The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
M Mclean - One of the best experts on this subject based on the ideXlab platform.
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tension Compression Creep asymmetry in a turbine disc superalloy roles of internal stress and thermal ageing
Acta Materialia, 2004Co-Authors: S K Sondhi, B F Dyson, M McleanAbstract:Abstract The tension and Compression Creep behaviour of an as-received and pre-aged IN100 disc alloy have been characterised in order to validate a previous hypothesis that the unusual response of low and even negative initial Creep rates in tension was caused by the presence of an internal stress field within the alloy. Absolute values of initial Creep rates in Compression were found to be much greater than in tension and this asymmetric Creep response is conclusive proof of the presence of an internal compressive stress field in the alloy matrix. The asymmetry was virtually removed by pre-ageing prior to Creep and this is attributed to the decay of the internal stress. These features have been simulated using a microstructure-based Creep model incorporating an evolving internal stress field. The model also simulates the additional (and complicating) reduction in general Creep strength that is thought to be due to coarsening and dissolution of the smallest particles of the tri-modal γ ′ distribution in the alloy. The net consequence of these two competing thermal processes is that the short-term Creep response is dominated by the initial magnitude of the internal stress field whereas coarsening and dissolution of the smallest γ ′ particles determines the long-term behaviour.
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Tension–Compression Creep asymmetry in a turbine disc superalloy: roles of internal stress and thermal ageing
Acta Materialia, 2004Co-Authors: S K Sondhi, B F Dyson, M McleanAbstract:Abstract The tension and Compression Creep behaviour of an as-received and pre-aged IN100 disc alloy have been characterised in order to validate a previous hypothesis that the unusual response of low and even negative initial Creep rates in tension was caused by the presence of an internal stress field within the alloy. Absolute values of initial Creep rates in Compression were found to be much greater than in tension and this asymmetric Creep response is conclusive proof of the presence of an internal compressive stress field in the alloy matrix. The asymmetry was virtually removed by pre-ageing prior to Creep and this is attributed to the decay of the internal stress. These features have been simulated using a microstructure-based Creep model incorporating an evolving internal stress field. The model also simulates the additional (and complicating) reduction in general Creep strength that is thought to be due to coarsening and dissolution of the smallest particles of the tri-modal γ ′ distribution in the alloy. The net consequence of these two competing thermal processes is that the short-term Creep response is dominated by the initial magnitude of the internal stress field whereas coarsening and dissolution of the smallest γ ′ particles determines the long-term behaviour.
John J Lesko - One of the best experts on this subject based on the ideXlab platform.
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Mechanistic Approach to Structural Fire Modeling of Composites
Fire Technology, 2011Co-Authors: Steven E Boyd, Scott W Case, John V. Bausano, John J LeskoAbstract:In this paper, a framework is presented for the modeling of the response of structural composites subjected to combined mechanical loading and fire. An emphasis is placed on the response of composites at temperatures below the decomposition temperature, where the viscoelastic response of the composite material becomes important. Material property characterization results are presented for an E-glass reinforced vinyl ester composite typical of that used for naval ship applications. Time-temperature equivalence is used in a Compression strength model to predict the time to failure of composites subjected to isothermal Compression loading (Compression Creep rupture failure). These predictions are compared with experimentally determined times to failure with good agreement. In particular, shift factors obtained from shear compliance testing are able to collapse the Compression Creep rupture data at different temperatures, indicating that viscolelasticity is the dominant mechanism driving the failure. This model is combined with a standard diffusion model for heat transfer in the composite to predict the time-dependent failure of composites subjected to simultaneous one-sided heat flux and Compression loading. Predicted times to failure are compared with experimental results with good agreement.
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Compression Creep rupture behavior of a glass vinyl ester composite subject to isothermal and one sided heat flux conditions
Composites Part A-applied Science and Manufacturing, 2007Co-Authors: Steven E Boyd, Scott W Case, John J LeskoAbstract:Given the expanding applications of polymer matrix composites to civil infrastructure, the marine industry, and the military, we examine the Compression Creep rupture behavior of a glass/vinyl ester composite subject to combined load and one sided heating simulating fire exposure. We focus on reversible non-linear viscoelastic effects which dominate delayed failure at lower temperatures in the vicinity of the glass transition temperature. A Compression strength model which predicts local Compression failure due to micro-buckling is extended to include viscoelasticity. Times to failure under combined mechanical load and one sided heating are estimated to within an order of magnitude.
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Compression Creep rupture behavior of a glass/vinyl ester composite subject to isothermal and one-sided heat flux conditions
Composites Part A-applied Science and Manufacturing, 2007Co-Authors: Steven E Boyd, Scott W Case, John J LeskoAbstract:Given the expanding applications of polymer matrix composites to civil infrastructure, the marine industry, and the military, we examine the Compression Creep rupture behavior of a glass/vinyl ester composite subject to combined load and one sided heating simulating fire exposure. We focus on reversible non-linear viscoelastic effects which dominate delayed failure at lower temperatures in the vicinity of the glass transition temperature. A Compression strength model which predicts local Compression failure due to micro-buckling is extended to include viscoelasticity. Times to failure under combined mechanical load and one sided heating are estimated to within an order of magnitude.
S K Sondhi - One of the best experts on this subject based on the ideXlab platform.
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tension Compression Creep asymmetry in a turbine disc superalloy roles of internal stress and thermal ageing
Acta Materialia, 2004Co-Authors: S K Sondhi, B F Dyson, M McleanAbstract:Abstract The tension and Compression Creep behaviour of an as-received and pre-aged IN100 disc alloy have been characterised in order to validate a previous hypothesis that the unusual response of low and even negative initial Creep rates in tension was caused by the presence of an internal stress field within the alloy. Absolute values of initial Creep rates in Compression were found to be much greater than in tension and this asymmetric Creep response is conclusive proof of the presence of an internal compressive stress field in the alloy matrix. The asymmetry was virtually removed by pre-ageing prior to Creep and this is attributed to the decay of the internal stress. These features have been simulated using a microstructure-based Creep model incorporating an evolving internal stress field. The model also simulates the additional (and complicating) reduction in general Creep strength that is thought to be due to coarsening and dissolution of the smallest particles of the tri-modal γ ′ distribution in the alloy. The net consequence of these two competing thermal processes is that the short-term Creep response is dominated by the initial magnitude of the internal stress field whereas coarsening and dissolution of the smallest γ ′ particles determines the long-term behaviour.
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Tension–Compression Creep asymmetry in a turbine disc superalloy: roles of internal stress and thermal ageing
Acta Materialia, 2004Co-Authors: S K Sondhi, B F Dyson, M McleanAbstract:Abstract The tension and Compression Creep behaviour of an as-received and pre-aged IN100 disc alloy have been characterised in order to validate a previous hypothesis that the unusual response of low and even negative initial Creep rates in tension was caused by the presence of an internal stress field within the alloy. Absolute values of initial Creep rates in Compression were found to be much greater than in tension and this asymmetric Creep response is conclusive proof of the presence of an internal compressive stress field in the alloy matrix. The asymmetry was virtually removed by pre-ageing prior to Creep and this is attributed to the decay of the internal stress. These features have been simulated using a microstructure-based Creep model incorporating an evolving internal stress field. The model also simulates the additional (and complicating) reduction in general Creep strength that is thought to be due to coarsening and dissolution of the smallest particles of the tri-modal γ ′ distribution in the alloy. The net consequence of these two competing thermal processes is that the short-term Creep response is dominated by the initial magnitude of the internal stress field whereas coarsening and dissolution of the smallest γ ′ particles determines the long-term behaviour.
Jerren Yang - One of the best experts on this subject based on the ideXlab platform.
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a unified constitutive model for asymmetric tension and Compression Creep ageing behaviour of naturally aged al cu li alloy
International Journal of Plasticity, 2017Co-Authors: Yong Li, Yolun Yang, Qi Rong, Boming Huang, Tsaifu Chung, Chengsi Tsao, Jerren Yang, Daniel S BalintAbstract:Abstract A set of unified constitutive equations is presented that predict the asymmetric tension and Compression Creep behaviour and recently observed double primary Creep of pre-stretched/naturally aged aluminium-cooper-lithium alloy AA2050-T34. The evolution of the primary micro- and macro-variables related to the precipitation hardening and Creep deformation of the alloy during Creep age forming (CAF) are analysed and modelled. Equations for the yield strength evolution of the alloy, including an initial reversion and subsequent strengthening, are proposed based on a theory of concurrent dissolution, re-nucleation and growth of precipitates during artificial ageing. We present new observations of so-called double primary Creep during the CAF process. This phenomenon is then predicted by introducing effects of interacting microstructures, including evolving precipitates, diffusing solutes and dislocations, into the sinh-law Creep model. In addition, concepts of threshold Creep stress σ t h and a microstructure-dependant Creep variable H, which behave differently under different external stress directions, are proposed and incorporated into the Creep model. This enables prediction of the asymmetric tension and Compression Creep-ageing behaviour of the alloy. Quantitative transmission electron microscopy (TEM) and related small-angle X-ray scattering (SAXS) analysis have been carried out for selected Creep-aged samples to assist the development and calibration of the constitutive model. A good agreement has been achieved between the experimental results and the model. The model has the potential to be applied to Creep age forming of other heat-treatable aluminium alloys.
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experimental investigation of tension and Compression Creep ageing behaviour of aa2050 with different initial tempers
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: Yong Li, Yolun Yang, Boming Huang, Tsaifu Chung, Jerren YangAbstract:Abstract Creep-ageing behaviour of aluminium alloy 2050 with different initial tempers (T34, T84 and as-quenched) has been experimentally investigated under both tension and Compression Creep-ageing conditions, with different stress levels at 155 °C for 18 h. Corresponding strengthening phenomena have been studied by interrupted Creep-ageing tests and subsequent tensile tests. Moreover, the microstructures of some selected specimens after Creep-ageing tests have been examined by transmission electron microscopy (TEM) and the precipitation process has been analysed. It has been found that Creep strains under tensile stresses are much larger than those under compressive stresses during the tests. A new “double primary Creep feature” has been observed in both the as-quenched alloys and the pre-stretched/natural-aged (T34) alloys, in which an intermediate inverse Creep stage with an increasing Creep strain rate locates between the initial primary+transient steady-state Creep stages and the second primary+second steady-state Creep stages. While for the alloy with peak-aged initial temper (T84), typical primary and steady-state secondary Creep stages are observed during tension Creep-ageing tests and little Creep strain occurs under compressive stresses of 150 and 175 MPa. The mechanisms for these phenomena are discussed in terms of microstructural interactions among the changing dislocations, solute-matrix bonding and precipitates, and their effects on the Creep resistance of the alloy during Creep-ageing tests are analysed.
Steven E Boyd - One of the best experts on this subject based on the ideXlab platform.
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Mechanistic Approach to Structural Fire Modeling of Composites
Fire Technology, 2011Co-Authors: Steven E Boyd, Scott W Case, John V. Bausano, John J LeskoAbstract:In this paper, a framework is presented for the modeling of the response of structural composites subjected to combined mechanical loading and fire. An emphasis is placed on the response of composites at temperatures below the decomposition temperature, where the viscoelastic response of the composite material becomes important. Material property characterization results are presented for an E-glass reinforced vinyl ester composite typical of that used for naval ship applications. Time-temperature equivalence is used in a Compression strength model to predict the time to failure of composites subjected to isothermal Compression loading (Compression Creep rupture failure). These predictions are compared with experimentally determined times to failure with good agreement. In particular, shift factors obtained from shear compliance testing are able to collapse the Compression Creep rupture data at different temperatures, indicating that viscolelasticity is the dominant mechanism driving the failure. This model is combined with a standard diffusion model for heat transfer in the composite to predict the time-dependent failure of composites subjected to simultaneous one-sided heat flux and Compression loading. Predicted times to failure are compared with experimental results with good agreement.
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Compression Creep rupture behavior of a glass vinyl ester composite subject to isothermal and one sided heat flux conditions
Composites Part A-applied Science and Manufacturing, 2007Co-Authors: Steven E Boyd, Scott W Case, John J LeskoAbstract:Given the expanding applications of polymer matrix composites to civil infrastructure, the marine industry, and the military, we examine the Compression Creep rupture behavior of a glass/vinyl ester composite subject to combined load and one sided heating simulating fire exposure. We focus on reversible non-linear viscoelastic effects which dominate delayed failure at lower temperatures in the vicinity of the glass transition temperature. A Compression strength model which predicts local Compression failure due to micro-buckling is extended to include viscoelasticity. Times to failure under combined mechanical load and one sided heating are estimated to within an order of magnitude.
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Compression Creep rupture behavior of a glass/vinyl ester composite subject to isothermal and one-sided heat flux conditions
Composites Part A-applied Science and Manufacturing, 2007Co-Authors: Steven E Boyd, Scott W Case, John J LeskoAbstract:Given the expanding applications of polymer matrix composites to civil infrastructure, the marine industry, and the military, we examine the Compression Creep rupture behavior of a glass/vinyl ester composite subject to combined load and one sided heating simulating fire exposure. We focus on reversible non-linear viscoelastic effects which dominate delayed failure at lower temperatures in the vicinity of the glass transition temperature. A Compression strength model which predicts local Compression failure due to micro-buckling is extended to include viscoelasticity. Times to failure under combined mechanical load and one sided heating are estimated to within an order of magnitude.