Simulated data for high temperature composite design

The Probability simulation of materials property degradation on the constituent level is performed by integrating finite element method, composite laminate theory, composite micromechanics, and probability theory. A multifactor interaction model (MFIM) subjected to various random effects and their mutual interactions is implemented, and the degradation of material properties of fiber, matrix, and interface is evaluated. In order to account for the statistical nature in MFIM, appropriate types of probability distribution functions (such as normal, log normal, and Weibull) are considered for primary variables. Two numerical examples are presented for probability distribution of constituent property degradation and fatigue behavior simulation of composites. It is shown that the results are in excellent agreement with the experimental results. achieved. The uncertainties of the processing and service parameters, such as thermal and

The creep resistance of martensitic power plant steels depends strongly on the dispersion of various types of precipitates in the microstructure. Reliable prediction of rupture strength of such alloys thus demands accurate description of the microstructure evolution during service. A material model that calculates the simultaneous precipitation kinetics and hardening in these steels has been reported previously. The creep rupture model reported here is a natural extension of the previous research. This model has been validated against experimental creep rupture data of wide-used 9–12% Cr steels. It allows the effect of variation in alloy conditions, such as composition and heat treatments, on rupture strength to be quantitatively evaluated for a given alloy grade. Results show that such variations can lead to significant differences in the calculated rupture strength, which are believed to be largely responsible for the wide scatter in the experimental data.

As an aim toward developing novel class of form‐stable polymer‐matrix phase change materials for thermal energy storage, ultrafine composite fibers based on cellulose acetate and polyethylene glycol (PEG) with five different molecular weight (Mn) grades were prepared by electrospinning. The effects of Mn of PEG on morphology, thermal properties and mechanical properties of the composite fibers were studied by field emission scanning electron microscopy, differential scanning calorimetry, and tensile testing, respectively. It was found that the composite fibers were smooth and cylindrical shape, with the average diameters ranging from about 1000 to 1750 nm which increased with Mn of PEG. Thermal analysis results showed that the composite fibers imparted balanced thermal storage and release properties in different temperature ranges with the variation of Mn of PEG. Thermal cycling test indicated that the prepared composites had excellent thermal stability and reliability even they were subjected to 100 heating‐cooling thermal cycles. © 2009 American Institute of Chemical Engineers AIChE J, 2009

In this study, the tensile behavior of TiNi super elastic alloy under various hydrogen environments was investigated by using thin wires with various diameters. Ductility and tensile strength of TiNi super elastic alloy which absorbed hydrogen decreased. At the same charging time, tensile strength decreased with decreasing wire diameter. Compared TiNi super elastic alloy with TiNi shape memory alloy, tensile strength of TiNi super elastic alloy is higher than that of TiNi shape memory alloy in spite of hydrogen charging times. However, there is little difference in growth behavior of brittle layer formed by hydrogen charging between TiNi super elastic alloy and TiNi shape memory alloy.

A new family of glasses derived from hafnium fluoride (HfF4), barium fluoride (BaF2), and various rare earth fluorides has been studied. The spectral and thermal properties are given, as well as hardness, rupture strength, and coefficients of expansion. Reactive atmosphere processing (RAP) of the individual components and the molten glass with anhydrous CF4, BF3, HF and CC14 are described. RAP eliminates anionic impurities such as 0H- and 0= which enter the condensed phase through hydrolysis during the melting and mixing stages of preparation. Elimination of these impurities through RAP maximizes IR transparency and mechanical strength. The glasses are resistant to room temperature hydrolysis, are hard and strong, and are continuously transparent from 0.2 μm to 9 μm.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The effects of large additions of Sb, P, and Sn on the creep properties of cast as well as forged 1·25Cr–0·5Mo steels at 538°C were investigated. Results show that the addition of impurity elements did not modify the creep and rupture strengths or the rupture ductility of the steels. Analysis of the present results in the light of other reported results in the literature shows that a systematic investigation of several other variables, such as the alloy system, microstructure, strength level, and test temperature is needed before a unified picture can emerge concerning the role of impurities as they affect the creep properties of ferritic steels.

Thermal and microstructural properties of paraffin/diatomite composite

<abstract> <p>We propose an asymptotic concentration approach combined with isogeometric analysis (IGA) for the topology optimization of two-dimensional (2D) linear elasticity structures under the commonly-used framework of the solid isotropic materials and penalty (SIMP) model. Based on the SIMP framework, the B-splines are used as basis functions to describe geometric model in structural finite element analysis, which closely combines geometric modeling with structural analysis. Isogeometric analysis is utilized to define the geometric characteristics of the 2D linear elasticity structures, which can greatly improve the calculation accuracy. In addition, to eliminate the gray-scale intervals usually caused by the intermediate density in the SIMP approach, we utilize the asymptotic concentration method to concentrate the intermediate density values on either 0 or 1 gradually. Consequently, the intermediate densities representing gray-scale intervals in topology optimization results are sufficiently eliminated by virtue of the asymptotic concentration method. The effectiveness and applicability of the proposed method are illustrated by several typical examples.</p> </abstract>

Thermal protection system (TPS) is one of the most important subsystems for vehicle reentry. Because of the uncertainties in thermal loads, material properties, and manufacture tolerances, the thermal response of TPS has strong randomness, which brings great challenges to the engineering design and reliability evaluation. Because the uncertain aerodynamic heating loads are stochastic processes in time history, it is difficult to model them in the conventional surrogate models that usually take scalar random variables as input. This paper thus proposes an effective characterization method that can represent the uncertainties of aerodynamic heating by a set of random variables using Karhunen–Loève expansion. The random variables that describe the uncertainty of thermal loads, material properties, and geometric thickness are taken as inputs for probabilistic analyses. A kriging surrogate model is constructed to solve the transient heat conduction with high accuracy. Taking a typical multilayer TPS as an example, the probabilistic thermal analyses are carried out considering different degrees of heat rate uncertainties. The results show that the uncertainties of aerodynamic heating intensify the randomness of the thermal response of TPS, and thus have a great impact on the thermal reliability. The sensitivities of temperature response to various uncertain parameters are investigated as well, which provide a reference for system design and reliability improvement.

The presence of end-to-end connectors for lengthening the glass fiber reinforced polymer (GFRP) pipes in elastic gridshell causes imperfections in the structure. Such geometrical imperfections alter the structural properties of members and affect the overall performance of the structure. Hence, for a comprehensive analysis of such structures, the aforementioned imperfections need to be acknowledged. In this study, an equivalent rigid part (ERP) for the connector was proposed for taking into account the effect of connectors in the structural analysis. The applicability of ERP for predicting the deformation of structural members was first verified by bending beam models. A typical GFRP elastic gridshell was further utilized for investigating the effects of connectors (with two different arrangement) in the shape and stress of the structure. Results show that proposed ERP is practicable for simplifying the end-to-end connectors in the structural analysis model. Significant differences in results were found between the analysis with and without the consideration of end-to-end connectors, and therefore the effect of connectors should be considered during structural analysis of elastic gridshell.

To study the capacity of reactor containment under pressurization, it is important to know the way that this structure reacts under internal pressure loading. This is usually performed through structural fragility analysis for assuring that the containment structure has high capability of withstanding the loads associated with severe accident phenomena and its consequent pressurization, therefore the potential for significant radioactive release is small. In this paper, the methodology of structural fragility analysis for pressurization is thoroughly reviewed, and its practical application is demonstrated on a real case Pressurized Water Reactor containment. The reactor containment is analyzed using finite element method, and the ultimate pressure is computed. Containment performance is further analyzed using the structural fragility method. The structural fragility serves as the interface between the structural analysis model and the risk model of the systems. Therefore, a probabilistic scheme is used to represent the structural fragility. Final outcome of this study is the overpressure fragility curve which depicts the probability of failure of the containment at a given value of pressure. This curve is a key element in conducting probabilistic safety assessment (level 2 PSA) of nuclear power plants.

The present paper shows how loading path affects the low cyclic fatigue failure of a glass fabric/vinylester resin composite. The focus is placed on the stress-strain response both in tension and shear as well as on the fatigue life under tension/torsion biaxial loading at low cycle fatigue up to 10,000 cycles. Three types of loading paths were applied: Type I-Biaxial loads were applied proportionally to the specimens. Namely the resultant stresses, tensile and shear stresses increased simultaneously. Type II-A tensile load was first applied. Then, a torsion moment was applied to attain a (biaxial stress ratio) = 3/1 while the tensile load was kept constant. The applied loads were removed in the reverse order. Type Il I-Contrary to Type II loading, first a torsion moment was applied. Then, a tensile load was applied to attain a L = 3/1 while the torsional moment was kept constant. The maximum stress states in the laminate during each loading period are the same for all loading cases. The experimental results revealed that: (1) No significant effect of loading path on the fatigue life exists. (2) The modulus decay in shear with respect to the number of loading cycles is affected by loading path while the modulus decay in tension was not significantly affected. (3) There exist peculiar responses in stress-strain relations both in tension and shear when loading path is changed although the final strain state is almost the same in all loading cases as long as the internal damage is not much accumulated. A model for explaining the peculiar stress-strain behaviors was proposed based on the Continuum Damage Mechanics (CDM) in conjunction with the lamination theory. The calculated stress-strain responses reasonably agree with the experimental stress-strain behaviors under biaxial loadings having different loading paths.

Chemical treatment of sisal fiber using alkali and clay method

Mixed oxides (MOX) of uranium, plutonium, and neptunium are proposed as fast-reactor fuels with the aim to transmute long-lived neptunium into shorter-lived, less radioactive products. The use of molecular dynamics (MD) simulations to accurately predict high-temperature thermophysical properties, essential for fuel design, performance modelling, and safety assessment, requires the availability of suitable interatomic potentials of the component oxides. Although the Cooper-Rushton-Grimes (CRG) potential for NpO2 exists, it cannot predict the melting temperature and other high-temperature thermophysical properties of NpO2 accurately. In the present work, a new interatomic potential for NpO2 is developed by re-optimizing the CRG potential, with the target of accurate prediction of the melting temperature (MT). The re-optimized potential predicts the MT (3025 ± 50 K) of NpO2 in good agreement with the experimental result (3070 ± 62 K), representing a significant improvement over the predicted value (3550 ± 50 K) in this work using the CRG potential, without significantly affecting the other characteristics of the material at lower temperatures. Other thermal properties, such as thermal expansion coefficients (α), enthalpy increments, and specific heats (Cp) of U1-yNpyO2 and Pu1-yNpyO2 (for 0 < y < 0.5) systems computed from MD simulations using the re-optimized potential across temperatures up to MT, show excellent agreement with experimental results, wherever available. The calculated data for the α and Cp of U1-yNpyO2 and Pu1-yNpyO2 (for 0 < y < 0.5) are fitted to the Bathellier equation, enabling the prediction of high temperature fuel behaviour in regimes where experimental measurements are lacking. Additionally, the influence of hyper/hypostoichiometry, prevalent in high-temperature MOX fuels, on the thermal properties is also investigated, providing information highly relevant to reactor operations.

The aim of this work is to investigate the effects of rubberwood sawdust (RWS) size and content as well as the ratio of natural rubber (NR)/high-density polyethylene (HDPE) blend on properties of RWS reinforced thermoplastic natural rubber (TPNR) composites. The addition of RWS about 30–50 wt% improved the modulus of the rupture and tensile strength of TPNR composites blending with NR/HDPE ratios of 60/40 and 50/50. TPNR composites reinforced with RWS 80 mesh yielded better tensile strength and modulus of rupture than the composites with RWS 40 mesh. The TPNR/RWS composites with larger HDPE content gave higher tensile, flexural, and Shore hardness properties and thermal stability as well as lower water absorption. The TPNR/RWS composites with larger plastic content were therefore suggested for applications requiring high performance of thermal, physical, and mechanical properties.