterparts. Also, the approach to the thermodynamic limit follows a different scaling: inversely proportional to the logarithm of the system size for buckled materials, rather than the usual power-law approach. In graphene samples of ˜1000 atoms, different boundary conditions can cause differences exceeding 10 eV. Besides presenting numerical evidence in simulations, we show that the universal features in this behavior can be understood with simple bead-spring models. Fundamentally, our findings imply that it is necessary to specify the boundary conditions for the energy of the lattice defects in the buckled two-dimensional crystals to be uniquely defined, and this may explain the lack of agreement in the reported values of formation energies in graphene. We argue that boundary conditions may also have an impact on other physical observables such as the melting temperature.

  10. Anomalous creep in Sn-rich solder joints

    SciTech Connect

    Song, Ho Geon; Morris Jr., John W.; Hua, Fay

    2002-03-15

    This paper discusses the creep behavior of example Sn-rich solders that have become candidates for use in Pb-free solder joints. The specific solders discussed are Sn-3.5Ag, Sn-3Ag-0.5Cu, Sn-0.7Cu and Sn-10In-3.1Ag, used in thin joints between Cu and Ni-Au metallized pads.

  11. Proton Irradiation Creep in Pyrocarbon

    SciTech Connect

    Was, Gary S.; Campbell, Anne

    2011-10-01

    This project aims to understand irradiation creep in pyrocarbon using proton irradiation under controlled stresses and temperatures. Experiments will be conducted over a range of temperatures and stresses per the proposal submitted. The work scope will include the preparation of samples, measurement of deposition thickness, thickness uniformity, and anisotropy. The samples produced will be made in strips, which will be used for the creep experiments. Materials used will include pyrolytic carbon (PyC), Highly Oriented Pyrolytic Graphite (HOPG), or graphite strip samples in that order depending upon success. Temperatures tested under will range from 800°C to 1200°C, and stresses from 6MPa to 20.7MPa. Optional testing may occur at 900°C and 1100°C and stresses from 6MPa to 20.7MPa if funding is available.

  12. Creep of Structural Nuclear Composites

    SciTech Connect

    Will Windes; R.W. Lloyd

    2005-09-01

    A research program has been established to investigate fiber reinforced ceramic composites to be used as control rod components within a Very High Temperature Reactor (VHTR) design. Two candidate systems have been identified, carbon fiber reinforced carbon (Cf/C) and silicon carbide fiber reinforced silicon carbide (SiCf/SiC) composites. One of the primary degradation mechanisms anticipated for these core components is high temperature thermal and irradiation enhanced creep. As a consequence, high temperature test equipment, testing methodologies, and test samples for very high temperature (up to 1600º C) tensile strength and long duration creep studies have been established. Actual testing of both tubular and flat, "dog-bone"-shaped tensile composite specimens will begin next year. Since there is no precedence for using ceramic composites within a nuclear reactor, ASTM standard test procedures are currently being established from these high temperature mechanical tests.

  13. Creep dynamics in soft matter

    NASA Astrophysics Data System (ADS)

    Cabriolu, Raffaela

    Detecting any precursors of failure in Soft Matter Systems (SMS) is an inter-disciplinary topic with important applications (e.g. prediction of failure in engineering processes). Further, it provides an ideal benchmark to understand how mechanical stress and failure impacts the flow properties of amorphous condensed matter. Furthermore, some SMS are viscoelastic, flowing like viscous liquids or deforming like a solid according to applied forces. Often SMS are fragile and local rearrangements trigger catastrophic macroscopic failure. Despite the importance of the topic little is known on the local creep dynamics before the occurrence of such catastrophic events. To study creep and failure at an atomic/molecular level and at time scales that are not easily accessible by experiments we chose to carry out microscopic simulations. In this work we present the response of a colloidal system to uniaxial tensile stress applied and we compare our results to experimental works [8].

  14. Thermal creep model for CWSR zircaloy-4 cladding taking into account the annealing of the irradiation hardening

    SciTech Connect

    Cappelaere, Chantal; Limon, Roger; Duguay, Chrstelle; Pinte, Gerard; Le Breton, Michel; Bouffioux, Pol; Chabretou, Valerie; Miquet, Alain

    2012-02-15

    After irradiation and cooling in a pool, spent nuclear fuel assemblies are either transported for wet storage to a devoted site or loaded in casks for dry storage. During dry transportation or at the beginning of dry storage, the cladding is expected to be submitted to creep deformation under the hoop stress induced by the internal pressure of the fuel rod. The thermal creep is a potential mechanism that might lead to cladding failure. A new creep model was developed, based on a database of creep tests on as-received and irradiated cold-worked stress-relieved Zircaloy-4 cladding in a wide range of temperatures (310 degrees C to 470 degrees C) and hoop stress (80 to 260 MPa). Based on three laws-a flow law, a strain-hardening recovery law, and an annealing of irradiation hardening law this model allows the simulation of not only the transient creep and the steady-state creep, but also the early creep acceleration observed on irradiated samples tested in severe conditions, which was not taken into account in the previous models. The extrapolation of the creep model in the conditions of very long-term creep tests is reassuring, proving the robustness of the chosen formalism. The creep model has been assessed in progressively decreasing stress conditions, more representative of a transport. Set up to predict the cladding creep behavior under variable temperature and stress conditions, this model can easily be implemented into codes in order to simulate the thermomechanical behavior of spent fuel rods in various scenarios of postirradiation phases. (authors)

  15. Advances in Shell Buckling: Theory and Experiments

    NASA Astrophysics Data System (ADS)

    Thompson, J. Michael T.

    In a recent feature article in this journal, coauthored by Gert van der Heijden, I described the static-dynamic analogy and its role in understanding the localized post-buckling of shell-like structures, looking exclusively at integrable systems. We showed the true significance of the Maxwell energy criterion load in predicting the sudden onset of "shock sensitivity" to lateral disturbances. The present paper extends the survey to cover nonintegrable systems, such as thin compressed shells. These exhibit spatial chaos, generating a multiplicity of localized paths (and escape routes) with complex snaking and laddering phenomena. The final theoretical contribution shows how these concepts relate to the response and energy barriers of an axially compressed cylindrical shell. After surveying NASA's current shell-testing programme, a new nondestructive technique is proposed to estimate the "shock sensitivity" of a laboratory specimen that is in a compressed metastable state before buckling. A probe is used to measure the nonlinear load-deflection characteristic under a rigidly applied lateral displacement. Sensing the passive resisting force, it can be plotted in real time against the displacement, displaying an equilibrium path along which the force rises to a maximum and then decreases to zero: having reached the free state of the shell that forms a mountain-pass in the potential energy. The area under this graph gives the energy barrier against lateral shocks. The test is repeated at different levels of the overall compression. If a symmetry-breaking bifurcation is encountered on the path, computer simulations show how this can be suppressed by a controlled secondary probe tuned to deliver zero force on the shell.

  16. Buckling analysis of curved composite sandwich panels subjected to inplane loadings

    NASA Technical Reports Server (NTRS)

    Cruz, Juan R.

    1993-01-01

    Composite sandwich structures are being considered for primary structure in aircraft such as subsonic and high speed civil transports. The response of sandwich structures must be understood and predictable to use such structures effectively. Buckling is one of the most important response mechanisms of sandwich structures. A simple buckling analysis is derived for sandwich structures. This analysis is limited to flat, rectangular sandwich panels loaded by uniaxial compression (N(sub x)) and having simply supported edges. In most aerospace applications, however, the structure's geometry, boundary conditions, and loading are usually very complex. Thus, a general capability for analyzing the buckling behavior of sandwich structures is needed. The present paper describes and evaluates an improved buckling analysis for cylindrically curved composite sandwich panels. This analysis includes orthotropic facesheets and first-order transverse shearing effects. Both simple support and clamped boundary conditions are also included in the analysis. The panels can be subjected to linearly varying normal loads N(sub x) and N(sub y) in addition to a constant shear load N(sub xy). The analysis is based on the modified Donnell's equations for shallow shells. The governing equations are solved by direct application of Galerkin's method. The accuracy of the present analysis is verified by comparing results with those obtained from finite element analysis for a variety of geometries, loads, and boundary conditions. The limitations of the present analysis are investigated, in particular those related to the shallow shell assumptions in the governing equations. Finally, the computational efficiency of the present analysis is considered.

  17. Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

    SciTech Connect

    Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya

    2014-10-30

    The research built upon a prior investigation to develop a unified constitutive model for design-­by-­analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-­fatigue and creep-­ratcheting tests were conducted on the nickel-­base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-­controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-­fatigue and creep-­ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-­fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-­ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched

  18. Postseismic relaxation and transient creep

    USGS Publications Warehouse

    Savage, J.C.; Svarc, J.L.; Yu, S.-B.

    2005-01-01

    Postseismic deformation has been observed in the epicentral area following the 1992 Landers (M = 7.3), 1999 Chi-Chi (M = 7.6), 1999 Hector Mine (M = 7.1), 2002 Denali (M = 7.9), 2003 San Simeon (M = 6.5), and 2004 Parkfield (M = 6.0) earthquakes. The observations consist of repeated GPS measurements of the position of one monument relative to another (separation ???100 km). The early observations (t < 0.1 year) are well fit by the function a' + c'log(t), where t is the time after the earthquake and a' and c' are constants chosen to fit the data. Because a log(t) time dependence is characteristic of transient (primary) creep, the early postseismic response may be governed by transient creep as Benioff proposed in 1951. That inference is provisional as the stress conditions prevailing in postseismic relaxation are not identical to the constant stress condition in creep experiments. The observed logarithmic time dependence includes no characteristic time that might aid in identifying the micromechanical cause.

  19. Cumulative creep damage for polycarbonate and polysulfone

    NASA Technical Reports Server (NTRS)

    Zhang, M.; Brinson, H. F.

    1985-01-01

    The literature for creep to failure cumulative damage laws are reviewed. Creep to failure tests performed on polycarbonate and polysulfone under single and two step loadings are discussed. A cumulative damage law or modified time fraction rule is developed using a power law for transient creep response as the starting point. Experimental results are approximated well by the new rule. Damage and failure mechanisms associated with the two materials are suggested.

  20. Interface Evolution During Transient Pressure Solution Creep

    NASA Astrophysics Data System (ADS)

    Dysthe, D. K.; Podladchikov, Y. Y.; Renard, F.; Jamtveit, B.; Feder, J.

    When aggregates of small grains are pressed together in the presence of small amounts of solvent the aggregate compacts and the grains tend to stick together. This hap- pens to salt and sugar in humid air, and to sediments when buried in the Earths crust. Stress concentration at the grain contacts cause local dissolution, diffusion of the dissolved material out of the interface and deposition on the less stressed faces of the grains{1}. This process, in geology known as pressure solution, plays a cen- tral role during compaction of sedimentary basins{1,2}, during tectonic deformation of the Earth's crust{3}, and in strengthening of active fault gouges following earth- quakes{4,5}. Experimental data on pressure solution has so far not been sufficiently accurate to understand the transient processes at the grain scale. Here we present ex- perimental evidence that pressure solution creep does not establish a steady state inter- face microstructure as previously thought. Conversely, cumulative creep strain and the characteristic size of interface microstructures grow as the cubic root of time. A sim- ilar transient phenomenon is known in metallurgy (Andrade creep) and is explained here using an analogy with spinodal dewetting. 1 Weyl, P. K., Pressure solution and the force of crystallization - a phenomenological theory. J. Geophys. Res., 64, 2001-2025 (1959). 2 Heald, M. T., Cementation of Simpson and St. Peter Sandstones in parts of Okla- homa, Arkansas and Missouri, J. Geol. Chicago, 14, 16-30 (1956). 3 Schwartz, S., Stöckert, B., Pressure solution in siliciclastic HP-LT metamorphic rocks constraints on the state of stress in deep levels of accretionary complexes. Tectonophysics, 255, 203-209 (1996). 4 Renard, F., Gratier, J.P., Jamtveit, B., Kinetics of crack-sealing, intergranular pres- sure solution, and compaction around active faults. J. Struct. Geol., 22, 1395-1407, (2000). 5 Miller, S. A., BenZion, Y., Burg, J. P.,A three-dimensional fluid-controlled earth