Modeling the Tensile Strength of Carbon Fiber − Reinforced Ceramic − Matrix Composites Under Multiple Fatigue Loading

An analytical method has been developed to investigate the effect of interface wear on the tensile strength of carbon fiber ? reinforced ceramic ? matrix composites (CMCs) under multiple fatigue loading. The Budiansky ? Hutchinson ? Evans shear ? lag model was used to describe the micro stress field of the damaged composite considering fibers failure and the difference existed in the new and original interface debonded region. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. The interface shear stress degradation model and fibers strength degradation model have been adopted to analyze the interface wear effect on the tensile strength of the composite subjected to multiple fatigue loading. Under tensile loading, the fibers failure probabilities were determined by combining the interface wear model and fibers failure model based on the assumption that the fiber strength is subjected to two ? parameter Weibull distribution and the loads carried by broken and intact fibers satisfy the Global Load Sharing criterion. The composite can no longer support the applied load when the total loads supported by broken and intact fibers approach its maximum value. The conditions of a single matrix crack and matrix multicrackings for tensile strength corresponding to multiple fatigue peak stress levels and different cycle number have been analyzed.     

High-Entrapment Liposomes for 6-Mercaptopurine—A Prodrug Approach

Low entrapment of drugs into liposomes is a serious challenge in their commercial application. 6-Mercaptopurine (6-MP), an antineoplastic agent, is such a drug with low entrapment efficiency (EE). We devised their lipophilic derivatization as a means of enhancing EE by covalently coupling 6-MP with glyceryl monostearate (GMS) via a succinic anhydride spacer. This prodrug had an improved partition coefficient value of 25.16 compared to 1.22 for free drug, confirming higher lipophilicity. A hydrolysis rate study of prodrug indicated 2.90%, 12.5%, 24.1%, and 25.1% hydrolysis in phosphate buffered saline (PBS) (pH 7.4) and 10%, 20%, and 30% serum, respectively. Liposomes of phosphatidylcholine (PC)/sphingomyelin, cholesterol, and dicetyl phosphate bearing drug or prodrug were prepared by shaking by hand and sonication methods. The EE was found to increase from 1.92% for free drug to 91.8% for drug-conjugate. An in vitro cell line toxicity study on L1210 leukemia cells showed improved performance of liposome-encapsulated drug-conjugate compared to free drug. The plasma drug level profile following administration of free drug and the liposomal formulation containing prodrug (HE liposome) manifested a higher sustained level of the latter, which was further improved in case of sphingomyelin-containing liposomes (STHE liposome). The pharmacokinetic parameters revealed an increase in half-life, from 61 min to 120 min for the HE liposomes and 296 min for the STHE liposomes. Therefore, increased entrapment was made possible through lipophilic derivatization, and it was subsequently tested in vivo.     

A Step-by-Step Approach to Using the SAS™ System for Factor Analysis and Structural Equation Modeling

Radiation detection systems are deployed at U.S. borders to guard against entry of illicit radioactive material. This article uses realistic simulated data under different vehicle and illicit material scenarios to compare the performance of six detection methods for analyzing neutron count data collected as a vehicle passes through a radiation portal monitor, that is, a neutron count vehicle profile. The six methods are based on the cumulative count, the maximum count, sequential cumulative sum, sequential exponentially weighted moving average, comparison against a matched filter (MF) library, and a new estimated MF that estimates the shape of a neutron count vehicle profile.     

An Efficient SQUID NDE Defect Detection Approach by?Using?an?Adaptive?Finite-Element?Modeling

Incorporating the finite-element method for the modeling of the SQUID NDE response to a predefined defect pattern, an adaptive algorithm has been developed for the reconstruction of unknown defects using an optimization algorithm for updating of the forward problem. The defect reconstruction algorithm starts with an initial estimation for the defect pattern. Then the forward problem is solved and the obtained field pattern is compared with the measured signal from the SQUID NDE system. The result is used by an optimization algorithm to update the defect structure to be incorporated in the FEM forward problem for the next iteration. Since the mentioned model based inverse algorithm normally consumes a lot of computational resources, the number of iterations plays an important role in the determination of the total response convergence time. Consequently, different optimization algorithms have been applied and their performances are compared. In this work by incorporating an efficient forward model and using the stochastic and deterministic optimization algorithms for defect updating we have investigated their performance on the inversion of the SQUID NDE signal and also their ability to defect reconstruction in the noisy environment.     

Modeling of an ammonia–water absorption heat pump water heater for residential applications

An investigation of a direct gas-fired single-effect ammonia–water absorption heat pump water heater for residential applications is presented. Combustion of natural gas provides heat to the desorber where refrigerant is generated. The absorber and condenser are hydronically coupled in parallel to a hot water storage tank, while the evaporator is hydronically coupled to an ambient air heat exchanger that extracts ambient heat. A thermodynamic model is developed and the system configuration is optimized to provide a baseline heating capacity of 2.79 kW at a coefficient of performance of 1.74. A detailed parametric study over a range of water and ambient temperatures is used to understand the variation in system performance as the water is heated from 14.5 to a minimum of 57.0 °C. The performance of the heat pump coupled to a 227-liter storage tank is also modeled for three different scenarios, a cold start response to a 76-liter draw, and response to stand-by losses. The absorption heat pump water heater is found to achieve coefficients of performance better than those of commercially available gas fired heaters and electric heat pump units.     

Ultrasonic spot welding of aluminium to steel for automotive applications—microstructure and optimisation

Energy efficient methods for joining aluminium to steel have potential for major applications in the automobile industry. Results are reported where 1 mm gauge 6111 aluminium and DC04 steel automotive sheet have been successfully joined using the novel process of high power ultrasonic spot welding. The microstructure and performance of the joints were examined, as a function of the welding conditions. A maximum failure load of 2·8 kN was obtained in lap shear tests, compared with 2·9 kN for comparable AI-AI joints. The failure mode changed from interfacial debonding to nugget pullout and back to interfacial failure as the weld energy increased. A thin <2 μm reaction layer of FeAI₃ and Fe₂Al₅ formed at the interface with increasing weld energy. The factors determining the joint characteristics, interface reaction, and the microstructure evolution in the welds are discussed.     

Tailoring Sandwich Face/Core Interfaces for Improved Damage Tolerance—Part II: Experiments

Various modifications of the face/core interface in foam core sandwich specimens are examined in a series of two papers. This paper constitutes part I and describes the finite element analysis of a sandwich test specimen, i.e. a DCB specimen loaded by uneven bending moments (DCB-UBM). Using this test almost any mode-mixity between pure mode I and mode II can be obtained. A cohesive zone model of the mixed mode fracture process involving large-scale bridging is developed. Results from the analysis are used in Part II, which describes methods and results of a series of experiments.     

A Combined Convex Approximation—Interior Point Approach for Large Scale Nonlinear Programming

The method of moving asymptotes (MMA) and its globally convergent extension SCP (sequential convex programming) are known to work well in the context of structural optimization. The two main reasons are that the approximation scheme used for the objective function and the constraints fits very well to these applications and that at an iteration point a local optimization model is used such that additional expensive function and gradient evaluations of the original problem are avoided. The subproblems that occur in both methods are special nonlinear convex programs and have traditionally been solved using a dual approach. This is now replaced by an interior point approach. The latter one is more suitable for large problems because sparsity properties of the original problem can be preserved and the separability property of the approximation functions is exploited. The effectiveness of the new method is demonstrated by a few examples dealing with problems of structural optimization.     

Tailoring Sandwich Face/Core Interfaces for Improved Damage Tolerance—Part I: Finite Element Analysis

Various modifications of the face/core interface in foam core sandwich specimens are examined in a series of two papers. This paper constitutes part I and describes the finite element analysis of a sandwich test specimen, i.e. a DCB specimen loaded by uneven bending moments (DCB-UBM). Using this test almost any mode-mixity between pure mode I and mode II can be obtained. A cohesive zone model of the mixed mode fracture process involving large-scale bridging is developed. Results from the analysis are used in Part II, which describes methods and results of a series of experiments.     

Modeling Recrystallization of Austenite for C—Mn Steels during Hot Deformation by Cellular Automaton

By using a cellular automaton method,microstructure evolution of recrystallization in austenite during hot deformation was simulated for C-Mn steels.A model takes into account the influence of deformation temperature,strain,and strain rate on the dynamic recrystallization fraction,and the effect of the keeping time on the static recrystallization fraction based on a hot deformation test on a Gleeble-1500 simulator.In addition,the size changing of γgrains during continuous hot deformation was simulated by applying the model.     

Conditions for Formation of a Zero Temperature Coefficient of Resistance in Matrix Systems of Metal—Semiconductor

Using the method of finite elements, the authors have calculated the parameters of a heterophase metal—semiconductor system for which the minimum temperature coefficients of resistance (TCRs) are realized. The temperatureconcentration region in which the TCR acquires values approaching zero has been established.     

“Assessment of Metal Matrix Composites for Innovations” — intermediate report of a European Thematic Network

The Thematic Network “Assessment of Metal Matrix Composites for Innovations” (acronym MMC-ASSESS) is a consortium of 21 partners from industry, research organisations and universities involved in research, development and application of metal matrix composites (MMC). The general goal of the project is to increase market acceptance of MMC by collecting and evaluating information related to the engineering potential of these materials. The working groups of the network are referring to production, characterisation and properties as well as modelling and applications of MMC. These topics are considered as well specifically for the four categories of MMC: particulate, short fibre and whisker, continuous fibre, and monofilament reinforced metals. A web page has been established (http://mmc-assess.tuwien.ac.at/) as an ongoing dissemination activity. An intermediate report on the network's activities is presented, which started in October 1998 by funding of the European Commission for a 36 months period.     

Proof testing of ceramic materials—an analytical basis for failure prediction

An analysis is presented which permits the accurate prediction of component lifetimes after proof testing. The analysis applies to crack propagation controlled fracture but can be used as a conservative prediction when crack initiation is predominant. The analytical predictions are confirmed in a series of time-to-failure measurements.

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Zusammenfassung Man berichtet von einer Analyse die die genaue Voraussagung der Lebensdauer eines Keramikbestandteiles. nach den Abnahmeversuchen, ermöglicht. Die Analyse wird auf den durch Rißausdehnung kontrolierten Bruch angewandt, kann aber auch als eine konservative Voraussagung benützt werden im Fall wo die Rißeinleitung ausschlaggebend ist.Die analytische Voraussagung wurde durch eine Reihe von Zeit bis zum Bruch Messungen bestätigt.

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Résumé On présente une analyse permettant de prédire avec précision la durée de vie d'un composant céramique après épreuve de réception. L'analyse a trait aux ruptures dont la propagation des fissures est contrôlée, mais est utilisable en tant que prédiction conservative, dans le cas où l'amorçage de la fissure est la phase prédominante.Les prédictions analytiques se voient confirmées par des séries de mesures de durée de vie à rupture.

     

A matrix system for production management—a description and an application

This paper presents a morphological model of an integrated production management system. The model is designed as an intersecting point structure. The two dimensions in the model are the phases in a control cyclus and the objects of control. Each point in the structure represents an activity in the total production management system.

The model has proved successful as a tool for analysis and redesign of of production management systems. An example of the application of the model is given.     

Oxide single crystals for research and production—an adventure for producer and user or functional technique?

Oxide single crystals have been used during the last 100 years in very different industries. In the first 50 years the jewellery and watch industries were the main users of oxide single crystals like ruby, sapphire and spinel. At that time Europe was the main producer of oxide crystals. Production plants were in France, Switzerland and Germany. In the Second World War the aviation industry started to use these materials for instrumentation systems. This production was mainly in the USA, Russia and Germany. Today, the use of all kinds of oxide single crystals is well established within many industries. However, only a small range of crystals is used in very high quantities. These are crystals such as quartz, aluminium oxide, titanium dioxide, strontium titanate, lithium niobate and tantalate, BBO and garnets. The other crystal materials are widely developed at R&D centres and universities but not really in industrial production. Among the problems are the unstable market places and the rapid change in material specifications from OEM customers.     

Mesoscopic Modeling Approach and Application for Steel Fiber Reinforced Concrete under Dynamic Loading: A ReviewOA

Steel fiber reinforced concrete(SFRC) has drawn extensive attention in recent years for its superior mechanical response to dynamic and impact loadings. Based on the existing test results, the highstrength steel fibers embedded in a concrete matrix usually play a strong bridging effect to enhance the bonding force between fiber and the matrix, and directly contribute to the improvement of the post-cracking behavior and residual strength of SFRC. To gain a better understanding of the action behav...